Crisscross addition polymerization of alkyl aldazines (i.e., acetaldehyde azine, propionaldehyde azine, and butyraldehyde azine (BuAz)) and 1,4-phenylene diisocyanate (Ph(IC)(2)) was investigated under various conditions. The crisscross addition polymerizations in pyridine yielded polymers in higher yields. The polymers obtained in the present study exhibited very limited solubilities and contained fractions insoluble in conventional organic solvents. However, since the BuAz/Ph(IC)(2) polymers obtained at 24 and 48 h were soluble in pyridine, the M-W values for these polymers were determined to be 2.2 x 10(3) and 4.4 x 10(3), respectively, by small angle X-ray scattering. These data indicated that molecular weights of the pyridine-insoluble polymers were as high as or close to 10(4). IR, H-1 NMR, and MALDI-TOF-MS data confirmed the formation of linear polymers by crisscross addition polymerization. Thermogravimetric analyses indicated that the polymers were considerably decomposed in the region of 300-400 degrees C, but the polymers exhibited residual weights of 15-25% even at 500 degrees C. Differential scanning calorimetry data indicated that glass transition temperatures for the polymers were higher than the onset of decomposition presumably because of the rigid backbone. (C) 2009 Elsevier Ltd. All rights reserved.