Catalytic effect of DMSO in metal-catalyzed radical polymerization mediated by disproportionation facilitates living and immortal radical polymerizations

DMSO, an interesting solvent for copper-catalyzed living radical polymerization (LRP) mediated by disproportionation, does not exhibit the greatest disproportionation of Cu(I)X into Cu(0) and Cu(II)X-2. Under suitable conditions, DMSO provides 100% conversion and absence of termination, facilitating the development of complex-architecture methodologies by living and immortal polymerizations. The mechanism yielding this level of precision is being investigated. Here we compare Cu(0)-wire-catalyzed LRP of methyl acrylate mediated by disproportionating ligands tris(2-dimethylaminoethyl)amine, Me-6-TREN, tris(2-aminoethyl)amine, TREN, and Me-6-TREN/TREN = 1/1 in presence of eight disproportionating solvents, some more efficient than DMSO in disproportionation. Unexpectedly, we observed that all solvents increased the rate of polymerization when monomer concentration decreased. This reversed trend from that of conventional LRPs demonstrates catalytic effect for disproportionating solvents. Above a certain concentration, the classic concentration-rate dependence was observed. The external order of reaction of the apparent rate constant of propagation, k(p)(app) on solvent concentration demonstrated the highest order of reaction for the least disproportionating DMSO. Of all solvents investigated, DMSO has the highest ability to stabilize Cu(0) nanoparticles and therefore, yields the highest activity of Cu(0) nanoparticles rather than their greatest concentration. The implications of the catalytic effect of solvent in this and other reactions were discussed.