Abstract
Polyurethanes were prepared so as to get homologous series of polymers with respect to the concentration of polar groups and croslink density. Viscoelastic properties and glass transition phenomena were studied in the glass to rubber transition region.
Glass temperature is raised and the steepness of viscoelastic dispersion is decreased when the concentrations of urethane and biuret groups and the crosslink density are increased. In each case a large discrepancy was found to exist between the thermal expansion coefficient of specific volume and that of free volume derived by comparing WLF equation with Doolittle's equation in which the value of parameter B was assumed to be unity. As a possible way to account for this discrepancy, B is assumed to be a decreasing function of temperature supposing that the thermal dissociation of secondary linkages between polar groups may have an effect to reduce the size of elemental unit of molecular motion.
