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

Melt processing of polymers is preferable in industry. Unfortunately, for high molecular weight (M-w) 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 M-w 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 M-w and content of PEG, and the crystallinity of sc crystallites increases with increasing content or decreasing M-w of PEG. More importantly, exclusive formation of sc crystallites is achieved in the blends with 10% PEG having M-w 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 M-w PLA by melt blending and enlarge the applications of PLA.