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Thermoresponsive Brush Copolymers with Poly(propylene oxide-ran-ethylene oxide) Side Chains via Metal-Free Anionic Polymerization "Grafting From" Technique
Pispas, Stergios
Zhang, Guangzhao
Thermoresponsive brush copolymers with poly(propylene oxide-ran-ethylene oxide) side chains were synthesized via a "grafting from" technique. Poly(p-hydroxystyrene) was used as the backbone, and the brush copolymers were prepared by random copolymerization of mixtures of oxyalkylene monomers, using metal-free anionic ring-opening polymerization, with the phosphazene base (t-BuP(4)) being the polymerization promoter. By controlling the monomer feed ratios in the graft copolymerization, two samples with the same side-chain length and different compositions were prepared, both of which possessed high molecular weights and low molecular weight distributions. The results from light scattering and fluorescence spectroscopy indicated that the brush copolymers in their dilute aqueous solutions were near completely solvated at low temperature and underwent slight intramolecular chain contraction/association and much more profound intermolecular aggregation at different stages of the step-by-step heating process. Above 50 degrees C, very turbid solutions, followed by macrophase separation, were observed for both of the samples, which implied that it was difficult for the brush copolymers to form stable nanoscopic aggregates at high temperature. All these observations were attributed, at least partly, to the distribution of the oxyalkylene monomers along the side chains and the overall brush-like molecular architecture.
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