CAL-B catalyzed regioselective bulk polymerization of l-aspartic acid diethyl ester to α-linked polypeptides

This paper reports that the bulk polymerization of l-aspartic acid diethyl ester catalyzed by immobilized CAL-B at 80 °C for 24 h gives primarily (∼95%) α-linked poly(l-aspartate) in 70% yield with DP_avg = 50 and regioselectivity (α/β) = 94 : 6. Plots of log{[M]₀/[M]_t} vs. time and DP_avgvs. conversion indicate that this polymerization proceeds in a controlled manner by a chain-growth mechanism up to 90% conversion. Thereafter, competition occurs between chain growth and step mechanisms.