Degradable poly(ethylene oxide) through metal-free copolymerization of ethylene oxide with l-lactide†
A simple and convenient method for the preparation of degradable poly(ethylene oxide) (PEO) is presented in this work. Through metal-free copolymerization of ethylene oxide with L-Lactide (LLA), very low content of LLA could be randomly incorporated into the backbone of PEO in the presence of triethylborane. In the presence of the latter Lewis acid, the reactivity of LLA could be curtailed, and transesterification reactions suppressed. The copolymerization of EO with LLA resulted in P(EO-co-LLA) samples of low to moderate content in ester units, and of controlled molar mass and low dispersity value. Reactivity ratios were determined using the non-terminal model (Beckingham-Sanoja-Lynd BSL equation) and the terminal model (Meyer–Lowry ML equation), respectively. The NMR characterization of the copolymer samples conbined with the kinetic treatment shows that non-terminal model describes adequately the copolymerization of EO with LLA. The resulting copolymers were further studied by differential scanning calorimetry (DSC); hydrolysis experiments were carried out to show the degradability of the prepared PEO samples containing a few percentage of ester units.