| 초록 |
The use of supercritical CO2(sc CO2) as a solvent for polymerization is attractive because the product may be easily collected from solution after processing. Several common polymers have been synthesized in sc CO2. Polymers previously synthesized in sc CO2 include, but are not limited to, various fluoropolymers, polysiloxanes, poly(methyl methacrylate), polystyrene, polycarbonates and aliphatic polyesters. These polymerizations are either homogeneous or heterogeneous in nature, depending on the polymer of interest and its solubility in sc CO2. Unfortunately, many polymers beyond specific fluoropolymers, polysiloxanes and a recently studied series of aliphatic polyesters have limited solubility in sc CO2, leading to low molecular weight and making the range of possible homogeneous polymerizations extremely narrow. On the other hand, sc chlorodifluoromethane has been known to be a good solvent for polar polymers. It was observed that biodegradable polymers such as poly(L-lactide) and poly(D,L-lactide-co-glycolide) were insoluble in nonpolar sc CO2 but were soluble in polar sc chlorodifluoromethane. Here we describe the conversion and molecular weight of PLLA produced via a homogeneous polymerization in sc chlorodifluoromethane with respect to time, reaction temperature, reaction pressure and total concentration. |
