Seven polynorbornene samples containing trimethylsilyl side groups that were prepared by the addition polymerization of 5-trimethylsilyl-2-norbornene in the presence of catalytic systems (π-C₅H₉NiCl) ₂-methylaluminoxane and nickel naphthenate-methylaluminoxane have been studied by translational isothermal diffusion and viscometry. The molecular masses of the polymer samples are measured. Kuhn-Mark-Houwink equations for diffusion coefficient D and intrinsic viscosity [η] are determined in toluene at 25°C: D = 6.94 × 10^-4 M^-0.61 and [η] = 1.53 × 10^-3 M^0.82. The equilibrium rigidity of polymers chains is estimated as A = 47 ± 9 Å. The conformational features of the silicon-containing polynorbornene are analyzed by the PM3 quantumchemical semiempirical method on the basis of simulation of its decamer chain fragments. In terms of microstructure and equilibrium rigidity, the above-described addition poly(trimethylsilylnorbornene) is close to poly(trimethylsilylpropyne) synthesized using niobium pentachloride as a catalyst. This finding explains similar membrane gas-separation properties of these polymers.