LIPASE-CATALYZED FORMATION OF MACROCYCLES BY RING-OPENING POLYMERIZATION OF EPSILON-CAPROLACTONE

Studies were undertaken to gain mechanistic information on lactone rin g-opening polymerisation reactions using Candida antarctica lipase B ( Novozym 435) as the catalyst and epsilon-caprolactone as the monomer. Polymerisations were performed in organic solvents as well as without solvent at 60 degrees C. Candida antarctica lipase B catalysed concurr ently with the intermolecular ring-opening polymerisation, and also th e formation of macrocycles by an intramolecular condensation reaction. Candida antarctica lipase B had the highest initial rate of consumpti on of epsilon-caprolactone (1.2 mu mol mg(-1) min(-1)) in the bulk pol ymerisation, without solvent. Under these conditions, the highest aver age M-w, 4701 D, of poly(epsilon-caprolactone) was obtained. There wer e small amounts of cyclic oligomers present. When comparing the polyme risations performed in dioxane, acetonitrile and THF after 24 h reacti on time with the bulk polymerisation, the average M-w of poly(epsilon- caprolactone) [2984, 1297, 1862 D, respectively] and the initial rates of monomer conversion of the enzyme (0.1, 0.05, 0.013 mu mol mg(-1) m in(-1), respectively) were lower, however, the formation of cyclic oli gomers was high. In dioxane, macrocycles of up to 2623 D corresponding to 23 monomer units were formed, and in acetonitrile there were mostl y cyclic oligomers present. (C) 1998 Elsevier Science Ltd. All rights reserved.