Rare Earth Triflate Initiators in the Cationic Polymerization of Tung Oil-Based Thermosetting Polymers for Self-Healing Applications

Rare earth triflates were successfully used to initiate the cationic polymerization of tung-oil-based thermosetting polymers. These bio-renewable thermosets were developed and evaluated for use as an encapsulated healing agent in self-healing materials. The tung-oil-based polymer is comprised of predominantly tung oil with styrene and divinylbenzene used as a reactive diluent and to improve the initiator solubility and the homogeneity of the resulting thermoset. While traditional cationic polymerization utilizes moisture-sensitive Lewis acids as initiators, rare earth triflates offer a new approach to polymerization where moisture sensitivity is not a significant concern. Nine different rare earth triflates were investigated: ytterbium, scandium, samarium, cerium, gadolinium, erbium, terbium, holmium, and neodymium. The thermomechanical properties of the thermosets were tested and the analysis included effects of initiator type on the storage modulus, loss modulus, tan delta, glass transition temperature, and thermal stability. Finally, the adhesive properties of the thermosets were studied using compressive lap shear tests, and the fracture surfaces were analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy.