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 °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 °C using the above-synthesized PNMP polymer as a macromolecular chain transfer agent. Temperature-variation 1 H 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 D 2 O at ambient temperature, e.g. 22 °C. Upon elevating the solution temperature, the dehydration process of this fully hydrated PNMP polymer was triggered at 46.1 °C, leading to a dramatic decrease of integral ratios of proton resonance signals of PNMP to that of D 2 O. Further elevating the solution temperature to 51.9 °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.

Highly efficient and well‐controlled ambient temperature reversible addition–fragmentation chain transfer (RAFT) polymerization is readily carried out under environmentally friendly mild solar radiation. This discovery has significantly extended studies from man‐made separated‐spectroscopic‐emission UV‐vis radiation (Macromolecules 2006, 39, 3770) to natural continuous‐spectroscopic‐emission solar radiation for ambient temperature RAFT polymerization.

Early in 1998, Davis and co-workers 1 reported the synthesis of N-(2-methacryloyloxyethyl)pyrrolidone; this monomer was polymerized in bulk under nitrogen using azobis(isobutyronitrile) (AIBN) initiator at 60°C. Elvira and co-workers also reported the polymerization and random copolymerization of this monomer with methyl methacrylate using AIBN initiator in DMF solution at 60°C. 2According to the literature as reported by Davis and co-workers, 1 this polymer is water-soluble at room temperature and exhibits a lower critical solution temperature (LCST) in the range 29-33°C. As comparison, our experimental results reveal that this polymer exhibits a higher LCST, covering a wider range from 71.5 to 52.8°C, as increasing the weight-average molecular weight from 20.6 to 105.4 kg mol. This difference is most presumably caused by the differences in molecular weights and distributions. Under conventional radical polymerization conditions, the molecular weights and distributions of polymers are ill-controlled, giving a polymer with wide molecular weight distribution. The polymers with large molecular weights first phase separate on elevating the solution temperature, leading to a relatively low LCST. However, under mild conditions of visible light radiation at 30°C, using a (2,4,6-trimethylbenzoyl)diphenylphosphine oxide photoinitiator, RAFT polymerization of this monomer was well controlled, giving a polymer with quite narrow molecular weight distributions (M w /M n <1.20).