Investigation on lipase-catalyzed solution polymerization of cyclic carbonate

In this study, 26-membered macrocyclic carbonate, cyclobis(decamethylene carbonate) [(DMC)2] was attempted to undergo ring-opening polymerization by lipase catalysis in toluene. Novozym-435 exhibited even higher catalytic activity towards (DMC)2 polymerization compared with SnOCt2 while high molecular weight (Mn) of 5.4 × 104 and yield of 99% was still achieved at ultra-low enzyme/substrate (E/S) weight ratio of 1/200. 1H NMR spectra demonstrated the existence of terminal hydroxyl group. Solid phase polymerization in the absence of toluene unexpectedly took place at the temperature lower than (DMC)2’s melting point of 110 °C. Compared with solvent-free case, the addition of toluene solvent resulted in marked increase in reaction rate. As to the polymerization during 48 h with the E/S weight ratio of 1/100, a region existed at around toluene/carbonate (vol/wt, ml/g) ratio of 1∼2 where the polymerizations gave optimal results in terms of both higher molecular weight and monomer conversion. It was found that much higher molecular weight polymers may be obtained by decreasing enzyme concentrations. Plots of ln{[M]0:[M]t} versus reaction time were in linear agreement, indicating no chain termination, and monomer consumption follows a first-order rate law. The Novozym-435 catalyzed polymerization of (DMC)2 in toluene presented pseudo-living characteristic. Compared with 6-membered trimethylene carbonate, much lower reaction activity of large-sized (DMC)2 is observed, which is opposite to the result concerning the enzymatic polymerization of lactones with different ring-size.