Stereoblock Poly(lactic acid): Synthesis via Solid‐State Polycondensation of a Stereocomplexed Mixture of Poly(L‐lactic acid) and Poly(D‐lactic acid)

Abstract

Abstract Summary: Stereoblock poly(lactic acid) consisting of D ‐ and L ‐lactate stereosequences can be successfully synthesized by solid‐state polycondensation of a 1:1 mixture of poly( L ‐lactic acid) and poly( D ‐lactic acid). In the first step, melt‐polycondensation of L ‐ and D ‐lactic acids is conducted to synthesize poly( L ‐lactic acid) and poly( D ‐lactic acid) with a medium‐molecular‐weight, respectively. In the next step, these poly( L ‐lactic acid) and poly( D ‐lactic acid) are melt‐blended in 1:1 ratio to allow formation of their stereocomplex. In the last step, this melt‐blend is subjected to solid‐state polycondensation at temperature where the dehydrative condensation is allowed to promote chain extension in the amorphous phase with the stereocomplex crystals preserved. Finally, stereoblock poly(lactic acid) having high‐molecular‐weight is obtained. The stereoblock poly(lactic acid) synthesized by this way shows a higher melting temperature in consequence of the controlled block lengths and the resulting higher‐molecular‐weight. The product characterization as well as the optimization of the polymerization conditions is described. Changes in $\overline M _{\rm w}$ of stereoblock poly(lactic acid) (sb‐PLA) as a function of the reaction time. image Changes in $\overline M _{\rm w}$ of stereoblock poly(lactic acid) (sb‐PLA) as a function of the reaction time.