Ionizing radiations, chain scission cross-linking

According to most sources, the homopolymer of the vinyl alkyl ethers react to ionizing radiation predominantly by cross-linking 18). It is safe to conclude that maleic anhydride has contributed a predominance of chain scissioning to the copolymer and that, if cross-linking does take place, it is in very small proportion. 

Polymers can be classified into two groups according to their response to ionizing radiation. One group exhibits predominant cross-linking, the other predominant chain scission (see Table 5.1). ... 

To study the structural sensitivity of poly silanes to ionizing radiation, a number of samples were irradiated with a calibrated Co source, and the degraded materials were analyzed by GPC in a manner similar to that described for the determination of photochemical quantum yields (59). In radiation processes, the slopes of the plots of molecular weight versus absorbed dose yield the G values for scissioning, G(s), and cross-linking, G(x), rather than the respective quantum yields. These values, which represent the number of chain breaks or cross-links per 100 eV of absorbed dose, are indicative of the relative radiation sensitivity of the material. The data for a number of polysilanes are given in Table IV. Also included in Table IV for comparison is the value for a commercial sample of poly(methyl methacrylate) run under the same conditions. The G(s) value of this sample compares favorably with that reported in the literature (83). 

Table 1. Cross-Linking vs Chain Scission for the Poiymer Ciassss on Exposure to Ionizing Radiation in Vacuum...

Resistance to ionizing radiation. In contrast to chemically cross-linked elastomers, which change the properties and exhibit brittleness when exposed to electron beams or gamma rays, as a consequence of crosslinking or main chain scission, TPEEs are resistant to radiation doses up to 150 kGy. 

Radiation damage a measure of the loss of certain physical properties of organic substances, such as elastomers, due principally to ionization of the long chain molecule. It is believed that this ionization process (i.e. electron loss) results in redundant cross-linking and possible scission of the molecule. This effect is cumulative. 

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