Lipase-Catalyzed Ring-Opening Copolymerization of ε‑Caprolactone and β‑Lactam

The enzymatic ring-opening copolymerization of ε-caprolactone (ε-CL) and β-lactam by using Candida antarctica lipase B (CAL-B) as catalyst was studied. Variation of the feed ratios of 25:75, 50:50, and 75:25 of ε-CL/β-lactam was performed. The products contain poly­(ε-CL-co-β-lactam) and the homopolymers of poly­(ε-CL) and poly­(β-lactam). The structure of the copolymers was determined by MALDI-ToF MS. Poly­(ε-CL-co-β-lactam) has an alternating and random structure consisting of alternating repeating units with oligo­(ε-CL) or oligo­(β-lactam). The highest fraction of the alternating copolymers resulted from the reaction with a feed ratio 50:50. The copolymer is a semicrystalline polymer with a T_m at 124 °C and T_gs at −15 and 50 °C. Interestingly, the copolymer also demonstrated cold crystallization at 29 and 74 °C, after quenching the sample from the melt in liquid nitrogen.