Hydrolytic Degradation of a Copoly(ether ester) Elastomer

Hydrolytic degradation was studied for a thermoplastic elastomer comprising polybutylene (terephthalate-co-isophthalate) hard segments and polypropylene oxide soft segments. Pellets and injection-molded bars were aged by immersion in deionized water and artificial sea water at temperatures of ~23, 50, 75, and 95C for times up to 200 days. Degradation of mechanical properties was manifested much later than marked increases in melt flow rate. For example, after 27 days in water at 75C, melt flow rate had increased by 533%, while tensile strength and elongation each decreased only ~10% and modulus showed little change. The addition of sea salt, which raises pH from 7 to ~8, did not significantly affect the degradation rate.