The bismaleimides chain-extended by ureylene linkages were obtained by the reaction of a diamine with maleic anhydride (1 : 1 molar ratio) first and then by the reaction of the resulting solution with a diisocyanate, followed by the cyclodehydration of the diamic acid. The bismaleimides were characterized by elemental analysis, IR, H-1-NMR, and C-13-NMR. The results of thermal analysis show that the solidification reaction takes place above 200 degrees C for most bismaleimides and the crosslinking products decompose at higher temperatures.