Living radical polymerization of methyl methacrylate with a rhodium(III) complex-organic halide system in dimethyl sulfoxide

The polymerization of methyl methacrylate (MMA) with the rhodium(III) complex dihydrido(1,3-diphenyltriazenido)bis(triphenylphosphine)rhodium(III) [RhH2(Ph2N3)(PPh3)(2)] as a catalyst and an organic halide (CCl4, BrCCl3, or CBr4) as an initiator in dimethyl sulfoxide (DMSO) was studied. For the CCl4 initiator system, a kinetic study of MMA polymerization indicated that polymerization follows first-order kinetics with respect to the monomer and that the number-average molecular weight (M.) of the polymers produced increases in direct proportion to the monomer conversion. Monomer-addition experiments showed that after addition of further MMA, the M-n of the polymers continues to increase in direct proportion to the monomer conversion. These results confirmed that the polymerization of MMA in the CCl4-initiated system proceeds in a living radical manner. In contrast, the systems involving the bromo compounds BrCCl3 or CBr4 did not show such a living radical nature. For all these initiator systems, the polymers produced had broad molecular-weight distributions. The catalytic activities are discussed in relation to the reaction product between RhH2(Ph2N3)(PPh3)(2) and DMSO.