Abstract:

Poly(L-lactide)-poly(ethylene glycol)(PLLA-PEG) diblock copolymers were characterized by ¹H NMR, SEC, XRD and DSC. Depending on the composition, one or two melting peaks were detected although both components were intrinsically semi-crystalline. A copolymer with equivalent block lengths was selected for melt crystallization studies by DSC and POM. The experimental data were calculated with Avrami equation. On the other hand, the crystallization characteristics of PLLA-PEG were analyzed by using Lauritzen-Hoffmann theory. The nucleation constant K_g(POM) was found to be 5.23×10⁵ K₂ in the temperature range from 343 to 367 K. Both values of K_g and fold surface free energy σ_e of the copolymer are higher than those of the PLLA homopolymer, which suggests that the crystallization behavior of PLLA is affected by the presence of PEG block, nucleation being more difficult in the case of the copolymers.

Key words: Poly(L-lactide), Poly(ethylene glycol), Block copolymers, Melt crystallization