A Method of Liquid-Phase Fluorination of Polymers to Increase the Selectivity of O2/N2 Separation

One-sided modification of homogeneous polymer films of poly(vinyltrimethylsilane) (PVTMS), poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and polybenzodioxane (PIM-1) by liquid-phase fluorination with a fluorine–nitrogen mixture in perfluorodecalin is carried out in the work. The fluorination time is 10 up to 60 min. It is shown by X-ray diffraction analysis for the samples of PPO that the initial samples include a β nanocrystalline phase (48%) in addition to the amorphous phase and it is found that fluorination does not significantly affect the crystallinity index of the films under study. The effect of the fluorination time on the effective permeability, diffusion, and solubility coefficients of oxygen and nitrogen is studied. It is found that the modification leads to a decrease in both the effective diffusion coefficients and effective solubility coefficients of the gases; here, the resulting growth in the permeability selectivity ranges from 30% for PVTMS to a twofold increase in the case of PPO and PIM-1. It is found that such an improvement in the permeability selectivity is predominantly achieved due to the increase in the solubility selectivity. The values of the effective gas permeability coefficients are obtained for an O₂–N₂ mixture. It is found that the achieved values of separation factors for the modified samples are close to the ideal selectivity of the films. The obtained results demonstrate the possibility of effective application of this method not only for the modification of the homogeneous polymer films of the polymers under study but also for membranes with a selective nonporous layer based on them.