摘要:

AbstractThe effect of blending polymers of different molecular weight on theQvalue (Q=M̄w/M̄n) of the blend has been considered. A mathematical expression is derived, and its shows by a simple application to monodisperse systems that blending over a wide molecular weight range is necessary to give highQvalues. These principles are then applied to the case of Ziegler and Phillips type high density polyethylenes having wide log‐normal molecular weight distributions. In this way it is shown that only blending over a very wide melt index range, e.g., 1000/1, can be expected to have a measurable effect onQ. A series of physical measurements on blended and homogenized Ziegler polyethylenes shows no significant differences between blends and directly produced polym

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020701

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractCopolymerizations of propylene and styrene were carried out with various Ziegler‐Natta type catalysts in order to find the catalytic activity, the monomer reactivity ratios, and some properties of the copolymer. The polymerization products were confirmed to be copolymers from the facts that special behaviors were observed in the infrared and NMR spectra and that the melting point dropped with increasing styrene content. Generally, copolymer produced with a AlR3–TiCl4catalyst had low stereoregularity and comparatively low molecular weight. On the contrary, a copolymer produced with a AlR3–TiCl3catalyst had high stereoregularity and high molecular weight (viscosity). In order to reduce the viscosity various additives were examined. Monomer reactivity ratios obtained by the catalysts areas follows: for Al(i‐Bu)3–TiCl3:r1= 20.0 ± 3.5,r2= 0.20 ± 0.13; for AlEt3–TiCl3:r1= 20.5 ± 3.0,r2= 0.30 ± 0.15; for AiEt3–VCl4:r1= 7.2 ± 0.7,r2= 0.16 ± 0.08. All cases show that the reactivity of propylene is much larger t

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020702

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractMeasurement of butadiene absorption at constant volume, and of polymer formation, indicated that the rate of polymerization was first order in monomer concentration, up to 1.5 mole/l., and also in initial total catalyst concentration, for given molar ratio of alkyl to titanium ester. The overall activation energy was 11.5 kcal./mole. A fast initiation, accompanied by the evolution of ethylene or a mixture of ethane and ethylene, a relatively slow propagation, and chain transfer to monomer, appeared to be the main steps of the reaction. Termination was essentially absent. Insoluble, gellike material was formed roughly at 20% conversion and was attributed to a random crosslinking, involveing very few crosslinks per molecule, or possibly trifunctional branching. The molecular weight distribution was very narrow. A polymer of over 80% in 1,2 units, having a predominantly syndiotactic structure and about 10% crystallinity, was obtained. In the absence of monomer, the catalyst components reacted rapidly to form complexes, accompanied by strong ethane evolution. A complex series of reactions leading to the possible formation of more than one active species was indicated. The active catalyst suffered bimolecular decomposition on prolonged standing. For optimal molar ratio of alkyl to ester of 5/1, the concentration of active species was estimated as having an upper limit of 4.8 × 10−6mole

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020703

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractThe crosslinking of ethylene–propylene rubber by means of dicumyl peroxide has been followed in detail. The overall crosslinking efficiency has been found to be about 0.4 crosslinks per peroxide molecule, and this result has been shown by stress relaxation and permanent set experiments to result from a mixture of both scission and crosslinking reactions. The results obtained with two different rubbers are consistent with the view that scission results from abstraction of a tertiary hydrogen atom while crosslinking arises from attack at a secondary hydrogen. Such a scheme allows a relative reactivity of tertiary :secondary of 6:1 to be calculated. The action of sulfur in peroxide cures has been shown to be to introduce labile, presumably sulfur‐containing, crosslinks. Such labile crosslinks explain the increased tensile strength of such vulcanizates. Allyl compounds are effective in increasing the crosslinking efficiency of the perox

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020704

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractEqual radiation yields of hydrogen are obtained from bulk polyethylene and thin films of solution crystallized polyethylene, with aGvalue of 4.6. The corresponding value for very thick mats of the solution crystallized material is 3.4. Reasoning from material balance considerations indicates that the yield of radiation‐induced crosslinking for bulk and thin films is about twice that for thick mats of polyethylene. It is suggested that thin films and thick mats differ only in fold surface contact, and that crosslinking is preferential at the folds. The retention of xylene between fold surfaces following crystallization is compatible with the effect of irradiation on trapped solven

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020705

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractPrecipitation temperature measurements have been the exclusive source of thermodynamic parameters used for the comparison of polymers differing in tacticity. The Flory theta temperatures differ for the various tactic forms, although not in a manner which exhibits any obvious consistency. The precipitation temperature entropy parameters, on the other hand, have been larger for the isotactic polymer in every case but one. The theoretical treatment underlying the evaluation of ψ1from precipitation temperature data is, unfortunately, not strictly valid. Thus, the interpretation of this behavior is in some doubt. We report the results of an osmotic study of isotactic and atactic poly‐l‐pentene in phenetole at three temperatures. For the isotactic and atactic modification the respective values found were Θ = 329.0 and 321.5°K., while for ψ1the values were 0.45 and 0.72. The theta temperatures fall in the same order as those previously obtained for a closely related system, poly‐l‐butene–anisole, by precipitation temperature measurements. The osmotic ψ1values are larger than those reported here‐tofore for other systems, but of more importance, they fall in the reverse of the order consistently obtained from precipitation temperatures. This suggests that the regular variation of the precipitation temperature ψ1values can not have its origin in local pair interaction effects; instead, it must reflect some difference in the concentration dependence of the chemical potential for solutions of the var

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020706

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractValues ofdlnr02/dT, for polystyrene, poly(vinyl acetate), poly(methyl methacrylate), and polydimethylsiloxane recently obtained by different authors are compared. The large discrepancies among values reported are taken as an indication of the effects played by polymer–solvent interactions on unperturbed dimension

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020707

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractResults enabling the determination of the temperature variation of the unperturbed mean‐square end‐to‐end distancer02for linear polymer chains from stress–temperature measurements are surveyed. Out of 31 polymer systems which have been studied, only two show a clear decrease ofr02with temperature. An increase or an independence ofr02upon temperature is the most common trend. These results appear at variance with expectations and with theoretical considerations. Experimental difficulties and possible limitations of said theories are di

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020708

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractA new theoretical relationship for the heat of copolymerization is described. The heat of copolymerization for low conversion copolymers can be related to the heats of homopolymerization, the polymer composition, and two parameters which characterize the alternation tendency in copolymerization.

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020709

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY

摘要:

AbstractWhen primary free radicals approach their stationary‐state concentration at a rate which is of the same order of magnitude as that with which chain radicals approach their stationary‐state concentration, the familiar nonstationary‐state equation relating the chain radical concentration to the time of reaction is no longer adequate. An accurate mathematical description of this situation has now been obtained which not only allows one to examine the dependence of chain radical concentration on the reaction time but also provides a basis for predicting under what conditions the primary radicals will be slow to approach a steady state. On the basis of these results the degree of error which is introduced into measurements of termination rate constants has been calculated and an experimental approach for measuring specific rate constants of chain initiation has been sugg

ISSN:0449-2951    

DOI:10.1002/pol.1964.100020710

出版商:John Wiley&Sons, Inc.    

年代:1964

数据来源: WILEY