Study on the synthesis of new blocked polyisocyanates as crosslinking agents for hydrophobic polyurethane powder clear coatings

Blocked polyisocyanate crosslinkers for powder coatings were synthesized using isophorone diisocyanate (IPDI), formic acid and ε-caprolactam. They were modified with fluorinated polyols. Two kinds of catalyst i.e. dibutyltin dilaurate and dibutyl phosphate for the synthesis were employed. The chemical structures of these compounds were confirmed by nuclear magnetic resonance (NMR) spectroscopy. The molecular mass distribution was investigated using gel permeation chromatography (GPC). During the thermal degradation of modified polyisocyanate three main stages of decomposition can be seen. The degradation of modifier occurs in the last decomposition stage at temperature range of 375-500 °C, which is confirmed by coupled TG-FTIR technique. Additionally, polyurethane powder coating systems composed of polyester resin and modified blocked polyisocyanate, were examined. The cross-linked polyurethane powder coatings resulted in improved thermal stability and surface properties i.e. lower roughness and surface free energy values as well as higher hydrophobicity, oleophobicity, gloss, scratch and abrasion resistance.