摘要:

The thionyl chloride/titanium tetrachloride combination in methylene chloride solution is found to be a good cationic initiating system for styrene polymerization. the efficiency of the initiation is governed by the amount of titanium chloride used. It was found by the IMA and AMI techniques that the system possesses a partially living character, and the polystyrenes obtained exhibit some stereoregular structure.

ISSN:0022-233X    

DOI:10.1080/00222339009349550

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The aim of the present investigation is the development of a unifying framework for modeling free-radical suspension and bulk vinyl chloride polymerizations. A fairly comprehensive but realistic model is described that has the ability to predict the rate of polymerization as well as the molecular properties of polymer as a function of the process conditions. It is shown that no significant differences exist between the predictions of the present model and those obtained by various well-known two-phase PVC models published before. in addition to the prediction of fractional monomer conversion and rate of polymerization, the new model predicts the anomalous structures observed in commercial PVC, namely, the number of short- and long-chain branches as well as the number of unsaturated terminal double bonds per polymer molecule. Simulation results show that the present model provides realistic predictions of the important molecular properties in agreement with experimental observations reported in the literature. Finally, the validity of the quasi-steady-state approximation for growing macroradicals is tested by comparing conversion and molecular weight results obtained with or without its application.

ISSN:0022-233X    

DOI:10.1080/00222339009349551

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Pyridine ring functionalization and additional crosslinking in crosslinked poly(styrene-co-4-vinylpyridine) with various dibromoalkanes depend on the chain length of the dibromoalkane, the solvent polarity, and the molar ratio between the pyridine rings and the dibromoalkane. the effect of chain length on additional crosslinking becomes more pronounced when the good swelling solvent dimethylformamide is replaced by dibromoalkane. on the other hand, the degree of crosslinking of poly(styrene-co-4-vinylpyridine) influences both the reactivity and the additional crosslinking.

ISSN:0022-233X    

DOI:10.1080/00222339009349552

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Transient species (T1and T2), formed respectively by the reactions of hydrated electrons and hydroxyl radicals with methyl vinyl ketone monomer in aqueous solution, were characterized by their spectra, redox behavior, and decay kinetics. These were found to have λmaxat 290 and 310 nm with low extinction coefficient values of 94 and 70 m2/mol, respectively. Rate constants for the reactions of methyl vinyl ketone with eaaq- and OH were found to be 3.2 × 109 and 7 × 108 dm3·mol−1·s−1, respectively. the first propagation step for species T2 was found to be much faster (κpl∼ 1.5 × 106 dm3·s−1than that for species T1(κpl∼7.0 × 105 dm3·mol−1·s−1). Both were found to be reducing in nature, and the rate constants for the reduction of thionine and safranine with these species were determined. the most probable structures of these species are suggested.

ISSN:0022-233X    

DOI:10.1080/00222339009349553

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The chain propagation and termination rate coefficients of vinyl acetate radical polymerization were determined by the rotating sector method at 25°C. the values determined are in good agreement with those of Kwart, Matheson, and Swain. the chain termination rate coefficient essentially differs from that determined by Burnett.

ISSN:0022-233X    

DOI:10.1080/00222339009349554

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Electroinitiated polymerization of acrolein has been achieved by controlled potential electrolysis at the reduction peak potential of the monomer for direct electron transfer. Kinetics and type of mechanism of the polymerization have been investigated. the structure of the polymer has also been examined by IR spectroscopy. in a separate experiment, a small amount of CCI4was added to a polymerization system. Since the reduction peak potential of CCI4appears at a more anodic region than that of acrolein on mercurized platinum, initiation proceeds via the electrolytic product of CCI4. the direct and indirect initiation mechanisms are compared. It is found that electroinitiated polymerization of acrolein carried out by direct electron transfer from cathode to monomer (in the absence of CCI4) proceeds simultaneously via radical and anionic mechanism.

ISSN:0022-233X    

DOI:10.1080/00222339009349555

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

New polyamides, polyimides, and a polyamide-imide containing ester linkages were prepared by the reaction of trimethylene glycol di-p-aminobenzoate with terephthaloyl chloride, isophthaloyl chloride, adipoyl chloride, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, and trimellitoyl chloride. the low temperature solution and interfacial polymerization techniques were utilized to prepare the above-mentioned polymers. the polymers thus prepared were found to be soluble in solvents like DMAC and DMSO and had inherent viscosities in the 0.15-0.60 range. the polyimides prepared formed transparent and flexible films.

ISSN:0022-233X    

DOI:10.1080/00222339009349556

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Molecular Hartree-Fock calculations have been performed ontrans-cisoidalpolyacetylene to study the effect of simultaneous rotation about two successive single bonds on the energy of this polymer. A potential energy surface mapped out for this molecule shows that theall-transconformation corresponding to the simultaneous rotations of all single bonds by 180° is the lowest energy state for this polymer.

ISSN:0022-233X    

DOI:10.1080/00222339009349557

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Chemical polymerization of aniline in five different protonic acids, HCl, H2SO4, HBr, HNO3, and acetic acid (HAc), has been studied. the resulting polymers are characterized by elemental analysis, thermogravimetric analysis, infrared and x-ray photoelectron spectroscopy, and electrical conductivity measurements. It is found that a large fraction of the bromine and a smaller fraction of the chlorine in the product is covalently bonded. Thus a more accurate indicator of the degree of protonation would be the halogen anion rather than total halogen content. When H2SO4 is used for protonation, the anion incorporated in the polyaniline appears to be the HSO4- rather than the SO42- species. the degree of protonation of H2SO4 protonated polyaniline is significantly reduced when it is washed with water after the synthesis step. Treatment of the H2SO4, HBr, and HNO3 protonated polyaniline with HCl results in almost complete replacement of the respective anion by the chloride anion. the HBr protonated polyaniline sample shows partial solubility in CHCl3, with the insoluble fraction showing a slight improvement in conductivity after CHCl3 treatment.

ISSN:0022-233X    

DOI:10.1080/00222339009349558

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

13C solid-state NMR has been used for quantitative determination of the proportion of various functional groups present in uncured urea-formaldehyde (UF) resins. the quantitative interpretation of the structural units present in UF resins synthesized in different pH conditions was made possible by using appropriate rotors and pulse techniques. Resin prepared in acid medium showed more methylene units in the polymer branch and less methylol moieties in the polymer chain compared to resin prepared in alkaline condition. Plausible mechanistic routes are proposed to explain the structural differences due to pH change.

ISSN:0022-233X    

DOI:10.1080/00222339009349559

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor