Synthesis and Studies on the Dissociation of Aromatic Secondary Amine Blocked Isocyanates

N-methylaniline (NMA) blocked 4,4'-methylenebis(phenyl isocyanate) (MDI), 2,4-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and 4,4'-methylenebis(cyclohexyl isocyanate) (H12MD1) have been prepared and characterised by FTIR, H-1-NMR and C-13-NMR spectroscopic techniques and elemental analysis. A new method - rheometry for determining the minimum deblocking and curing temperature of the blocked isocyanate is described. This method has the advantage that it can be used to find out the minimum deblocking temperature of even nonvolatile blocking agents. The structure-property relationship of these adducts was-established by reacting them with hydroxyl terminated polybutadiene (HTPB), and corresponding changes in viscosity were studied by rheometry. The minimum deblocking and curing temperature of the adducts was found to be in the following order 4,4'-methylenebis(phenyl isocyanate) (MDI)-N-methylaniline < 2,4-toluene diisocyanate (TDI)-N-methylaniline < 4,4'- methylenebis (cyclohexyl isocyanate) (H12MD1)- N-methylaniline < isophorone diisocyanate (IPD1)- N-methylaniline. The minimum deblocking temperature of the adducts was also confirmed using thermal analyses. The regeneration of the isocyanate and the blocking agent was-confirmed by gas chromatography - mass spectrometry (GC-MS) and FT-IR spectroscopy