Effects of salts of metals on vinyl polymerization. Part 7.—Spectrophotometric studies of the ferric chloride-photosensitized polymerization of acrylonitrile in dimethylformamide

Abstract

A study has been made of the ultra-violet and visible spectrum of the reaction mixture during the photolysis of 5 × 10^–3 M ferric chloride in a 3.02 M solution of acrylonitrile in N,N-dimethyl formamide at 25°. Under these conditions, the spectrum is attributable entirely to the presence of the metal salt, which acts as both initiator and terminator for the polymerization. A marked change in the type of spectrum is noted as the reaction proceeds, as a result of which optical density cannot always be used as a measure of ferric iron concentration during reaction. The species present after reaction has commenced do not correspond to ferric chloride; the change of spectrum is interpreted as being due to interaction between chlorides produced in the reaction and the cation Fe(DMF)_nCl⁺₂, to increase the relative concentration of the FeCl^–₄ species, the two complexes formed when ferric chloride is dissolved in N,N-dimethyl formamide. Possible reaction products are capable of bringing about the change of spectrum. Both cationic and anionic species must be considered as possible initiators, but changes in their relative concentration do not seem to have a significant effect on either initiation or termination steps.