RADIATION CHEMISTRY OF POLYETHYLENE. V. HYDROGEN ISOTOPE EXCHANGE STUDIES

Abstract

After irradiation in vacuo with Co/sup 60 / gamma rays at liquid nitrogen temperature, Marlex-50 polyethylene was exposed to deuterium gas at room temperature. Considerable D/sub 2/ exchange oecurred, and the exchange was studied as a function of deuterium pressure, exchange cell volume, irradiation dose, and time of initiating the exchange after irradiation. Kinetic equations were derived for three cases of constant free radical concentration, firstorder free radical decay, and second-order free radical decay. The data agree best with the first-order decay equations; the decay constant and duration of exchange - agree to an order of magnitude with estimates from the previous ESR work of others. The D/sub 2/-free radical reaction rate constant is about 1000-fold faster than calcuiated for a gas phase reaction between D/sub 2/ and RCHR', but close to that for the D/sub 2/ and CH/sub 3/CH/sub 2/Faye a raised dot goes her e) reaction. The exchange, as expected, does not continue until isotopic exchange equilibrium has been established. The total observable number of D- H exchanges was estimated to be between 1 and 2fold the number of free radical sites initially present. For reasons given, the exchange probably involves hydrogen atoms close to the free radicalmore » or on the nearest neighbor sites, and provides a new mechanlsm for free radical migration in the solid polyethylene. (auth)« less