Functionalization of an alkyd resin with (meth)acrylate groups for photoinitiated polymerization

Abstract

Alkyd resin based on phthalic acid, soybean oil, pentaerythritol, and a small amount on fumaric acid was synthesized and functionalized with (meth)acrylate groups. Functionalization was carried out in two different ways. These were direct acrylation of the alkyd resin using acrylic acid and N-bromo succinimide on the one hand and a two step synthesis starting with epoxidation of the internal double bonds comprising in the alkyd resin followed by ring opening reaction with (meth)acrylic acid in a consecutive reaction on the other hand. The (meth)acrylate functionalized alkyd resins were characterized by 1H- and 13C NMR spectroscopy, FT-IR spectroscopy, GPC, iodine value (IN), and glass transition temperature (Tg). Photoinitiated polymerization of the functionalized alkyd resins using bis(4-methoxybenzoyl) diethyl germanium as photoinitiator was investigated by photo-DSC under nitrogen and in the presence of air. The maximum of the polymerization rate (Rpmax), the time (tmax) to obtain Rpmax, and the conversion on double bonds give information about the strong increase in the reactivity of the (meth)acrylate functionalized alkyd resins caused by their (meth)acrylate substituents. Additional bromo or hydroxy substituent attribute to reactivity differences between the functionalized alkyd resins. Moreover, (meth)acrylate functionalized alkyd resins were investigated as additives (10 wt %) in traditional monomers (1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate) or in acrylate functionalized methyl oleate model monomers. Photo-DSC investigation of the mixtures under nitrogen and in the presence of air showed no significant influence of the hydroxy substituted (meth)acrylated alkyd resin additives on photopolymerization kinetics of the traditional monomers. Although incorporation of bromine into the acrylated alkyd resin resulted in a slight decrease of both the Rpmax value and the conversion on double bonds if used as additive in a mixture comprising trimethylolpropane triacrylate or 9-acryloyloxy-10-bromo methyl oleate. Hydroxy substituted (meth)acrylated alkyd resins may be prefered as additives in traditional monomers.