Promotion of Cross-Linking by Polythiols

The above-mentioned radical acceptors are not the only effective protective agents against radiation. Studies performed with benzene and nitrobenzene in natural rubber and styrene butadiene rubber (SBR) with N-phenyl-p-naphtylamine demonstrated radiation protection of the respective compounds. 

Many of the studied radical-accepting compounds were found to reduce the yield of scissions. - The antirads tested proved effective not only in the presence of air but also in its absence (see Table 5.3). 

Different pol)uneric materials respond to irradiation by electron beam in different ways. A large number of them will be modified by the formation of a cross-linked network, by changing their surface properties or structure, and some will be degraded. Another field applicable to polymeric systems is polymerization and grafting. Electron beam can also be used for pol5unerization and cross-linking of oligomers and monomers, i.e., in conversion of liquids to solids. 

Plastics are by far the largest group of polymeric materials being processed by electron beam irradiation. Cross-linking of polyolefins, PVC, polyesters, polyurethanes, fluoropolymers, and fiber-reinforced composites is a common practice. 

Irradiation of polyolefins, particularly the family of polyethylenes, represents an important segment of the radiation processing. Polyolefins can be 

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The basis for cross-linking in the elastomers in these studies is the addition of thiols to olefmic double bonds. This reaction has been studied by a number of investigators.61-65 It has been shown that the addition reaction proceeds by a radical mechanism. The rate of cross-linking of polybutadiene can be strongly promoted by relatively small amounts of polythiols.66 For example, G(X) values increased from 5 (pure polybutadiene) to 29 when 1 wt. percent of dimercaptodecane was added and to more than 49 on the further addition of o-dichlorobenzene (see Table 5.2). 

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