ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
A large-scale precise fractionation of GR-S (X-55) was performed using the fractional precipitation technique at 25°C. 9 fractions, each weighing approximately 150 g. and comprising approximately 11% by weight of the original unfractionated sample, were obtained and a detailed study was made showing the effect of number-average molecular weight and related sol-gel properties on various physical and chemical properties of the crude and vulcanized fractions. Using a Santocure tread-type recipe, preliminary compounding work indicated the sulfur ratios required to give vulcanizates with 300% modulus values of 1000 p.s.i. All fractions were recompounded using these indicated optimum sulfur values. Generally, as the number-average molecular weight increased, better stress-strain and quality index data were obtained. These and other physical properties of the vulcanizates of these fractions are discussed in detail. As found in past fractionation studies pertaining to unsaturated high polymers, the higher molecular weight fractions, obtained from the unfractionated sample which was totally soluble in benzene, undergo considerable gelation when isolated and vacuum dried at 25°C. in the dark. As the indicated molecular weight of the fraction increased, higher per cent gel contents were obtained. Compared to unfractionated butadiene-styrene copolymers of similar gel contents, the gel portions of the higher molecular weight fractions had unusually high swelling indices. indicating qualitatively that the average molecular weights between points of effective cross linking in the three-dimensional gel structure were higher than those encountered in the past in unfractionated samples of similar gel contents. Other data are given pertaining to these fractions, such as the bound styrene content, per cent shrinkage of the compounded unvulcanized stocks, and the rate of gel breakdown with cold milling.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1948.120030412
