The synthesis and gas transport properties of aromatic polyisophthalamides (PIPAs) based on isophthaloyl chloride (LPC) derivatives bearing a pendent phenyl group and a hexafluoroisopropylidene (6F) linkage in the main chain are reported. The properties of these polymers are compared with the properties of similar PIPAs containing sulfonyl (SO2) rather than 6F in the main chain. Polymers containing a phenyl pendent group at the five position of the isophthaloyl linkage are more permeable than those bearing only a hydrogen atom at this position, although increases in permeability are generally accompanied by decreases in selectivity. In the SO2-bearing polymer, the addition of a phenyl pendent group hinders chain packing more than in the 6F containing PIPAs. Consequently, permeability coefficients increase more upon addition of a pendent phenyl group in SO2-containing rather than 6F-containing PIPAs. The effect of amide linkage reversal on the gas transport properties of a polymer containing 6F linkages in the chain backbone and a hydrogen atom at the five position of the isophthaloyl linkage was minimal. All the PIPAs considered in this study were more permeable to nitrogen than to methane, some with nitrogen/methane selectivities of more than two.