The kinetics of dissociation of blocked 2,4‐diisocyanatotoluene (tdi) in amines

The kinetics of dissociation of blocked diisocyanates based on commercial diisocyanatotoluene (TDI) (80/20 mixture of 2,4‐ and 2,6‐ isomers) in the presence of amino compounds was studied by a volumetric method and Fourier Transform IR (FTIR) spectral data. Second‐order rate constants for the dissociation of TDI adducts (with phenol, thiophenol and p ‐chlorophenol) in the presence of amines (dibenzyl, benzyl, cyclohexyl, n ‐hexyl and di‐ n ‐butyl) in cyclohexanone solvent are reported. The relative effects of various blocking agents, basicity of the amines and temperature on the dissociation of blocked TDI have been determined. An FTIR spectroscopic method was used to study the dissociation of blocked TDI (with blocking agents such as phenol, thiophenol, p ‐chlorophenol, p ‐nitrophenol, p ‐cresol, α‐naphthol and resorcinol) in the presence of excess triethylamine and in cyclohexanone solvent. Pseudo‐first‐order rate constants were calculated from NCO concentrations as determined from FTIR spectra.