Synthesis and properties of imidazole-blocked diisocyanates

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. (C) 1999 Society of Chemical Industry.