Isothermal Crystallization Behavior of the Poly(L-lactide) Block in Poly(L-lactide)-Poly(ethylene glycol) Diblock Copolymers: Influence of the PEG Block as a Diluted Solvent



Junliang Yang1), Ting Zhao1), Leijing Liu1), Yunchun Zhou1), Gao Li1), Enle Zhou1) and Xuesi Chen1)

1) State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Graduate School of Chinese Academy of Sciences, Chinese Academy of Sciences

ABSTRACT:  Isothermal crystallization kinetics and morphology of the poly(L-lactide) block in poly(L-lactide)-poly(ethylene glycol) diblock copolymers were studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The results were compared with that of the PLLA homopolymer. The introduction of the PEG block accelerated the crystallization rate of the PLLA block and promoted to form ring-banded spherulites. The analysis of isothermal crystallization kinetics has shown that the PLLA homopolymer accorded with the Avrami equation. But the PLLA block of the diblock copolymers deviated from the Avrami equation, which resulted from increasing of the crystallization rate and occurring of the second crystallization process. The equilibrium melting temperature (Tmo) of the PLLA block fell with its molecular weight decreasing. The conditions to obtain more regular ring-banded spherulites were below: the sample was the PLLA block of LA5EG5; the crystallization temperature was about from 95 °C to 100 °C, which almost corresponded to regime II.

KEY WORDS  Isothermal Crystallization/ Diluted Solvent/ PLLA Block/ PEG Block/ Ring-banded Spherulites