The ongoing development of new methods for the synthesis of polymers of complex architecture has led to a continuing interest in controlled/living polymerization. Inspired by rapid progress in photoredox catalysis, a few research groups (e.g., Hawker, Boyer, Boydston) have recently begun to explore the application of these systems for controlled polymerization.
In a collaboration with Prof. Dave Nicewicz (UNC Chapel Hill), we carried out initial studies into the methanol-controlled visible light photoinitiated polymerization of 4-methoxystyrene using pyrylium salts. First order kinetic behavior, linear Mn growth with respect to monomer consumption, narrow Ð, and continued polymerization upon monomer addition all indicate the controlled/living nature of the polymerization. The accumulated data suggest methanol plays a role as a reversible chain transfer agent, analogous to that of dithiocarbamates in RAFT polymerization. The polymerization does not require the use of strong Lewis or Brønsted acids or the prior synthesis or formation of small molecule co-initiators. Poly(4-methoxystyrene) of low Ð can be prepared, with Mn controlled by the concentration of methanol.
Furthermore, we are actively pursuing general approaches to precisely control the synthesis of conjugated polymers at full scale (structure, sequence, molecular weight and dispersity), aiming for next generation production and application of high performance materials.
Photoinitiated, Living Cationic Polymerization