Living/Controlled Free Radical Polymerization of N-Vinyl Caprolactam

Poly (N-vinylcaprolactam) (PNVCL) is a thermoresponsive polymer with a lower critical solution temperature (LCST) close to body temperature. The hydrolysis of PNVCL does not produce toxic amine compounds. And PNVCL derives from an inexpensive commercially available monomer, N-vinyl caprolactam (NVCL). These make PNVCL and PNVCL-based polymers highly useful for biomedical applications and open perspectives for industrialization. But NVCL is a typical non-conjugated monomer and it can only be polymerized via radical polymerization, thus living/controlled free radical polymerization of NVCL is the only possible means to obtain the desired well-defined polymeric structure. This review summarizes recent advances regarding the living/controlled radical polymerization of N-vinylcaprolactam, including atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and cobalt-mediated radical polymerization (CMRP). The influence of ligands, solvents, and initiators on ATRP of NVCL is introduced. RAFT polymerizations of NVCL are discussed by xanthate-mediated, dithiocarbamate-mediated, dithioester-mediated and trithiocarbonate-mediated controlled radical polymerization. We also highlight recent results in influence of the sequence of monomer addition on synthesis of NVCL-based block copolymers and the controlled synthesis of PNVCL-containing topological macromolecules, such as linear-dendritic block copolymers, star polymers, hyperbranched block copolymers and cyclic polymers obtained by controlled radical polymerization of NVCL. The future directions in living/controlled free radical polymerization of N-vinylcaprolactam are also discussed.