Acetaldehyde azine (AcAz) underwent 'crisscross' addition with two equivalents of phenyl isocyanate to form a one-to-two adduct in a moderate yield (63.0%). Using crisscross addition of AcAz, polymeric products were obtained from AcAz and 1,4-phenytene diisocyanate in a high yield (> 80%). The polymer obtained was soluble in 1,1,1,3,3,3-hexafluoro-2-propanol, and insoluble in many organic solvents, including n-hexane, benzene, toluene, chloroform, diethyl ether, tetrahydrofuran, acetone, ethanol, methanol, dimethyl sulfoxide, and N,N-dimethylformamide. The structure of the polymer obtained was characterized by IR and H-1 NMR spectroscopies. The thermal behavior of the polymer was also investigated by thermogravimetric analysis. (c) 2005 Elsevier Ltd. All rights reserved.