Acetone–water biphasic mixtures as solvents for ultrafast SET-LRP of hydrophobic acrylates

Abstract

Acetone is an excellent solvent for polymers including poly(acrylate)s and a well understood and established reagent for organic synthesis. Therefore, it is surprising that being also the least expensive organic solvent after methanol, so far it has not become a common solvent for metal catalyzed living radical polymerizations. Here we report the elaboration of acetone–water biphasic mixtures as solvents for ultrafast single electron transfer living radical polymerization (SET-LRP) that provides close to 100% conversion of methyl and n-butyl acrylates to the corresponding polymers with near quantitative chain-end functionality in 20 to 35 min reaction time at room temperature. Two methodologies were elaborated for this process. The first involves the generation of Cu(0) nano-colloidal particles as catalysts via the in situ reduction of Cu(II)Br₂ with NaBH₄ by two different procedures. The second involves the use of non-activated Cu(0) wire as a catalyst. Control experiments for the organic reactions of acetone and monomers with CuBr₂ and other reagents have been used to eliminate the bromination of acetone and monomers, the aldol condensation of acetone, and the hydrolysis of CuBr₂ to Cu(OH)₂. Control experiments have also established that the most probable deactivating species, at least in the case of the first methodology, may not be CuBr₂, but bromocuprates. Addition of tetra-n-butylammonium bromide was found to increase the linearity of the first order kinetic plots of the first SET-LRP process. We expect that these results will help establish acetone and other ketones as common solvents for metal catalyzed LRPs of both hydrophobic and hydrophilic monomers.