Pyrrolidone-Functional Smart Polymers via Nitroxide-Mediated Polymerization

Nitroxide-mediated polymerization (NMP) of N-(2-methacryloyloxyethyl) pyrrolidone (MAEPYR) with 2-([tert-butyl[1-(diethoxyphosphoryl)-2,2-diethylpropyl]amino]oxy)-2-methylpropanoic acid (BlocBuilder) initiator and N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] (SG1) nitroxide permitted controlled synthesis of poly(N-(2-methacryloyloxyethyl)-pyrrolidone-stat-9-(4-vinylbenzyl)-9H-carbazole) (poly(MAEPYR-stat-VBK)) statistical copolymers. With at least 5 mol % VBK, the dispersity D of the copolymers was below 1.4 at conversions less than 50%. At conversions higher than 50%, and at lower VBK feed content, there was a significant amount of termination reactions, which broadened the molecular weight distribution of the final polymers (D = 1.4-2.3). The MAEPYR-rich statistical copolymers were subsequently tested for thermoresponsive behavior in aqueous media. The cloud point temperatures (CPTs) in aqueous solution were tuned by changing the VBK composition, solution concentration, and heating rate, and the transitions were thermally reversible with partial loss of reversibility at higher heating rates. The CPT decreased from 59.0 to 49.7 C with addition of only 1 mol % of VBK in the copolymer, and at more than 6 mol % VBK, the copolymer was water insoluble.