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 λmax= 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.