Free Radicals Produced by Irradiation of Polymers with Ionizing Radiation

1 Free Radicals Produced by Irradiation of Polymers with Ionizing Radiation 

Cross-linking and degradation are well known radiation effects in polymers. The molecular weight increases and gels are formed for the cross-linked type poiymers 

In order to confirm the anisotropy due to the a-hydrogen, Salovey et al. [9] and Shimada et al. [10] studied the patterns of the ESR spectra from irradiated solution grown crystals of polyethylene. The crystal c-axis was oriented perpendicular to the plane of the sample while the a- and b-axes were randomly oriented in the plane as shown in Fig. 7.8. Six- and ten-line spectra were observed when the c-axis of the crystal was set to be parallel (Fig. 7.9(a)) and perpendicular (Fig. 7.9(b)) to the direction of the applied magnetic field, respectively. From these results, the anisotropic hyperfine splitting due to the a-hydrogen Ay = 0.75 mT, Ax = 1.72 mT and Az = 3.70 mT were determined and were related to the molecular orientation of the crystal. The x-, y- and z-axes coincide with the directions of the p-orbital, the (Ca )— Ha bond, and the main chain axis, respectively, as shown in Fig. 7.10. 

The primary radical species —C(0)0(C )H2 converts to the secondary product —CpHp2(Ca )R(CH3) upon warming the sample above 180 K. Various degradation mechanisms starting with the initial formation of primary species such as the cation and anion of PMMA were suggested. 

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B-1) Assignment of unstable free radicals produced by irradiation of polymers with ionizing radiation and ultraviolet light, mechanical fracture, and deterioration of polymers and polymerization. 

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