| Reversible addition-fragmentation chain transfer, a living radical polymerization was used successfully to synthesize poly(N -isopropylacrylamide) (PNIPAAm), poly(methacrylic acid) (PMAA) and their block copolymers. The homopolymerization of PNIPAAm and PMAA demonstrated living characteristics that include constant number of propagating chains, linearly increasing Mn with conversion, controlled Mn, low polydispersity (PDI), and polymers that can be re-activated to produce block copolymers. The RAFT agent, carboxymethyl dithiobenzoate, proved to control Mn and PDI in a manner that improved with increasing concentration but showed evidence of having a relatively low chain transfer constant as well as degradation during polymerization. The block copolymers displayed temperature reversible characteristics at a LCST of 31°C. At a 5 wt % concentration in pH 7.4 PBS, the copolymers form gels above the LCST. At the low PMAA content of these copolymers, however, the gels showed undesirable syneresis. This work is the first report on the successful synthesis of linear block copolymers of PNIPAAm and PMAA in solution. |
