Novel moisture-cured hyperbranched urethane alkyd resin for coating application

A hyperbranched polyol (HBP) was synthesized using dipentaerythritol as a core material and 2,2-bis(methylol) propionic acid as a chain extender. This was reacted with varying concentrations of soya fatty acid to make hyperbranched alkyd (HBA) resins. The HBA resins containing unreacted hydroxyl groups were reacted with isophorone diisocyanate at NCO/OH ratio of 1.6:1 to make high solid hyperbranched urethane alkyd (HBUA) resins. The excess NCO content in the HBUA resins was used to cure with atmospheric moisture, and thus moisture-cured HBUA coatings were formed. The resins were characterized by FTIR, and 13C NMR spectroscopic analysis. A series of such resins were made using different fatty acid/isocyanate ratios with respect to the hydroxyl groups present in the HBP. The effect of compositions on the mechanical and weathering properties of the cured resins was investigated. It was observed that there was an optimum fatty acid–isocyanate ratio in terms of the requirements of solvent, mechanical and weathering properties of the resin. The requirement of solvents for formulating HBUA coatings is much lower compared to linear alkyd-based coatings. The present study reveals that the moisture-cured HBUA resins can be used as a binder material in the field of low-pollution weather-resistance coatings.