Acetone-water biphasic mixtures as solvents for ultrafast SET-LRP of hydrophobic acrylates
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 did 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 catalyst 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 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 monomer, 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.