Scission and cross-linking

In analogy with thermal and light radiations, high-energy radiation may also lead to scission and cross-linking. The relative stabilities of various polymer stmctures are shown in Figure Whilst some materials cross-link others... 

Note 1 Radiation reactions involving polymers often lead to chain scission and cross-linking. 

Molecular Weight Distribution. A given polymer sample is composed of many polymer chains, which in most cases are not of the same length. This variability can be a result of the synthesis process or of possible random scission and cross-linking that can occur upon processing. For economic reasons, it is not possible to separate the various polymer chains by length prior to use so it is important to characterize this distribution in order to describe the polymer and understand its performance. As with any distribution, no single number is a totally satisfactory descriptor. 

Antidegmdents. This group of chemicals is added to prevent undesirable chemical reactions with the polymer network. The most important are the antioxidants, which trap free radicals and prevent chain scission and cross-linking. Antiozonants are added to prevent ozone attack on the rubber, which can lead to the formation and growth of cracks. Antiozonants function by diffusion of the material to the surface of the rubber, thereby providing a protective film. Certain antioxidants have this characteristic, and waxes also are used for this purpose. 

Figure 2. (a) Random scission and cross-linking of narrow molecular... 

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