An Electron Spin Resonance Study of Trapped Electrons in y-irradiated Hydrocarbon Polymers

Trapped electrons have been detected by ESR spectroscopy in poly ethylene, isotactlc polypropylene, and poly(U-methylpentene-l) following 7-irradiation at 77°K. In all cases, the ESR spectrum consists of a narrow singlet at g = 2.0023 ± 0.0002 superimposed on a broad free radical spectrum. The singlet can he photobleached by near infrared light (A > 1000 nm) and is readily saturated at low microwave powers. The singlet is assigned to a trapped electron since this behavior is analogous to that known to be characteristic of trapped electrons in 7-irradiated alkane glasses.

Initial G-values for trapped electrons in these systems range from O.kG for linear polyethylene down to O.O8 for isotactic poly(i+-methylpentene- l). Both G-values and the maximum value attained in the concentration-dose curve for trapped electrons appear to he correlated with the crystallinity of the polymer and decrease with decreasing crystallinity. Little or no trapped electrons could be detected in non-crystalline polymers such as atactic polypropylene or polyisobutylene. These results strongly suggest that the electron trap is associated with crystalline regions of the polymer.