The polymerization of acrylonitrile in aqueous solution. Part II. The reaction photosensitized by Fe³⁺, Fe³⁺OH⁻, Fe²⁺, and I⁻ ions

Abstract

Abstract The polymerization of acrylonitrile in aqueous solution photosensitized by Fe 2+ , Fe 3+ OH − , and I − has been determined dilatometrically at 25°C. After an acceleratory phase caused partly by increasing intensity of absorbed light due to light‐scattering by the insoluble polymer particles, a steady rate R p is established and continues up to ∼10% conversion. R p is proportional to I abs [m 1 ] 1.0 , where x is slightly greater than 0.5 unless ferric ions are present which may oxidize and terminate polyacrylonitrile radicals and cause x to be greater than 0.5. In accordance with earlier measurements, ϕ for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Fe}^{3 +} {\rm OH}- {{{3130\ {\rm A}.} \atop {-\hskip-4pt-\hskip-4pt-\hskip-4pt-\hskip-4pt-\hskip-4pt-\hskip-4pt-\hskip-5pt\longrightarrow}}\atop{}}{\rm Fe}^{2 +} + {\rm OH}$$\end{document} is found to be 0.15. Propagation occurs by addition ( a ) of dissolved monomer molecules to polymer radicals S * ( k p = 1.45 × 10 4 l. mole −1 sec. −1 ) and ( b ) of adsorbed monomer molecules to the radical in suspended polymer particles P * which contain several polymer molecules and one growing radical. S * radicals are subject to mutual termination ( k t = 2 × 10 9 l. mole −1 sec. −1 ) and oxidative termination by ferric ion ( k 4 = 1.3 × 10 4 l. mole −1 sec. −1 ). As soon as the steady state is established [P * ] is constant, but after stopping irradiation [P * ] decays slowly and bimolecularly and therefore gives rise to a small aftereffect. Agitation causing the polymer suspension to coagulate ( a ) reduces R p due to changes in I abs and a decrease in the number of particles and ( b ) decreases the half‐life of the aftereffect by increasing the rate of mutual destruction of P * particles.