Polyurethane elastomers with hydrolytic and thermooxidative stability. II. 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 M?_n 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.