A Novel Synthetic Approach to Stereo‐Block Poly(lactic acid)

Stereoblock poly(lactic acid) (sb‐PLA), consisting of poly(L‐lactic acid) (PLLA) and poly(D‐lactic acid) (PDLA) in a blocky sequence, can successfully be synthesized by solid‐state polycondensation of a stereocomplexed mixture of PLLA and PDLA. First, the melt polyconden‐sation of L‐ and D‐lactic acids is conducted to obtain PLLA and PDLA with medium molecular weights. Then, both polymers are melt‐blended to easily form the stereocomplex. The resulting stereocomplexed mixture (melt‐blend) is subjected to solid‐state polycondensation for chain extension. The molecular weight (Mw) of the resultant sb‐PLA is strongly affected by the lactide/oligomer content in the melt‐blend, which is determined by the melt‐blending conditions, because it is directly correlated with the polymer crystallinity of the polycondensation products.