The Kinetics of Hydrolytic Aging of Polyester Urethane Elastomers.

摘要

The hydrolytic degradation of polyester urethane elastomers is due to the acid catalyzed hydrolysis of the ester group. Acid content (A) and the reciprocal of the number average molecular weight increase by equivalent amounts indicating that each molecular chain scission produces one acid group. The fractional rate of increase in acidity, k, is a pseudo first order rate constant because the ester and water contents change only slightly with degradation. Values of k at 85 C and 100% relative humidity are in the 15-20% per day for polyurethanes, based on polycaprolactone and polytetramethylene adipate diols. At 100% relative humidity k obeys the Arrhenius equation between 35 and 85 C with activation energies in the range 68-83 kJ/mol (16-20 kcal/mol). Values of k decrease with relative humidity, becoming zero in dry air.