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Polymer Composition (polymer + composition)
Selected AbstractsCombinatorial Material Mechanics: High-Throughput Polymer Synthesis and Nanomechanical Screening,ADVANCED MATERIALS, Issue 21 2005A. Tweedie Combinatorial materials science requires parallel advances in materials characterization. A high-throughput nanoscale synthesis/nanomechanical profiling approach capable of accurately screening the mechanical properties of 1,700 photopolymerizable materials (see Figure, scale bar: 100 ,m) within a large, discrete polymer library is presented. This approach enables rapid correlation of polymer composition, processing, and structure with mechanical performance metrics. [source] Storage of biodegradable polymers by an enriched microbial community in a sequencing batch reactor operated at high organic load rateJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2005Davide Dionisi Abstract The production of polyhydroxyalkanoates (PHAs) from organic acids by mixed bacterial cultures using a process based on aerobic enrichment of activated sludge, that selects for mixed microbial cultures able to store PHAs at high rates and yields, is described. Enrichment resulted from the selective pressure established by periodic feeding the carbon source in a sequencing batch reactor (SBR); a mixture of acetic, lactic and propionic acids was fed at high frequency (2 hourly), high dilution rate (1 d,1), and at high organic load rate (12.75 g chemical oxygen demand (COD) L,1 d,1). The performance of the SBR was assessed by microbial biomass and PHA production as well as the composition and polymer content of the biomass. A final batch stage was used to increase the polymer concentration of the excess sludge produced in the SBR and in which the behaviour of the biomass was investigated by determining PHA production rates and yields. The microbial biomass selected in the SBR produced PHAs at high rate [278 mg PHAs (as COD) g biomass (as COD),1 h,1, with a yield of 0.39 mg PHAs (as COD) mg removed substrates (as COD),1], reaching a polymer content higher than 50% (on a COD basis). The stored polymer was the copolymer poly(3-hydroxybutyrate/3-hydroxyvalerate) [P(HB/HV)], with an HV fraction of 18% mol mol,1. The microbial community selected in the SBR was analysed by DGGE (denaturing gradient gel electrophoresis). The operating conditions of the SBR were shown to select for a restricted microbial population which appeared quite different in terms of composition with respect to the initial microbial cenosis in the activated sludge used as inoculum. On the basis of the sequencing of the major bands in the DGGE profiles, four main genera were identified: a Methylobacteriaceae bacterium, Flavobacterium sp, Candidatus Meganema perideroedes, and Thauera sp. The effects of nitrogen depletion (ie absence of growth) and pH variation were also investigated in the batch stage and compared with the SBR operative mode. Absence of growth did not stimulate higher PHA production, so indicating that the periodic feed regime fully exploited the storage potential of the enriched culture. Polymer production rates remained high between pH 6.5 and 9.5, whereas the HV content in the stored polymer strongly increased as the pH value increased. This study shows that polymer composition in the final batch stage can readily be controlled independently from the feed composition in the SBR. Copyright © 2005 Society of Chemical Industry [source] Solid-state solubility influences encapsulation and release of hydrophobic drugs from PLGA/PLA nanoparticlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2004Jayanth Panyam Abstract Biodegradable nanoparticles formulated from poly(D,L -lactide- co -glycolide) (PLGA) and polylactide (PLA) polymers are being extensively investigated for various drug delivery applications. In this study, we hypothesize that the solid-state solubility of hydrophobic drugs in polymers could influence their encapsulation and release from nanoparticles. Dexamethasone and flutamide were used as model hydrophobic drugs. A simple, semiquantitative method based on drug,polymer phase separation was developed to determine the solid-state drug,polymer solubility. Nanoparticles using PLGA/PLA polymers were formulated using an emulsion,solvent evaporation technique, and were characterized for size, drug loading, and in vitro release. X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) were used to determine the physical state of the encapsulated drug. Results demonstrated that the solid-state drug,polymer solubility depends on the polymer composition, molecular weight, and end-functional groups (ester or carboxyl) in polymer chains. Higher solid-state drug,polymer solubility resulted in higher drug encapsulation in nanoparticles, but followed an inverse correlation with the percent cumulative drug released. The XRD and DSC analyses demonstrated that the drug encapsulated in nanoparticles was present in the form of a molecular dispersion (dissolved state) in the polymer, whereas in microparticles, the drug was present in both molecular dispersion and crystalline forms. In conclusion, the solid-state drug,polymer solubility affects the nanoparticle characteristics, and thus could be used as an important preformulation parameter. © 2004 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 93:1804,1814, 2004 [source] Enhancing the oral bioavailability of the poorly soluble drug dicumarol with a bioadhesive polymerJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2003Chris G. Thanos Abstract This article investigates the effect of particle size and the incorporation of a bioadhesive polymer, poly(fumaric- co -sebacic) anhydride p(FA:SA), on the relative bioavailability of dicumarol. A novel method was used to reduce particle size of the drug, and encapsulated formulations were fabricated using a phase inversion technique to produce nanospheres and microspheres with varying size. Groups of Yorkshire swine were catheterized and gavaged after fasting for 12 h with each formulation in a 50 mg/mL suspension. Blood was collected at different time points, from 0 to 96 h, and pharmacokinetic analysis revealed that formulations incorporating the smaller drug particles showed the highest bioavailability: micronized drug with 7% p(FA:SA) 17:83 polymer had 190% relative bioavailability, and phase inverted p(FA:SA) 17:83 microspheres with 31% (w/w) loading had 198% relative bioavailability to spray dried formulation. Formulations with larger drug particles achieved 71% relative bioavailability. A nonadhesive formulation, fabricated with poly(lactic acid) (PLA), showed 91% relative bioavailability. Both particle size and polymer composition play a role in oral absorption of dicumarol. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:1677,1689, 2003 [source] A paradigm for the mechanisms and products of spontaneous polymerizationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2009H. K. Hall Jr. Abstract In spontaneous vinyl and ring-opening copolymerizations, polar and resonance effects on the intermediates from bond-forming initiation offer a continuous spectrum of reactivities and polymer structures. In bond-forming initiation, an electron-rich donor monomer forms a bond to an acceptor monomer. The donor monomer may be a vinyl monomer with O, N, or aryl substituent or it may be an aza- or oxacycle. The acceptor monomer may be a vinyl monomer carrying CN, COOR, or SO2R substituent or it may be a cyclic anhydride or maleimide. Beyond this, the donor may have a ,-like strained single bond, whereas the acceptor may be an electrophilic quinodimethane. Lewis acids may be used to enhance the electrophilicity of acceptor monomers. Reaction rates and polymer composition are determined by systematically varying the stability of the first intermediate, designated P (for polymethylene). The nature of the intermediate will vary from a highly reactive trans biradical, which initiates chain alternating copolymerization, to a cis/gauche zwitterion, which can initiate chain ionic homopolymerization, to an extremely stabilized zwitterion, which cannot add monomer, but builds up in concentration and terminates by combination, forming alternating copolymer. This model embraces the existing literature for a wide variety of monomers and possesses predictive power. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 [source] Separation techniques for the analysis of artists' acrylic emulsion paintsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 4 2004Dominique Scalarone Abstract Emulsion paints are complex chemical systems. The main problems in their characterization are related to the similarities in polymer composition and to the presence of many different types of additives. Thus high resolution separations, sensitivity, and response specificity are required to identify simultaneously the polymer matrix and the minor components. Especially surfactants and pigments are thought to affect significantly the properties of the paint layers during ageing and their identification is the first step in evaluating the behaviour of these products in working conditions. Representative samples of acrylic emulsion paints for artists have been investigated by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and size exclusion chromatography-Fourier transform infrared spectroscopy (SEC-FTIR), and the results have been compared. All the analysed samples were bound in ethyl acrylate-methyl methacrylate, poly(EA-co-MMA), or n -butyl acrylate-methyl methacrylate, poly(nBA-co-MMA), copolymers. Two types of nonionic surfactants, ethoxylated fatty alcohols and alkylaryl polyethoxylates, commonly used as emulsifiers and dispersive agents have been identified, together with a number of organic pigments. [source] Cell wall composition of vascular and parenchyma tissues in broccoli stemsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 13 2003S Müller Abstract Broccoli stems can become tough and stringy owing to excessive development of the vascular ring. Thickened cell walls from the vascular ring were isolated and their composition was determined. They were derived principally from anatomically recognisable xylem vessels, fibres and tracheids but contained an assemblage of polysaccharides typical of primary cell walls. Their pectin content was particularly high and they contained only 6% lignin as estimated by solid state 13C NMR spectroscopy. They did not differ markedly in composition from parenchyma cell walls within the same stems. Thus, despite their thickness and anatomical appearance, these cell walls resembled the walls of non-woody cells in their polymer composition. Copyright © 2003 Society of Chemical Industry [source] In Vitro Degradation of Trimethylene Carbonate Based (Co)polymersMACROMOLECULAR BIOSCIENCE, Issue 9 2002Ana Paula Pęgo Abstract Trimethylene carbonate (TMC) was copolymerized with D,L -lactide (DLLA) or with , -caprolactone (CL), and the degradation of melt-pressed solid copolymer films in phosphate-buffered saline at pH 7.4 and 37,°C was followed for a period of over two years. The parent homopolymers were used as reference materials. The degradation profile of TMC-DLLA- and TMC-CL based copolymers was similar and was best described by autocatalyzed bulk hydrolysis, preferentially of ester bonds. The hydrolysis rates varied by two orders of magnitude, depending on polymer composition and physical characteristics under the degradation conditions. TMC-DLLA copolymers degraded faster than the parent homopolymers. The copolymers lost their tensile strength in less than five months, after which mass loss occurred. Copolymers with 50 or 80 mol-% of TMC underwent total degradation in eleven months. For TMC-CL copolymers, a slow and gradual decrease in molecular weight and deterioration of the mechanical performance was observed. These copolymers maintained suitable mechanical properties for seventeen months or longer. Chain scission in the semicrystalline copolymers resulted in an increase in crystallinity. In comparison with the CL homopolymer, the introduction of a small amount of TMC (10 mol-%) significantly reduced the increase in crystallinity during degradation. Poly(TMC) specimens were dimensionally stable and showed a negligible decrease in molecular weight. A 60% decrease in the initial tensile strength of the polymer samples was observed after two years. [source] Comparative Study of the Solid,Liquid Interface Behavior of Amphiphilic Block and Block-Like CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3-4 2009Nikolay Bulychev Abstract Amphiphilic block and "block-like" copolymers based on poly(isobornyl acrylate) and poly(acrylic acid) were used as stabilizers for hydrophilic (titanium dioxide) and hydrophobic (copper phthalocyanine) pigments. As reflected by the dispersion stabilities and electrokinetic sonic amplitude (ESA) measurements, the molecular architecture of the copolymer is of great importance for its interaction with the pigment surface. It was observed that irrespective of polymer composition, block-like copolymers exhibit lower stabilization ability and quite different adsorption behavior in comparison to block copolymers with sharp block boundaries. Models for the adsorption behavior of both block and block-like copolymers are proposed. [source] Biodegradable comb polyesters containing polyelectrolyte backbones facilitate the preparation of nanoparticles with defined surface structure and bioadhesive properties,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002A. Breitenbach Abstract A major challenge in oral peptide and protein delivery remains the search for suitable carrier systems. Therefore, a new concept was investigated combining a modified three-dimensional architecture, increased hydrophilicity of poly(lactic- co -glycolic acid) (PLGA) and charged groups in a single polymer. Biodegradable comb PLGA were synthesized by grafting short PLGA chains onto different poly(vinyl alcohol) (PVA) based backbone polyols, poly(2-sulfobutyl-vinyl alcohol) and poly(diethylaminoethyl-vinyl alcohol). The polyelectrolyte backbones were obtained by etherification of PVA with charge-containing pendent groups. The comb polymer structure could be confirmed by nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, elemental analysis and measurement of intrinsic viscosity. Nanoparticles (NP), as potential mucosal carriers systems, were prepared by controlled precipitation and investigated as a function of polymer composition. The amphiphilic character and the three-dimensional architecture of the novel polyesters allowed the preparation of small nanoparticles even without the use of surfactants. Surface NMR, surface charge and hydrophobicity determination indicate a core,corona-like NP structure, especially in the case of negatively charged polyesters. A structural model is proposed for the NP with an inner polyester core and an outer charged-groups-containing surface, depending on polymer composition and backbone charge density. The higher the polymer backbone charge density, the more pronounced its influence on the nanoparticle surface properties. The possibility of preparing NP without the use of a surfactant, as well as of designing the NP surface characteristics by polymer backbone charge density and polymer hydrophilic,hydrophobic balance, will be a major advantage in protein adsorption, bioadhesion and organ distribution. This makes these biodegradable polymers promising candidates for colloidal protein and peptide delivery. Copyright © 2003 John Wiley & Sons, Ltd. [source] Synthesis and characterization of temperature-sensitive block copolymers from poly(N -isopropylacrylamide) and 4-methyl-,-caprolactone or 4-phenyl-,-caprolactoneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Ren-Shen Lee Abstract This study synthesizes thermally sensitive block copolymers poly(N -isopropylacrylamide)- b -poly(4-methyl-,-caprolactone) (PNIPA- b -PMCL) and poly(N -isopropylacrylamide)- b -poly(4-phenyl-,-caprolactone) (PNIPA- b -PBCL) by ring-opening polymerization of 4-methyl-,-caprolactone (MCL) or 4-phenyl-,-caprolactone (BCL) initiated from hydroxy-terminated poly(N -isopropylacrylamide) (PNIPA) as the macroinitiator in the presence of SnOct2 as the catalyst. This research prepares a PNIPA bearing a single terminal hydroxyl group by telomerization using 2-hydroxyethanethiol (ME) as a chain-transfer agent. These copolymers are characterized by differential scanning calorimetry (DSC), 1H-NMR, FTIR, and gel permeation chromatography (GPC). The thermal properties (Tg) of diblock copolymers depend on polymer compositions. Incorporating larger amount of MCL or BCL into the macromolecular backbone decreases Tg. Their solutions show transparent below a lower critical solution temperature (LCST) and opaque above the LCST. LCST values for the PNIPA- b -PMCL aqueous solution were observed to shift to lower temperature than that for PNIPA homopolymers. This work investigates their micellar characteristics in the aqueous phase by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 0.29,2.74 mg L,1, depending on polymer compositions, which dramatically affect micelle shape. Drug entrapment efficiency and drug loading content of micelles depend on block polymer compositions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Sumatriptan succinate transdermal delivery systems for the treatment of migraineJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2008C. Balaguer-Fernández Abstract We have successfully obtained sumatriptan transdermal systems with different polymer compositions: methyl cellulose (MC), polyvinyl pyrrolidone (PVP) and a polyvinyl pyrrolidone (PVP)-polyvinyl alcohol (PVA) mixture. The systems contained 1,2-propilenglycol (MC) or sorbitol as a plasticizer (PVP and PVP-PVA), methacrylate copolymer as an adhesive agent, and an occlusive liner. Azone® (5%, w/w) was incorporated into all the systems as a percutaneous enhancer. Transdermal systems are thin, transparent and non-adhesive when in a dry state. The permeation of sumatriptan succinate across pig ear skin was studied using the systems prepared. The formulation with MC polymer produced a statistically significant increment with respect to the PVP and PVP-PVA formulations (p,<,0.05). Azone® incorporation into the systems produced an increment in the sumatriptan flux values of all three transdermal systems with respect to those of the controls (p,<,0.05). In addition, the application of iontophoresis to the wet methyl cellulose-Azone® formulation produced a much higher increase of sumatriptan transdermal flux. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:2102,2109, 2008 [source] Synthesis and characterization of amphiphilic block copolymer of polyphosphoester and poly(L -lactic acid)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2008Xian-Zhu Yang Abstract Aliphatic polyesters and polyphosphoesters (PPEs) have received much interest in medical applications due to their favorable biocompatibility and biodegradability. In this work, novel amphiphilic triblock copolymers of PPE and poly(L -lactic acid) (PLLA) with various compositions were synthesized and characterized. The blocky structure was confirmed by GPC analyses. These triblock copolymers formed micelles composed of hydrophobic PLLA core and hydrophilic PPE shell in aqueous solution. Critical micellization concentrations of these triblock copolymers were related to the polymer compositions. Incubation of micelles at neutral pH followed by GPC analyses revealed that these polymer micelles were hydrolysized and resulted in decreased molecular weights and small oligomers, whereas its degradation in basic and acid mediums was accelerated. MTT assay also demonstrated the biocompatibility against HEK293 cells. These biodegradable polymers are potential as drug carriers for biomedical application. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6425,6434, 2008 [source] In situ crosslinked hydrogels formed using Cu(I)-free Huisgen cycloaddition reactionPOLYMER INTERNATIONAL, Issue 10 2009Meredith Clark Abstract BACKGROUND: ,Click' chemistry, or the 1,3-dipolar cycloaddition of organic azides with alkynes, has been evaluated for many biomedical purposes; however, its utility in crosslinking hydrogels in situ is limited by the toxicity of the requisite copper(I) catalyst. We report the first use of catalyst-free Huisgen cycloaddition to generate crosslinked hydrogels under physiological conditions using multivalent azide-functionalized polymers and an electron-deficient dialkyne crosslinker. RESULTS: Water-soluble azide-functionalized polymers were crosslinked with an electron-deficient dialkyne crosslinker to form hydrogels at physiological temperature without the addition of copper(I) catalyst. Crosslinking was confirmed using scanning electron microscopy, Fourier transform infrared and 1H NMR analyses. Flow by vial inversion and dynamic rheological methodologies were implemented to evaluate gelation kinetics at 37 °C of variable polymer compositions, concentrations and stoichiometric ratios. Kinetic studies revealed gelation in as little as 12 h at 37 °C, although strong gels that withstand inversion were observed by 1,8 days. CONCLUSION: The ability to form hydrogel networks under mild conditions demonstrates the potential viability of the catalyst-free ,click' crosslinking chemistry for in situ gelling and other biological applications. Further chemical modifications in the crosslinking moieties, as well as polymer and crosslinker conformations, are expected to enhance gelation kinetics to a more biomedically practical rate. Copyright © 2009 Society of Chemical Industry [source] Studies on cellulose acetate,carboxylated polysulfone blend ultrafiltration membranes,Part IIPOLYMER INTERNATIONAL, Issue 1 2003J Sajitha Abstract Hydrophilic polysulfone ultrafiltration membranes were prepared from blends of cellulose acetate and carboxylated polysulfones of 0.43 and 0.75 degrees of carboxylation. The effects of degree of carboxylation on membrane characteristics such as compaction, pure water flux, water content and membrane hydraulic resistance, have been investigated to evaluate the performance of the membranes. The influence of the degree of carboxylation on the performance of the blend membranes of various blend polymer compositions has been investigated and also compared with earlier reports on blend membranes prepared from cellulose acetate and polysulfone or carboxylated polysulfone of 0.14 degree of carboxylation. © 2003 Society of Chemical Industry [source] | |||||||||||||