Four aromatic tetraamine monomers possessing flexible ether linkages were successfully synthesized by nucleophilic aromatic substitution of hydroquinone, 4,4'-dihydroxybiphenyl, 2,2'-bis(4-hydroxyphenyl)propane, and 2,7-dihydroxynaphthalene with 5-chloro-2-nitroaniline, followed by reduction, respectively. With these monomers, a new class of soluble poly[ bis(benzimidazobenzisoquinolinones)] was prepared by a one-step, high-temperature solution polycondensation. The resulting polymers were completely soluble in phenolic solvents and had high inherent viscosities ranging from 1.2 to 1.5 g dL(-1). These polymers had glass transition temperatures in the range of 427-449 degrees C. Thermogravimetric analysis showed that all polymers were thermally stable, with 5% weight loss recorded above 510 degrees C in nitrogen. The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 79.5-114.5 MPa, 10.3-23.0%, and 1.1-1.7 GPa, respectively. It is demonstrated that these semiladder polymer membranes displayed high CO2 permeability coefficients (P-CO2 = 31.6 - 96.5barrer) and permeability selectivity Of CO2 to CH4 (P-CO2/P-CH4 = 30-6 - 43.4). (C) 2008 Elsevier Ltd. All rights reserved.