Figure 4 (a) G’ and G’ ’ values of a gel sample prepared with 180 mmol M2 and 10 mmol M3 adding into 100 mmol M1 during strain sweep from 0.1% to 400%, and (b)G’ and G’ ’ values of the sample during the time sweep at a scan frequency of 10 rad/s, time-dependent strain sweep from 0.1% to 200% and then returned to 1% strain in 200 s. Furthermore, three cycles were performed.
Considering the presence of noncovalent and dynamic covalent bonds in poly[2]catenane gels, the gels were expected to exhibit self-healing properties.[30] In order to verify this property, rheological experiments were performed. First, strain sweep tests were performed on the poly[2]catenane gel prepared from adding 180 mmolM2 and 10 mmol M3 added into 100 mmol M1 (Figure 4a). The results showed that when the strain was less than 80%, the storage modulus of the samples was larger than loss modulus, thus the sample mainly exhibited elastic; whereas, when the strain was larger than 80%, the loss modulus was larger than storage modulus. In this way, the samples mainly exhibited viscous, which was due to the fact that the network of the samples was broken under larger strains. According to the above strain sweep results, the strain greater than the damage of the gel networks (greater than 80%) was further tested. In Figure 4b, during the strain scanning of the sample from 0.1% to 200% strain at scan frequency of 10 rad/s for 550 s, loss modulus was gradually larger than storage modulus, which was leading by the break of the network at higher strains. Subsequently, time sweep experiments were performed for 200 s with a strain of 1% and a scanning frequency of 10 rad/s. It could be observed that storage modulus became larger than loss modulus in a short period of time, which was due to the rapid recovery of networks. Two other cycles of time sweep experiments were performed on the same gel, for which the similar trends were observed. The above test results showed that the poly[2]catenane gels possessed self-healing properties.[31] Therefore, it was inferred that the self-healing mechanism of poly[2]catenane gels was due to reversible noncovalent and dynamic covalent bonds. When the gel was subjected to a large strain, the noncovalent and dynamic covalent bonds disintegrated. Without any external strain, the noncovalent and dynamic covalent bonds recombined again resulting in self-healing behavior.
Conclusions
In conclusion, poly[2]catenane gels were prepared by sequential self-assembly of small molecules. Firstly, monomer M1 , which consisted of an alkyl chain linking isophthaloyl bis(diamine) groups, was prepared. SPs were formed by self-assembly of M1 through hydrogen bonding and π-π interactions at high concentrations in chloroform. Upon the addition of monomers M2 and M3 into SPs, the amino groups in SPs reacted with the aldehyde groups to form imine bonds, which resulted in ring-closing and the crosslinking process of SPs. As a result, the linear SPs were transformed into poly[2]catenane gels with network structures. The formation of the gel was demonstrated by 1H NMR spectroscopy, infrared spectroscopy, and rheological testing. Furthermore, the experiment results showed that the poly[2]catenane gels also possessed solvent responsiveness and self-healing properties. This work provided a new method for the preparation of poly[2]catenane gels. In addition, it also promoted the development of dynamic polymer materials.
Supporting Information
The supporting information for this article is available on the WWW under https://doi.org/10.1002/cjoc.202400xxx.
Acknowledgement
X. Ji acknowledges funding from the National Natural Science Foundation of China (No. 22001087). X. Ji also appreciates the support from the Huazhong University of Science and Technology, where he is being supported by Fundamental Research Funds for the Central Universities (Grant 2020kfyXJJS013). X. Ji appreciates for support from the Interdisciplinary Research Program of HUST (2023JCYJ013).
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