Abstract
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.
Highlights
Polyurethane is one of the most widely used engineering materials, which can be efficiently tailored as fibers, elastomers, foams, adhesives, and coatings for designed purposes by chemistry and processing [1]
These adducts are relatively inert at room temperature, but they can regenerate free isocyanates at the deblocking temperature, which can rapidly react with adducts containing the active hydrogen to form more thermally stable bonds [5,6]
The deblocking temperature is increased with pyridinol nucleophilicity based on differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), and CO2 evolution method
Summary
Polyurethane is one of the most widely used engineering materials, which can be efficiently tailored as fibers, elastomers, foams, adhesives, and coatings for designed purposes by chemistry and processing [1]. Two different mechanisms named as “elimination‐addition” and of blocking-deblocking reaction by using chemical titration [9], infrared spectrum [10], and “addition‐elimination” have been proposed to explain the reaction between blocked isocyanates and NMR spectroscopy [11,12]. According to the first mechanism, the blocked isocyanate decomposes to “addition-elimination” have been proposed to explain the reaction between blocked isocyanates produce the free isocyanate, which reacts with the nucleophilic adducts. The reaction mechanism, the nucleophilic adducts react directly with the blocked isocyanate to form a procedure of the reaction has not been comprehensively studied and the two proposed mechanisms tetrahedral intermediate. Friedman–Reich–Levi (FRL) equation, the Flynn–Wall–Ozawa (FWO) equation, and the Crane the thermal decomposition reaction kinetics by thermo-gravimetric analysis (TGA) based on the equation. These results may provide some valuable information in theoretical research for the application of blocked isocyanates
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