Nickel-catalyzed supported ATRP of methyl methacrylate using cross-linked polystyrene triphenylphosphine as ligand

A new supported catalytic system efficient for synthesizing methacrylate-based (co)polymers is described. This catalyst consists of nickel(II) bromide immobilized onto a polystyrene resin carrying triphenylphosphine moieties (PS-PPh₃/NiBr₂). This system was first used for promoting atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by ethyl 2-bromoisobutyrate (EBr ¹B) in toluene. Used without any additional reagent, this supported catalyst did not promote controlled ATRP of MMA as attested by the low initiation efficiency and the broad polydispersity indices. However, when triphenylphosphine ligand was added, poly(methyl methacrylate) (PMMA) chains of low polydispersity indices were readily recovered, the molecular weight of which linearly increased with monomer conversion and agreed with the expected values. The as-recovered polymers proved to be almost completely deprived of residual transition-metal catalyst. Moreover, the recovered supported transition-metal complex maintained its catalytic activity for additional polymerization reactions without any further addition of fresh catalyst. Only soluble ligand was added in conjunction to monomer, initiator, and solvent to maintain the control over the molecular parameters in terms of molar masses as well as molecular weight distributions.