A set of poly[bis(trimethylsilyl) tricyclononenes] bearing two trimethylsilyl side groups at geminal position in monomer unit has been synthesized by ring-opening metathesis polymerization technique and investigated via static and dynamic light scattering, viscometry and H-1 NMR relaxation in diluted solutions. Molecular properties of this type polymer have been under study for the first time. Its scaling relations and chain rigidity are obtained and compared to polymer synthesized by means of addition polymerization of the same monomer. There is shown that additive and metathesis polymers considerably differ by their chain rigidity, both equilibrium and kinetic. Metathesis analogue is typical flexible chain polymer characterizing by Kuhn segment length 1.6 nm, while the additive one, whose Kuhn segment is 5.6 nm, belongs to semirigid range. The influence of chain rigidity on thin film properties of substituted polytricyclononenes is also discussed because the synthesized by addition or metathesis routes polymers display very different gas permeability in films.