Synthesis and characterization of ricinoleic acid based hyperbranched alkyds for coating application

Abstract

Hyperbranched alkyds based on ditrimethylolpropane, dimethylolpropionic acid, and ricinoleic acid were synthesized. The synthesized resins were characterized by the determination of hydroxyl and acid numbers, viscosity, average molecular masses, and molecular masses distribution. Compared with conventional alkyd resins of similar molar masses, the synthesized hyperbranched alkyds have significantly lower viscosity values at a given temperature. Therefore, a significantly smaller amount of organic solvents is required for their dissolution and can be used as precursors to obtain eco-friendly coatings. The obtained hyperbranched alkyd resins were cured by two commercial melamine resins (mass ratio 70:30). The curing of the resin mixtures was examined by FTIR spectroscopy, rheometry, and by the determination of gel content. The curing of the resin mixtures proceeds via the reactions between hydroxyl and carboxyl groups of hyperbranched alkyds with isobutoxymethyl and methoxymethyl groups in melamine resins. Hyperbranched alkyd/melamine resin mixtures were cured at 150 °C for 60 min. Thermal properties, dynamic mechanical behavior, physico-mechanical characteristics, and chemical resistance of cured films were determined. The crosslinking densities of films obtained from mixtures using hexamethoxymethyl melamine resin are significantly higher than those based on mixtures using isobutylated melamine resin. The thermal degradation of cured films is a complex process, and their thermal stability increases slightly with the increase of hyperbranched alkyds generation. It is assumed that mixtures of synthesized hyperbranched alkyds with melamine resins would be suitable for obtaining the coatings with good chemical resistance and physical-mechanical properties.