writer：He, X.; Wang, F. F.; Tian, D. L.; Yang, Z. J.; Li, T.; Sun, P. C.*
keywords：Epoxy; Self-healing; Reversible crosslink; Solid-state NMR
source：期刊
specific source：ACTA POLYMERICA SINICA, 2018, 7, 949
Issue time：2018年
The structure-property relationship of reversible crosslinked high performance polymer with self-healing and recyclable properties has attracted significant attention in the past decades. Herein, a thermally reversible crosslinked epoxy resin (DAERs) based on Diels-Alder covalent bonds was designed and prepared, where furan functional groups were incorporated into the side chains of linear epoxy resin and then cross-linked by maleimide. Different characterization techniques were used to investigate the structure-property relationship of DAERs. In situ variable-temperature C-13 solid-state NMR was used to follow the evolution of dynamic Diels-Alder bonds in non-soluble cross-linked networks of DAERs, providing clear evidence of the cycling process of the DA reaction via displaying the consumption, appearing and disappearing of free furan group resonances in the network at different temperatures. NMR results provided a molecular level understanding of their equilibrated structure, and the reversible reconstruction and disconnection of the cross-link networks. Thermal behavior of DAERs was measured by repeated DSC cycles to verify the reversible temperature dependence of the DA and RDA reaction. Repeated endothermic and exothermic transition of DAERs during successive thermal cycles were observed, indicating the presence of RDA and DA reactions, respectively. The DSC results clearly demonstrated the capability of DAERs as a thermal re-mendable and recyclable material. The results of both DSC and DMA experiments indicated that the DA cross-linkage enhanced the glass transition and DA/retro-DA transition temperatures, and the heat-resistance of the materials increased with increasing cross-link density. Especially, DMA is a powerful and sensitive tool to distinguish the overlapped glass transition and DA/RDA temperatures. Tensile experiments indicated that the mechanical property also increased with the increase in crosslink density, and the synthesized DAERs exhibited good comprehensive mechanical properties, including high stiffness, strength, and toughness, and had good solvent and heat resistance. These materials can be easily thermally recycled, and this makes the material eco-friendly, with great potential for industrial applications.