Hydrolysis of lactic acid based poly(ester-urethane)s

The hydrolysis behaviour of lactic acid based poly(ester-urethane)s has been studied in a buffer solution of pH 7.00 at 37 and 55 degrees C. Samples were prepared using a straight two step lactic acid polymerization process. The lactic acid was first polymerized by condensation with a low molecular weight by hydroxyl terminated telechelic prepolymer and the molecular weight then was increased with a chain extender such as a diisocyanate. In the hydrolysis study, the effect on the hydrolysis rate of different stereostructures (different amount of D-units in the polymer chain) and the length of the ester units were studied. The rate of hydrolysis was examined by various techniques including weighing (water absorption and weight loss), GPC (molecular weight and polydispersity), and DSC (thermal properties). GPC measurements showed that at 37 degrees C the weight average molecular weight of the poly(ester-urethane)s started to decrease slowly during the first week of hydrolysis, but that at 55 degrees C the weight average molecular weight decreased dramatically during the first week of hydrolysis. Significant mass loss occurred later at both temperatures. (C) 1998 Society of Chemical Industry.