Fundamental features of the direct fluorination of poly(vinyl trimethylsilane) (PVTMS) and poly(phenylene oxide) (PPO) have been investigated. The influence of the fluorination conditions (fluorinating mixture composition, treatment duration) and polymer molecular weight on the rate of formation of the fluorinated layer and on physical-chemical properties (chemical composition, density, refractive index, absorption spectra in the visible and UV, surface energy) was investigated.