Abstract <p>Metathesis and hydrogenated oligomers of 5-ethyl-2-norbornene were prepared via tandem synthesis: metathesis polymerization in the presence of first- and second-generation Grubbs catalysts in an ethylene atmosphere and subsequent one-pot hydrogenation. The structure of metathesis and modified products was studied using ¹Н and ¹³С NMR spectroscopy and IR spectroscopy. The effect of the catalyst type on the molecular weight and ratio of components in a mixture of metathesis and hydrogenated oligomers, as well as the effect of the molecular weight on the glass transition temperature of the products, was demonstrated.</p>