A novel triptycene-based diamine, 2,6-diaminotriptycene-14-carboxylic acid, was synthesized and used for preparing carboxylic acid containing triptycene-based Troger's base copolymers, CoPIM-TB-1 and CoPIM-TB-2, with another diamine monomer, 2,6-diaminotriptycene. The copolymers were subsequently post-crosslinked by glycidol to form C-CoPIM-TB-1 and C-CoPIM-TB-2. Glycidol crosslinking greatly impeded inter-chain mobility of the triptycene-based copolymers and subsequently restricted both physical aging rate and CO2 induced plasticization. Gas permeabilities of 40 days old C-CoPIM-TB-2 film decreased by 7%, 5%, and 9%, to gases H-2, CO2, and O-2, respectively, which were slower than those of the uncrosslinked PIM-Trip-TB polymer of which permeabilities decreased by 21%, 42%, and 30%, respectively. Mixed gas permeation results showed no CO2 induced plasticization at a CO2 partial pressure up to 20 atm. Moreover, separation performance of C-CoPIM-TB-1 and C-CoPIM-TB-2 went over the Robeson 2008 upper bounds for gas pairs including O-2/N-2, CO2/CH4, CO2/N-2 and H-2/N-2. All these results indicated a great potential for the post-crosslinked Triptycene-Based Troger's Base polymers for natural gas sweetening.