Poly(oxindolylidene arylene)s (PDXINARs), a family polymers with high performance in terms of thermal stability properties and with ether-bond-free aromatic back-bones alternating with bulky, torsion resistant oxindolylidene fragments, have been synthesized by superacid catalyzed polyhydroxyalkylation, and their useful physical properties have been assessed to determine their performance as gas separation membranes. The room temperature synthesis allows a variety of fully soluble, high-molecular-weight polymers in a single pot "click" reaction. These polymers can form flexible and transparent films, and they possess high glass transition temperatures (>500 degrees C); high decomposition temperatures (ranging from 500 to 524 degrees C); and FFVs (0.130-0.194) comparable to those reported for the polysulfone, polycarbonate, and polyarylate families. However, their selectivity-permeability combinations are very attractive because some fall close to the 2008 upper-bound limits. Membranes made from isatin and 9,9-dimethyl-9H-fluorene (2aD) display P(O-2) = 15.4 Barrer for the O-2/N-2 gas pair and an O-2/N-2 selectivity of 6.4, whereas for the H-2/CH4 gas pair, they display P(H-2) = 170 Barrer and a H-2/CH4 selectivity of 77.