Macromolecular Engineering Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
J Am Chem Soc. 2020 Sep 9;142(36):15371-15385. doi: 10.1021/jacs.0c06192. Epub 2020 Aug 31.
Dynamic covalent networks (DCvNs) are increasingly used in advanced materials design with applications ranging from recyclable thermosets to self-healing hydrogels. However, the relationship between the underlying chemistry at the junctions of DCvNs and their macroscopic properties is still not fully understood. In this work, we constructed a robust framework to predict how complex network behavior in DCvNs emerges from the chemical landscape of the dynamic chemistry at the junction. Ideal dynamic covalent boronic ester-based hydrogels were used as model DCvNs. We developed physical models that describe how viscoelastic properties, as measured by shear rheometry, are linked to the molecular behavior of the dynamic junction, quantified via fluorescence and NMR spectroscopy and DFT calculations. Additionally, shear rheometry was combined with Transition State Theory to quantify the kinetics and thermodynamics of network rearrangements, enabling a mechanistic understanding including preferred reaction pathways for dynamic covalent chemistries. We applied this approach to corroborate the "loose-bolt" postulate for the reaction mechanism in Wulff-type boronic acids. These findings, grounded in molecular principles, advance our understanding and rational design of dynamic polymer networks, improving our ability to predict, design, and leverage their unique properties for future applications.
动态共价网络（DCvNs）在先进材料设计中的应用越来越广泛，从可回收热固性材料到自修复水凝胶等应用。然而，DCvNs 连接点的基础化学与它们宏观性能之间的关系仍未完全理解。在这项工作中，我们构建了一个强大的框架，以预测 DCvNs 中的复杂网络行为如何从连接点的动态化学的化学景观中出现。理想的动态共价硼酸酯基水凝胶被用作模型 DCvNs。我们开发了物理模型，描述了如何通过剪切流变学测量的粘弹性性质与通过荧光和 NMR 光谱和 DFT 计算量化的动态连接点的分子行为相关联。此外，剪切流变学与过渡态理论相结合，以量化网络重排的动力学和热力学，从而实现对动态共价化学的优先反应途径的机械理解。我们应用这种方法来证实 Wulff 型硼酸的反应机制的“松螺栓”假设。这些基于分子原理的发现，提高了我们对动态聚合物网络的理解和合理设计能力，提高了我们预测、设计和利用它们独特性质的能力，以满足未来的应用需求。
