AbstractThe composition of crosslinked polyester–urethanes has been varied by adjusting the ratio of ester to urethane groups. The crosslinking density of these materials has been varied by changes in the polyester functionality. The polyester–urethanes have been subjected to solvent extraction, wherein it was found that at high crosslinking densities, the solubility of the polymers is unaffected by the ester‐urethane ratio. At low crosslinking densities, solubility increases slightly with increasing urethane concentration. The solubility was also found to increase with decreasing crosslinking density. Data obtained from isothermal heat aging and thermogravimetric analysis, both carried out in air and in inert atmosphere, indicate that thermal stability increases with increasing ester/urethane ratio and is independent of crosslinking density where the ester/urethane ratio is held constant. In addition, data obtained from heat aging and thermogravimetric analysis have indicated that decomposition of the samples occurs as rapidly in inert atmosphere as in air, indicating that the decomposition occurs chiefly by a nonoxidative mech
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