Initiation of Free Radical Polymerization by Manganese Carbonyl and Carbon Tetrachloride

Abstract

INITIATION of free radical polymerization by metal carbonyls in the presence of organic halides has been shown, in all cases studied, to involve a rate determining primary activation of the carbonyl, in which the halide does not participate1,2. In the system Mn2(CO)10+CCl4+monomer, the monomer does not enter into this process2, which would therefore seem likely to consist either of scission of carbon monoxide from the carbonyl molecule or rupture of the metal–metal bond. After considering both possibilities, we concluded that experimental data from polymerization studies favour the former2. Wawersik and Basolo reached a similar conclusion for substitution reactions of manganese carbonyl3. On the other hand, Hopgood and Poe reported that substitution, oxidation and decomposition reactions of Mn2(CO)10 involve primary fission of the manganese–manganese bond4, although more recently Haines and Poe have stated that carbon monoxide-scission contributes an additional rate determining step5. Haines and Poe therefore propose5 that in the initiation of polymerization both primary steps occur, giving rise to two independent mechanisms, A and B.