Random, thermoresponsive copolymers of 2-hydroxyethyl methacrylate (HEMA) and oligo(ethylene glycol) methyl ether methacrylate M n = 300 (OEGMA) were synthesized via atom transfer radical polymerization (ATRP) in a DMSO/H2O solvent mixture. Reactivity ratios were determined by the extended Kelen-Tudos method and found to be close to 1. Studies confirmed the randomness of the obtained copolymers. The thermoresponsiveness in water and in phosphate buffer (PBS) solutions and the influence of copolymer composition and solution concentration on the cloud point temperature (T cp) were investigated. Phase transitions in water solutions were reversible and narrow. The response of P(HEMA-co-OEGMA) to temperature could be adjusted in the range from 66.5 °C to 21.5 °C by changing the HEMA content. In PBS solutions, significant differences in the heating/cooling cycle were observed for all investigated concentrations. The presence of kosmotropic salts in PBS decreased the T cp value and caused thermal aggregation of chains to form a macroscopic aggregate at temperatures above the T cp.
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