Lipase-Catalyzed Reactive Extrusion: Copolymerization of ε-Caprolactone and ω-Pentadecalactone

This study assesses the use of immobilized lipase catalyst N435 during reactive extrusion (REX) versus magnetically stirred bulk and solution reaction conditions for the copolymerization of ε-caprolactone with ω-pentadecalactone (CL/PDL 1:1 molar). N435-catalyzed REX for reaction times from 1 to 3 h results in total %-monomer conversion, M_n , and Đ values increase from 92.7% to 98.8%, 36.1 to 51.3 kDa, and 1.85 to 1.96, respectively. Diad fraction analysis by quantitative ¹³ C NMR reveals that, after just 1 h, rapid N435-catalyzed transesterification reactions occur that give random copolyesters. In contrast, for bulk polymerization with magnetic stirring in round bottom flasks, reaction times from 1 to 3 h result in the following: M_n  increases from 12.4 to 25.6 kDa, Đ decreases from 2.98 to 1.87, and the randomness index increases from 0.74 and 0.86 as PDL*-PDL diads are dominant. These results highlight that REX avoids problems associated with internal batch mixing that are encountered in bulk polymerizations. In sharp contrast to a previous study of 1:1 molar PDL/δ-valerolactone (VL) copolymerizations by N435-catalyzed REX, VL %-conversion increases to just 40.1% in 1 h whereas CL reaches 94.7%.