Quantitative EPR study of poly(vinylidene fluoride) activated by electron beam treatment

The electron paramagnetic resonance (EPR) spectra of poly (vinylidene fluoride) (PVDF) films were studied in order to identify type and intensity of trapped radicals after an electron treatment with 150 kGy in air at room temperature. The observed EPR spectra consist of superimposed spectra of eight different radicals. The individual spectra were simulated by first derivatives of normalized Gaussian functions including intensity, linewidth, g value, and hyperfine splitting constants of the unpaired electron with hydrogen or fluorine atoms in alpha or beta positions. In addition, the number of trapped radicals was estimated using a standard sample of known spin concentrations. Although initially generated radicals tend to be converted to peroxy radicals in the presence of oxygen, the predominant radical is the CH-based mid-chain radical (-CF2-C*H-CF2-) with a relative intensity of 62.3%. This is attributed to CH-based radicals in the crystalline domains with low molecular mobility leading to an enhancement in its linewidth (Delta Hpp similar to 3.6 mT). A fraction of 20.7% of all radicals are peroxy radicals with anisotropic g values, g(parallel to) = 2.0210 and g(perpendicular to) = 2.0095. The relative intensity of allyl, dienyl and polyenyl radicals amounts to 4.9%.

Automated summary

The EPR spectra of PVDF films trapped various radicals after electron treatment, with CH-based mid-chain radicals being the predominant type. While initially generated radicals tend to convert to peroxy radicals in the presence of oxygen, the CH-based radicals in crystalline domains account for a relatively high proportion.