Styrene-free unsaturated polyester resins derived from itaconic acid curable by cobalt-free accelerators

Abstract A series of polyester prepolymers was synthesized from itaconic acid, phthalic anhydride, propane-1,2-diol and diethylene glycol by condensation polymerization. The use of itaconic acid as a source of unsaturation (instead of more common maleic anhydride giving fumarate moieties) enabled to replace styrene reactive diluent by methyl methacrylate. Room temperature curing of a model polyester resin was initiated by butanone peroxide in combination with several cobalt-, iron- and vanadium-based accelerators. Measurements of gelation time and exothermic behavior in thermally isolated installation revealed very promising catalytic properties for oxidovanadium(IV) dibutylphosphate. In follow-up tests, mechanical properties of the model unsaturated polyester resin were tuned by variation in propane-1,2-diol/diethylene glycol ratio and composition of acrylate/methacrylate reactive diluent. Mixtures of methyl methacrylate with secondary crosslinking agents (e.g., ethylene dimethacrylate, triethyleneglycol dimethacrylate and trimethylolpropane triacrylate) enabled to improve ultimate tensile strength, Young’s modulus, tensile toughness and impact toughness. Reported experimental data indicate that the described styrene- and cobalt-free system is very promising for reduction in health and ecological issues of currently used unsaturated polyester resins curable at room temperature. Graphical Abstract