Ternary stereocomplex crystallization of poly(L-2-hydroxybutanoic acid), poly(D-2-hydroxybutanoic acid), and poly(D-lactic acid) from the melt

Ternary stereocomplex (TSC) crystallization of optically active polyesters, L-configured poly(L-2-hydroxybutanoic acid) [P(L-2HB)], D-configured poly(D-2-hydroxybutanoic acid) [P(D-2HB)] and poly(D-lactic acid) (PDLA) from the melt 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 crystallization in the blends from the melt was investigated using wide-angle X-ray diffractometry and differential scanning calorimetiy. For all the crystallization temperature (T-c) range of 60-180 degrees C, the interplane distances of melt-crystallized blends estimated from the 2 theta values at around 11 degrees and 22 degrees and the melting temperatures of stereocomplex increased continuously with increasing the P(D-2HB) content relative to that of PDLA in the blends. This result indicates that the crystallization of ternary stereocomplex and the continuous changes of stereocomplex lattice dimensions, irrespective of T-c. The equilibrium melting temperature values of TSC crystallites increased continuously with increasing the content of P(D-2HB) relative to that of PDLA. For all the T-c, the higher crystallinity values of SC crystallites in the ternary blends compared to those of the binary blends strongly suggested the relatively random incorporation or no strict selection of D-configured P(D-2HB) and PDLA, resulting in higher crystallinity of ternary stereocomplex in the limited period of time of isothermal crystallization compared to those of binary P(L-2HB)/PDLA hetero-stereocomplex in P(L-2HB)/PDLA blends and P(L-2HB)/P(D-2HB) homo-stereocomplex in P(L-2HB)/P(D-2HB) blends. (C) 2013 Elsevier Ltd. All rights reserved.