Radiation chemistry of polymers

olymeric materials are exposed to high energy radiation either deliberately to alter their properties or inadvertently during their use in high dose environments. As a consequence, an understanding of how radiation modifies polymer structure, and hence properties, is essential for many applications. In addition, the understanding of the degradation of polymers with light or heat can benefit from knowledge of the reaction pathways of radical and charged species formed on irradiation with high energy photons. This article aims to provide a broad overview of the fundamental processes occurring during radiolysis of polymers. This is achieved through a discussion of the interaction of high energy photons with matter, and the subsequent reactions of mainly radical intermediates. Polymers either cross-link or degrade on exposure to radiation, and the final properties of the polymers depend critically on the balance of these main reaction pathways. Examples are taken from the literature to illustrate how the tendency to undergo cross-linking or main-chain scission depends on the polymer structure. The overall yield of reactions can be greatly reduced by the introduction of aromatic groups into the polymer structure. On the other hand, yields can be increased by the inclusion of radiation-sensitive groups such as sulfones. Similarly, the rates of reactions and the balance between cross-linking and scission can depend sensitively on the radiolysis temperature. While this review focuses on a discussion of the reactions occurring on radiolysis in vacuo, the effect of the presence of dissolved oxygen on the reaction pathways is also briefly addressed