Radiation initiated grafting on fluoro polymers III. Grafting of N‐vinylpyrrolidone in aqueous solution on poly(vinylidene fluoride) films by accelerated electrons

Abstract

Abstract The radiation induced grafting of N‐vinylpyrrolidone in aqueous solution onto poly(vinylidene fluoride) (PVF 2 ) films by preirradiation technique using 160 keV electrons has been investigated. Among the grafting parameters, the most important are storage time after irradiation, grafting time, grafting temperature, and absorbed dose. Trapped radicals in PVF 2 are very stable; peroxy radicals generated by storage of irradiated samples in air can initiate grafting, too. The grafting of PVF 2 proceeds slowly from the film surface to the inner part, ceasing when the middle of the film is reached from both sides. The penetration of the grafting front has been observed by “Differential‐Interference‐Contrast” (DIC)‐microscopy. At constant other parameters, the penetration depth depends on the grafting time and can be correlated with the time conversion curves. For the discussion of the grafting reaction a simple kinetic model has been developed. A very high activation energy of diffusion of ∼ 80 kJ mol −1 has been estimated both by sorption measurements and by application of the kinetic model with regard to the activation energies of grafting rate and saturation grafting yield (SGY). From the SGY‐dose relationship the ratio of the rate constants k p k t −1 has been calculated. As for other grafting systems this ratio has about the 10 5 ‐fold value in relation to homopolymerization of the same monomer. This indicates the restrained mobility of propagating macroradicals in the highly viscous grafting medium leading particularly to a lower k t in comparison with homopolymerization.