Manganese pentacarbonyl chloride as a thermal initiator of free radical polymerization

Abstract

Manganese pentacarbonyl chloride is a new and powerful thermal initiator of free radical polymerization in the presence of low concentrations of additives of “halide” and “non-halide” types. At 60°C it is ten times as active as azobisisobutyronitrile towards methyl methacrylate. With the halide type of additive (e.g. CCl₄), initiation proceeds by halogen atom abstraction, R radicals being generated from RCl. On the other hand, non-halide additives such as C₂F₄ or MeOOCCCCOOMe produce initiating radicals containing a manganese atom e.g.(CO)₅MnCF₂ĊF₂. The corresponding end groups appear in the polymers.

Spectral and other evidence indicates that the initiating species under our conditions is most probably the dimer [graphic omitted] (M = methyl methacrylate). This undergoes a rate determining decomposition to yield manganese chloride and a fragment Mn°M(CO)₃ which subsequently interacts with the additive. When no additive is present, manganese carbonyl [Mn₂(CO)₁₀] is produced from this fragment. Dimer formation is strongly suppressed by carbon monoxide, so that the latter is a powerful inhibitor of polymerization. The energy of activation and frequency factor for initiation are 26.2 kcal mol^–1 and 4.4 × 10¹³ s^–1, respectively.