A comparative study of the SET-LRP of oligo(ethylene oxide) methyl ether acrylate in DMSO and in H2O

Abstract

A comparative analysis of the SET-LRP of oligo(ethylene oxide) methyl ether acrylate (OEOMEA) in DMSO and in H₂O at 25 °C is reported. Both the catalysis with activated Cu(0) wire/Me₆-TREN and with mimics of “nascent” Cu(0) nanoparticles/Me₆-TREN resulted in a higher rate of polymerization in water than in DMSO. This result is consistent with the acceleration expected for SET-LRP by a more polar reaction solvent, and with the difference between the equilibrium constants of disproportionation of CuBr in DMSO (K_d = 1.4–4.4) and in water (K_d = 10⁶ to 10⁷), both much higher in the presence of Me₆-TREN. The inefficient access of the Cu(0) catalyst to the hydrophobic reactive centers of the monomer and initiator assembled in micellar structures explains the induction time observed in the SET-LRP of OEOMEA in water. This induction period is longer for Cu(0) wire. The use of “nascent” Cu(0) nanoparticles prepared by the disproportionation of CuBr in DMSO, in combination with 5 mol% CuBr₂, led to an extremely efficient SET-LRP of OEOMEA in water. This SET-LRP in water is fast and follows first order kinetics to complete monomer conversion with linear dependence of experimental M_n on conversion, and narrow molecular weight distribution. Under the polymerization conditions investigated in both water and DMSO, no reduction in the absorbance of CuBr₂/Me₆-TREN was observed by online UV-vis spectroscopy. This excludes the formation of CuBr by reduction of CuBr₂ by Cu(0) during the SET-LRP in DMSO and in water.