Thermal reactions of perfluoromethyl and perfluoroacetyl manganese pentacarbonyls. Part 2.—Initiation of free-radical polymerization and formation of methyl(2-methyl 4-oxo-5,5,5-trifluoropentanoate)

Abstract

This paper continues the study of the thermal reactions of low-molecular-weight analogues of macroinitiators carrying terminal Mn(CO)₅ groups e.g. [graphic omitted]CF₂ CF₂ Mn(CO)₅. The reactions of CF₃Mn(CO)₅ and CF₃COMn(CO)₅ in methylmethacrylate solution at 100°C have been examined.

Both derivatives initiate free-radical polymerization; retardation is less marked than with the unfluorinated analogues, especially in the case of CF₃Mn(CO)₅. Rates of polymerization ω are increased by the presence of “halide” and “non-halide” type additives; with CF₃Mn(CO)₅ the increase corresponds to a factor of 2 in the rate of initiation. The dependence of ω on [CCl₄] is very sharp and a plateau value is reached for [CCl₄] > 5 × 10^–3 mol dm^–3.

The reaction of CF₃COMn(CO)₅ yields methyl(2-methyl-4-oxo-5,5,5-trifluoropentanoate), CF₃COCH₂CH(CH₃)COOCH₃. Reaction in the presence of D₂O yields CF₃COCH₂CD(CH₃)COOCH₃, indicating that the mechanism is of a polar type involving intramolecular attack by a CF₃CO anion on a coordinated monomer molecule, with subsequent acquisition of a proton from water present in trace quantities. No corresponding reaction with CF₃Mn(CO)₅ has been observed under similar conditions.

On heating these derivatives in methyl methacrylate at 100°C a peak with λ_max= 342 nm slowly develops in the u.v.-visible spectrum and represents the formation of Mn₂(CO)₁₀. In the presence of added water a peak near 385 nm appears, attributable to Mn(CO)₅OH.

The bearing of these results on the use of macroinitiators for block-copolymer synthesis is discussed.