The mechanical robustness and network reconstruction have always been paradoxical in dynamically cross-linked polymers. It is highly desirable to consider polymer architecture while studying chemical bond dissociation to acquire reversible cross-linking networks with high performance. Recently, one paper was published on Macromolecules. A versatile dynamic covalent bond, e.g., a conjugated and hindered urea bond (CHUB), and its dissociation chemistry are reported. Benefiting from the dual effects of conjugation and steric hindrance, CHUB displayed significant and highly tunable reversibility with respect to the polymer network design. Three kinds of dynamically cross-linked networks with widely tuned properties were developed, including the pristine polyurea network, expanded polyurea network containing epoxy cores and networks both cross-linked with traditional and dynamic covalent bonds. The aromatic, stiff backbone of CHUB ensured dynamically cross-linked networks with a considerable glass transition temperature and outstanding mechanical properties. By tuning the ratio of CHUBs with respect to conventional covalent cross-linking points, dynamically cross-linked polymers with good creep resistance were also obtained. The CHUB with both a rigid backbone and high reversibility thus effectively expanded the scope of dynamic covalent bonds and provided efficient routes to catalyst-free, easy-to-synthesis, and efficient renewable networks that are beneficial for theoretical study or practical applications.

The first author of the paper is Prof. Yu Li and the corresponding author is Prof. Xinli Jing. 

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优异的力学稳定性和突出的网络重构能力在通常的动态交联高分子中往往难以兼得。近日，本课题一篇组论文在Macromolecules发表。本文报道了一种新型具有刚性骨架的动态共价键——共轭位阻脲键(CHUB)并探讨了其在构建高强度可逆交联高分子网络中的应用潜力。相比于普通的动态脲键，在共轭效应和位阻效应双重影响下，CHUB的可逆性更加显著、普适性更强，使其在构建多样化的动态交联网络中大有作为。基于CHUB，本文构建了三类动态交联网络，常规聚脲网络、环氧化合物修饰的聚脲网络以及动态脲键和传统共价键协同交联的网络。这些动态交联网络具有方便可调的玻璃化转变温度、优异的力学性能以及良好的可再生性。通过调节CHUB相对与传统共价键的比例，还显著提高了动态交联高分子的热稳定性和抗蠕变性能。基于CHUB的动态交联高分子原料易得、合成方便，利用CHUB基团有助于广泛调节动态交联网络拓扑结构，丰富动态交联高分子体系的结构与性能研究，并推动实用化的可再生热固性高分子发展进程。

论文的第一作者李瑜副教授，通讯作者为井新利教授。