Premium
Investigations on the morphology and melt crystallization of poly( L ‐lactide)‐poly(ethylene glycol) diblock copolymers
Author(s) -
Wu Tong,
He Yong,
Fan Zhongyong,
Wei Jia,
Li Suming
Publication year - 2008
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.20955
Subject(s) - materials science , copolymer , spherulite (polymer physics) , polymer chemistry , ethylene glycol , nucleation , crystallization , crystallinity , avrami equation , chemical engineering , composite material , polymer , thermodynamics , crystallization of polymers , physics , engineering
Abstract Ring opening polymerization of L ‐lactide was realized in the presence of monomethoxy poly(ethylene glycol), using zinc lactate as catalyst. The resulting PLLA‐PEG diblock copolymers were characterized by using 1 H‐NMR, SEC, WAXD, and DSC. All the copolymers were semicrystalline, one or two melting peaks being detected depending on the composition. Equilibrium melting temperature ( T m 0 ) of PLLA blocks was determined for three copolymers with different EO/LA molar ratios. T m 0 decreased with decreasing PLLA block length. A copolymer with equivalent PLLA and PEG block lengths was selected for melt crystallization studies and the resulting data were analyzed with Avrami equation. The obtained Avrami exponent is equal to 2.6 ± 0.2 in the crystallization temperature range from 80 to 100°C. In addition, the spherulite growth rate of PLLA‐PEG was analyzed by using Lauritzen‐Hoffmann theory in comparison with PLLA homopolymers. The nucleation constant was found to be 2.39 × 10 5 K 2 and the free energy of folding equal to 53.8 erg/cm 2 in the range of 70–94°C, both higher than those of PLLA homopolymers, while the spherulite growth rate of the diblock copolymer was lower. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers