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Polymers, Volume 6, Issue 2 (February 2014), Pages 264-603

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Editorial

Jump to: Research, Review

Open AccessEditorial Acknowledgement to Reviewers of Polymers in 2013
Polymers 2014, 6(2), 601-603; doi:10.3390/polym6020601
Received: 24 February 2014 / Accepted: 24 February 2014 / Published: 24 February 2014
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Abstract The editors of Polymers would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2013. [...] Full article

Research

Jump to: Editorial, Review

Open AccessArticle RGD-Functionalization of Poly(2-oxazoline)-Based Networks for Enhanced Adhesion to Cancer Cells
Polymers 2014, 6(2), 264-279; doi:10.3390/polym6020264
Received: 16 November 2013 / Revised: 8 January 2014 / Accepted: 15 January 2014 / Published: 27 January 2014
Cited by 8 | PDF Full-text (3646 KB) | HTML Full-text | XML Full-text
Abstract
Poly(2-oxazoline) networks with varying swelling degrees and varying hydrophilicity can be synthesized from 2-ethyl-2-oxazoline, 2-nonyl-2-oxazoline, 2-9’-decenyl-2-oxazoline and 2,2’-tetramethylene-bis-2-oxazoline in one-pot/one-step strategies. These gels can be loaded with organic molecules, such as fluorescein isothiocyanate, either during the polymerization (covalent attachment of the dye) [...] Read more.
Poly(2-oxazoline) networks with varying swelling degrees and varying hydrophilicity can be synthesized from 2-ethyl-2-oxazoline, 2-nonyl-2-oxazoline, 2-9’-decenyl-2-oxazoline and 2,2’-tetramethylene-bis-2-oxazoline in one-pot/one-step strategies. These gels can be loaded with organic molecules, such as fluorescein isothiocyanate, either during the polymerization (covalent attachment of the dye) or according to post-synthetic swelling/deswelling strategies (physical inclusion of the dye). Surface functionalization of ground gels by thiol-ene reactions with cysteine-bearing peptides exhibiting the arginine-glycine-aspartic acid (RGD) motif yields microparticles with enhanced recognition of human cancer cells compared to healthy endothelial cells. Full article
(This article belongs to the Special Issue Polymers for Drug Delivery)
Open AccessArticle Retrofitting Masonry Walls with Carbon Mesh
Polymers 2014, 6(2), 280-299; doi:10.3390/polym6020280
Received: 2 December 2013 / Revised: 21 January 2014 / Accepted: 22 January 2014 / Published: 27 January 2014
Cited by 3 | PDF Full-text (3641 KB) | HTML Full-text | XML Full-text
Abstract
Static-cyclic shear load tests and tensile tests on retrofitted masonry walls were conducted at UAS Fribourg for an evaluation of the newly developed retrofitting system, the S&P ARMO-System. This retrofitting system consists of a composite of carbon mesh embedded in a specially [...] Read more.
Static-cyclic shear load tests and tensile tests on retrofitted masonry walls were conducted at UAS Fribourg for an evaluation of the newly developed retrofitting system, the S&P ARMO-System. This retrofitting system consists of a composite of carbon mesh embedded in a specially adapted high quality spray mortar. It can be applied with established construction techniques using traditional construction materials. The experimental study has shown that masonry walls reinforced by this retrofitting system reach a similar strength and a higher ductility than retrofits by means of bonded carbon fiber reinforced polymer sheets. Hence, the retrofitting system using carbon fiber meshes embedded in a high quality mortar constitutes a good option for static or seismic retrofits or reinforcements for masonry walls. However, the experimental studies also revealed that the mechanical anchorage of carbon mesh may be delicate depending on its design. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Enhancement Corrosion Resistance of (γ-Glycidyloxypropyl)-Silsesquioxane-Titanium Dioxide Films and Its Validation by Gas Molecule Diffusion Coefficients Using Molecular Dynamics (MD) Simulation
Polymers 2014, 6(2), 300-310; doi:10.3390/polym6020300
Received: 28 November 2013 / Revised: 17 January 2014 / Accepted: 20 January 2014 / Published: 27 January 2014
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Abstract
Based on silsesquioxanes (SSO) derived from the hydrolytic condensation of (γ-glycidyloxypropyl)trimethoxysilane (GPMS) and titanium tetrabutoxide (TTB), hybrid films on aluminum alloy (AA), film-GPMS-SSO (f-GS) and f-GS-TTBi% (f-GSTT5%–25%, i = 5, 10, 15, 20 and 25 wt%), were [...] Read more.
Based on silsesquioxanes (SSO) derived from the hydrolytic condensation of (γ-glycidyloxypropyl)trimethoxysilane (GPMS) and titanium tetrabutoxide (TTB), hybrid films on aluminum alloy (AA), film-GPMS-SSO (f-GS) and f-GS-TTBi% (f-GSTT5%–25%, i = 5, 10, 15, 20 and 25 wt%), were prepared and tested by electrochemical measurements with typical potentiodynamic polarization curves. The Icorr values of the samples were significantly lower, comparing with the Icorr values of the f-GS, AA and f-GS modified tetraethoxysilane (TEOS) in the previous study, which implies that the TTB5%–25% (TiO2) additions in the coatings indeed enhance the electrochemical corrosion resistance. Correlations between the film structures and anticorrosion properties were discussed. To validate the corresponding anticorrosion experiment results, different 3D-amorphous cubic unit cells were employed as models to investigate the self-diffusion coefficient (SDC) for SO2, NO2 and H2O molecules by molecular dynamics (MD) simulation. All of the SDCs calculated for SO2, NO2 and H2O diffusing in f-GSTT5%–25% cells were less than the SDCs in f-GS. These results validated the corresponding anticorrosion experiment results. Full article
(This article belongs to the Special Issue Polymer Colloids)
Open AccessArticle Macromolecular Architectures Designed by Living Radical Polymerization with Organic Catalysts
Polymers 2014, 6(2), 311-326; doi:10.3390/polym6020311
Received: 27 December 2013 / Accepted: 22 January 2014 / Published: 27 January 2014
Cited by 6 | PDF Full-text (1478 KB) | HTML Full-text | XML Full-text
Abstract
Well-defined diblock and triblock copolymers, star polymers, and concentrated polymer brushes on solid surfaces were prepared using living radical polymerization with organic catalysts. Polymerizations of methyl methacrylate, butyl acrylate, and selected functional methacrylates were performed with a monofunctional initiator, a difunctional initiator, [...] Read more.
Well-defined diblock and triblock copolymers, star polymers, and concentrated polymer brushes on solid surfaces were prepared using living radical polymerization with organic catalysts. Polymerizations of methyl methacrylate, butyl acrylate, and selected functional methacrylates were performed with a monofunctional initiator, a difunctional initiator, a trifunctional initiator, and a surface-immobilized initiator. Full article
(This article belongs to the Special Issue Complex Macromolecular Architectures)
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Open AccessArticle Exergetical Evaluation of Biobased Synthesis Pathways
Polymers 2014, 6(2), 327-345; doi:10.3390/polym6020327
Received: 13 January 2014 / Revised: 26 January 2014 / Accepted: 27 January 2014 / Published: 29 January 2014
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Abstract
The vast majority of today’s chemical products are based on crude oil. An attractive and sustainable alternative feedstock is biomass. Since crude oil and biomass differ in various properties, new synthesis pathways and processes have to be developed. In order to prioritize [...] Read more.
The vast majority of today’s chemical products are based on crude oil. An attractive and sustainable alternative feedstock is biomass. Since crude oil and biomass differ in various properties, new synthesis pathways and processes have to be developed. In order to prioritize limited resources for research and development (R & D), their economic potential must be estimated in the early stages of development. A suitable measure for an estimation of the economic potential is based on exergy balances. Different structures of synthesis pathways characterised by the chemical exergy of the main components are evaluated. Based on a detailed evaluation of the underlying processes, general recommendations for future bio-based synthesis pathways are derived. Full article
(This article belongs to the Special Issue Polymers from Biomass)
Open AccessArticle A Unified Theoretical Model for the Monotonic and Cyclic Response of FRP Strips Glued to Concrete
Polymers 2014, 6(2), 370-381; doi:10.3390/polym6020370
Received: 30 November 2013 / Revised: 20 January 2014 / Accepted: 27 January 2014 / Published: 3 February 2014
Cited by 9 | PDF Full-text (551 KB) | HTML Full-text | XML Full-text
Abstract
The mechanical behavior of the adhesive interface between the fiber-reinforced polymer (FRP) strip and the concrete substrate often controls the response of FRP-strengthened reinforced concrete (RC) members. Plenty of studies devoted to understanding the mechanical behavior of FRP strips glued to concrete [...] Read more.
The mechanical behavior of the adhesive interface between the fiber-reinforced polymer (FRP) strip and the concrete substrate often controls the response of FRP-strengthened reinforced concrete (RC) members. Plenty of studies devoted to understanding the mechanical behavior of FRP strips glued to concrete are currently available in the scientific literature. However, they are mainly focused on the response under monotonic actions, which is certainly relevant in a wide class of practical applications. Conversely, few contributions are currently available to better understand the response of FRP-to-concrete interfaces under cyclic actions, such as those deriving from either seismic excitations or traffic loads. This paper presents a unified numerical approach to simulate both monotonic and cyclic behavior of FRP plates glued on quasi-brittle substrates like those made of concrete. Particularly, a damage-based approach is proposed to simulate the fracture behavior of FRP-to-concrete joints under loading/unloading cycling tests. The model is formulated within the general framework of Fracture Mechanics and is based on assuming that fracture at the FRP-to-concrete interface develops in (pure shear) mode II, as widely accepted in similar problems. Two alternative expressions of the bond-slip behavior are herein considered and their preliminary validation is finally proposed. The proposed results highlight the difference between the monotonic and the cyclic response; particularly, they show that the latter is characterized by a significantly lower force and displacement capacity. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Numerical Study of FRP Reinforced Concrete Slabs at Elevated Temperature
Polymers 2014, 6(2), 408-422; doi:10.3390/polym6020408
Received: 2 January 2014 / Revised: 6 February 2014 / Accepted: 7 February 2014 / Published: 10 February 2014
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Abstract
One-way glass fibre reinforced polymer (GFRP) reinforced concrete slabs at elevated temperatures are investigated through numerical modeling. Serviceability and strength requirements of ACI-440.1R are considered for the design of the slabs. Diagrams to determine fire endurance of slabs by employing “strength domain” [...] Read more.
One-way glass fibre reinforced polymer (GFRP) reinforced concrete slabs at elevated temperatures are investigated through numerical modeling. Serviceability and strength requirements of ACI-440.1R are considered for the design of the slabs. Diagrams to determine fire endurance of slabs by employing “strength domain” failure criterion are presented. Comparisons between the existing “temperature domain” method with the more representative “strength domain” method show that the “temperature domain” method is conservative. Additionally, a method to increase the fire endurance of slabs by placing FRP reinforcement in two layers is investigated numerically. The amount of fire endurance gained by placing FRP in two layers increases as the thickness of slab increases. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Biobased Contents of Natural Rubber Model Compound and Its Separated Constituents
Polymers 2014, 6(2), 423-442; doi:10.3390/polym6020423
Received: 30 December 2013 / Accepted: 7 February 2014 / Published: 10 February 2014
Cited by 6 | PDF Full-text (1021 KB) | HTML Full-text | XML Full-text
Abstract
Production of rubber products with biobased constituents from biomass resources is desirable for conserving our planet’s limited resources and preventing global warming. Herein, a natural rubber model compound was produced to determine the biobased contents as per various indices for calculating the [...] Read more.
Production of rubber products with biobased constituents from biomass resources is desirable for conserving our planet’s limited resources and preventing global warming. Herein, a natural rubber model compound was produced to determine the biobased contents as per various indices for calculating the amount of biomass resources used in rubber products. The biobased mass and biobased carbon contents of the natural rubber model compound were 38.7% and 39.2%, respectively, which were calculated from the feed amounts of the constituents as per the International Organization for Standardization (ISO)/the draft of International Standard (DIS) 16620-2 and 16620-4. The model compound was separated into its constituents such as polymer, additive, carbon black, and zinc oxide using ISO 1407, 4650, 7720-2, and 9924-3. The biobased carbon content of this model compound was 37.6%, calculated from the percent of modern carbon (pMC), which was measured directly using accelerator mass spectrometry (AMS). The calculated values for this model compound agreed with those calculated from the feed amounts of the constituents. Thus, it was confirmed that these calculation and determination methods of the biobased mass and the biobased carbon contents for rubber products should be published as new ISO international standards after a discussion at technical committee 45, “rubber and rubber products” to evaluate rubber products with larger biobased contents of natural rubber and other biobased ingredients. Full article
(This article belongs to the Special Issue Polymers from Biomass)
Open AccessArticle CFRP-Strengthening and Long-Term Performance of Fatigue Critical Welds of a Steel Box Girder
Polymers 2014, 6(2), 443-463; doi:10.3390/polym6020443
Received: 29 November 2013 / Accepted: 28 January 2014 / Published: 11 February 2014
Cited by 4 | PDF Full-text (1906 KB) | HTML Full-text | XML Full-text
Abstract
Empa’s research efforts in the 1990s provided evidence that a considerable increase of the fatigue strength of welded aluminum beams can be achieved by externally bonding pultruded carbon fiber reinforced polymer (CFRP) laminates using rubber-toughened epoxies over the fatigue-weak welding zone on [...] Read more.
Empa’s research efforts in the 1990s provided evidence that a considerable increase of the fatigue strength of welded aluminum beams can be achieved by externally bonding pultruded carbon fiber reinforced polymer (CFRP) laminates using rubber-toughened epoxies over the fatigue-weak welding zone on their tensile flange. The reinforcing effect obtained is determined by the stiffness of the unidirectional CFRP laminate which has twice the elastic modulus of aluminum. One can therefore easily follow that an unstressed CFRP laminate reinforcement of welded beams made of steel will not lead to a substantial increase in fatigue strength of the steel structure. This consideration led to the idea of prestressing an external reinforcement of the welded zone. The present investigation describes experimental studies to identify the adhesive system suitable for achieving high creep and fatigue strength of the prestressed CFRP patch. Experimental results (Wöhler-fields) of shear-lap-specimens and welded steel beams reinforced with prestressed CFRP laminates are presented. The paper concludes by presenting a field application, the reinforcement of a steel pendulum by adhesively bonded prestressed CFRP laminates to the tensile flanges of the welded box girder. Inspections carried out periodically on this structure revealed neither prestress losses nor crack initiation after nine years of service. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Nonlinear Analyses of Adobe Masonry Walls Reinforced with Fiberglass Mesh
Polymers 2014, 6(2), 464-478; doi:10.3390/polym6020464
Received: 5 December 2013 / Revised: 30 January 2014 / Accepted: 10 February 2014 / Published: 17 February 2014
Cited by 6 | PDF Full-text (2389 KB) | HTML Full-text | XML Full-text
Abstract
Adobe constructions were widespread in the ancient world, and earth was one of the most used construction materials in ancient times. Therefore, the preservation of adobe structures, especially against seismic events, is nowadays an important structural issue. Previous experimental tests have shown [...] Read more.
Adobe constructions were widespread in the ancient world, and earth was one of the most used construction materials in ancient times. Therefore, the preservation of adobe structures, especially against seismic events, is nowadays an important structural issue. Previous experimental tests have shown that the ratio between mortar and brick mechanical properties (i.e., strength, stiffness and elastic modulus) influences the global response of the walls in terms of strength and ductility. Accurate analyses are presented in both the case of unreinforced and reinforced with fiberglass mesh when varying the mechanical properties of the materials composing the adobe masonry structure. The main issues and variability in the behavior of seismic resisting walls when varying the mechanical properties are herein highlighted. The aim of the overall research activity is to improve the knowledge about the structural behavior of adobe structural members unreinforced and reinforced with fiberglass mesh inside horizontal mortar joints. Full article
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
Open AccessArticle Antimicrobial Plant Extracts Encapsulated into Polymeric Beads for Potential Application on the Skin
Polymers 2014, 6(2), 479-490; doi:10.3390/polym6020479
Received: 12 December 2013 / Revised: 4 February 2014 / Accepted: 10 February 2014 / Published: 18 February 2014
Cited by 10 | PDF Full-text (297 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the in vitro bacterial growth inhibition, antioxidant activity and the content in bioactive components of Plectranthus barbatus, P. hadiensis var. tomentosus, P. madagascarensis, P. neochilus and P. verticillatus aqueous extracts were investigated and compared by three extraction [...] Read more.
In this study, the in vitro bacterial growth inhibition, antioxidant activity and the content in bioactive components of Plectranthus barbatus, P. hadiensis var. tomentosus, P. madagascarensis, P. neochilus and P. verticillatus aqueous extracts were investigated and compared by three extraction methods (infusion, decoction and microwave extractions). The microwave extract of P. madagascariensis showed the higher antimicrobial activity against the Staphylococcus epidermidis strain with a minimum inhibitory concentration of 40 µg/mL. This extract also showed no toxicity in a general toxicity assay and no considerable cytotoxicity against a human keratinocyte cell line. The antioxidant activity of the extracts was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH method), and all showed antioxidant activity. The microwave extract of P. madagascariensis was the one with the highest antioxidant activity (IC50 value of 41.66 µg/mL). To increase extract stability, the microwave P. madagascariensis extract was then successfully encapsulated into alginate beads with high efficiency. This effective and low-cost strategy seems to be easy to extrapolate to an industrial scale with a future application on the skin. Full article
(This article belongs to the Special Issue Polymers for Drug Delivery)
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Open AccessArticle Computational Study of a Heterostructural Model of Type I Collagen and Implementation of an Amino Acid Potential Method Applicable to Large Proteins
Polymers 2014, 6(2), 491-514; doi:10.3390/polym6020491
Received: 7 January 2014 / Revised: 8 February 2014 / Accepted: 11 February 2014 / Published: 18 February 2014
Cited by 6 | PDF Full-text (3509 KB) | HTML Full-text | XML Full-text
Abstract
Collagen molecules are the primary structural proteins of many biological systems. Much progress has been made in the study of the structure and function of collagen, but fundamental understanding of its electronic structures at the atomic level is still lacking. We present [...] Read more.
Collagen molecules are the primary structural proteins of many biological systems. Much progress has been made in the study of the structure and function of collagen, but fundamental understanding of its electronic structures at the atomic level is still lacking. We present the results of electronic structure and bonding calculations of a specific model of type I collagen using the density functional theory-based method. Information on density of states (DOS), partial DOS, effective charges, bond order values, and intra- and inter-molecular H-bonding are obtained and discussed. We further devised an amino-acid-based potential method (AAPM) to circumvent the full self-consistent field (SCF) calculation that can be applied to large proteins. The AAPM is validated by comparing the results with the full SCF calculation of the whole type I collagen model with three strands. The calculated effective charges on each atom in the model retained at least 95% accuracy. This technique provides a viable and efficient way to study the electronic structure of large complex biomaterials at the ab initio level. Full article
(This article belongs to the Special Issue Computational Chemistry)
Open AccessArticle Optimal Focusing and Scaling Law for Uniform Photo-Polymerization in a Thick Medium Using a Focused UV Laser
Polymers 2014, 6(2), 552-564; doi:10.3390/polym6020552
Received: 5 December 2013 / Revised: 13 February 2014 / Accepted: 14 February 2014 / Published: 21 February 2014
Cited by 4 | PDF Full-text (721 KB) | HTML Full-text | XML Full-text
Abstract
We present a modeling study of photoinitiated polymerization in a thick polymer-absorbing medium using a focused UV laser. Transient profiles of the initiator concentration at various focusing conditions are analyzed to define the polymerization boundary. Furthermore, we demonstrate the optimal focusing conditions [...] Read more.
We present a modeling study of photoinitiated polymerization in a thick polymer-absorbing medium using a focused UV laser. Transient profiles of the initiator concentration at various focusing conditions are analyzed to define the polymerization boundary. Furthermore, we demonstrate the optimal focusing conditions that yield more uniform polymerization over a larger volume than the collimated or non-optimal cases. Too much focusing with the focal length f < f* (an optimal focal length) yields a fast process; however, it provides a smaller polymerization volume at a given time than in the optimal focusing case. Finally, a scaling law is derived and shows that f* is inverse proportional to the product of the extinction coefficient and the initiator initial concentration. The scaling law provides useful guidance for the prediction of optimal conditions for photoinitiated polymerization under a focused UV laser irradiation. The focusing technique also provides a novel and unique means for obtaining uniform photo-polymerization within a limited irradiation time. Full article
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Open AccessArticle Synthesis of Narrow Molecular Weight Distribution Norbornene-Lactone Functionalized Polymers by Nitroxide-Mediated Polymerization: Candidates for 193-nm Photoresist Materials
Polymers 2014, 6(2), 565-582; doi:10.3390/polym6020565
Received: 16 January 2014 / Revised: 10 February 2014 / Accepted: 17 February 2014 / Published: 21 February 2014
Cited by 4 | PDF Full-text (587 KB) | HTML Full-text | XML Full-text
Abstract
One hundred ninety three-nanometer candidate photoresist materials were synthesized by nitroxide-mediated polymerization (NMP). Statistical copolymerizations of 5-methacryloyloxy-2,6-norboranecarbolactone (NLAM) with 5–10 mol% of controlling co-monomers (which are necessary for controlled polymerizations of methacrylates by NMP with the initiator used) in the feed, such [...] Read more.
One hundred ninety three-nanometer candidate photoresist materials were synthesized by nitroxide-mediated polymerization (NMP). Statistical copolymerizations of 5-methacryloyloxy-2,6-norboranecarbolactone (NLAM) with 5–10 mol% of controlling co-monomers (which are necessary for controlled polymerizations of methacrylates by NMP with the initiator used) in the feed, such as styrene (ST), p-acetoxystyrene (AcOST), 2-vinyl naphthalene (VN) and pentafluorostyrene (PFS), using the unimolecular BlocBuilder® initiator in 35 wt% dioxane solution at 90 °C were performed. As little as 5 mol% controlling comonomer in the feed was demonstrated to be sufficient to lead to linear evolution of number average molecular weight  with respect to conversion up to 50%, and the resulting copolymers had dispersities  of ~1.3 in most cases, an attractive feature for reducing line width roughness (LWR) in photoresists. The copolymers generally showed relatively low absorbance at 193 nm, comparable to other 193-nm candidate photoresists reported previously, despite the inclusion of a small amount of the styrenic co-monomers in the copolymer. Full article
(This article belongs to the Special Issue Controlled/Living Radical Polymerization)
Open AccessArticle Molecular Weight and Crystallization Temperature Effects on Poly(ethylene terephthalate) (PET) Homopolymers, an Isothermal Crystallization Analysis
Polymers 2014, 6(2), 583-600; doi:10.3390/polym6020583
Received: 19 December 2013 / Revised: 7 February 2014 / Accepted: 14 February 2014 / Published: 21 February 2014
Cited by 6 | PDF Full-text (2385 KB) | HTML Full-text | XML Full-text
Abstract
The isothermal crystallization of poly(ethylene terephthalate) (PET) homopolymers with different molecular weight was studied in a wide temperature range (140–230 °C) using different experimental techniques. Three different morphological regions, labeled r1, r2 and r3, were distinguished as [...] Read more.
The isothermal crystallization of poly(ethylene terephthalate) (PET) homopolymers with different molecular weight was studied in a wide temperature range (140–230 °C) using different experimental techniques. Three different morphological regions, labeled r1, r2 and r3, were distinguished as a function of crystallization temperature (Tc). In r1 (low Tc) crystallized samples were characterized by a low crystalline degree with a small spherulite texture containing thin crystals. In r2 (intermediate Tc) samples showed medium size spherulites composed of two distinct crystalline families (thin and thick crystals). In this temperature range, the crystallization exhibited a maximum value and it was associated with a high content of secondary crystals. In r3 (high Tc), samples presented considerable amorphous zones and regions consisting of oversized spherulites containing only thick crystals. Time-resolved wide-angle X-ray diffraction measurements, using synchrotron radiation, indicated a rapid evolution of the crystalline degree within the second region, in contrast with the quite slow evolution observed in the third region. On the other hand, by small-angle X-ray scattering (SAXS) and time-resolved SAXS experiment, it was found that the long period (L) as well as the lamellar thickness (lc) increase as a function of Tc, corroborating the formation of the thickest crystals in the third region. From all these observations, a morphological model was proposed for each region. Full article
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Review

Jump to: Editorial, Research

Open AccessReview Hyaluronic Acid Bioconjugates for the Delivery of Bioactive Molecules
Polymers 2014, 6(2), 346-369; doi:10.3390/polym6020346
Received: 3 December 2013 / Revised: 22 January 2014 / Accepted: 23 January 2014 / Published: 30 January 2014
Cited by 29 | PDF Full-text (794 KB) | HTML Full-text | XML Full-text
Abstract
Hyaluronic acid (HA) has currently several therapeutic applications: in ophthalmology, osteoarthritis, wound healing, tissue regeneration, postoperative anti-adhesion and anesthetic medicine. In the last ten years, it has also been successfully investigated in the field of drug delivery, in the form of conjugates [...] Read more.
Hyaluronic acid (HA) has currently several therapeutic applications: in ophthalmology, osteoarthritis, wound healing, tissue regeneration, postoperative anti-adhesion and anesthetic medicine. In the last ten years, it has also been successfully investigated in the field of drug delivery, in the form of conjugates or hydrogel depot systems. HAylation, the covalent conjugation of HA to bioactive molecules, allows the overcoming of disadvantages associated with some pharmaceuticals, such as insolubility, instability and fast kidney clearance. These issues can be addressed also by covalent attachment of polyethylene glycol (PEGylation), but HA has the relevant advantages of biodegradability, high loading and specific targeting. In this review, the novel HA derivatives and the latest advances in HA-based drug delivery with a particular focus on the chemistry of conjugation will be discussed. Although, so far, there are no HA-drug conjugates on the market, several derivatives are presently under clinical investigation, and the promising results encourage further investigations and the exploitation of this versatile polysaccharide. Full article
(This article belongs to the Special Issue Polymers for Drug Delivery)
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Open AccessReview Development of Polymer Acceptors for Organic Photovoltaic Cells
Polymers 2014, 6(2), 382-407; doi:10.3390/polym6020382
Received: 15 January 2014 / Revised: 6 February 2014 / Accepted: 7 February 2014 / Published: 10 February 2014
Cited by 27 | PDF Full-text (375 KB) | HTML Full-text | XML Full-text
Abstract
This review provides a current status report of the various n-type polymer acceptors for use as active materials in organic photovoltaic cells (OPVs). The polymer acceptors are divided into four categories. The first section of this review focuses on rylene diimide-based [...] Read more.
This review provides a current status report of the various n-type polymer acceptors for use as active materials in organic photovoltaic cells (OPVs). The polymer acceptors are divided into four categories. The first section of this review focuses on rylene diimide-based polymers, including perylene diimide, naphthalene diimide, and dithienocoronene diimide-based polymers. The high electron mobility and good stability of rylene diimides make them suitable for use as polymer acceptors in OPVs. The second section deals with fluorene and benzothiadiazole-based polymers such as poly(9,9’-dioctylfluorene-co-benzothiadiazole), and the ensuing section focuses on the cyano-substituted polymer acceptors. Cyano-poly(phenylenevinylene) and poly(3-cyano-4-hexylthiophene) have been used as acceptors in OPVs and exhibit high electron affinity arising from the electron-withdrawing cyano groups in the vinylene group of poly(phenylenevinylene) or the thiophene ring of polythiophene. Lastly, a number of other electron-deficient groups such as thiazole, diketopyrrolopyrrole, and oxadiazole have also been introduced onto polymer backbones to induce n-type characteristics in the polymer. Since the first report on all-polymer solar cells in 1995, the best power conversion efficiency obtained with these devices to date has been 3.45%. The overall trend in the development of n-type polymer acceptors is presented in this review. Full article
(This article belongs to the Special Issue Semiconducting Polymers for Organic Electronic Devices)
Open AccessReview Peptide-Based Polymer Therapeutics
Polymers 2014, 6(2), 515-551; doi:10.3390/polym6020515
Received: 28 December 2013 / Revised: 6 February 2014 / Accepted: 7 February 2014 / Published: 21 February 2014
Cited by 17 | PDF Full-text (1090 KB) | HTML Full-text | XML Full-text
Abstract
Polypeptides are envisaged to achieve a major impact on a number of different relevant areas such as biomedicine and biotechnology. Acquired knowledge and the increasing interest on amino acids, peptides and proteins is establishing a large panel of these biopolymers whose physical, [...] Read more.
Polypeptides are envisaged to achieve a major impact on a number of different relevant areas such as biomedicine and biotechnology. Acquired knowledge and the increasing interest on amino acids, peptides and proteins is establishing a large panel of these biopolymers whose physical, chemical and biological properties are ruled by their controlled sequences and composition. Polymer therapeutics has helped to establish these polypeptide-based constructs as polymeric nanomedicines for different applications, such as disease treatment and diagnostics. Herein, we provide an overview of the advantages of these systems and the main methodologies for their synthesis, highlighting the different polypeptide architectures and the current research towards clinical applications. Full article
(This article belongs to the Special Issue Polymers for Drug Delivery)
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