Among various recycling strategies required for a circular economy of polymers, dynamic covalent chemistry (DCC) is gaining increasing interest. Established amine–aldehyde chemistry suffers from limited scope and toxicity. Ketones are alternatives but commonly less reactive and, as a consequence, have been investigated to the lower extent in the context of DCC. Here we report three bis(piperidin-4-one) derivatives as reactive, ketone-based building blocks for dynamic network formations with amines. By varying the bispiperidone linker unit, the electrophilicity of the carbonyl can be modulated. Contributions of aminal, hemiaminal, imine and enamine units are determined using model compounds, linear polymers and networks. NMR and AT-IR spectroscopic analyses suggest imine and enamine functionalities to be the main condensation products. The thermodynamics of the formation of the aminal, hemiaminal, imine and enamine functionalities are investigated using density functional theory (DFT) calculations, which confirm imine and enamine units to be the most stable reaction products. The DFT results further demonstrate how altering the experimental conditions can change product distribution different from those obtained in the experiments. Degradation of the networks in water depends on the pH of the medium and enables bispiperidone recovery.

中文翻译：

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可降解双哌啶酮衍生物胺网络与单体回收

在聚合物循环经济所需的各种回收策略中，动态共价化学（DCC）越来越受到人们的关注。已建立的胺醛化学受到范围有限和毒性的影响。酮是替代品，但通常反应性较低，因此在 DCC 中的研究程度较低。在这里，我们报道了三种双（哌啶-4-一）衍生物作为反应性、基于酮的构建块，用于与胺形成动态网络。通过改变双哌啶酮连接单元，可以调节羰基的亲电性。使用模型化合物、线性聚合物和网络确定缩醛胺、半缩醛胺、亚胺和烯胺单元的贡献。NMR 和 AT-IR 光谱分析表明亚胺和烯胺官能团是主要的缩合产物。使用密度泛函理论 (DFT) 计算研究了缩醛胺、半缩醛胺、亚胺和烯胺官能团形成的热力学，证实亚胺和烯胺单元是最稳定的反应产物。DFT 结果进一步证明了改变实验条件如何改变与实验中获得的产品分布不同的产品分布。水中网络的降解取决于介质的 pH 值，并且可以回收双哌啶酮。