Ring-opening polymerization of L-lactide in supercritical chlorodifluoromethane

The ring-opening polymerization of L-lactide initiated by 1-dodecanol/stannous 2-ethylhexanoate (DoOH/Sn(OCt)(2)) was carried out in supercritical chlorodifluoromethane at various reaction times, pressures, and temperatures. The monomer conversion increased to ca 70 % on increasing the reaction time to 25 h. The molecular weight of the product also increased to ca 75,000 g/mol over the same period. Increasing the pressure resulted in an accelerated polymerization rate. The pressure-induced increase in the rate of L-LA polymerization can be explained by the formation of chemical bonds in the transition state, which implies the production of a transition state with a lower partial molar volume than the reactants.