1195 ISSN 0965-5441, Petroleum Chemistry, 2017, Vol. 57, No. 13, pp. 1195–1206. © Pleiades Publishing, Ltd., 2017. Original Russian Text © Yu.P. Yampolksii, S. Banerjee, 2017, published in Membrany i Membrannye Tekhnologii, 2017, Vol. 7, No. 6, pp. 371–383. Effects of Bulky Substituents on Transport Properties of Membrane Gas Separation Materials 1 Yu. P. Yampolksii a, * and S. Banerjee b a Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia b Materials Science Centre, Indian Institute of Technology Kharagpur, Kharagpur, India *e-mail: Yampol@ips.ac.ru Received June 1, 2017 AbstractIn this review membrane gas separation properties of two groups of glassy polymers are considered and compared. The first group comprises highly permeable polymers with large free volume. They contains bulky substituents of the structure MR 3 , where M = Si, Ge, C, and R = Me, Et, Ph. The second group is represented by polycondensation materials (polyamides, polyimides etc.) with various bulky side groups. It was noted that introduction of such substituents into various main chains of polymers of both groups results in increases in gas permeability, free volume and diffusivity. Robeson diagrams for both cases are considered. Keywords: highly permeable polymers, polycondensation materials, permeability, diffusion, solubility, selec- tivity of gas separation, free volume DOI: 10.1134/S0965544117130114 INTRODUCTION Directed search for polymers with certain structure and desirable transport properties became recently an important direction of membrane science [1–3]. Dif- ferent approaches are known today for variation of the polymer design in attempts to achieve the desirable results – high gas permeability in combination with great selectivity of gas separation and stability in sepa- rated mixtures. Let us summarize briefly some known features of design that can affect the resulting mem- brane properties. 1. Rigidity or flexibility of chains; 2. Role of intermolecular interactions (dipole- dipole, H-bonding etc.); 3. Cross-linking; 4. Configuration of side groups (chains); 4.1 Bulky substituents attached directly to the main chains; 4.2 Bulky substituents attached via spacers. Different approaches are characterized by different efficiency. The strongest, popular and studied in detail is the approach 4.1. It results in obtaining of the most permeable membrane materials. However, in reality all of them work in combinations. For example, a bulky substituent (BS) can include polar groups (4.1 + 2), and this decreases permeability. The effects of BS strongly depend on the rigidity of main chain, so we always deal with the case 1 + 4.1. At last in the pro- cess of search for and creation of novel materials of gas separation membranes one must always pay attention on difficulties (or easiness) of synthesis, observed yields and cost of preparation of the polymer. There is huge literature on introduction of BS (mainly SiMe 3 groups) into carbochain, predomi- nantly vinylic and polyene chains [4, 5]. On the other hand, there are reasons to consider the efficacy of introduction of other BS and into the chains of other nature, into the products of polycondensation (poly- imiders, polyamides, etc.). According to this, we plan in this brief review to compare these two directions of the works. Usually, in the literature they are consid- ered independently. TYPES OF SUBSTITUENTS Let us consider the main types of BS introduced into various polymer chains. It should be noted that the definition of BS is not well defined. Thus, replace- ment of H by Me the latter can be considered as bulky, but we shall not consider such trivial cases. However, in some cases for example the group CF 3 can be con- sidered as BS. It is convenient to consider separately BS introduced into carbochain polymers or polycon- densation materials (Table 1). It is seen that substituents introduced into the first group of polymers are distinguished by lower struc- tural variation: they differ mainly by the central atom in symmetrically substituted nonpolar group. The 1 The article was translated by the authors.