Lipase-catalyzed transesterification reactions between polymers of high molecular weight
Our group discovered that lipases are highly active for catalysis of transesterification reactions between polyesters (Kumar et al., 2000). For polymers that have melting points below 100 oC, transesterification reactions can be conducted in-bulk. Transacylation reactions between polyesters involve intrachain cleavage by lipase-catalysis to form an enzyme-activated-chain segment, followed by reaction of this activated segment with the terminal hydroxyl unit of another chain. Immobilized Candida antartica lipase B (Novozyme-435) catalyzed transacylation reactions were successfully performed using pre-formed polyester chains with Mn > 40 K (Scheme 5). These reactions, conducted under mild conditions, were used to regulate block lengths along copolymer chains. In fact, by extending the reaction time of transesterification reactions, copolymers are formed with random repeat unit sequence distributions.
Scheme 5. CALB catalyzes intra-chain transesterification reactions between aliphatic polyesters at high rates so that physical mixtures of two homopolymers can be converted to random copolymers.
References
- A Kumar, R.A Gross, “Lipase-Catalyzed Transesterification: New Synthetic Routes To Copolyesters”, J. Am. Chem. Soc.; 122; 11767-11770 (2000).(PDF)