Synthesis of poly(lactic acid) by direct polycondensation of lactic acid using 1,1′-carbonyldiimidazole, N,N,N′,N′-tetramethylchloroformamidinium chloride, and N,N′-dicyclohexylcarbodiimide as condensing agents

The direct polycondensation of racemic lactic acid using condensing agents, such as 1,1-carbonyldiimidazole (CDI), N,N,N',N'-tetramethylchloroformamidinium chloride (TMCFAC), and N,N'-dicyclohexylcarbodiimide/4-dimethylaminopyridine (DCC/DMAP), was investigated. Reactions using CDI proceeded slightly. Polycondensation using TMCFAC with pyridine gave a polymer in 83% yield, but the number-average molecular weight ((M) over bar(n)) was 3700. Thus, TMCFAC is not effective in the direct polycondensation of lactic acid. However, DCC/DMAP is effective, and polycondensation in dichloromethane at room temperature for 24 h afforded poly(lactic acid) having (M) over bar(n) of 15400 in 89% yield.