Thermoplastic urethane elastomers. II. Effects of variations in hard-segment concentration

Abstract

The dynamic mechanical properties of thermoplastic urethane elastomers have been charac-terized for polymers composed of varying hard-segment concentrations and for two different molecular weight polyester diols as soft segments. The urethane polymers based on an 830 M̄n polycaprolactone diol exhibited a progressive increase in glass transition temperature at increased levels of hard segments. In contrast, a similar series of polymers prepared with a 2100 M̄n polycaprolactone diol as the soft segment maintained a relatively constant glass transition temperature. These differences are attributed to the relative degree of phase separation between the constitutive blocks of the copolymer. The polymers of both series possessed two lower-temperature, secondary relaxations, which are ascribed to methylene sequence mobility within the polycaprolactone units and to possible disruption of interfacial associations between the hard- and soft-segment structures.