Triblock copolymers of lactide with poly(ethylene glycol) and influence of stereochemical composition
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Polymerization of L-lactide (LLA) and poly(ethylene glycol) (PEG) at 120°C using stannous 2-ethyl hexanoate results in ABA triblock copolymers in good yields. The glass transition temperature of the copolymers shows strong dependence on the composition. One- and two-phase triblock copolymers can be prepared by controlling the molecular weight of the PEG soft block, as well as the initial LLA/PEG charge ratio. Incorporation of racemic lactide during polymerization drastically affects the crystallinity of the block copolymers obtained. 1H and 13C (solid state) NMR are powerful tools for characterization of the polymer materials.