Phosphorus-containing thermosetting resins derived from high oleic sunflower oil were prepared through phospha-Michael addition of a difunctional secondary phosphine oxide, the 1,3-bis(phenylphosphino)propane dioxide on the ,-unsaturated ketone derived from high oleic acid (ETR). The aim of this approach was to introduce phosphorus and to crosslink the material in one single step. Materials with increasing aromatic content were also prepared by addition 4,4-diaminodiphenylmethane and co-crosslinking through aza-Michael addition. The kinetics of the phospha and aza-Michael additions was investigated using the enone derivative of methyl oleate (EO) in presence of BF3 center dot Et2O as catalyst and in absence of catalyst at different temperatures. Competitive experiments showed that phospha-Michael addition proceeds faster than the aza-Michael addition. The new triglyceride-based thermosets containing up to 4.2% of P, were characterized and their thermal and flame retardant properties evaluated. Limiting oxygen index values increase from 21.5 for the phosphorus free material up to 38.0 for the final material with 4.2% P content. These results demonstrate that the flame retardant properties of vegetable oil-based thermosets can be significantly improved by adding covalently bonded phosphorus to the polymer. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 1808-1815