POLYURETHANE ELASTOMERS WITH HYDROLYTIC AND THERMOOXIDATIVE STABILITY .2. POLYURETHANES WITH N-ALKYLATED POLYURETHANE SOFT BLOCKS

Block copolyurethanes with N‐alkylated polyurethanes as nonself‐associating soft segments are prepared. The polymers compare well in hydrolytic stability with block copoly(N‐alkylamide urethane)s prepared in an earlier study but have better dimensional stability on exposure to moist heat. They show comparable hydrolytic stability and better oxidative stability than a poly(ether urethane) from the earlier study. The effect of different alkyl substituents on tensile properties and thermostability is studied. The tensile properties are also examined as a function of soft‐segment molecular weight at constant weight‐percent of hard‐block. It is shown that yield stress and ultimate stress increase and elongations decrease as the soft‐block M̄n increases. DSC measurements do not generally show well defined endotherms with few exceptions but dynamic mechanical testing of some samples does show transitions between 14 and 23°C. Copyright © 1990 John Wiley & Sons, Inc.