Effects of soft segments and hydrolysis on the crystallization behavior of degradable poly(oxyethylene)/poly(<scp>L</scp>‐lactide) block copolymers

Abstract

Abstract The crystallization behavior of poly(oxyethylene) (PEG)/poly( L ‐lactide) (PLLA) block copolymers with PEG (number‐average molecular weights M n = 1000–6000) contents ≦ 18,3 wt.‐% has been studied under different isothermal temperature and linear cooling conditions. A differential scanning calorimeter was used to monitor the energetics of the crystallization process from the melt state. The influence of copolymer composition and hydrolysis on radial growth rates of spherulites, G , in PEG/PLLA copolymer was investigated using polarized light video‐microscopy. The data were analyzed in terms of a model describing two processes, namely crystal nucleation and growth which were observed experimentally in a typical Avrami plot for the isothermal data. At a given crystallization temperature, G 's are increased with increasing PEG content and with decreasing PEG segment length in PEG/PLLA copolymer spherulites. The Avrami exponent n and rate coefficient k of PEG/PLLA copolymers decrease with increasing hydrolysis time up to 200 h. The spherulite morphology appeared to be a complex function of copolymer composition, hydrolysis time and crystallization temperature.