1056 ISSN 0965-5441, Petroleum Chemistry, 2016, Vol. 56, No. 11, pp. 1056–1060. © Pleiades Publishing, Ltd., 2016. Original Russian Text © P.P. Chapala, I.L. Borisov, M.V. Bermeshev, V.V. Volkov, E.Sh. Finkelshtein, 2016, published in Membrany i Membrannye Tekhnologii, 2016, Vol. 6, No. 4, pp. 406–411. Synthesis and Gas Separation Properties of Metathesis Poly(5-Ethylidene-2-Norbornene) P. P. Chapala, I. L. Borisov, M. V. Bermeshev*, V. V. Volkov, and E. Sh. Finkelshtein** Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow *e-mail: bmv@ips.ac.ru **e-mail: fin314@gmail.com Received March 16, 2016 Abstract⎯High molecular weight metathesis poly(5-ethylidene-2-norbornene) (PENB) has been synthe- sized in the presence of the 1st generation Grubbs catalyst at a high monomer/catalyst ratio (3000/1 and higher). The yields of the corresponding polymer have been more than 90% at all monomer/catalyst ratios and molecular weights (M w ) of PENB have been higher than 3 × 10 5 . The gas permeability of different gases (He, H 2 , O 2 , N 2 , CO 2 , and CH 4 ) through PENB films has been studied, and diffusivity and selectivity coef- ficients have been determined. It has been found that PENB is more permeable than unsubstituted metathesis polynorbornene and cycloalkyl-substituted polynorbornene dicarboximides, but it is less permeable than some Si-containing polynorbornenes. Despite the fact that PENB is more permeable than metathesis poly- norbornene and cycloalkyl-substituted polynorbornene dicarboximides, it is close to these polymers in ideal selectivities for some gas pairs . Keywords: 5-ethylidene-2-norbornene, metathesis polynorbornenes, gas permeability DOI: 10.1134/S0965544116110049 INTRODUCTION Currently, wide assortment of additive and metath- esis polymers has been synthesized on the basis of sub- stituted norbornenes and tricyclononenes, and their gas-transport properties have been studied as well [1– 9]. It has been shown using silicon- and germanium- containing additive polynorbornenes as an example that these polymers belong to a class of the most per- meable polymers [1–3]. Metathesis polynorbornenes are of interest because of the possibility of synthesis of various polymer structures with a predefined number and required nature of substituents on their basis [10, 11]. Here, little attention has been paid to the synthesis and investigation of the properties of metathesis poly- norbornenes containing side alkyl or alkenyl substitu- ents. The presence of additional double bonds in the substituents might allow further additional functional- ization by them, e.g., the introduction of bulk macro- cycles of the required nature or crosslinking with their participation. Therefore, synthesis and investigation of the properties of polymer materials consisting of monomer units of such a type or containing them appears to be of current interest. As the study object in this work, a polymer on the basis of 5-ethylidene-2- norbornene (ENB) was chosen and synthesized. The choice of this monomer is determined, on the one hand, by the fact that it is a commercially available bifunctional monomer containing two chemically reactive double bonds, endocyclic and exocyclic [12]. On the other hand, ENB is currently successfully used as the third component in the production of a com- mercial copolymer of ethylene and propylene which is further cross-linked by the exocyclic double bonds of ENB [13]. Accordingly, in future, it is possible to try to obtain in a similar way copolymers on the basis of sil- icon-containing norbornenes and ENB, conduct their cross-linking and, therefore, impart higher stability to the polymers being created—potential materials for gas-separation membranes. In connection therewith, it is necessary to know the properties, in particular, gas-transport properties, of the corresponding homopolymers. Earlier, we have studied in detail the polymerization and gas permeability of silicon-con- taining polynorbornenes [1, 2]. Therefore, in this work, we selectively involved ENB in the metathesis polymerization by the endocyclic double bond and studied its gas-transport properties. EXPERIMENTAL Materials A 1st generation Grubbs catalyst for metathesis polymerization (Аldrich) was used without prelimi- nary purification. 5-Ethylidene-2-norbornene was refluxed over sodium in an argon atmosphere and then distilled under argon. The inhibitor 2,2'-methylen-