摘要:

AbstractMethyl methacrylate was polymerized in an aqueous medium in the presence of gelatin using potassium persulfate as initiator. The dispersion mode of polymerization, when the monomer is completely miscible with water, was investigated and compared with an emulsion process, which proceeds at higher monomer concentration. Spherical and relatively uniform polymer particles were formed. Macroscopic precipitation of polymer is prevented by combination of the steric stabilization by grafted gelatin and of repulsive electrostatic interactions from the initiator residues attached to the particle surface. Static and dynamic light scattering have been used to determine the molar mass (molar mass of the whole dispersion particle,MwD∼ 108‐109g mol−1) and hydrodynamic radius (RhD∼ 50‐120 nm) of the particles. The number of particles per unit volume does not depend on overall monomer concentration, and it is higher, and therefore the particle size is smaller, than that observed for the soapless emulsion polymerization. The addition of gelatin may be thus used to modify the particle size.Acrylonitrile dispersions were prepared under similar conditions. Unlike methyl methacrylate, this monomer does not swell the polymer particles. While poly(methyl methacrylate) particles are spherical and relatively uniform, the polyacrylonitrile dispersions consist of polydisperse aggregates of tiny polymer

ISSN:0959-8103    

DOI:10.1002/pi.4990300112

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractFractionation of partly hydrolysed polyvinyl acetate (PVA) was performed by warming of its aqueous solutions. The following properties of the obtained fractions were determined: viscosity, molecular weight and molecular weight distribution, surface tension, and absorbance in the IR range. The blockiness of the polymer molecules, characterized by their behaviour towards iodine‐containing systems such as I2,‐H3BO3and I2,‐KI, was estimated. Fractionation of the aqueous solutions of PVA by warming is based mainly on the different internal molecular structure of the separated products, i.e. on the length of the vinyl acetate blocks in the PVA molecules and, to a lesser extent, on the degree of hydrolysis and the degree of polymerization. The more blocklike are the PVA molecules, the less compatible are the polymers in the PVA‐hydroxypropyl methylcellulose (HPMC)‐water system. At phase separation in this sytem the PVA molecules which are not compatible with HPMC are, in the first place, those of the highest b

ISSN:0959-8103    

DOI:10.1002/pi.4990300113

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractPoly(4‐methylstyrene)‐graft‐poly(ethylene oxide)s were prepared via polymerisation of ethylene oxide on to poly(4‐methylstyrene)s functionalised with hydroxyl groups. In this way, many ‘comb‐like’ polymers having different hydrophobic backbone length, hydrophilic branch length and frequency of branches were synthesised. These polymers were tested as dispersants in coal‐water mixtures in order to correlate the dispersing properties of this class of polymers with the investig

ISSN:0959-8103    

DOI:10.1002/pi.4990300114

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rate of E/Z isomerization for the propagating end in group transfer polymerization (GTP) of methyl methacrylate (MMA) is comparable to the rate of propagation for bifluoride catalysis, in contrast to bibenzoate catalysis where propagation is faster. Methyl 2,2,4‐trimethyl‐5‐methoxy‐5‐(trimethylsiloxy)pent‐4‐enoate,4(the product of the initiation step in the GTP of MMA), was used as the model of the GTP living end. The rate of monomer addition to4was independent of the starting E/Z isomer ratio. The observation of random tacticity in the polymers prepared via anionically catalyzed GTP can be adequately explained by comparable rates of E/Z isomerization and propagation or in the case of bibenzoate catalysis, by the assumption that E and Z propagating ends react with similar stereochemistry. Silyl ketene acetal2(a model of the polyacrylate propagating end) underwent HgI2catalyzed E/Z isomerization at a rate comparable to the polymerization of e

ISSN:0959-8103    

DOI:10.1002/pi.4990300115

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractPermeation of CO2and O2through a low density polyethylene film was studied with CO2‐N2mixtures in the temperature range 263‐283 K, and with CO2‐O2‐N2mixtures in the range 257‐313 K. The temperature dependence of the permeabilities of these gases agreed with the Arrhenius expression. The activation energy for carbon dioxide diffusion was between 3.53 × 104and 3.74 × 104J/mol; the activation energy for oxygen diffusion was 3.13 × 104J/mol. The pre‐exponential constant for oxygen was higher than that of carbon dioxide in various mixtures. It was also found that the pre‐exponential constant of carbon dioxide decreased with increasing CO2concentration

ISSN:0959-8103    

DOI:10.1002/pi.4990300116

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractGel/sol and order/disorder transitions can be observed in a segmented rigid‐rod polyimide solution at different concentrations and molecular weights. This polyimide was synthesized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl in refluxing 3‐cresol in a one‐step process. Above about 140°C, the polymers are completely soluble in 3‐cresol in a concentration range up to 12(w/w)%. During cooling, the hot solutions undergo a mechanical sol/gel transition to form thermally reversible gels. In the gel state, an ordered structure develops. Both the gel/sol and order/disorder transitions are dependent upon concentration, temperature, and molecular weight, but the two transitions exhibit different kinetics. Possible mechanisms of these t

ISSN:0959-8103    

DOI:10.1002/pi.4990300117

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractModified poly(vinyl alcohol) (PVA) membranes prepared by the ‘solution technique’ were tested for ethanol‐water mixtures by varying the reaction density (Xcr= 0.05, 0.1) at various temperatures. The results are compared with those of PVA membranes (Xcr= 0.05) prepared by the technique of the GFT Company, Ge

ISSN:0959-8103    

DOI:10.1002/pi.4990300118

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe ‘solution technique’ modification of poly(vinyl alcohol) (PVA) using maleic acid was carried out with the help of triethanolamine/water catalysts. The resulting PVA membranes were characterized by differential scanning calorimetry, infrared spectroscopy, and tensile studies to investigate the reaction between PVA polymer and maleic acid. It was found that the resulting PVA membranes had two portions, branched and crosslinked, and there were no more branched than cross‐linked portions. For the pervaporation separation of the acetic acid‐water system, two reaction densities (Xcr= mole maleic acid per mole monomeric unit of PVA) of 0.05 and 0.1 were studied for the separation of the entire range of mixture compositions at 25° C. The separation factors of theXcr= 0.05 modified PVA membranes were higher than those of theXcr0.1 modified ones and the highest separation factor of 7.80 was obtained at 70wt% water in the feed with theXcr= 0.05 modified PVA

ISSN:0959-8103    

DOI:10.1002/pi.4990300119

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0959-8103    

DOI:10.1002/pi.4990300121

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0959-8103    

DOI:10.1002/pi.4990300124

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY