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Weight Poly (weight + poly)
Kinds of Weight Poly Selected AbstractsCovalent Attachment of Low Molecular Weight Poly(ethylene imine) Improves Tat Peptide Mediated Gene Delivery,ADVANCED MATERIALS, Issue 16 2006F. Alexis A polymer-peptide hybrid biomaterial synthesized by coupling poly(ethylene imine) directly to resin-supported Tat peptide takes advantage of the unique features associated with the two original cationic materials and functions as a novel gene-delivery vector with good biocompatibility. The figure shows cells transfected with green fluorescent protein (GFP) using complexes of the polymer-peptide hybrid and GFP (scale bar: 100,,m). [source] Towards an understanding of adsorption behaviour in non-aqueous systems: adsorption of poly(vinyl pyrrolidone) and poly(ethylene glycol) onto silica from 2H, 3H-perfluoropentaneJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 11 2005Alison Paul The adsorption behaviour of low molecular weight poly(ethylene glycol) (PEG 600) and poly(vinyl pyrrolidone) (PVP K25) to silica particles has been investigated at room temperature (21°C) in the partially fluorinated solvent 2H,3H-perfluoropentane (HPFP). PVP (absorbed amount, , = 12 mgg,1) was found to adsorb more strongly than PEG (, = 4 mgg,1). Both of these values were higher than observed in water. In a further distinction to the aqueous case, where PVP displaces PEG from the interface, no competitive adsorption effects were observed between these two polymers in HPFP, with the adsorbed amounts of each polymer being unchanged by the presence of the other. The stability of silica suspensions in HPFP was primarily dependent on the presence of PVP; PEG/silica systems were unstable, but PVP/silica and PEG/PVP/silica systems formed stable suspensions. All suspensions were destabilized by the addition of small (0.15 wt%) amounts of water. The observations made in this work would point to a flocculation phenomenon due to the addition of water, and not Ostwald ripening. The mechanism of this destabilization is likely to be water acting as a flocculation bridge between particles. [source] Polymerization of ,-pinene with Schiff-base nickel complexes catalyst: Synthesis of relatively high molecular weight poly(,-pinene) at high temperature with high productivityJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2007Peng Yu Abstract A series of easily accessible and stable Schiff-base nickel complexes (complex 1,4) in conjunction with methylaluminoxane (MAO) were employed for the synthesis of relatively high molecular weight ,-pinene polymers at high temperature with high productivity. The ligand structure of the complex had a substantial effect on the polymerization in terms of the productivity and the molecular weight. With complex 4 in the presence of MAO, high molecular weight polymers of ,-pinene (Mn , 10,900) were obtained at 40 °C with an extremely high productivity up to 1.25 × 107 g poly,-pinene/mol of Ni. 1H NMR analyses showed that the obtained ,-pinene polymer was structurally identical to that formed by conventional cationic Lewis acid initiators. The polymerization was presumably initiated by the nickel cation formed by the reaction of the schiff-base nickel complex and MAO, while the propagation proceeded in a manner typical for a conventional carbocationic polymerization process. Direct evidence for the carbocationic polymerization was offered by the fact that quenching of the polymerization with methanol at a low monomer conversion resulted in incorporation of a methoxyl end group into the polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3739,3746, 2007 [source] Synthesis, characterization, and antimicrobial activity of some novel poly(ether ketone)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2003Samir A. Patel Abstract Low molecular weight poly(ether ketone)s were synthesized from phenol, 1,4-phenylenedioxy diacetylchloride, chloroacetylchloride, and dichloroalkanes [1,2-dichloroethane and dichloromethane] by a Friedel,Crafts reaction with anhydrous aluminum chloride as a catalyst and carbon disulfide as a solvent. The conditions for the preparation of the poly(ether ketone)s and the chlorine contents obtained with the Carius method were examined, and a reaction scheme for each resin was established. The molecular weights and polydispersities of the resins were obtained by gel permeation chromatography. The polyketones were characterized by IR spectroscopy. The characteristic frequencies due to different functional groups were assigned. The thermal properties of the resins were studied with thermogravimetry and differential scanning calorimetry. The characteristic temperatures of thermal degradation for the poly(ether ketone)s were evaluated with thermogravimetric analysis. The kinetic parameters for the decomposition reactions of the resins were obtained with Broido and Doyle's method, and the heats of fusion were obtained from differential scanning calorimetry thermograms. The polyketones were thermally stable up to 200 °C. All the polyketones were tested for their microbial properties against bacteria, fungi, and yeast. The effect of poly(ether ketone)s on the growth of these microorganisms was investigated, and the polyketones were found to inhibit the growth of the microorganisms to a considerable extent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2335,2344, 2003 [source] Viscosity effects in cobaloxime-mediated catalytic chain-transfer polymerization of methacrylatesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2002G. Evan Roberts Abstract The effect of bulk viscosity on the cobaloxime-mediated catalytic chain-transfer polymerization of methacrylates at 60 °C was investigated by both the addition of high molecular weight poly(methyl methacrylate) to methyl methacrylate polymerization and the dilution of benzyl methacrylate polymerization by toluene. The results indicate that the bulk viscosity is not directly linked to the chain-transfer activity. The previously measured relationship between chain-transfer-rate coefficient and monomer viscosity therefore probably reflects changes at the molecular level. However, the results in this article do not necessarily disprove a diffusion-controlled reaction rate because cobaloxime diffusion is expected to scale with the monomer friction coefficient rather than bulk viscosity. Considering the published data, to date we are not able to distinguish between a diffusion-controlled reaction rate or a mechanism directly affected by the methacrylate substituent. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 782,792, 2002; DOI 10.1002/pola.10152 [source] Lipase-Catalyzed Synthesis and Properties of Poly[(12-hydroxydodecanoate)- co -(12-hydroxystearate)] Directed towards Novel Green and Sustainable ElastomersMACROMOLECULAR BIOSCIENCE, Issue 1 2008Hiroki Ebata Abstract Novel green and sustainable elastomers having both good biodegradability and chemical recyclability properties were designed and synthesized using potentially biobased materials and lipase as an environmentally benign catalyst. High molecular weight poly[(12-hydroxydodecanoate)- co -(12-hydroxystearate)] [poly(12HD- co -12HS)] samples with varying monomer ratios were prepared by the polycondensation of 12-hydroxydodecanoic acid and methyl 12-hydroxystearate using immobilized lipase from Candida antarctica (IM-CA) in toluene in the presence of molecular sieves 4A at 90,°C. Although poly(12HD) is a highly crystalline polyester having a melting temperature (Tm) of 87.6,°C and crystalline temperature (Tc) of 64,°C, by the copolymerization of 12HD with 12HS, both the Tm and Tc of the copolymer decreased with increasing 12HS contents, and poly(12HD- co -12HS) containing more than 60 mol-% 12HS was a viscous liquid at room temperature. At the same time, the Young's modulus and hardness also decreased with increasing 12HS content, and poly(12HD- co -36 mol-% 12HS) exhibited an elastic behavior, having a hardness of 70 A using a durometer A. In addition, it showed an excellent biodegradability by activated sludge and chemical recyclability by lipase. [source] Concurrent Initiation by Air in the Atom Transfer Radical Polymerization of Methyl MethacrylateMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2003Ajaya Kumar Nanda Abstract The effect of air in atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was studied. Air initiated polymerization was clearly noticed by the appearance of a low molecular weight peak in the synthesis of high molecular weight poly(isobutylene)- graft -poly(methyl methacrylate) (Mn,=,5.0,×,105 g/mol). The concentration of chains initiated by oxygen (air) was ,8,×,10,4 mol/L, determined using the Gladstone-Dale relationship. The tentatively proposed mechanism for air initiated polymerization was supported by kinetic studies. Similar to typical ATRP systems, the rate of air initiated polymerization increased with temperature, [MMA], amount of air, and activity of the catalyst complex. Polymers with lower polydispersities (Mw/Mn,=,1.13) were obtained in the presence of Cu(II) as compared to Cu(I) catalyst complex system. Kinetic plots for the air initiated bulk polymerization of MMA at (,) 20,°C, (,) 50,°C, and (,) 90,°C. [source] Nonstoichiometric polycondensation I. synthesis of polythioether from dibromomethane and 4,4,-thiobisbenzenethiolMACROMOLECULAR SYMPOSIA, Issue 1 2003Hirokazu Iimori Abstract High molecular weight poly(phenylene thioether) (3) was successfully obtained by the polycondensation of 4,4,-thiobisbenzenethiol (1) and dibromomethane (2) with a variety of feed ratios in the presence of 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) in 1-methyl-2-pyrrolidinone (NMP) at 75°C. The resulting polymer showed the maximum inherent viscosity (,inh) of 0.50 dL/g in 4 h when 1.5 equivalents excess of 2 was used. The model reaction using benzenethiol (4) and dichloromethane (5) in the presence of DBU in deuterated dimethylsulfoxide (DMSO- d6) at 25°C indicated that the rate of the second nucleophilic displacement reaction (k2) is 61 times faster than that of the first one (k1). The maximum of theoretical molecular weights calculated at various stoichiometric imbalance (S) under the condition of k2/k1 = 61 showed a good agreement with the experimental molecular weights at specific polymerization times. [source] Nitroxide spin probe study of probe size, hydrogen bonding and polymer matrix rigidity effects on poly(acrylic acid)/poly(ethylene oxide) complexesMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003Li Tan Abstract An electron spin resonance (ESR) spin probe study was performed on 1 : 1 by weight poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) complex over the 100,450 K temperature range with a series of tetramethylpiperidyloxy-based spin probes. Measurements of the parameters T5mT, Ta and Td demonstrated the effects of probe size and the strength of hydrogen bonding. The probes in the series Tempone, Tempo, Tempol and Tamine (respectively 4-oxo-, unsubstituted, 4-hydroxy- and 4-amino-2,2,6,6,-tetramethylpiperidine -1-oxyl) displayed noticeable increases in the hydrogen-bonding effect, as indicated by Ta and Td. These increases correlated with increasing hydrogen bond acceptor strength. On the other hand, as the probe size became larger, T5mT gradually increased due to the free volume decrease. These effects were analyzed using the established theoretical relationship of T5mT to probe volume expressed by f. Meanwhile, in order to investigate the effect of polymer matrix rigidity, a similar study was performed with a nitroxide spin probe, 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (Tempo), on PAA/PEO complexes of different weight compositions. The quantitative fast motion fraction in the composite ESR spectrum was calculated. The influence of changes in the composition of PAA on the molecular mobility was characterized by changes of the spectral parameters and ,c. The molecular mobility was shown to diminish with increasing content of PAA in PAA/PEO blends duo to the restriction of the polymer matrix rigidity increase. Copyright © 2003 John Wiley & Sons, Ltd. [source] Some important aspects in designing high molecular weight poly(L -lactic acid),clay nanocomposites with desired propertiesPOLYMER INTERNATIONAL, Issue 12 2008Subhendu Ray Chowdhury Abstract BACKGROUND: The main aim of the work reported here was to investigate the effect of clay aspect ratio and functional edge group on the dispersion, degree of order of clays and interfacial strength of high molecular weight poly(L -lactic acid) (PLLA),clay amorphous nanocomposites and consequently their properties. Three kinds of clays (two montmorillonites (SMMTC18 and NMMTC18) and one fluoro-mica (MC18) with the same surfactant) were used to synthesize three amorphous nanocomposites. Thermomechanical properties, permeability, etc., were compared among composites and with pure PLLA. RESULTS: From X-ray diffraction and transmission electron microscopy, both MMTs with lower aspect ratio showed better dispersion and greater degree of disorder, which led to stronger interfacial strength and consequently higher storage modulus than MC18-based composites. All composites showed better properties than pure PLLA. The oxygen barrier efficiencies of SMMTC18- and NMMTC18-based composites were higher than that of the MC18-based composites. Due to the highest exposed area and probably stronger interactions, SMMTC18 had the highest nucleating efficiency. CONCLUSIONS: Along with aspect ratio, dispersion and degree of intercalation, the interfacial strength of composites and degree of order of clays are also important issues for property development. Compared to reported results in the literature, our amorphous composites showed less of an improvement of thermomechanical properties as real reinforcement was solely from clays. Copyright © 2008 Society of Chemical Industry [source] Thermally stable and high molecular weight poly(propylene carbonate)s from carbon dioxide and propylene oxide,POLYMER INTERNATIONAL, Issue 10 2002Q Zhu Abstract The copolymerization of carbon dioxide and propylene oxide was carried out to afford alternating poly(propylene carbonate) in high yield. Thermal stable and high molecular weight copolymers were successfully obtained by optimizing the reaction conditions. The catalyst used was zinc glutarate supported on a perfluorinated compound containing 7,12 carbon atoms. Copolymerization parameters, such as the ratio of propylene oxide to catalyst, stirring strength and purity of propylene oxide, were studied. The alternating copolymer with a molecular weight of 56,100 in a very high yield (126,g polymer per gram of catalyst) was achieved, which is the highest yield ever reported. The thermal and mechanical properties of the alternating PPC copolymer were examined by the means of modulated differential scanning calorimetry (MDSC), thermogravimetric analysis (TGA) and tensile test. MDSC and TGA results showed that the alternating PPC copolymer exhibits an extremely high glass transition temperature (maximum 46.46,°C) and decomposition temperature (255.8,°C) when compared to those values reported in literature. Tensile test revealed that thin film of alternating PPC copolymer exhibits superior mechanical strength. © 2002 Society of Chemical Industry [source] Low versus high molecular weight poly(ethylene glycol)-induced states of stem bromelain at low pH: Stabilization of molten globule and unfolded statesBIOPOLYMERS, Issue 5 2006Basir Ahmad Abstract The effect of low, medium, and high molecular weight poly(ethylene glycol) (e.g., PEG-400, -6000, and -20,000) on the structure of the acid unfolded state of unmodified stem bromelain (SB) obtained at pH 2.0 has been studied by various spectroscopic methods. The conformation of stem bromelain at pH 2.0 exhibits substantial loss of secondary structure and almost complete loss of native tertiary contacts and has been termed the acid unfolded state (AU). Addition of PEG-400 to AU led to an increase in the mean residue ellipticity (MRE) value at 222 nm, indicating formation of ,-helical structure. On the other hand, PEG-6000 and 20,000 led to a decrease in the MRE value at 222 nm, indicating unfolding of the AU state. Interestingly, at 70% (w/v) PEG-400 and 40% (w/v) PEG-20,000, MRE values at 222 nm almost approach the native state at pH 7.0 and the unfolded state (6 M GnHCl) of stem bromelain, respectively. The probes for tertiary structure showed formation of nonnative tertiary contacts in the presence of 70% (w/v) PEG-400, while 40% (w/v) PEG-6000 and 20,000 were found to stabilize the unfolded state of SB. An increase in binding of 1-anilino 8-naphthalene sulfonic acid and a decrease in fractional accessibility of tryptophan residues (fa) compared to AU in the presence of 70% PEG-400 indicate that the PEG-400,induced state has a significant amount of exposed hydrophobic patches and is more compact than AU. The results imply that the PEG-400,induced state has characteristics of molten globule, and higher molecular weight PEGs led to the unfolding of the AU state. © 2005 Wiley Periodicals, Inc. Biopolymers 81: 350,359, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Titration of poly(dA-dT) · poly(dA-dT) in solution at variable NaCl concentrationBIOPOLYMERS, Issue 2 2004Marta Airoldi Abstract CD and uv absorption data showed that high molecular weight poly(dA-dT) · poly(dA-dT), at 298 K, undergoes an acid-induced transition from B-double helix to random coil in NaCl solutions of different concentrations, ranging from 0.005 to 0.600M. Similarly, titration of the polynucleotide with a strong base causes duplex-to-single strands transition. The base- and acid-induced transitions were both reversible by back-titration (with an acid or, respectively, with a base): the apparent pKa were the same in both directions. However, the number of protons per titratable site (adenine N1) required to reach half-denaturation was in great excess over the stoichiometric value; to a much larger extent, the same effect was observed also for the deprotonation of the N3H sites of thymine. Moreover, in the basic denaturation experiments, at low salt concentrations ([NaCl],0.300M) less acid than calculated was needed to back-titrate the base excess to half-denaturation. Both effects could be qualitatively justified on the basis of the counterion condensation theory of polyelectrolytes and considering the energy barrier created by the negatively charged phosphodiester groups to the penetration of the OH, ions inside the double helix and the screening effect of the Na+ ions on such charges, in the deprotonation experiments. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source] Crystallization of recombinant human growth hormone at elevated pressures: Pressure effects on PEG-induced volume exclusion interactionsBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010Ryan L. Crisman Abstract Crystallization of recombinant human growth hormone (rhGH) at elevated pressures was investigated in the presence of 6,000 molecular weight poly(ethylene glycol; PEG-6000). Crystallization of rhGH at atmospheric pressure occurred at a protein concentration of 15,mg/mL in 6% PEG-6000. Crystallization did not occur in the same solutions at 250,MPa. In contrast, at a pressure of 250,MPa in the presence of 8% PEG-6000, rhGH readily crystallized from solutions containing 35,mg/mL rhGH, whereas amorphous precipitate formed in the same solutions at atmospheric pressure. Osmotic virial coefficients were determined from static light scattering measurements and combined with a hard-sphere activity coefficient model to predict rhGH activity coefficients as a function of pressure and PEG concentration. Predicted activity coefficients quantitatively matched those determined from equilibrium solubility measurements. The ability to adjust the thermodynamic non-ideality with pressure provides a valuable tool to study protein crystallization in addition to providing a methodology for obtaining crystals at elevated pressures. Biotechnol. Bioeng. 2010;107:663,672. © 2010 Wiley Periodicals, Inc. [source] Polynorbornene with pentafluorophenyl imide side chain groups: Synthesis and sulfonationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2010Arlette A. Santiago Abstract The mixtures of exo-endo -monomers and isomerically pure endo -monomers of N -pentafluorophenyl-norbornene-5,6-dicarboximide (2a) and N -phenyl-norbornene-5,6-dicarboximide (2b) were synthesized and polymerized via ring opening metathesis polymerization using bis(tricyclohexylphosphine) benzylidene ruthenium (IV) dichloride (I) and tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene][benzylidene] ruthenium dichloride (II). Ring opening metathesis polymerization of mixtures of exo-endo -monomers (2a) and (2b) and pure endo - 2b gave the corresponding high molecular weights poly(N -pentafluorophenyl-norbornene-5,6-dicarboximide) (3a) and poly(N -phenyl-norbornene-5,6-dicarboximide) (3b). The isomerically pure endo - 2a did not polymerize by I in these conditions, since I is the least active catalyst and endo - 2a is the least active monomer because of the intramolecular complex formation between the Ru active center and the fluorine atom of ring-opened endo - 2a on the one hand and steric hindrances caused by the pentafluorinated ring on the other. The quantitative hydrogenation of the polymer 3a, at room temperature and 115 bar, was achieved by a Wilkinson's catalyst. The new polynorbornene bearing highly fluorinated sulfonic acid groups (5) was obtained by the reaction of the hydrogenated poly(N -pentafluorophenyl-norbornene-5,6-dicarboximide) (4) with sodium 4-hydroxybenzenesulfonate dihydrate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2925,2933, 2010 [source] | |||||||||||||