Polymers

635 KiB

Open AccessArticle

Spiral Assembly of the 1D Chain Sheet of Fe(NCBH3)2(bpa)2·(biphenyl) (bpa = 1,2-bis(4-pyridyl)ethane) and its Stepwise Spin-Crossover Phenomenon

by Satoru Nakashima, Takaki Morita, Katsuya Inoue and Shinya Hayami

Polymers 2012, 4(1), 880-888; https://doi.org/10.3390/polym4010880 - 07 Mar 2012

Cited by 4 | Viewed by 6998

Abstract

The assembled complex, Fe(NCBH3)2(bpa)2, enclathrating biphenyl has been synthesized, the skeleton of which is a 1D chain. Several 1D chains gather together to form 1D chain sheet. The 1D chain sheet is stacked spirally to form novel spiral assembly. The average Fe-N distances [...] Read more.

The assembled complex, Fe(NCBH3)2(bpa)2, enclathrating biphenyl has been synthesized, the skeleton of which is a 1D chain. Several 1D chains gather together to form 1D chain sheet. The 1D chain sheet is stacked spirally to form novel spiral assembly. The average Fe-N distances were 2.020(2), 2.083(2), and 2.191(2) Å at 100, 175, and 298 K, respectively, reflecting spin-state change of the iron ion. The assembly showed a stepwise spin-crossover phenomenon. Full article

(This article belongs to the Special Issue Coordination Polymers)

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1162 KiB

Open AccessReview

Polyester Dendrimers

by Jean–d’Amour K. Twibanire and T. Bruce Grindley

Polymers 2012, 4(1), 794-879; https://doi.org/10.3390/polym4010794 - 07 Mar 2012

Cited by 47 | Viewed by 14762

Abstract

Polyester dendrimers have been comprehensively reviewed starting from their first synthesis in the early 1990s by Hawker and Fréchet. Polyester dendrimers have attracted and continue to attract extensive interest because they are comparatively easy to make and because, whenever they have been tested, [...] Read more.

Polyester dendrimers have been comprehensively reviewed starting from their first synthesis in the early 1990s by Hawker and Fréchet. Polyester dendrimers have attracted and continue to attract extensive interest because they are comparatively easy to make and because, whenever they have been tested, they have been found to be non-toxic. A number of different strategies for their synthesis have been examined and the methods employed for formation of the ester bond during dendrimer assembly have been summarized. The newest approaches, including the use of bifunctional orthogonally reacting dendrons and accelerated synthesis have been surveyed. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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1541 KiB

Open AccessReview

Enzyme Initiated Radical Polymerizations

by Frank Hollmann and Isabel W. C. E. Arends

Polymers 2012, 4(1), 759-793; https://doi.org/10.3390/polym4010759 - 06 Mar 2012

Cited by 179 | Viewed by 20050

Abstract

Biocatalysis is propagating into practically every area of organic chemistry, amongst them radical polymerizations. A review of the recent developments of this dynamic and quickly evolving area of research is presented together with a critical evaluation of its potential to yield novel polymers [...] Read more.

Biocatalysis is propagating into practically every area of organic chemistry, amongst them radical polymerizations. A review of the recent developments of this dynamic and quickly evolving area of research is presented together with a critical evaluation of its potential to yield novel polymers and/or environmentally more benign synthetic procedures. Full article

(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)

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418 KiB

Open AccessArticle

Antibacterial Activity of Four Human Beta-Defensins: HBD-19, HBD-23, HBD-27, and HBD-29

by Bryan T. Chow, Maira Soto, Bonnie L. Lo, David C. Crosby and David Camerini

Polymers 2012, 4(1), 747-758; https://doi.org/10.3390/polym4010747 - 01 Mar 2012

Cited by 7 | Viewed by 7665

Abstract

Human β-defensins (HBD) are a family of small antimicrobial peptides that play important roles in the innate and adaptive immune defenses against microbial infection. In this study, we predicted the mature sequences and assessed the antibacterial properties of synthetic HBD-19, HBD-23, HBD-27, and [...] Read more.

Human β-defensins (HBD) are a family of small antimicrobial peptides that play important roles in the innate and adaptive immune defenses against microbial infection. In this study, we predicted the mature sequences and assessed the antibacterial properties of synthetic HBD-19, HBD-23, HBD-27, and HBD-29 against three species of clinically relevant bacteria: Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. We also examined the cytotoxicity of each β-defensin to human cells. HBD-19 exhibited modest antibacterial effects against E. coli and S. aureus but had little effect on the growth of P. aeruginosa. HBD-23 exhibited substantial antibacterial effects against all three bacterial species and was particularly potent against the Gram-negative species, E. coli and P. aeruginosa. HBD-27 exerted modest antibacterial activity only towards S. aureus while HBD-29 had modest antibacterial activity for E. coli and P. aeruginosa. HBD-23 and HBD-27 showed little or no toxicity to human peripheral blood mononuclear cells, while HBD-19 and HBD-29 decreased cell viability by 20% at 30 μg/mL. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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169 KiB

Open AccessArticle

Kinetics of Model Reactions for Interfacial Polymerization

by Jeffrey Robertson, Trevor Centeno-Hall, Anne Padias, Robert Bates and Henry Hall

Polymers 2012, 4(1), 741-746; https://doi.org/10.3390/polym4010741 - 29 Feb 2012

Cited by 4 | Viewed by 6679

Abstract

To model the rates of interfacial polycondensations, the rates of reaction of benzoyl chloride and methyl chloroformate with various aliphatic monoamines in acetonitrile were determined at 25 °C. Buffering with picric acid slowed these extremely fast reactions so the rate constants could be [...] Read more.

To model the rates of interfacial polycondensations, the rates of reaction of benzoyl chloride and methyl chloroformate with various aliphatic monoamines in acetonitrile were determined at 25 °C. Buffering with picric acid slowed these extremely fast reactions so the rate constants could be determined from the rate of disappearance of picrate ion. The rates of the amine reactions correlated linearly with their Swain-Scott nucleophilicities. Full article

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Open AccessArticle

Papain Catalyzed (co)Oligomerization of α-Amino Acids

by Leendert W. Schwab, Wouter M. J. Kloosterman, Jakob Konieczny and Katja Loos

Polymers 2012, 4(1), 710-740; https://doi.org/10.3390/polym4010710 - 29 Feb 2012

Cited by 33 | Viewed by 14734

Abstract

Four hydrophobic amino acids (Leu, Tyr, Phe, Trp) were oligomerized by the protease papain in homo-oligomerization, binary co-oligomerization and ternary co-oligomerization. After 24 h, solid polydisperse reaction products of the homo-oligomerization were obtained in yields ranging from 30–80% by weight. A DP_avg [...] Read more.

Four hydrophobic amino acids (Leu, Tyr, Phe, Trp) were oligomerized by the protease papain in homo-oligomerization, binary co-oligomerization and ternary co-oligomerization. After 24 h, solid polydisperse reaction products of the homo-oligomerization were obtained in yields ranging from 30–80% by weight. A DP_avg was calculated based on MALDI-ToF MS results using the ion counts for the chains in the product. Based on the DP_avg and the yield of the homo-oligomerization it was determined that the amino acids can be ranked according to reactivity in the order: Tyr > Leu > Phe > Trp. Thermal degradation of the homo-oligomers shows two degradation steps: at 178–239 °C and at 300–330 °C. All the products left a significant amount of char ranging from 18–57% by weight at 800 °C. Binary co-oligomers were obtained as a polydisperse precipitate with a compositional distribution of the chains. Both the compositional and chain length distribution are calculated from MALDI-ToF mass spectra. By comparing the amount of each amino acid present in the chains it was determined that the amino acids are incorporated with a preference: Leu > Tyr > Phe > Trp. Ternary co-oligomers were also obtained as a precipitate and analyzed by MALDI-ToF MS. The compositional distribution and the chain length distribution were calculated from the MALDI-ToF data. The quantity of every amino acid in the chains was determined. Also determined was the influence on the DP_avg when the oligomers were compared with corresponding binary co-oligomers. From the combined results it was concluded that in the co-oligomerization of three amino acids the reactivity preference is Leu > Tyr > Phe > Trp. Thermal degradation of all the co-oligomers showed a weight loss of 2 wt% before the main oligomer degradation step at 300–325 °C. Full article

(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)

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Open AccessReview

Human Defensins: Potential Tools for Clinical Applications

by Jochen Winter and Matthias Wenghoefer

Polymers 2012, 4(1), 691-709; https://doi.org/10.3390/polym4010691 - 28 Feb 2012

Cited by 34 | Viewed by 10888

Abstract

As components of the innate immune system, antimicrobial peptides in the form of human defensins play an important role in host defense by serving as the epithelial layer’s biochemical barrier against local infections. Recent studies have shown these molecules to have far more [...] Read more.

As components of the innate immune system, antimicrobial peptides in the form of human defensins play an important role in host defense by serving as the epithelial layer’s biochemical barrier against local infections. Recent studies have shown these molecules to have far more additional cellular functions besides their antimicrobial activity. Defensins play a role in cell division, attraction and maturation of immune cells, differentiation and reorganization of epithelial tissues, wound healing and tumor suppression. This multitude of function makes human defensins appear to be excellent tools for therapeutic approaches. These antimicrobial peptides may be used directly as a remedy against bacterial and viral infections. Furthermore, the application of human defensins can be used to promote wound healing and epithelial reorganization. In particular, human β-defensins have a strong impact on osteoblast proliferation and differentiation. Human β-defensins have already been applied as a vaccination against HIV-1. Another potentially useful characteristic of defensins is their suitability as diagnostic markers in cancer therapy. In particular, α-defensins have already been used for this purpose. Human α-defensin-3, for example, has been described as a tumor marker for lymphocytes. High gene expression levels of α-defensin-3 and -4 have been detected in benign oral neoplasia, α-defensin-6 is considered to be a tumor marker for colon cancer. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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581 KiB

Open AccessArticle

Synthesis of Hyperbranched Glycoconjugates by the Combined Action of Potato Phosphorylase and Glycogen Branching Enzyme from Deinococcus geothermalis

by Jeroen van der Vlist, Martin Faber, Lizette Loen, Teunis J. Dijkman, Lia A. T. W. Asri and Katja Loos

Polymers 2012, 4(1), 674-690; https://doi.org/10.3390/polym4010674 - 27 Feb 2012

Cited by 25 | Viewed by 14434

Abstract

Potato phosphorylase is able to synthesize linear polyglucans from maltoheptaose primers. By coupling maltoheptaose to butane diamine, tris(2-aminoethyl)amine and amine functionalized amine functionalized poly ethyleneglycol (PEG), new primer molecules became available. The resulting di-, tri- and macro-primers were incubated with potato phosphorylase and [...] Read more.

Potato phosphorylase is able to synthesize linear polyglucans from maltoheptaose primers. By coupling maltoheptaose to butane diamine, tris(2-aminoethyl)amine and amine functionalized amine functionalized poly ethyleneglycol (PEG), new primer molecules became available. The resulting di-, tri- and macro-primers were incubated with potato phosphorylase and glycogen branching enzyme from Deinococcus geothermalis. Due to the action of both enzymes, hyperbranched polyglucan arms were grown from the maltoheptaose derivatives with a maximum degree of branching of 11%. The size of the synthesized hyperbranched polyglucans could be controlled by the ratio monomer over primer. About 60%–80% of the monomers were incorporated in the glycoconjugates. The resulting hyperbranched glycoconjugates were subjected to Dynamic Light Scattering (DLS) measurements in order to determine the hydrodynamic radius and it became obvious that the structures formed agglomerates in the range of 14–32 nm. Full article

(This article belongs to the Collection Polysaccharides)

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568 KiB

Open AccessArticle

Fabrication and Packaging of Flexible Polymeric Microantennae for in Vivo Magnetic Resonance Imaging

by Magdalèna Couty, Marion Woytasik, Jean-Christophe Ginefri, Anne Rubin, Emile Martincic, Marie Poirier-Quinot, Luc Darrasse, Fawzi Boumezbeur, Franck Lethimonnier, Michael Tatoulian and Elisabeth Dufour-Gergam

Polymers 2012, 4(1), 656-673; https://doi.org/10.3390/polym4010656 - 27 Feb 2012

Cited by 19 | Viewed by 10139

Abstract

In this paper, we detail how microantennae dedicated to Magnetic Resonance Imaging (MRI) can benefit from the advantages offered by polymer substrates, especially flexibility and dielectric properties. We present a monolithic and wireless design based on the transmission lines between conductor windings on [...] Read more.

In this paper, we detail how microantennae dedicated to Magnetic Resonance Imaging (MRI) can benefit from the advantages offered by polymer substrates, especially flexibility and dielectric properties. We present a monolithic and wireless design based on the transmission lines between conductor windings on both sides of a dielectric substrate and its fabrication process. This last one requires specific plasma treatments to improve polymer/metal adhesion. We have led a comparative study on the effects of the ageing time on the wettability and the metal adhesion to Kapton and Teflon surfaces. Correlation between wettability (water contact angle) and adhesion (tensile strength) has been established. Then, the use of PolyDiMethylSiloxane (PDMS) as biocompatible packaging material and the optimization of its thickness allows us to conserve suitable f₀ and Q values in a conducting environment such as the biological tissues. These studies allow us to perform 7 Tesla in vivo MRI of the rat brain with a high spatial resolution of 100 x 100 x 200 µm³ and a Signal to Noise Ratio of 80. Full article

(This article belongs to the Special Issue Polymers for Bioimaging)

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5904 KiB

Open AccessArticle

Variational Models of Network Formation and Ion Transport: Applications to Perfluorosulfonate Ionomer Membranes

by Nir Gavish, Jaylan Jones, Zhengfu Xu, Andrew Christlieb and Keith Promislow

Polymers 2012, 4(1), 630-655; https://doi.org/10.3390/polym4010630 - 24 Feb 2012

Cited by 35 | Viewed by 7429

Abstract

We present the functionalized Cahn-Hilliard (FCH) energy, a continuum characterization of interfacial energy whose minimizers describe the network morphology of solvated functionalized polymer membranes. With a small set of parameters the FCH characterizes bilayer, pore-like, and micelle network structures. The gradient flows derived [...] Read more.

We present the functionalized Cahn-Hilliard (FCH) energy, a continuum characterization of interfacial energy whose minimizers describe the network morphology of solvated functionalized polymer membranes. With a small set of parameters the FCH characterizes bilayer, pore-like, and micelle network structures. The gradient flows derived from the FCH describe the interactions between these structures, including the merging and pinch-off of endcaps and formation of junctions central to the generation of network morphologies. We couple the FCH gradient flow to a model of ionic transport which incorporates entropic effects to localize counter-ions, yielding a flow which dissipates a total free energy, and an expression for the excess electrochemical potential which combines electrostatic and entropic effects. We present applications to network bifurcation and membrane casting. Full article

(This article belongs to the Special Issue Polymer Thin Films and Membranes)

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728 KiB

Open AccessArticle

A New Esterase from Thermobifida halotolerans Hydrolyses Polyethylene Terephthalate (PET) and Polylactic Acid (PLA)

by Doris Ribitsch, Enrique Herrero Acero, Katrin Greimel, Anita Dellacher, Sabine Zitzenbacher, Annemarie Marold, Rosario Diaz Rodriguez, Georg Steinkellner, Karl Gruber, Helmut Schwab and Georg M. Guebitz

Polymers 2012, 4(1), 617-629; https://doi.org/10.3390/polym4010617 - 21 Feb 2012

Cited by 130 | Viewed by 16773

Abstract

A new esterase from Thermobifida halotolerans (Thh_Est) was cloned and expressed in E. coli and investigated for surface hydrolysis of polylactic acid (PLA) and polyethylene terephthalate (PET). Thh_Est is a member of the serine hydrolases superfamily containing the -GxSxG- motif with 85–87% homology [...] Read more.

A new esterase from Thermobifida halotolerans (Thh_Est) was cloned and expressed in E. coli and investigated for surface hydrolysis of polylactic acid (PLA) and polyethylene terephthalate (PET). Thh_Est is a member of the serine hydrolases superfamily containing the -GxSxG- motif with 85–87% homology to an esterase from T. alba, to an acetylxylan esterase from T. fusca and to various Thermobifida cutinases. Thh_Est hydrolyzed the PET model substrate bis(benzoyloxyethyl)terephthalate and PET releasing terephthalic acid and mono-(2-hydroxyethyl) terephthalate in comparable amounts (19.8 and 21.5 mmol/mol of enzyme) while no higher oligomers like bis-(2-hydroxyethyl) terephthalate were detected. Similarly, PLA was hydrolyzed as indicated by the release of lactic acid. Enzymatic surface hydrolysis of PET and PLA led to a strong hydrophilicity increase, as quantified with a WCA decrease from 90.8° and 75.5° to 50.4° and to a complete spread of the water drop on the surface, respectively. Full article

(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)

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875 KiB

Open AccessReview

Characterizations of Polyamidoamine Dendrimers with Scattering Techniques

by Xiangyu Wang, Ludovic Guerrand, Bin Wu, Xin Li, Lauren Boldon, Wei-Ren Chen and Li Liu

Polymers 2012, 4(1), 600-616; https://doi.org/10.3390/polym4010600 - 21 Feb 2012

Cited by 32 | Viewed by 10681

Abstract

Dendrimers are highly branched, open, covalent assemblies of branch cells (monomers) radially attached to a core in successive layers or generations. Major types of dendrimers include polyamidoamine, polypropylenimine, multiple antigen peptide, chiral, and Fréchet-type dendrimers. Their structure and dynamics can be explored by [...] Read more.

Dendrimers are highly branched, open, covalent assemblies of branch cells (monomers) radially attached to a core in successive layers or generations. Major types of dendrimers include polyamidoamine, polypropylenimine, multiple antigen peptide, chiral, and Fréchet-type dendrimers. Their structure and dynamics can be explored by various techniques, such as scattering, spectrometry, and microscopy techniques. Specifically, the scattering techniques include small-angle neutron scattering (SANS), quasi-elastic neutron scattering (QENS), small-angle X-ray scattering (SAXS), and light scattering. Examples of their properties that can be explored by scattering techniques include: inter-molecular structure, intra-molecular cavity, radius-of-gyration (RG), hydrodynamic radius (RH), molecular weight, effective charge number of a single dendrimer molecule, water penetration into the interior of the dendrimers, and the internal dynamics. Of these properties, the hydrodynamic radius and molecular weight may be explored by DLS; the internal dynamics of dendrimers may be studied by QENS; and the others may be explored through SAXS and SANS. During the past several years, SANS and QENS have been used to study the structural properties and internal dynamics of various generations of polyamidoamine dendrimers (PAMAMs). Their potential prospects as anticancer polymer drug carriers are also discussed. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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2085 KiB

Open AccessCommentary

Reinforced Materials Based on Chitosan, TiO₂ and Ag Composites

by Khairul Anuar Mat Amin and Marc in het Panhuis

Polymers 2012, 4(1), 590-599; https://doi.org/10.3390/polym4010590 - 16 Feb 2012

Cited by 65 | Viewed by 8277

Abstract

This study investigates the mechanical reinforcement of chitosan with TiO₂ and Ag nanoparticles, as well as their water vapour transmission rates and water resistance behaviour. The mechanical properties of chitosan were improved by addition of TiO₂ or Ag, with significant increases [...] Read more.

This study investigates the mechanical reinforcement of chitosan with TiO₂ and Ag nanoparticles, as well as their water vapour transmission rates and water resistance behaviour. The mechanical properties of chitosan were improved by addition of TiO₂ or Ag, with significant increases in Young’s modulus (from 25 MPa to ~300 MPa), tensile strength (from 6 MPa to 18–35 MPa) and toughness (from 1.3 J g⁻¹ to 7–8 J g⁻¹). The water vapour transmission rates (368–413 g m⁻² d⁻¹) were found to be similar for both materials. Inclusion of Ag reduced the water resistance (from 823% to 1,000%), while inclusion of TiO₂ yielded significant improvement in water resistance (from 823% to 100%). Full article

(This article belongs to the Collection Polysaccharides)

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Open AccessArticle

Versatile Route to Synthesize Heterobifunctional Poly(ethylene glycol) of Variable Functionality for Subsequent Pegylation

by Redouan Mahou and Christine Wandrey

Polymers 2012, 4(1), 561-589; https://doi.org/10.3390/polym4010561 - 16 Feb 2012

Cited by 89 | Viewed by 36597

Abstract

Pegylation using heterotelechelic poly(ethylene glycol) (PEG) offers many possibilities to create high-performance molecules and materials. A versatile route is proposed to synthesize heterobifunctional PEG containing diverse combinations of azide, amine, thioacetate, thiol, pyridyl disulﬁde, as well as activated hydroxyl end groups. Asymmetric activation [...] Read more.

Pegylation using heterotelechelic poly(ethylene glycol) (PEG) offers many possibilities to create high-performance molecules and materials. A versatile route is proposed to synthesize heterobifunctional PEG containing diverse combinations of azide, amine, thioacetate, thiol, pyridyl disulﬁde, as well as activated hydroxyl end groups. Asymmetric activation of one hydroxyl end group enables the heterobifunctionalization while applying selective monotosylation of linear, symmetrical PEG as a key step. The azide function is introduced by reacting monotosyl PEG with sodium azide. A thiol end group is obtained by reaction with sodium hydrosulfide. The activation of the hydroxyl end group and subsequent reaction with potassium carbonate/thioacetic acid yields a thioacetate end group. The hydrolysis of the thioester end group by ammonia in presence of 2,2′-dipyridyl disulfide provides PEG pyridyl disulﬁde. Amine terminated PEG is prepared either by reduction of the azide or by nucleophilic substitution of mesylate terminated PEG using ammonia. In all cases, >95% functionalization of the PEG end groups is achieved. The PEG derivatives particularly support the development of materials for biomedical applications. For example, grafting up to 13% of the Na-alg monomer units with α-amine-ω-thiol PEG maintains the gelling capacity in presence of calcium ions but simultaneous, spontaneous disulfide bond formation reinforces the initial physical hydrogel. Full article

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Open AccessReview

Antimicrobial Peptides: Multifunctional Drugs for Different Applications

by Lars-Ove Brandenburg, Julika Merres, Lea-Jessica Albrecht, Deike Varoga and Thomas Pufe

Polymers 2012, 4(1), 539-560; https://doi.org/10.3390/polym4010539 - 16 Feb 2012

Cited by 92 | Viewed by 15836

Abstract

Antimicrobial peptides (APs) are an important part of the innate immune system in epithelial and non-epithelial surfaces. So far, many different antimicrobial peptides from various families have been discovered in non-vertebrates and vertebrates. They are characterized by antibiotic, antifungal and antiviral activities against [...] Read more.

Antimicrobial peptides (APs) are an important part of the innate immune system in epithelial and non-epithelial surfaces. So far, many different antimicrobial peptides from various families have been discovered in non-vertebrates and vertebrates. They are characterized by antibiotic, antifungal and antiviral activities against a variety of microorganisms. In addition to their role as endogenous antimicrobials, APs participate in multiple aspects of immunity. They are involved in septic and non-septic inflammation, wound repair, angiogenesis, regulation of the adaptive immune system and in maintaining homeostasis. Due to those characteristics AP could play an important role in many practical applications. Limited therapeutic efficiency of current antimicrobial agents and the emerging resistance of pathogens require alternate antimicrobial drugs. The purpose of this review is to highlight recent literature on functions and mechanisms of APs. It also shows their current practical applications as peptide therapeutics and bioactive polymers and discusses the possibilities of future clinical developments. Full article

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Open AccessReview

Synthetic Strategies towards Fullerene-Rich Dendrimer Assemblies

by Uwe Hahn, Fritz Vögtle and Jean-François Nierengarten

Polymers 2012, 4(1), 501-538; https://doi.org/10.3390/polym4010501 - 14 Feb 2012

Cited by 18 | Viewed by 19983

Abstract

The sphere-shaped fullerene has attracted considerable interest not least due to the peculiar electronic properties of this carbon allotrope and the fascinating materials emanating from fullerene-derived structures. The rapid development and tremendous advances in organic chemistry allow nowadays the modification of C₆₀ [...] Read more.

The sphere-shaped fullerene has attracted considerable interest not least due to the peculiar electronic properties of this carbon allotrope and the fascinating materials emanating from fullerene-derived structures. The rapid development and tremendous advances in organic chemistry allow nowadays the modification of C₆₀ to a great extent by pure chemical means. It is therefore not surprising that the fullerene moiety has also been part of dendrimers. At the initial stage, fullerenes have been examined at the center of the dendritic structure mainly aimed at possible shielding effects as exerted by the dendritic environment and light-harvesting effects due to multiple chromophores located at the periphery of the dendrimer. In recent years, also many research efforts have been devoted towards fullerene-rich nanohybrids containing multiple C₆₀ units in the branches and/or as surface functional groups. In this review, synthetic efforts towards the construction of dendritic fullerene-rich nanostructures have been compiled and will be summarized herein. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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Open AccessArticle

Enzymatic Synthesis and Crosslinking of Novel High Molecular Weight Polyepoxyricinoleate

by Ayaki Kazariya and Shuichi Matsumura

Polymers 2012, 4(1), 486-500; https://doi.org/10.3390/polym4010486 - 10 Feb 2012

Cited by 10 | Viewed by 8321

Abstract

Methyl epoxyricinoleate was prepared in high yield by the lipase-catalyzed epoxidation of methyl ricinoleate with H₂O₂. A high molecular weight polyepoxyricinoleate (PER) with a maximum weight average molecular weight (M_w) of 272,000 was enzymatically prepared by [...] Read more.

Methyl epoxyricinoleate was prepared in high yield by the lipase-catalyzed epoxidation of methyl ricinoleate with H₂O₂. A high molecular weight polyepoxyricinoleate (PER) with a maximum weight average molecular weight (M_w) of 272,000 was enzymatically prepared by the polycondensation of methyl epoxyricinoleate using immobilized lipase from Burkholderia cepacia (lipase PS-IM) in bulk at 80 °C for 5 d. PER showed good low temperature fluidability. PER was readily cured by maleic anhydride (MA) at 80 °C to produce a chloroform-insoluble PER-MA film. Both the glass transition temperature and Young’s modulus increased with increasing MA content and PER M_w. In contrast, the elongation at break decreased with increasing MA content and PER M_w. Methyl epoxyricinoleate, PER and PER-MA showed biodegradability by activated sludge, and that of the PER-MA film decreased with increasing MA content. Full article

(This article belongs to the Special Issue Enzymes in Monomer and Polymer Synthesis)

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Open AccessReview

Multiscale Modeling for Host-Guest Chemistry of Dendrimers in Solution

by Seung Ha Kim and Monica H. Lamm

Polymers 2012, 4(1), 463-485; https://doi.org/10.3390/polym4010463 - 10 Feb 2012

Cited by 18 | Viewed by 6916

Abstract

Dendrimers have been widely used as nanostructured carriers for guest species in a variety of applications in medicine, catalysis, and environmental remediation. Theory and simulation methods are an important complement to experimental approaches that are designed to develop a fundamental understanding about how [...] Read more.

Dendrimers have been widely used as nanostructured carriers for guest species in a variety of applications in medicine, catalysis, and environmental remediation. Theory and simulation methods are an important complement to experimental approaches that are designed to develop a fundamental understanding about how dendrimers interact with guest molecules. This review focuses on computational studies aimed at providing a better understanding of the relevant physicochemical parameters at play in the binding and release mechanisms between polyamidoamine (PAMAM) dendrimers and guest species. We highlight recent contributions that model supramolecular dendrimer-guest complexes over the temporal and spatial scales spanned by simulation methods ranging from all-atom molecular dynamics to statistical field theory. The role of solvent effects on dendrimer-guest interactions and the importance of relating model parameters across multiple scales is discussed. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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694 KiB

Open AccessArticle

In Situ and Ex Situ Syntheses of Magnetic Liquid Crystalline Materials: A Comparison

by Ophelie Riou, Lacramioara Zadoina, Barbara Lonetti, Katerina Soulantica, Anne-Françoise Mingotaud, Marc Respaud, Bruno Chaudret and Monique Mauzac

Polymers 2012, 4(1), 448-462; https://doi.org/10.3390/polym4010448 - 10 Feb 2012

Cited by 11 | Viewed by 7136

Abstract

Magnetic hybrid liquid crystalline composites have been obtained either by thermal decomposition of a cobalt precursor in a solution containing a liquid crystal polymer or by dispersing preformed cobalt nanorods in a liquid crystal polymer matrix. The final materials are all mesomorphous and [...] Read more.

Magnetic hybrid liquid crystalline composites have been obtained either by thermal decomposition of a cobalt precursor in a solution containing a liquid crystal polymer or by dispersing preformed cobalt nanorods in a liquid crystal polymer matrix. The final materials are all mesomorphous and ferromagnetic. Their magnetic characteristics are compared as a function of the synthesis method. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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Open AccessReview

Polysilane Dendrimers

by Clemens Krempner

Polymers 2012, 4(1), 408-447; https://doi.org/10.3390/polym4010408 - 09 Feb 2012

Cited by 34 | Viewed by 10724

Abstract

The synthesis, structure and electronic properties of polysilane dendrimers, a relatively new class of highly branched and silicon-rich molecular architectures is reviewed. After a detailed discussion of main synthetic strategies to well-defined single-core and double-core polysilane dendrimers, important structural and conformational features determined [...] Read more.

The synthesis, structure and electronic properties of polysilane dendrimers, a relatively new class of highly branched and silicon-rich molecular architectures is reviewed. After a detailed discussion of main synthetic strategies to well-defined single-core and double-core polysilane dendrimers, important structural and conformational features determined by single crystal X-ray crystallography and ²⁹Si-NMR spectroscopy are presented. The last part highlights the most interesting photochemical properties of polysilane dendrimers such as UV absorption and emission behavior, which are compared with those of linear and branched polysilanes. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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275 KiB

Open AccessArticle

Degree of Branching in Hyperbranched Poly(glycerol-co-diacid)s Synthesized in Toluene

by Victor T. Wyatt and Gary D. Strahan

Polymers 2012, 4(1), 396-407; https://doi.org/10.3390/polym4010396 - 06 Feb 2012

Cited by 50 | Viewed by 14668

Abstract

¹H NMR and ¹³C NMR spectrometry (1-dimensional and 2-dimensional) have been used to assign chemical resonances and determine the degrees of branching for polyesters synthesized by the Lewis acid (dibutyltin(IV)oxide)-catalyzed polycondensation of glycerol with either succinic acid (n (aliphatic chain length) [...] Read more.

¹H NMR and ¹³C NMR spectrometry (1-dimensional and 2-dimensional) have been used to assign chemical resonances and determine the degrees of branching for polyesters synthesized by the Lewis acid (dibutyltin(IV)oxide)-catalyzed polycondensation of glycerol with either succinic acid (n (aliphatic chain length) = 2), glutaric acid (n = 3) or azelaic acid (n = 7) in quasi-melt solutions with toluene. When 1:1 and 2:1 (diacid:glycerol) molar ratios were used, it was found that the glutaric acid-derived polymers gave the highest degree of polymer branching (31.2%, 85.6%, respectively) after the 24 h reaction period followed by the succinic acid-derived polymers (39.4%, 41.9%, respectively) and the azelaic acid-derived polymers (9.9%, 13.9%, respectively). Reactions performed at reflux for 24 h resulted in a 70.8% and 56.7% decrease in degree of branching for succinic acid and glutaric acid-derived polyesters, respectively. There is no indication that degree of branching is significantly affected by the presence or absence of solvent according to the results obtained in this research. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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1893 KiB

Open AccessReview

Dendronization: A Useful Synthetic Strategy to Prepare Multifunctional Materials

by Julieta I. Paez, Marisa Martinelli, Verónica Brunetti and Miriam C. Strumia

Polymers 2012, 4(1), 355-395; https://doi.org/10.3390/polym4010355 - 02 Feb 2012

Cited by 84 | Viewed by 12798

Abstract

Dendronization is a synthetic methodology that offers important advantages. The resulting products, which are called dendronized materials, present new and specific properties. This review shows numerous examples in which individual dendrons are used as building blocks to prepare more complex arrays via covalent [...] Read more.

Dendronization is a synthetic methodology that offers important advantages. The resulting products, which are called dendronized materials, present new and specific properties. This review shows numerous examples in which individual dendrons are used as building blocks to prepare more complex arrays via covalent or non-covalent interactions. In particular, it points out how the structural information programmed into the dendritic architecture can be used in the dendronization process to generate nanostructures with specific tailored properties. We emphasize the use of different dendrons, with diverse chemical structure and size, to functionalize diverse substrates like linear polymers, and plane and curved inorganic surfaces. Apart from this, the review also demonstrates that self-assembly represents an ideal approach to create well-defined hyperbranched surfaces and it includes some discussion about the ability of both organic and inorganic building blocks to direct this process. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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319 KiB

Open AccessArticle

Effects of Emulsion-Based Resonant Infrared Matrix Assisted Pulsed Laser Evaporation (RIR-MAPLE) on the Molecular Weight of Polymers

by Ryan D. McCormick, Jeremy Lenhardt and Adrienne D. Stiff-Roberts

Polymers 2012, 4(1), 341-354; https://doi.org/10.3390/polym4010341 - 01 Feb 2012

Cited by 33 | Viewed by 9668

Abstract

The molecular weight of a polymer determines key optoelectronic device characteristics, such as internal morphology and charge transport. Therefore, it is important to ensure that polymer deposition techniques do not significantly alter the native polymer molecular weight. This work addresses polymers deposited by [...] Read more.

The molecular weight of a polymer determines key optoelectronic device characteristics, such as internal morphology and charge transport. Therefore, it is important to ensure that polymer deposition techniques do not significantly alter the native polymer molecular weight. This work addresses polymers deposited by resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE). By using a novel emulsion-based target technique, the deposition of smooth, contiguous films with no evidence of chemical degradation have been enabled. However, structural degradation via a reduction in molecular weight remains an open question. The common polymer standard, PMMA, and the optoelectronic polymers, P3HT and MEH-PPV, have been characterized before and after emulsion-based RIR-MAPLE deposition via gel permeation chromatography to determine if RIR-MAPLE affects the deposited polymer molecular weight. Proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy measurements have also been conducted to verify the absence of chemical degradation. These measurements verify that there is no chemical degradation of the polymers, and that PMMA and P3HT show no structural degradation, but MEH-PPV exhibits a halving of the weight-averaged molecular weight after RIR-MAPLE deposition. Compared with competing laser deposition techniques, RIR-MAPLE is shown to have the least effect on the molecular weight of the resulting thin films. Full article

(This article belongs to the Special Issue Polymer Thin Films and Membranes)

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821 KiB

Open AccessReview

Nanoparticle-Liquid Crystalline Elastomer Composites

by Yan Ji, Jean E. Marshall and Eugene M. Terentjev

Polymers 2012, 4(1), 316-340; https://doi.org/10.3390/polym4010316 - 30 Jan 2012

Cited by 68 | Viewed by 12581

Abstract

Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including a uniquely high-stroke reversible mechanical actuation triggered by external stimuli. Fundamentally, all such stimuli affect the degree of liquid crystalline order in the polymer chains cross-linked into an elastic network. Heat [...] Read more.

Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including a uniquely high-stroke reversible mechanical actuation triggered by external stimuli. Fundamentally, all such stimuli affect the degree of liquid crystalline order in the polymer chains cross-linked into an elastic network. Heat and the resulting thermal actuation act by promoting entropic disorder, as does the addition of solvents. Photo-isomerization is another mechanism of actuation, reducing the orientational order by diminishing the fraction of active rod-like mesogenic units, mostly studied for azobenzene derivatives incorporated into the LCE composition. Embedding nanoparticles provides a new, promising strategy to add functionality to LCEs and ultimately enhance their performance as sensors and actuators. The motivation for the combination of nanoparticles with LCEs is to provide better-controlled actuation stimuli, such as electric and magnetic fields, and broad-spectrum light, by selecting and configuring the appropriate nanoparticles in the LCE matrix. Here we give an overview of recent advances in this area with a focus on preparation, physical properties and actuation performance of the resultant nanocomposites. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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662 KiB

Open AccessArticle

Selective Grafting of Primary Amines onto Carbon Nanotubes via Free-Radical Treatment in Microwave Plasma Post-Discharge

by Benoit Ruelle, Sophie Peeterbroeck, Thomas Godfroid, Carla Bittencourt, Michel Hecq, Rony Snyders and Philippe Dubois

Polymers 2012, 4(1), 296-315; https://doi.org/10.3390/polym4010296 - 30 Jan 2012

Cited by 17 | Viewed by 9301

Abstract

A novel strategy to graft functional groups at the surface of carbon nanotubes (CNTs) is discussed. Aiming at grafting nitrogen containing groups, and more specifically primary amine covalent functionalization, CNTs were exposed under atomic nitrogen flow arising from an Ar + N₂ [...] Read more.

A novel strategy to graft functional groups at the surface of carbon nanotubes (CNTs) is discussed. Aiming at grafting nitrogen containing groups, and more specifically primary amine covalent functionalization, CNTs were exposed under atomic nitrogen flow arising from an Ar + N₂ microwave plasma. The primary amine functions were identified and quantified through chemical derivatization with 4-(trifluoromethyl)benzaldehyde and characterized through X-ray photoelectron spectroscopy. The increase of the selectivity in the primary amines grafting onto CNTs, up to 66.7% for treatment of CNT powder, was performed via the reduction of post-treatment oxygen contamination and the addition of hydrogen in the experimental set-up, more particularly in the plasma post-discharge chamber. The analyses of nitrogenated and primary amine functions grafting on the CNT surface suggest that atomic nitrogen (N•) and reduced nitrogen species (NH• and NH₂•) react preferentially with defect sites of CNTs and, then, only atomic nitrogen continues to react on the CNT surface, creating defects. Full article

(This article belongs to the Special Issue Carbon Nanotubes: Synthesis, Characterization and Applications)

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1264 KiB

Open AccessReview

Dispersion of Carbon Nanotubes: Mixing, Sonication, Stabilization, and Composite Properties

by Yan Yan Huang and Eugene M. Terentjev

Polymers 2012, 4(1), 275-295; https://doi.org/10.3390/polym4010275 - 23 Jan 2012

Cited by 517 | Viewed by 30473

Abstract

Advances in functionality and reliability of carbon nanotube (CNT) composite materials require careful formulation of processing methods to ultimately realize the desired properties. To date, controlled dispersion of CNTs in a solution or a composite matrix remains a challenge, due to the strong [...] Read more.

Advances in functionality and reliability of carbon nanotube (CNT) composite materials require careful formulation of processing methods to ultimately realize the desired properties. To date, controlled dispersion of CNTs in a solution or a composite matrix remains a challenge, due to the strong van der Waals binding energies associated with the CNT aggregates. There is also insufficiently defined correlation between the microstructure and the physical properties of the composite. Here, we offer a review of the dispersion processes of pristine (non-covalently functionalized) CNTs in a solvent or a polymer solution. We summarize and adapt relevant theoretical analysis to guide the dispersion design and selection, from the processes of mixing/sonication, to the application of surfactants for stabilization, to the final testing of composite properties. The same approaches are expected to be also applicable to the fabrication of other composite materials involving homogeneously dispersed nanoparticles. Full article

(This article belongs to the Special Issue Carbon Nanotubes: Synthesis, Characterization and Applications)

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593 KiB

Open AccessArticle

Shrinkage Characteristics of Experimental Polymer Containing Composites under Controlled Light Curing Modes

by Alain Pefferkorn

Polymers 2012, 4(1), 256-274; https://doi.org/10.3390/polym4010256 - 18 Jan 2012

Cited by 3 | Viewed by 7531

Abstract

The adsorption of polymethylmethacrylate polymer of different molecular weight at the aerosil/ethyleneglycol- or 1,3 butanediol-dimethacrylate interfaces was determined to provide microstructured networks. Their structural characteristics were determined to be controlled by the amount of polymer initially supplied to the system. The sediment (the [...] Read more.

The adsorption of polymethylmethacrylate polymer of different molecular weight at the aerosil/ethyleneglycol- or 1,3 butanediol-dimethacrylate interfaces was determined to provide microstructured networks. Their structural characteristics were determined to be controlled by the amount of polymer initially supplied to the system. The sediment (the settled phase) characteristics, determined as a function of the polymer concentration and the rate of the polymerization shrinkage determined for composite resins, obtained by extrusion of the sediment after centrifugation, were found to be correlated. The specific role of the adsorbed polymer was found to be differently perturbed with the supplementary supply of dimethacrylate based monomer additives. Particularly, the bisphenol A dimethacrylate that generated crystals within the sediment was found to impede the shrinkage along the crystal lateral faces and strongly limit the shrinkage along its basal faces. Addition of ethyleneglycol- or polyethylene-glycoldimethacrylate monomers was determined to modify the sedimentation characteristics of the aerosil suspension and the shrinkage properties of the composites. Finally, the effects of stepwise light curing methods with prolonged lighting-off periods were investigated and found to modify the development and the final values of the composite shrinkage. Full article

(This article belongs to the Special Issue Polymers for Oro-Dental and Cranio- Maxillo-Facial Applications)

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1726 KiB

Open AccessArticle

Conformational Effects in Non-Stoichiometric Complexes of Two Hyperbranched Molecules with a Linear Polyelectrolyte

by George Dalakoglou, Kostas Karatasos, Sergey Lyulin, Sergey Larin, Anatoly Darinskii and Alexey Lyulin

Polymers 2012, 4(1), 240-255; https://doi.org/10.3390/polym4010240 - 17 Jan 2012

Cited by 10 | Viewed by 7480

Abstract

We report results from Brownian dynamics computer simulations of systems comprised by two terminally charged hyperbranched molecules preferentially branched in the periphery, with an oppositely charged linear chain of varying length. Comparison of the findings from the present study to stoichiometric counterparts and [...] Read more.

We report results from Brownian dynamics computer simulations of systems comprised by two terminally charged hyperbranched molecules preferentially branched in the periphery, with an oppositely charged linear chain of varying length. Comparison of the findings from the present study to stoichiometric counterparts and to analogous dendrimer-based complexes, reveal that the presence of the second hyperbranched molecule incurs significant changes in the conformational characteristics of both components of the complex. Instead of step-like changes in the average size and shape of the hyperbranched component that were noted in the previously studied stoichiometric systems, a rather smooth change is observed upon increase of the length of the linear component. In addition, a markedly different behavior is also noticed in the conformational characteristics of the linear chain when compared to that in similar dendrimer-based systems. The above findings are consistent with the higher degree of deformability of the peripherally branched molecules which allow appropriate rearrangements in shape in order to accommodate the favorable Coulombic interactions between the two components of the complex. This behavior offers new insight towards the design of more efficient hyperbranched-based systems which can take advantage of the multifunctionality and the structural properties of the highly branched polymer components. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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399 KiB

Open AccessReview

Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation

by Jean Duhamel

Polymers 2012, 4(1), 211-239; https://doi.org/10.3390/polym4010211 - 17 Jan 2012

Cited by 76 | Viewed by 10961

Abstract

This review exposes the current poor understanding of the internal segmental chain dynamics of dendrimers in solution probed by monitoring the process of excimer formation between pyrene labels covalently attached to the chain ends of dendrimers. The review begins by covering the bases [...] Read more.

This review exposes the current poor understanding of the internal segmental chain dynamics of dendrimers in solution probed by monitoring the process of excimer formation between pyrene labels covalently attached to the chain ends of dendrimers. The review begins by covering the bases of fluorescence and the kinetics of pyrene excimer formation before describing a procedure based on the Model Free (MF) analysis that is used to analyze quantitatively the fluorescence decays acquired for dendrimers, the ends of which have been fully and covalently labeled with pyrene. Comparison of the various trends obtained by different research groups describing the efficiency of pyrene excimer formation with the generation number of dendrimers illustrates the lack of consensus between the few studies devoted to the topic. One possible reason for this disagreement might reside in the presence of minute amounts of unattached pyrene labels which act as potent fluorescent impurities and affect the analysis of the fluorescence spectra and decays in an uncontrolled manner. The review points out that the MF analysis of the fluorescence decays acquired with pyrene-labeled dendrimers enables one to account for the presence of unattached pyrene and to retrieve information about the internal segmental dynamics of the dendrimer. It provides guidelines that should enable future studies on pyrene-labeled dendrimers to yield results that are more straightforward to interpret. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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2281 KiB

Open AccessArticle

The Mechanical Properties of Epoxy Composites Filled with Rubbery Copolymer Grafted SiO₂

by Jianing Gao, Junting Li, Brian C. Benicewicz, Su Zhao, Henrik Hillborg and Linda S. Schadler

Polymers 2012, 4(1), 187-210; https://doi.org/10.3390/polym4010187 - 16 Jan 2012

Cited by 66 | Viewed by 11015

Abstract

This study demonstrated a method for toughening a highly crosslinked anhydride cured DGEBA epoxy using rubbery block copolymer grafted SiO₂ nanoparticles. The particles were synthesized by a sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The inner rubbery block poly(n-hexyl methacrylate) (PHMA) had [...] Read more.

This study demonstrated a method for toughening a highly crosslinked anhydride cured DGEBA epoxy using rubbery block copolymer grafted SiO₂ nanoparticles. The particles were synthesized by a sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The inner rubbery block poly(n-hexyl methacrylate) (PHMA) had aglass transition temperature below room temperature. The outer block poly(glycidyl methacrylate) (PGMA) was matrix compatible. A rubbery interlayer thickness of 100% and 200% of the particle core radius was achieved by grafting a 20 kg/mol and a 40 kg/mol PHMA at a graft density of 0.7 chains/nm² from the SiO₂ surface. The 20 kg/mol rubbery interlayer transferred load more efficiently to the SiO₂ cores than the 40 kg/mol rubbery interlayer and maintained the epoxy modulus up to a loading of 10 vol% of the rubbery interlayer. Both systems enabled cavitation or plastic dilatation. Improvement of the strain-to-break and the tensile toughness was found in both systems. We hypothesize that plastic void growth in the matrix is the primary mechanism causing the improvement of the ductility. Full article

(This article belongs to the Special Issue Polymer-Inorganic Hybrids and Their Applications)

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Polymers, Volume 4, Issue 1 (March 2012) – 38 articles , Pages 1-888

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