9-Alkylated fluorene-based poly(ether imide)s and their gas transport properties

• New diamine monomer containing 9-alkylated fluorene moiety was synthesized.
• Poly(ether imide)s (PEIs) were synthesized using new diamine monomer.
• PEIs showed good thermal stability, mechanical strength and low dielectric constant (ε=2.35).
• PEIs showed good combination of gas permeability and permselectivity.

The effect of cardo fluorene moiety and long-branched aliphatic chain in poly(ether imide) (PEI) membranes on gas transport properties have been investigated. Accordingly, this article reports the synthesis of a new cardo bis(ether amine) monomer with long and branched aliphatic chain namely, 9,9-bis(2-ethylhexyl)-2,7-bis(4-aminophenoxy-3-trifluoromethylphenyl)-9H-fluorene and its polymerization with five different dianhydrides. The monomer and the PEIs were characterized by elemental analysis, 1H-NMR and ATR-FTIR techniques. The polymers showed high molecular weight, glass transition temperature (Tg) up to 248 °C, 10% degradation temperature up to 409 °C and 437 °C under air and nitrogen respectively, tensile strength up to 100 MPa and dielectric constant (ε) as low as 2.35. Gas transport properties of these PEI membranes were investigated at three different temperatures (35, 45 and 55 °C) using four different gases (e.g., CH4, N2, O2 and CO2). The PEIs showed high gas permeability [P(CO2)=73.91 and P(O2)=17.12] and permselectivity [α(CO2/CH4)=78.24, α(O2/N2)=20.24] in comparison to many other previously reported PEIs.

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