Paramagnetic centers in ion bombarded poly(vinylidene fluoride)

• Ion bombardment of PVDF films decreased crystallinity and caused unsaturation. • Ion bombardment of PVDF generates polyenyl, peroxyl, and alkyl radicals. • Formation and degradation of peroxyl radicals caused backbone cleavage of PVDF. • Interior backbone CF radicals may form through post-bombardment F atom shifts. • Radicals stabilized in the membrane may further functionalize PVDF. Stabilized radicals formed by irradiation of thin poly(vinylidene fluoride) films with high-energy accelerated 22 Ne +4 , 132 Xe +26 and 209 Bi +51 ions with respective energies of 24, 158 and 670 MeV were studied by EPR, Fourier transform infrared, and UV-visible spectroscopies. The bombarding ions cause significant excitation and ionization along the ion tracks throughout the thickness of the film. The reduction of crystallinity and the formation of unsaturated bonds in the irradiated polymer were explored spectroscopically The presence of alkyl, peroxide, and polyenyl radicals were identified in the spectra of the irradiated polymer; mechanisms for radical formation are proposed. Preliminary freezing of the irradiated films to dry ice temperature and subsequent study after storage at room temperature led to quantitative estimates of the loss of radicals during storage. Computational chemistry was used to predict the thermodynamics of the degradation processes and resulting peroxide radical reactions. Localized energy due to the ion bombardment enabled thermodynamically unfavorable reactions to proceed. The results of the study should be useful for optimization of processes for creating PVDF-based membranes for various applications.