Volatile evolution from room temperature cured polysiloxane rubber induced by irradiation with He2+ ions

A room temperature cured polysiloxane rubber (Rhodorsil RTV5370) has been irradiated using an accelerated beam of He2+ ions. Such an irradiation simulates the effects of large alpha radiation doses. A mass spectrometer linked directly to the sample chamber allowed the analysis of volatile species evolved as a result of exposure. The polydimethylsiloxane rubber showed high resistance to radiation damage when exposed to He2+ ions at doses up to 3.5 MGy. At higher doses, the cyclic hexamethylcyclotrisiloxane was evolved and is indicative of damage to the main chain. The cyclic octamethylcyclotetrasiloxane was only observed at very high doses (10 MGy and above) and is indicative of significant head-to-tail unzipping reactions. Methane, benzene and carbon dioxide were the three main gases evolved. The ratio of phenyl (2%) to methyl groups (93%) within RTV5370 rubber is very small but the amount of benzene evolved was found to be significant. The results suggest that the aromatic groups within the rubber appear to have a much greater susceptibility to radiation induced volatile evolution than other groups making up the polymer structure. In addition, the depletion of phenyl groups (from the reduction in evolution of benzene) from the irradiated zone corresponds to an increase in damage of the siloxane linkages (from the increased evolution of octamethylcyclotetrasitoxane) suggesting the aromatic groups offer a protective action from the incident radiation. Crown Copyright (C) 2003 Published by Elsevier Ltd. All rights reserved.