The molecular properties of the additive poly(bis(trimethylsilyl)tricyclononene) with the vicinal position of two side groups Si(CH3)(3) in the monomer unit are studied for the first time, and its conformational and kinetic properties are compared with those of the isomer with the geminal position of the same groups. Using the methods of static/dynamic light scattering and viscometry for the samples of the vicinal isomer, the hydrodynamic parameters of molecules are determined and their molecular mass dependences in toluene are ascertained. In addition, the Kuhn segment length of this isomer is estimated. The kinetic rigidity of vicinal and geminal isomers is evaluated by H-1 NMR relaxation from the mobility of protons in Si(CH3)(3) groups. The reasons behind different gas permeabilities of the films based on the polymers with the vicinal and geminal positions of Si(CH3)3 side groups in the monomer unit are discussed.