Temperature dependence of gas evolution from polyolefins on irradiation under vacuum

The yields of gases evolved from three types of polyethylene and ethylene-propylene copolymer during radiation were precisely measured after gamma ray irradiation under vacuum over a wide range of temperatures (-196 to 200 degrees C). For all polymers the major gas evolved was H-2 and the minor products were C-1, C-2, C-3 hydrocarbons and the oxidation compounds CO2 and CO. The total gas yield increased with an increase in the irradiation temperature, but the ratio of the yields among the gas components was not greatly changed. The H-2 would originate from H-bond scission and the concomitant formation of crosslinks and double bonds in the polymer chains. The minor products of C-1, C-2, C-3 hydrocarbons were products of chain scission at the chain ends, including branched chains, and the oxidation compounds of CO and CO2 were the products formed by reactions of oxygen remaining trapped in the polymer matrix. The yield of H-2 increased with increasing irradiation temperature, which is closely related to the molecular motions of the polymer chains during irradiation. (C) 2012 Elsevier Ltd. All rights reserved.