Polymerization of norbornene bearing Si(CH3)(3) groups in the 5-position with the opening of double bonds and its copolymerization with 5-(n-hexyl) norbornene were realized in the presence of nickel(II) naphthenate/methylaluminoxane catalyst system. The completely saturated homopolymer containing Si(CH3)(3) group (APNSi) and a copolymer containing both Si(CH3)(3) and n-hexyl side groups (ACPNHSi) were prepared. The polymers have molecular mass of about 300 000 and a high glass transition temperature (T-g > 340 degrees C). Gas permeation properties of the polymers obtained were studied. APNSi reveals unusually high gas permeation parameters, e. g., P(O-2) of about 800 Barrer for different samples. This polymer also exhibits solubility controlled gas permeation: the permeability coefficients increase in the series of n-alkanes C-1-C-4 when the size of the penetrant increases. Free volume in addition type substituted polynorbornenes was studied using positron annihilation lifetime spectroscopy (PALS). This method indicated that very large sizes of free volume elements are characteristic for APNSi what explains its great gas permeability. Another interesting feature of this polymer is an independence of the annihilation parameters (lifetimes tau(i) and intensities I-i) of temperature in a wide range of its variation. Thus, APNSi is a novel representative of high free volume, high permeability glassy polymers, and it is a potential material for gas separation membranes.