Polymeric materials containing dynamic crosslinks and adaptable networks have obscured the line between the “thermosets” and “thermoplastics”, since they are able to be reprocessed or welded while being permanently cross-linked at the same time. However, it is still a great challenge to combine the good mechanical properties and excellent dynamic properties. Herein, cation-π interactions between indole groups and Eu 3+ were applied as cross-links in rigid networks of thermosetting epoxy to form tough non-covalent adaptable networks (NANs). The cation-π cross-linked epoxy exhibited outstanding solvent resistance and excellent mechanical properties with the tensile strength of 38 MPa, while the glass transition temperature (T g ) was up to 87 °C. Moreover, the cross-linked epoxy could be readily reprocessed and welded at moderate temperature of 120 °C, while the tensile strength recovered to 32 MPa after recycling. Meanwhile, the epoxy exhibited other dynamic properties including triple shape memory and tension triggered fluorescence. The readily prepared cation-π cross-linked epoxy provides a general way to develop tough NANs with high performance and excellent dynamic properties, which may be suitable for other non-covalent dynamic bonds and thermosetting matrix.
Lin Zhou,Linfang Zhou,Ruiqi Chen,Guanjun Chang,Kuibao Zhang,Mao Chen
Covalent adaptable networks (CANs) that are cross-linked by reversible dynamic bonds have been widely investigated, aiming at making the permanently cross-linked thermosets degradable and recyclable from the awareness of economic and environmental aspects. However, it is still a great challenge to make rigid thermosets like epoxy degradable upon programmed or coded stimuli, which will highly improve the combination of the degradable properties and stability. Herein, coded interlocked covalent adaptable networks (ICANs) in rigid epoxy were cross-linked by two distinct dynamic bonds of cation−π interactions and aromatic disulfide bonds in parallel connection, which exhibited high performance and coded or programmed degradation behavior. The coded ICANs were prepared by one-pot reactions from epoxy monomers and two curing agents that contained different dynamic bonds of cation−π interactions and aromatic disulfide bonds. The coded ICANs exhibited excellent mechanical properties and outstanding solvent resistance compared to the reference CANs or noncovalent adaptable networks (NCANs) relying on single dynamic bonds. Moreover, the coded ICANs exhibited unique programmed degradation behaviors, which could only be degraded after sequential exposure to two different chemical stimuli. Unlike the normal ICANs that could be degraded by two stimuli in any sequence, the coded ICANs were insoluble when the two stimuli were applied in the wrong sequence. The coded ICANs of epoxy provided a way to construct degradable CANs with more stable networks, while this concept and function might be applicable in other skeletons, leading to other types of highly coded ICANs with high performance and controlled degradation properties.
危险品化学品经营许可证（带存储）