Experimental results for high polymer systems

3 Experimental results for high polymer systems (a) Radical decay in polyethylene 

The decay of trapped radicals in polyethylene has been studied by many workers in recent years [226—242]. The usual pattern of step-like decay is observed below room temperature. The radicals studied, the experimental conditions and the measured reaction orders are given in Table 12. This clearly shows that disagreement exists between the results obtained by the various workers. The general problems of solid state reaction kinetics and the problems related to inter- and intraspur recombination have been discussed in section 3. It must be remembered, however, that usual kinetic analyses cannot be applied to step-like reactions and that the determination of the order of reaction by the integration method requires very accurate analytical methods. A strong dependence of the rate of radical decay on the crystallinity of the sample was nevertheless clearly demonstrated by Charlesby et al. [228] the specific rate 

Radical Temp, of irradiation Temp, of observation Order Ref. 

However, a high activation energy of 12.5 kcal mole 1 was found by 

The number of radicals formed in PMMA irradiated at 77°K increases linearly with dose up to 8 Mrad [220]. The G value is 0.72. Data on the decay of the radicals has been reported [220, 244]. Stepwise decay occurs between 77 and 370°K [220]. 

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