Synthesis of Thermosensitive Water-Soluble Polystyrenics with Pendant Methoxyoligo(ethylene glycol) Groups by Nitroxide-Mediated Radical Polymerization

Abstract

Nitroxide-mediated radical polymerizations of 4-vinylbenzyl methoxytris(oxyethylene) ether (TEGSt), 4-vinylbenzyl methoxytetrakis(oxyethylene) ether (TrEGSt), and 4-vinylbenzyl methoxypentakis(oxyethylene) ether (PEGSt) were carried out at 120 °C using 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane as initiator. Kinetics study and gel permeation chromatography analysis showed that the polymerizations were living processes yielding polymers with controlled molecular weights and narrow molecular weight distributions. The polymers can be dissolved in water forming transparent solutions and undergo phase transitions when the temperature is above a critical point. The cloud points of the homopolymers of TEGSt, TrEGSt, and PEGSt were around 13, 39, and 55 °C, respectively, which were also supported by variable temperature 1H NMR spectroscopy analysis. The high level of alkoxyamine chain end retention allowed the synthesis of diblock copolymers with low polydispersities (<1.15). Cloud point measurements and 1H NMR studies indicated that the diblock copolymers undergo phase transition in water at a temperature between the cloud points of the two corresponding homopolymers.