Lipase-Catalyzed Synthesis of Aliphatic Poly(carbonate-co-esters)

Candida antarctica Lipase B (CALB) was found to catalyze condensation reactions of diethyl carbonate (DEC), diester, and diol to form aliphatic poly(carbonate-co-esters). Poly(butylene carbonate-co-butylene succinate), poly(BC-co-BS), and poly(hexamethylene carbonate-co-hexamethylene adipate), poly(HC-co-HA), with about 1:1 mol/mol ester-to-carbonate repeat units, were prepared by maintaining the diol/diester monomer feed ratio (mol/mol) at 2 to 1. By varying the [DEC] to [1,4-butanediol minus diethyl succinate] ratio from 1:1 to 4:1, poly(BC-co-BS) with terminal groups of up to 96 mol % hydroxyl and 90 mol % ethyl carbonate plus ethyl ester, respectively, were prepared. Weight-average molecular weights (Mw) of poly(BC-co-BS) and poly(HC-co-HA), without product fractionation, reached 26 000 and 59 000 at 80 and 90 °C, respectively. Low polydispersities of poly(HC-co-HA) (Mw/Mn ∼ 1.5) indicate that the polymerization proceeds with chain selectivity. NMR analysis revealed poly(BC-co-BS) copolymers contain c...