In this work we present the results from studies on novel poly(arylene ether ketone)s, including gas permeability, wide-angle x-ray diffraction (WAXD), and dynamic mechanical analysis (DMA). Poly(arylene ether ketone)s containing 2,2＇- and 3,3＇-dibenzoylbiphenyl (DBBP) moieties were characterized to study the effect of biphenyl substitution on gas transport properties. Gas permeabilities of naphthalene-containing poly(arylene ether ketone)s were also measured. Higher permeabilities were observed for polymers prepared with GF-BPA, compared to 9,9-bis(4-hydroxyphenyl)fluorene (HPF). The naphthalene-containing polymers exhibited higher permeabilities than the DBBP polymers, except for a polymer having the 2,2＇-DBBP and tetramethylbiphenyl moieties. Based on our work, and results reported in the literature, the 3,3＇-DBBP polymers showed the lowest permeabilities for DBBP-containing poly(arylene ether ketone!)s. The low permeabilities are due to more efficiently packed chains brought on by greater flexibility of the backbone, compared to the other polymers studied. DMA studies confirmed the higher barriers to rotation which are believed to be responsible for 2,2＇-DBBP polymers having similar selectivities compared to 3,3＇-DBBP polymers.