To
date, all epoxy vitrimer systems reported in the literature
rely on addition of significant amounts of catalysts to achieve the
dynamic transesterification reaction (TER). However, the catalysts
used in vitrimers are often toxic and have poor miscibility with organic
compounds, and they may further comprise the application performance
like corrosion resistance. Moreover, the reprocessing and recycling
properties are highly dependent on the loading amount and the type
of catalyst. In this study, two hyperbranched epoxy (HBE) prepolymers
are synthesized and then reacted with succinic anhydride to prepare
a catalyst-free epoxy vitrimer system. It is demonstrated that both
the curing during the preparation of the cross-linked materials and
the TER in the resulting cross-linked materials proceed properly without
addition of external catalyst. We attributed this phenomenon to the
abundant free hydroxyl groups in HBE which serve as both reacting
moiety and catalyst in both curing and the TER processes. At elevated
temperatures (>120 °C), the TER is activated to enable fast
stress
relaxation of the cross-linked network. In addition, the epoxy vitrimers
exhibit glass transition temperatures (T
g’s) in the range 70–96 °C, excellent thermostability,
and mechanical properties similar to those of the traditional epoxy
materials. By taking advantages of these features, we also demonstrate
a promising self-healable and catalyst-free coating.
The design of high glass transition temperature (T g ) thermoset materials with considerable reparability is a challenge. In this study, a novel biobased triepoxy (TEP) is synthesized and cured with an anhydride monomer in the presence of zinc catalyst. The cured TEP exhibits a high T g (187 °C) and comparable strength and modulus to the cured bisphenol A epoxy. By adopting the vitrimer chemistry, the cross-linked polymer materials are imparted significant stress relaxation and reparability via dynamic transesterification. It is noted that the reparability is closely related to the repairing temperature, external force, catalyst content, and the magnitude of rubbery modulus of the sample. The width of the crack from the cured TEP can be efficiently repaired within 10 min. This work introduces the first high-T g biobased epoxy material with excellent reparability and provides a valuable method for the design of high-T g self-healing materials suitable for high service temperature.
This work introduces a simple and green method for the preparation of a fully biobased vitrimer material and demonstrates a potential application for recoverable adhesives.
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