A novel fluorine-containing telechelic polyimide end-capped with acetylene group which derived from 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,4-diaminodiphenyl ether (DADE), and 4-(2-phenylethynyl) phthalic anhydride (PEPA) was synthesized using polycondensation. The physical and CO2 permeation properties of its crosslinked membranes prepared by the cyclotrimerization reaction of the acetylene groups at the polymer chain end using tantalum (V) chloride (TaCl5) as a catalyst under thermal treatment was investigated in terms of CO2-induced membrane plasticization. The crosslinked membranes showed a gel content in organic solvent, which was good solvent of noncrosslinked membranes, and improved their thermal stability. Based on the measurement of the high-pressure time dependence on CO2 permeation, the crosslinked 6FDA-DADE-PEPA membranes exhibited more resistance to CO2-induced plasticization than noncrosslinked 6FDA-DADE and thermal treated 6FDA-DADE-PEPA. Furthermore, the increase in TaCl5 content resulted in more resistance to plasticization. The cyclotrimerization reaction of the acetylene groups at the polymer chain ends using a transition metal catalyst under thermal treatment was found to be more effective than conventional thermal treatments for suppressing membrane plasticization without the membrane densification. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers