Polymer degradation by high-energy radiation

Fundamental understanding of the mechanism of degradation of polymers by high-energy radiation has been based mainly on structural cban ol erved in the polymers, and to a much smaller extent on measurements of small molecule products. ESR has been used since 1960 to observe radicals produced in irradiated polymers, and hence to provide evidence for intermediate species in the radiolysis. However, recent improvements in the stability and sensitivity of ESR spectrometers and in computer manipulation of the spectra have enhanced the use of this technique. 

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Fundamental Aspects of Polymer Degradation By High-Energy Radiation... 

Polytetrafluorethylene (p.t.f.e.) This polymer does not absorb water, has no solvents and is almost completely inert to chemical attack molten alkali metals and sodium in liquid ammonia are the rare exceptions. Furthermore it does not soften below 320°C, is electrically inert and has a very low coefficient of friction. It is more expensive than general purpose plastics, requires special fabrication techniques, is degraded by high energy radiation, and has a low creep resistance. 

Some polymers like PE and NR get cross-linked on exposure to radiation while others like those based on vinylidene polymers, e.g., polymethylmethacrylate (PMMA), polyisobutylene, degrade. Certain other types of polymer stmctures (high aromatic content or thermoset) resist degradation by high-energy radiation. Coating polymers usually contain acrylic, methacryUc, or fumaric vinyl unsaturation along or attached to the backbone. 

Section 7.2.2). This feature makes it unique among vinylidene polymers, which typically are degraded by high-energy radiation.74... 

We have studied the degradation by high-energy radiation of a number of families of polymers by using a variety of techniques, including ESR spectroscopy [10,11]. In this paper we show the similarities and differences in the role of free radicals in the radiolysis of polyfmethyl methacrylate), polystyrene, and random copolymers of methyl methacrylate and styrene. 

Schnabel, W. (1978) Degradation by high energy radiation, in Aspects of Degradation and Stabilization of Polymers (ed. H.H.G. Jellinek), Elsevier Scientific, Amsterdam, Ch. 4. 

Volume 14 deals with all aspects of polymer degradation, classified on the basis of the method of initiation for the process. Thus, Chapter 1 covers thermal degradation, Chapter 2 radiolysis initiated by high-energy radiation such as X- and 7-radiation and electrons, Chapter 3 photodegradation arising from exposure of polymers to visible or ultraviolet radiation and Chapter 4 discusses oxidative degradation, oxidation and photooxidation. 

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