Efficient Ring-Opening Polymerization and Copolymerization of ε-Caprolactone and ω-Pentadecalactone Catalyzed by Candida antartica Lipase B

In this paper, Novozyme-435-catalyzed ω-pentadecalactone and ω-pentadecalactone/ε-caprolactone polymerizations were investigated. Novozyme-435-catalyzed ω-pentadecalactone polymerizations were studied in bulk and at ω-pentadecalactone-to-toluene ratios from 1:1 to 1:10 (wt/vol). By carrying out polymerizations with ω-pentadecalactone to toluene 1:1 wt/vol instead of in bulk, the monomer conversion (32 to 90%) and product M n (22 × 10 3 to 86 × 10 3 g/mol) increased. Effects of reaction temperature on monomer conversion and product molecular weights also were studied. ω-Pentadecalactone polymerization at 90 °C in toluene (1:2 ω-pentadecalactone to toluene wt/vol) resulted in the fastest kinetics thus far reported for lipase-catalyzed polyester production. However, reduction of the polymerization temperature from 90 to 55 °C gave polypentadecalactone with increased M n (66 × 10 3 to 81 × 10 3 g/mol). Novozyme-435-catalyzed ω-pentadecalactone/ε-caprolactone copolymerizations conducted at 70 °C in toluene occurred at unexpectedly rapid rates. Studies of monomer coreactivity ratios ( r 1 = 1.742 and r 2 = 0.135) showed that ω-pentadecalactone reacted 13 times faster than ε-caprolactone. 13 C NMR studies showed that copolymers with random repeat unit sequence distributions were formed after 10 min at monomer conversions ≥44%). We believe that Novozyme-435 actively promotes interchain transesterification reactions that tend to randomize the repeat unit sequence distribution.