Enhanced Formation of Stereocomplex Crystallites of High Molecular Weight Poly(l-lactide)/Poly(d-lactide) Blends from Melt by Using Poly(ethylene glycol)

Abstract

Melt processing of polymers is preferable in industry. Unfortunately, for high molecular weight (Mw) poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends, exclusive formation of stereocomplex (sc) crystallites from the melt has never been achieved. We proposed a new and simple approach to enhance the melt crystallization of sc crystallites from high Mw PLLA/PDLA by using poly(ethylene glycol) (PEG). The crystallizability of the PLLA/PDLA blend is greatly enhanced by PEG during crystallization from the melt. The resulted crystalline structures depend on the Mw and content of PEG, and the crystallinity of sc crystallites increases with increasing content or decreasing Mw of PEG. More importantly, exclusive formation of sc crystallites is achieved in the blends with 10% PEG having Mw values of 1000 or 2000 g mol–1. Polarized optical microscopy (POM) observation shows that the spherulitic growth rates of sc crystallites are accelerated. The results demonstrate that segmental mobility of polylactides (PLA) chains plays a dominant role on the formation of sc crystallites from melt and provide a simple way to prepare sc crystallites from high Mw PLA by melt blending and enlarge the applications of PLA.