Copper-based supported catalysts for ATRP of methyl methacrylate: how can activity and control be tuned up?

This article is aimed at revisiting the synthesis of copper-based catalysts immobilized onto crosslinked polystyrene (PS) resins carrying pyridinimine groups (PS-pyridinimine/CuBr). These supported catalytic systems were used for promoting the atom transfer radical polymerization of methyl methacrylate as initiated by ethyl-2-bromoisobutyrate. It was evidenced that the control over the polymerization reaction was strongly influenced by the coordination ability and extent of the transition-metal salt on the supported pyridinimine ligands. For instance, increasing the ligand-to-catalyst molar ratio allowed for increasing the polymerization rate and improving the control over the molecular parameters of the synthesized poly(methyl)methacrylate (PMMA) in terms of the molar masses and molecular weight distributions. The PS-pyridinimine/CuBr supported catalyst was recycled and reused for further polymerization reactions. After two recycling steps, the reaction activity appeared to be preserved, and the control was improved in terms of the initiation efficiency. However, a slight increase in the polydispersity indices was observed. Interestingly, the introduction of a flexible polydimethylsiloxane spacer between the PS support and the catalytic sites led to some more improvement of the control over the molecular parameters of PMMA chains, which displayed narrower molecular weight distributions.