Polymerization of norbornene bearing Si(CH3)(3) groups in the five position with the opening of double bonds was performed. By accurate selection of the ratios catalyst/co-catalyst and monomer/catalyst the samples with increased molecular mass (about 400,000) were obtained. Transport parameters of this, addition type poly(trimethylsilyl norbornene) (PTMSN) were measured using the gas chromatographic and mass spectrometric methods for different gases (H-2, He. O-2, N-2, CO2, CH4, C2H6, C3H8 and n-C4H10). Temperature dependence of the permeability coefficients (P) indicated that low activation energies of permeation (E-P) and diffusion (E-D) are characteristic for PTMSN. In some cases (CO2, C2H6) negative E-P values were observed. Thermodynamics of vapor sorption in this polymer was studied using the inverse gas chromatography method. It was shown that PTMSN is characterized by very large solubility coefficients S similar to those of poly(trimethylsilyl propyne)(PTMSP). The comparison of the PA and S values of these highly permeable polymers showed that the greater permeability of PTMSP is determined by the larger D values. Application of different approaches for the determination of the size of microcavities in PTMSN indicated that this polymer is characterized by large size of microcavity (800-1200 angstrom(3)). (C) 2008 Elsevier B.V. All rights reserved.