摘要:

Differential thermal analysis and composition, texture, and coverage measurements were carried out and gave evidences for chemical interaction between chromium oxide and the silica-alumina support of an olefin polymerization catalyst. Such interactions are related to the activity vs. propene polymerization and these relations allow to suggest that the active centers involve a layer of trivalent chromium oxide linked to the support by chromosiloxan bonds and covered with one or more layers of hexavalent chromium oxide.

ISSN:0022-233X    

DOI:10.1080/00222336808053353

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The conditions under which previous kinetic measurements have been carried out on esterification and polyesterification reactions have been examined in relation to the significance of the conclusions reached. It is suggested that only in the later stages of the reactions are conditions achieved which yield sensible kinetic results.

ISSN:0022-233X    

DOI:10.1080/00222336808053354

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Simple modification of conventional temperature-programmed thermogravimetric apparatus permits direct recording of the thermal degradation spectrum (TDS) of polymers and the rate of weight loss with rising temperature. The effect of heating rate on the TDS of poly(methyl methacrylate) is discussed.

ISSN:0022-233X    

DOI:10.1080/00222336808053355

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The conventional kinetic scheme for a free-radical homopolymerization is modified to incorporate dilution by a feed stream and the effect of propagation on solution density. Neglect of the volume change can result in prediction of erroneously high conversions. The distribution of average molecular weight fractions is evaluated. In the absence of gelation and transfer reactions, the broadening, which is usually thought to arise from varying composition, is found to be small compared to that which is intrinsic to the addition mechanism.

ISSN:0022-233X    

DOI:10.1080/00222336808053356

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Acetalization of poly(vinyl alcohol) molecules results in acetal ring formation between two successive hydroxyl groups. This will dominate the chain stiffness of poly(vinyl acetal) in different ways, depending on the stereospecificity of poly(vinyl alcohol) used as the starting material. The present paper first deals with calculations of statistical dimensions of hypothetical poly(vinyl acetal) chains with a 100% degree of substitution and different stereospecificities (isotacticity and syndiotacticity). The calculations are essentially identical with those made by Wall and Markovitz, but recent stereochemical knowledges of the acetal ring and poly(vinyl alcohol) are taken into account. The results show that the chain dimension of poly-(vinyl acetal) chain derived from isotactic poly(vinyl alcohol) is much larger than that of poly(vinyl acetal) derived from the syndiotactic one. The treatment used above is extended to more realistic chains that have any degree of stereoregularity and of substitution. As has been anticipated intuitively, it is ascertained that the chain dimensions increase with increase in the degree of substitution for each stereospecificity.

ISSN:0022-233X    

DOI:10.1080/00222336808053357

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

ISSN:0022-233X    

DOI:10.1080/00222336808053358

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

In a recent paper [1], anomalies in ebulliometric measurements with polyethylene in different solvents were reported. Anomalies were claimed because the elevation of the boiling point ΔT exhibited an unusual concentration dependence. A strong increase of ΔT with c was followed by a weaker one and again by a strong increase. The anomalies at low concentrations were attributed to unaccounted-for factors.

ISSN:0022-233X    

DOI:10.1080/00222336808053359

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

ISSN:0022-233X    

DOI:10.1080/00222336808053360

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0022-233X    

DOI:10.1080/00222336808053342

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor