Radiation Chemistry of Polymers

Abstract

Polymeric 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 radiolysisin vacuo, the effect of the presence of dissolved oxygen on the reaction pathways is also briefly addressed.

Electron beam technology for Re-processing of personal protective equipment

“…There is extensive information focusing on ionizing irradiation-induced effects on polymer properties available in the literature ( Hill and Whittaker, 2016 ; Giberson and Harrington, 1958 ; Atchison, 2003 ; Gheysari and Behjat, 2001 ; CHARLESBY, 2009 ; Mishra et al, 2001 ; Dawes et al, 2007 ). Theoretically, crosslinking increases the molecular weight via bond formation, leading to weakened elongation at break and improved tensile strength with less mobility of polymer chains.…”

A Quantum-Based Approach to Predict Primary Radiation Damage in Polymeric Networks

“…Purposeful exposure of materials to ionizing radiation is a reliable means of sterilization − and is a common approach taken in accelerated aging experiments. − In molecular materials, radiation exposure can induce atomic-level chemical reactions that alter or degrade many properties, including those which impart functional characteristics that must meet tolerance specifications. Chemical degradation of polymer materials is thought to arise from network-altering reactions such as chain scissions and formation of cross-links, which can lead to macroscopic mechanical changes including permanent set, embrittlement, or breaking under load. ,, Experimental diagnostics that probe chemical degradation are often indirect and capture highly integrated responses from which it can be hard to infer fundamental chemical events, for instance measuring viscosity, gelation, stress–strain responses, vibrational spectra, or evolved off-gassing products. − Nuclear magnetic and electron paramagnetic resonance experiments provide some of the most direct measures of time- and dose-dependent chemistry and network changes in irradiated polymers. ,,− Atomistic modeling techniques such as reactive molecular dynamics (MD) can provide insight into underlying network-altering chemistry in polymers, ,− but upscaling these insights to inform models for macroscale responses is challenging. A desirable foundation for multiscale modeling of radiation damage in polymers would incorporate accurate high-throughput sampling of atomic-scale chemistry and an automated scheme for extracting statistics on changes to the network.…”

“…Chemical degradation of polymer materials is thought to arise from network-altering reactions such as chain scissions and formation of cross-links, which can lead to macroscopic mechanical changes including permanent set, embrittlement, or breaking under load. 2,7,8 Experimental diagnostics that probe chemical degradation are often indirect and capture highly integrated responses from which it can be hard to infer fundamental chemical events, for instance measuring viscosity, gelation, stress−strain responses, vibrational spectra, or evolved off-gassing products. 9−15 Nuclear magnetic and electron paramagnetic resonance experiments provide some of the most direct measures of time-and dosedependent chemistry and network changes in irradiated polymers.…”