Kinetic behavior of the thermal and mechanical properties of segmented urethanes

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Abstract
Commerical and experimental urethane polymers were studied by thermal‐mechanical methods including DSC and stress‐strain analysis. The studies reveal that following thermal treatment these polymers show time‐dependent mechanical properties. This time‐dependent period may be many days while the degree of this dependence is influenced by annealing temperature. By DSC analysis it has been shown that the glass transition temperature of the soft segment, Tgs, is also greatly influenced by annealing treatment. Immediately following annealing temperatures above 130 °C, Tgs may be as much as 40 °C higher than its ’’long‐time’’ value. With time, however, Tgs decreases to its original value. Higher‐temperature endothermic behavior associated with hard‐segment domains is also time dependent. Both the degree of Tgs shift and higher endothermic effects are correlated with annelaing temperature. The time‐dependent behavior for a given annealing temperature has been related to to chemical structure (ester vs ether, and hydrogen bonding effects). The data are explained in terms of the thermal stability of domains.