Polymerization of styrene in alcohol/water mediated by a macro-RAFT agent of poly(N-isopropylacrylamide) trithiocarbonate: From homogeneous to heterogeneous RAFT polymerization

The reversible addition fragmentation chain transfer (RAFT) polymerization of styrene in alcohol/water mixture mediated with the poly(N-isopropylacrylamide) trithiocarbonate macro-RAFT agent (PNIPAM-TTC) is studied and compared with the general RAFT dispersion polymerization in the presence of a small molecular RAFT agent. Both the homogeneous/quasi-homogeneous polymerization before particle nucleation and the heterogeneous polymerization after particle nucleation are involved in the PNIPAM-TTC-mediated RAFT polymerization, and the two-stage increase in the molecular weight (Mn) and nanoparticle size of the synthesized block copolymer is found. In the initial homogeneous/quasi-homogeneous polymerization, the Mn and nanoparticle size slowly increase with monomer conversion, whereas the Mn and particle size quickly increase in the subsequent heterogeneous RAFT polymerization, which is much different from those in the general RAFT dispersion polymerization. Besides, the PNIPAM-TTC-mediated RAFT polymerization runs much faster than the general RAFT dispersion polymerization. This study is anticipated to be helpful to understand the polymer chain extension through RAFT polymerization under dispersion conditions. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012