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, 13C-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.