Abstract: Blends of elastomers of chlorinated or chlorosulfonated polyethylene and ultra high molecular weight, i.e. at least one million, when cured with conventional curing systems for the chlorinated or chlorosulfonated polyethylene have higher tear strengths at temperatures of about 150.degree. C. than do the unblended elastomers. The amount of polyethylene in the blend is 5 to 50 parts by weight per 100 parts by weight of elastomer. The blend, thus produced has a modulus (M.sub.100) of greater than 1000 psi prior to curing.

Abstract: Reaction of a large excess of 1,4-butanediol with methylenebis (4-phenyl isocyanate) gives a mixture of urethanediols which is a suitable curing agent for isocyanate-terminated polyurethane prepolymers, especially prepolymers made from methylenebis (4-phenyl isocyanate) and polyols. It is desirable to have a urethanediol mixture in which at least about 88 weight percent consists of the reaction product of 2 moles of 1,4-butanediol with 1 mole of the diisocyanate, about 10 weight percent of the reaction product of 3 moles of 1,4-butanediol with 2 moles of the diisocyanate, and no more than about 2 weight percent of 1,4-butanediol. The novel cured polyurethanes have higher hardness and better overall physical properties than methylenebis-(4-phenyl isocyanate)-based polyurethanes cured with conventional commercial diols providing "hard" cured products.