Novel glycolides with pendent oligo(ethylene oxide) monomethyl ether substituents were synthesized. Subsequent ring-opening polymerization using 4- tert -butylbenzyl alcohol as the initiator and Sn(2-ethylhexanote) 2 as the catalyst yielded homogeneous oligo(ethylene oxide)-grafted polylactides with high molecular weights and low polydispersities. Polymers with short oligo(ethylene oxide) chains (1 or 2 ethylene oxide repeat units) are more hydrophilic than polylactide but insoluble in water, whereas polymers having 3 or 4 ethylene oxide repeat units are water-soluble. Aqueous solutions of polymers with 3 and 4 ethylene oxide repeat units in each pendent chain are thermoresponsive, with lower critical solution temperatures (LCSTs) at 19 and 37 °C, respectively. The LCST transitions were confirmed by cloud point measurements, variable temperature dynamic light scattering, and changes in line widths measured by variable temperature 1 H NMR spectroscopy.
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Jiang et al. (2007) studied this question.
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