Gas transport of helium, hydrogen, oxygen, nitrogen, methane and carbon dioxide gases in two polyarylates based on 9,9-bis(4-hydroxyphenyl)anthrone and isophthalic acid or t-butyl isophthalic acid has been examined. Substitution of a t-butyl group on the isophthalate ring increases polymer permeability two- to three-fold, primarily due to higher diffusion coefficients. The physical properties of these materials are very similar to those of their fluorene bisphenol-based analogues; however, the former are more permselective but less permeable than the latter. The favourable interaction of CO2 with the anthronylidene carbonyl unit and the higher degree of polarity in the repeat unit apparently contribute to these differences.