Ring-opening polymerization of epsilon-caprolactone in Supercritical Carbon Dioxide

The ring-opening polymerization of ε-caprolactone (CL) initiated by dibutyltin dimethoxide was studied in supercritical carbon dioxide at 40 °C, under a pressure of 210−215 bar. The polymerization is controlled as assessed by the linear dependence of Mn,SEC on conversion and of ln([CL]0/[CL]) on time. Moreover, there is a good agreement between Mn,SEC and Mn,calc, at least until 20 000 g/mol. The apparent rate constants of polymerization in different media increase as follows: sc CO2, CFC-113, toluene, bulk. The kinetic order in initiator for the polymerization in solution and in sc CO2 was extracted from the slope of ln kapp vs ln [Sn]0. It appears to depend on the initiator concentration in solution, which is not the case in sc CO2.