Polyisoprene radiolysis

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

Katzer and Heusinger127 studied the radiolysis of polyisoprenes with high content of 1,2- and 3,4-units. They found that G(-double bonds) is about 130 and G(cross-linking) is about 10. These values depend slightly on the molecular weight. 

About 98% of gas formed during radiolysis of natural rubber and polyisoprene is hydrogen the rest consists of methane and higher-molecular-weight hydrocarbons. The yield of hydrogen is directly proportional to dose, up to 200 Mrad (2000 kGy). 

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