Insight into the structure-property relationships of intramolecularly-catalyzed epoxy vitrimers

Vitrimers are emerging dynamic polymers with exchangeable associated networks that can potentially be used as substitutes for conventional thermosetting polymers, whose healing and recycling are difficult. However, vitrimers have limited engineering applications due to their process complexity, the addition of extra catalysts, and the unclear factors that affect network rearrangement. Herein, epoxy vitrimers with intramolecularly-catalyzed transesterification were prepared by curing an ester-containing epoxy resin with diethylenetriamine and monoamines. The obtained diethylenetriamine-cured vitrimer had favorable tensile stress and modulus (60.86 MPa and 0.94 GPa). The intramolecularly-catalyzed vitrimers exhibited fast stress relaxation, and the relaxation time of monoamine-containing vitrimers was reduced to 253 s at 180 °C. The effect of structure variation on the vitrimers' properties was investigated by controlling the influencing parameters. The molality of the tertiary amine and β-hydroxy esters were directly proportional to faster stress relaxation. A higher crosslink density led to better mechanical properties and a higher glass transition temperature but retarded the stress relaxation. Side-chains with low steric hindrance accelerated the stress relaxation. Repair and remolding were more efficient in the vitrimers with lower stiffness. This study contributes to the design and practical applications of various epoxy vitrimers according to the desired final properties.