Relation between ESR Spectra and Molecular Orientation in Irradiated Polyethylene

Measurements have been made of the electron spin resonance spectra of irradiated polyethylene filaments with various draw ratios. The feature of the spectra is that the doublet splitting in each component of a quintet structure depends on the degree of molecular orientation in filaments. This can be ascribed to σ‐proton anisotropy in alkyl radicals mainly trapped in irradiated polyethylene. From the information about CH radicals of irradiated organic crystals and the molecular orientation of polymers, the relation between the doublet splitting D and the degree of molecular orientation f is obtained as follows: $${\text{D=13.9(1−0.35f)}}^{\frac{1}{2}}{\text{+5.1(1−0.65f)}}^{\frac{1}{2}}\mathrm{\hspace{0.17em}(}\mathrm{gauss})$$ for the high‐density polyethylene, consisting predominantly of the crystalline regions, and the spin density of the central carbon atom of the radical is 0.70.