Here, we report the fabrication of a dynamic enamine-one bond based vitrimer through amino-yne click chemistry. In contrast to amine-acetoacetate condensation, the amino-yne click reaction yields a dynamic enamine-one motif that is composed of cis/trans (3:1) isomers and has a relatively lower activation energy (35 ± 3 kJ/mol vs 59 ± 6 kJ/mol), owing to the absence of a methyl substituent. The resulting vitrimer network has superior mechanical properties and faster dynamic exchange than that of a reference vitrimer derived from amine-acetoacetate condensation, and they are attributed to the fewer network defects and the less sterically hindered exchange reaction, respectively. Lastly, the efficient amino-yne click reaction is demonstrated to be compatible with the secondary-amine substrate, which has a low reactivity toward the amine-acetoacetate condensation. The efficient and side product-free amino-yne reaction offers a powerful chemical tool for vitrimer fabrication and is potentially desirable for sealing and adhesion applications.
Polymer networks embedded with dynamic covalent bonds have been demonstrated to be capable of network reconfiguration. This reprocessability is often related to the network dynamics or flowability, the precise control of which highly depends on the underlying chemistry. Particularly, vitrimer materials flow at a constant crosslinking density because of the associative dynamic chemistry involved. Here, we report the fabrication of enamine-one vitrimers through an amino-yne click reaction using secondary amine substrates. Compared with primary amines, the secondary amine-based amino-yne click reaction is mild and yields less gel content (70 vs 97%) in our curing system. By modulating the substituents of the secondary amine, we show that the activation energy of the exchange reaction increases (52–90 kJ/mol) with increasing steric hindrance (piperidyl ∼ methyl < ethyl < isopropyl < tert-butyl), and a similar trend was observed in the vitrimer networks. Interestingly, piperidine exhibits reactivities (including the yielded gel content and network dynamics) comparable to that of primary amines because of the less steric hindrance related to the constrained cyclic structure. This study not only enriches the scope of amine substrates for vitrimer fabrication but also offers a convenient means to tune the network dynamics through substrate choices or combination strategies (i.e., mixing primary and secondary amines or various secondary amines).
Introducing dynamic covalent bonding into thermoset polymers has received considerable attention because they can repair or recover when damaged, thereby minimizing waste and extending the service life of thermoset polymers. However, most of the yielded dynamic covalent bonds require an extra catalyst, high temperature and high-pressure conditions to trigger their self-healing properties. Herein, we report on a catalyst-free bis-dynamic covalent polymer network containing vinylogous urethane and disulfide bonds. It is revealed that the introduction of disulfide bonds significantly reduces the activation energy (reduced from 94 kJ/mol to 51 kJ/mol) of the polymer system for exchanging and promotes the self-healing efficiency (with a high efficiency of 86.92% after being heated at 100 °C for 20 h) of the material. More importantly, the mechanical properties of the healed materials are comparable to those of the initial ones due to the special bis-dynamic covalent polymer network. These results suggest that the bis-dynamic covalent polymer network made of disulfide and inter-vinyl ester bonds opens a new strategy for developing high-performance vitrimer polymers.
This paper studies the effects of planting plants and coupled microbial fuel cells (MFCs) on the decontamination capacity and purification mechanism of constructed wetlands (CWs). Four systems were set, namely CW-without plants (A1), CW-with plants (A2), CW-MFC-without plants (A3) and CW-MFC-with plants (A4). The daily reductions per unit area of chemical oxygen demand (COD) were 48.72 ± 5.42, 51.26 ± 4.10, 53.49 ± 5.44 and 58.54 ± 4.16 g·(d·m2)−1, respectively. The daily reductions per unit area of nitrogen (N) were 11.89 ± 0.73, 12.38 ± 0.76, 12.24 ± 0.79 and 13.61 ± 1.07 g·(d·m2)−1, respectively. After studying the pollutant removal efficiency, it was found that the unit area of A4 removes the highest number of pollutants, improving the area efficiency of the wetland system and fundamentally alleviating the disadvantage of the large land footprint of wetland processes. The average output voltages of A3 and A4 were 568.29 and 717.46 mV, respectively, and the maximum power densities were 4.59 and 15.87 mW/m3, respectively. In addition, after high-throughput analysis of microbial samples, anaerobic ammonia oxidising (anammox) bacteria were found to remove N from the system in the anaerobic anode region.
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