Enhancing the recrystallization ability of bio-based polylactide stereocomplex by in situ construction of multi-block branched conformation

To enhance the formation and regeneration ability and the toughness of stereocomplex polylactide (sc-PLA), a high molecular weight stereocomplex branched multi-block polylactide (sb-PCLDA) was synthesized from d-lactide, l-lactide and poly(e-caprolactone) diol (PCL). High molecular weight sc-PLA has attracted much attention in bioengineering because of its good mechanical and thermal properties, but its brittleness and the poor regeneration ability of the sc crystallites hindered the practical processability, that is, the mixed homochiral and sc crystallites would form in the sc-PLA products after the complete melting and recrystallization processing. The high molecular weight sc-PLA which is easy to form complete stereocomplex and suitable for melt processing needs further research. Herein, sb-PCLDA having PCL, PLLA and PDLA segments on one molecular chain has been synthesized by polymerization of l-lactied and d-lactide with PCL and in situ hydrolysis condensation with silane coupling agents. Differential scanning calorimetry and wide angle X-ray diffraction indicated that sb-PCLDA formed complete sc with high crystallinity and exhibited good sc reformulation ability after multiple melting, suggesting much improved processability. Meanwhile, the sb-PCLDA maintained good thermal properties and hydrolysis resistance. The polymer exhibited significant tensile toughness with an elongation at break of 185%. This facile method could simultaneously improve the mechanical property and recrystallization ability of sc-PLA.