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High Molecular Weight (high + molecular_weight)
Terms modified by High Molecular Weight Selected AbstractsPoly(vinyl acetate)/Silver Nanocomposite Microspheres Prepared by Suspension Polymerization at Low TemperatureMACROMOLECULAR MATERIALS & ENGINEERING, Issue 1 2005Jeong Hyun Yeum Abstract Summary: High molecular weight (HMW) poly(vinyl acetate)/silver nanocomposite microspheres (PVAc/Ag), which are promising precursors of embolic materials with radiopacity, were prepared via a suspension polymerization approach in the presence of silver nanoparticles. It was found that a high yield and high molecular weight PVAc/Ag could be concurrently obtained even using a low-temperature initiator 2,2,-azobis(2,4-dimethylvaleronitrile) (,30,°C). In the case of presence of silver nanoparticles, the rate of polymerization was slightly slower than that without Ag. The suspension polymerization approach introduced could produce PVAc/Ag composite with conversion and viscosity-average molecular weight () up to 95% and 1,300,000, respectively, in spite of the low polymerization temperature (,30,°C), in sharp contrast with an only ,30% conversion of VAc under bulk polymerization. Morphology studies revealed that except normal suspension microspheres with a smooth surface, a golf ball-like appearance of the microspheres was observed, due to the migration and aggregating of the hydrophilic Ag nanoparticles at the sublayer beneath the microsphere's surface. [source] Computer-assisted 2-D agarose electrophoresis of Haemophilus influenzae type B meningitis vaccines and analysis of polydisperse particle populations in the size range of viruses: A reviewELECTROPHORESIS, Issue 4 2007Dietmar Tietz Dr. Abstract When protein,polysaccharide conjugated vaccines were first developed for the immunization of small children against meningitis caused by infection with Haemophilus influenzae type b (Hib), the vaccine preparations varied in immunogenicity. Testing for immunogenicity was time-consuming and alternative analytical procedures for determining vaccine quality were unsatisfactory. For example, due to the very high molecular weight of the vaccine particles, immunogens could only be physically characterized as a fraction in the void volume of Sepharose gel filtration. In search of better analytical methods, a computer-assisted electrophoretic technique for analyzing such vaccines was developed in the period from 1983 to 1995. This new approach made it possible to analyze highly negatively charged particles as large as or larger than intact viruses. 2-D gel patterns were generated that varied depending on the conditions of the particular vaccine preparation and were therefore characteristic of each vaccine sample. Thus, vaccine particle populations with a continuous size variation over a wide range (polydisperse) could be characterized according to size and free mobility (related to particle surface net charge density). These advances are reviewed in this article, since the developed methods are still a promising tool for vaccine quality control and for predicting immunogen effectiveness in the production of vaccines. The technique is potentially beneficial for Hib immunogens and other high-molecular-mass vaccines. Additional biomedical applications for this nondenaturing electrophoretic technique are briefly discussed and detailed information about computational and mathematical procedures and theoretical aspects is provided in the Appendices. [source] Macroscopically Aligned Ionic Self-Assembled Perylene-Surfactant Complexes within a Polymer Matrix,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2008Ari Laiho Abstract Ionic self-assembled (ISA) surfactant complexes present a facile concept for self-assembly of various functional materials. However, no general scheme has been shown to allow their overall alignment beyond local polydomain-like order. Here we demonstrate that ionic complexes forming a columnar liquid-crystalline phase in bulk can be aligned within polymer blends upon shearing, taken that the matrix polymers have sufficiently high molecular weight. We use an ISA complex of N,N,-bis(ethylenetrimethylammonium)perylenediimide/bis(2-ethylhexyl) phosphate (Pery-BEHP) blended with different molecular weight polystyrenes (PS). Based on X-ray scattering studies and transmission electron microscopy the pure Pery-BEHP complex was found to form a two-dimensional oblique columnar phase where the perylene units stack within the columns. Blending the complex with PS lead to high aspect ratio Pery-BEHP aggregates with lateral dimension in the mesoscale, having internal columnar liquid-crystalline order similar to the pure Pery-BEHP complex. When the Pery-BEHP/PS blend was subjected to a shear flow field, the alignment of perylenes can be achieved but requires sufficiently high molecular weight of the polystyrene matrix. The concept also suggests a simple route for macroscopically aligned nanocomposites with conjugated columnar liquid-crystalline functional additives. [source] Effect of glutenin subfractions on bread-making quality of wheatINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2001Sudesh Jood Five glutenin subfractions (R2,R6) were extracted by sequential centrifugation and addition of sodium chloride, from defatted flours of three wheat cultivars viz. Aubaine (extra-strong), Hereward (strong) and Riband (weak). Seven minutes mixing time was used to carry out fractionation on the basis of depolymerization of glutenin macropolymers (GMP) by using a 2-g Mixograph traces. Depolymerization of GMP occurred at much higher rates in dough of weak cultivars compared with strong and extra-strong cultivars. Protein content was also estimated in GMP (SDS-unextractable) and supernatant (SDS-extractable). Extra-strong cv. Aubaine contained maximum amount of all the glutenin fractions (R2,R6) followed by strong cv. Hereward and weak cv. Riband. Polypeptide compositions of different glutenin fractions were determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS,PAGE) under reduced and unreduced conditions, followed by densitometric scanning of stained patterns. The pattern areas of reduced fractions were divided into subareas representative of three main protein classes: high molecular weight (HMW) glutenin subunits; ,-gliadins and a mixture of low molecular (LMW) glutenin subunits and ,, , and ,-gliadins. The amounts of various subunits were proportionate according to the molecular weight of the fractions in each cultivar. The ratio of HMW-glutenin subunits to the LMW-glutenin subunits in each cultivar were found to decrease with the fractionation from R2 to R6. Bread-making quality of three cultivars was also assessed by adding various fractions to a base flour and measuring mixograph peak development time and loaf volume in an optimized baking test. The quality of bread prepared from flour of weak cv. Riband was improved significantly by the addition of HMW fraction (R2) when measured in terms of loaf volume. However, the addition of LMW fraction (R5 + R6) did not cause any appreciable improvement in bread quality over control. On the other hand, addition of HMW fraction (R2) in the flour of good bread wheat cv. Hereward caused adverse effects on the bread-making quality by disturbing the viscoelastic properties. Supplementation of R2 fractions in extra strong wheat cv. Aubaine caused marginal reduction in loaf volume over control. Therefore, the precise proportion present of the two classes of subunit is essential to achieving a proper balance between elastic and viscous properties. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Catal. The cover picture, provided by Maurice S. Brookhart, shows an example of a cationic palladium diimine complex which catalyzes polymerization of ethylene to high molecular weight, highly branched polyethylene. The catalyst resting states are the alkyl ethylene complexes as modeled by the ethyl ethylene complex shown. Migratory insertion of these alkyl ethylene species leads to ,-agostic complexes in which palladium can rapidly migrate along the chain ("chain-walking") through ,-elimination/readdition reactions. Trapping of branched alkyl complexes followed by insertion leads to formation of branches in the polymer chain. Polyethylenes formed exhibit branches-on-branches since chain-walking through tertiary centers is facile. [source] Rheological behavior and mechanical properties of high-density polyethylene blends with different molecular weightsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Lu Bai Abstract The dynamic rheological and mechanical properties of the binary blends of two conventional high-density polyethylenes [HDPEs; low molecular weight (LMW) and high molecular weight (HMW)] with distinct different weight-average molecular weights were studied. The rheological results show that the rheological behavior of the blends departed from classical linear viscoelastic theory because of the polydispersity of the HDPEs that we used. Plots of the logarithm of the zero shear viscosity fitted by the Cross model versus the blend composition, Cole,Cole plots, Han curves, and master curves of the storage and loss moduli indicated the LMW/HMW blends of different compositions were miscible in the melt state. The tensile yield strength of the blends generally followed the linear additivity rule, whereas the elongation at break and impact strength were lower than those predicted by linear additivity; this suggested the incompatibility of the blends in solid state. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Synphilin-1 degradation by the ubiquitin-proteasome pathway and effects on cell survivalJOURNAL OF NEUROCHEMISTRY, Issue 2 2002Gwang Lee Abstract Parkinson's disease is characterized by loss of nigral dopaminergic neurons and the presence of cytoplasmic inclusions known as Lewy bodies. ,-Synuclein and its interacting partner synphilin-1 are among constituent proteins in these aggregates. The presence of ubiquitin and proteasome subunits in these inclusions supports a role for this protein degradation pathway in the processing of proteins involved in this disease. To begin elucidating the kinetics of synphilin-1 in cells, we studied its degradation pathway in HEK293 cells that had been engineered to stably express FLAG-tagged synphilin-1. Pulse-chase experiments revealed that this protein is relatively stable with a half-life of about 16 h. Treatment with proteasome inhibitors resulted in attenuation of degradation and the accumulation of high molecular weight ubiquitinated synphilin-1 in immunoprecipitation/immunoblot experiments. Additionally, proteasome inhibitors stimulated the formation of peri-nuclear inclusions which were immunoreactive for synphilin-1, ubiquitin and ,-synuclein. Cell viability studies revealed increased susceptibility of synphilin-1 over-expressing cells to proteasomal dysfunction. These observations indicate that synphilin-1 is ubiquitinated and degraded by the proteasome. Accumulation of ubiquitinated synphilin-1 due to impaired clearance results in its aggregation as peri-nuclear inclusions and in poor cell survival. [source] Myotonic dystrophy expanded CUG repeats disturb the expression and phosphorylation of , in PC12 cellsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 4 2006Oscar Hernández-Hernández Abstract Mental retardation is a main feature of the congenital form of myotonic dystrophy (DM1), however, the molecular mechanisms underlying the central nervous system symptoms of DM1 are poorly understood. We have established a PC12 cell line-based model expressing the DM1 expanded CUG repeats (CTG90 cells) to analyze the effects of this mutation on neuronal functions. Previously, we have reported that CTG90 cells displayed impaired NGF-induced neuronal differentiation. Because disruption of normal expression of the microtubule associated protein , and neuronal aggregates of hyperphosphorylated , have been associated with DM1, this study analyzes the behavior of , in the CTG90 cells. Several alterations of , were observed in the PC12 cells that express expanded CUG repeats, including a subtle but reproducible reduction in the expression of the , mRNA splicing isoform containing exon 10, decreased expression of , and hyperphosphorylation of both , and high molecular weight , as well as abnormal nuclear localization of , phosphorylated at Ser396/404. Interestingly, phosphorylation regulates negatively the activity of , as microtubule-associated protein. In addition, impaired activity of the Akt/GSK3, pathway, which phosphorylates ,, was also identified in the CTG90 cells. Besides , phosphorylation, the Akt/GSK3, signaling pathway regulates other key processes of PC12 cells, such as apoptosis and neuronal differentiation. Our results indicate that defective neuronal differentiation exhibited by the PC12 cells expressing expanded CUG repeats could be the result of combinatory effects derived from the altered behavior of , and the impaired activation of the Akt/GSK3, signaling pathway. © 2006 Wiley-Liss, Inc. [source] Amelioration of disease severity by intraarticular hylan therapy in bilateral canine osteoarthritisJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2000K. W. Marshall Because of its high molecular weight, the glycosaminoglycan molecule hyaluronan is responsible for the viscoelastic properties of normal synovial fluid. In osteoarthritis, the concentration and molecular weight of hyaluronan in synovial fluid is diminished; this impairs the ability of synovial fluid to effectively lubricate joints, absorb loads, and exert anti-inflammatory effects. Using a bilateral anterior cruciateligament transection and partial neurectomy canine model of osteoarthritis, this study examined the effect of viscosupplementation with hylan G-F 20 as a treatment for osteoarthritis, this study examined the effect of viscosupplementation with hylan G-F 20 as a treatment for osteoarthritis. Twelve dogs underwent bilateral arthroscopic anterior cruciate-ligament transections and partial neurectomy of the knee joints. Beginning 1 week after the operation, six dogs received three weekly 500-,l injections of hylan G-F 20 in one knee and a sham injection of saline solution in the contralateral knee (early-treatment group). The remaining six animals underwent the same treatment 2 months following the procedure (late-treatment group). All dogs were killed at 8 months, and both knees were evaluated for gross pathology, histology, and proteoglycan content. In addition, with use of 500-MHz [1H] magnetic resonance spectroscopy, the synovial fluid from both knees was assessed for changes in metabolic profile. Differences in outcome were analyzed with paired t tests. Gross pathological and histological examination revealed significantly less severe changes of osteoarthritis in knees treated with hylan G-F 20 2 months after surgery than in the contralateral untreated knees. Magnetic resonance spectroscopy of the specimens in this late-treatment group showed significantly decreased glucose concentrations and significantly elevated isoleucine levels in the synovial fluid from knees treated with hylan G-F 20 compared with the controls. Previous magnetic resonance spectroscopy had shown that glucose concentrations increase with the onset of osteoarthritis and eventually diminish in end-stage osteoarthritis. The three injections of hylan were given after osteoarthritis was established, and the severity of the disease was ameliorated in the treated knees 6 months after treatment. This occurred although hylan G-F 20 is almost certainly cleared from joints by lymphatics within 4 weeks of injection, suggesting that hylan therapy can retard the progression of osteoarthritis for periods of time extending beyond the intraarticular residence time of the injected molecules and that hylan injections given at relatively early stages of osteoarthritis may have a chondroprotective effect. No changes in outcome were noted in the animals that received hylan G-F 20 immediately following surgery. [source] BACTERIA-INDUCED MOTILITY REDUCTION IN LINGULODINIUM POLYEDRUM (DINOPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 4 2008Xavier Mayali Biotic factors that affect phytoplankton physiology and behavior are not well characterized but probably play a crucial role in regulating their population dynamics in nature. We document evidence that some marine bacteria can decrease the swimming speed of motile phytoplankton through the release of putative protease(s). Using the dinoflagellate Lingulodinium polyedrum (F. Stein) J. D. Dodge as a model system, we showed that the motility-reducing components of bacterial-algal cocultures were mostly heat labile, were of high molecular weight (>50 kDa), and could be partially neutralized by incubations with protease inhibitors. We further showed that additions of the purified protease pronase E decreased dinoflagellate swimming speed in a concentration-dependent manner. We propose that motility can be used as a marker for dinoflagellate stress or general unhealthy status due to proteolytic bacteria, among other factors. [source] An environmentally benign room temperature aqueous homo- and copolymerization of styrene and methylmethacrylate catalyzed by [Cp2TiCl2]/NaBPh4JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2009Sudip K. De Abstract [Cp2TiCl2] has been found to be an effective precatalyst for room temperature aqueous homo- and copolymerization of methyl methacrylate and styrene in the presence of a cocatalyst, NaBPh4 and an emulsifier, sodium n -dodecyl sulfate. The polymers obtained are of high molecular weight with low molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6496,6503, 2009 [source] Synthesis and characterization of high molecular weight hexafluoroisopropylidene-containing polybenzimidazole for high-temperature polymer electrolyte membrane fuel cellsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2009Guoqing Qian Abstract A high molecular weight, thermally and chemical stable hexafluoroisopropylidene containing polybenzimidazole (6F-PBI) was synthesized from 3,3,-diaminobenzidine (TAB) and 2,2-bis(4-carboxyphenyl) hexafluoropropane (6F-diacid) using polyphosphoric acid (PPA) as both the polycondensation agent and the polymerization solvent. Investigation of polymerization conditions to achieve high molecular weight polymers was explored via stepwise temperature control, monomer concentration in PPA, and final polymerization temperature. The polymer characterization included inherent viscosity (I.V.) measurement and GPC as a determination of polymer molecular weight, thermal and chemical stability assessment via thermo gravimetric analysis and Fenton test, respectively. The resulting high molecular weight polymer showed excellent thermal and chemical stability. Phosphoric acid doped 6F-PBI membranes were prepared using the PPA process. The physiochemical properties of phosphoric acid doped membranes were characterized by measuring the phosphoric acid doping level, mechanical properties, and proton conductivity. These membranes showed higher phosphoric acid doping levels and higher proton conductivities than the membranes prepared by the conventional membrane fabrication processes. These membranes had sufficient mechanical properties to be easily fabricated into membrane electrode assemblies (MEA) and the prepared MEAs were tested in single cell fuel cells under various conditions, with a focus on the high temperature performance and fuel impurity tolerance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4064,4073, 2009 [source] Ethylene polymerization and ethylene/hexene copolymerization with vanadium(III) catalysts bearing heteroatom-containing salicylaldiminato ligandsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2009Ji-Qian Wu Abstract A series of novel vanadium(III) complexes bearing heteroatom-containing group-substituted salicylaldiminato ligands [RNCH(ArO)]VCl2(THF)2 (Ar = C6H4, R = C3H2NS, 2a; C7H4NS, 2c; C7H5N2, 2d; Ar = C6H2tBu2 (2,4), R = C3H2NS, 2b) have been synthesized and characterized. Structure of complex 2c was further confirmed by X-ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a,d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmolV h bar), and affording polymer with unimodal molecular weight distributions at 25,70 °C in the first 5-min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 °C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a,d were also explored in the presence of Et2AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled over a wide range by the variation of catalyst structure and the reaction parameters, such as comonomer feed concentration, polymerization time, and polymerization reaction temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3573,3582, 2009 [source] Functional syndiotactic poly(,-hydroxyalkanoate)s via stereoselective ring-opening copolymerization of rac -,-butyrolactone and rac -allyl-,-butyrolactoneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2009Noureddine Ajellal Abstract The copolymerization of racemic ,-butyrolactone (rac -BLMe) with racemic "allyl-,-butyrolactone" (rac -BLallyl) in toluene, catalyzed by the discrete amino-alkoxy-bis(phenolate) yttrium-amido complex 1, gave new poly(,-hydroxyalkanoate)s with unsaturated side chains. The poly(BLMe - co -BLallyl) copolymers produced have a highly syndiotactic backbone structure (Pr = 0.80,0.84) with a random enchainment of monomer units, as evidenced by 13C NMR, and high molecular weight (Mn up to 58,000 g mol,1) with a narrow polydispersity (Mw/Mn = 1.07,1.37), as determined by GPC. The comonomer incorporation (5,50 mol % rac -BLallyl) was a linear function of the feed ratio. The pendant vinyl bond of the side-chains in those poly(BLMe - co -BLallyl) copolymers allowed the effective introduction of hydroxy or epoxy groups via dihydroxylation, hydroboration-oxidation or epoxidation reactions. NMR studies indicated that all of these transformations proceed in an essentially quantitative conversion and do not affect the macromolecular architecture. Some thermal properties (Tm, ,Hm, Tg) of the prepared polymers have been also evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3177,3189, 2009 [source] Synthesis and characterization of postsulfonated poly(arylene ether sulfone) diblock copolymers for proton exchange membranesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2009Shogo Takamuku Abstract Sulfonated poly(arylene ether sulfone) diblock copolymers were studied through the postsulfonation process. Two kinds of hydrophobic oligomers with a molecular weight of 20 kDa were prepared in advance as block sequences and then coupled together to obtain diblock copolymers. One oligomer was synthesized from bis(4-hydroxyphenyl) sulfone (BHPS) and 4,4,-difluorodiphenyl sulfone (DFDPS), which was thought to be incapable of postsulfonation. The other oligomer was synthesized from hydroquinone (HQ) and 4,4,-dichlorodiphenyl sulfone (DCDPS), which successfully proceeded to a hydrophilic sequence as a result of sulfonation onto the HQ moiety after the coupling reaction. Consequently, a diblock copolymer with high molecular weight was obtained; although its intrinsic viscosity was too low to form a tough membrane because of its high rigidity and high crystallinity. Therefore, the use of decafluorobiphenyl (10F) as a termination reagent was investigated with the aim of achieving higher coupling reactivity and a kinky property. As a result, a sulfonated diblock copolymer was successfully obtained with sufficient molecular weight and intrinsic viscosity to form the membrane, as well as with adequate thermal properties. It was observed that proton conductivity, water uptake, and the water diffusion coefficient increased with higher ion exchange capacity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 700,712, 2009 [source] Styrene/1,3-butadiene copolymerization by C2 -symmetric group 4 metallocenes based catalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008Mariagrazia Napoli Abstract C2 -symmetric group 4 metallocenes based catalysts (rac -[CH2(3- tert -butyl-1-indenyl)2]ZrCl2(1), rac -[CH2(1-indenyl)2]ZrCl2(2) and rac -[CH2(3- tert -butyl-1-indenyl)2]TiCl2(3)) are able to copolymerize styrene and 1,3-butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by 13C NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain-end happens prevailingly with 1,4- trans configuration. In the butadiene homosequences, using zirconocene-based catalysts, the 1,4- trans arrangement is favored over 1,4- cis, but the latter is prevailing in the presence of titanocene (3). Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r1 × r2 = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene,butadiene copolymers (r1 × r2 = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (ns = 16, in the copolymer at highest styrene molar fraction). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1476,1487, 2008 [source] Targeted delivery of proteins by nanosized carriersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Roberto Solaro Abstract Proteic drug administration poses some additional issues as compared with conventional drugs because of protein high molecular weight and short half-life in plasma. It is well known that protein delivery canbe significantly improved by using targeted nanocarriers. Among the diverse investigated systems, this overview focuses onliposomes and nanoparticles. Indeed, because of their subcellular size, nanocarriers can cross the fenestration of the vascular epithelium and penetrate tissues. Moreover, nanosystems can be confined at the location of choice by conjugation to molecules that strongly bind the target cells. In spite of the significant progress made in the design and engineering of liposomes and nanoparticles tailored to the targeted delivery of proteins, these nanocarriers seldom succeed in delivering proteins directly inside the cell cytosol. Accordingly, some attention is also paid to virosomes and fusion proteins. These systems have a few advantages over conventional nanocarriers, particularly the ability to cross the cell membrane. They also share the main drawback of being highly immunogenic. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1,11, 2008 [source] | |||||||||||||||||||