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Molecular Weight Measurements (molecular + weight_measurement)
Selected AbstractsEnd-functionalized copolymers prepared by the addition,fragmentation chain-transfer method: Vinyl acetate/methacrylonitrile systemJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2001W. Ken Busfield Abstract Copolymers of vinyl acetate and methacrylonitrile were prepared by free-radical polymerization in the presence of the chain-transfer agent (CTA) ethyl-,- (t -butanethiomethyl)acrylate. Molecular weight measurements showed that the chain-transfer constants increased with the vinyl acetate content of the comonomer mixture, ranging from 0.42 for methacrylonitrile to 6.3 for the copolymerization of a vinyl acetate-rich monomer mix (89/11). The bulk copolymer composition was not appreciably affected by the amount of CTA used in the copolymerization. The efficiency of the addition,fragmentation mechanism in producing specifically end-functionalized copolymers was investigated with 1H NMR spectroscopy. Spectral peaks consistent with all the expected end groups were observed for all comonomer feeds. Peaks consistent with other end groups were also observed, and these were particularly prominent for copolymers made with lower CTA concentrations. At the highest concentrations used, quantitative measurements of end-group concentrations indicated that 70,80% of the end groups were those expected on the basis of the addition,fragmentation chain-transfer mechanism. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2911,2919, 2001 [source] The effect of hyperbranched polymers on processing and thermal stability of biodegradable polyestersPOLYMER ENGINEERING & SCIENCE, Issue 3 2009Yanir Shaked Nanomodification of poly-hydroxy-butyrate (PHB), with hyperbranched polymers (HBP), was studied. Solid-hyperbranched polyesters of different generations were incorporated into a biobased and biodegradable, thermoplastic, polyester. Thermal, rheological, and molecular weight measurements had indicated that due to the interactions between the hydroxyl groups and the polar esters in PHB, the rate of recrystallization was significantly increased. Furthermore, the degree of crystallinity and nonisothermal crystallization temperature were also increased. Molecular weight measurements did not indicate a reduction or retention when HBPs were incorporated. These results are of great significance for the processing of biodegradable polymers and specifically for PHB, where improved processability and enhanced crystallization are of importance. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] A Novel ABC Triblock Copolymer with Very Low Surface Energy: Poly(dimethylsiloxane)- block -Poly(methyl methacrylate)- block -Poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate)MACROMOLECULAR REACTION ENGINEERING, Issue 5 2008Zhenghong Luo Abstract Poly(dimethylsiloxane)- block -poly(methyl methacrylate)- block -poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate) was successfully synthesized via ATRP. The chemical composition and structure of the copolymer was characterized by NMR and FT-IR spectroscopy and molecular weight measurement. Gel permeation chromatography was used to study the molecular weight distribution of the triblock copolymer. The surface properties of the resulting copolymer were investigated. The effects of fluorine content and bulk structure on surface energy were investigated by static water contact angle measurements. Surface composition was studied by XPS. [source] Synthesis, spectral and antimicrobial studies of diorganotin(IV)3(2,-hydroxyphenyl)-5-(4-substituted phenyl) pyrazolinatesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2006U. N. Tripathi Abstract Diorganotin(IV) dipyrazolinates of the type R2Sn(C15H12N2OX)2 [where C15H12N2OX = 3(2,-Hydroxyphenyl)-5(4-X-phenyl)pyrazoline {where X = H (a); CH3 (b); OCH3 (c); Cl (d) and R = Me, Prn and Ph}] have been synthesized by the reaction of R2SnCl2 with sodium salt of pyrazolines in 1:2 molar ratio, in anhydrous benzene. These newly synthesized derivatives have been characterized by elemental analysis (C, H, N, Cl and Sn), molecular weight measurement as well as spectral [IR and multinuclear NMR (1H, 13C and 119Sn)] studies. The bidentate behaviour of the pyrazoline ligands was confirmed by IR, 1H and 13C NMR spectral data. A distorted trans -octahedral structure around tin(IV) atom for R2Sn(C15H12N2OX)2 has been suggested. The free pyrazoline and diorganotin(IV) dipyrazolinates have also been screened for their antibacterial and antifungal activities. Some diorganotin(IV) dipyrazolinates exhibit higher antibacterial and antifungal effect than free ligand and some of the antibiotics. Copyright © 2006 John Wiley & Sons, Ltd. [source] Influence of Microwave Irradiation on the Lipase-Catalyzed Ring-Opening Polymerization of , -CaprolactoneMACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2006Patrick Kerep Abstract Summary: The microwave (MW)-assisted lipase-catalyzed ring-opening polymerization of , -caprolactone in boiling solvents was investigated for the first time. In case of boiling toluene or benzene the MW-assisted reaction proceeded significantly slower compared to oil bath heating. On the other hand, using boiling diethyl ether as solvent, an increase of the polymerization rate due to MW irradiation was found. Yield, molecular weight measurements, and MALDI-TOF analysis supported the results. Reactivity of the MW-assisted ring-opening polymerization of , -caprolactone compared with conventional thermal heating in different solvents. [source] The effect of hyperbranched polymers on processing and thermal stability of biodegradable polyestersPOLYMER ENGINEERING & SCIENCE, Issue 3 2009Yanir Shaked Nanomodification of poly-hydroxy-butyrate (PHB), with hyperbranched polymers (HBP), was studied. Solid-hyperbranched polyesters of different generations were incorporated into a biobased and biodegradable, thermoplastic, polyester. Thermal, rheological, and molecular weight measurements had indicated that due to the interactions between the hydroxyl groups and the polar esters in PHB, the rate of recrystallization was significantly increased. Furthermore, the degree of crystallinity and nonisothermal crystallization temperature were also increased. Molecular weight measurements did not indicate a reduction or retention when HBPs were incorporated. These results are of great significance for the processing of biodegradable polymers and specifically for PHB, where improved processability and enhanced crystallization are of importance. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Comparison of properties of acrylic,polyurethane hybrid emulsions prepared by batch and semibatch processes with monomer emulsion feedPOLYMER INTERNATIONAL, Issue 5 2003ebenik Abstract Aqueous acrylic,polyurethane hybrid emulsions were prepared by batch and semibatch polymerization of acrylic monomer mixtures (butyl acrylate, methyl methacrylate and acrylic acid) in the presence of polyurethane dispersion. The acrylic component was introduced in the monomer emulsion feed. The weight ratio between acrylic and polyurethane components was varied to obtain different emulsion properties, microphase structure and mechanical film properties. Scanning electron microscopy, average particle size and molecular weight measurements were performed to characterize the latex systems. Mechanical properties were examined by measuring Koenig hardnesses of dried films. The average particle size increased with the acrylic/polyurethane ratio. Particles of larger than average size and, to some extent, higher than average molecular weights by batch process were formed. Koenig hardnesses decreased with increasing acrylic/polyurethane ratio. Properties of emulsions synthesized by semibatch processes were compared with the results reported for a different polyurethane dispersion. Copyright © 2003 Society of Chemical Industry [source] Self and nonself recognition of chiral catalysts: The origin of nonlinear effects in the amino-alcohol catalyzed asymmetric addition of diorganozincs to aldehydesTHE CHEMICAL RECORD, Issue 2 2001Ryoji Noyori Abstract Asymmetric addition of dialkylzincs to aldehydes in the presence of (2S)-3- exo -(dimethylamino)isoborneol [(S)-DAIB] exhibits various nonclassical phenomena. The enantiomeric excess (ee) of the alkylation product, obtained with partially resolved DAIB, is much higher than that of the chiral amino alcohol, while the rate decreases considerably as the ee of DAIB is lowered. The asymmetric amplification effects reflect the relative turnover numbers of two enantiomorphic catalytic cycles, where an essential feature is the reversible homochiral and heterochiral dimerization of the coexisting enantiomeric DAIB-based Zn catalysts. The interplay between the thermodynamics of the monomer/dimer equilibration and the kinetics of alkylation reaction strongly affect the overall profile of asymmetric catalysis. The self and nonself recognition of the chiral Zn catalysts is a general phenomenon when (S)-DAIB is mixed with its enantiomer, diastereomer, or even an achiral ,-amino alcohol. The degree of nonlinearity is highly affected not only by the structures and purity of catalysts but also by various reaction parameters. The salient features have been clarified on the basis of molecular weight measurements, NMR and X-ray crystallographic studies of organozinc complexes, and kinetic experiments, as well as computer-aided quantitative analysis. © 2001 John Wiley & Sons, Inc. and The Japan Chemical Journal Forum Chem Rec 1:85,100, 2001 [source] | |||||||||||||