A new metathesis polynorbornene containing three SiMe3 groups per monomer unit directly connected to the norbornene moiety via SiC bonds is synthesized. The ring-opening metathesis polymerization of sterically hindered 3,3,4-tris(trimethylsilyl)tricyclononene-7 is successfully conducted in yields 80-85% in the presence of first generation Grubbs catalyst. The corresponding polymer is obtained with molecular weight Mw up to 5.4 × 105 Da. It is an amorphous glassy ( Tg = 200 °C) polymer with high thermal stability. Gas permeability and diffusivity coefficients are studied for a range of gases (He, H2, O2, N2, CO2, CH4). This polymer containing three SiMe3 groups per monomer unit turns out to be more permeable ( P(O2) = 125 Barrer) than similar polymers with one or two SiMe3 groups per monomer unit ( P(O2) = 30-50 Barrer). Wide angle X-ray diffraction, positron annihilating lifetime spectroscopy, as well as Brunauer-Emmett-Teller investigations are also performed and discussed. [ABSTRACT FROM AUTHOR]