Kinetics of enzymatic ring-opening polymerization of ε-caprolactone in supercritical carbon dioxide

The kinetics of enzymatic ring-opening polymerization (eROP) of epsilon-caprolactone in supercritical carbon dioxide (scCO(2)) was investigated using a new, high-pressure sampling autoclave. The polymerization was performed using Candida antarctica lipase B (CALB) as catalyst and was found to be approximately first order with respect to monomer up to 80% conversion. For the first time we have been able to present kinetic results on the eROP of caprolactone in scCO(2). These results show that high molecular weight polymer could be obtained (up to 50 kDa) with polydispersities in the range of 2. The relatively poor molecular weight control was attributed to the large degree of enzyme-catalyzed transesterification that forms both cyclic species (intramolecular transesterification) and linear polymer (intermolecular transesterification). This effect has also been observed for eROP of epsilon-caprolactone in conventional solvents. The formation of cyclic oligomers of poly(caprolactone) (PCL) was investigated as a function of conversion, and comparisons were made to similar studies undertaken in conventional solvents.