In this study, linseed oil was directly polymerized with different oil soluble resoles. p-Ethyl (PEP), p-tertiary butyl (PTB), p-tertiary octyl (PTO), and p-phenyl (PPP) phenols were separately reacted with formaldehyde to give linseed oil soluble resoles. These were then reacted with linseed oil to give transparent rubbery polymers. A model reaction was performed with methyl oleate and PTB phenol resole to clarify the reaction mechanism. Reaction products were characterized with H-1-NMR and IR techniques. Spectral examination of the model reaction showed that polymerization reaction proceeded via ene reaction of the quinone methide formed at the end group of the resole with the allylic positions of the fatty ester. Rubbery polymers were obtained with linseed oil using 10 to 40% of the different resoles. Hard, load bearing and tough materials were obtained at 40% phenolic resin loading. Mechanical properties of the materials were characterized by dynamic mechanical analyzer (DMA) and stress strain tests. The best mechanical and thermal properties were obtained with PEP resole which showed a storage modulus of 350 MPa and a tan 8 peak at 65 degrees C. Storage moduli of 275, 250, and 30 were obtained for PPP, PTB, and PTO resoles-linseed oil polymers, respectively. At the same phenolic resin loading, elongation at break and swelling ratios in CH2Cl2 increased with the longer alkyl substitution on the resole resins. The highest thermal stability was observed by PEP resole linseed oil polymer which has a 5% weight loss temperature of 340 degrees C as determined by TGA. The lowest thermal stability was observed for PTB resole-linseed oil polymer at 220 degrees C. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 849-856, 2010