Investigating 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) system depends on the judicious selection of solvents that fully dissolve 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 active ATRP ligand, poly(ethylene glycol)-300-methyl methacrylate and alkyl ammonium bromide–based ionic liquid monomers, with anisole employed as a solvent pair to broaden the solubility range and improve the sustainability of the TPSC-based ICAR ATRP system. The assessment of this system's kinetic studies at 5000 ppm CuBr2 catalyst loading exhibited excellent polymerization control, reaching 92% monomer conversion in 7 h and narrow Mw/Mn ≤ 1.38 at 80 ℃. 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 leached metal residue from 10.3 to 3.4 ppm, although the recycling efficiency declined further to 73.2% after five cycles. Meanwhile, at higher AIBN concentrations, polymerization control slightly decreased, as indicated by moderate deviations of Mn,GPC from Mn,th despite maintaining narrow Mw/Mn ˂ 1.5. These results have 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.