Polymer networks containing dynamic covalent crosslinks can undergo bond rearrangements when subjected to external stimuli such as light, heat or a change in pH. As a result, these networks have enhanced re-processability, thermoresponsiveness, and recyclability potential relative to classical permanently crosslinked thermosets. In this work, sulfur- and selenium-bicyclononane (BCN) dichloride small molecules with neighboring group participation (NGP) are used to crosslink pyridine-functionalized polymers. The resulting networks undergo transalkylation crosslinker exchange at elevated temperatures (&gt; 100 °C), which is probed via stress relaxation studies. The characteristic relaxation times (and thus transalkylation efficiency) of the BCN networks are greater than a control system crosslinked with para-xylene dichloride, which lacks NGP. Chemical recycling of the linear polymer starting material is achieved by swelling the sulfur- and selenium-BCN-crosslinked networks with an external nucleophile. In summary, this work highlights the NGP-promoted crosslinker exchange in ionic dynamic networks, which gives rise to temperature-dependent viscous flow and chemical recyclability.

Thermally-activated covalent adaptable networks containing selena- and thia-bicyclo[3.3.1]nonane crosslinkers: a study in recyclable and re-processable materials

ACS Spring 2022

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