Polymers

575 KiB

Open AccessArticle

Diasteromeric Effect on the Homolysis of the C–ON Bond in Alkoxyamines: A DFT Investigation of 1,3-Diphenylbutyl-TEMPO

by Alexandra Blachon, Sylvain R. A. Marque, Valérie Roubaud and Didier Siri

Polymers 2010, 2(3), 353-363; https://doi.org/10.3390/polym2030353 - 27 Sep 2010

Cited by 11 | Viewed by 7573

The rate constants k_d of the homolysis of the C–ON bond in styryl dyads TEMPO-based alkoxyamines have recently been published (Li et al. Macromolecules 2006, 39, 9201). The diastereoisomers exhibited different values which were higher than for the unimer TEMPO-styryl [...] Read more.

The rate constants k_d of the homolysis of the C–ON bond in styryl dyads TEMPO-based alkoxyamines have recently been published (Li et al. Macromolecules 2006, 39, 9201). The diastereoisomers exhibited different values which were higher than for the unimer TEMPO-styryl alkoxyamine 1. At a first glance, the localization of the steric strain was not obvious. To decipher this problem, diastereoisomer models 2 (RR/SS) and 3 (RS/SR), as well as the released alkyl radicals, were calculated at the \B3LYP/6-31G(d) level. It was revealed that the increase in k_d from 1 to 3 was due to the compression (buttressing effect) of the reactive center by the second styryl moiety. The difference in k_d for the diastereoisomer was clearly an activation entropy effect DS^≠ because the alkyl fragment of the RS/SR diastereoismer exhibited the same conformation as the released radical whereas the conformation for the RR/SS diastereoisomer was quite different and thus required the rotation of several bonds to reach the correct TS, which cost DS^≠, and thus lowers k_d. Full article

(This article belongs to the Special Issue Advanced Polymer Architectures)

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1413 KiB

Open AccessReview

Bio-Inspired/-Functional Colloidal Core-Shell Polymeric-Based NanoSystems: Technology Promise in Tissue Engineering, Bioimaging and NanoMedicine

by Ziyad S. Haidar

Polymers 2010, 2(3), 323-352; https://doi.org/10.3390/polym2030323 - 20 Sep 2010

Cited by 63 | Viewed by 15091

Abstract

Modern breakthroughs in the fields of proteomics and DNA micro-arrays have widened the horizons of nanotechnology for applications with peptides and nucleic acids. Hence, biomimetic interest in the study and formulation of nanoscaled bio-structures, -materials, -devices and -therapeutic agent delivery vehicles has been [...] Read more.

Modern breakthroughs in the fields of proteomics and DNA micro-arrays have widened the horizons of nanotechnology for applications with peptides and nucleic acids. Hence, biomimetic interest in the study and formulation of nanoscaled bio-structures, -materials, -devices and -therapeutic agent delivery vehicles has been recently increasing. Many of the currently–investigated functionalized bio-nanosystems draw their inspiration from naturally-occurring phenomenon, prompting the integration of molecular signals and mimicking natural processes, at the cell, tissue and organ levels. Technologically, the ability to obtain spherical nanostructures exhibiting combinations of several properties that neither individual material possesses on its own renders colloidal core-shell architectured nanosystems particularly attractive. The three main developments presently foreseen in the nanomedicine sub-arena of nanobiotechnology are: sensorization (biosensors/ biodetection), diagnosis (biomarkers/bioimaging) and drug, protein or gene delivery (systemic vs. localized/targeted controlled–release systems). Advances in bio-applications such as cell-labelling/cell membrane modelling, agent delivery and targeting, tissue engineering, organ regeneration, nanoncology and immunoassay strategies, along the major limitations and potential future and advances are highlighted in this review. Herein, is an attempt to address some of the most recent works focusing on bio-inspired and -functional polymeric-based core-shell nanoparticulate systems aimed for agent delivery. It is founded, mostly, on specialized research and review articles that have emerged during the last ten years. Full article

(This article belongs to the Special Issue Bioinspired Polymers)

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500 KiB

Open AccessReview

The Use of Polymers in the Treatment of Retinal Detachment: Current Trends and Future Perspectives

by Francesco Baino

Polymers 2010, 2(3), 286-322; https://doi.org/10.3390/polym2030286 - 9 Sep 2010

Cited by 17 | Viewed by 11335

Abstract

Procedures for the treatment of retinal detachment and related conditions have been successfully improved upon in recent years thanks to the advent of new therapies and biomaterials. This review, after giving an overview on eye structure and function, focuses on the treatment of [...] Read more.

Procedures for the treatment of retinal detachment and related conditions have been successfully improved upon in recent years thanks to the advent of new therapies and biomaterials. This review, after giving an overview on eye structure and function, focuses on the treatment of retinal detachment and examines the role and features of the materials used in vitreoretinal surgery, emphasizing scleral buckling and short-term/long-term vitreous tamponade. Specifically, the limitations of existing biomaterials are underlined, based on experimental studies and with particular reference to cells/material interactions. Finally, current and future trends of biomaterials’ research in the field of vitreoretinal surgery are considered and discussed. Full article

(This article belongs to the Special Issue Biofunctional Polymers for Medical Applications)

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701 KiB

Open AccessArticle

Synthesis of Ethylene Glycol Dimethacrylate-Methyl Methacrylate Copolymers, Determination of their Reactivity Ratios, and a Study of Dopant and Temperature Effects on their Conductivities

by Ulku S. Ramelow and Sreedhar Pingili

Polymers 2010, 2(3), 265-285; https://doi.org/10.3390/polym2030265 - 26 Aug 2010

Cited by 27 | Viewed by 15705

Abstract

Ultraviolet radiation was used as a photochemical initiator to synthesize ethylene glycol dimethacrylate-methyl methacrylate copolymers. Infrared spectroscopy was used to calculate reactivity ratios and to identify the type of copolymerization. The reactivity ratios of EGDMA and MMA were calculated as 0.6993 and 1.8635, [...] Read more.

Ultraviolet radiation was used as a photochemical initiator to synthesize ethylene glycol dimethacrylate-methyl methacrylate copolymers. Infrared spectroscopy was used to calculate reactivity ratios and to identify the type of copolymerization. The reactivity ratios of EGDMA and MMA were calculated as 0.6993 and 1.8635, respectively. The effect of lithium perchlorate as a dopant on copolymer conductivity and conversion was studied. The addition of dopant increased the conductivity of copolymers. For copolymers containing 5% MMA in the feed, dopant increased conductivity about 775 times; when the MMA percentage was 20% in the feed, dopant increased conductivity about 100 times. As MMA percentage increases in the copolymer, the conductivity values decrease from the mS to the µS region. This is consistent with the fact that PMMA has a lower conductivity than PEGDMA. The conductivity change of homopolymers and copolymers at various temperatures were studied. Both MMA and EGDMA polymers and their copolymers show a minimum in their conductivity vs. temperature graphs, indicating that they first act as a conductor and after a minimum temperature, become semiconductors and can be used to control current in electrical devices by temperature change. The measurement of conductivity change with time provided a new way to follow the kinetics of polymer/dopant reactions. The activation energy of interaction with dopant was calculated as 31.52 kJ/mol for MMA/EGDMA copolymers; for PEGDMA alone it was 54.7 kJ/mol. Full article

(This article belongs to the Special Issue Conductive Polymers)

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563 KiB

Open AccessArticle

Synthesis and Characterization of Carboxymethylcellulose-Methacrylate Hydrogel Cell Scaffolds

by Robert Reeves, Andreia Ribeiro, Leonard Lombardo, Richard Boyer and Jennie B. Leach

Polymers 2010, 2(3), 252-264; https://doi.org/10.3390/polym2030252 - 26 Aug 2010

Cited by 67 | Viewed by 14039

Abstract

Many carbohydrates pose advantages for tissue engineering applications due to their hydrophilicity, degradability, and availability of chemical groups for modification. For example, carboxymethylcellulose (CMC) is a water-soluble cellulose derivative that is degradable by cellulase. Though this enzyme is not synthesized by mammalian cells, [...] Read more.

Many carbohydrates pose advantages for tissue engineering applications due to their hydrophilicity, degradability, and availability of chemical groups for modification. For example, carboxymethylcellulose (CMC) is a water-soluble cellulose derivative that is degradable by cellulase. Though this enzyme is not synthesized by mammalian cells, cellulase and the fragments derived from CMC degradation are biocompatible. With this in mind, we created biocompatible, selectively degradable CMC-based hydrogels that are stable in routine culture, but degrade when exposed to exogenous cellulase. Solutions of CMC-methacrylate and polyethylene glycol dimethacrylate (PEG-DM) were co-crosslinked to form stable hydrogels; we found that greater CMC-methacrylate content resulted in increased gel swelling, protein diffusion and rates of degradation by cellulase, as well as decreased gel shear modulus. CMC-methacrylate/PEG-DM gels modified with the adhesive peptide RGD supported fibroblast adhesion and viability. We conclude that hydrogels based on CMC-methacrylate are suitable for bioengineering applications where selective degradability may be favorable, such as cell scaffolds or controlled release devices. Full article

(This article belongs to the Special Issue Natural Polymers)

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1119 KiB

Open AccessReview

Responsive Polymers for Crop Protection

by Serban F. Peteu, Florin Oancea, Oana A. Sicuia, Florica Constantinescu and Sorina Dinu

Polymers 2010, 2(3), 229-251; https://doi.org/10.3390/polym2030229 - 19 Aug 2010

Cited by 99 | Viewed by 16995

Abstract

This review outlines the responsive polymer methods currently in use with their potential application to plant protection and puts forward plant-specific mechanisms as stimuli in newly devised methods for smart release of crop protection agents (CPAs). CPAs include chemicals (fungicides, insecticides, herbicides), biochemicals [...] Read more.

This review outlines the responsive polymer methods currently in use with their potential application to plant protection and puts forward plant-specific mechanisms as stimuli in newly devised methods for smart release of crop protection agents (CPAs). CPAs include chemicals (fungicides, insecticides, herbicides), biochemicals (antibiotics, RNA-based vaccines for plant viruses), semiochemicals (pheromones, repellents, allomones), microbial pesticides, growth regulators (insect and plant) or micronutrients, all with crop protection effects. This appraisal focuses on emerging uses of polymer nano-encapsulated CPAs. Firstly, the most interesting advances in controlled release methods are critically discussed with their advantages and drawbacks. Secondly, several plant-specific stimuli-based smart methods are anticipated for use alongside the polymer nano- or micro-capsules. These new CPA release methods are designed to (i) protect plants against infection produced by fungi or bacteria, and (ii) apply micro-nutrients when the plants need it the most. Thus, we foresee (i) the responsive release of nano- encapsulated bio-insecticides regulated by plant stress enzymes, and (ii) the delivery of micro-nutrients synchronized by the nature or intensity of plant root exudates. Such continued advances of nano-scale smart polymer-based CPAs for the protection of crops herald a “small revolution” for the benefit of sustainable agriculture. Full article

(This article belongs to the Special Issue Novel Stimuli-Responsive (co)Polymers)

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702 KiB

Open AccessArticle

Borate Minerals and RNA Stability

by Cristina Cossetti, Claudia Crestini, Raffaele Saladino and Ernesto Di Mauro

Polymers 2010, 2(3), 211-228; https://doi.org/10.3390/polym2030211 - 16 Aug 2010

Cited by 19 | Viewed by 9864

Abstract

The abiotic origin of genetic polymers faces two major problems: a prebiotically plausible polymerization mechanism and the maintenance of their polymerized state outside a cellular environment. The stabilizing action of borate on ribose having been reported, we have explored the possibility that borate [...] Read more.

The abiotic origin of genetic polymers faces two major problems: a prebiotically plausible polymerization mechanism and the maintenance of their polymerized state outside a cellular environment. The stabilizing action of borate on ribose having been reported, we have explored the possibility that borate minerals stabilize RNA. We observe that borate itself does not stabilize RNA. The analysis of a large panel of minerals tested in various physical-chemical conditions shows that in general no protection on RNA backbone is exerted, with the interesting exception of ludwigite (Mg₂Fe₃+BO₅). Stability is a fundamental property of nucleic polymers and borate is an abundant component of the planet, hence the prebiotic interest of this analysis. Full article

(This article belongs to the Special Issue Natural Polymers)

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415 KiB

Open AccessArticle

Fabrication of Extrinsically Conductive Silicone Rubbers with High Elasticity and Analysis of Their Mechanical and Electrical Characteristics

by Anjum Saleem, Lars Frormann and Alexandru Soever

Polymers 2010, 2(3), 200-210; https://doi.org/10.3390/polym2030200 - 10 Aug 2010

Cited by 38 | Viewed by 12477

Abstract

Conductive plastics are attracting more and more interest in electronics due to their light weight and inability to rust, which are common problems associated with metals. The field of conducting plastics is not new. Much work has been done to impart electrical conductivity [...] Read more.

Conductive plastics are attracting more and more interest in electronics due to their light weight and inability to rust, which are common problems associated with metals. The field of conducting plastics is not new. Much work has been done to impart electrical conductivity to mechanically strong polymers such as polypropylene, polycarbonate and epoxies, etc. However there is a need to fabricate more flexible and elastic conductive polymers such as conducting silicone rubbers for use in various applications. In this work silicone rubbers reinforced with conductive fillers have been fabricated for use as sensors in textiles to detect the resistance change produced by stretching or relaxing. The variations of electrical resistance have been investigated by stretching and releasing the strands of conductive rubbers as a function of time. Two types of silicone rubbers—addition cured and condensation cured—were compounded with different electrically conductive fillers, among which carbon fibers have shown the best results. The carbon fibers improved the electrical conductance of the rubbers, even in very low weight percentages. The increasing concentration of fillers decreases the elasticity of the rubber. In order to keep the original properties of silicones, the filler concentration was kept as low as possible to produce a significantly detectable signal. The fabricated compounds were analyzed for their mechanical properties by stress strain curves. Such materials find their applications in electronics, antistatic applications, sports and the automotive industry where they can be used as deformation sensors. Full article

(This article belongs to the Special Issue Conductive Polymers)

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260 KiB

Open AccessArticle

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

by Hanneke M. L. Lambermont-Thijs, Huub P. C. van Kuringen, Jeroen P. W. van der Put, Ulrich S. Schubert and Richard Hoogenboom

Polymers 2010, 2(3), 188-199; https://doi.org/10.3390/polym2030188 - 10 Aug 2010

Cited by 63 | Viewed by 13070

Abstract

The solution behavior of a series of poly(2-oxazoline)s with different side chains, namely methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, phenyl and benzyl, are reported in ethanol-water solvent mixtures based on turbidimetry investigations. The LCST transitions of [...] Read more.

The solution behavior of a series of poly(2-oxazoline)s with different side chains, namely methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, nonyl, phenyl and benzyl, are reported in ethanol-water solvent mixtures based on turbidimetry investigations. The LCST transitions of poly(2-oxazoline)s with propyl side chains and the UCST transitions of the poly(2-oxazoline)s with more hydrophobic side chains are discussed in relation to the ethanol-water solvent composition and structure. The poly(2-alkyl-2-oxazoline)s with side chains longer than propyl only dissolved during the first heating run, which is discussed and correlated to the melting transition of the polymers. Full article

(This article belongs to the Special Issue Novel Stimuli-Responsive (co)Polymers)

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318 KiB

Open AccessArticle

Study on Exothermic Oxidation of Acrylonitrile-butadiene-styrene (ABS) Resin Powder with Application to ABS Processing Safety

by Yih-Shing Duh, Ta-Cheng Ho, Jenq-Renn Chen and Chen-Shan Kao

Polymers 2010, 2(3), 174-187; https://doi.org/10.3390/polym2030174 - 4 Aug 2010

Cited by 46 | Viewed by 16799

Abstract

Oxidative degradation of commercial grade ABS (Acrylonitrile-butadiene-styrene) resin powders was studied by thermal analysis. The instabilities of ABS containing different polybutadiene (PB) contents with respect to temperature were studied by Differential Scanning Calorimeter (DSC). Thermograms of isothermal test and dynamic scanning were performed. [...] Read more.

Oxidative degradation of commercial grade ABS (Acrylonitrile-butadiene-styrene) resin powders was studied by thermal analysis. The instabilities of ABS containing different polybutadiene (PB) contents with respect to temperature were studied by Differential Scanning Calorimeter (DSC). Thermograms of isothermal test and dynamic scanning were performed. Three exothermic peaks were observed and related to auto-oxidation, degradation and oxidative decomposition, respectively. Onset temperature of the auto-oxidation was determined to be around 193 °C. However, threshold temperature of oxidation was found to be as low as 140 °C by DSC isothermal testing. Another scan of the powder after degeneration in air showed an onset temperature of 127 °C. Reactive hazards of ABS powders were verified to be the exothermic oxidation of unsaturated PB domains, not the SAN (poly(styrene-acrylonitrile)) matrix. Heat of oxidation was first determined to be 2,800 ± 40 J per gram of ABS or 4,720 ± 20 J per gram of PB. Thermal hazards of processing ABS powder are assessed by adiabatic temperature rise at process conditions. IR spectroscopy associated with heat of oxidation verified the oxidative mechanism, and these evidences excluded the heat source from the degradation of SAN. A specially prepared powder of ABS without adding anti-oxidant was analyzed by DSC for comparing the exothermic behaviors. Exothermic onset temperatures were determined to be 120 °C and 80 °C by dynamic scanning and isothermal test, respectively. The assessment successfully explained fires and explosions in an ABS powder dryer and an ABS extruder. Full article

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1289 KiB

Open AccessArticle

Synthesis and Properties of 1,8-Carbazole-Based Conjugated Copolymers

by Tsuyoshi Michinobu, Haruka Osako and Kiyotaka Shigehara

Polymers 2010, 2(3), 159-173; https://doi.org/10.3390/polym2030159 - 30 Jul 2010

Cited by 31 | Viewed by 11688

Abstract

A new series of conjugated carbazole polymers based on the 1,8-carbazolylene unit was synthesized by the Pd-catalyzed polycondensation between the 1,8-diiodocarbazole derivative and various bifunctional counter comonomers. An alkyne spacer was found to be a key to increasing the molecular weight of the [...] Read more.

A new series of conjugated carbazole polymers based on the 1,8-carbazolylene unit was synthesized by the Pd-catalyzed polycondensation between the 1,8-diiodocarbazole derivative and various bifunctional counter comonomers. An alkyne spacer was found to be a key to increasing the molecular weight of the resulting polymers. All the obtained polymers showed good solubilities in the common organic solvents, and they were fully characterized by Gel permeation chromatography (GPC), and ¹H NMR and infrared (IR) spectroscopies. The UV-vis absorption and fluorescence spectra revealed the relationship between the chemical structure and effective conjugation length. The efficiency order of the carbazole connectivity was 2,7-carbazolylene > 1,8-carbazolylene > 3,6-carbazolylene. The electrochemical properties of these polymers suggested the relatively facile oxidation at ca. +0.5–0.7 V vs. Fc/Fc⁺ or a high potential as p-type semiconductors. The combination of the electrochemical oxidation potentials and the optical band gaps allowed us to estimate the HOMO and LUMO levels of the polymers. It was shown that the energy levels of the 1,8-carbazole-based conjugated polymers can be tunable by selecting the appropriate comonomer structures. Full article

(This article belongs to the Special Issue Conductive Polymers)

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851 KiB

Open AccessReview

Review on the Functional Determinants and Durability of Shape Memory Polymers

by Thorsten Pretsch

Polymers 2010, 2(3), 120-158; https://doi.org/10.3390/polym2030120 - 28 Jul 2010

Cited by 114 | Viewed by 16021

Abstract

Shape memory polymers (SMP) belong to the class of stimuli-responsive materials and have generated significant research interest. Their capability to retain an imposed, temporary shape and to recover the initial, permanent shape upon exposure to an external stimulus depends on the “functional determinants”, [...] Read more.

Shape memory polymers (SMP) belong to the class of stimuli-responsive materials and have generated significant research interest. Their capability to retain an imposed, temporary shape and to recover the initial, permanent shape upon exposure to an external stimulus depends on the “functional determinants”, which in simplistic terms, can be divided into structural/morphological and processing/environmental factors. The primary aim of the first part of this review is to reflect the knowledge about these fundamental relationships. In a next step, recent advances in shape memory polymer composites are summarized. In contrast to earlier reviews, studies on the impairment of shape memory properties through various factors, such as aging, compression and hibernation, lubricants, UV light and thermo-mechanical cycling, are extensively reviewed. Apart from summarizing the state-of-the-art in SMP research, recent progress is commented. Full article

(This article belongs to the Special Issue Novel Stimuli-Responsive (co)Polymers)

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556 KiB

Open AccessArticle

Polyurethane Membranes Modified with Isopropyl Myristate as a Potential Candidate for Encapsulating Electronic Implants: A Study of Biocompatibility and Water Permeability

by Nima Roohpour, Jaroslaw M. Wasikiewicz, Alireza Moshaverinia, Deepen Paul, Mike F. Grahn, Ihtesham U. Rehman and Pankaj Vadgama

Polymers 2010, 2(3), 102-119; https://doi.org/10.3390/polym2030102 - 12 Jul 2010

Cited by 20 | Viewed by 10706

Abstract

Medical polyurethanes have shown good bio-stability and mechanical properties and have been used as coating for implantable medical devices. However, despite their excellent properties, they are relatively permeable to liquid water and water vapour which is a drawback for electronic implant encapsulation. In [...] Read more.

Medical polyurethanes have shown good bio-stability and mechanical properties and have been used as coating for implantable medical devices. However, despite their excellent properties, they are relatively permeable to liquid water and water vapour which is a drawback for electronic implant encapsulation. In this study polyether polyurethanes with different soft segment molecular weights were modified by incorporating isopropyl myristate (IPM), as a hydrophobic modifying agent, and the effect of IPM on water resistant and biocompatibility of membranes were investigated. IPM changed the surface properties of the polyurethane film and reduced its surface energy. Polyurethane films were found to be stable with IPM concentrations of 1–5 wt% based upon their chemistry; however it leached out in BSA at higher concentrations. Though, low concentrations of IPM reduced both liquid water and water vapour permeability; at higher IPM content liquid permeability did not improved significantly. In general, the polyurethane materials showed much lower water permeability compared with currently used silicone packaging material for electronic implants. In addition, cytotoxicity assessment of IPM containing polyurethanes showed no evidence of cytotoxcity up to 5 wt% IPM. Full article

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Polymers, Volume 2, Issue 3 (September 2010) – 13 articles , Pages 102-363

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