Stereoblock poly(lactic acid): Synthesis via solid-state polycondensation of a stereocomplexed mixture of poly(L-lactic acid) and poly(D-lactic acid)

Stereoblockpoly(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 POIY(L-lactic acid) and POIY(D-lactic acid) with a medium-molecular-weight, respectively. In the next step, these POIY(L-lactic acid) and POIY(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.