Synthesis and properties of imidazole-blocked diisocyanates

Imidazole-, 2-methylimidazole- and benzimidazole-blocked hexamethylene diis ocyanate and isophorone diisocyanate have been prepared and characterized b y elemental analyses, IR and NMR spectroscopy. The structure-property relat ionship of these adducts has been established by reacting with hydroxyl-ter minated polybutadiene (HTPB). The cure rate of the adduct increases from th e imidazole to 2-methylimidazole and to the benzimidazole-blocked adduct. A lso, the cure rate of the adducts based on hexamethylene diisocyanate is hi gher than those based on isophorone diisocyanate. Simultaneous TGA/DTA resu lts also confirm this trend. The gas chromatogram of the imidazole-blocked isocyanate confirms that the thermolysis products are blocking agent and is ocyanate. The solubilities of the adducts have been measured in polyether a nd hydrocarbon polyols: the 2-methylimidazole and benzimidazole-blocked hex amethylene diisocyanate adducts show higher solubility than the rest. (C) 1 999 Society of Chemical Industry.