Effect of x‐rays and γ‐rays on synthetic polymers in aqueous solution

A study has been made of the effect of ionizing radiation (x‐ and γ‐rays) on aqueous solution of the following vinyl polymers: polymethacrylic acid, polyacrylic acid, polyacrylamide, polystyrene sulfonate, polyvinylpyrrolidone, and polyvinyl alcohol. In dilute solutions (<0.3% for the samples of polymer used) all the polymers are degraded by main chain fracture although in some cases dissolved oxygen has to be present. In others, degradation occurs in carefully deoxygenated solution but is increased by the presence of oxygen. The breakdown of polystyrene sulfonate is independent of oxygen. At higher concentration, crosslinking becomes the dominant action for all the polymers studied with the exception of polymethacrylic acid and ionized polyacrylic acid, which degrade at all concentrations. The dose of radiation necessary to produce a gel has been studied as a function of concentration and passes through a minimum. No gel formation occurs below a minimum polymer concentration of about 0.4%. The results cannot be explained on the basis that indirect action by the free radicals formed in the water leads to degradation while direct energy uptake by the polymer itself produces crosslinking. Other possible mechanisms are examined. The manner by which added substances reduce the effectiveness of irradiation (i.e., protect) is discussed briefly.