Isophorone diisocyanate in blocking agent free polyurethane powder coating hardeners: analysis, selectivity, quantumchemical calculations

Blocking agent free polyurethane powder coating formulations are emission free and thus comply with the highest ecological requirements. In addition the resulting coatings exhibit an excellent performance in non-yellowing light-stable applications for exterior use. Essential component of the formulations is isophorone diisocyanate (IPDI)-uretdione, an internal blocked derivative of IPDI. For the first time it is now possible to identify each of the 10 isomers by 13 C -NMR-spectroscopy. This opportunity leads to fundamental conclusions concerning the selectivity of IPDI in the uretdione generating step and the reactivity of the different uretdione isomers in the crosslinking reaction. Quantumchemical calculations confirm the experimental results.