Probing the Influence of Polymer Architecture on Liquid−Liquid Phase Transitions of Aqueous Poly(N,N-dimethylacrylamide) Copolymer Solutions

Thermosensitive poly(N,N-dimethylacrylamide-co-N-phenylacrylamide) (DMA-co-PhAm) copolymers were prepared by atom transfer radical polymerization (ATRP) in methanol/water mixtures at room temperature with methyl 2-chloropropionate as the initiator and CuCl/Me6TREN as the catalyst. The resultant DMA-co-PhAm copolymers had tailored compositions and controlled molecular weights, and their aqueous solutions underwent liquid−liquid phase separation upon heating. These phase transition temperatures, measured by the cloud point method, were dependent on polymer concentrations, compositions, and molecular weights. The efficiency of the thermally induced liquid−liquid phase transition, i.e., the yield of phase-separated polymer, increased with increasing solution temperature, suggesting this thermally induced liquid−liquid phase transition to be a continuous equilibrium process. The efficiency of phase separation could be enhanced by adding NaCl to the solution.