摘要:

Understanding the mechanism of cationic olefin polymerization has led to the synthesis of various new materials of interesting and unusual physical properties. By elucidating details of initiation, various new graft and bigraft copolymers combining glassy/glassy, glassy/rubbery, and rubbery/rubbery sequences have been obtained. Recent research concerning fundamentals of alkylation and termination was exploited for the preparation of new block copolymers and terminally-functional block copolymers. Initiation by difunctional initiators has led to α,ω-difunctional polymers, e. g., !α,ω-diphenylpolyisobutylene. Cyclo-pentadienylation of lightly chlorinated polymers, e. g., chlorobutyl rubber, produced thermally reversible networks.

ISSN:0022-233X    

DOI:10.1080/00222338008063204

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

New evidence on the polymerization kinetics of methyl methacrylate and molar mass distributions is presented which together with earlier work on the stereochemistry of the polymerization of α,β-dideuteroacrylates shows that these are not typical anionic polymerizations. The persistence and stability of the active centers, together with evidence that the α-carbon of the monomer assumes the tetrahedral configuration it takes in the polymer chain as it becomes the active chain end, suggests that the active centers are covalent magnesium-carbon bonds. Existing hypotheses about the mechanism of steric control in homogeneous polymerizations are examined. Kinetic evidence confirms that complexing of the monomer to the active center does occur. However, intramolecular complexing of the penultimate or antepenultimate chain carbonyl group to the metal is not a prerequisite for isotactic polymerization though it may be involved in controlling the in-chain configuration of the β-carbon. Gel-permeation chromatography shows that in some systems more than one active center operates independently. These centers are established in the initiation stages and persist. The proportions of active centers of different reactivity and stereo-specificity are determined by conditions prevailing during initiation and it is these that primarily determine the structure of the polymers formed. Evidence is reported that confirms this.

ISSN:0022-233X    

DOI:10.1080/00222338008063205

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Recent studies have revealed that at temperatures around 200°K in tetrahydrofuran solvent, poly(methy1 methacrylate) ion pairs are long-lived and very reactive. At higher temperatures however termination of the ion pairs occurs, as evidenced by the broadening of the molecular weight distribution of the resultant polymer and by the incomplete polymerization of the monomer. Three mechanisms have been proposed to describe these termination reactions; an inter molecular reaction with the monomer ester function, an intramolecular cyclization of the anion, or reaction with the polymer ester function. In the absence of monomer only the last two mechanisms can be operative. A series of experiments was undertaken in which the molecular weight distribution broadening with temperature increase was measured under typical polymerization conditions or in the absence of monomer. The effect of each of the three counterions Li, Na, and K was also monitored. The results obtained are discussed in terms of these three possible termination mechanisms. Termination rate constants calculated from the molecular weight distribution are also presented.

ISSN:0022-233X    

DOI:10.1080/00222338008063206

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The interaction of strong acids with hydroperoxides at room temperature has been shown to result in the formation of radical species capable of initiating vinyl polymerization. For the reaction of tert-butyl hydroperoxide (tBHP) with sulfuric acid in methyl methacrylate (MMA), the rate of initiation of polymer varies in a complex manner with the concentration of the components but is first-order in [tBHP] and approximately second-order in [H2SO4] at low concentrations of tBHP and in the presence of excess acid. At high concentrations of tBHP, chain transfer to unprotonated hydroperoxide retards the rate of polymerization. The rate of polymer initiation parallels the ionization ratio [BH+]/[B] of a weak base (B = 4-chloro-2-nitroaniline) in MMA-H2SO4and the high order in [H2SO4] can be explained in terms of the requirement of more than one molecule of H2SO4for the monoprotonation of the hydroperoxide (homoconjugation). Endgroup analysis of the polymers has shown that the initiating species are the tert-butoxy and hydroxy radicals. These data are consistent with the homo-lytic scission of the O-O bond of the hydroperoxide being facilitated by protonation of one of the oxygen atoms. Comparison of the rate of polymer initiation with the overall rate of decomposition of tBHP has indicated that as much as 30% of the hydroperoxide decomposes by a radical path.

ISSN:0022-233X    

DOI:10.1080/00222338008063207

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Literature copolymer composition data on the bulk polymerizations of maleic anhydride-styrene, acrylonitrile-styrene, and fumaronitrile-styrene have been considered in terms of the complex participation model. An assessment has been made in each case as to whether sequence information would be able to distinguish between the complex and penultimate polymerization models.

ISSN:0022-233X    

DOI:10.1080/00222338008063208

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The polymerization of unsaturated monomers can be initiated by ultraviolet radiation. This method of initiation has been used to form polymers, to graft polymerize monomers onto existing polymers, and to crosslink prepolymer systems. These reactions usually require the presence of photosensitizer species in order to take place and electron donors, such as tertiary amines, have been shown to increase the rate of reaction. Many of these sensitizer systems have been reported for a large variety of polymerizations, but there appears to have been little attempt to relate activity to chemical structure using comparable conditions. The present study has statistically evaluated the activity of a number of sensitizers and amines over a range of concentrations by use of methyl acrylate as a common monomer. Other monomers have also been studied. Polymerization rates have been measured using refractometry. Relatively low intensity lamps have been used for irradiation to enable the polymerizations to proceed at a slow enough rate for measurements to be conveniently made. The results could be extrapolated to application of high intensity ultraviolet radiation as used in rapid polymerizing formulations.

ISSN:0022-233X    

DOI:10.1080/00222338008063209

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Methyl methacrylate can be readily graft copolymerized to polypropylene film by mutual γ-irradiation in vacuo. Graft yields in excess of 1000% can be obtained at low total doses (0.1 Mrad) and dose rates (0.05 Mrad/hr). When the monomer is diluted with solvent mixtures, similar yields can be obtained at lower monomer concentrations due to an accelerative effect. Besides swelling of the polypropylene, the results indicate the importance of solvent on the reaction kinetics of the growing poly(methy1 methacrylate) radicals. A possible explanation of the effect of diluent is presented in terms of polymer chain entanglement.

ISSN:0022-233X    

DOI:10.1080/00222338008063210

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The use of mineral acid to enhance the radiation grafting of monomers to trunk polymers such as polyethylene is shown to be of value for the insolubilization of enzymes and the hetero-genization of catalytically active homogeneous complexes. Two general methods are described showing how acid enhancement effects can be used in the immobilization reactions. In the first technique, styrene is grafted, and the resulting co-polymer can be nitrated followed by subsequent chemical reactions to yield an appropriate substituent to which the attach ment processes can occur. Alternatively, p-nitrostyrene can be grafted directly. In the latter method, the acid enhancement is shown to be valuable, since the monomer is deactivating in radiation grafting and any technique for improving yields is useful. The acid enhancement effect is also shown to be of value for grafting to polyethylene, since this backbone polymer is less susceptible to grafting than the other two trunk polymers studied, i. e., polypropylene and PVC. A novel mechanism for the acid effect is proposed. The grafting of p-nitrostyrene is more satisfactory for the insolubilization reactions when compared with the alternative of styrene grafting followed by nitration.

ISSN:0022-233X    

DOI:10.1080/00222338008063211

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The use of insoluble reagents in micro particle form has been extensively investigated in the search for new and simpler processes for purifying water. Very finely divided particles allow rapid rates of reaction to be attained. However, they pose a severe handling problem. To overcome this difficulty, the microparticles may be bound together to form a composite particle of conventional size, held together by a polymeric binder which is permeable to water and the impurities to be removed. Another technique involves incorporating small amounts of a magnetic material such as iron oxide within the micro particles of reagent. When magnetized, the particles flocculate strongly and quickly settle out. Variation of the nature of the reagent allows a wide variety of impurities to be adsorbed. The feasibility of using microparticles suitably modified has been demonstrated for a number of ion-exchange reactions, for a new clarification and decolorization process involving alkali-treated magnetite, and for a selective adsorption process based on a magnetic activated carbon which can adsorb only small molecules.

ISSN:0022-233X    

DOI:10.1080/00222338008063212

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The infrared spectrum of polytriallylamine prepared by the free-radical-initiated polymerization of triallylamine indicates the presence of a substantial amount of unsaturation. The usual quantitative methods of determining unsaturation (e. g., bromide/ bromate and mercuric acetate) cannot be used on polytriallylamine because of interference from the amino group. On the other hand, bisulfite was found to react rapidly and quantitatively with the pendant allyl groups of polytriallylamine. The reaction was studied over the pH range 4 to 10 and was fastest at pH 5.2. The reaction is a free-radical reaction which is catalyzed by metal ions and oxygen. The sulfonic acid groups which result from attack of bisulfite on the pendant allyl groups of polytriallylamine form strong zwitterion structures with the amine nitrogens. The addition of thiols is also a free-radical reaction. The reaction of HSCH2CH2OH, HSCH2CO2H, CH3SH, H2S, HSCH2CH2N(C2H5)2, CH5COSH, and C6H5SH with polytriallylamine was studied. Of these compounds, only HSCH2CH2OH and HSCH2CO2H reacted quantitatively. Some reasons for the differences in reactivity are presented.

ISSN:0022-233X    

DOI:10.1080/00222338008063213

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor