http://www.mdpi.com/journal/polymers Latest open access articles published in Polymers at http://www.mdpi.com/journal/polymers http://www.mdpi.com/2073-4360/4/2/1195 Biominerals such as bones, teeth and seashells, very often have advanced material properties and are a source of inspiration for material chemists. As in biological systems acidic proteins play an important role in regulating the formation of CaCO3 biominerals, we employ poly(amino acid)s to mimic the processes involved in the laboratory. Here we report on the synthesis of random aminoacid copolymers of glutamic acid (Glu), lysine (Lys) and alanine (Ala) using the ring opening polymerization (ROP) of their respective N-carboxy anhydrides (NCA). The synthetic approach yields a series of polymers with different monomer composition but with similar degrees of polymerization (DP 45–56) and comparable polydispersities (PDI 1.2–1.6). Using random copolymers we can investigate the influence of composition on the activity of the polymers without having to take into account the effects of secondary structure or specific sequences. We show that variation of the Glu content of the polymer chains affects the nucleation and thereby also the particle size. Moreover, it is shown that the polymers with the highest Glu content affect the kinetics of mineral formation such that the first precipitate is more soluble than in the case of the control. http://www.mdpi.com/2073-4360/4/2/1195 Wed, 23 May 2012 00:00:00 CEST Polymers 2012-05-23 4 2 Article 1195 1210 2073-4360 Random Poly(Amino Acid)s Synthesized by Ring Opening Polymerization as Additives in the Biomimetic Mineralization of CaCO3 2012-05-23 doi: 10.3390/polym4021195 Vladimir Dmitrovic Gijs J.M. Habraken Marco M.R.M. Hendrix Wouter J.E.M. Habraken Andreas Heise Gijsbertus de With Nico A.J.M Sommerdijk http://www.mdpi.com/2073-4360/4/2/1183 Controlled radical polymerization of N-vinylcarbazole (NVK) via microwave-assisted reversible addition-fragmentation chain transfer (RAFT) polymerization is described. As chain transfer agent, 1,3,5-benzyl tri (diethyldithiocarbamate), was used. The chain transfer agent, containing a 1.3.5-trisubstituted benzene ring as core and three dithiocarbamate functionalities attached through an intermediate for fragmenting covalent bonds, led to poly(N-vinylcarbazole) (PVK) with star architecture. Polymerizations were carried out in 1,4-dioxane as solvent, at 70 °C, and studied for different polymerization times and monomer/CTA/initiator ratios. The SEC molecular weight curves exhibit a trimodal distribution, assigned to the linear and star-star coupling polymers, accompanying the real star polymer (as main product). http://www.mdpi.com/2073-4360/4/2/1183 Tue, 15 May 2012 00:00:00 CEST Polymers 2012-05-15 4 2 Article 1183 1194 2073-4360 Synthesis of Star Poly(N-vinylcarbazole) by Microwave-Assisted Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT) 2012-05-15 doi: 10.3390/polym4021183 Mircea Grigoras Oana-Iuliana Negru http://www.mdpi.com/2073-4360/4/2/1170 Condensation polymerization of 5-aminoisophthalic acid methyl ester 1 bearing a N-tri(ethylene glycol) methyl ester (TEG) chain as an AB2 monomer was conducted and the properties of the resulting hyperbranched polyamides (HBPA) were investigated. When the polymerization of 1 was carried out with N-methyl core initiator 2b at various feed ratios of 1 to 2b ([1]0/[2b]0) in the presence of LiHMDS and LiCl at −10 °C, the Mn values of the obtained HBPA increased in proportion to the [1]0/[2b]0 ratio from 7 to 46 (Mn = 3810–18600), retaining a narrow molecular weight distribution (Mw/Mn = 1.11–1.19). The HBPA was soluble in water, and a 0.25 wt.−% aqueous solution of the HBPA exhibited a lower critical solution temperature (LCST). The cloud point was 21–23 °C, which is about 30 °C lower than that of the corresponding poly(m-benzamide) with the N-TEG unit. http://www.mdpi.com/2073-4360/4/2/1170 Mon, 14 May 2012 00:00:00 CEST Polymers 2012-05-14 4 2 Article 1170 1182 2073-4360 Synthesis of Well-Defined, Water-Soluble Hyperbranched Polyamides by Chain-Growth Condensation Polymerization of AB2 Monomer 2012-05-14 doi: 10.3390/polym4021170 Yoshihiro Ohta Yusuke Kamijyo Akihiro Yokoyama Tsutomu Yokozawa http://www.mdpi.com/2073-4360/4/2/1157 Novel hybrid magnetic hydrogels have demonstrated their influence in several areas, particularly in biomedical science where these innovative materials are showing interesting applications for controlled drug delivery. A hybrid hydrogel with CoFe2O4 nanoparticles (NPs) as cross-linker agents of carboxymethylcellulose (CMC) polymer was obtained with the aim of testing it as a system for controlled drug release. The NPs were functionalized with (3-aminopropyl)-trimethoxysilane (APTMS) in order to introduce-NH2 groups on the surface. Infrared spectroscopy, XPS and electrochemical analysis were performed to quantify the amino coating. The presence of magnetic nanoparticles makes the system suitable for an application with magnetic stimulus. Preliminary studies performed with alternating magnetic fields indicate a release of the drug-like molecules previously loaded in the matrix. http://www.mdpi.com/2073-4360/4/2/1157 Thu, 03 May 2012 00:00:00 CEST Polymers 2012-05-03 4 2 Article 1157 1169 2073-4360 Hybrid Magnetic Hydrogel: A Potential System for Controlled Drug Delivery by Means of Alternating Magnetic Fields 2012-05-03 doi: 10.3390/polym4021157 Gabriele Giani Serena Fedi Rolando Barbucci http://www.mdpi.com/2073-4360/4/2/1125 In recent years, controlled photoradical polymerization has been established using 2,2,6,6-tetramethylpiperidine-1-oxyl as a mediator. This review article will describe the molecular weight control, polymerization mechanism, influence of initiator structure, effect of substituents supported on photo-acid generator, stability of the propagating chain end, photo-latency of the polymerization, molecular design, and an application to heterogeneous polymerization in an alcoholic medium. http://www.mdpi.com/2073-4360/4/2/1125 Wed, 02 May 2012 00:00:00 CEST Polymers 2012-05-02 4 2 Review 1125 1156 2073-4360 Controlled Photoradical Polymerization Mediated by 2,2,6,6-Tetramethylpiperidine-1-Oxyl 2012-05-02 doi: 10.3390/polym4021125 Eri Yoshida http://www.mdpi.com/2073-4360/4/2/1109 Very few studies concern the isotropic phase of Side-Chain Liquid-Crystalline Polymers (SCLCPs). However, the interest for the isotropic phase appears particularly obvious in flow experiments. Unforeseen shear-induced nematic phases are revealed away from the N-I transition temperature. The non-equilibrium nematic phase in the isotropic phase of SCLCP melts challenges the conventional timescales described in theoretical approaches and reveal very long timescales, neglected until now. This spectacular behavior is the starter of the present survey that reveals long range solid-like interactions up to the sub-millimetre scale. We address the question of the origin of this solid-like property by probing more particularly the non-equilibrium behavior of a polyacrylate substituted by a nitrobiphenyl group (PANO2). The comparison with a polybutylacrylate chain of the same degree of polymerization evidences that the solid-like response is exacerbated in SCLCPs. We conclude that the liquid crystal moieties interplay as efficient elastic connectors. Finally, we show that the “solid” character can be evidenced away from the glass transition temperature in glass formers and for the first time, in purely alkane chains above their crystallization temperature. We thus have probed collective elastic effects contained not only in the isotropic phase of SCLCPs, but also more generically in the liquid state of ordinary melts and of ordinary liquids. http://www.mdpi.com/2073-4360/4/2/1109 Wed, 25 Apr 2012 00:00:00 CEST Polymers 2012-04-25 4 2 Article 1109 1124 2073-4360 Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids 2012-04-25 doi: 10.3390/polym4021109 Laurence Noirez Hakima Mendil-Jakani Patrick Baroni Joachim H. Wendorff http://www.mdpi.com/2073-4360/4/2/1084 Encapsulation of cells in hydrogel particles has been demonstrated as an effective approach to deliver therapeutic agents. The properties of hydrogel particles, such as the chemical composition, size, porosity, and number of cells per particle, affect cellular functions and consequently play important roles for the cell-based drug delivery. Microfluidics has shown unparalleled advantages for the synthesis of polymer particles and been utilized to produce hydrogel particles with a well-defined size, shape and morphology. Most importantly, during the encapsulation process, microfluidics can control the number of cells per particle and the overall encapsulation efficiency. Therefore, microfluidics is becoming the powerful approach for cell microencapsulation and construction of cell-based drug delivery systems. In this article, I summarize and discuss microfluidic approaches that have been developed recently for the synthesis of hydrogel particles and encapsulation of cells. I will start by classifying different types of hydrogel material, including natural biopolymers and synthetic polymers that are used for cell encapsulation, and then focus on the current status and challenges of microfluidic-based approaches. Finally, applications of cell-containing hydrogel particles for cell-based drug delivery, particularly for cancer therapy, are discussed. http://www.mdpi.com/2073-4360/4/2/1084 Mon, 23 Apr 2012 00:00:00 CEST Polymers 2012-04-23 4 2 Review 1084 1108 2073-4360 Microfluidic-Based Synthesis of Hydrogel Particles for Cell Microencapsulation and Cell-Based Drug Delivery 2012-04-23 doi: 10.3390/polym4021084 Jiandi Wan http://www.mdpi.com/2073-4360/4/2/1065 A new type of composite 3D biomaterial that provides extracellular cues that govern the differentiation processes of mesenchymal stem cells (MSCs) has been developed. In the present study, we evaluated the chondrogenecity of a biohybrid composed of a calcium carbonate scaffold in its calcite polymorph and hyaluronic acid (HA). The source of the calcite scaffolding is an exoskeleton of a sea barnacle Tetraclita rifotincta (T. rifotincta), Pilsbry (1916). The combination of a calcium carbonate-based bioactive scaffold with a natural polymeric hydrogel is designed to mimic the organic-mineral composite of developing bone by providing a fine-tuned microenvironment. The results indicate that the calcite-HA interface creates a suitable microenvironment for the chondrogenic differentiation of MSCs, and therefore, the biohybrid may provide a tool for tissue-engineered cartilage. http://www.mdpi.com/2073-4360/4/2/1065 Mon, 23 Apr 2012 00:00:00 CEST Polymers 2012-04-23 4 2 Article 1065 1083 2073-4360 Calcite Biohybrids as Microenvironment for Stem Cells 2012-04-23 doi: 10.3390/polym4021065 Liliana Astachov Zvi Nevo Razi Vago http://www.mdpi.com/2073-4360/4/2/1056 Nanosized hydroxyapatite (HAp) materials have received much attention in the context of their advanced biomedical applications, including tissue engineering and drug delivery systems. Hybridization of nanosized HAp with organic molecules is a promising approach to facilitate the preparation of HAp nanomaterials. Here, templated mineralization using self-assembled nanogels modified with tricarboxylate groups was performed to yield the hybrid HAp nanomaterial. In the pH gradient method, the nanogel acted as an excellent template for the formation of well-dispersed HAp particles. Transmission electron microscopy, selected area electron diffraction patterns and energy-dispersive X-ray spectroscopy of these particles revealed that amorphous nanoparticles of amorphous calcium phosphate formed first, followed by transformation to crystalline hydroxyapatite. http://www.mdpi.com/2073-4360/4/2/1056 Fri, 20 Apr 2012 00:00:00 CEST Polymers 2012-04-20 4 2 Article 1056 1064 2073-4360 Templated Formation of Hydroxyapatite Nanoparticles from Self-Assembled Nanogels Containing Tricarboxylate Groups 2012-04-20 doi: 10.3390/polym4021056 Yoshihiro Sasaki Setsuko Yamane Kei Kurosu Shin-Ichi Sawada Kazunari Akiyoshi http://www.mdpi.com/2073-4360/4/2/1037 Lipases were employed under solvent-free conditions to conjugate oligo-ricinoleic acid derivatives with 10-undecenoic acid, to incorporate a reactive terminal double bond into the resultant product. First, undecenoic acid was covalently attached to oligo-ricinoleic acid using immobilized Candida antarctica lipase (CAL) at a 30% yield. Thirty percent conversion also occurred for CAL-catalyzed esterification between undecenoic acid and biocatalytically-prepared polyglycerol polyricinoleate (PGPR), with attachment of undecenoic acid occurring primarily at free hydroxyls of the polyglycerol moiety. The synthesis of oligo-ricinoleyl-, undecenoyl- structured triacylglycerols comprised two steps. The first step, the 1,3-selective lipase-catalyzed interesterification of castor oil with undecenoic acid, occurred successfully. The second step, the CAL-catalyzed reaction between ricinoleyl-, undecenoyl structured TAG and ricinoleic acid, yielded approximately 10% of the desired structured triacylglycerols (TAG); however, a significant portion of the ricinoleic acid underwent self-polymerization as a side-reaction. The employment of gel permeation chromatography, normal phase HPLC, NMR, and acid value measurements was effective for characterizing the reaction pathways and products that formed. http://www.mdpi.com/2073-4360/4/2/1037 Tue, 17 Apr 2012 00:00:00 CEST Polymers 2012-04-17 4 2 Article 1037 1055 2073-4360 Modification of oligo-Ricinoleic Acid and Its Derivatives with 10-Undecenoic Acid via Lipase-Catalyzed Esterification 2012-04-17 doi: 10.3390/polym4021037 Douglas G. Hayes Vinay K. Mannam Ran Ye Haizhen Zhao Salvadora Ortega M. Claudia Montiel http://www.mdpi.com/2073-4360/4/2/1025 The radical-scavenging activities of two thiols, eight (thio)barbituric acid derivatives and six chain-breaking phenolic antioxidants were investigated using the induction period method for polymerization of methyl methacrylate (MMA) initiated by thermal decomposition of 2,2’-azobisisobutyronitrile (AIBN) and monitored by differential scanning calorimetry (DSC). The induction period (IP) for the thiols 2-mercaptoethanol (ME) and 2-mercapto-1-methylimidazole (MMI) was about half that for phenolic antioxidants. Except for the potent inhibitor 5,5-dimethyl-2-thiobarbituric acid (3), the IP for thiobarbituric acid derivatives was about one tenth of that for phenolic antioxidants. The IP for 1,3,5-trimethyl-2-thiobarbituric acid (1) and 5-allyl-1, 3-dimethyl-2-thiobarbituric acid (7) was less than that of the control, possibly due to inhibition by a small amount of atmospheric oxygen in the DSC container. The ratio of the chain inhibition to that of chain propagation (CI/CP) for the thiols and thiobarbituric acid compounds except for 1, 3 and 7 was about 10 times greater or greater than that for phenolic compounds. A kinetic chain length (KCL) about 10% greater than that of the control was observed for 1, suggesting that 1 had chain transfer reactivity in the polymerization of MMA. The average molecular weight of polymers formed from thiobarbituric acid derivatives is discussed. http://www.mdpi.com/2073-4360/4/2/1025 Mon, 16 Apr 2012 00:00:00 CEST Polymers 2012-04-16 4 2 Article 1025 1036 2073-4360 Radical-Scavenging Activity of Thiols, Thiobarbituric Acid Derivatives and Phenolic Antioxidants Determined Using the Induction Period Method for Radical Polymerization of Methyl Methacrylate 2012-04-16 doi: 10.3390/polym4021025 Yoshinori Kadoma Seiichiro Fujisawa http://www.mdpi.com/2073-4360/4/2/1012 Cellulose tri-stearate (CTs) was synthesized employing trifluoroacetic anhydride (TFAA), stearic acid (SA), with microcrystal cellulose (MCC) and characterized with FT-IR and 1H-NMR. The degree of substitution of CTs was determined by the traditional saponification method and 1H-NMR. The thermal properties of CTs were investigated by the thermogravimetric analysis (TGA) under Ar flow in dynamic heating conditions. Thermal stability, activation energy, as well as the degradation mechanism of the decomposition process were revealed. The results showed that the thermal stability of CTs is superior to that of raw materials-MCC, and that the degradation of CTs in argon is a first-order weight loss; the initial decomposition temperature and the temperature corresponding to maximum degradation rate (Tp) increase with an increase in heating rate. The activation energy values were calculated with the Ozawa method, Coats-Redfern method and Kinssinger method, respectively. Analyses of experimental results suggest that the degradation mechanism 0.10 < α < 0.80 is F2 type, A3 for α < 0.1, and R3 for α > 0.80. The degradation mechanism of CTs in the whole conversion range is a complex mechanism, and is the combination of A3, F2 and R3. http://www.mdpi.com/2073-4360/4/2/1012 Mon, 16 Apr 2012 00:00:00 CEST Polymers 2012-04-16 4 2 Article 1012 1024 2073-4360 Thermal Properties and Thermal Degradation of Cellulose Tri-Stearate (CTs) 2012-04-16 doi: 10.3390/polym4021012 Feng-Yuan Huang http://www.mdpi.com/2073-4360/4/2/997 Hybrid hydrogels from biopolymers have been applied for various indications across a wide range of biomedical, pharmaceutical, and functional food industries. In particular, hybrid hydrogels synthesized from two biopolymers have attracted increasing attention. The inclusion of a second biopolymer strengthens the stability of resultant hydrogels and enriches its functionalities by bringing in new functional groups or optimizing the micro-environmental conditions for certain biological and biochemical processes. This article presents approaches that have been used by our groups to synthesize biopolymer hybrid hydrogels for effective uses for immunotherapy, tissue regeneration, food and functional food applications. The research has achieved some challenging results, such as stabilizing physical structure, increasing mucoadhesiveness, and the creation of an artificial extracellular matrix to aid in guiding tissue differentiation. http://www.mdpi.com/2073-4360/4/2/997 Fri, 13 Apr 2012 00:00:00 CEST Polymers 2012-04-13 4 2 Review 997 1011 2073-4360 Hydrogels from Biopolymer Hybrid for Biomedical, Food, and Functional Food Applications 2012-04-13 doi: 10.3390/polym4020997 Lin Shu Liu Joseph Kost Fang Yan Robert C. Spiro http://www.mdpi.com/2073-4360/4/2/986 Polymeric surfaces in contact with blood in vivo are foreign bodies and are quickly isolated from blood by the non-specific defense systems. Nanoparticles (NP) used as drug carriers are normally quickly taken up by phagocytes and sequestered in liver and spleen to which they can deliver drugs. Long-circulating and/or low complement activating core-shell NPs can be obtained from PEO/PEG amphiphilic copolymers forming brush or loops on the surface. Core-shell NPs can also be obtained from polysaccharidic graft or block amphiphilic copolymers. Complement activation by the NPs and protein adsorption both depend on the structure, nature and molecular weight of the polysaccharide chains composing the shell. NPs showing low complement activation can be obtained if the polysaccharide on the surface is long and in a brush configuration. Fragile molecules such as hemoglobin or siRNA can be loaded and protected by appropriate brush shells without modifying the low complement activation properties. http://www.mdpi.com/2073-4360/4/2/986 Fri, 13 Apr 2012 00:00:00 CEST Polymers 2012-04-13 4 2 Review 986 996 2073-4360 The Interactions between Blood and Polymeric Nanoparticles Depend on the Nature and Structure of the Hydrogel Covering the Surface 2012-04-13 doi: 10.3390/polym4020986 Denis Labarre http://www.mdpi.com/2073-4360/4/2/964 A series of homopolymeric and copolymeric hydrogels containing the N-isopropylacrylamide and vinyl monomers with α-amino acid (L-valine and L-phenylalanine) residues have been synthesized and their swelling properties were evaluated under different external stimulations. The hydrogels, obtained with different cross-linking agents (EBA and PEG-DA), have shown unique properties such as biocompatibility in addition to the stimuli-responsive characters. These ‘smart’ hydrogels exhibit single or multiple stimuli-responsiveness which could be used in biomedical applications, including controlled drug delivery. This article focuses on recent developments dealing with the delivery of metal-based drug (cisplatin, lithium) from the stimuli-responsive hydrogels proposed as platforms for cancer and bipolar disorder therapies. http://www.mdpi.com/2073-4360/4/2/964 Tue, 27 Mar 2012 00:00:00 CEST Polymers 2012-03-27 4 2 Article 964 985 2073-4360 Multiple Stimuli-Responsive Hydrogels for Metal-Based Drug Therapy 2012-03-27 doi: 10.3390/polym4020964 Mario Casolaro Ilaria Casolaro http://www.mdpi.com/2073-4360/4/2/913 The relentless increase in the demand for useable power from energy-hungry economies continues to drive energy-material related research. Fuel cells, as a future potential power source that provide clean-at-the-point-of-use power offer many advantages such as high efficiency, high energy density, quiet operation, and environmental friendliness. Critical to the operation of the fuel cell is the proton exchange membrane (polymer electrolyte membrane) responsible for internal proton transport from the anode to the cathode. PEMs have the following requirements: high protonic conductivity, low electronic conductivity, impermeability to fuel gas or liquid, good mechanical toughness in both the dry and hydrated states, and high oxidative and hydrolytic stability in the actual fuel cell environment. Water soluble polymers represent an immensely diverse class of polymers. In this comprehensive review the initial focus is on those members of this group that have attracted publication interest, principally: chitosan, poly (ethylene glycol), poly (vinyl alcohol), poly (vinylpyrrolidone), poly (2-acrylamido-2-methyl-1-propanesulfonic acid) and poly (styrene sulfonic acid). The paper then considers in detail the relationship of structure to functionality in the context of polymer blends and polymer based networks together with the effects of membrane crosslinking on IPN and semi IPN architectures. This is followed by a review of pore-filling and other impregnation approaches. Throughout the paper detailed numerical results are given for comparison to today’s state-of-the-art Nafion® based materials. http://www.mdpi.com/2073-4360/4/2/913 Mon, 26 Mar 2012 00:00:00 CEST Polymers 2012-03-26 4 2 Review 913 963 2073-4360 Water Soluble Polymers as Proton Exchange Membranes for Fuel Cells 2012-03-26 doi: 10.3390/polym4020913 Yun-Sheng Ye John Rick Bing-Joe Hwang http://www.mdpi.com/2073-4360/4/2/889 Because of their extraordinary properties, such as high thermal stability, flame retardant, high chemical resistance and high mechanical strength, thermotropic liquid crystalline polymers (TLCPs) have recently gained more attention while being useful for many applications which require chemical inertness and high strength. Due to the recent advance in nanotechnology, TLCPs are usually compounded with nanoparticles to form particulate composites to enhance their properties, such as barrier properties, electrical properties, mechanical properties and thermal properties. Carbon-based nanofillers such as carbon nanotube (CNT), graphene and graphene oxide are the most common fillers used for the TLCP matrices. In this review, we focus on recent advances in thermotropic main-chain liquid crystalline polymer nanocomposites incorporated with CNTs. However, the biggest challenges in the preparation of CNT/TLCP nanocomposites have been shown to be inherent in the dispersion of CNTs into the TLCP matrix, the alignment and control of CNTs in the TLCP matrix and the load-transfer between the TLCP matrix and CNTs. As a result, this paper reviews recent advances in CNT/TLCP nanocomposites through enhanced dispersion of CNTs in TLCPs as well as their improved interfacial adhesion with the TLCP matrices. Case studies on the important role of chemically modified CNTs in the TLCP/thermoplastic polymer blends are also included. http://www.mdpi.com/2073-4360/4/2/889 Fri, 23 Mar 2012 00:00:00 CET Polymers 2012-03-23 4 2 Review 889 912 2073-4360 Current Advances in the Carbon Nanotube/Thermotropic Main-Chain Liquid Crystalline Polymer Nanocomposites and Their Blends 2012-03-23 doi: 10.3390/polym4020889 Henry Kuo Feng Cheng Tanya Basu Nanda Gopal Sahoo Lin Li Siew Hwa Chan http://www.mdpi.com/2073-4360/4/1/880 The assembled complex, Fe(NCBH3)2(bpa)2, enclathrating biphenyl has been synthesized, the skeleton of which is a 1D chain. Several 1D chains gather together to form 1D chain sheet. The 1D chain sheet is stacked spirally to form novel spiral assembly. The average Fe-N distances were 2.020(2), 2.083(2), and 2.191(2) Å at 100, 175, and 298 K, respectively, reflecting spin-state change of the iron ion. The assembly showed a stepwise spin-crossover phenomenon. http://www.mdpi.com/2073-4360/4/1/880 Wed, 07 Mar 2012 00:00:00 CET Polymers 2012-03-07 4 1 Article 880 888 2073-4360 Spiral Assembly of the 1D Chain Sheet of Fe(NCBH3)2(bpa)2·(biphenyl) (bpa = 1,2-bis(4-pyridyl)ethane) and its Stepwise Spin-Crossover Phenomenon 2012-03-07 doi: 10.3390/polym4010880 Satoru Nakashima Takaki Morita Katsuya Inoue Shinya Hayami http://www.mdpi.com/2073-4360/4/1/794 Polyester dendrimers have been comprehensively reviewed starting from their first synthesis in the early 1990s by Hawker and Fréchet. Polyester dendrimers have attracted and continue to attract extensive interest because they are comparatively easy to make and because, whenever they have been tested, they have been found to be non-toxic. A number of different strategies for their synthesis have been examined and the methods employed for formation of the ester bond during dendrimer assembly have been summarized. The newest approaches, including the use of bifunctional orthogonally reacting dendrons and accelerated synthesis have been surveyed. http://www.mdpi.com/2073-4360/4/1/794 Wed, 07 Mar 2012 00:00:00 CET Polymers 2012-03-07 4 1 Review 794 879 2073-4360 Polyester Dendrimers 2012-03-07 doi: 10.3390/polym4010794 Jean–d’Amour K. Twibanire T. Bruce Grindley http://www.mdpi.com/2073-4360/4/1/759 Biocatalysis is propagating into practically every area of organic chemistry, amongst them radical polymerizations. A review of the recent developments of this dynamic and quickly evolving area of research is presented together with a critical evaluation of its potential to yield novel polymers and/or environmentally more benign synthetic procedures. http://www.mdpi.com/2073-4360/4/1/759 Tue, 06 Mar 2012 00:00:00 CET Polymers 2012-03-06 4 1 Review 759 793 2073-4360 Enzyme Initiated Radical Polymerizations 2012-03-06 doi: 10.3390/polym4010759 Frank Hollmann Isabel W. C. E. Arends http://www.mdpi.com/2073-4360/4/1/747 Human β-defensins (HBD) are a family of small antimicrobial peptides that play important roles in the innate and adaptive immune defenses against microbial infection. In this study, we predicted the mature sequences and assessed the antibacterial properties of synthetic HBD-19, HBD-23, HBD-27, and HBD-29 against three species of clinically relevant bacteria: Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. We also examined the cytotoxicity of each β-defensin to human cells. HBD-19 exhibited modest antibacterial effects against E. coli and S. aureus but had little effect on the growth of P. aeruginosa. HBD-23 exhibited substantial antibacterial effects against all three bacterial species and was particularly potent against the Gram-negative species, E. coli and P. aeruginosa. HBD-27 exerted modest antibacterial activity only towards S. aureus while HBD-29 had modest antibacterial activity for E. coli and P. aeruginosa. HBD-23 and HBD-27 showed little or no toxicity to human peripheral blood mononuclear cells, while HBD-19 and HBD-29 decreased cell viability by 20% at 30 μg/mL. http://www.mdpi.com/2073-4360/4/1/747 Thu, 01 Mar 2012 00:00:00 CET Polymers 2012-03-01 4 1 Article 747 758 2073-4360 Antibacterial Activity of Four Human Beta-Defensins: HBD-19, HBD-23, HBD-27, and HBD-29 2012-03-01 doi: 10.3390/polym4010747 Bryan T. Chow Maira Soto Bonnie L. Lo David C. Crosby David Camerini http://www.mdpi.com/2073-4360/4/1/741 To model the rates of interfacial polycondensations, the rates of reaction of benzoyl chloride and methyl chloroformate with various aliphatic monoamines in acetonitrile were determined at 25 °C. Buffering with picric acid slowed these extremely fast reactions so the rate constants could be determined from the rate of disappearance of picrate ion. The rates of the amine reactions correlated linearly with their Swain-Scott nucleophilicities. http://www.mdpi.com/2073-4360/4/1/741 Wed, 29 Feb 2012 00:00:00 CET Polymers 2012-02-29 4 1 Article 741 746 2073-4360 Kinetics of Model Reactions for Interfacial Polymerization 2012-02-29 doi: 10.3390/polym4010741 Jeffrey Robertson Trevor Centeno-Hall Anne Padias Robert Bates Henry Hall http://www.mdpi.com/2073-4360/4/1/710 Four hydrophobic amino acids (Leu, Tyr, Phe, Trp) were oligomerized by the protease papain in homo-oligomerization, binary co-oligomerization and ternary co-oligomerization. After 24 h, solid polydisperse reaction products of the homo-oligomerization were obtained in yields ranging from 30–80% by weight. A DPavg was calculated based on MALDI-ToF MS results using the ion counts for the chains in the product. Based on the DPavg and the yield of the homo-oligomerization it was determined that the amino acids can be ranked according to reactivity in the order: Tyr > Leu > Phe > Trp. Thermal degradation of the homo-oligomers shows two degradation steps: at 178–239 °C and at 300–330 °C. All the products left a significant amount of char ranging from 18–57% by weight at 800 °C. Binary co-oligomers were obtained as a polydisperse precipitate with a compositional distribution of the chains. Both the compositional and chain length distribution are calculated from MALDI-ToF mass spectra. By comparing the amount of each amino acid present in the chains it was determined that the amino acids are incorporated with a preference: Leu > Tyr > Phe > Trp. Ternary co-oligomers were also obtained as a precipitate and analyzed by MALDI-ToF MS. The compositional distribution and the chain length distribution were calculated from the MALDI-ToF data. The quantity of every amino acid in the chains was determined. Also determined was the influence on the DPavg when the oligomers were compared with corresponding binary co-oligomers. From the combined results it was concluded that in the co-oligomerization of three amino acids the reactivity preference is Leu > Tyr > Phe > Trp. Thermal degradation of all the co-oligomers showed a weight loss of 2 wt% before the main oligomer degradation step at 300–325 °C. http://www.mdpi.com/2073-4360/4/1/710 Wed, 29 Feb 2012 00:00:00 CET Polymers 2012-02-29 4 1 Article 710 740 2073-4360 Papain Catalyzed (co)Oligomerization of α-Amino Acids 2012-02-29 doi: 10.3390/polym4010710 Leendert W. Schwab Wouter M. J. Kloosterman Jakob Konieczny Katja Loos http://www.mdpi.com/2073-4360/4/1/691 As components of the innate immune system, antimicrobial peptides in the form of human defensins play an important role in host defense by serving as the epithelial layer’s biochemical barrier against local infections. Recent studies have shown these molecules to have far more additional cellular functions besides their antimicrobial activity. Defensins play a role in cell division, attraction and maturation of immune cells, differentiation and reorganization of epithelial tissues, wound healing and tumor suppression. This multitude of function makes human defensins appear to be excellent tools for therapeutic approaches. These antimicrobial peptides may be used directly as a remedy against bacterial and viral infections. Furthermore, the application of human defensins can be used to promote wound healing and epithelial reorganization. In particular, human β-defensins have a strong impact on osteoblast proliferation and differentiation. Human β-defensins have already been applied as a vaccination against HIV-1. Another potentially useful characteristic of defensins is their suitability as diagnostic markers in cancer therapy. In particular, α-defensins have already been used for this purpose. Human α-defensin-3, for example, has been described as a tumor marker for lymphocytes. High gene expression levels of α-defensin-3 and -4 have been detected in benign oral neoplasia, α-defensin-6 is considered to be a tumor marker for colon cancer. http://www.mdpi.com/2073-4360/4/1/691 Tue, 28 Feb 2012 00:00:00 CET Polymers 2012-02-28 4 1 Review 691 709 2073-4360 Human Defensins: Potential Tools for Clinical Applications 2012-02-28 doi: 10.3390/polym4010691 Jochen Winter Matthias Wenghoefer http://www.mdpi.com/2073-4360/4/1/674 Potato phosphorylase is able to synthesize linear polyglucans from maltoheptaose primers. By coupling maltoheptaose to butane diamine, tris(2-aminoethyl)amine and amine functionalized amine functionalized poly ethyleneglycol (PEG), new primer molecules became available. The resulting di-, tri- and macro-primers were incubated with potato phosphorylase and glycogen branching enzyme from Deinococcus geothermalis. Due to the action of both enzymes, hyperbranched polyglucan arms were grown from the maltoheptaose derivatives with a maximum degree of branching of 11%. The size of the synthesized hyperbranched polyglucans could be controlled by the ratio monomer over primer. About 60%–80% of the monomers were incorporated in the glycoconjugates. The resulting hyperbranched glycoconjugates were subjected to Dynamic Light Scattering (DLS) measurements in order to determine the hydrodynamic radius and it became obvious that the structures formed agglomerates in the range of 14–32 nm. http://www.mdpi.com/2073-4360/4/1/674 Mon, 27 Feb 2012 00:00:00 CET Polymers 2012-02-27 4 1 Article 674 690 2073-4360 Synthesis of Hyperbranched Glycoconjugates by the Combined Action of Potato Phosphorylase and Glycogen Branching Enzyme from Deinococcus geothermalis 2012-02-27 doi: 10.3390/polym4010674 Jeroen van der Vlist Martin Faber Lizette Loen Teunis J. Dijkman Lia A. T. W. Asri Katja Loos http://www.mdpi.com/2073-4360/4/1/656 In this paper, we detail how microantennae dedicated to Magnetic Resonance Imaging (MRI) can benefit from the advantages offered by polymer substrates, especially flexibility and dielectric properties. We present a monolithic and wireless design based on the transmission lines between conductor windings on both sides of a dielectric substrate and its fabrication process. This last one requires specific plasma treatments to improve polymer/metal adhesion. We have led a comparative study on the effects of the ageing time on the wettability and the metal adhesion to Kapton and Teflon surfaces. Correlation between wettability (water contact angle) and adhesion (tensile strength) has been established. Then, the use of PolyDiMethylSiloxane (PDMS) as biocompatible packaging material and the optimization of its thickness allows us to conserve suitable f0 and Q values in a conducting environment such as the biological tissues. These studies allow us to perform 7 Tesla in vivo MRI of the rat brain with a high spatial resolution of 100 x 100 x 200 µm3 and a Signal to Noise Ratio of 80. http://www.mdpi.com/2073-4360/4/1/656 Mon, 27 Feb 2012 00:00:00 CET Polymers 2012-02-27 4 1 Article 656 673 2073-4360 Fabrication and Packaging of Flexible Polymeric Microantennae for in Vivo Magnetic Resonance Imaging 2012-02-27 doi: 10.3390/polym4010656 Magdalèna Couty Marion Woytasik Jean-Christophe Ginefri Anne Rubin Emile Martincic Marie Poirier-Quinot Luc Darrasse Fawzi Boumezbeur Franck Lethimonnier Michael Tatoulian Elisabeth Dufour-Gergam http://www.mdpi.com/2073-4360/4/1/630 We present the functionalized Cahn-Hilliard (FCH) energy, a continuum characterization of interfacial energy whose minimizers describe the network morphology of solvated functionalized polymer membranes. With a small set of parameters the FCH characterizes bilayer, pore-like, and micelle network structures. The gradient flows derived from the FCH describe the interactions between these structures, including the merging and pinch-off of endcaps and formation of junctions central to the generation of network morphologies. We couple the FCH gradient flow to a model of ionic transport which incorporates entropic effects to localize counter-ions, yielding a flow which dissipates a total free energy, and an expression for the excess electrochemical potential which combines electrostatic and entropic effects. We present applications to network bifurcation and membrane casting. http://www.mdpi.com/2073-4360/4/1/630 Fri, 24 Feb 2012 00:00:00 CET Polymers 2012-02-24 4 1 Article 630 655 2073-4360 Variational Models of Network Formation and Ion Transport: Applications to Perfluorosulfonate Ionomer Membranes 2012-02-24 doi: 10.3390/polym4010630 Nir Gavish Jaylan Jones Zhengfu Xu Andrew Christlieb Keith Promislow http://www.mdpi.com/2073-4360/4/1/617 A new esterase from Thermobifida halotolerans (Thh_Est) was cloned and expressed in E. coli and investigated for surface hydrolysis of polylactic acid (PLA) and polyethylene terephthalate (PET). Thh_Est is a member of the serine hydrolases superfamily containing the -GxSxG- motif with 85–87% homology to an esterase from T. alba, to an acetylxylan esterase from T. fusca and to various Thermobifida cutinases. Thh_Est hydrolyzed the PET model substrate bis(benzoyloxyethyl)terephthalate and PET releasing terephthalic acid and mono-(2-hydroxyethyl) terephthalate in comparable amounts (19.8 and 21.5 mmol/mol of enzyme) while no higher oligomers like bis-(2-hydroxyethyl) terephthalate were detected. Similarly, PLA was hydrolyzed as indicated by the release of lactic acid. Enzymatic surface hydrolysis of PET and PLA led to a strong hydrophilicity increase, as quantified with a WCA decrease from 90.8° and 75.5° to 50.4° and to a complete spread of the water drop on the surface, respectively. http://www.mdpi.com/2073-4360/4/1/617 Tue, 21 Feb 2012 00:00:00 CET Polymers 2012-02-21 4 1 Article 617 629 2073-4360 A New Esterase from Thermobifida halotolerans Hydrolyses Polyethylene Terephthalate (PET) and Polylactic Acid (PLA) 2012-02-21 doi: 10.3390/polym4010617 Doris Ribitsch Enrique Herrero Acero Katrin Greimel Anita Dellacher Sabine Zitzenbacher Annemarie Marold Rosario Diaz Rodriguez Georg Steinkellner Karl Gruber Helmut Schwab Georg M. Guebitz http://www.mdpi.com/2073-4360/4/1/600 Dendrimers are highly branched, open, covalent assemblies of branch cells (monomers) radially attached to a core in successive layers or generations. Major types of dendrimers include polyamidoamine, polypropylenimine, multiple antigen peptide, chiral, and Fréchet-type dendrimers. Their structure and dynamics can be explored by various techniques, such as scattering, spectrometry, and microscopy techniques. Specifically, the scattering techniques include small-angle neutron scattering (SANS), quasi-elastic neutron scattering (QENS), small-angle X-ray scattering (SAXS), and light scattering. Examples of their properties that can be explored by scattering techniques include: inter-molecular structure, intra-molecular cavity, radius-of-gyration (RG), hydrodynamic radius (RH), molecular weight, effective charge number of a single dendrimer molecule, water penetration into the interior of the dendrimers, and the internal dynamics. Of these properties, the hydrodynamic radius and molecular weight may be explored by DLS; the internal dynamics of dendrimers may be studied by QENS; and the others may be explored through SAXS and SANS. During the past several years, SANS and QENS have been used to study the structural properties and internal dynamics of various generations of polyamidoamine dendrimers (PAMAMs). Their potential prospects as anticancer polymer drug carriers are also discussed. http://www.mdpi.com/2073-4360/4/1/600 Tue, 21 Feb 2012 00:00:00 CET Polymers 2012-02-21 4 1 Review 600 616 2073-4360 Characterizations of Polyamidoamine Dendrimers with Scattering Techniques 2012-02-21 doi: 10.3390/polym4010600 Xiangyu Wang Ludovic Guerrand Bin Wu Xin Li Lauren Boldon Wei-Ren Chen Li Liu http://www.mdpi.com/2073-4360/4/1/590 This study investigates the mechanical reinforcement of chitosan with TiO2 and Ag nanoparticles, as well as their water vapour transmission rates and water resistance behaviour. The mechanical properties of chitosan were improved by addition of TiO2 or Ag, with significant increases in Young’s modulus (from 25 MPa to ~300 MPa), tensile strength (from 6 MPa to 18–35 MPa) and toughness (from 1.3 J g−1 to 7–8 J g−1). The water vapour transmission rates (368–413 g m−2 d−1) were found to be similar for both materials. Inclusion of Ag reduced the water resistance (from 823% to 1,000%), while inclusion of TiO2 yielded significant improvement in water resistance (from 823% to 100%). http://www.mdpi.com/2073-4360/4/1/590 Thu, 16 Feb 2012 00:00:00 CET Polymers 2012-02-16 4 1 Commentary 590 599 2073-4360 Reinforced Materials Based on Chitosan, TiO2 and Ag Composites 2012-02-16 doi: 10.3390/polym4010590 Khairul Anuar Mat Amin Marc in het Panhuis http://www.mdpi.com/2073-4360/4/1/561 Pegylation using heterotelechelic poly(ethylene glycol) (PEG) offers many possibilities to create high-performance molecules and materials. A versatile route is proposed to synthesize heterobifunctional PEG containing diverse combinations of azide, amine, thioacetate, thiol, pyridyl disulfide, as well as activated hydroxyl end groups. Asymmetric activation of one hydroxyl end group enables the heterobifunctionalization while applying selective monotosylation of linear, symmetrical PEG as a key step. The azide function is introduced by reacting monotosyl PEG with sodium azide. A thiol end group is obtained by reaction with sodium hydrosulfide. The activation of the hydroxyl end group and subsequent reaction with potassium carbonate/thioacetic acid yields a thioacetate end group. The hydrolysis of the thioester end group by ammonia in presence of 2,2′-dipyridyl disulfide provides PEG pyridyl disulfide. Amine terminated PEG is prepared either by reduction of the azide or by nucleophilic substitution of mesylate terminated PEG using ammonia. In all cases, >95% functionalization of the PEG end groups is achieved. The PEG derivatives particularly support the development of materials for biomedical applications. For example, grafting up to 13% of the Na-alg monomer units with α-amine-ω-thiol PEG maintains the gelling capacity in presence of calcium ions but simultaneous, spontaneous disulfide bond formation reinforces the initial physical hydrogel. http://www.mdpi.com/2073-4360/4/1/561 Thu, 16 Feb 2012 00:00:00 CET Polymers 2012-02-16 4 1 Article 561 589 2073-4360 Versatile Route to Synthesize Heterobifunctional Poly(ethylene glycol) of Variable Functionality for Subsequent Pegylation 2012-02-16 doi: 10.3390/polym4010561 Redouan Mahou Christine Wandrey http://www.mdpi.com/2073-4360/4/1/539 Antimicrobial peptides (APs) are an important part of the innate immune system in epithelial and non-epithelial surfaces. So far, many different antimicrobial peptides from various families have been discovered in non-vertebrates and vertebrates. They are characterized by antibiotic, antifungal and antiviral activities against a variety of microorganisms. In addition to their role as endogenous antimicrobials, APs participate in multiple aspects of immunity. They are involved in septic and non-septic inflammation, wound repair, angiogenesis, regulation of the adaptive immune system and in maintaining homeostasis. Due to those characteristics AP could play an important role in many practical applications. Limited therapeutic efficiency of current antimicrobial agents and the emerging resistance of pathogens require alternate antimicrobial drugs. The purpose of this review is to highlight recent literature on functions and mechanisms of APs. It also shows their current practical applications as peptide therapeutics and bioactive polymers and discusses the possibilities of future clinical developments. http://www.mdpi.com/2073-4360/4/1/539 Thu, 16 Feb 2012 00:00:00 CET Polymers 2012-02-16 4 1 Review 539 560 2073-4360 Antimicrobial Peptides: Multifunctional Drugs for Different Applications 2012-02-16 doi: 10.3390/polym4010539 Lars-Ove Brandenburg Julika Merres Lea-Jessica Albrecht Deike Varoga Thomas Pufe http://www.mdpi.com/2073-4360/4/1/501 The sphere-shaped fullerene has attracted considerable interest not least due to the peculiar electronic properties of this carbon allotrope and the fascinating materials emanating from fullerene-derived structures. The rapid development and tremendous advances in organic chemistry allow nowadays the modification of C60 to a great extent by pure chemical means. It is therefore not surprising that the fullerene moiety has also been part of dendrimers. At the initial stage, fullerenes have been examined at the center of the dendritic structure mainly aimed at possible shielding effects as exerted by the dendritic environment and light-harvesting effects due to multiple chromophores located at the periphery of the dendrimer. In recent years, also many research efforts have been devoted towards fullerene-rich nanohybrids containing multiple C60 units in the branches and/or as surface functional groups. In this review, synthetic efforts towards the construction of dendritic fullerene-rich nanostructures have been compiled and will be summarized herein. http://www.mdpi.com/2073-4360/4/1/501 Tue, 14 Feb 2012 00:00:00 CET Polymers 2012-02-14 4 1 Review 501 538 2073-4360 Synthetic Strategies towards Fullerene-Rich Dendrimer Assemblies 2012-02-14 doi: 10.3390/polym4010501 Uwe Hahn Fritz Vögtle Jean-François Nierengarten http://www.mdpi.com/2073-4360/4/1/486 Methyl epoxyricinoleate was prepared in high yield by the lipase-catalyzed epoxidation of methyl ricinoleate with H2O2. A high molecular weight polyepoxyricinoleate (PER) with a maximum weight average molecular weight (Mw) of 272,000 was enzymatically prepared by the polycondensation of methyl epoxyricinoleate using immobilized lipase from Burkholderia cepacia (lipase PS-IM) in bulk at 80 °C for 5 d. PER showed good low temperature fluidability. PER was readily cured by maleic anhydride (MA) at 80 °C to produce a chloroform-insoluble PER-MA film. Both the glass transition temperature and Young’s modulus increased with increasing MA content and PER Mw. In contrast, the elongation at break decreased with increasing MA content and PER Mw. Methyl epoxyricinoleate, PER and PER-MA showed biodegradability by activated sludge, and that of the PER-MA film decreased with increasing MA content. http://www.mdpi.com/2073-4360/4/1/486 Fri, 10 Feb 2012 00:00:00 CET Polymers 2012-02-10 4 1 Article 486 500 2073-4360 Enzymatic Synthesis and Crosslinking of Novel High Molecular Weight Polyepoxyricinoleate 2012-02-10 doi: 10.3390/polym4010486 Ayaki Kazariya Shuichi Matsumura http://www.mdpi.com/2073-4360/4/1/463 Dendrimers have been widely used as nanostructured carriers for guest species in a variety of applications in medicine, catalysis, and environmental remediation. Theory and simulation methods are an important complement to experimental approaches that are designed to develop a fundamental understanding about how dendrimers interact with guest molecules. This review focuses on computational studies aimed at providing a better understanding of the relevant physicochemical parameters at play in the binding and release mechanisms between polyamidoamine (PAMAM) dendrimers and guest species. We highlight recent contributions that model supramolecular dendrimer-guest complexes over the temporal and spatial scales spanned by simulation methods ranging from all-atom molecular dynamics to statistical field theory. The role of solvent effects on dendrimer-guest interactions and the importance of relating model parameters across multiple scales is discussed. http://www.mdpi.com/2073-4360/4/1/463 Fri, 10 Feb 2012 00:00:00 CET Polymers 2012-02-10 4 1 Review 463 485 2073-4360 Multiscale Modeling for Host-Guest Chemistry of Dendrimers in Solution 2012-02-10 doi: 10.3390/polym4010463 Seung Ha Kim Monica H. Lamm http://www.mdpi.com/2073-4360/4/1/448 Magnetic hybrid liquid crystalline composites have been obtained either by thermal decomposition of a cobalt precursor in a solution containing a liquid crystal polymer or by dispersing preformed cobalt nanorods in a liquid crystal polymer matrix. The final materials are all mesomorphous and ferromagnetic. Their magnetic characteristics are compared as a function of the synthesis method. http://www.mdpi.com/2073-4360/4/1/448 Fri, 10 Feb 2012 00:00:00 CET Polymers 2012-02-10 4 1 Article 448 462 2073-4360 In Situ and Ex Situ Syntheses of Magnetic Liquid Crystalline Materials: A Comparison 2012-02-10 doi: 10.3390/polym4010448 Ophelie Riou Lacramioara Zadoina Barbara Lonetti Katerina Soulantica Anne-Françoise Mingotaud Marc Respaud Bruno Chaudret Monique Mauzac http://www.mdpi.com/2073-4360/4/1/408 The synthesis, structure and electronic properties of polysilane dendrimers, a relatively new class of highly branched and silicon-rich molecular architectures is reviewed. After a detailed discussion of main synthetic strategies to well-defined single-core and double-core polysilane dendrimers, important structural and conformational features determined by single crystal X-ray crystallography and 29Si-NMR spectroscopy are presented. The last part highlights the most interesting photochemical properties of polysilane dendrimers such as UV absorption and emission behavior, which are compared with those of linear and branched polysilanes. http://www.mdpi.com/2073-4360/4/1/408 Thu, 09 Feb 2012 00:00:00 CET Polymers 2012-02-09 4 1 Review 408 447 2073-4360 Polysilane Dendrimers 2012-02-09 doi: 10.3390/polym4010408 Clemens Krempner http://www.mdpi.com/2073-4360/4/1/396 1H NMR and 13C NMR spectrometry (1-dimensional and 2-dimensional) have been used to assign chemical resonances and determine the degrees of branching for polyesters synthesized by the Lewis acid (dibutyltin(IV)oxide)-catalyzed polycondensation of glycerol with either succinic acid (n (aliphatic chain length) = 2), glutaric acid (n = 3) or azelaic acid (n = 7) in quasi-melt solutions with toluene. When 1:1 and 2:1 (diacid:glycerol) molar ratios were used, it was found that the glutaric acid-derived polymers gave the highest degree of polymer branching (31.2%, 85.6%, respectively) after the 24 h reaction period followed by the succinic acid-derived polymers (39.4%, 41.9%, respectively) and the azelaic acid-derived polymers (9.9%, 13.9%, respectively). Reactions performed at reflux for 24 h resulted in a 70.8% and 56.7% decrease in degree of branching for succinic acid and glutaric acid-derived polyesters, respectively. There is no indication that degree of branching is significantly affected by the presence or absence of solvent according to the results obtained in this research. http://www.mdpi.com/2073-4360/4/1/396 Mon, 06 Feb 2012 00:00:00 CET Polymers 2012-02-06 4 1 Article 396 407 2073-4360 Degree of Branching in Hyperbranched Poly(glycerol-co-diacid)s Synthesized in Toluene 2012-02-06 doi: 10.3390/polym4010396 Victor T. Wyatt Gary D. Strahan http://www.mdpi.com/2073-4360/4/1/355 Dendronization is a synthetic methodology that offers important advantages. The resulting products, which are called dendronized materials, present new and specific properties. This review shows numerous examples in which individual dendrons are used as building blocks to prepare more complex arrays via covalent or non-covalent interactions. In particular, it points out how the structural information programmed into the dendritic architecture can be used in the dendronization process to generate nanostructures with specific tailored properties. We emphasize the use of different dendrons, with diverse chemical structure and size, to functionalize diverse substrates like linear polymers, and plane and curved inorganic surfaces. Apart from this, the review also demonstrates that self-assembly represents an ideal approach to create well-defined hyperbranched surfaces and it includes some discussion about the ability of both organic and inorganic building blocks to direct this process. http://www.mdpi.com/2073-4360/4/1/355 Thu, 02 Feb 2012 00:00:00 CET Polymers 2012-02-02 4 1 Review 355 395 2073-4360 Dendronization: A Useful Synthetic Strategy to Prepare Multifunctional Materials 2012-02-02 doi: 10.3390/polym4010355 Julieta I. Paez Marisa Martinelli Verónica Brunetti Miriam C. Strumia http://www.mdpi.com/2073-4360/4/1/341 The molecular weight of a polymer determines key optoelectronic device characteristics, such as internal morphology and charge transport. Therefore, it is important to ensure that polymer deposition techniques do not significantly alter the native polymer molecular weight. This work addresses polymers deposited by resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE). By using a novel emulsion-based target technique, the deposition of smooth, contiguous films with no evidence of chemical degradation have been enabled. However, structural degradation via a reduction in molecular weight remains an open question. The common polymer standard, PMMA, and the optoelectronic polymers, P3HT and MEH-PPV, have been characterized before and after emulsion-based RIR-MAPLE deposition via gel permeation chromatography to determine if RIR-MAPLE affects the deposited polymer molecular weight. Proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy measurements have also been conducted to verify the absence of chemical degradation. These measurements verify that there is no chemical degradation of the polymers, and that PMMA and P3HT show no structural degradation, but MEH-PPV exhibits a halving of the weight-averaged molecular weight after RIR-MAPLE deposition. Compared with competing laser deposition techniques, RIR-MAPLE is shown to have the least effect on the molecular weight of the resulting thin films. http://www.mdpi.com/2073-4360/4/1/341 Wed, 01 Feb 2012 00:00:00 CET Polymers 2012-02-01 4 1 Article 341 354 2073-4360 Effects of Emulsion-Based Resonant Infrared Matrix Assisted Pulsed Laser Evaporation (RIR-MAPLE) on the Molecular Weight of Polymers 2012-02-01 doi: 10.3390/polym4010341 Ryan D. McCormick Jeremy Lenhardt Adrienne D. Stiff-Roberts http://www.mdpi.com/2073-4360/4/1/316 Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including a uniquely high-stroke reversible mechanical actuation triggered by external stimuli. Fundamentally, all such stimuli affect the degree of liquid crystalline order in the polymer chains cross-linked into an elastic network. Heat and the resulting thermal actuation act by promoting entropic disorder, as does the addition of solvents. Photo-isomerization is another mechanism of actuation, reducing the orientational order by diminishing the fraction of active rod-like mesogenic units, mostly studied for azobenzene derivatives incorporated into the LCE composition. Embedding nanoparticles provides a new, promising strategy to add functionality to LCEs and ultimately enhance their performance as sensors and actuators. The motivation for the combination of nanoparticles with LCEs is to provide better-controlled actuation stimuli, such as electric and magnetic fields, and broad-spectrum light, by selecting and configuring the appropriate nanoparticles in the LCE matrix. Here we give an overview of recent advances in this area with a focus on preparation, physical properties and actuation performance of the resultant nanocomposites. http://www.mdpi.com/2073-4360/4/1/316 Mon, 30 Jan 2012 00:00:00 CET Polymers 2012-01-30 4 1 Review 316 340 2073-4360 Nanoparticle-Liquid Crystalline Elastomer Composites 2012-01-30 doi: 10.3390/polym4010316 Yan Ji Jean E. Marshall Eugene M. Terentjev http://www.mdpi.com/2073-4360/4/1/296 A novel strategy to graft functional groups at the surface of carbon nanotubes (CNTs) is discussed. Aiming at grafting nitrogen containing groups, and more specifically primary amine covalent functionalization, CNTs were exposed under atomic nitrogen flow arising from an Ar + N2 microwave plasma. The primary amine functions were identified and quantified through chemical derivatization with 4-(trifluoromethyl)benzaldehyde and characterized through X-ray photoelectron spectroscopy. The increase of the selectivity in the primary amines grafting onto CNTs, up to 66.7% for treatment of CNT powder, was performed via the reduction of post-treatment oxygen contamination and the addition of hydrogen in the experimental set-up, more particularly in the plasma post-discharge chamber. The analyses of nitrogenated and primary amine functions grafting on the CNT surface suggest that atomic nitrogen (N•) and reduced nitrogen species (NH• and NH2•) react preferentially with defect sites of CNTs and, then, only atomic nitrogen continues to react on the CNT surface, creating defects. http://www.mdpi.com/2073-4360/4/1/296 Mon, 30 Jan 2012 00:00:00 CET Polymers 2012-01-30 4 1 Article 296 315 2073-4360 Selective Grafting of Primary Amines onto Carbon Nanotubes via Free-Radical Treatment in Microwave Plasma Post-Discharge 2012-01-30 doi: 10.3390/polym4010296 Benoit Ruelle Sophie Peeterbroeck Thomas Godfroid Carla Bittencourt Michel Hecq Rony Snyders Philippe Dubois http://www.mdpi.com/2073-4360/4/1/275 Advances in functionality and reliability of carbon nanotube (CNT) composite materials require careful formulation of processing methods to ultimately realize the desired properties. To date, controlled dispersion of CNTs in a solution or a composite matrix remains a challenge, due to the strong van der Waals binding energies associated with the CNT aggregates. There is also insufficiently defined correlation between the microstructure and the physical properties of the composite. Here, we offer a review of the dispersion processes of pristine (non-covalently functionalized) CNTs in a solvent or a polymer solution. We summarize and adapt relevant theoretical analysis to guide the dispersion design and selection, from the processes of mixing/sonication, to the application of surfactants for stabilization, to the final testing of composite properties. The same approaches are expected to be also applicable to the fabrication of other composite materials involving homogeneously dispersed nanoparticles. http://www.mdpi.com/2073-4360/4/1/275 Mon, 23 Jan 2012 00:00:00 CET Polymers 2012-01-23 4 1 Review 275 295 2073-4360 Dispersion of Carbon Nanotubes: Mixing, Sonication, Stabilization, and Composite Properties 2012-01-23 doi: 10.3390/polym4010275 Yan Yan Huang Eugene M. Terentjev http://www.mdpi.com/2073-4360/4/1/256 The adsorption of polymethylmethacrylate polymer of different molecular weight at the aerosil/ethyleneglycol- or 1,3 butanediol-dimethacrylate interfaces was determined to provide microstructured networks. Their structural characteristics were determined to be controlled by the amount of polymer initially supplied to the system. The sediment (the settled phase) characteristics, determined as a function of the polymer concentration and the rate of the polymerization shrinkage determined for composite resins, obtained by extrusion of the sediment after centrifugation, were found to be correlated. The specific role of the adsorbed polymer was found to be differently perturbed with the supplementary supply of dimethacrylate based monomer additives. Particularly, the bisphenol A dimethacrylate that generated crystals within the sediment was found to impede the shrinkage along the crystal lateral faces and strongly limit the shrinkage along its basal faces. Addition of ethyleneglycol- or polyethylene-glycoldimethacrylate monomers was determined to modify the sedimentation characteristics of the aerosil suspension and the shrinkage properties of the composites. Finally, the effects of stepwise light curing methods with prolonged lighting-off periods were investigated and found to modify the development and the final values of the composite shrinkage. http://www.mdpi.com/2073-4360/4/1/256 Wed, 18 Jan 2012 00:00:00 CET Polymers 2012-01-18 4 1 Article 256 274 2073-4360 Shrinkage Characteristics of Experimental Polymer Containing Composites under Controlled Light Curing Modes 2012-01-18 doi: 10.3390/polym4010256 Alain Pefferkorn http://www.mdpi.com/2073-4360/4/1/240 We report results from Brownian dynamics computer simulations of systems comprised by two terminally charged hyperbranched molecules preferentially branched in the periphery, with an oppositely charged linear chain of varying length. Comparison of the findings from the present study to stoichiometric counterparts and to analogous dendrimer-based complexes, reveal that the presence of the second hyperbranched molecule incurs significant changes in the conformational characteristics of both components of the complex. Instead of step-like changes in the average size and shape of the hyperbranched component that were noted in the previously studied stoichiometric systems, a rather smooth change is observed upon increase of the length of the linear component. In addition, a markedly different behavior is also noticed in the conformational characteristics of the linear chain when compared to that in similar dendrimer-based systems. The above findings are consistent with the higher degree of deformability of the peripherally branched molecules which allow appropriate rearrangements in shape in order to accommodate the favorable Coulombic interactions between the two components of the complex. This behavior offers new insight towards the design of more efficient hyperbranched-based systems which can take advantage of the multifunctionality and the structural properties of the highly branched polymer components. http://www.mdpi.com/2073-4360/4/1/240 Tue, 17 Jan 2012 00:00:00 CET Polymers 2012-01-17 4 1 Article 240 255 2073-4360 Conformational Effects in Non-Stoichiometric Complexes of Two Hyperbranched Molecules with a Linear Polyelectrolyte 2012-01-17 doi: 10.3390/polym4010240 George Dalakoglou Kostas Karatasos Sergey Lyulin Sergey Larin Anatoly Darinskii Alexey Lyulin http://www.mdpi.com/2073-4360/4/1/211 This review exposes the current poor understanding of the internal segmental chain dynamics of dendrimers in solution probed by monitoring the process of excimer formation between pyrene labels covalently attached to the chain ends of dendrimers. The review begins by covering the bases of fluorescence and the kinetics of pyrene excimer formation before describing a procedure based on the Model Free (MF) analysis that is used to analyze quantitatively the fluorescence decays acquired for dendrimers, the ends of which have been fully and covalently labeled with pyrene. Comparison of the various trends obtained by different research groups describing the efficiency of pyrene excimer formation with the generation number of dendrimers illustrates the lack of consensus between the few studies devoted to the topic. One possible reason for this disagreement might reside in the presence of minute amounts of unattached pyrene labels which act as potent fluorescent impurities and affect the analysis of the fluorescence spectra and decays in an uncontrolled manner. The review points out that the MF analysis of the fluorescence decays acquired with pyrene-labeled dendrimers enables one to account for the presence of unattached pyrene and to retrieve information about the internal segmental dynamics of the dendrimer. It provides guidelines that should enable future studies on pyrene-labeled dendrimers to yield results that are more straightforward to interpret. http://www.mdpi.com/2073-4360/4/1/211 Tue, 17 Jan 2012 00:00:00 CET Polymers 2012-01-17 4 1 Review 211 239 2073-4360 Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation 2012-01-17 doi: 10.3390/polym4010211 Jean Duhamel http://www.mdpi.com/2073-4360/4/1/187 This study demonstrated a method for toughening a highly crosslinked anhydride cured DGEBA epoxy using rubbery block copolymer grafted SiO2 nanoparticles. The particles were synthesized by a sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The inner rubbery block poly(n-hexyl methacrylate) (PHMA) had a glass transition temperature below room temperature. The outer block poly(glycidyl methacrylate) (PGMA) was matrix compatible. A rubbery interlayer thickness of 100% and 200% of the particle core radius was achieved by grafting a 20 kg/mol and a 40 kg/mol PHMA at a graft density of 0.7 chains/nm2 from the SiO2 surface. The 20 kg/mol rubbery interlayer transferred load more efficiently to the SiO2 cores than the 40 kg/mol rubbery interlayer and maintained the epoxy modulus up to a loading of 10 vol% of the rubbery interlayer. Both systems enabled cavitation or plastic dilatation. Improvement of the strain-to-break and the tensile toughness was found in both systems. We hypothesize that plastic void growth in the matrix is the primary mechanism causing the improvement of the ductility. http://www.mdpi.com/2073-4360/4/1/187 Mon, 16 Jan 2012 00:00:00 CET Polymers 2012-01-16 4 1 Article 187 210 2073-4360 The Mechanical Properties of Epoxy Composites Filled with Rubbery Copolymer Grafted SiO2 2012-01-16 doi: 10.3390/polym4010187 Jianing Gao Junting Li Brian C. Benicewicz Su Zhao Henrik Hillborg Linda S. Schadler http://www.mdpi.com/2073-4360/4/1/150 Photocontrol of molecular alignment is an exceptionally-intelligent and useful strategy. It enables us to control optical coefficients, peripheral molecular alignments, surface relief structure, and actuation of substances by means of photoirradiation. Azobenzene-containing polymers and functionalized liquid crystalline polymers are well-known photocontrollable materials. In this paper, we introduce recent applications of these materials in the fields of mechanics, self-organized structuring, mass transport, optics, and photonics. The concepts in each application are explained based on the mechanisms of photocontrol. The interesting natures of the photocontrollable materials and the conceptual applications will stimulate novel ideas for future research and development in this field. http://www.mdpi.com/2073-4360/4/1/150 Mon, 09 Jan 2012 00:00:00 CET Polymers 2012-01-09 4 1 Review 150 186 2073-4360 Optical and Physical Applications of Photocontrollable Materials: Azobenzene-Containing and Liquid Crystalline Polymers 2012-01-09 doi: 10.3390/polym4010150 Akira Emoto Emi Uchida Takashi Fukuda http://www.mdpi.com/2073-4360/4/1/134 Photonic materials (PMs) that are capable of manipulating and controlling light in systems have immense potential for the computing and communications industries. These materials are formed by assembling components of differing refractive indices in a periodic array. Light then interacts with this assembly, which results in constructive and destructive interference, and hence color. While many three-dimensional PMs have been reported, and have the most potential for the applications mentioned above, one-dimensional PMs have a multitude of potential uses, e.g., light filtration. In this review, we focus on one-dimensional PMs; specifically poly (N-isopropylacrylamide) microgel based etalons. The etalons can be fabricated to exhibit a single bright color, and because the diameter of the microgels is dependent on temperature and pH, the mirror-mirror spacing can be dynamically tuned; therefore the etalon’s color is dynamically tunable. http://www.mdpi.com/2073-4360/4/1/134 Mon, 09 Jan 2012 00:00:00 CET Polymers 2012-01-09 4 1 Review 134 149 2073-4360 Color-Tunable Etalons Assembled from Poly (N-Isopropylacrylamide) Based Microgels 2012-01-09 doi: 10.3390/polym4010134 Liang Hu Michael J. Serpe http://www.mdpi.com/2073-4360/4/1/116 This paper reviews preparation and applications of amylose supramolecules by means of phosphorylase-catalyzed enzymatic polymerization. When the enzymatic polymerization of α-d-glucose 1-phosphate (G-1-P) as a monomer was carried out in the presence of poly(tetrahydrofuran) (PTHF) of a hydrophobic polyether as a guest polymer, the supramolecule, i.e., an amylose-PTHF inclusion complex, was formed in the process of polymerization. Because the representation of propagation in the polymerization is similar to the way that vines of plants grow twining around rods, this polymerization method for the preparation of amylose-polymer inclusion complexes was proposed to be named “vine-twining polymerization”. Various hydrophobic polyethers, polyesters, poly(ester-ether), and polycarbonates were also employed as the guest polymer in the vine-twining polymerization to produce the corresponding inclusion complexes. To obtain the inclusion complex from a strongly hydrophobic guest polymer, the parallel enzymatic polymerization system was developed as an advanced extension of the vine-twining polymerization. In addition, it was found that amylose selectively includes one side of the guest polymer from a mixture of two resemblant guest polymers, as well as a specific range in molecular weights of the guest PTHF. Amylose also exhibited selective inclusion behavior toward stereoisomers of poly(lactide)s. Moreover, the preparation of hydrogels through the formation of inclusion complexes of amylose in vine-twining polymerization was achieved. http://www.mdpi.com/2073-4360/4/1/116 Mon, 09 Jan 2012 00:00:00 CET Polymers 2012-01-09 4 1 Review 116 133 2073-4360 Preparation and Applications of Amylose Supramolecules by Means of Phosphorylase-Catalyzed Enzymatic Polymerization 2012-01-09 doi: 10.3390/polym4010116 Jun-ichi Kadokawa http://www.mdpi.com/2073-4360/4/1/72 Hyperbranched polymers show an outstanding potential for applications ranging from chemistry over nanotechnology to pharmacy. In order to take advantage of this potential, the underlying phase behaviour must be known. From the thermodynamic point of view, the modelling of these phase diagrams is quite challenging, because the thermodynamic properties depend on the architecture of the hyperbranched polymer as well as on the number and kind of present functional end groups. The influence of architecture can be taken into account via the lattice cluster theory (LCT) as an extension of the well-known Flory–Huggins theory. Whereas the Flory–Huggins theory is limited to linear polymer chains, the LCT can be applied to an arbitrary chain architecture. The number and the kind of functional groups can be handled via the Wertheim perturbation theory, applicable for directed forces between the functional groups and the surrounding solvent molecules. The combination of the LCT and the Wertheim theory can be established for the modelling or even prediction of the liquid-liquid equilibria (LLE) of polymer solutions in a single solvent or in a solvent mixture or polymer blends, where the polymer can have an arbitrary structure. The applied theory predicts large demixing regions for mixtures of linear polymers and hyperbranched polymers, as well as for mixtures made from two hyperbranched polymers. The introduction of empty lattice sites permits the theoretical investigation of pressure effects on phase behaviour. The calculated phase diagrams were compared with own experimental data or to experimental data taken from literature. http://www.mdpi.com/2073-4360/4/1/72 Mon, 09 Jan 2012 00:00:00 CET Polymers 2012-01-09 4 1 Review 72 115 2073-4360 Phase Diagrams for Systems Containing Hyperbranched Polymers 2012-01-09 doi: 10.3390/polym4010072 Sabine Enders Kai Langenbach Philipp Schrader Tim Zeiner http://www.mdpi.com/2073-4360/4/1/46 The control of microbial infections is a very important issue in modern society. In general there are two ways to stop microbes from infecting humans or deteriorating materials—disinfection and antimicrobial surfaces. The first is usually realized by disinfectants, which are a considerable environmental pollution problem and also support the development of resistant microbial strains. Antimicrobial surfaces are usually designed by impregnation of materials with biocides that are released into the surroundings whereupon microbes are killed. Antimicrobial polymers are the up and coming new class of disinfectants, which can be used even as an alternative to antibiotics in some cases. Interestingly, antimicrobial polymers can be tethered to surfaces without losing their biological activity, which enables the design of surfaces that kill microbes without releasing biocides. The present review considers the working mechanisms of antimicrobial polymers and of contact-active antimicrobial surfaces based on examples of recent research as well as on multifunctional antimicrobial materials. http://www.mdpi.com/2073-4360/4/1/46 Mon, 09 Jan 2012 00:00:00 CET Polymers 2012-01-09 4 1 Review 46 71 2073-4360 Antimicrobial Polymers in Solution and on Surfaces: Overview and Functional Principles 2012-01-09 doi: 10.3390/polym4010046 Felix Siedenbiedel Joerg C. Tiller http://www.mdpi.com/2073-4360/4/1/32 Water-soluble copolymers of N-acryloyl-N′-ethylpiperazine (AcrNEP) with methyl methacrylate (MMA) were synthesized to high conversion by free-radical solution polymerization. The composition of the copolymers was determined using Fourier Transform Infra-red Spectroscopy (FTIR). Copolymers containing AcrNEP content above 44 mol% were readily soluble in water and exhibited the critical solution temperature behavior. The copolymers were strongly responsive to changes in pH of the external medium due to the presence of tertiary amine functions that could be protonated at low pH. The influence of various factors such as copolymer composition, pH, temperature, salt and surfactant concentration on the LCST of the copolymers were systematically studied. The intrinsic viscosity of the copolymers in dimethyl formamide decreased with increase in temperature due to a decrease in thermodynamic affinity between polymer chains and solvent molecules. The viscosity behavior of the copolymers in sodium chloride solution was similar to that of classical polyelectrolytes and hydrophobically modified polyacrylate systems. http://www.mdpi.com/2073-4360/4/1/32 Thu, 05 Jan 2012 00:00:00 CET Polymers 2012-01-05 4 1 Article 32 45 2073-4360 Solution Properties of Water-Soluble “Smart” Poly(N-acryloyl-N′-ethyl piperazine-co-methyl methacrylate) 2012-01-05 doi: 10.3390/polym4010032 G. Roshan Deen http://www.mdpi.com/2073-4360/4/1/20 The four first generations of dendrigraft poly-L-lysine have been studied in dimethylformamide (aprotic solvent) and in 0.2 M NaCl aqueous solutions by isothermal translation diffusion, 1H NMR and viscometry methods. The relationships between diffusion coefficient, intrinsic viscosity and molar mass have been determined for dendrigraft poly-L-lysines, and the scaling index values have been compared to classical trifunctional dendrimers. Dendrimers and dendrigraft poly-L-lysines exhibited similitudes in their hydrodynamic behaviors. Nevertheless, dendrigraft poly-L-lysines displayed a specific behavior in solution. In contrast to dendrimers, a significant change of hydrodynamic dimension of dendrigraft poly-L-lysines according to the nature of the solvent has been observed. In aprotic solvent, the dendrigraft poly-L-lysine dimensions are about two times lower than in aqueous media (i.e., the hydrodynamic volume is contracted by a factor 8 in dimethylformamide), revealing the softness of dendrigraft poly-L-lysine compared to classical trifunctional dendrimers. http://www.mdpi.com/2073-4360/4/1/20 Mon, 02 Jan 2012 00:00:00 CET Polymers 2012-01-02 4 1 Article 20 31 2073-4360 Hydrodynamic Behavior of Dendrigraft Polylysines in Water and Dimethylformamide 2012-01-02 doi: 10.3390/polym4010020 Natalia Yevlampieva Anatolii Dobrodumov Olga Nazarova Olga Okatova Hervé Cottet http://www.mdpi.com/2073-4360/4/1/1 In this mini-review we report on current developments of hybrid materials based on semiconductor nanocrystals integrated into polymer matrices for direct light conversion, their present limitations, as well as their high potential for future applications. http://www.mdpi.com/2073-4360/4/1/1 Tue, 27 Dec 2011 00:00:00 CET Polymers 2011-12-27 4 1 Review 1 19 2073-4360 Polymer-Nanocrystal Hybrid Materials for Light Conversion Applications 2011-12-27 doi: 10.3390/polym4010001 Ying Yuan Michael Krüger http://www.mdpi.com/2073-4360/3/4/2156 Colloidal gels are intermediates in the production of highly porous particle systems. In the production process, the gels are fragmented after their creation. These gel fragments consolidate to particles whose application-technological properties are determined by their size and porosity. A model of the consolidation process is proposed: The consolidation process of a gel fragment is simulated with the Molecular Dynamics (MD) method with the assumption of van der Waals forces in interplay with the thermal motion as driving forces for the consolidation. The simulation results are compared with experimental data and with a Monte Carlo (MC) simulation. http://www.mdpi.com/2073-4360/3/4/2156 Tue, 20 Dec 2011 00:00:00 CET Polymers 2011-12-20 3 4 Article 2156 2171 2073-4360 Experimentally Justified Model-Like Description of Consolidation of Precipitated Silica 2011-12-20 doi: 10.3390/polym3042156 Hussein Sahabi Matthias Kind http://www.mdpi.com/2073-4360/3/4/2142 Plasma nanocoating of allylamine were deposited on the surfaces of multi-walled carbon nanotubes (MWCNTs) to provide desirable functionalities and thus to tailor the surface characteristics of MWCNTs for improved dispersion and interfacial adhesion in epoxy matrices. Plasma nanocoated MWCNTs were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), surface contact angle, and pH change measurements. Mechanical testing results showed that epoxy reinforced with 1.0 wt % plasma coated MWCNTs increased the tensile strength by 54% as compared with the pure epoxy control, while epoxy reinforced with untreated MWCNTs have lower tensile strength than the pure epoxy control. Optical and electron microscopic images show enhanced dispersion of plasma coated MWCNTs in epoxy compared to untreated MWCNTs. Plasma nanocoatings from allylamine on MWCNTs could significantly enhance their dispersion and interfacial adhesion in epoxy matrices. Simulation results based on the shear-lag model derived from micromechanics also confirmed that plasma nanocoating on MWCNTs significantly improved the epoxy/fillers interface bonding and as a result the increased composite strength. http://www.mdpi.com/2073-4360/3/4/2142 Mon, 19 Dec 2011 00:00:00 CET Polymers 2011-12-19 3 4 Article 2142 2155 2073-4360 Plasma Treated Multi-Walled Carbon Nanotubes (MWCNTs) for Epoxy Nanocomposites 2011-12-19 doi: 10.3390/polym3042142 Andrew C. Ritts Qingsong Yu Hao Li Stephen J. Lombardo Xu Han Zhenhai Xia Jie Lian http://www.mdpi.com/2073-4360/3/4/2133 We attempted synthesis of the hydrogen adsorption material suitable for the fuel cell vehicles (FCEVs). The designed and synthesized Cu2(3,5-Pyridinedicarboxylate)2 (=Cu2PDC2) metal complex showed an extremely high volumetric uptake density for a physisorption material, even though the specific surface area was only about 1,000 m2 g−1. Factors for high uptake properties are considered to be the increased adsorption sites per unit area, the increased adsorption energy, and the optimized design of pore shapes. High hydrogen uptake on volumetric basis is especially effective for FCEV because the tank volume is reduced. It is expected that property prediction using computational simulation and sophisticated analysis at the micro and nano levels will become an indispensable tool in the design of functional materials. http://www.mdpi.com/2073-4360/3/4/2133 Mon, 12 Dec 2011 00:00:00 CET Polymers 2011-12-12 3 4 Communication 2133 2141 2073-4360 Design of Improved Metal-Organic Framework (MOF) H2 Adsorbents 2011-12-12 doi: 10.3390/polym3042133 Terumi Furuta Izuru Kanoya Hiroshi Sakai Mitsuya Hosoe http://www.mdpi.com/2073-4360/3/4/2107 Responsive polymer brushes possess many interesting properties that enable them to control a range of important interfacial behaviours, including adhesion, wettability, surface adsorption, friction, flow and motility. The ability to design a macromolecular response to a wide variety of external stimuli makes polymer brushes an exciting class of functional materials, and has been made possible by advances in modern controlled polymerization techniques. In this review we discuss the physics of polymer brush response along with a summary of the techniques used in their synthesis. We then review the various stimuli that can be used to switch brush conformation; temperature, solvent quality, pH and ionic strength as well as the relatively new area of electric field actuation We discuss examples of devices that utilise brush conformational change, before highlighting other potential applications of responsive brushes in real world devices. http://www.mdpi.com/2073-4360/3/4/2107 Wed, 07 Dec 2011 00:00:00 CET Polymers 2011-12-07 3 4 Review 2107 2132 2073-4360 Water Soluble Responsive Polymer Brushes 2011-12-07 doi: 10.3390/polym3042107 Michael P. Weir Andrew J. Parnell http://www.mdpi.com/2073-4360/3/4/2088 Despite their potent antimicrobial activity, the usefulness of antimicrobial peptides (AMPs) as antibiotics has been limited by their toxicity to eukaryotic cells and a lack of stability in vivo. In the present study we examined the effects of introducing D-lysine residues into a 15-residue hybrid AMP containing residues 1–7 of cecropin A and residues 2–9 of melittin (designated CM15). Diastereomeric analogs of CM15 containing between two and five D-lysine substitutions were evaluated for their antimicrobial activity, lysis of human erythrocytes, toxicity to murine macrophages, ability to disrupt cell membranes, and protease stability. All of the analogs caused rapid permeabilization of the Staphylococcus aureus cell envelope, as indicated by uptake of SYTOX green. Permeabilization of the plasma membrane of RAW264.7 macrophages was also observed for CM15, but this was substantially diminished for the D-lysine containing analogs. The introduction of D-lysine caused moderate decreases in antimicrobial activity for all analogs studied, with a much more pronounced reduction in toxicity to eukaryotic cells, leading to marked improvements in antimicrobial efficacy. Circular dichroism studies indicated a progressive loss of helical secondary structure upon introduction of D-lysine residues, with a good correspondence between helical content and eukaryotic cell cytotoxicity. Overall, these studies indicate that disruption of amphipathic secondary structure reduces both antimicrobial activity and eukaryotic cell toxicity, but that the reduction in eukaryotic cell cytotoxicity is more pronounced, leading to an overall gain in antimicrobial selectivity. http://www.mdpi.com/2073-4360/3/4/2088 Tue, 06 Dec 2011 00:00:00 CET Polymers 2011-12-06 3 4 Article 2088 2106 2073-4360 Effects of D-Lysine Substitutions on the Activity and Selectivity of Antimicrobial Peptide CM15 2011-12-06 doi: 10.3390/polym3042088 Heather M. Kaminski Jimmy B. Feix http://www.mdpi.com/2073-4360/3/4/2078 In serial passaging cultures of mouse embryonic stem (ES) cells, we employed a dendrimer-immobilized substrate that displayed d-glucose as a terminal ligand. The d-glucose-displaying dendrimer (GLU/D) surface caused the ES cells to form loosely attached spherical colonies, while those on a gelatin-coated surface formed flatter colonies that were firmly attached to the surface. Despite the morphological similarities between the colonies on the GLU/D surface and aggregates on a conventional bacteriological dish, immunostaining and RT-PCR analyses revealed the maintenance of cells within the spherical colonies on the GLU/D surface in an undifferentiated state with very low expressions of primitive endoderm markers. On the bacteriological dish, however, the cells within the aggregates showed a different cellular state with partial differentiation into the primitive endoderm lineage, and the expression level increased gradually along with the number of passages. These results indicate that the GLU/D surface can be a potential tool for controlling the ES cell morphology and then govern their self-renewal and fate. http://www.mdpi.com/2073-4360/3/4/2078 Mon, 05 Dec 2011 00:00:00 CET Polymers 2011-12-05 3 4 Communication 2078 2087 2073-4360 Embryonic Stem Cells Maintain an Undifferentiated State on Dendrimer-Immobilized Surface with d-Glucose Display 2011-12-05 doi: 10.3390/polym3042078 Shohreh Mashayekhan Mee-Hae Kim Masahiro Kino-oka Jun-ichi Miyazaki Masahito Taya http://www.mdpi.com/2073-4360/3/4/2053 Since their earliest synthesis, much interest has arisen in the use of dendritic and structurally allied forms of polymer for light energy harvesting, especially as organic adjuncts for solar energy devices. With the facility to accommodate a proliferation of antenna chromophores, such materials can capture and channel light energy with a high degree of efficiency, each polymer unit potentially delivering the energy of one photon—or more, when optical nonlinearity is involved. To ensure the highest efficiency of operation, it is essential to understand the processes responsible for photon capture and channelling of the resulting electronic excitation. Highlighting the latest theoretical advances, this paper reviews the principal mechanisms, which prove to involve a complex interplay of structural, spectroscopic and electrodynamic properties. Designing materials with the capacity to capture and control light energy facilitates applications that now extend from solar energy to medical photonics. http://www.mdpi.com/2073-4360/3/4/2053 Mon, 05 Dec 2011 00:00:00 CET Polymers 2011-12-05 3 4 Review 2053 2077 2073-4360 Mechanisms of Light Energy Harvesting in Dendrimers and Hyperbranched Polymers 2011-12-05 doi: 10.3390/polym3042053 David S. Bradshaw David L. Andrews http://www.mdpi.com/2073-4360/3/4/2039 Organic ligand surface-treated Tb3+:LaF3 was synthesized in water and methanol for subsequent incorporation into polymethyl methacrylate (PMMA) via solution-precipitation chemistry in order to produce optically active polymer nanocomposites. Nanoparticle agglomerate diameters ranged from 388 ± 188 nm when synthesized in water and 37 ± 2 nm when synthesized in methanol. Suspension stability is paramount for producing optically transparent materials. Methanol nanoparticle synthesized at a pH of 3 exhibited the smallest agglomerate size. Optical spectroscopy, dynamic light scattering, transmission electron microscopy, scanning transmission electron microscopy, and zeta potential analysis were used to characterize the particles synthesized. http://www.mdpi.com/2073-4360/3/4/2039 Tue, 29 Nov 2011 00:00:00 CET Polymers 2011-11-29 3 4 Article 2039 2052 2073-4360 The Influence of Synthesis Parameters on Particle Size and Photoluminescence Characteristics of Ligand Capped Tb3+:LaF3 2011-11-29 doi: 10.3390/polym3042039 Kyle Gipson Courtney Kucera Derek Stadther Kathryn Stevens John Ballato Phil Brown http://www.mdpi.com/2073-4360/3/4/2018 Nafion membranes were impregnated with photocurable supramolecules, viz., hyperbranched polyester having pendant functional carboxylic acid groups (HBPEAc-COOH) by swelling in methanol and subsequently photocured in-situ after drying. Structure-property relationships of the HBPEAc-COOH impregnated Nafion membranes were analyzed on the basis of Fourier transform infrared (FTIR) spectroscopy, solid-state nuclear magnetic resonance (SSNMR) and dynamic mechanical analysis (DMA). FTIR and SSNMR investigations revealed that about 7 wt % of HBPEAc-COOH was actually incorporated into the ionic domains of Nafion. The FTIR study suggests possible complexation via inter-species hydrogen bonding between the carboxylic groups of HBPEAc-COOH and the sulfonate groups of Nafion. The α-relaxation peak corresponding to the glass transition temperature of the ionic domains of the neat Nafion-acid form was found to increase from ~100 to ~130 °C upon impregnation with enhanced modulus afforded by the cured polyester network within the ionic domains. The AC impedance fuel cell measurement of the impregnated membrane exhibited an increasing trend of proton conductivity with increasing temperature, which eventually surpassed that of neat Nafion above 100 °C. Of particular importance is that the present paper is the first to successfully incorporate polymer molecules/networks into the Nafion ionic domains by means of impregnation with hyperbranched supramolecules followed by in-situ photopolymerization. http://www.mdpi.com/2073-4360/3/4/2018 Mon, 28 Nov 2011 00:00:00 CET Polymers 2011-11-28 3 4 Article 2018 2038 2073-4360 Incorporation of Hyperbranched Supramolecules into Nafion Ionic Domains via Impregnation and In-Situ Photopolymerization 2011-11-28 doi: 10.3390/polym3042018 Nadzrinahamin A. Nazir Thein Kyu Anna M. Reinsel Matthew Espe Mami Nosaka Hiruto Kudo Tadatomi Nishikubo http://www.mdpi.com/2073-4360/3/4/2010 Inflammatory bowel diseases (IBD) are characterized by a chronic relapsing inflammation of the gastrointestinal mucosa. The etiology and pathogenesis of these disorders such as Crohn’s disease and ulcerative colitis are incompletely understood. Recently, antimicrobial peptides, which are expressed by leukocytes and epithelia, have been implicated in the pathogenesis of IBD. Antimicrobial peptides are pivotal for intestinal defense, shaping the composition of the luminal flora and contributing thereby to the maintenance of intestinal homeostasis. Apart from their antimicrobial activity affecting commensal bacteria, immunomodulatory properties of antimicrobial peptides have been identified, which link innate and adaptive immune response. There is increasing evidence that alterations in mucosal levels of these peptides contribute to IBD pathogenensis. http://www.mdpi.com/2073-4360/3/4/2010 Wed, 16 Nov 2011 00:00:00 CET Polymers 2011-11-16 3 4 Review 2010 2017 2073-4360 Role of Antimicrobial Peptides in Inflammatory Bowel Disease 2011-11-16 doi: 10.3390/polym3042010 Jan-Michel Otte Stefan Vordenbäumen http://www.mdpi.com/2073-4360/3/4/1972 Advances in polymer science have led to the development of novel drug delivery systems. Some polymers are obtained from natural resources and then chemically modified for various applications, while others are chemically synthesized and used. A large number of natural and synthetic polymers are available. In the present paper, only water soluble polymers are described. They have been explained in two categories (1) synthetic and (2) natural. Drug polymer conjugates, block copolymers, hydrogels and other water soluble drug polymer complexes have also been explained. The general properties and applications of different water soluble polymers in the formulation of different dosage forms, novel delivery systems and biomedical applications will be discussed. http://www.mdpi.com/2073-4360/3/4/1972 Fri, 11 Nov 2011 00:00:00 CET Polymers 2011-11-11 3 4 Review 1972 2009 2073-4360 Water Soluble Polymers for Pharmaceutical Applications 2011-11-11 doi: 10.3390/polym3041972 Veeran Gowda Kadajji Guru V. Betageri http://www.mdpi.com/2073-4360/3/4/1944 Various types of controlled/living radical polymerizations, or using the IUPAC recommended term, reversible-deactivation radical polymerization (RDRP), conducted inside nano-sized reaction loci are considered in a unified manner, based on the polymerization rate expression, Rp = kp[M]K[Interm]/[Trap]. Unique miniemulsion polymerization kinetics of RDRP are elucidated on the basis of the following two factors: (1) A high single molecule concentration in a nano-sized particle; and (2) a significant statistical concentration variation among particles. The characteristic particle diameters below which the polymerization rate start to deviate significantly (1) from the corresponding bulk polymerization, and (2) from the estimate using the average concentrations, can be estimated by using simple equations. For stable-radical-mediated polymerization (SRMP) and atom-transfer radical polymerization (ATRP), an acceleration window is predicted for the particle diameter range, . For reversible-addition-fragmentation chain-transfer polymerization (RAFT), degenerative-transfer radical polymerization (DTRP) and also for the conventional nonliving radical polymerization, a significant rate increase occurs for . On the other hand, for  the polymerization rate is suppressed because of a large statistical variation of monomer concentration among particles. http://www.mdpi.com/2073-4360/3/4/1944 Fri, 11 Nov 2011 00:00:00 CET Polymers 2011-11-11 3 4 Article 1944 1971 2073-4360 Threshold Particle Diameters in Miniemulsion Reversible-Deactivation Radical Polymerization 2011-11-11 doi: 10.3390/polym3041944 Hidetaka Tobita http://www.mdpi.com/2073-4360/3/4/1934 Two-dimensional (2D) grid coordination polymers were prepared by the reaction of 1,4-bis(4-pyridylmethyl)tetrafluorobenzene (bpf) with Cu(NO3)2 in the presence of aromatic compounds. Crystal structures of {[Cu(bpf)2(NO3)2]·(biphenyl)2}n (1), {[Cu(bpf)2(NO3)2]·(m-C6H4(OMe)2)2}n (2), {[Cu(bpf)2(NO3)2]·PhtBu}n (3) and {[Cu(bpf)2(NO3)(H2O)]NO3·(bpf)0.5}n (4) were determined. The grid networks were held together by C–H···O and C–H···F hydrogen bonds via the NO3− anions and the tetrafluorophenylene rings of bpf, respectively. Biphenyl, m-dimethoxybenzene, t-butylbenzene, and bpf molecules were clathrated in cyclic cavities of the grid networks through arene-perfluoroarene interactions. These coordination networks have remarkable clathration ability for aromatic compounds. http://www.mdpi.com/2073-4360/3/4/1934 Mon, 07 Nov 2011 00:00:00 CET Polymers 2011-11-07 3 4 Article 1934 1943 2073-4360 Synthesis and Characterization of Novel Copper(II) 2D Coordination Polymers from a Fluorinated Flexible Ligand with Remarkable Clathration Ability 2011-11-07 doi: 10.3390/polym3041934 Tomohiro Beni Kayoko Kasai http://www.mdpi.com/2073-4360/3/4/1911 Star shaped segmented macromolecules constitute an interesting class of polymeric materials whose properties differ remarkably from those appearing in their linear counterparts. This review highlights the work done in the last decade, dealing with the self-assembly of star-shaped block copolymers and terpolymers of various topologies in aqueous media. This article focuses on a specific class of star shaped macromolecules designated as stimuli responsive. These stars bearblock/arms undergo sharp phase transitions upon responding to stimuli, such as temperature, pH, ionic strength and so forth. These transitions impose dramatic transformations on the morphology and, accordingly, in the functionality of the nanostructured associates. The number of arms, the specific functionality and topology of the different arm/blocks and the overall macromolecular architecture of the star polymer, significantly influence their behavior in terms of self-assembly and responsiveness. http://www.mdpi.com/2073-4360/3/4/1911 Thu, 03 Nov 2011 00:00:00 CET Polymers 2011-11-03 3 4 Review 1911 1933 2073-4360 Water-Soluble Stimuli Responsive Star-Shaped Segmented Macromolecules 2011-11-03 doi: 10.3390/polym3041911 Zacharoula Iatridi Constantinos Tsitsilianis http://www.mdpi.com/2073-4360/3/4/1902 The bacterial inactivation kinetics of dialdehyde starch (DAS) aqueous suspension was studied by the relationship between the minimal lethal concentration (MLC) and the inactivation time at four different temperatures. The relationship between MLC and exposure time was found to follow the first-order Chick-Watson law. This first-order inactivation kinetics was modeled by pseudo-first order chemical reaction. This model was validated by the successful predication of the bacterial inactivation response at room temperature. http://www.mdpi.com/2073-4360/3/4/1902 Thu, 03 Nov 2011 00:00:00 CET Polymers 2011-11-03 3 4 Communication 1902 1910 2073-4360 Bacterial Inactivation Kinetics of Dialdehyde Starch Aqueous Suspension 2011-11-03 doi: 10.3390/polym3041902 Le Song Samuel R. Farrah Ronald H. Baney http://www.mdpi.com/2073-4360/3/4/1875 The physicochemical nature of chitin and chitosan, which influences the biomedical activity of these compounds, is strongly related to the source of chitin and the conditions of the chitin/chitosan production process. Apart from widely described key factors such as weight-averaged molecular weight (MW) and degree of N-acetylation (DA), other physicochemical parameters like polydispersity (MW/MN), crystallinity or the pattern of acetylation (PA) have to be taken into consideration. From the biological point of view, these parameters affect a very important factor—the solubility of chitin and chitosan in water and organic solvents. The physicochemical properties of chitosan solutions can be controlled by manipulating solution conditions (temperature, pH, ionic strength, concentration, solvent). The degree of substitution of the hydroxyl and the amino groups or the degree of quaternization of the amino groups also influence the mechanical and biological properties of chitosan samples. Finally, a considerable research effort has been directed towards developing safe and efficient chitin/chitosan-based products because many factors, like the size of nanoparticles, can determine the biomedical characteristics of medicinal products. The influence of these factors on the biomedical activity of chitin/chitosan-based products is presented in this report in more detail. http://www.mdpi.com/2073-4360/3/4/1875 Thu, 03 Nov 2011 00:00:00 CET Polymers 2011-11-03 3 4 Review 1875 1901 2073-4360 Biomedical Activity of Chitin/Chitosan Based Materials—Influence of Physicochemical Properties Apart from Molecular Weight and Degree of N-Acetylation 2011-11-03 doi: 10.3390/polym3041875 Jolanta Kumirska Mirko X. Weinhold Jorg Thöming Piotr Stepnowski http://www.mdpi.com/2073-4360/3/4/1866 A homochiral metal-organic framework (MOF) based on enantiopure (R)-2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylic acid was synthesized. X-ray crystal diffraction studies revealed that the MOF adopts a one-dimensional infinite right-handed helical tubular structure along the a-axis, which serves as a host for the inclusion of guest dimethylformamide (DMF) molecules. http://www.mdpi.com/2073-4360/3/4/1866 Tue, 01 Nov 2011 00:00:00 CET Polymers 2011-11-01 3 4 Article 1866 1874 2073-4360 One-Dimensional Helical Homochiral Metal-Organic Framework Built from 2,2′-Dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylic Acid 2011-11-01 doi: 10.3390/polym3041866 Koichi Tanaka Yuki Kikumoto Motoo Shiro http://www.mdpi.com/2073-4360/3/4/1849 Novel tetra-functional hydrolyzing monomers were prepared from the reaction of TEOS and select alkene-containing alcohols, ethylene glycol vinyl ether or 2-allyloxy ethanol, and combined with trimethylolpropane tris(3-mercaptopropionate) (tri-thiol) in a thiol-ene “click” polymerization reaction to produce clear, colorless thiol-ene networks using both radiation and thermal-cure techniques. These networks were characterized for various mechanical characteristics, and found to posses Tg’s (DSC), hardness, tack, and thermal stability (TGA) consistent with their molecular structures. A new ene-modified urethane oligomer was prepared based on the aliphatic polyisocyanate Desmodur® N 3600 and added to the thiol-ene hydrolyzable network series in increasing amounts, creating a phase-segregated material having two Tg’s. An increase in water absorption in the ene-modified urethane formulations leading to a simultaneous increase in the rate of hydrolysis was supported by TGA data, film hardness measurements, and an NMR study of closely related networks. This phenomenon was attributed to the additional hydrogen bonding elements and polar functionality brought to the film with the addition of the urethane segment. SEM was utilized for visual analysis of topographical changes in the film’s surface upon hydrolysis and provides support for surface-driven erosion. Coatings prepared in this study are intended for use as hydrolyzing networks for marine coatings to protect against ship fouling. http://www.mdpi.com/2073-4360/3/4/1849 Tue, 25 Oct 2011 00:00:00 CEST Polymers 2011-10-25 3 4 Article 1849 1865 2073-4360 Preparation of Novel Hydrolyzing Urethane Modified Thiol-Ene Networks 2011-10-25 doi: 10.3390/polym3041849 Nicole M. Mackey Bridget S. Confait James H. Wynne J. Paige Buchanan http://www.mdpi.com/2073-4360/3/4/1833 Gold-poly(methyl methacrylate) nanocomposites are prepared by an in situ method, by irradiating spin-coated films containing the polymer and the gold precursor dissolved in acetone. The reduction of gold ions results in the formation of Au that nucleates and grows within the polymer film. It is shown that, depending on the energy source, gold nanoparticles with different shapes can be formed. Nanocomposites prepared through UV-, thermal-, and MW-irradiation, respectively, show a low sensitivity toward the environment. However, by annealing the samples at temperatures well above the glass transition temperature of the polymer, the response to dielectric environment appears to be enhanced significantly. The sensitivity of samples synthesized through the three different methods is found to be comparable, around 100 nm/RIU. The increased sensitivity of the annealed sample is accounted for by the increased mobility of both polymer chains and gold nanoparticles in the rubbery state of the material and the presence of the monomer. Gold nanoparticles “freed” from the strong interaction with the polymer are now able to feel the molecules from the surrounding environment. The results show that, by using adequate post-synthesis heat treatments, gold-polymer nanocomposites can be used as plasmonic sensing platforms. http://www.mdpi.com/2073-4360/3/4/1833 Tue, 25 Oct 2011 00:00:00 CEST Polymers 2011-10-25 3 4 Article 1833 1848 2073-4360 Gold-Poly(methyl methacrylate) Nanocomposite Films for Plasmonic Biosensing Applications 2011-10-25 doi: 10.3390/polym3041833 Mohammed Alsawafta Simona Badilescu Abhilash Paneri Vo-Van Truong Muthukumaram Packirisamy http://www.mdpi.com/2073-4360/3/4/1805 Chemically cross-linked polymer networks of poly(vinyl alcohol)/poly(methacrylate) form monolitic hydrogels and microgels suitable for biomedical applications, such as in situ tissue replacement and drug delivery. In this work, molecular dynamics (MD) simulation and incoherent neutron scattering methods are used to study the local polymer dynamics and the polymer induced modification of water properties in poly(vinyl alcohol)/poly(methacrylate) hydrogels. This information is particularly relevant when the diffusion of metabolites and drugs is a requirement for the polymer microgel functionality. MD simulations of an atomic detailed model of the junction domain at the experimental hydration degree were carried out at 283, 293 and 313 K. The polymer-water interaction, the polymer connectivity and the water dynamics were investigated as a function of temperature. Simulation results are compared with findings of elastic and quasi-elastic incoherent neutron scattering measurements, experimental approaches which sample the same space-time window of MD simulations. This combined analysis shows a supercooled water component and an increase of hydrophilicity and mobility with temperature of these amphiphilic polymer networks. http://www.mdpi.com/2073-4360/3/4/1805 Mon, 17 Oct 2011 00:00:00 CEST Polymers 2011-10-17 3 4 Article 1805 1832 2073-4360 Polymer and Water Dynamics in Poly(vinyl alcohol)/Poly(methacrylate) Networks. A Molecular Dynamics Simulation and Incoherent Neutron Scattering Investigation 2011-10-17 doi: 10.3390/polym3041805 Gaio Paradossi Ivana Finelli Francesca Natali Mark T. F. Telling Ester Chiessi http://www.mdpi.com/2073-4360/3/4/1794 Thiol-capped silver nanoparticles were prepared by in situ thermal decomposition of different silver(I)-thiolates precursors in a polymeric matrix. Depending on the structure of the organic coating, contact-free distribution of metal nanoparticles or nanoparticles aggregates were achieved. The structure and morphology of nanocomposites was analyzed by Transmission Electron Microscopy (TEM), and X-Ray Diffraction (XRD). Nanoparticles’ interaction was investigated by differential scanning calorimetry (DSC), and UV-Visible spectroscopy. In particular, only silver nanoparticles coated by n-alkyl thiols aggregated, while a contact-free dispersion was obtained by cyclohexyl thiol-capped silver nanoparticles. http://www.mdpi.com/2073-4360/3/4/1794 Thu, 13 Oct 2011 00:00:00 CEST Polymers 2011-10-13 3 4 Article 1794 1804 2073-4360 Dependence of Optical and Microstructure Properties of Thiol-Capped Silver Nanoparticles Embedded in Polymeric Matrix 2011-10-13 doi: 10.3390/polym3041794 Angela Longo Gianfranco Carotenuto Mariano Palomba Sergio De Nicola http://www.mdpi.com/2073-4360/3/4/1776 In current dental practice, restorative and endodontic procedures have been developed in an attempt to preserve the vitality of dental pulp after exposure to external stimuli such as caries infection. When damage to dental pulp is reversible, pulp wound healing can proceed, whereas irreversible damage induces pathological changes in dental pulp, eventually requiring its removal. Furthermore, dentists sometimes extract non-vital teeth because of severe caries progression, critical size of periapical lesion, and tooth fracture. To overcome the limitations of presently available therapies, it is important to develop regeneration therapy for dental pulp and periapical tissues. In this review, we focus on the regeneration of dental pulp and periapical tissues by application of exogenous growth factors and scaffolds, as well as low-intensity laser irradiation as an auxiliary therapy for regeneration therapy. http://www.mdpi.com/2073-4360/3/4/1776 Wed, 12 Oct 2011 00:00:00 CEST Polymers 2011-10-12 3 4 Review 1776 1793 2073-4360 Regeneration Approaches for Dental Pulp and Periapical Tissues with Growth Factors, Biomaterials, and Laser Irradiation 2011-10-12 doi: 10.3390/polym3041776 Chiaki Kitamura Tatsuji Nishihara Masamichi Terashita Yasuhiko Tabata Eijiro Jimi Ayako Washio Shizu Hirata http://www.mdpi.com/2073-4360/3/4/1750 The perceptible appearance of biomolecules as prospective building blocks in the architecture of coordination polymers (CPs) and metal-organic frameworks (MOFs) are redolent of their inclusion in the synthon/tecton library of reticular chemistry. In this frame, for the first time a synthetic strategy has been established for amine derivatization in amino acids into 1,2,4-triazoles. A set of novel 1,2,4-triazole derivatized amino acids were introduced as superlative precursors in the design of 1D coordination polymers, 2D chiral helicates and 3D metal-organic frameworks. Applications associated with these compounds are diverse and include gas adsorption-porosity partitioning, soft sacrificial matrix for morphology and phase selective cadmium oxide synthesis, FeII spin crossover materials, zinc-b-lactamases inhibitors, logistics for generation of chiral/non-centrosymmetric networks; and thus led to a foundation of a new family of functional CPs and MOFs that are reviewed in this invited contribution. http://www.mdpi.com/2073-4360/3/4/1750 Tue, 11 Oct 2011 00:00:00 CEST Polymers 2011-10-11 3 4 Review 1750 1775 2073-4360 Coordination Polymers and Metal Organic Frameworks Derived from 1,2,4-Triazole Amino Acid Linkers 2011-10-11 doi: 10.3390/polym3041750 Anil D. Naik Marinela M. Dîrtu Antoine P. Railliet Jacqueline Marchand-Brynaert Yann Garcia http://www.mdpi.com/2073-4360/3/4/1734 The non-miscibility of the reactants during solvent free poly-ε-caprolactone grafting onto poly(ethylene-co-vinyl alcohol) (EVOH) dramatically affects reaction kinetics. Different solutions were proposed to accelerate the exchange reactions between poly(ethylene-co-vinyl alcohol) and poly-ε-caprolactone. Reactions were conducted in a batch reactor or a mini twin-screw extruder. The addition of a poly(ethylene-co-vinyl alcohol)-g-poly-ε-caprolactone copolymer increased the compatibility of the reactants and led to a higher reaction rate. This copolymer was either prepared separately and added at the reaction beginning or prepared in situ grafting caprolactone from EVOH. The reactive system evolution was analyzed using molar mass evolution, microstructure characterization, thermal properties and the reactive blend morphology. The compatibilization effect combined with optimized reaction conditions, such as concentration and nature of catalyst and temperature, resulted in an important increase in reaction rates. Among the tested catalysts, 1,5,7-Triazabicyclo [4.4.0]dec-5-ene was a more efficient catalyst for grafting reactions than Tin (II) 2-ethylhexanoate. http://www.mdpi.com/2073-4360/3/4/1734 Tue, 11 Oct 2011 00:00:00 CEST Polymers 2011-10-11 3 4 Article 1734 1749 2073-4360 Effect of Compatibilization on Poly-ε-Caprolactone Grafting onto Poly(ethylene-co-vinyl alcohol) 2011-10-11 doi: 10.3390/polym3041734 Samira Touhtouh Frederic Becquart Caroline Pillon Mohamed Taha http://www.mdpi.com/2073-4360/3/4/1684 Central and peripheral neural injuries are traumatic and can lead to loss of motor and sensory function, chronic pain, and permanent disability. Strategies that bridge the site of injury and allow axonal regeneration promise to have a large impact on restoring quality of life for these patients. Engineered materials can be used to guide axonal growth. Specifically, nanofiber structures can mimic the natural extracellular matrix, and aligned nanofibers have been shown to direct neurite outgrowth and support axon regeneration. In addition, cell-seeded scaffolds can assist in the remyelination of the regenerating axons. The electrospinning process allows control over fiber diameter, alignment, porosity, and morphology. Biodegradable polymers have been electrospun and their use in tissue engineering has been demonstrated. This paper discusses aspects of electrospun biodegradable nanofibers for neural regeneration, how fiber alignment affects cell alignment, and how cell-seeded scaffolds can increase the effectiveness of such implants. http://www.mdpi.com/2073-4360/3/4/1684 Mon, 10 Oct 2011 00:00:00 CEST Polymers 2011-10-10 3 4 Review 1684 1733 2073-4360 Biodegradable Cell-Seeded Nanofiber Scaffolds for Neural Repair 2011-10-10 doi: 10.3390/polym3041684 Dong Han Karen C. Cheung http://www.mdpi.com/2073-4360/3/4/1673 “Click” chemistry has become an efficient avenue to unimolecular polymeric nanoparticles through the self-crosslinking of individual polymer chains containing appropriate functional groups. Herein we report the synthesis of ultra-small (7 nm in size) polymethyl methacrylate (PMMA) nanoparticles (NPs) by the “metal-free” cross-linking of PMMA-precursor chains prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization containing b-ketoester functional groups. Intramolecular collapse was performed by the one-pot reaction of b-ketoester moieties with alkyl diamines in tetrahydrofurane at r.t. (i.e., by enamine formation). The collapsing process was followed by size exclusion chromatography and by nuclear magnetic resonance spectroscopy. The size of the resulting PMMA-NPs was determined by dynamic light scattering. Enamine “click” chemistry increases the synthetic toolbox for the efficient synthesis of metal-free, ultra-small polymeric NPs. http://www.mdpi.com/2073-4360/3/4/1673 Fri, 07 Oct 2011 00:00:00 CEST Polymers 2011-10-07 3 4 Article 1673 1683 2073-4360 Metal-Free Polymethyl Methacrylate (PMMA) Nanoparticles by Enamine “Click” Chemistry at Room Temperature 2011-10-07 doi: 10.3390/polym3041673 Lorea Buruaga José A. Pomposo http://www.mdpi.com/2073-4360/3/4/1662 Supramolecular coordination polymers with wavelike structures have been synthesized by self-assembly and their structures analyzed using the sine trigonometric function. Slow evaporation of a methylene chloride-methanol solution of a 1:1 molar mixture of [M(tmhd)2], where M = Co or Ni, and quinoxaline; a 1:2:1 molar mixture of [M(acac)2], where M = Co or Ni, 2,2,6,6-tetramethyl-3,5-heptadione and quinoxaline; or a 1:2:1 molar mixture of [Co(acac)2], dibenzoylmethane, and quinoxaline, yielded the crystalline coordination polymers. In the presence of the nitrogenous base, ligand scrambling occurs yielding the most insoluble product. The synthesis and structures of the following wavelike polymers are reported: trans-[Co(DBM)2(qox)]n·nH2O (2), trans-[Co(tmhd)2(qox)]n (3), trans-[Ni(tmhd)2(qox)]n (4), where DBM− = dibenzoylmethanate, tmhd− = 2,2,6,6-tetramethyl-3,5-heptadionate, and qox = quinoxaline. The wavelike structures are generated by intramolecular steric interactions and crystal packing forces between the chains. Some of the tert-butyl groups show a two-fold disorder. The sine function, φ = A sin 2πx/λ, where φ = distance (Ǻ) along the polymer backbone, λ = wavelength (Ǻ), A = amplitude (Ǻ), x = distance (Ǻ) along the polymer axis, provides a method to approximate and visualize the polymer structures. http://www.mdpi.com/2073-4360/3/4/1662 Fri, 07 Oct 2011 00:00:00 CEST Polymers 2011-10-07 3 4 Article 1662 1672 2073-4360 Crystal Engineering: Synthesis and Structural Analysis of Coordination Polymers with Wavelike Properties 2011-10-07 doi: 10.3390/polym3041662 Omar W. Steward Miles V. Kaltenbach Ashley B. Biernesser Matthew J. Taylor Katie J. Hovan Jordan J. S. VerPlank Ameera Haamid Irina Karpov Matasebia T. Munie http://www.mdpi.com/2073-4360/3/4/1652 The first MMX-type quasi-one-dimensional (Q1D) Pt chain complex (MMX chain) that contains a mono-protonated diamine as countercation, {o-(H3NC6H4NH2)}4[Pt2(pop)4I]·H2O (pop = P2H2O52–), was synthesized. According to the crystal structural analysis, –NH2 group was hydrogen-bonded to either lattice H2O molecule or –NH3+ group in addition to typical hydrogen bond between –NH3+ group and pop ligand. To control the partial deprotonation of the countercation will be an important method for achieving the high-conductive MMX-chain polymer by the hole doping. http://www.mdpi.com/2073-4360/3/4/1652 Thu, 06 Oct 2011 00:00:00 CEST Polymers 2011-10-06 3 4 Article 1652 1661 2073-4360 Novel Countercation in MMX-Type Mixed-Valence Chain Compound: Coexistence of Neutral and Protonated Amino Substituents 2011-10-06 doi: 10.3390/polym3041652 Hiroaki Iguchi Deli Jiang Jimin Xie Shinya Takaishi Masahiro Yamashita http://www.mdpi.com/2073-4360/3/4/1607 Polysaccharides are complex but essential compounds utilized in many areas such as biomaterials, drug delivery, cosmetics, food chemistry or renewable energy. Modifications and functionalizations of such polymers are often necessary to achieve molecular structures of interest. In this area, the emergence of the “click” chemistry concept, and particularly the copper-catalyzed version of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides, had an impact on the polysaccharides chemistry. The present review summarizes the contribution of “click” chemistry in the world of polysaccharides. http://www.mdpi.com/2073-4360/3/4/1607 Tue, 27 Sep 2011 00:00:00 CEST Polymers 2011-09-27 3 4 Review 1607 1651 2073-4360 Polysaccharides: The “Click” Chemistry Impact 2011-09-27 doi: 10.3390/polym3041607 Pierre-Henri Elchinger Pierre-Antoine Faugeras Benjamin Boëns François Brouillette Daniel Montplaisir Rachida Zerrouki Romain Lucas http://www.mdpi.com/2073-4360/3/4/1600 Organic-inorganic hybrid hydrogel electrolytes were prepared by mixing hydrotalcite, cross-linked potassium poly(acrylate) and 6 M KOH solution. The organic-inorganic hybrid hydrogel electrolytes had high ionic conductivity (0.456–0.540 S cm−1) at 30 °C. Moreover, the mechanical strength of the hydrogel electrolytes was high enough to form a 2–3 mm thick freestanding membrane because of the reinforcement with hydrotalcite. http://www.mdpi.com/2073-4360/3/4/1600 Mon, 26 Sep 2011 00:00:00 CEST Polymers 2011-09-26 3 4 Article 1600 1606 2073-4360 Preparation and Characterization of Organic-Inorganic Hybrid Hydrogel Electrolyte Using Alkaline Solution 2011-09-26 doi: 10.3390/polym3041600 Masanobu Chiku Shoji Tomita Eiji Higuchi Hiroshi Inoue http://www.mdpi.com/2073-4360/3/4/1591 Electro-optic polymers have unique photonic, electro-optic and mechanical properties that make them attractive to use in a wide range of devices starting from ultra-high bandwidth light modulators for optical communications to miniature low power components for on-chip optical interconnects. The main building blocks of those devices are optical waveguides, that due to versatility of the polymers can be fabricated as either traditional multi-layer polymer structures, silicon nano-slots filled with the polymer, or dynamically created waveguides based on field-induced guiding. In this paper we cover various types of waveguides and analyze their optimum designs depending on application. http://www.mdpi.com/2073-4360/3/4/1591 Mon, 26 Sep 2011 00:00:00 CEST Polymers 2011-09-26 3 4 Review 1591 1599 2073-4360 Guiding Light in Electro-Optic Polymers 2011-09-26 doi: 10.3390/polym3041591 Anna L. Pyayt http://www.mdpi.com/2073-4360/3/4/1575 The swelling/deswelling behaviour of microgel particles in the bulk and at the surface was studied and correlated to their mechanical properties. We focused on two kinds of particles: pure PNIPAM and PNIPAM-co-AAc particles. It was shown that the two step volume phase transition found for PNIPAM-co-AAc particles in the bulk disappears after the adsorption at the surface and only a one step transition was identified. The transition temperature increased strongly with increasing the co-monomer content. The dependence of the Young’s modulus of the adsorbed microgel particles on the temperature and the co-monomer content was discussed. The investigations were performed via DLS and SFM. http://www.mdpi.com/2073-4360/3/4/1575 Mon, 26 Sep 2011 00:00:00 CEST Polymers 2011-09-26 3 4 Article 1575 1590 2073-4360 The Effect of Co-Monomer Content on the Swelling/Shrinking and Mechanical Behaviour of Individually Adsorbed PNIPAM Microgel Particles 2011-09-26 doi: 10.3390/polym3041575 Anna Burmistrova Marcel Richter Michael Eisele Cagri Üzüm Regine von Klitzing http://www.mdpi.com/2073-4360/3/3/1565 We have studied the loading of two related, similar porous metal-organic frameworks (MOFs) [Cu2(bdc)2(dabco)] (1), and [Cu2(ndc)2(dabco)] (2) with ferrocene by exposing bulk powder samples to the corresponding vapor. On the basis of powder X-ray diffraction data and molecular dynamics (MD) calculations we propose that each pore can store one ferrocene molecule. Despite the rather pronounced similarity of the two MOFs a quite different behavior is observed, for 1 loading with ferrocene leads to an anisotropic 1% contraction, whereas for 2 no deformation is observed. Mössbauer spectroscopy studies reveal that the Fe oxidation level remains unchanged during the process. Time dependent studies reveal that the diffusion constant governing the loading from the gas-phase for 1 is approximately three times larger than the value for 2. http://www.mdpi.com/2073-4360/3/3/1565 Wed, 21 Sep 2011 00:00:00 CEST Polymers 2011-09-21 3 3 Article 1565 1574 2073-4360 Loading of Two Related Metal-Organic Frameworks (MOFs), [Cu2(bdc)2(dabco)] and [Cu2(ndc)2(dabco)], with Ferrocene 2011-09-21 doi: 10.3390/polym3031565 Romain Heck Osama Shekhah Olexandra Zybaylo Peter G. Weidler Frank Friedrich Robert Maul Wolfgang Wenzel Christof Wöll http://www.mdpi.com/2073-4360/3/3/1554 We propose a low cost polymeric optical waveguides-based optical CDMA encoder and decoder modules. The structures of the optical CDMA encoder and decoder modules are presented. The performance of the optical CDMA encoder and decoder modules is simulated using 10-chip binary phase-shift keying (BPSK) coding schemes. The optical CDMA encoder and decoder modules can effectively transmit and recover optical CDMA data streams. The SNR of the received signal is analyzed and determined to be primarily from the cross correlation with other channels. http://www.mdpi.com/2073-4360/3/3/1554 Mon, 19 Sep 2011 00:00:00 CEST Polymers 2011-09-19 3 3 Article 1554 1564 2073-4360 Polymeric Optical Code-Division Multiple-Access (CDMA) Encoder and Decoder Modules 2011-09-19 doi: 10.3390/polym3031554 Xuejun Lu Ray T. Chen http://www.mdpi.com/2073-4360/3/3/1533 A series of synthetic benzylpenicillinoylated dendrimers has been prepared using up to 4th generation PAMAM dendrimers. These nanoconjugates, as nanosized Dendritic Antigens, are useful in the diagnostic evaluation of drug allergy due to specific molecular recognition with the Human Immunological System (IgE). The morphology and dimensions of the conjugates coupled to the orientation of the peripheral benzylpenicillin residues in the dendrimers may play key roles in such molecular recognition processes. Herein, the characterization and conformation of these structures are studied by a detailed analysis of 1D (1H and 13C NMR) and 2D NMR (1H,1H-NOESY) spectra. These dendrimers in explicit solvent were studied by the atomistic forcefield-based molecular dynamics. Structural properties such as shape, radius-of-gyration and distribution of the monomers will be discussed in relation to the experimental observations. http://www.mdpi.com/2073-4360/3/3/1533 Tue, 13 Sep 2011 00:00:00 CEST Polymers 2011-09-13 3 3 Article 1533 1553 2073-4360 NMR Studies and Molecular Dynamic Simulation of Synthetic Dendritic Antigens 2011-09-13 doi: 10.3390/polym3031533 Maria Isabel Montañez Francisco Najera Ezequiel Perez-Inestrosa http://www.mdpi.com/2073-4360/3/3/1512 Cationic amphiphilic polymethacrylate derivatives (PMAs) have shown potential as a novel class of synthetic antimicrobials. A panel of PMAs with varied ratios of hydrophobic and cationic side chains were synthesized and tested for antimicrobial activity and mechanism of action. The PMAs are shown to be active against a panel of pathogenic bacteria, including a drug-resistant Staphylococcus aureus, compared to the natural antimicrobial peptide magainin which did not display any activity against the same strain. The selected PMAs with 47–63% of methyl groups in the side chains showed minimum inhibitory concentrations of ≤2–31 µg/mL, but cause only minimal harm to human red blood cells. The PMAs also exhibit rapid bactericidal kinetics. Culturing Escherichia coli in the presence of the PMAs did not exhibit any potential to develop resistance against the PMAs. The antibacterial activities of PMAs against E. coli and S. aureus were slightly reduced in the presence of physiological salts. The activity of PMAs showed bactericidal effects against E. coli and S. aureus in both exponential and stationary growth phases. These results demonstrate that PMAs are a new antimicrobial platform with no observed development of resistance in bacteria. In addition, the PMAs permeabilized the E. coli outer membrane at polymer concentrations lower than their MIC values, but they did not show any effect on the bacterial inner membrane. This indicates that mechanisms other than membrane permeabilization may be the primary factors determining their antimicrobial activity. http://www.mdpi.com/2073-4360/3/3/1512 Tue, 13 Sep 2011 00:00:00 CEST Polymers 2011-09-13 3 3 Article 1512 1532 2073-4360 Activity and Mechanism of Antimicrobial Peptide-Mimetic Amphiphilic Polymethacrylate Derivatives 2011-09-13 doi: 10.3390/polym3031512 Iva Sovadinova Edmund F. Palermo Michael Urban Philomene Mpiga Gregory A. Caputo Kenichi Kuroda http://www.mdpi.com/2073-4360/3/3/1475 The reaction of hot (~95 °C) aqueous solutions of Tl2CO3 with solid HL (HL = NC-C(=N-OH)-R is a cyanoxime, and R is an electron-withdrawing group; 37 ligands are known up-to-date) leads to crystalline yellow/orange TlL. Similarly, the reaction between AgNO3 and ML (M = K+, Na+; L = anion of the monodeprotonated cyanoxime) this time at room temperature in mixed ethanol/aqueous solutions leads to sparingly soluble, colored AgL in high-yield. All synthesized monovalent Tl and Ag complexes were characterized using a variety of spectroscopic methods and X-ray analysis, which revealed the formation of primarily 2D coordination polymers of different complexity. In all cases cyanoxime mono-anions act as bridging ligands. Thallium(I) cyanoximates adopt in most cases a double-stranded motif that is originated from centrosymmetric (TlL)2 dimers in which two Tl2O2 rhombs are fused into infinite “ladder-type” structure. There are very short (3.65–3.85 Å) intermetallic distances in (TlL)n, which are close to that (3.46 Å) in metallic thallium. This opens the possibility for the electrochemical or chemical generation of mixed valence Tl(I)/Tl(III) polymers that may exhibit electrical conductivity. Synthesized silver(I) compounds demonstrate a very significant (for multiple years!) stability towards visible light. There are three areas of potential practical applications of these unusual complexes: (1) battery-less detectors of UV-radiation, (2) non electrical sensors for gases of industrial importance, (3) antimicrobial additives to light-curable acrylate polymeric glues, fillers and adhesives used during introduction of indwelling medical devices. Chemical, structural, technological and biological aspects of application of Tl(I) and Ag(I) cyanoximes-based coordination polymers are reviewed. http://www.mdpi.com/2073-4360/3/3/1475 Tue, 13 Sep 2011 00:00:00 CEST Polymers 2011-09-13 3 3 Review 1475 1511 2073-4360 An Excursion into the Intriguing World of Polymeric Tl(I) and Ag(I) Cyanoximates 2011-09-13 doi: 10.3390/polym3031475 Nikolay Gerasimchuk http://www.mdpi.com/2073-4360/3/3/1458 Reaction of cadmium perchlorate and the prototypical linear bridging ligand 4,4’-bipyridine (4,4’-bipy) in an ethanol/water mixture affords the one-dimensional coordination polymer, [{Cd(m-4,4’-bipy)(4,4’-bipy)2(H2O)2}(ClO4)2 × 2 4,4’-bipy × 4.5 H2O]n (1). The Cd2+ ions adopt an octahedral coordination sphere and are joined into linear chains by 4,4’-bipy via two trans coordination sites. The remaining two trans sites in the equatorial plane carry terminally monodentate-bound 4,4’-bipy ligands, resulting in a molecular antenna arrangement. The two axial sites of each Cd2+ ion are occupied by aqua ligands. Compound 1 crystallizes in the non-centrosymmetric, monoclinic space group C2 with three similar, crystallographically independent, cationic coordination polymer strands in the unit cell, which essentially differ only in the conformations of the 4,4’-bipyridyl ligands. Consistent with the similarity of the local coordination environments of the three independent Cd atoms in the structure, 113Cd MAS NMR spectroscopy reveals a single resonance line at 89 ppm. http://www.mdpi.com/2073-4360/3/3/1458 Mon, 05 Sep 2011 00:00:00 CEST Polymers 2011-09-05 3 3 Article 1458 1474 2073-4360 A Molecular Antenna Coordination Polymer from Cadmium(II) and 4,4’-Bipyridine Featuring Three Distinct Polymer Strands in the Crystal 2011-09-05 doi: 10.3390/polym3031458 Rüdiger W. Seidel Richard Goddard Bodo Zibrowius Iris M. Oppel http://www.mdpi.com/2073-4360/3/3/1447 Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work summarizes and contrasts the photomechanical response of glassy polydomain, monodomain, and twisted nematic azo-LCN materials to blue-green irradiation. Building from this summary, the combinatorial photomechanical response observed upon irradiation of composite cantilevers is examined. Large scale shape adaptations are realized, with novel responses that may be of potential use in future employment of these materials in actuation. http://www.mdpi.com/2073-4360/3/3/1447 Fri, 02 Sep 2011 00:00:00 CEST Polymers 2011-09-02 3 3 Article 1447 1457 2073-4360 Photomechanical Response of Composite Structures Built from Azobenzene Liquid Crystal Polymer Networks 2011-09-02 doi: 10.3390/polym3031447 Kyung Min Lee Timothy J. White http://www.mdpi.com/2073-4360/3/3/1433 The inclusion of carbon nanotubes in polymer matrix has been proposed to enhance the polymer’s physical and electrical properties. In this study, microscopic and spectroscopic techniques are used to investigate the interaction between poly(3-hexylthiophene) (P3HT) and nanotubes and the reciprocal modification of physical properties. The presence of P3HT-covered nanotubes dispersed in the polymer matrix has been observed by atomic force microscopy and transmission electron microscopy. Then, the modification of P3HT optical properties due to nanotube inclusion has been evidenced with spectroscopic techniques like absorption and Raman spectroscopy. The study is completed with detailed nanoscale analysis by scanning probe techniques. The ordered self assembly of polymer adhering on the nanotube is unveiled by showing an example of helical wrapping of P3HT. Scanning tunneling spectroscopy study provides information on the electronic structure of nanotube-polymer assembly, revealing the charge transfer from P3HT to the nanotube. http://www.mdpi.com/2073-4360/3/3/1433 Mon, 29 Aug 2011 00:00:00 CEST Polymers 2011-08-29 3 3 Article 1433 1446 2073-4360 Microscopic and Spectroscopic Investigation of Poly(3-hexylthiophene) Interaction with Carbon Nanotubes 2011-08-29 doi: 10.3390/polym3031433 Michele Giulianini Eric R. Waclawik John M. Bell Manuela Scarselli Paola Castrucci Maurizio De Crescenzi Nunzio Motta http://www.mdpi.com/2073-4360/3/3/1423 Colloidal gels are possible intermediates in the generation of highly porous particle systems. In the production process the gels are fragmented after their formation. These gel fragments compact to particles whose application-technological properties are determined by their size and porosity. In the case of precipitated silica gels, this consolidation process depends on temperature and pH, among other parameters. It is shown that these dependencies can be characterized by oedometer measurements. Originally, the oedometer test (one-dimensional compression test) stemmed from soil mechanics. It has proven to be an interesting novel examination method for gels. Quantitative data of the time-dependent shrinkage of gel samples can be obtained. The consolidation of the gels shows a characteristic dependence on the above parameters. http://www.mdpi.com/2073-4360/3/3/1423 Mon, 29 Aug 2011 00:00:00 CEST Polymers 2011-08-29 3 3 Article 1423 1432 2073-4360 Consolidation of Inorganic Precipitated Silica Gel 2011-08-29 doi: 10.3390/polym3031423 Hussein Sahabi Matthias Kind http://www.mdpi.com/2073-4360/3/3/1398 2-(Dimethylamino)ethyl methacrylate/styrene statistical copolymers (poly(DMAEMA-stat-styrene)) with feed compositions fDMAEMA = 80–95 mol%, (number average molecular weights Mn = 9.5–11.2 kg mol−1) were synthesized using succinimidyl ester-functionalized BlocBuilder alkoxyamine initiator at 80 °C in bulk. Polymerization rate increased three-fold on increasing fDMAEMA = 80 to 95 mol%. Linear Mn increases with conversion were observed up to about 50% conversion and obtained copolymers possessed monomodal, relatively narrow molecular weight distributions (polydispersity = 1.32–1.59). Copolymers with fDMAEMA = 80 and 90 mol% were also cleanly chain-extended with DMAEMA/styrene mixtures of 95 and 90 mol% DMAEMA, respectively, confirming the livingness of the copolymers. Copolymer phase behavior in aqueous solutions was examined by dynamic light scattering and UV-Vis spectroscopy. All copolymers exhibited lower critical solution temperature (LCST)-type behavior. LCST decreased with increasing styrene content in the copolymer and with increasing solution concentration. All copolymers were completely water-soluble and temperature insensitive at pH 4 but were more hydrophobic at pH 10, particularly copolymers with fDMAEMA = 80 and 85 mol%, which were water-insoluble. At pH 10, LCST of copolymers with fDMAEMA = 90 and 95 mol% were more than 10 °C lower compared to their solutions in neutral, de-ionized water. Block copolymers with two statistical blocks with different DMAEMA compositions exhibited a single LCST, suggesting the block segments were not distinct enough to exhibit separate LCSTs in water. http://www.mdpi.com/2073-4360/3/3/1398 Fri, 26 Aug 2011 00:00:00 CEST Polymers 2011-08-26 3 3 Article 1398 1422 2073-4360 Synthesis of Stimuli-responsive, Water-soluble Poly[2-(dimethylamino)ethyl methacrylate/styrene] Statistical Copolymers by Nitroxide Mediated Polymerization 2011-08-26 doi: 10.3390/polym3031398 Chi Zhang Milan Maric http://www.mdpi.com/2073-4360/3/3/1377 In past two decades poly lactic-co-glycolic acid (PLGA) has been among the most attractive polymeric candidates used to fabricate devices for drug delivery and tissue engineering applications. PLGA is biocompatible and biodegradable, exhibits a wide range of erosion times, has tunable mechanical properties and most importantly, is a FDA approved polymer. In particular, PLGA has been extensively studied for the development of devices for controlled delivery of small molecule drugs, proteins and other macromolecules in commercial use and in research. This manuscript describes the various fabrication techniques for these devices and the factors affecting their degradation and drug release. http://www.mdpi.com/2073-4360/3/3/1377 Fri, 26 Aug 2011 00:00:00 CEST Polymers 2011-08-26 3 3 Review 1377 1397 2073-4360 Poly Lactic-co-Glycolic Acid (PLGA) as Biodegradable Controlled Drug Delivery Carrier 2011-08-26 doi: 10.3390/polym3031377 Hirenkumar K. Makadia Steven J. Siegel http://www.mdpi.com/2073-4360/3/3/1363 Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n−/n+ ratio of the molar charges of the polyelectrolytes and the procedure of formation were varied. The colloidal stability of the systems and the size, shape, and structure of the PEC particles were investigated by turbidimetry, dynamic light scattering (DLS) and atomic force microscopy (AFM). Dynamic light scattering indicates that beside large PEC particle aggregates distinct smaller particles were formed by the copolymers which have the highest hydrophobicity (styrene). These findings could be proved by AFM. Fractal dimension (D), root mean square (RMS) roughness and the surface profiles of the PEC particles adsorbed on mica allow the following conclusions: the higher the hydrophobicity of the polyelectrolytes, the broader is the particle size distribution and the minor is the swelling of the PEC particles. Hence, the most compact particles are formed with the very hydrophobic copolymer. http://www.mdpi.com/2073-4360/3/3/1363 Thu, 25 Aug 2011 00:00:00 CEST Polymers 2011-08-25 3 3 Article 1363 1376 2073-4360 Influence of the Hydrophobicity of Polyelectrolytes on Polyelectrolyte Complex Formation and Complex Particle Structure and Shape 2011-08-25 doi: 10.3390/polym3031363 Mandy Mende Simona Schwarz Stefan Zschoche Gudrun Petzold Andreas Janke http://www.mdpi.com/2073-4360/3/3/1352 Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SR)x, where R is a linear aliphatic hydrocarbon group, –CnH2n+1) undergo a thermolysis reaction at moderately low temperatures (close to 200 °C), which produces metal atoms or metal sulfide species and an organic by-product, disulfide (RSSR) or thioether (RSR) molecules, respectively. Alkane-thiolates are non-polar chemical compounds that dissolve in most techno-polymers and the resulting solid solutions can be annealed to generate polymer-embedded metal or metal sulfide clusters. Here, the preparation of silver and gold clusters embedded into amorphous polystyrene by thermolysis of a dodecyl-thiolate precursor is described in detail. However, this chemical approach is quite universal and a large variety of polymer-embedded metals or metal sulfides could be similarly prepared. http://www.mdpi.com/2073-4360/3/3/1352 Mon, 22 Aug 2011 00:00:00 CEST Polymers 2011-08-22 3 3 Article 1352 1362 2073-4360 Nanocomposites Based on Metal and Metal Sulfide Clusters Embedded in Polystyrene 2011-08-22 doi: 10.3390/polym3031352 Gianfranco Carotenuto Cinzia Giannini Dritan Siliqi Luigi Nicolais