Influence of molecular weight on the thermal and mechanical properties of polyurethane elastomers based on 4,4′-diisocyanato dicyclohexylmethane

Two series of segmented polyurethane elastomers based on 4,4′‐diisocyanato dicyclohexylmethane were investigated with respect to their thermal properties and deformation behavior. We used a crystallizable soft segment, 1,4‐poly(tetramethylene glycol), for one series and a noncrystallizable soft segment, 1,2‐poly(propylene glycol), for the other. Both systems exhibited mechanical self‐reinforcement that depended strongly on the deformation rate. We propose a mechanism for the observed stress/strain behavior in terms of two competing processes: (1) the buildup of orientation caused by deformation and (2) the loss of orientation caused by plastic slippage and segmental relaxation during deformation. The kinetics of these processes depend stronly on the deformation rate and overall molecular weight.