Transformation of the films with the pores of different radii under the action of vacuum ultraviolet radiation was studied experimentally and theoretically. Simulation results showed that Si-O-Si angle depends on pore size. Fourier Transform infrared spectra provide indirect confirmation of this statement. The experimental data and calculation results suggest that methyl group decreases pi bonding, which causes a decrease in Si-O-Si angle. The action of ultraviolet radiation is to be considered as a photochemical reaction; the fragments formed in this reaction (CH3*, CH2*) can participate in polymerization, which leads to pore sealing. (C) 2016 Elsevier B.V. All rights reserved.