METHOD FOR PRODUCING POLYLACTIC ACID BLOCK COPOLYMER

摘要

A method for producing a polylactic acid block copolymer that is constituted by a segment composed of L-lactic acid unit and a segment composed of D-lactic acid unit, the method including: a step of obtaining a mixture having the weight-average molecular weight of 90000 or more and the rate of stereocomplex formation (Sc) satisfying the following equation, by mixing poly-L-lactic acid and poly-D-lactic acid, one of the poly-L-lactic acid and the poly-D-lactic acid having the weight-average molecular weight of 60000 to 300000 and the other having the weight-average molecular weight of 10000 to 50000; and a step of solid-phase polymerizing the mixture at a lower temperature than the melting point of the mixture. Sc = ?Hh/(?Hl + ?Hh) × 100 > 60, wherein ?Hh is an amount of heat (J/g) based on stereocomplex crystallization, and ?Hl is an amount of heat (J/g) based on crystal melting of poly-L-lactic acid single crystal and poly-D-lactic acid single crystal. According to this production method, a polylactic acid block copolymer forming a polylactic acid stereocomplex that has a high molecular weight and a high melting point can be obtained.