<p>The degree of crosswlinking of a polymer plays an important role in the formation of the free volume and mobility of polymer chains, which directly influences the sorption and transport properties of the material. Determining the influence of the degree of crosslinking on interaction parameters is of great importance for target-oriented design of membrane materials. In the present work, we have considered for the first time the influence of the amount of a crosslinking agent (1,7 octadiene, OD) in polydecylmethylsiloxane (S10) on the imaginary crosslinking density determined from the data of equilibrium sorption in toluene and of spectroscopic ellipsometry in a toluene vapor. The interaction of the membrane material with the penetrant is an important topic which will largely determine the efficiency of the separation process. In the present work, using the crosslinked S10 with a varying concentration of OD as an example, we have considered the difference between the interaction of the membrane and the penetrant in the liquid and gas phases. It has been established that with growth in the fraction of crosslinking diene in S10, the value of sorption and the degree of swelling of the polymer in toluene decrease. It has been shown that there is the disagreement of crosslinking densities in different methods of determining the sorption, which seems to be due to the varying interaction of the polymer and the penetrant under experimental conditions.</p>