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Polymers occupy a central role in the development of modern society. One of the important application of polymers is in the field of membrane based technologies. Membrane-based gas separation is an active area of research due to its high demands in industrial applications, such as, preparation of nitrogen or oxygen enriched air, removal of CO2 for natural gas and mitigation of carbon dioxide from greenhouse gas-producing sources [1,2]. However, the inherent trade-off between gas permeability(P) and selectivity(α) for a pair of gases limits the large scale applications of this technique [3]. In fact, there is no strict “design rules” for the polymers to obtain optimal gas separation efficiency. However, the structural elements which simultaneously enhanced the polymer rigidity and fractional free volumes (FFV), are the important design rules in preparing superior membrane materials for gas permeation applications. Among several other polymeric materials, aromatic polyamides (PAs) and polyimides (PIs) can be used as alternative membrane materials for gas separation due to their excellent mechanical and thermal properties. Considering the above facts, we have designed and synthesized several organo-soluble PAs and PIs containing different bulky groups like, fluorenone, adamantane, tert-butyl, triphenylamine (TPA)etc. All the membranes showed high thermal and mechanical stability. The effect of these bulky groups on gas permeation and diffusion processes were investigated. The PAs with tri-tert-butylphenol substituted triphenylamine moiety showed very high gas permeability with moderate gas selectivity [PCO2 = 119.0, PO2 = 29.0 Barrer and PCO2/PCH4 = 37.19, PO2/PN2 = 9.67] [4, 5]. Whereas, the PEIs with cardo fluorene moiety and long-branched aliphatic chain showed moderate gas permeability [P(CO2)= 73.91 and P(O2)= 17.12] and very high permselectivity [α(CO2/CH4)= 78.24, α(O2/N2)= 20.24] [5]. |