Relationship between the crystallization behavior of poly(ethylene glycol) and stereocomplex crystallization of poly(L-lactic acid)/poly(D-lactic acid)

Poly(l-lactic acid) (PLLA) is a good biomedical polymer material with wide applications. The addition of poly(ethylene glycol) (PEG) as a plasticizer and the formation of stereocomplex crystals (SCs) have been proved to be effective methods for improving the crystallization of PLLA, which will promote its heat resistance. In this work, the crystallization behavior of PEG and PLLA/poly(d-lactic acid) (PDLA) in PLLA/PDLA/PEG and PEG-b-PLLA/PEG-b-PDLA blends has been investigated using differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. Both SCs and homocrystals (HCs) were observed in blends with asymmetric mass ratio of PLLA/PDLA, while exclusively SCs were observed in blends with approximately equal mass ratio of PLLA/PDLA. The crystallization of PEG was only observed for the symmetric blends of PLLA(39k)/PDLA(35k)/PEG(2k), PLLA(39k)/PDLA(35k)/PEG(5k), PLLA(69k)/PDLA(96k)/PEG(5k) and PEG-b-PLLA(31k)/PEG-b-PDLA(27k), where the mass ratio of PLLA/PDLA was approximately 1/1. The results demonstrated that the formation of exclusively SCs would facilitate the crystallization of PEG, while the existence of both HCs and SCs could restrict the crystallization of PEG. The crystallization of PEG is related to the crystallinity of PLLA and PDLA, which will be promoted by the formation of SCs. (c) 2017 Society of Chemical Industry