Photoinitiation of free-radical polymerization by transition metal carbonyls in systems without halides

Abstract

New photoinitiating systems for free-radical polymerization are described, which are based on transition metal carbonyls [Mn₂(CO)₁₀, Re₂(CO)₁₀] but include no halogen-containing component. In addition to the metal carbonyl, the systems examined incorporate one of the following: acetylene, acetylenedicarboxylic acid, acetylenedicarboxylic acid dimethyl ester, diethyl fumarate, diethyl maleate, maleic anhydride. In the presence of acetylene or its derivatives, Re₂(CO)₁₀ photoinitiates polymerization (λ= 365 nm) with a quantum yield approaching unity. Manganese carbonyl is active only in the presence of the acetylene derivatives (λ= 435.8 nm).

The kinetics and mechanism of initiation have been studied with methyl methacrylate as monomer. The polymers show an infrared absorption spectrum attributed to terminal groups [graphic omitted], [graphic omitted] or [graphic omitted] and it is concluded that the primary radicals responsible for initiation arise from addition of a metal carbonyl fragment to a multiple bond in the acetylenic or olefinic derivatives listed. Kinetic observations are consistent with a mechanism similar to that already proposed for photoinitiating systems containing a metal carbonyl and a fluoro-olefin.