Facile synthesis and thermoresponsive behaviors of a well-defined pyrrolidone based hydrophilic polymer

A well-defined pyrrolidone based thermoresponsive polymer, poly [N-(2-methacryloyloxyethyl) pyrrolidone] (PNMP), was synthesized via reversible addition-fragmentation chain transfer radical polymerization or RAFT polymerization of N-(2-methacryloyloxyethyl) pyrrolidone monomer in methanol under a mild visible light radiation at 30 degrees C. The average molecular weights and polydispersity indices of PNMP polymers were characterized by gel permeation chromatography (GPC) and static light scattering analysis. The kinetic studies indicated that this RAFT polymerization exhibited a well-controlled behavior. The living character of this RAFT polymerization was confirmed by the facile synthesis of a series of well-defined PNMP-based block copolymers via RAFT polymerization under this mild visible light radiation at 30 degrees C using the above-synthesized PNMP polymer as a macromolecular chain transfer agent. Temperature-variation H-1 NMR unambiguously revealed that the PNMP polymer with weight-average molecular weight (M-w) of 105.4 kg mol(-1) and polydispersity index (M-w/M-n) of 1.11 was molecularly dissolved in D2O at ambient temperature, e.g. 22 degrees C. Upon elevating the solution temperature, the dehydration process of this fully hydrated PNMP polymer was triggered at 46.1 degrees C, leading to a dramatic decrease of integral ratios of proton resonance signals of PNMP to that of D2O. Further elevating the solution temperature to 51.9 degrees C led to a sharp phase separation of PNMP polymer from aqueous solution. Laser light scattering analyses demonstrated that the cloud point of the PNMP polymer decreased with molecular weight in the M-w range of 20.6-105.4 kg mol(-1). Moreover, this PNMP polymer exhibited a remarkably reversible thermoresponsive dehydration/hydration and phase transition behaviors in aqueous solution. Unlike what was observed in PNIPAM aqueous solution, no hysteresis phenomenon was observed in PNMP aqueous solution during one heating-and-cooling cycle.