Degradable bispiperidone derivative amine networks with monomer recovery

Abstract

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.