Patent ID: 8642717

Claim:
A process for producing an aliphatic polyester resin where a polyhydroxy acid skeleton is a main component, which comprises subjecting starting monomers to a ring-opening polymerization reaction in the presence of a polymerization catalyst, wherein an organophosphorus compound represented by the formula is added to the reaction system to lower the activity of the polymerization catalyst wherein in the formula, R 1 , R 2 , R 3 and R 4 are same or different and each is hydrogen or alkyl group; and n is an integer of 1 or more, wherein the organophosphorus compound is added to the reaction system before initiation of the ring-opening polymerization reaction and compound to metal element (B) derived from the polymerization catalyst in the resin satisfies the following relation 1 ≦ Phosphorus ⁢ ⁢ element ⁢ ⁢ ( A ) ⁢ ⁢ derived ⁢ ⁢ from ⁢ ⁢ the organophosphorus ⁢ ⁢ compound Metal ⁢ ⁢ element ⁢ ⁢ ( B ) ⁢ ⁢ derived ⁢ ⁢ from ⁢ ⁢ the polymerization ⁢ ⁢ catalyst ≦ 30.