Synthesis and gas separation properties of polyimide membranes derived from oxygencyclic pseudo-Tröger's base

Abstract

Two neoteric oxygencyclic pseudo-Tröger's base (TB) -derived naphthalene diamines characterized by large π conjugated naphthalene rings and half-open cavity structure unit, 16H-8,16-methanodinaphtho [2,1-d:1′,2′-g] (Yampolskii, 2012; Maqsood et al., 2014) [1,3]dioxocine-3,13-diamine (OTB) and its furan-based bicyclic analogue, 7a, 14c-dihydronaphtho [( Xu et al., 2014; Yampolskii, 2012) 2,12,1-b]naphth [1′,2':4,5]furo [( Maqsood et al., 2014; Xu et al., 2014) 3,23,2-d] furan-3,12- diamine (FB), were successfully synthesized. Their 6FDA-based polyimides (6FDA-OTB and 6FDA-FB) were obtained for membrane-based gas separation study. 6FDA-OTB and 6FDA-FB exhibited good solubility and excellent thermal stability due to the presence of large π conjugated aromatic rings and half-open cavity structure unit. The two polymer membranes showed high gas pair selectivity and modest gas permeability as well as good physical aging properties. The 6FDA-FB membrane performed a high selectivity of H2/CH4 (104.0) and CO2/CH4 (49.1), which arises from the larger permeation activation energy difference of different gases. The performances of 100 days aged 6FDA-OTB and 6FDA-FB membranes are almost overlapped with the 1991 Robeson upper bounds for CO2/CH4 and H2/CH4. In short, introducing the novel rigid oxygencyclic pseudo-Tröger's base into the polyimide chains could make attractive membrane materials for various gas separation applications.