Synthesis and photoinitiated cationic polymerization of epoxy monomers derived from oleic acid comprising one to three epoxy groups

Abstract

A series of bio-based epoxy compounds based on oleic acid combined with aliphatic or aromatic structures were studied regarding selected properties such as melting behavior and viscosity as well as their reactivity in a photoinitiated cationic polymerization. The new epoxy compounds derived from oleic acid and either eugenol or isoeugenol, epoxidized triolein, and an epoxy compound derived from oleic acid and popane diol-1,3 contain 100 % renewable carbon. Atom economy differs not only for the esterification and epoxidation reaction, also selection of hydrogen peroxide or m-chloroperbenzoic acid for the epoxidation significantly influences the atom economy of this reaction step. Variation of the chemical structure of the bio-based epoxy compounds derived from oleic acid and either an aliphatic alcohol or a phenolic compound results in differences in both melting behavior and viscosity of the epoxy monomers that is important for the photoinitiated cationic polymerization. Kinetic investigation of the photoinitiated cationic polymerization of the bio-based epoxy compounds using photo-DSC shows significant differences in the polymerization rate and conversion as a function of the irradiation time for the epoxy monomers. RT-FTIR spectroscopy gives additional information about the polymerization kinetics for epoxy monomers that are liquid at room temperature. The glass transition temperature of the photopolymers analyzed by DSC is mostly below room temperature that is attributed to the high content of flexible structures containing in the polymers. Additional investigation of the soluble photopolymers by GPC resulted in a molecular weight corresponding to the oligomer region and a dispersity higher than one. The bio-based epoxy monomers comprising two or three epoxy groups may be interesting for application, e. g. in coatings or adhesives, because photoinitiated polymerization results in crosslinking. Epoxy compounds containing only one epoxy group may be useful for viscosity reduction of the photopolymerizing mixtures because of their lower viscosity compared to the epoxy monomers comprising more than one epoxy group.