Herein the stereoselective two-step synthesis of pure exo-5-trimethylsilylnorbornene is reported. The monomer proved to be highly reactive in both metathesis and addition polymerization. ROMP polymerization was catalyzed by the first-generation Grubbs catalyst. High-molecular-weight saturated addition polymers were prepared using nickel or palladium complexes as precatalysts and Na+[B(3,5-(CF3)(2)C6H3)(4)](-) and/or MAO as cocatalysts. The obtained addition polynorbornenes are highly gas permeable and microporous materials possessing large free volume and BET surface area (up to 540 m(2)/g). The influence of the substituent orientation (exo- vs. exo-/endo-mixture) on polymer properties was established. The metathesis polymer based on exo-isomer exhibits 1.5- to 2-fold increase of permeability coefficients for all gases in comparison to the similar polymer based on the mixture of exo- and endo-isomers. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1234-1248