Visible-light induced controlled radical polymerization of methacrylates with Cu(dap)2Cl as a photoredox catalyst

Abstract

With ethyl-α-bromophenylacetate (EBPA) as an initiator and Cu(dap)₂Cl (dap = 2,9-bis(p-anisyl)-1,10-phenanthroline) as a photoredox catalyst, controlled radical polymerizations of poly(ethylene glycol)methyl ether methacrylate (PEGMA) and methyl methacrylate (MMA) are demonstrated under LED light lamp irradiation (4500 μW cm⁻²@420 nm). The catalysis cycles proceed in the presence of N,N-dimethylaniline (DMA) or tris[2-(dimethylamino)ethyl]amine (Me₆TREN), which could serve as reductants to regenerate a Cu(I) complex from the oxidized Cu(II) complex. In addition, Me₆TREN plays another important role as an efficient ligand for the copper-based photopolymerization of methacrylate monomers. Good linear evolution of molecular weight (M_n) with monomer conversion is observed under the optimized conditions. Specifically, with [PEGMA] : [EBPA] : [Cu(dap)₂Cl] : [Me₆TREN] = 31 : 1 : 0.015 : (0.15–0.45), poly(PEGMA) (PPEGMA) with polydispersity indexes (PDI) as low as 1.15 are obtained. To further verify the living nature of this system, block copolymers of PPEGMA-b-PMMA with high molecular weights and narrow molecular weight distributions (M_n,GPC = 59 200 g mol⁻¹, PDI = 1.28 and M_n,GPC = 93 700 g mol⁻¹, PDI = 1.44, respectively) are prepared using PPEGMA-Br (M_n,GPC = 11 600 g mol⁻¹; PDI = 1.13) as a macroinitiator. The polymers produced with Cu(dap)₂Cl/Me₆TREN as a catalyst and the PMMA obtained with Cu(dap)₂Cl/DMA as a catalyst are colorless which is different from the heterogeneously catalyzed ATRP for its notorious Cu metal residue.