Crystallization Studies on the Stereocomplexation of Poly(?-lactide) / 4-Armed Poly(& epsilon;-caprolactone-co-d,?-lactide)- block-poly(d-lactide) Blends

A series of four-armed poly(& epsilon;-caprolactone-co-d,?-lactide)-block-poly(d-lactide) (4a-CDL-D) copolymers with different poly(d-lactide) (PDLA) block lengths (M-n,M-PDLA) were synthesized via ring opening polymerization using pentaerythritol as initiator. They were blended with poly(?-lactide) (PLLA) to improve its crystallization rate and mechanical properties. It was found that the crystallization of PLLA in the PLLA/4a-CDL-D blend was affected differently when M-n,M-PDLA changed. In the PLLA/4a-CDL blend without PDLA blocks, the crystallization was retarded obviously because of the dilution effect of 4a-CDL on PLLA crystallization. Interestingly, a crystallization acceleration effect was found when M-n,M-PDLA was 0.5k although no stereocomplex (SC) crystallites existed. When M-n,M-PDLA was 1k or higher (1.5k and 2k), SC crystallites could be formed in the PLLA/4a-CDL-D blends. However, when M-n,M-PDLA was 1k or 1.5 k, the formation of SC crystallites was difficult and they showed weaker acceleration effect on PLLA crystallization. While when M-n,M-PDLA was 2k, the crystallization of PLLA was accelerated markedly due to the significant increase of nucleation sites. At last, these blends had longer elongation at breaks than neat-PLLA. This work provided a novel method for the acceleration of PLLA crystallization by adjusting the PDLA chain length in PLLA blends.