EFFECTS OF SOFT SEGMENTS AND HYDROLYSIS ON THE CRYSTALLIZATION BEHAVIOR OF DEGRADABLE POLY(OXYETHYLENE) POLY(L-LACTIDE) BLOCK-COPOLYMERS

The crystallization behavior of poly(oxyethylene) (PEG)/poly(L-lactide) (PLLA) block copolymers with PEG (number-average molecular weights M(n)BAR = 1000 - 6000) contents less-than-or-equal-to 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.