High-energy radiation polymer degradation

Like almost all synthetic polymers, styrene plastics ate susceptible to degradation by heat, oxidation, uv radiation, high energy radiation, and shear, although... 

Ejfects of Thermal, Photochemical and High-energy Radiation 97 Table 5.9 Thermal degradation of selected polymers (Ref, 7)... 

The polymers also have excellent resistance to oxidative degradation, most chemicals other than strong bases and high-energy radiation. Exposure for 1500 hours to a radiation of about 10 rads at 175°C led to embrittlement but the sample retained form stability. 

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. 

Changes in the properties of polymer materials caused by absorption of high-energy radiation result from a variety of chemical reactions subsequent to the initial ionization and excitation. A number of experimental procedures may be used to measure, directly or indirectly, the radiation chemical yields for these reactions. The chemical structure of the polymer molecule is the main determinant of the nature and extent of the radiation degradation, but there are many other parameters which influence the behaviour of any polymer material when subjected to high-energy radiation. 

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

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

A basic requirement of the ESR technique is the presence of molecules or atoms containing unpaired electrons. Such species can be generated in polymeric systems by homolytic chemical scission reactions or by polymerization processes involving unsaturated monomers. These reactions can be initiated thermally, photochemically, or with a free-radical initiator, and, in the case of scission, by mechanical stress applied to the system. Therefore, ESR can be used to study free-radical-initiated polymerization processes and the degradation of polymers induced by heat, light, high-energy radiation, or the application of stress. 

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