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.)
Reticulation du chlorure de polyvinyle sous l'action des radiations ionisantes
Certains polymeres se reticulent sous l'acton de radiations ionisantes. Les produits reticules etant insolubles et infusibles leur tenue aux solvants et a la chaleur est considerablement amelioree. Cet effet est particulierement net pour le polyethylene, pour le chlorure de polyvinyle, par contre, les observations faites par differents chercheurs se contredisent, les unes indiquent ue degradation, les autres une reticulation de ce polymere sous l'action des radiations. Nos propres experiences sur des poudres de chlorure de polyvinyle pur irradie a l'aide d'une source de 60 Co montrent que les deux mecanismes coexistent. Suivant que l'irradiation se fait sous vide ou a l'air l'un ou l'autre predomine. Toutefois meme apres des irradiations a des doses de 150 MR les modifications restent relativement faibles. Par contre, nous montrons qu'il est possible de reticuler totalement le chlorure de polyvinyle avee des doses de l'ordre de 50 Mr en l'irradiant en presence de certains solvants sous forme de gels. Nous determinons d'une part la quantite de C.P.V. insoluble en fonction de la dose d'irradiation, d'autre part, la masse moleculaire moyenne en poids de la fraction soluble. Ces measures sont confrontees avec les resultats theoriques publies par Charlesby. Elles permettent d'avoir une idee sur la repartition initiale des masses moleculaires. 
 
 
 
Some polymers are crosslinked under the influence of ionizing radiation. The crosslinked products are insoluble and infusible; therefore, their behavior with respect to solvents and temperature is considerably improved. This effect is particularly sharp in the case of polyethylene. In the case of polyvinyl chloride, the literature data from several authors are contradictory; some indicating a degradation, others a polymer crosslinking. Our own experiments carried out with pure polyvinyl chloride powders irradiated with a Co60 source indicate that both mechanisms coexist. Depending on the presence or absence of air, one mechanism is predominant. Nevertheless, even after irradiations with doses of 150 mr, the modifications are relatively small. Polyvinyl chloride can be completely crosslinked with doses of 50 mr if the irradiation on the gel is carried out in the presence of some solvents. We determined both the amount of insoluble PVC as a function of the doses of irradiation, and the weight average molecular weight of the soluble fraction. These measurements have been compared with the theoretical results of Charlesby. This makes it possible to gain an idea of the initial molecular weight distribution.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.