Light scattering and viscosity study of electron‐irradiated polystyrene and polymethacrylates

Abstract

Abstract The solution viscosity behavior of polymers previously irradiated by high‐energy sources is treated theoretically by a combination of existing random crosslinking and degradation theory and branched‐polymer solution viscosity theory. The derived relations are applied to data on polystyrene, polymethyl methacrylate and poly‐ tert ‐butyl methacrylate irradiated as films in air with 1000 kvp. electrons. Polystyrene films underwent gelation exhibiting an energy dissipation per crosslinked unit E c = 855 electron volts and a main‐chain scission to crosslinked unit ratio α/β = 0.35. Pregelation light‐scattering molecular weights of the irradiated polystyrene predicted an incident gelation dose (9.4 megareps) in good agreement with that (10.3 megareps) observed by gel measurements. Theory satisfactorily reproduced the solution viscosity data over a wide range of pregelation radiation doses. A combination of light‐scattering and intrinsic viscosity data proved conclusively that no appreciable crosslinking occurs during the degradation of polymethyl methacrylate under 1000 kvp. electrons. The apparent energy dissipation per main‐chain scission, E d = 58–62 e.v., determined by viscometry is therefore the true E d in this instance. Reactions leading to crosslinking in polyacrylates are either blocked or diverted by the methyl group on the polymethacrylate backbone. Poly‐ tert ‐butyl methacrylate degrades under electron bombardment with an E d = 43 e.v.