Thermal stabilities of different polyurethanes after hydrolytic treatment

Different polyester urethanes and polyether urethanes were exposed to hydrolytic degradation at 70 degrees C for up to 16 weeks. The dried samples were subsequently analysed in thermooxidation tests in the range 250-300 degrees C by measuring the lifetime relating to 5% mass loss. The experimental results showed that polyether urethanes have lower thermal stabilities than those of polyester urethanes; the activation energies determined from the Arrhenius plot are around 65 and 80 kJ mol(-1), respectively. The activation energies of polyether urethanes did not change significantly as hydrolysis proceeded. In contrast, the polyester urethanes exhibited a progressive decrease in activation energy, which fell (after 16 weeks of hydrolysis) to the values characterizing polyether urethanes. The entropic parameter of the Arrhenius equation was also evaluated and related to the chemical composition of the as-received and hydrolysed polymers.