Initiation of free-radical polymerization by hexakis (phenylisocyano) derivatives of metals of group 6

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Abstract
This paper describes studies of the initiation of the free-radical polymerization of methyl methacrylate by the hexakis(phenylisocyano) derivatives of Cr, Mo, W in the presence of carbon tetrachloride. In addition to the kinetics of initiation, changes in optical density accompanying the reactions have been investigated. The polymerization kinetics resemble those found with many initiating systems based on metal carbonyls, but are more complicated in that the rate of polymerization decreases rapidly in the early stages of reaction. The optical density at 25° C behaves similarly. A kinetic study suggests that these observations are attributable to the comparatively rapid transformation of the original derivative, through a carbonyl-type mechanism involving monomer and CCl4, into a new complex (III) without radical formation. The latter complex, which contributes to the optical density, is itself a free-radical initiator, but decomposes more slowly than the phenylisocyano derivative giving rise to a prolonged polymerization. Most of the initial phenylisocyano complex forms (III) on reaction, only a minor portion giving free radicals. Carbon monoxide increases the rates of polymerization somewhat, while greatly increasing the rate of decay of optical density, presumably by reducing the concentration of (III).

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