Relation of Structure to Properties in Polyurethanes. Effect of Branching

Abstract

Abstract Attaching short N-arylurethane branches to a high molecular weight, linear polyether urethane introduces interchain forces—very likely arising from hydrogen bonding—which increase as the side chains become more polar. These forces are sufficiently strong to increase the bulk viscosity of the raw polymers and, with the more highly polar groups, are strong enough to impart an appreciable elastic memory. At slightly elevated temperatures (80° C) these forces are reduced considerably, which is to be expected if they arise through hydrogen bonding. However they are either not strong enough or are too limited in number to compete with the covalent crosslinks in the elastomer vulcanizates. Thus no significant alteration is observed in the vulcanizate properties which are customarily measured. The marked effect of these short aryl side chains to reduce crystallization tendencies can most likely be attributed to the bulkiness. of the pendant aryl moiety, which prevents—or slows down—the ordering of the polytetramethyleneether chains into a crystal lattice. Long chain branches influence dynamic properties considerably. Present evidence indicates that optimum dynamic properties—as measured by Yerzley resilience—are obtained when “loose ends” are absent.