Patent ID: 7538179

Claim:
A process for producing an aliphatic polyester, comprising: subjecting a cyclic ester containing water and an alcohol which function as initiators or/and molecular weight-adjusting agents to ring-opening polymerization while controlling (A) a total concentration in a range of above 0.09 mol % and below 2.0 mol % of proton sources which include carboxyl (carboxylic acid)-source compounds including water, free α-hydroxycarboxylic acid dimer thereof and also alkoxylcarbonyl (ester)-source compounds including the alcohol, and (B) a ratio in a range of 100/-2/98 between a mol concentration of the carboxyl (carboxylic acid)-source compounds and a mol concentration of the alkoxylcarbonyl (ester)-source compounds, so as to provide a desired weight-average molecular weight and a desired hydrolyzation rate constant, respectively, of resultant aliphatic polyester by varying the contents of the water and the alcohol in the cyclic ester.