Investigating an anisole/Cu(ii)-macroligand-complex pair to broaden solubility scope and catalyst recycling for atom transfer radical polymerization

Abstract

The performance of thermoregulated, phase-separable catalysis-based initiators for continuous activator regeneration atom transfer radical polymerization (TPSC-based ICAR ATRP) systems depends on the judicious selection of solvents that fully dissolve the polymers while enabling efficient catalyst separation and recycling after polymerization. Herein, an active poly(ionic liquid) macroligand, PILLL1, was synthesized via free-radical polymerization of an active ATRP ligand, poly(ethylene glycol)-300-methyl methacrylate and alkyl ammonium bromide-based ionic liquid monomers, with anisole employed as a solvent to broaden the solubility range and improve the sustainability of the TPSC-based ICAR ATRP system. Kinetic studies of this system at 5000 ppm CuBr₂ catalyst loading indicated excellent polymerization control, reaching 92% monomer conversion in 7 h and a narrow M_w/M_n ≤ 1.38 at 80 °C. However, catalyst leaching remained relatively high, ranging from 141 to 189 ppm with a recycling efficiency of 83.9% after five cycles. Interestingly, further optimization at a reduced CuBr₂ loading of 125 ppm significantly decreased the leached metal residue from 10.3 to 3.4 ppm, although the recycling efficiency further declined to 73.7% after five cycles. Meanwhile, at higher AIBN concentrations, polymerization control slightly decreased, as indicated by moderate deviations of M_n,GPC from M_n,th despite maintaining a narrow M_w/M_n < 1.5. These results indicate the potential for developing TPSC-based ATRP systems with high control and recyclability at low catalyst loadings using greener, highly soluble organic solvents as sustainable alternatives.