Radiation effect on poly ( p-sodium styrene sulphonate) of different degrees of polymerization in aqueous solution: pulse radiolysis and steady state study

Abstract

Radiation induced effects on poly ( p-sodium styrene sulphonate) (PSSS) of two molecular weights, namely 10 6 and 70,000 in aqueous solution have been investigated by steady state and pulse radiolysis (PR) techniques. The reactions of primary radicals of water radiolysis such as OH radical, e aq −, H atom, some oxidizing radicals like N 3 , Cl 2 − and SO 4 − and reducing species like CO 2 − with PSSS have been investigated. The results indicate that the reactivity of these species towards PSSS is a function of molecular weight of PSSS. The absorption spectra of transient species produced when dilute aqueous solutions of PSSS of different molecular weights are subjected to pulse radiolysis have been compared. Rate constants for the reaction of OH radical and H atom with PSSS have been evaluated both by competition kinetics method and by direct observation of build up of transient species. The results indicate that OH radical and H atom react with PSSS in different ways. Near neutral pH, the OH radical reacts with substituted pendant aromatic ring of the PSSS to form an adduct, with a rate constant of 5.5×10 8 and 1.1×10 9 dm 3 mol −1 s −1 for PSSS of molecular weights 10 6 and 70,000, respectively. H atom on the other hand abstracts H atom from the PSSS backbone as well as forms an adduct by reacting with aromatic ring. The rate constant values for reaction of aqueous electron with PSSS were found to be 5×10 7 dm 3 mol −1 s −1 ( M w=10 6) and 2.2×10 8 dm 3 mol −1 s −1 ( M w=70,000). The anion formed did not transfer electron to methyl viologen in the pH range of 6–10.5. The viscosity of the aqueous PSSS solution decreases with irradiation, up to doses of 1000 kGy indicating degradation of PSSS in this dose range. The PSSS of higher molecular weight is more prone to degradation. The chain scission is a function of dose rate, concentration of polymer and ambient of irradiation. At doses beyond ∼2500 kGy there is a sharp increase in viscosity of the PSSS solutions till the solutions set to a soft, sticky gel mass. The gelation dose ( D gel) is a function of molecular weight of the polymer and initial polymer concentration. In the presence of crosslinking agent like N, N-methylene bis acrylamide, the gelation was faster for PSSS of higher molecular weight. Gelation was most efficient for 20% (w/w) polymer concentration.