High Tg, processable fluorinated polyimides containing benzoisoindoledione unit and evaluation of their gas transport properties

Abstract

This article describes the preparation of a series of processable fluorinated poly(ether imide)s from a new diamine monomer 4,9-bis-[4-(4′-amino-3-trifluoromethyl-biphenyl-4-yloxy)-phenyl]-2-phenyl-benzo[f]-isoindole-1,3-dione. The polymers showed extremely high T_g (up to 335 °C), outstanding thermal stability (up to 559 °C) and high tensile strength (up to 102 MPa). The transparent (λ_cut-off ≥ 363 nm) membranes from these polymers were investigated for their gas transport properties for CO₂, O₂, N₂ and CH₄ at three different temperatures. The effect of the benzo[f]isoindole-1,3-dione moiety and the aromatic dianhydrides (BPADA, 6FDA, BTDA, ODPA and PMDA) towards the glass transition temperatures of the polymers and their consequences on gas transport properties have been investigated. The polymer prepared from 6FDA showed the highest permeability coefficient for all the gases (P_CO2 = 71.3, P_O2 = 25.4) whereas BPADA based polymer exhibited the highest permselectivity (CO₂/CH₄ ∼ 37.2 and O₂/N₂ ∼ 8.4), staying closer to the latest upper boundary limit drawn by L. M. Robeson.