Research on the Thermal Decomposition Reaction Kinetics and Mechanism of Pyridinol-Blocked Isophorone Diisocyanate

A series of pyridinol- blocked isophorone isocyanates, based on pyridinol including 2- hydroxypyridine, 3- hydroxypyridine, and 4- hydroxypyridine, was synthesized and characterized by 1H- NMR, C-13- NMR, and FTIR spectra. The deblocking temperature of blocked isocyanates was established by thermo- gravimetric analysis ( TGA), differential scanning calorimetry ( DSC), and the CO2 evaluation method. The deblocking studies revealed that the deblocking temperature was increased with pyridinol nucleophilicity in this order: 3- hydroxypyridine > 4- hydroxypyridine > 2- hydroxypyridine. The thermal decomposition reaction of 4- hydroxypyridine blocked isophorone diisocyanate was studied by thermo- gravimetric analysis. The Friedman- Reich- Levi ( FRL) equation, Flynn- Wall- Ozawa ( FWO) equation, and Crane equation were utilized to analyze the thermal decomposition reaction kinetics. The activation energy calculated by FRL method and FWO method was 134.6 kJ mol-1 and 126.2 kJ mol(-1), respectively. The most probable mechanism function calculated by the FWO method was the Jander equation. The reaction order was not an integer because of the complicated reactions of isocyanate.