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Polymers, Volume 4, Issue 2 (June 2012), Pages 889-1330

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Research

Jump to: Review

Open AccessArticle Multiple Stimuli-Responsive Hydrogels for Metal-Based Drug Therapy
Polymers 2012, 4(2), 964-985; doi:10.3390/polym4020964
Received: 31 January 2012 / Revised: 15 March 2012 / Accepted: 20 March 2012 / Published: 27 March 2012
Cited by 6 | PDF Full-text (432 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
Open AccessArticle Thermal Properties and Thermal Degradation of Cellulose Tri-Stearate (CTs)
Polymers 2012, 4(2), 1012-1024; doi:10.3390/polym4021012
Received: 13 February 2012 / Revised: 2 April 2012 / Accepted: 5 April 2012 / Published: 16 April 2012
Cited by 14 | PDF Full-text (763 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
Open AccessArticle Radical-Scavenging Activity of Thiols, Thiobarbituric Acid Derivatives and Phenolic Antioxidants Determined Using the Induction Period Method for Radical Polymerization of Methyl Methacrylate
Polymers 2012, 4(2), 1025-1036; doi:10.3390/polym4021025
Received: 27 February 2012 / Revised: 2 April 2012 / Accepted: 5 April 2012 / Published: 16 April 2012
Cited by 4 | PDF Full-text (351 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
Open AccessArticle Modification of oligo-Ricinoleic Acid and Its Derivatives with 10-Undecenoic Acid via Lipase-Catalyzed Esterification
Polymers 2012, 4(2), 1037-1055; doi:10.3390/polym4021037
Received: 8 February 2012 / Revised: 24 March 2012 / Accepted: 5 April 2012 / Published: 17 April 2012
Cited by 11 | PDF Full-text (1263 KB) | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)
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Open AccessArticle Templated Formation of Hydroxyapatite Nanoparticles from Self-Assembled Nanogels Containing Tricarboxylate Groups
Polymers 2012, 4(2), 1056-1064; doi:10.3390/polym4021056
Received: 27 February 2012 / Revised: 10 April 2012 / Accepted: 11 April 2012 / Published: 20 April 2012
PDF Full-text (554 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
Open AccessArticle Calcite Biohybrids as Microenvironment for Stem Cells
Polymers 2012, 4(2), 1065-1083; doi:10.3390/polym4021065
Received: 20 February 2012 / Revised: 11 April 2012 / Accepted: 12 April 2012 / Published: 23 April 2012
PDF Full-text (1007 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
Open AccessArticle Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids
Polymers 2012, 4(2), 1109-1124; doi:10.3390/polym4021109
Received: 6 March 2012 / Revised: 1 April 2012 / Accepted: 20 April 2012 / Published: 25 April 2012
Cited by 2 | PDF Full-text (393 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Liquid Crystalline Polymers)
Open AccessArticle Hybrid Magnetic Hydrogel: A Potential System for Controlled Drug Delivery by Means of Alternating Magnetic Fields
Polymers 2012, 4(2), 1157-1169; doi:10.3390/polym4021157
Received: 28 February 2012 / Revised: 19 April 2012 / Accepted: 25 April 2012 / Published: 3 May 2012
Cited by 19 | PDF Full-text (1581 KB) | HTML Full-text | XML Full-text
Abstract
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)
[...] Read more.
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. Full article
Open AccessArticle Synthesis of Well-Defined, Water-Soluble Hyperbranched Polyamides by Chain-Growth Condensation Polymerization of AB2 Monomer
Polymers 2012, 4(2), 1170-1182; doi:10.3390/polym4021170
Received: 12 March 2012 / Revised: 18 April 2012 / Accepted: 8 May 2012 / Published: 14 May 2012
Cited by 10 | PDF Full-text (435 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Living Polymerization Techniques)
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Open AccessArticle Synthesis of Star Poly(N-vinylcarbazole) by Microwave-Assisted Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT)
Polymers 2012, 4(2), 1183-1194; doi:10.3390/polym4021183
Received: 27 February 2012 / Revised: 12 April 2012 / Accepted: 4 May 2012 / Published: 15 May 2012
Cited by 6 | PDF Full-text (184 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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). Full article
(This article belongs to the Special Issue Living Polymerization Techniques)
Open AccessArticle Random Poly(Amino Acid)s Synthesized by Ring Opening Polymerization as Additives in the Biomimetic Mineralization of CaCO3
Polymers 2012, 4(2), 1195-1210; doi:10.3390/polym4021195
Received: 12 March 2012 / Revised: 8 May 2012 / Accepted: 9 May 2012 / Published: 23 May 2012
Cited by 12 | PDF Full-text (450 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)
Open AccessArticle Superparamagnetic Nanocomposites Templated with Pyrazole-Containing Diblock Copolymers
Polymers 2012, 4(2), 1211-1225; doi:10.3390/polym4021211
Received: 19 March 2012 / Revised: 26 April 2012 / Accepted: 14 May 2012 / Published: 31 May 2012
Cited by 2 | PDF Full-text (611 KB) | HTML Full-text | XML Full-text
Abstract
Monodisperse maghemite nanoparticles, templated in novel, well-defined pyrazole-containing norbornene-based block copolymers, provided a superparamagnetic nanocomposite with high saturation magnetization at room temperature under an applied magnetic field. The synthesis of the polymer nanocomposites and physical, morphological, and magnetic chracaterization of the nanocomposites are
[...] Read more.
Monodisperse maghemite nanoparticles, templated in novel, well-defined pyrazole-containing norbornene-based block copolymers, provided a superparamagnetic nanocomposite with high saturation magnetization at room temperature under an applied magnetic field. The synthesis of the polymer nanocomposites and physical, morphological, and magnetic chracaterization of the nanocomposites are reported. Micelle-encapsulated superparamagnetic nanocomposites were generated for dispersal in aqueous medium. Their stability in water in the presence of a magnetic field was investigated as was their morphology and cell viability, strongly suggesting the potential of these superparamagnetic polymer-based nanocomposites in certain biomedical imaging and associated applications. Full article
(This article belongs to the Special Issue Polymers for Bioimaging)
Open AccessArticle Synthesis and Optical Study of a New Oligophenylene
Polymers 2012, 4(2), 1226-1241; doi:10.3390/polym4021226
Received: 16 April 2012 / Revised: 10 May 2012 / Accepted: 14 May 2012 / Published: 31 May 2012
Cited by 1 | PDF Full-text (1002 KB) | HTML Full-text | XML Full-text
Abstract
A new substituted oligophenylene was prepared by the Knoevenagel condensation of 4-methoxybezaldehyde with a functionalized oligophenylene (OMPA). The latter was obtained by (4-methoxy phenyl) acetonitrile electrochemical oxidation. The resulting modified oligomer was characterized by various spectroscopic techniques: NMR, FTIR and UV. The thermal
[...] Read more.
A new substituted oligophenylene was prepared by the Knoevenagel condensation of 4-methoxybezaldehyde with a functionalized oligophenylene (OMPA). The latter was obtained by (4-methoxy phenyl) acetonitrile electrochemical oxidation. The resulting modified oligomer was characterized by various spectroscopic techniques: NMR, FTIR and UV. The thermal study showed that the modified material exhibited a lower thermal stability compared with OMPA. Finally, the optical study revealed that in solution, the emission was red-shifted when compared with the non-modified oligomer emission and that the optical gap changed from 3.1 eV to 2.75 eV. In thin layer solid state, photoluminescence was again red-shifted by 120 nm, which is probably due to an interaction between the oligomer chains. In addition, a transient photoluminescence study was undertaken for the synthesized materials. It showed that the lifetimes of the photo-generated species were shortened by the conjugation extension in the modified oligomer and by the inter-chain interactions in the solid state. Full article
Open AccessArticle A Nanoparticle Approach towards Morphology Controlled Organic Photovoltaics (OPV)
Polymers 2012, 4(2), 1242-1258; doi:10.3390/polym4021242
Received: 16 April 2012 / Revised: 24 May 2012 / Accepted: 4 June 2012 / Published: 11 June 2012
Cited by 5 | PDF Full-text (619 KB) | HTML Full-text | XML Full-text
Abstract
Silicon nano-particles grafted with two different organic oligomers were prepared; the oligomers used were a phenylene-vinylene (PV) oligomer and a 3,3'''-didodecylquaterthiophene. The graftings were performed by the use of two different functional groups, the PV oligomer was grafted by a hydroxyl-group in the
[...] Read more.
Silicon nano-particles grafted with two different organic oligomers were prepared; the oligomers used were a phenylene-vinylene (PV) oligomer and a 3,3'''-didodecylquaterthiophene. The graftings were performed by the use of two different functional groups, the PV oligomer was grafted by a hydroxyl-group in the form of a phenol and a lithium derivative was used to graft the 3,3'''-didodecylquaterthiophene. The morphology and size of the grafted particles were analyzed by atomic force microscopy (AFM) and the extent of the grafting was analyzed by NMR. Organic photovoltaics with normal geometry (ITO/PEDOT:PSS/active layer/Al) were prepared using these materials as a donor and phenyl-C61-butyric acid methyl ester ([60]PCBM) as the acceptor and yielded a power conversion efficiency (PCE) of 0.27%, an open circuit voltage (VOC) of 0.93 V, a short circuit current density (JSC) of 0.89 mA/cm2, and a fill factor (FF) of 32.5% for a lead device with an active area of 0.25 cm2. Full article
(This article belongs to the Special Issue Polymers for Fuel Cells & Solar Energy)
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Open AccessArticle Enzymatic Synthesis and Chemical Recycling of Novel Polyester-Type Thermoplastic Elastomers
Polymers 2012, 4(2), 1259-1277; doi:10.3390/polym4021259
Received: 26 April 2012 / Revised: 28 May 2012 / Accepted: 13 June 2012 / Published: 19 June 2012
Cited by 8 | PDF Full-text (656 KB) | HTML Full-text | XML Full-text
Abstract
Novel polyester-type thermoplastic elastomers based on poly(alkylene succinate)s were synthesized by the lipase-catalyzed copolymerization of cyclic diol/succinate oligomer and cyclic diol/alkylthiosuccinate oligomer. These copolymers exhibited biodegradabilities by activated sludge and a wide range of thermal and mechanical properties that were dependent on the
[...] Read more.
Novel polyester-type thermoplastic elastomers based on poly(alkylene succinate)s were synthesized by the lipase-catalyzed copolymerization of cyclic diol/succinate oligomer and cyclic diol/alkylthiosuccinate oligomer. These copolymers exhibited biodegradabilities by activated sludge and a wide range of thermal and mechanical properties that were dependent on the molecular structure and the content of side alkylthio groups. The degree of crystallinity of the copolymer decreased with increasing content of alkylthio groups, which were introduced into the polymer chain as a soft segment. Furthermore, lipase-catalyzed depolymerization of these copolymers into cyclic oligomers and repolymerization of the oligomers was carried out. A repolymerized copolymer having the same Mw and monomer composition as the initial copolymer was obtained, indicating the chemical recyclability of the copolymer. Full article
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Review

Jump to: Research

Open AccessReview Current Advances in the Carbon Nanotube/Thermotropic Main-Chain Liquid Crystalline Polymer Nanocomposites and Their Blends
Polymers 2012, 4(2), 889-912; doi:10.3390/polym4020889
Received: 10 January 2012 / Revised: 12 March 2012 / Accepted: 14 March 2012 / Published: 23 March 2012
Cited by 13 | PDF Full-text (1372 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Liquid Crystalline Polymers)
Open AccessReview Water Soluble Polymers as Proton Exchange Membranes for Fuel Cells
Polymers 2012, 4(2), 913-963; doi:10.3390/polym4020913
Received: 14 February 2012 / Revised: 1 March 2012 / Accepted: 14 March 2012 / Published: 26 March 2012
Cited by 35 | PDF Full-text (2199 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Polymer Thin Films and Membranes)
Open AccessReview The Interactions between Blood and Polymeric Nanoparticles Depend on the Nature and Structure of the Hydrogel Covering the Surface
Polymers 2012, 4(2), 986-996; doi:10.3390/polym4020986
Received: 28 February 2012 / Revised: 30 March 2012 / Accepted: 1 April 2012 / Published: 13 April 2012
Cited by 2 | PDF Full-text (292 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
Open AccessReview Hydrogels from Biopolymer Hybrid for Biomedical, Food, and Functional Food Applications
Polymers 2012, 4(2), 997-1011; doi:10.3390/polym4020997
Received: 1 March 2012 / Revised: 27 March 2012 / Accepted: 29 March 2012 / Published: 13 April 2012
Cited by 18 | PDF Full-text (635 KB) | HTML Full-text | XML Full-text
Abstract
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
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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. Full article
Open AccessReview Microfluidic-Based Synthesis of Hydrogel Particles for Cell Microencapsulation and Cell-Based Drug Delivery
Polymers 2012, 4(2), 1084-1108; doi:10.3390/polym4021084
Received: 14 March 2012 / Revised: 17 April 2012 / Accepted: 17 April 2012 / Published: 23 April 2012
Cited by 38 | PDF Full-text (1421 KB) | HTML Full-text | XML Full-text
Abstract
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
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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. Full article
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Open AccessReview Controlled Photoradical Polymerization Mediated by 2,2,6,6-Tetramethylpiperidine-1-Oxyl
Polymers 2012, 4(2), 1125-1156; doi:10.3390/polym4021125
Received: 1 March 2012 / Revised: 13 April 2012 / Accepted: 19 April 2012 / Published: 2 May 2012
Cited by 5 | PDF Full-text (832 KB) | HTML Full-text | XML Full-text
Abstract
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
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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. Full article
(This article belongs to the Special Issue Living Polymerization Techniques)
Open AccessReview Microfluidics-Nano-Integration for Synthesis and Sensing
Polymers 2012, 4(2), 1278-1310; doi:10.3390/polym4021278
Received: 29 May 2012 / Accepted: 13 June 2012 / Published: 20 June 2012
Cited by 16 | PDF Full-text (4675 KB) | HTML Full-text | XML Full-text
Abstract
The recent progress and achievements in the development of preparation of nano and microparticles in a microfluidic environment is reviewed. Microfluidics exploit fluid mechanics to create particles with a narrow range of sizes and offers a finely controllable route to tune the shape
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The recent progress and achievements in the development of preparation of nano and microparticles in a microfluidic environment is reviewed. Microfluidics exploit fluid mechanics to create particles with a narrow range of sizes and offers a finely controllable route to tune the shape and composition of nanomaterials. The advantages of both continuous flow- and droplet-based synthesis of polymers and nanoparticles, in comparison with the traditional stirred flasks methods are discussed in detail by using numerous recent examples from the literature as well as from the authors’ work. The controllability of the size distribution of the particles is discussed in terms of the fabrication approach and the characteristics of the microfluidic reactors. A special attention is paid to metal-polymer nanocomposites prepared through microfluidic routes and their application in bio-sensing. Directions for future development of microfluidic synthesis of high quality nanoparticles are discussed. Full article
Open AccessReview Enzyme-Catalyzed Modifications of Polysaccharides and Poly(ethylene glycol)
Polymers 2012, 4(2), 1311-1330; doi:10.3390/polym4021311
Received: 24 April 2012 / Revised: 12 June 2012 / Accepted: 14 June 2012 / Published: 21 June 2012
Cited by 12 | PDF Full-text (779 KB) | HTML Full-text | XML Full-text
Abstract
Polysaccharides are used extensively in various industrial applications, such as food, adhesives, coatings, construction, paper, pharmaceuticals, and personal care. Many polysaccharide structures need to be modified in order to improve their end-use properties; this is mostly done through chemical reactions. In the past
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Polysaccharides are used extensively in various industrial applications, such as food, adhesives, coatings, construction, paper, pharmaceuticals, and personal care. Many polysaccharide structures need to be modified in order to improve their end-use properties; this is mostly done through chemical reactions. In the past 20 years many enzyme-catalyzed modifications have been developed to supplement chemical derivatization methods. Typical reactions include enzymatic oxidation, ester formation, amidation, glycosylation, and molecular weight reduction. These reactions are reviewed in this paper, with emphasis placed on the work done by the authors. The polymers covered in this review include cellulosic derivatives, starch, guar, pectin, and poly(ethylene glycol). Full article
(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)
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