Polymers

606 KiB

Open AccessArticle

New Insight into Organic Metal Polyaniline Morphology and Structure

by Bernhard Wessling

Polymers 2010, 2(4), 786-798; https://doi.org/10.3390/polym2040786 - 17 Dec 2010

Cited by 50 | Viewed by 18394

Polyaniline is known to be a true metal, though a nanometal. Previous experimental and theoretical evidence is reviewed. Two important structural features are presented, which have not publicly been discussed so far: (a) The formation of complexes between polyaniline and metals (Cu, Fe, [...] Read more.

Polyaniline is known to be a true metal, though a nanometal. Previous experimental and theoretical evidence is reviewed. Two important structural features are presented, which have not publicly been discussed so far: (a) The formation of complexes between polyaniline and metals (Cu, Fe, Zn, In, etc.) which are crucial for most practical applications of the organic metal, polyaniline; and (b) a model for the polyaniline chain structure within the smallest morphological unit, the roughly 10 nm primary particle. Full article

(This article belongs to the Special Issue Conductive Polymers)

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1068 KiB

Open AccessArticle

Modeling Textural Processes during Self-Assembly of Plant-Based Chiral-Nematic Liquid Crystals

by Yogesh K. Murugesan and Alejandro D. Rey

Polymers 2010, 2(4), 766-785; https://doi.org/10.3390/polym2040766 - 15 Dec 2010

Cited by 23 | Viewed by 8259

Abstract

Biological liquid crystalline polymers are found in cellulosic, chitin, and DNA based natural materials. Chiral nematic liquid crystalline orientational order is observed frozen-in in the solid state in plant cell walls and is known as a liquid crystal analogue characterized by a helicoidal [...] Read more.

Biological liquid crystalline polymers are found in cellulosic, chitin, and DNA based natural materials. Chiral nematic liquid crystalline orientational order is observed frozen-in in the solid state in plant cell walls and is known as a liquid crystal analogue characterized by a helicoidal plywood architecture. The emergence of the plywood architecture by directed chiral nematic liquid crystalline self assembly has been postulated as the mechanism that leads to optimal cellulose fibril organization. In natural systems, tissue growth and development takes place in the presence of inclusions and secondary phases leaving behind characteristic defects and textures, which provide a unique testing ground for the validity of the liquid crystal self-assembly postulate. In this work, a mathematical model, based on the Landau-de Gennes theory of liquid crystals, is used to simulate defect textures arising in the domain of self assembly, due to presence of secondary phases representing plant cells, lumens and pit canals. It is shown that the obtained defect patterns observed in some plant cell walls are those expected from a truly liquid crystalline phase. The analysis reveals the nature and magnitude of the viscoelastic material parameters that lead to observed patterns in plant-based helicoids through directed self-assembly. In addition, the results provide new guidance to develop biomimetic plywoods for structural and functional applications. Full article

(This article belongs to the Special Issue Natural Polymers)

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712 KiB

Open AccessReview

Cellulosic Bionanocomposites: A Review of Preparation, Properties and Applications

by Gilberto Siqueira, Julien Bras and Alain Dufresne

Polymers 2010, 2(4), 728-765; https://doi.org/10.3390/polym2040728 - 13 Dec 2010

Cited by 1079 | Viewed by 42556

Abstract

Cellulose is the most abundant biomass material in nature. Extracted from natural fibers, its hierarchical and multi-level organization allows different kinds of nanoscaled cellulosic fillers—called cellulose nanocrystals or microfibrillated cellulose (MFC)—to be obtained. Recently, such cellulose nanoparticles have been the focus of an [...] Read more.

Cellulose is the most abundant biomass material in nature. Extracted from natural fibers, its hierarchical and multi-level organization allows different kinds of nanoscaled cellulosic fillers—called cellulose nanocrystals or microfibrillated cellulose (MFC)—to be obtained. Recently, such cellulose nanoparticles have been the focus of an exponentially increasing number of works or reviews devoted to understanding such materials and their applications. Major studies over the last decades have shown that cellulose nanoparticles could be used as fillers to improve mechanical and barrier properties of biocomposites. Their use for industrial packaging is being investigated, with continuous studies to find innovative solutions for efficient and sustainable systems. Processing is more and more important and different systems are detailed in this paper depending on the polymer solubility, i.e., (i) hydrosoluble systems, (ii) non-hydrosoluble systems, and (iii) emulsion systems. This paper intends to give a clear overview of cellulose nanoparticles reinforced composites with more than 150 references by describing their preparation, characterization, properties and applications. Full article

(This article belongs to the Collection Polysaccharides)

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219 KiB

Open AccessArticle

Preparation and Characterization of Insoluble Silk Fibroin/Chitosan Blend Films

by Mariana Agostini de Moraes, Grinia Michelle Nogueira, Raquel Farias Weska and Marisa Masumi Beppu

Polymers 2010, 2(4), 719-727; https://doi.org/10.3390/polym2040719 - 13 Dec 2010

Cited by 79 | Viewed by 11113

Abstract

The aim of this study was to prepare and characterize membranes of silk fibroin (SF) and chitosan (CHI) blends. Moreover, a conformation transition of SF to a more stable form induced by the addition of CHI was verified. Blend membranes were prepared, after [...] Read more.

The aim of this study was to prepare and characterize membranes of silk fibroin (SF) and chitosan (CHI) blends. Moreover, a conformation transition of SF to a more stable form induced by the addition of CHI was verified. Blend membranes were prepared, after pH adjustment, in different ratios, and physical integrity, crystallinity, structural conformation and thermal stability were characterized. The results of crystallographic analysis (XRD) indicated the tendency to higher structural organization caused by the addition of CHI. Fourier transformed infrared spectroscopy (FTIR) showed that SF is present in a more stable form in the presence of a CHI content of only 25 wt%. Thermal analysis indicated that SF is thermally stable and that when its proportion in the blend increases, the temperature at which degradation is initiated also increases. Full article

(This article belongs to the Collection Polysaccharides)

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108 KiB

Open AccessArticle

Simvastatin Release from Poly(lactide-co-glycolide) Membrane Scaffolds

by Hassan Rashidi, Marianne J. Ellis, Sarah H. Cartmell and Julian B. Chaudhuri

Polymers 2010, 2(4), 709-718; https://doi.org/10.3390/polym2040709 - 09 Dec 2010

Cited by 9 | Viewed by 9599

Abstract

Statins, a group of potent inhibitors of 3-hydroxy-3-methylglutaryl Coenzyme A reductase in cholesterol biosynthesis pathway, have been widely used as a cholesterol lowering drug. The plieotrophic effect of statins on bone metabolism in long-term usage has been begun to be studied during recent [...] Read more.

Statins, a group of potent inhibitors of 3-hydroxy-3-methylglutaryl Coenzyme A reductase in cholesterol biosynthesis pathway, have been widely used as a cholesterol lowering drug. The plieotrophic effect of statins on bone metabolism in long-term usage has been begun to be studied during recent years and several in vitro and in vivo studies have demonstrated the ability of statins to promote expression of bone morphogenetic protein-2 (BMP-2), inhibition of osteoclast differentiation and reduction of osteoporotic fractures risk. The high liver specificity and low oral bioavailability of statins, leading to poor peripheral distribution, are the main obstacles to benefit anabolic effects of hydrophobic statins on bone formation. Therefore, developing new administration roots for direct delivery to achieve optimum concentration in the bone microenvironment is of interest. Here we present and compare two approaches of combining statins with bone tissue engineering scaffolds. Simvastatin was combined with a poly(lactide-co-glycolide) (PLGA) membrane scaffold for diffusion-controlled release by dissolving simvastatin (dis-sim) in the membrane casting dope, and for degradation-controlled release by covalently bonding saponifiedsimvastatin (sap-sim) to the PLGA in the spinning dope. Rheological and concentration-dependent membrane morphology changes were observed with saponifiedsimvastatin, suggesting ester bond cleavage and covalent bonding of the statin to the PLGA, but not with dissolved simvastatin. Dissolved simvastatin membranes showed a logarithmic decay release profile while the saponifiedsimvastatin membranes showed constant release. It can be concluded that the covalent bonding of simvastatinto PLGA scaffolds is showing potential for use as a controlled releasescaffold for bone tissue engineering. Full article

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

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3974 KiB

Open AccessArticle

Polyelectrolytes: Influence on Evaporative Self-Assembly of Particles and Assembly of Multilayers with Polymers, Nanoparticles and Carbon Nanotubes

by Irina Marchenko, Alexey Yashchenok, Sergey German, Olga Inozemtseva, Dmitry Gorin, Tatiana Bukreeva, Helmuth Mohwald and Andre Skirtach

Polymers 2010, 2(4), 690-708; https://doi.org/10.3390/polym2040690 - 09 Dec 2010

Cited by 9 | Viewed by 11688

Abstract

Assembling polyelectrolyte multilayers in a bottom-up approach is reported for polymers, particles, nanoparticles, and carbon nanotubes. Effects of polyelectrolyte multilayers on evaporative self-assembly of particles, which are of interest to a number of applications including photonic crystals, films and substrates, are investigated. Polyelectrolyte [...] Read more.

Assembling polyelectrolyte multilayers in a bottom-up approach is reported for polymers, particles, nanoparticles, and carbon nanotubes. Effects of polyelectrolyte multilayers on evaporative self-assembly of particles, which are of interest to a number of applications including photonic crystals, films and substrates, are investigated. Polyelectrolyte multilayer coatings bring multifunctionality to spherical particles and planar films. Studying the construction of polyelectrolyte assemblies is convenient in the planar layout: it is reported here for incorporation of gold and magnetic nanoparticles as well as of carbon nanotubes. Gold nanoparticles concentration is controlled within the films. Potential applications of both spherical structures and planar films are highlighted. Full article

(This article belongs to the Special Issue Polyelectrolytes)

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351 KiB

Open AccessArticle

Glucan Particle Encapsulated Rifampicin for Targeted Delivery to Macrophages

by Ernesto Soto, Yun Seong Kim, Jinhee Lee, Hardy Kornfeld and Gary Ostroff

Polymers 2010, 2(4), 681-689; https://doi.org/10.3390/polym2040681 - 06 Dec 2010

Cited by 64 | Viewed by 10347

Abstract

Glucan particles (GPs) are 2–4 mm spherical, hollow, porous shells extracted from Baker’s yeast, Saccharomyces cerevisae. The surface of the GPs is composed primarily of 1,3-b-glucan and the particles are efficiently phagocytosed via receptor-mediated cell uptake by macrophages, phagocytic cells expressing glucan receptors. [...] Read more.

Glucan particles (GPs) are 2–4 mm spherical, hollow, porous shells extracted from Baker’s yeast, Saccharomyces cerevisae. The surface of the GPs is composed primarily of 1,3-b-glucan and the particles are efficiently phagocytosed via receptor-mediated cell uptake by macrophages, phagocytic cells expressing glucan receptors. The hollow cavity of the GPs allows for efficient absorption and encapsulation of payload molecules. Rifampicin (Rif), a drug used in tuberculosis treatment, was encapsulated by precipitation in GPs and trapped using a calcium alginate or chitosan hydrogel to seal the pores of GPs and slow Rif release. Unplugged GP formulations immediately released Rif following particle resuspension in aqueous buffer. Alginate and chitosan sealing of GPs loaded with Rif was able to extend drug release for 24–72 h. GP-Rif formulations containing 10% w/w Rif/GP plugged with a calcium alginate hydrogel were effective at reducing colony forming units of M. tuberculosis strain mc²6020 in infected bone marrow macrophages ~80–90% at 24 and 72 hours. The amount of Rif delivered in the GP formulations was below the free Rif minimal inhibitory concentration demonstrating that GP targeted Rif delivery to macrophages enhances Rif antimicrobial effects. Full article

(This article belongs to the Special Issue Polyelectrolytes)

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561 KiB

Open AccessArticle

Tailoring Mechanical Properties of Collagen-Based Scaffolds for Vascular Tissue Engineering: The Effects of pH, Temperature and Ionic Strength on Gelation

by Matteo Achilli and Diego Mantovani

Polymers 2010, 2(4), 664-680; https://doi.org/10.3390/polym2040664 - 06 Dec 2010

Cited by 166 | Viewed by 20123

Abstract

Collagen gels have been widely studied for applications in tissue engineering because of their biological implications. Considering their use as scaffolds for vascular tissue engineering, the main limitation has always been related to their low mechanical properties. During the process of in vitro [...] Read more.

Collagen gels have been widely studied for applications in tissue engineering because of their biological implications. Considering their use as scaffolds for vascular tissue engineering, the main limitation has always been related to their low mechanical properties. During the process of in vitro self-assembly, which leads to collagen gelation, the size of the fibrils, their chemical interactions, as well as the resulting microstructure are regulated by three main experimental conditions: pH, ionic strength and temperature. In this work, these three parameters were modulated in order to increase the mechanical properties of collagen gels. The effects on the gelation process were assessed by turbidimetric and scanning electron microscopy analyses. Turbidity measurements showed that gelation was affected by all three factors and scanning electron images confirmed that major changes occurred at the microstructural level. Mechanical tests showed that the compressive and tensile moduli increased by four- and three-fold, respectively, compared to the control. Finally, viability tests confirmed that these gels are suitable as scaffolds for cellular adhesion and proliferation. Full article

(This article belongs to the Special Issue Natural Polymers)

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878 KiB

Open AccessArticle

Surface Roughening of Polystyrene and Poly(methyl methacrylate) in Ar/O₂ Plasma Etching

by Yuk-Hong Ting, Chi-Chun Liu, Sang-Min Park, Hongquan Jiang, Paul F. Nealey and Amy E. Wendt

Polymers 2010, 2(4), 649-663; https://doi.org/10.3390/polym2040649 - 02 Dec 2010

Cited by 66 | Viewed by 15032

Abstract

Selectively plasma-etched polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer masks present a promising alternative for subsequent nanoscale patterning of underlying films. Because mask roughness can be detrimental to pattern transfer, this study examines roughness formation, with a focus on the role of cross-linking, during plasma [...] Read more.

Selectively plasma-etched polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer masks present a promising alternative for subsequent nanoscale patterning of underlying films. Because mask roughness can be detrimental to pattern transfer, this study examines roughness formation, with a focus on the role of cross-linking, during plasma etching of PS and PMMA. Variables include ion bombardment energy, polymer molecular weight and etch gas mixture. Roughness data support a proposed model in which surface roughness is attributed to polymer aggregation associated with cross-linking induced by energetic ion bombardment. In this model, RMS roughness peaks when cross-linking rates are comparable to chain scissioning rates, and drop to negligible levels for either very low or very high rates of cross-linking. Aggregation is minimal for very low rates of cross-linking, while very high rates produce a continuous cross-linked surface layer with low roughness. Molecular weight shows a negligible effect on roughness, while the introduction of H and F atoms suppresses roughness, apparently by terminating dangling bonds. For PS etched in Ar/O₂ plasmas, roughness decreases with increasing ion energy are tentatively attributed to the formation of a continuous cross-linked layer, while roughness increases with ion energy for PMMA are attributed to increases in cross-linking from negligible to moderate levels. Full article

(This article belongs to the Special Issue Nano-Structures of Block Copolymers)

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448 KiB

Open AccessReview

Photo-Induced Micellization of Block Copolymers

by Eri Yoshida and Satoshi Kuwayama

Polymers 2010, 2(4), 623-648; https://doi.org/10.3390/polym2040623 - 26 Nov 2010

Cited by 3 | Viewed by 7734

Abstract

We found novel photo-induced micellizations through photolysis, photoelectron transfer, and photo-Claisen rearrangement. The photolysis-induced micellization was attained using poly(4-tert-butoxystyrene)-block-polystyrene diblock copolymer (PBSt-b-PSt). BSt-b-PSt showed no self-assembly in dichloromethane and existed as isolated copolymers. Dynamic light [...] Read more.

We found novel photo-induced micellizations through photolysis, photoelectron transfer, and photo-Claisen rearrangement. The photolysis-induced micellization was attained using poly(4-tert-butoxystyrene)-block-polystyrene diblock copolymer (PBSt-b-PSt). BSt-b-PSt showed no self-assembly in dichloromethane and existed as isolated copolymers. Dynamic light scattering demonstrated that the copolymer produced spherical micelles in this solvent due to irradiation with a high-pressure mercury lamp in the presence of photo-acid generators, such as bis(alkylphenyl)iodonium hexafluorophosphate, diphenyliodonium hexafluorophosphate, and triphenylsulfonium triflate. The ¹H NMR analysis confirmed that PBSt-b-PSt was converted into poly(4-vinylphenol)-block-PSt by the irradiation, resulting in self-assembly into micelles. The irradiation in the presence of the photo-acid generator also induced the micellization of poly(4-pyridinemethoxymethylstyrene)-block-polystyrene diblock copolymer (PPySt-b-PSt). Micellization occurred by electron transfer from the pyridine to the photo-acid generator in their excited states and provided monodispersed spherical micelles with cores of PPySt blocks. Further, the photo-Claisen rearrangement caused the micellization of poly(4-allyloxystyrene)-block-polystyrene diblock copolymer (PASt-b-PSt). Micellization was promoted in cyclohexane at room temperature without a catalyst. During micellization, the elimination of the allyl groups competitively occurred along with the photorearrangement of the 4-allyloxystyrene units into the 3-allyl-4-hydroxystyrene units. Full article

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

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Open AccessReview

Phase-Segregated Dendrigraft Copolymer Architectures

by Lorena-Eugenia Sanchez Cadena and Mario Gauthier

Polymers 2010, 2(4), 596-622; https://doi.org/10.3390/polym2040596 - 25 Nov 2010

Cited by 8 | Viewed by 9344

Abstract

Dendrigraft polymers have a multi-level branched architecture resulting from the covalent assembly of macromolecular building blocks. Most of these materials are obtained in divergent (core-first) synthetic procedures whereby the molecule grows outwards in successive grafting reactions or generations. Two main types of dendrigraft [...] Read more.

Dendrigraft polymers have a multi-level branched architecture resulting from the covalent assembly of macromolecular building blocks. Most of these materials are obtained in divergent (core-first) synthetic procedures whereby the molecule grows outwards in successive grafting reactions or generations. Two main types of dendrigraft polymers can be identified depending on the distribution of reactive sites over the grafting substrate: Arborescent polymers have a large and variable number of more or less uniformly distributed sites, while dendrimer-like star polymers have a lower but well-defined number of grafting sites strictly located at the ends of the substrate chains. An overview of the synthesis and the characterization of dendrigraft copolymers with phase-segregated morphologies is provided in this review for both dendrigraft polymer families. The tethering of side-chains with a different composition onto branched substrates confers unusual physical properties to these copolymers, which are highlighted through selected examples. Full article

(This article belongs to the Special Issue Nano-Structures of Block Copolymers)

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282 KiB

Open AccessReview

Tri-n-Butylborane/WaterComplex-Mediated Copolymerization of Methyl Methacrylate with Proteinaceous Materials and Proteins: A Review

by Seiichiro Fujisawa and Yoshinori Kadoma

Polymers 2010, 2(4), 575-595; https://doi.org/10.3390/polym2040575 - 15 Nov 2010

Cited by 13 | Viewed by 8650

Abstract

Previous studies of tri-n-butylborane–initiated graft copolymerization of methyl methacrylates with hydrated proteinous materials and proteins have focused on the number of grafted-poly (MMA) branches as well as the percent graft and graft efficiency. The number of branches in silk fibroin is [...] Read more.

Previous studies of tri-n-butylborane–initiated graft copolymerization of methyl methacrylates with hydrated proteinous materials and proteins have focused on the number of grafted-poly (MMA) branches as well as the percent graft and graft efficiency. The number of branches in silk fibroin is 1.3, whereas the number in collagen, gelatin, ovalbumin and wool are 0.1, 0.04, 0.02 and 0.03, respectively. The number of grafted-PMMA branches in synthetic poly-L-peptides is approximately 10-fold less than that in gelatin, and decline, in the order poly-Ala > poly-Ser > poly-Pro > poly-Glu > poly-Lys. By contrast, poly-Gly, poly-Tyr and poly-Leu have no branches. The co-catalytic effect (the ratio of the number of polymer formed relative to that of control) of amino acids on tri-n-butylborane-initiated polymerization of MMA in the presence of water has been linearly correlated with their ionization potential (IP_koopman); |Äå HOMO (Highest Occupied Molecular Orbital)| (r²= 0.6, outliers: Cys and His); Äå HOMO = [åHOMO_aqua − åHOMO_vacuum] calculated using the semiempirical AM1 method. Also, a significant exponential relationship between the number of branches of poly-L-polypeptides and the Äå HOMO of the corresponding amino acids has been observed (r²= 0.9). A possible grafting site of protein (polypeptide) is discussed. Full article

(This article belongs to the Special Issue Natural Polymers)

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854 KiB

Open AccessArticle

Functionalization, Compatibilization and Properties of Polyolefin Composites with Natural Fibers

by Mariano Pracella, Md. Minhaz-Ul Haque and Vera Alvarez

Polymers 2010, 2(4), 554-574; https://doi.org/10.3390/polym2040554 - 15 Nov 2010

Cited by 121 | Viewed by 17714

Abstract

The article is focused on analyzing the effect of functionalization and reactive processing on the morphological, thermal, rheological and mechanical properties of composites of isotactic polypropylene (PP), polystyrene (PS), poly(ethylene-vinyl acetate) (EVA), with cellulose fibers, hemp or oat as natural fillers. Both polymers [...] Read more.

The article is focused on analyzing the effect of functionalization and reactive processing on the morphological, thermal, rheological and mechanical properties of composites of isotactic polypropylene (PP), polystyrene (PS), poly(ethylene-vinyl acetate) (EVA), with cellulose fibers, hemp or oat as natural fillers. Both polymers and fibers were modified with bi-functional monomers (glycidyl methacrylate, GMA; maleic anhydride, MA) capable of facilitating chemical reactions between the components during melt mixing. Polyolefin copolymers containing reactive groups (PP-g-GMA, SEBS-g-MA, PS-co-MA, etc.) were used as compatibilizers. Optical and SEM microscopy, FTIR, RX, DSC, TGA, DMTA, rheological and mechanical tests were employed for the composites characterization. The properties of binary and ternary systems have been analyzed as a function of both fiber and compatibilizer content. All compatibilized systems showed enhanced fiber dispersion and interfacial adhesion. The phase behavior and the thermal stability of the composites were affected by the chemical modification of the fibers. Marked changes in the overall crystallization processes and crystal morphology of PP composites were observed owing to the nucleating effect of the fibers. The tensile mechanical behavior of the compatibilized composites generally resulted in a higher stiffness, depending on the fiber amount and the structure and concentration of compatibilizer. Full article

(This article belongs to the Special Issue Natural Polymers)

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Open AccessReview

The Use of Natural Polymers in Tissue Engineering: A Focus on Electrospun Extracellular Matrix Analogues

by Scott A. Sell, Patricia S. Wolfe, Koyal Garg, Jennifer M. McCool, Isaac A. Rodriguez and Gary L. Bowlin

Polymers 2010, 2(4), 522-553; https://doi.org/10.3390/polym2040522 - 09 Nov 2010

Cited by 465 | Viewed by 33883

Abstract

Natural polymers such as collagens, elastin, and fibrinogen make up much of the body’s native extracellular matrix (ECM). This ECM provides structure and mechanical integrity to tissues, as well as communicating with the cellular components it supports to help facilitate and regulate daily [...] Read more.

Natural polymers such as collagens, elastin, and fibrinogen make up much of the body’s native extracellular matrix (ECM). This ECM provides structure and mechanical integrity to tissues, as well as communicating with the cellular components it supports to help facilitate and regulate daily cellular processes and wound healing. An ideal tissue engineering scaffold would not only replicate the structure of this ECM, but would also replicate the many functions that the ECM performs. In the past decade, the process of electrospinning has proven effective in creating non-woven ECM analogue scaffolds of micro to nanoscale diameter fibers from an array of synthetic and natural polymers. The ability of this fabrication technique to utilize the aforementioned natural polymers to create tissue engineering scaffolds has yielded promising results, both in vitro and in vivo, due in part to the enhanced bioactivity afforded by materials normally found within the human body. This review will present the process of electrospinning and describe the use of natural polymers in the creation of bioactive ECM analogues in tissue engineering. Full article

(This article belongs to the Special Issue Natural Polymers)

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401 KiB

Open AccessArticle

Periodate Oxidation of Methylcellulose: Characterization and Properties of Oxidized Derivatives

by Marguerite Rinaudo

Polymers 2010, 2(4), 505-521; https://doi.org/10.3390/polym2040505 - 29 Oct 2010

Cited by 33 | Viewed by 11491

Abstract

In this paper, the behavior of oxidized methylcelluloses is compared with that of the initial methylcellulose, an amphiphilic cellulose derivative. Methylcelluloses are important for many applications in the cosmetic and food industries. The mechanism of thermo-gelation of methylcellulose is briefly explained as well [...] Read more.

In this paper, the behavior of oxidized methylcelluloses is compared with that of the initial methylcellulose, an amphiphilic cellulose derivative. Methylcelluloses are important for many applications in the cosmetic and food industries. The mechanism of thermo-gelation of methylcellulose is briefly explained as well as the method of oxidation of polysaccharides. Then, our experiments involve the preparation of oxidized methylcelluloses: three degrees of oxidation are prepared and the new polymers are characterized by NMR, IR, SEC and rheology. Oxidation with periodate theoretically allows introduction of two aldehydic groups on C2–C3 glycol positions of anhydroglucose units. This reaction not only enhances the flexibility of the cellulosic backbone, but also causes a decrease in the molecular weight. In particular, the rheological behavior of methylcellulose and oxidized methylcellulose as a function of temperature is examined. The oxidized methylcelluloses prepared, being rich in aldehyde functions, become interesting intermediaries to prepare new cellulose derivatives. In this paper, three examples of reductive amination based on the reaction of modified methylcelluloses and −NH₂ groups of different molecules are described: β-alanine produces a polyelectrolyte; chitosan and hyaluronan-ADH (derivative obtained with adipic dihydrazide allowing introduction of −NH₂functions on HA backbone) are crosslinked and give new biocompatible hydrogels. Full article

(This article belongs to the Collection Polysaccharides)

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Open AccessArticle

Enhanced Photophysical Properties of Nanopatterned Titania Nanodots/Nanowires upon Hybridization with Silica via Block Copolymer Templated Sol-Gel Process

by Dinakaran Kannaiyan, Saji Thomas Kochuveedu, Yoon Hee Jang, Yu Jin Jang, Ji Yong Lee, Jieun Lee, Juyon Lee, Jooyong Kim and Dong Ha Kim

Polymers 2010, 2(4), 490-504; https://doi.org/10.3390/polym2040490 - 25 Oct 2010

Cited by 43 | Viewed by 13297

Abstract

We fabricated titanium dioxide (TiO₂)-silica (SiO₂) nanocomposite structures with controlled morphology by a simple synthetic approach using cooperative sol-gel chemistry and block copolymer (BCP) self-assembly. Mixed TiO₂-SiO₂ sol-gel precursors were blended with amphiphilic poly(styrene-block-ethylene oxide) (PS- [...] Read more.

We fabricated titanium dioxide (TiO₂)-silica (SiO₂) nanocomposite structures with controlled morphology by a simple synthetic approach using cooperative sol-gel chemistry and block copolymer (BCP) self-assembly. Mixed TiO₂-SiO₂ sol-gel precursors were blended with amphiphilic poly(styrene-block-ethylene oxide) (PS-b-PEO) BCPs where the precursors were selectively incorporated into the hydrophilic PEO domains. Changing the volumetric ratio of TiO₂-SiO₂ sol-gel precursor from 5% to 20%, a stepwise structural inversion occurred from nanodot arrays to discrete nanowires. Template free hybrid inorganic nanostructures were produced after the removal of PS-b-PEO by irradiation of UV light. The morphological evolution and photophysical properties were investigated by microscopic studies, UV-visible absorption and photocatalytic properties. Full article

(This article belongs to the Special Issue Nano-Structures of Block Copolymers)

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880 KiB

Open AccessReview

Block Copolymer Nanostructures for Technology

by Yu-Chih Tseng and Seth B. Darling

Polymers 2010, 2(4), 470-489; https://doi.org/10.3390/polym2040470 - 20 Oct 2010

Cited by 127 | Viewed by 21971

Abstract

Nanostructures generated from block copolymer self-assembly enable a variety of potential technological applications. In this article we review recent work and the current status of two major emerging applications of block copolymer (BCP) nanostructures: lithography for microelectronics and photovoltaics. We review the progress [...] Read more.

Nanostructures generated from block copolymer self-assembly enable a variety of potential technological applications. In this article we review recent work and the current status of two major emerging applications of block copolymer (BCP) nanostructures: lithography for microelectronics and photovoltaics. We review the progress in BCP lithography in relation to the requirements of the semiconductor technology roadmap. For photovoltaic applications, we review the current status of the quest to generate ideal nanostructures using BCPs and directions for future research. Full article

(This article belongs to the Special Issue Nano-Structures of Block Copolymers)

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Open AccessReview

Design and Application of Nanoscale Actuators Using Block-Copolymers

by Joshua M. G. Swann and Paul D. Topham

Polymers 2010, 2(4), 454-469; https://doi.org/10.3390/polym2040454 - 15 Oct 2010

Cited by 19 | Viewed by 14365

Abstract

Block copolymers are versatile designer macromolecules where a “bottom-up” approach can be used to create tailored materials with unique properties. These simple building blocks allow us to create actuators that convert energy from a variety of sources (such as chemical, electrical [...] Read more.

Block copolymers are versatile designer macromolecules where a “bottom-up” approach can be used to create tailored materials with unique properties. These simple building blocks allow us to create actuators that convert energy from a variety of sources (such as chemical, electrical and heat) into mechanical energy. In this review we will discuss the advantages and potential pitfalls of using block copolymers to create actuators, putting emphasis on the ways in which these materials can be synthesised and processed. Particular attention will be given to the theoretical background of microphase separation and how the phase diagram can be used during the design process of actuators. Different types of actuation will be discussed throughout. Full article

(This article belongs to the Special Issue Nano-Structures of Block Copolymers)

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428 KiB

Open AccessReview

Oleic and Undecylenic Acids as Renewable Feedstocks in the Synthesis of Polyols and Polyurethanes

by Gerard Lligadas, Juan C. Ronda, Marina Galià and Virginia Cádiz

Polymers 2010, 2(4), 440-453; https://doi.org/10.3390/polym2040440 - 14 Oct 2010

Cited by 92 | Viewed by 13197

Abstract

Nowadays, the utilization of raw materials derived from renewable feedstock is in the spotlight of the chemical industry, as vegetable oils are one of the most important platform chemicals due to their universal availability, inherent biodegradability and low price. Taking into account that [...] Read more.

Nowadays, the utilization of raw materials derived from renewable feedstock is in the spotlight of the chemical industry, as vegetable oils are one of the most important platform chemicals due to their universal availability, inherent biodegradability and low price. Taking into account that polyurethanes are one of the most important industrial products exhibiting versatile properties suitable for use in many fields, our research is focused on exploiting fatty acids in the preparation of biobased polyols and polyurethanes. This review is organized as a function of the nature of the final polyurethane systems; hence we describe the preparation of linear thermoplastic and crosslinked polyurethanes derived from oleic and undecylenic acids-based diols and polyols, respectively. Full article

(This article belongs to the Special Issue Natural Polymers)

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New Biocompatible Polyesters Derived from α-Amino Acids: Hydrolytic Degradation Behavior

by Naomi Cohen-Arazi, Abraham J. Domb and Jeoshua Katzhendler

Polymers 2010, 2(4), 418-439; https://doi.org/10.3390/polym2040418 - 13 Oct 2010

Cited by 19 | Viewed by 10458

Abstract

New polymers were synthesized from α-hydroxy acids derived from the natural amino acids Ile, Leu, Phe, and Val, combined with lactic acid, glycolic acid and 6-hydroxyhexanoic acid by direct condensation. The toxicity was determined and the degradation process of these polyesters was investigated [...] Read more.

New polymers were synthesized from α-hydroxy acids derived from the natural amino acids Ile, Leu, Phe, and Val, combined with lactic acid, glycolic acid and 6-hydroxyhexanoic acid by direct condensation. The toxicity was determined and the degradation process of these polyesters was investigated under physiological conditions by analyzing the composition of the degraded polymers and the oligomers cleaved in the buffer medium. The polymers were found to be non toxic to two cell lines. Polymers displayed a biphasic degradation behavior. In most cases, a linear relationship was found between the weight loss constant and the hydrophobicity of the polymers, Log P. Regarding the second stage of weight loss, it is apparent that polymers derived from α-hydroxy(L)isoleucine ((L)HOIle) and α-hydroxy(L)Valine ((L)HOVal) degraded much faster than those derived from α-hydroxy(L)leucine ((L)HOLeu) and α-hydroxy(L)phenylalanine ((L)HOPhe), probably due to different spatial orientation of the side chains. Copolymers of 6-hydroxyhexanoic acid displayed slow degradation rates as expected, whereas the degradation profile of copolymers of lactic acid was similar to the other homopolymers. These new polyesters may serve as potential biocompatible materials for medical applications. Full article

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

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Synthesis of Propargyl-Terminated Heterobifunctional Poly(ethylene glycol)

by Changhai Lu and Wen Zhong

Polymers 2010, 2(4), 407-417; https://doi.org/10.3390/polym2040407 - 13 Oct 2010

Cited by 16 | Viewed by 13680

Abstract

Novel propargyl-ended heterobifunctional poly(ethylene glycol) (PEG) derivatives with hydroxyl, carboxyl, mercapto or hydrazide end groups were synthesized with simplicity yet high efficiency. PEG (M_w = 3500 Da) with an α-hydroxyl group and an ω-carboxyl was used as the starting polymer. The [...] Read more.

Novel propargyl-ended heterobifunctional poly(ethylene glycol) (PEG) derivatives with hydroxyl, carboxyl, mercapto or hydrazide end groups were synthesized with simplicity yet high efficiency. PEG (M_w = 3500 Da) with an α-hydroxyl group and an ω-carboxyl was used as the starting polymer. The carboxyl group of the bifunctional PEG was modified into a propargyl, then carboxyl, mercapto or hydrazide groups were introduced to the other end of the bifunctional PEG by modifying the bifunctional PEG’s hydroxyl group with succinic anhydride, cysteamide or tert-butyl carbazate, respectively. This method can be useful to the development of PEG-based bioconjugates for a variety of biomedical applications. Full article

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

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Polymerization in Liquid Crystal Medium: Preparation of Polythiophene Derivatives Bearing a Bulky Pyrimidine Substituent

by Satoshi Ohkawa, Reina Ohta, Kohsuke Kawabata and Hiromasa Goto

Polymers 2010, 2(4), 393-406; https://doi.org/10.3390/polym2040393 - 11 Oct 2010

Cited by 8 | Viewed by 8359

Abstract

We carried out polycondensation of monomers bearing a bulky pyrimidine substituent in a liquid crystal solvent. The resultant polymers formed nematic liquid crystals. The polymers prepared in liquid crystals had higher coplanarity than the polymers prepared in toluene. This can be due to [...] Read more.

We carried out polycondensation of monomers bearing a bulky pyrimidine substituent in a liquid crystal solvent. The resultant polymers formed nematic liquid crystals. The polymers prepared in liquid crystals had higher coplanarity than the polymers prepared in toluene. This can be due to the fact that the ordered medium of the liquid crystal produces an aggregated structure with well-developed π-stacking between the main chains. The present results demonstrated that polymerization of bulky monomers is possible in liquid crystal solvents. Full article

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Open AccessArticle

Fine-Tuning of Polymeric Resins and their Interfaces with Amorphous Calcium Phosphate. A Strategy for Designing Effective Remineralizing Dental Composites

by Joseph M. Antonucci and Drago Skrtic

Polymers 2010, 2(4), 378-392; https://doi.org/10.3390/polym2040378 - 29 Sep 2010

Cited by 11 | Viewed by 8008

Abstract

For over a decade our group has been designing, preparing and evaluating bioactive, remineralizing composites based on amorphous calcium phosphate (ACP) fillers embedded in polymerized methacrylate resin matrices. In these studies a major focus has been on exploring structure-property relationships of the matrix [...] Read more.

For over a decade our group has been designing, preparing and evaluating bioactive, remineralizing composites based on amorphous calcium phosphate (ACP) fillers embedded in polymerized methacrylate resin matrices. In these studies a major focus has been on exploring structure-property relationships of the matrix phase of these composites on their anti-cariogenic potential. The main challenges were to gain a better understanding of polymer matrix/filler interfacial properties through controlling the surface properties of the fillers or through fine-tuning of the resin matrix. In this work, we describe the effect of chemical structure and composition of the resin matrices on some of the critical physicochemical properties of the copolymers and their ACP composites. Such structure-property studies are essential in formulating clinically effective products, and this knowledge base is likely to have strong impact on the future design of therapeutic materials, appropriate for mineral restoration in defective tooth structures. Full article

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Chemically Induced Dynamic Nuclear Polarization during the Thermolysis of Alkoxyamines: A New Approach to Detect the Occurrence of H-Transfer Reactions

by Maria Edeleva, Sylvain R. A. Marque, Denis Bertin, Didier Gigmes, Yohann Guillaneuf and Elena Bagryanskaya

Polymers 2010, 2(4), 364-377; https://doi.org/10.3390/polym2040364 - 28 Sep 2010

Cited by 9 | Viewed by 8952

Abstract

Thermal decomposition of alkoxyamines in the presence of scavengers was found to proceed with the formation of chemically induced nuclear polarization detected by 1H NMR. The distinctive Chemically Induced Dynamic Nuclear Polarization (CIDNP) features were studied using the example of three alkoxyamines: 4-nitrophenyl [...] Read more.

Thermal decomposition of alkoxyamines in the presence of scavengers was found to proceed with the formation of chemically induced nuclear polarization detected by 1H NMR. The distinctive Chemically Induced Dynamic Nuclear Polarization (CIDNP) features were studied using the example of three alkoxyamines: 4-nitrophenyl 2-(2,2,6,6-tetramethylpiperidin-1-yloxy)-2-methylpropanoate (1a), 4-nitrophenyl 2-(2,2-diphenyl-3-phenylimino-2,3-dihydroindol-1-yloxy)-2-methylpropanoate (2a) and 4-nitrophenyl 2-(2,2,5,5-tetramethyl-4-phenyl-2H-imidazol-1-oxy)-2-methylpropanoate (3a) in the presence of PhSH. The analysis of CIDNP signs of methacrylate protons allows us to conclude on the occurrence of hydrogen atom transfer reaction in geminate radical pair formed in alkoxyamine thermolysis. Thus, CIDNP is a fast and sensitive method to detect the occurrence of intra/intermolecular hydrogen transfer in alkoxyamine thermolysis. Full article

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

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Polymers, Volume 2, Issue 4 (December 2010) – 24 articles , Pages 364-798

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