Synthesis and characterization of a microporous 6FDA-polyimide made from a novel carbocyclic pseudo Troger's base diamine: Effect of bicyclic bridge on gas transport properties

A newly designed carbocyclic pseudo Troger's base diamine (CTB) monomer, 2,8-dimethyl-3,9-diamino5,6,11,12-tetrahydro-5,11-methanodibenzo[a,e][8]annulene (CTBDA) and its isomeric analogue 2,8dimethyl-(1,7)(4,10)(3,9)-diamino-5,6,11,12-tetrahydro-5,11-methanodibenzo[a, e][8] annulene (iCTBDA), were designed for the synthesis of microporous 6FDA-based polyimides (6FDA-CTBDA and 6FDA-iCTBDA). Both polyimides were soluble, exhibited excellent thermal stability of similar to 490 degrees C, and had high surface areas of 587 m(2) g(-1) (6FDA-CTBDA) and 562 m(2) g(-1) (6FDA-iCTBDA). A 6FDA-based polyimide derived from 4,10-dimethyl-3,9-diamino-6H,12H-5,11-methanodibenzo[b,f][1,5]-diazocine (6FDA-TBDA) was made for comparison to investigate the effects of the basic tertiary nitrogen functionality in the Troger's base diamine on the polymer properties relative to the carbocyclic 6FDA-CTBDA analogue. 6FDA-TBDA displayed lower gas permeabilities but moderately higher gas-pair permselectivities than 6FDA-CTBDA. The enhanced permselectivity of 6FDA-TBDA resulted exclusively from higher diffusion-based selectivity. Direct gas sorption measurements demonstrated that the basicity in the Troger's base bridge moiety enhanced the sorption capacity of CO2 only slightly and had no effect on the CO2/CH4 solubility selectivity in 6FDA-TBDA vs. 6FDA-CTBDA. (C) 2017 Elsevier Ltd. All rights reserved.