Six polyamideimides (PAI) were synthesized from six dianhydride monomers containing amide functions. The dianhydride monomers were obtained from the reaction of trimellitic anhydride chloride with six aromatic diamines-1,4,4-phenylenediamine, 2,2-bis(4-aminophenyl) propane, 4,4'-oxydianiline, 4,4'-methylenedianiline, 1,1-bis(4-aminophenyl)cyclohexane, and bis(4-aminophenyl)sulfone-by a low-temperature condensation with yields ranging from 35 to 98% depending on the monomer solubility in organic media. The monomers were characterized by Fourier transform infrared (FTIR) and H-1 NMR. In accordance with a synthesis scheme implying the reaction of a macrodiisocyanate with dianhydride monomers containing amide functions, six PAIs with a highly flexible soft block (polytetramethylene glycol PTMG 650) were synthesized with inherent viscosities ranging from 0.38 to 1.3 dL/g. Their characterization by FTIR and 1H NMR fully confirmed their chemical structure. The strong physical crosslinking provided by polar hard blocks containing up to eight aromatic rings enabled the casting of PAI films that were very tough in the dry state and could withstand exposure to rather strong solvating media (e.g., ethers, alcohols, and chlorinated solvents). First experiments showed these materials could be good candidates for membrane-separation applications. They revealed interesting features for the separation of organic aprotic-protic mixtures as shown by the first results obtained for the purification of a fuel octane enhancer (ethyl-tert-butyl ether) used in the European Community.