Two new diamines, 1-(1-naphthoxy)-2,4-diaminobenzene and 1-(biphenylyl-4-oxy)-2,4-diaminobenzene, were synthesized and used for the preparation of modified polyamides and polyimides bearing bulky ether groups. Their properties were compared with those of the corresponding unmodified polymers. Characterization of polymers was accomplished by inherent viscosity measurements, Fourier transform infra-red, H-1 nuclear magnetic resonance, X-ray, differential thermal and thermomechanical, thermogravimetric and isothermal gravimetric analyses. The modified polyamides and polyimides showed considerably higher solubility than analogous unsubstituted polymers and dissolved in polar aprotic solvents and certain inorganic and organic acids upon heating or even at room temperature in some cases. The incorporation of the ether groups along the polymer backbone decreased the glass transition temperatures, which ranged from 110 to 195 degrees C. In addition, certain modified polymers softened at the region 190-273 degrees C. The modified polymers were more thermally stable than the parent counterparts, being stable up to 350-404 degrees C and affording char yields of 59-70% at 800 degrees C in N-2.