The role of radiolytically generated species in radiation-induced polymerization of vinylbenzyltrimethylammonium chloride (VBT) in aqueous solution: steady-state and pulse radiolysis study.

Abstract

Radiation-induced polymerization of vinylbenzyltrimethylammonium chloride (VBT) in aqueous solution has been investigated by steady-state and pulse radiolysis techniques. The effects of dose, dose rate, monomer concentration, pH, and ambient conditions on steady state polymerization were investigated. The reactions of primary radicals of water radiolysis, such as OH radical, e(-)aq, and H atom, were studied. The reactions of other chemically active species such as O*-, oxidizing radicals such as N3*, Cl2(*-), Br(2*), SO4(*-), and a reducing specie such as CO2(*-) with VBT were also investigated. The reaction of VBT with OH radical and H atom were investigated by formation kinetics and by competition kinetics. The rate constant values for the reaction of OH radical with VBT were 4.7 x 10(9) dm3 mol(-1) s(-1) and 1.7 x 10(10) dm3 mol(-1) s(-1) by formation kinetics and by competition kinetics, respectively. The results indicate that OH radicals undergo electron transfer reactions (resulting in a radical cation) and addition reactions. The hydrated electron reacts with VBT with a rate constant of 1.9 x 10(10) dm3 mol(-1) s(-1) to form an anion. At pH approximately 1, H atom reaction with VBT is diffusion controlled with a rate constant of 5.1 x 10(9) dm3 mol(-1) s(-1) as determined by formation kinetics and 1.7 x 10(10) dm3 mol(-1) s(-1) as determined by competition kinetics. VBT radical anion reacts with VBT at a rate that is almost twice the rate at which VBT radical cation reacts with VBT, indicating anionic initiation of the polymerization of VBT. VBT undergoes very fast steady-state polymerization and dose rate; the presence of efficient radical quenchers such as oxygen and concentration of VBT in the aqueous solution affects the extent of polymerization. Typically, a dose of 4 kGy is sufficient to achieve 80-85% polymerization. The monomer solution shows a drastic increase in the viscosity of the solution, which finally gels to a soft rubbery mass.