Radiation-induced Crosslinking of Poly(vinylidene fluoride)

Abstract

The radiation-induced crosslinking, chain scission, and oxidation of poly(vinylidene fluoride) (PVdF) have been studied. The irradiation was carried out with γ-rays and electron beams at ambient temperature under vacuum and in the presence of oxygen. The gel formation, solution viscosities, and number average molecular weight of the PVdF so treated, as well as the evolution of hydrogen fluoride (HF) and other gases were measured. IR and UV spectra were also obtained. When PVdF was irradiated under vacuum, the G value for crosslinking was 0.6~0.8. This was equal to the G value for chain scission (Table 1). Double bonds including polyenes were formed as a result of dehydrofluorination. The concentration of polyenes was, however, low and decreased with increase in the number of conjugated unsaturation. Polyenes longer than tetraene were hardly observable (Fig. 6). The G value for the formation of HF was reduced from 3.5 to 3.0 when HF was removed with dry potassium hydroxide during irradiation (Table 3). This result suggests the accelerating effect of HF on the radiolytic dehydrofluorination of PVdF. Oxygen accelerated the chain scission and dehydrofluorination of PVdF (Figs. 1, 3, 4, and Table 3). Those effects are dependent on dose rate and the thickness of samples. At high dose rate (electron beams), there was little effect, while the remarkable effect was observed at low dose rate; the thinner the sample the more the effect. Carbonyls such as acid fluoride and carboxylic acid were detected as the oxidation products (Figs. 8 and 9). The reaction mechanism is discussed in connection with the results obtained here and ESR measurement. © 1973, The Chemical Society of Japan. All rights reserved.