Thermally curable benzoxazine-modified vegetable oil as a coating material Can Yildirim, A. Tuncer Erciyes, Yusuf Yagci Ó American Coatings Association & Oil and Colour Chemists’ Association 2013 Abstract In this article, a new synthetic approach for the modification of partial glycerides (PG) obtained from sunflower oil with thermally curable benzoxazine units and its potential use as a coating material are described. For this purpose, hydroxyl-containing benzoxazine monomer was first prepared by conven- tional ring-forming reaction of phenol with para- formaldehyde in the presence of 6-amino-1-hexanol. The subsequent urethane reaction between PG and the benzoxazine monomer using toluene diisocyanate yields corresponding modified oil. The structures of the intermediates, and the modified triglycerides are confirmed by FTIR and 1 H NMR spectral analysis. Thermally activated curing behaviors of the precursor and the modified oil in the absence of any catalyst were studied by differential scanning calorimetry. Thermal and film properties of the cured products were also investigated. Keywords Vegetable oil, Triglyceride, Benzoxazine, Thermoset, Coating Introduction Triglyceride oils are one of the most widely used, naturally renewable sources. In addition to nutritional purposes, these natural products are also used for various technical applications particularly in the man- ufacture of coating materials. Despite extensive usage, these materials exhibit poor film properites and there- fore need to be modified. The well-known modified product developed as a coating material is styrenated oil. Conventionally, oil and styrene are heated together at elevated temperatures such as 250°C for 24 h in the presence of an initiator. 1–3 However, besides the yield of the essentially required product, concomitant homo- polymer formation is unavoidable. Homopolymers formed from the radicals stemming from the initiator essentially contribute to an opaque appearance. Previ- ously, we proposed several strategies involving macromo- nomer and macroinitiator techniques to eliminate the homopolystyrene formation. 4–11 The film properties of triglyceride oil coating mate- rials can also be improved by the incorporation of nonvinyl monomers into the structure. Succesful exam- ples include incorporation of methylolated abietic acid, 12 diisocyanates, 13 3-aminopropyltriethoxysilane (APES), 14 and vinyl alkoxysiloxane. 15 Although polybenzoxazines are newly developed thermoset resins, they have received enormous interest from academics and the chemical industry because of their many unique properties. These include volumetric stability upon curing, no requirement for curing strong acid catalysts or additives, high thermal stability, good mechanical performance, low water absorption, and high char yield of the cured products. 16 Benzoxazine resins were considered to be alternative materials for epoxides, bismaleimides, cyanate esters, and polyi- mides. They also overcome several limitations of conventional novolac- and resole-type phenolic resins. Moreover, benzoxazine chemistry offers molecular C. Yildirim, A. T. Erciyes (&) Department of Chemical Engineering, Istanbul Technical University, Maslak, Istanbul 34469, Turkey e-mail: erciyes@itu.edu.tr Y. Yagci (&) Department of Chemistry, Istanbul Technical University, Maslak, Istanbul 34469, Turkey e-mail: yusuf@itu.edu.tr Y. Yagci Faculty of Science, Chemistry Department, King Abdulaziz University, Jeddah, Saudi Arabia J. Coat. Technol. Res. DOI 10.1007/s11998-013-9472-8