Role of radiolytically generated species in radiation induced polymerization of sodium p-styrene sulphonate (SSS) in aqueous solution:: Steady state and pulse radiolysis study

Radiation induced polymerization of sodium p-styrene sulphonate (SSS) in aqueous solution has been investigated by steady state and pulse radiolysis techniques. Effect of dose, dose rate, monomer concentration, pH and ambient conditions on polymerization was investigated. The reactions of primary radicals of water radiolysis such as OH radical, e(aq)(-), H atom, O.- and some oxidizing radicals like N-3(.), Cl-2(.-),Br-2(.-), and reducing specie like CO2.- with SSS have also been investigated. SSS reacts with OH radical with a rate constant of 5.9 x 10(9) dm(3) mol(-1)s(-1) at pH 6.3. The results indicate that similar to 83% of OH radicals undergo electron transfer reaction resulting in a cation radical species while remaining similar to 17% react via addition reaction. The hydrated electron reacts with SSS with a rate constant 1.3 x 10(10) dm(3) mol(-1) s(-1) to form an anion that undergoes fast protonation to form H-adduct at pH 6.3. At high pH (>10) the anion is able to transfer electron to methyl vilogen and p-nitro aceto phenone (p-NAP) where as H-adduct is unable to transfer electron. At pH similar to 1 H atom reaction with SSS is diffusion controlled with a rate constant of 5 x 10(9) dm(3) mol(-1) s(-1) and results in formation of H adduct. It was seen that anion reacts with solute an order faster than cation generated radiolytically indicating anionic initiation of polymerization of SSS, Molecular weight of the polymer formed by radiation polymerization, determined by viscosity measurement, are of the order of 10(7) and higher molecular weight polymers are obtained at lower dose rates. In presence of a crosslinking agent gelation of polymer is much faster than the monomer and a polymer concentration similar to 20% is most efficiently crosslinked. (C) 2000 Elsevier Science Ltd. All rights reserved.