Synthesis of Poly(lactide) Blends by Melt/Solid Polycondensation

Different blend compositions of amorphous poly(D,L-lactic acid) (PDLLA) and crystalline poly(L-lactic acid) (PLLA) of various molecular weights are prepared in one step by melt/solid polycondensation in the presence of different concentrations of either SnCl ₂ ·2H ₂ O/p-toluene sulfonic acid (PTSA) 1 : 1 or Sb ₂ O ₃ as a catalyst. The prepared blends are characterized using differential scanning calorimeter (DSC) and gel permeation chromatography (GPC). The results confirm that using a monomer source in the form of a non-racemic D,L-lactic acid mixture leads to PLA containing both amorphous (DL-based) PLA and crystalline (L-based) PLA. In addition, the polymers prepared in the presence of Sb ₂ O ₃ as a catalyst acquire higher molecular weights (two- or three-fold) with respect to the comparable polymers prepared from a pure L-lactic acid source. The molecular weight measurements of the samples after exposure to degradation medium (phosphate buffer pH 7.4 at 37 ^° C) prove that the degradation occurs preferentially in the amorphous part.