Stereocomplex mesophase and its phase transition in enantiomeric polylactides

•Stereocomplex mesophase in PLLA/PDLA blends was disclosed.•Formation of stereocomplex mesophase was achieved just above Tg.•Stereocomplex mesophase underwent melting upon heating.•Homocrystals were induced from subsequent re-crystallization.

Stereocomplex mesophase is for the first time disclosed by annealing of 1:1 poly (l-lactide) (PLLA)/poly (d-lactide) (PDLA) blends just above glass transition temperature. Its structure is analogue to that of stereocomplex crystals, as a result of weak intermolecular interactions between PLLA and PDLA chains. In the limited temperature range formation of stereocomplex mesophase is enhanced with annealing temperatures; and its growth is well illustrated by Avrami formula with an index of about 3. Upon heating stereocomplex mesophase begins to melt at temperatures above 80 °C, followed by re-crystallization into homocrystals. The stereocomplex mesophase retards homocrystallization to some extent, since individual PLLA and PDLA chains need to be released from stereocomplex mesophase.

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