Degradation radiation

Polymer irradiation can produce crosslinking, backbone scission, hydrogen evolution, and various other reactions. A generalised sequence of events for the process may be set out as follows  

Initial interaction of each y-ray photon with the polymer yields fast electrons (similar to those involved in direct electron irradiation) which in turn cause subsequent ejection of secondary electrons of lower energy. The spread of damage from an initial y-ray photon strike can be extensive, with a radius of several microns. Under normal conditions of temperature and pressure, ion-electron recombination is rapid, resulting in the formation of excited states. These excited states can dissipate their energy via bond scission. 

Secondary reactions imdergone by the free radicals formed in the processes described previously will be similar to those noted for thermolysis and photolysis. 

The effect of high-energy radiation on the breakdown of aromatic polyesters has been studied, including the effect of electrons [64-66], protons [67, 68] and y-rays [69-80]. In general, these materials are less susceptible to radiation damage than, for example, polyamides and polyolefins. 

Low-temperature electron spin resonance studies of radiation degradation of PET have, to some extent, failed to clarify the fundamentals of the reaction. They produced evidence for positively 

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CSM is extensively used in constmction and electrical appHcations. This includes roofing membranes, automotive ignition boots and wire, toU compounds, and in some automotive hoses requiring good heat and oil resistance, eg, air conditioning and power steering. It is also used in nuclear power plants because of its exceUent resistance to radiation degradation. 

Bowmer and Bowden75 studied the radiation degradation of poly-2-methyl-l-pentene sulfone and found that at low radiation doses the S02/olefin ratio is 2 1, however at high doses this ratio is decreased and is close to unity. Thus the oligomerization of the olefin, which is the cause for the discrepancy between G(S02) and G(olefin), appears to be reversible. 

The main reaction in the radiation degradation of all the polyfolefin sulfone)s is the depropagation step... 

FIGURE 8. Overall reactions scheme for radiation degradation of poly(olefin sulfone)s. Reproduced by permission of the authors from Reference 74. 

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. 

The range of properties of polymers can be greatly extended and varied by copolymerization of two or more monomers. The effects of radiation on copolymers would be expected to show similarities to the homopolymers, but major differences from linear relationships are often experienced. Aromatic groups in one monomer frequently show an intramolecular protective effect so that the influence of that monomer may be much greater than its mole fraction. The Tg of a copolymer is normally intermediate between the homopolymers, except for block copolymers, and this can cause a discontinuity in radiation degradation at a fixed temperature. 

IAEA Consultants Meeting on Radiation Degradation of Organic Materials and Components, Cadarache France 1983 International Atomic Energy Agency, Vienna. 

The polymers used in this study were prepared by a nucleophilic activated aromatic substitution reaction of a bisphenate and dihalo diphenyl sulfone ( ). The reaction was carried out in an aprotic dipolar solvent (NMP) at 170°C in the presence of potassium carbonate (Scheme 1) (5,6). The polymers were purified by repeated precipitation into methanol/water, followed by drying to constant weight. The bisphenols used were bisphenol-A (Bis-A), hydroquinone (Hq) and biphenol (Bp). Thus, the aliphatic character of Bis-A could be removed while retaining a similar aromatic content and structure. The use of biphenol allows an investigation of the possible effect of extended conjugation on the radiation degradation. 

The relatively minor role of the isopropylidene group in the radiation degradation of Bis-A PSF was further demonstrated by the small difference in GISO ) for Bis-A PSF (0.146) and Hq PSF (0.136), a wholly aromatic polymer. The small reduction in G(S02) may be due to a slightly higher aromatic content in Hq PSF compared with Bis-A PSF. 

Radiolysis of hydrocarbons has been investigated and there is a review [108]. n-Dodecane is one of the saturated hydrocarbons, and its radiation degradation is rather known as compared with that of TBP. Main degradation products are H2 and dimers, as summarized in Table 3 [109,110]. Again, the values are dependent on the reports. Recently, systematic study on the radiolysis of n-paraffins has been reported [111-113]. The formation process of dimers and double bonds is assumed as follows. 

Using ion beam technologies denoted in Section 27.3, research and development of advanced materials and devices have been made for their space, nuclear, and industrial applications. As typical examples of such researches, evaluation and development of semiconductor devices for space application, characterization of radiation degradation of nuclear materials, beam analysis and modification of inorganic materials, and beam processing of organic materials are described in this section. 

Radiation Degradation and Film Solubility Rates of Poly(butene-l-sulfone)... 

Silicone acrylates. Acrylated organopolysiloxanes, which exhibit excellent release properties, are used as release coatings on papers and films. The silicone structure provides flexibility and resistance to heat, moisture, radiation degradation and shear forces.41... 

Nitrous oxide reduces the amount of radiation degradation of polyisobutylene (5), though this is a typical polymer which degrades under radiation. 

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