Strahlenchemische Veränderungen an Polyvinylchlorid bei Einwirkung von Kobalt-60-Gammastrahlung
The role of air oxygen in the radiochemical changes of polyvinyl chloride was investigated. A polyvinyl chloride emulsion polymeride with a K value of 60 to 65 was used as a sample. It was radiated in the form of powder, films, and massive cylinders in high vacuum and in air. The total viscosity of the powders undergoes, after irradiation in vacuum, a slight deterioration at doses up to 5 x 10/sup 6/ r but at higher doses a lattice-like polymerization occurs. In irradiation in air the color of the sample does not vary, but in vacuum a brown color occurs. The behavior of massive cylinders is quite different from that of powders after irradiation. There is no variation in the total viscosity after irradiation in air and vacuum. Decomposition was observed up to doses of 5 x 10/sup 5/ r, then an increasing lattice-life polymerization and insolubility occurred. A red color is observed after doses of 3 x 10/sup 5/ r and it deepens with increasing irradiation doses. Film irradiated in air was not colored, but coloration occurred in vacuum irradiation. (J.S.R.)
Irradiation of Polymers by High-Energy Electrons
THE interaction of high-energy radiation with various forms of matter has been shown to produce a variety of chemical effects, depending upon the system. These effects fall into various classes, among which are oxidation and reduction, polymerization and depolymerization. Recently, Charlesby and Little have reported the cross-linking of polymers by high-energy radiation1–3.
Light scattering and viscosity study of electron-irradiated polystyrene and polymethacrylates†
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 Ec = 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, Ed = 58–62 e.v., determined by viscometry is therefore the true Ed 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 Ed = 43 e.v.