Effect of triphenyl phosphite on polymerizations initiated by molybdenum carbonyl

Abstract

The kinetic features of the initiation of the free-radical polymerization of methyl methacrylate by the system molybdenum carbonyl + organic halide are greatly modified by the addition of triphenyl phosphite. In general, the phosphite behaves as an inhibitor similar to carbon monoxide; in its presence the rate of polymerization is depressed, the dependence of rate on halide concentration becomes much less sharp, the sensitivity of the system to carbon monoxide is reduced, and inhibition at high carbonyl concentrations is much less marked. All these effects are understandable if triphenyl phosphite deactivates the complex (I) formed by interaction of the carbonyl and monomer. The phosphite is somewhat less efficient than carbon monoxide in this respect, in agreement with its smaller capacity for π-acceptance. When ethyl trichloracetate is the organic halide the phosphite also interacts with a further complex (II) which is the immediate precursor of the initiating radical. The results furnish strong confirmatory evidence for the correctness of the mechanism of initiation previously proposed.