Weight fraction vulcanization

Polymers account for about 3—4% of the total butylene consumption and about 30% of nonfuels use. Homopolymerization of butylene isomers is relatively unimportant commercially. Only stereoregular poly(l-butene) [9003-29-6] and a small volume of polyisobutylene [25038-49-7] are produced in this manner. High molecular weight polyisobutylenes have found limited use because they cannot be vulcanized. To overcome this deficiency a butyl mbber copolymer of isobutylene with isoprene has been developed. Low molecular weight viscous Hquid polymers of isobutylene are not manufactured because of the high price of purified isobutylene. Copolymerization from relatively inexpensive refinery butane—butylene fractions containing all the butylene isomers yields a range of viscous polymers that satisfy most commercial needs (see Olefin polymers Elastomers, synthetic-butylrubber). 

Fig. 105.—Tensile strengths of butyl rubber fractions each vulcanized to the same cross-linking density p, corresponding to Me = 37,000, plotted against the primary molecular weight M. ...

The experimental details for this part of the work were the same as those used with natural rubber except that the recipes were modified such that the volume fraction of carbon black was held constant (at essentially the same level as it was with the natural rubber work) and the weight of the batch was adjusted to the same volume as it was in the case of natural rubber. The dispersion-rated samples were not vulcanized. 

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