Ternary Stereocomplex Formation of One l-Configured and Two d-Configured Optically Active Polyesters, Poly(l-2-hydroxybutanoic acid), Poly(d-2-hydroxybutanoic acid), and Poly(d-lactic acid)

Abstract

The ternary stereocomplex formation of optically active polyesters, l-configured poly(l-2-hydroxybutanoic acid) [P(l-2HB)] and d-configured poly(d-2-hydroxybutanoic acid) [P(d-2HB)] and poly(d-lactic acid) (PDLA), is reported. Ternary P(l-2HB)/P(d-2HB)/PDLA blends were prepared by solution-casting to have a fixed content (50 mol %) of l-configured P(l-2HB) and different contents of d-configured P(d-2HB) relative to those of PDLA, and stereocomplex formation in the blends was investigated using wide-angle X-ray scattering and differential scanning calorimetry. The interplane distances of solution- and melt-crystallized blends were estimated from the 2θ values at around 11° and 22°, and the melting temperatures of stereocomplex increased continuously with increasing the P(d-2HB) content relative to that of PDLA in the blends, indicating the formation of a ternary stereocomplex. The stereocomplex crystallinity values of ternary blends were much higher than the values calculated from binary P(l-2HB)/P(d-2HB) and P(l-2HB)/PDLA blends wherein respectively only the binary P(l-2HB)/P(d-2HB) homostereocomplex and P(l-2HB)/PDLA heterostereocomplex were formed, reflecting the facile crystallization of the ternary stereocomplex.