Preparation And Properties Of Epoxy Vitrimers Based On Dual/Multiple Dynamic Covalent Bonds

The traditional epoxy resin networks cannot be reprocessed,recycled and self-healed because of its permanent cross-linking network.Therefore,a large number of epoxy resin wastes are produced causing the serious environmental pollutions.Epoxy vitrimers,as a new type of polymer,have attracted more and more attentions because of their excellent network stability and reprocessing ability.Epoxy vitrimers possess self-healing,welding,shape memory and reprocessing capabilities.However,epoxy vitrimers based on single dynamic covalent bond show self-healing,welding,shape memory and reprocessing at high temperature.Stress relaxation of the network also requires higher temperature and network rearrangement requires high E_a.In this thesis,epoxy vitrimers with dual/multiple dynamic covalent bonds were prepared.The simultaneous presence of dual/multiple dynamic covalent bonds enables the networks to exhibit excellent dynamic thermomechanical properties.The networks display the excellent functionalities under mild conditions.The main contents and conclusions of these researches are as follows:（1）In the second chapter,epoxy vitrimers based on multiple dynamic covalent bonds（boronic ester bond,disulfide bond and ester bond）were prepared using TTE as matrix,BDB and DTDPA as cure agent.Structural characterization and performances testing have been conducted,it is shown that the self-healing,reprocessing and welding of the networks can be achieved at 80℃ and the recovery ratio of tensile strength of the welded sample is>80%.This is because the simultaneous occurrence of thermal-induced exchange reactions of boronic ester bond,disulfide bond and ester bond result in a rapid rearrangement of network topology,giving excellent functionalities of the obtained networks.（2）In the third chapter,itaconic acid（IA）-based epoxy vitrimers with dual-dynamic covalent bonds（boronic ester bond and ester bond）were prepared by epoxy-carboxylic acid reaction,IA derivative（EIA）as an epoxy monomer,synthesized tricarboxylic acid compound（HBN）with dynamic boronic ester bond as cure agent.The effects of different contents of HBN crosslinker on the structure and properties of IA-based epoxy vitrimers were studied.The results show that the epoxy vitrimers network possess high thermal stability（initial decomposition temperature:～330℃）and low activation energy(E_a=34.9 k J·mol^-1).Because exchange reactions of boronic ester bond and ester bond take place simultaneously contributing to a rapid rearrangement of the network topology,the IA-based epoxy vitrimers exhibit the excellent self-healing and chemical recycling properties.（3）In the fourth chapter,the novel di-carboxylic acid cure agent（BDCB）with dynamic boronic ester bond was synthesized.The IA-based epoxy vitrimer based on dual dynamic ester bond and boronic ester bond were prepared by the epoxy-carboxyl curing reaction between EIA and BDCB.The results show that the mechanical properties of the obtained epoxy vitrimers are comparable to conventional epoxy resins due to the rigid network structure.The scratches on the surface of the sample were almost completely healed after heat treatment at 150℃ for 2 h.The mechanical properties of the physically reprocessed and chemically recycled samples maintained85.5%and 78.9%of the original,respectively.The epoxy vitrimers exhibit the excellent self-healing,welding,physical reprocessing,and chemical recycling properties due to the simultaneous presence of dynamic ester bonds and boronic ester bonds in the network.