In continuation of our endeavor to develop synthetic resins of improved properties and performance, we report here the synthesis of mixed copolymer resins by the condensation of resorcinol, aniline, and formaldehyde with ortho-, meta-, and para-phenylenediamine separately. The resins were characterized by infrared (IR) and thermogravimetric analysis (TGA). The mixed copolymer resins were found to have superior thermal stability over conventional phenol-CH2O and resorcinol-CH2O resins. The solubility behavior of the resins showed that they are resistant to common solvents. However, they are soluble in concentrated Ha(2)O(4) and HNO3, but insoluble in concentrated HCl.