TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The method additionally comprises the step after polymerization is completed, in which an antisolvent dissolving the reaction solvent but not dissolving the produced polymer to form a single phase is introduced, and thus the pure polymer is precipitated. The antisolvent is directly introduced into a reaction container. The polymer in the polymerization-completed reaction container is sprayed into a precipitator and the antisolvent is introduced into the precipitator. The compressed gas reaction solvent completely dissolves polymer to perform a uniform solution-polymerization. A reaction temperature is 25-250 degrees C, the reaction time is 0.2-50 hours, and yield is at least 70%. The reaction pressure is 40-700 bar.Preferred Composition: The monomer is present in 1-50 wt.% based on the supercritical fluid. The molar ratio of the catalyst and the initiator is 10-4 to 10-2 based on monomer, respectively.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Materials: The antisolvent, carbon dioxide, HFCs, HCFCs, SF6, fluorocarbons (FCs), hydrocarbon, ether, or their mixture is used. Lactides, lactones, cyclic carbonates, cyclic anhydrides, and/or thiolactones are used as the cyclic monomer. Compounds of formulae (I) and/or (II) are used as the cyclic monomer. The cyclic monomer includes L-lactide, D-lactide, D,L-lactide, or glycolide. It includes epsilon-caprolactone. At least two monomers are used to be co-polymerized.R1 and R2 = H or 1-4C alkyl;n = 2-5.Preferred Catalyst: The organic metal catalyst is a tin-based catalyst comprising stannous octoate, stannic chloride, stannous oxide, stannous octylester, stannous chloride dihydrate, or tetraphenyl tin; a zinc-based catalyst comprising zinc powder, diethyl zinc, zinc octoate, zinc chloride, or zinc oxide; or an aluminum-based catalyst including aluminum chloride and aluminum ethoxide. The acid catalyst is zinc bis(2,2-dimethyl-3,5-heptanedionato-O,O'). 1.6-hexanediol is used as the initiator.