Enzymatic Hydrolysis of Copoly (succinic anhydride/ethylene oxide) and Copoly (succinic anhydride/ethylene oxide/phthalic anhydride)

Copoly [succinic anhydride (SA) /ethylene oxide (EO)] and copoly [SA/EO/phthalic anhydride (PHA)], synthesized by ring-opening copolymerization, were enzymatically hydrolyzed using the lipase fromRhizopus arrhizus. The weight losses (%) of these copolymers after the hydrolysis were in the range of 25 to 35%, and so the recovered polymers were hydrolyzed again with fresh lipase. The water-soluble products after the enzymatic hydrolysis were analyzed by GPC, 1H NMR, HPLC, and UV spectroscopy. The number-average molecular weight (Mn) and the composition of the residual copolymers did not change very much from those of the original copolymers. Large portions of the water-soluble degraded products were recovered by extraction with tetrahydrofuran (THF) and then with methanol. The EO contents in the extracts with THF were higher than those of the original copolymers. The GPC profiles of the extracts with THF showed a broad polymodal chromatogram, indicating that these polymers were randomly degraded by the lipase. The extract with methanol were derivatives of succinic acid. Copoly (SA/EO) with SA/EO=44/56 mol% and copoly (SA/EO/PHA) with SA/EO/PHA=39/56/5 mol% were perfectly hydrolyzed in 4 times repetition of hydrolysis. However, the increase of PHA content decreased the rate of the enzymatic hydrolysis of the copolymer. Both the melting temperature and the heat of fusion for the residual copolymer became high compared to those of the original copolymers, while glass transition point of the polymers scarcely changed. These results suggest that the enzymatic hydrolysis of these copolymers proceeds preferentially at the amorphous region on the copolymer surface.