RAFT synthesis of poly(N-isopropylacrylamide) and poly(methacrylic acid) homopolymers and block copolymers: Kinetics and characterization

Abstract

Reversible addition-fragmentation chain transfer (RAFT) polymerization was used successfully to synthesize temperature-responsive poly(N- isopropylacrylamide) (PNIPAAm), poly(methacrylic acid) (PMAA), and their temperature-responsive block copolymers. Detailed RAFT polymerization kinetics of the homopolymers was studied. PNIPAAm and PMAA homopolymerization showed living characteristics that include a linear relationship between M̄n and conversion, controlled molecular weights, and relatively narrow molecular weight distribution (PDI < 1.3). Furthermore, the homopolymers can be reactivated to produce block copolymers. The RAFT agent, carboxymethyl dithiobenzoate (CMDB), proved to control molecular weight and PDI. As the RAFT agent concentration increases, molecular weight and PDI decreased. However, CMDB showed evidence of having a relatively low chain transfer constant as well as degradation during polymerization. Solution of the block copolymers in phosphate buffered saline displayed temperature reversible characteristics at a lower critical solution temperature (LCST) transition of 31°C. A 5 wt % solution of the block copolymers form thermoreversible gels by a self-assembly mechanism above the LCST. © 2006 Wiley Periodicals, Inc.