The initiation of the free radical polymerization of vinyl monomers by hexakis(arylisocyano) derivatives of chromium (o)

The present paper describes studies carried out to determine the effect of structure on the free radical polymerization of vinyl monomers initiated by means of the hexakis(arylisocyano) derivatives of chromium (o) in which chlorine, methoxy, and methyl groups have been substituted into different positions of the benzene ring. The kinetics of the initiation reactions resembles that studied in detail for the parent compound hexakis(phenylisocyano) chromium (o). The observed changes in the initial rates of the polymerization of methyl methacrylate at 80°C in the presence of carbon tetrachloride can be accounted for by the electronic effects associated with these substituents. However, when steric overcrowding occurs, the initial rates of polymerization are reduced considerably. The results obtained confirm the mechanism of initiation proposed earlier in which the rate determining step is the S_n² displacement of an arylisocyano ligand by a monomer or reactive solvent molecule. An attempt has been made to explain the increased rate of radical formation observed when chlorine is substituted into the benzene ring.