Investigation of Methyl Methacrylate Grafting on Model Single Fatty Acid Alkyds

Four model alkyds were prepared by the fatty acid process using a single fatty acid (stearic, oleic, linoleic, or linolenic acid) with phthalic anhydride and glycerol. These model alkyds were reacted with methyl methacrylate (MMA) in the presence of benzoyl peroxide or azobis­(isobutyronitrile). 1H NMR, 2D gradient heteronuclear multiple quantum coherence NMR, matrix assisted laser desorption ionization mass spectrometry, solvent extraction, and gas chromatography were used to evaluate each model alkyd system. The conversion of MMA was quantified, and the grafting mechanism of MMA onto each model alkyd was elucidated. In general, both polymerization rates and MMA conversions were inhibited in the presence of alkyd resins. For oleic alkyd model systems, the grafting site was primarily located at the double bond on the fatty acid chain. Both the homopolymerization and copolymerization of the MMA are significantly retarded by chain transfer of the hydrogen from the double allylic site in the linoleic and linolenic model systems. For the linoleic alkyd and linolenic alkyd model systems, the grafting reaction predominately occurred at the activated double allylic methylene group on the fatty acid chain via hydrogen abstraction by the primary radical and MMA radical, followed by grafting in a termination reaction with a propagating MMA radical.