1,1-Bis(dimethylamino)ethylene (ketene N,N-acetal) (1) reacted with isocyanates to give either 1 : 1 adduct 3,3-bis(dimethylamino)acrylamides (3) or 1 : 2 adduct bis(dimethylamino)methylenemalonamides (4), depending on the amount of the charged isocyanate. 3 was obtained selectively in the case of isocyanate/1 = 1, while 4 was exclusively yielded in the case of isocyanate/1 = 2. Isothiocyanate showed similar reaction behavior as isocyanate. Polyaddition of 1 with diisocyanates afforded polyamides bearing a bis(dimethylamino)methylenemalonamide group with higher molecular weight. The obtained novel polyamides are soluble in various organic solvents, and reacted with diacid chloride to give crosslinked polymer quantitatively.