Copolymerization of L-lactide and ε-caprolactone in supercritical fluid

Copolymerization of L-lactide and ε-caprolactone initiated by tin (II) octoate (Sn(Oct)₂) was carried out in supercritical chlorodifluoromethane (R22) with varying reaction conditions (time and temperature) and amounts of monomer and catalyst, under a pressure of 250 bar. The optimum conditions were a reaction time of 10 h and a temperature of 130 °C, which is similar to the temperature used in bulk copolymerization system. The conversion increased from 56% to 76% by increasing the reaction time from 1 to 10 h. The molecular weight also increased to 75,900 g.mol ^-1 over the same period, while the increased monomer concentration resulted in a high molecular weight of 86,400 g.mol^-1 and a monomer conversion of 84%. Raising the reaction temperature from 90 to 130 °C increased the monomer conversion as well as the poly-L-lactide-co-ε- caprolactone (PLCL) molecular weight. The variation on the stannous octoate catalyst suggested that less catalyst would decrease the caprolactone content of the polymer.