3,5-Diamino-N-phenylbenzamide has been synthesized and thermoplastic polyimides prepared on its basis. Analysis of the gas transport and physicochemical properties of the obtained polymers has shown that the introduction of the phenylamide group into the diamine moiety of rigid- and flexible-chain polyimides has opposite effects on their properties. The observed effects can be explained by the formation of hydrogen bonds in the case of the more flexible polymer, as has been proved by high-temperature IR spectroscopy data. Thus, the properties of polyimides based on 3,5-diamino-N-phenylbenzamide are determined by inter-molecular interaction of the side phenylamide groups, opening new opportunities for the synthesis of membrane materials with active polar groups.