Dibromotrithiocarbonate iniferter for concurrent ATRP and RAFT polymerization. effect of monomer, catalyst, and chain transfer agent structure on the polymerization mechanism

An iniferter comprising atrithiocarbonate (TTC) moiety and two bromine chain ends was prepared and used to successfully conduct, independently or concurrently, atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. RAFT polymerization was carried out by self-initiation (styrene, (St)) or in the presence of a thermal initiator (acrylates) and yielded polymers with narrow molecular weight distribution (M-w/M-n <= 1.16 (St) and M-w/M-n <= 1.15 (acrylates)). Methyl methacrylate (MMA) polymerization under these conditions was poorly controlled. However, ATRP of MMA with the dibromotrithiocarbonate (DiBrTTC) iniferter was successful in the presence of copper catalysts formed with various nitrogen-based ligands. Polymers with narrow molecular weight distribution (M-w/M-n < 1.27) were obtained in every case. Depending on the ligand, polymerization proceeded only through the bromine chain ends or through both the bromine chain ends and the TTC moiety, providing the first example of an ATRP with a trithiocarbonate. ATRP and RAFT polymerization of St and n-butyl acrylate (nBA) were conducted concurrently using CuBr/ PMDETA as catalytic system. Polymers with broad molecular weight distribution (M-w/M-n approximate to 1.6) and polymodal size exclusion chromatography traces were obtained due to chain reshuffling through the TTC moiety. SEC analysis of the polymers after aminolysis or methanolysis showed that ATRP and RAFT occurred simultaneously, with good control, for each nBA and St (M-w/M-n < 1.3). Triblock, pentablock, or multiblock copolymers were prepared in two steps by appropriate selection of monomers and catalytic systems.