Boron–nitrogen coordination in polyurethane elastomers enhances the dynamics of the boronic ester while introduces inter- and intra-molecular interactions, leading to mechanical robustness and excellent self-healing efficiency simultaneously.

Vitrimer network polymers are very special in that, above a characteristic temperature T v , their dynamic covalent network connectivity allows macroscopic flow while remaining cross-linked. The vitrimer is able to change from being a typical elastomer to a network polymer with thermoreversible bond-exchange reactions. This has aroused enthusiastic interest, especially for designing novel materials to meet the increasing requirements of environmental protection, self-healing, and sustainable development. In this work, the viscoelasticity of the curing and cured epoxy vitrimer was investigated. Time-resolved multifrequency rheometry during the early stages of curing disclosed network ripening due to transesterification. After being fully cured, one of the most defining properties of vitrimers is a reversible, temperature-induced transition at T v , where the vitrimer assumes a pronounced critical state. Surprisingly, this transition state was found to behave like a critical gel having a relaxation modulus, G(t) = St −n , over a fairly broad temperature interval of 20 K. Viscoelastic moduli G′(ω,T) and G″(ω,T) can be approximately shifted into a single set of master curves for the entire experimental temperature range. Large strain behavior above T v becomes nonlinear very quickly. No resemblance was found with a glass transition near T v .

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It is urgently required to achieve good thermal conductivity and electrical insulation performance in polymerbased composites with the minimum incorporation of functional fillers. In this work, the selective distribution of multiwalled carbon nanotubes (MWCNTs) in the segregated network of hexagonal boron nitride (h-BN) in the epoxy vitrimer matrix was achieved by compression molding, in which interfacial welding was enabled by small-molecule-participated dynamic transesterification at elevated temperatures. Due to the synergistic contribution of the wellstructured nanofiller network, the epoxy vitrimer composites demonstrate enhanced thermal conductivity and electrical insulation at low filler content. The composite containing 1 wt % of MWCNTs and 8 wt % of h-BN shows thermal conductivity and electrical resistivity of 0.83 W/(m•K) and 1.92 × 10 11 Ω•cm, respectively. The electrical resistivity can be further improved by increasing the segregated h-BN content. This method provides a novel way to prepare cost-effective polymer composites with excellent thermal conductivity and electrical insulation.

Polyurethane (PU) grouting materials possess excellent fluidity and strong injectability. However, the high heat release during the reaction process restricts its application. In this study, with the addition of water glass (WG), a prepolymer was prepared by epoxy resin reacted with isocyanate to form modified polyurethane. The effects of epoxy resin and water glass on the compressive properties, expansion rate, structure of the cell, and maximum reaction temperature of the grouting materials were also investigated. The results showed that the cell size of modified PU was smaller and more regular, the maximum reaction temperature of the modified PU was reduced to 89 °C, and the compressive strength and expansion rate went up to 0.27 MPa and 57, respectively. This investigation will expand the application of PU grouting materials in underground engineering.