Synthesis and properties of imidazole-blocked diisocyanates

Abstract

Imidazole-, 2-methylimidazole- and benzimidazole-blocked hexamethylene diisocyanate and isophorone diisocyanate have been prepared and characterized by elemental analyses, IR and NMR spectroscopy. The structure–property relationship of these adducts has been established by reacting with hydroxyl-terminated polybutadiene (HTPB). The cure rate of the adduct increases from the imidazole to 2-methylimidazole and to the benzimidazole-blocked adduct. Also, the cure rate of the adducts based on hexamethylene diisocyanate is higher than those based on isophorone diisocyanate. Simultaneous TGA/DTA results also confirm this trend. The gas chromatogram of the imidazole-blocked isocyanate confirms that the thermolysis products are blocking agent and isocyanate. The solubilities of the adducts have been measured in polyether and hydrocarbon polyols: the 2-methylimidazole and benzimidazole-blocked hexamethylene diisocyanate adducts show higher solubility than the rest. © 1999 Society of Chemical Industry