SEGMENTED POLYURETHANS . PROPERTIES AS A FUNCTION OF SEGMENT SIZE AND DISTRIBUTION

Property-structure relationships in a series of segmented polyurethans (I) have been studied. The structural features of interest–hard segment size, size distribution, and spacing along the chain (i.e., soft segment distribution)–were varied independently by special synthetic techniques. The hard segments are crystalline and have well-defined melting points which increase with segment size. Reciprocal absolute melting temperature is inversely proportional to the number of repeat units in the segment. Degree of crystallinity varies little with size. Cocrystallization of different hard segments is a function of relative size. Narrowing of the hard segment size distribution increases modulus, tensile, and extension set drastically. Narrowing of the soft segment distribution causes a slight increase in modulus, a moderate increase in elongation and tensile, and a large increase in extension set. © 1969, American Chemical Society. All rights reserved.