A method of making polylactic acid using carbon dioxide adducts of carbenes, characterized in that the adducts of carbenes have a structure represented by formula: wherein the dotted line indicates an optional double bond; X 1 is chosen from S and N; X 2 is chosen from C and N; R 1 and R 2 are the same or different and are chosen from hydrogen, alkyl groups having 1 to 10 carbon atoms, alkyl groups having 1 to 10 carbon atoms and also having one or more substituents chosen from a halogen atom, a hydroxyl group, a phenyl group, and a cyano group, cycloalkyl groups having 3 to 6 carbon atoms, a halogen atom, an adamantyl group, a phenyl group, and a phenyl group having one or more substituents chosen from a halogen atom, a hydroxyl group, an alkyl group, and a cyano group; R 3 and R 4 are the same or different and are chosen from hydrogen, a halogen atom, a cyano group, a hydroxyl group, alkyl groups having 1 to 4 carbon atoms, alkyl groups having 1 to 4 carbon atoms and also having one or more substituents chosen from a halogen atom, a hydroxyl group, a phenyl group, and a cyano group, a phenyl group, and a substituted phenyl group, and alternatively, R 3 and R 4 are connected to form cycloalkyl or cycloalkenyl rings having 3 to 8 carbon atoms; or R 3 and R 4 are connected to form a benzene ring; or R 2 and R 3 are connected to form 5-or 6- N -heterocyclic compounds that do not have any substituent. X 1 is chosen from S and N; X 2 is chosen from C and N; R 1 and R 2 are the same or different and are chosen from hydrogen, alkyl groups having 1 to 10 carbon atoms, alkyl groups having 1 to 10 carbon atoms and also having one or more substituents chosen from a halogen atom, a hydroxyl group, a phenyl group, and a cyano group, cycloalkyl groups having 3 to 6 carbon atoms, a halogen atom, an adamantyl group, a phenyl group, and a phenyl group having one or more substituents chosen from a halogen atom, a hydroxyl group, an alkyl group, and a cyano group; hydrogen, alkyl groups having 1 to 10 carbon atoms, alkyl groups having 1 to 10 carbon atoms and also having one or more substituents chosen from a halogen atom, a hydroxyl group, a phenyl group, and a cyano group, cycloalkyl groups having 3 to 6 carbon atoms, a halogen atom, an adamantyl group, a phenyl group, and a phenyl group having one or more substituents chosen from a halogen atom, a hydroxyl group, an alkyl group, and a cyano group; R 3 and R 4 are the same or different and are chosen from hydrogen, a halogen atom, a cyano group, a hydroxyl group, alkyl groups having 1 to 4 carbon atoms, alkyl groups having 1 to 4 carbon atoms and also having one or more substituents chosen from a halogen atom, a hydroxyl group, a phenyl group, and a cyano group, a phenyl group, and a substituted phenyl group, and hydrogen, a halogen atom, a cyano group, a hydroxyl group, alkyl groups having 1 to 4 carbon atoms, alkyl groups having 1 to 4 carbon atoms and also having one or more substituents chosen from a halogen atom, a hydroxyl group, a phenyl group, and a cyano group, a phenyl group, and a substituted phenyl group, and alternatively, R 3 and R 4 are connected to form cycloalkyl or cycloalkenyl rings having 3 to 8 carbon atoms; or R 3 and R 4 are connected to form a benzene ring; or R 2 and R 3 are connected to form 5-or 6- N -heterocyclic compounds that do not have any substituent.