Unprecedented associative exchange in CO2-sourced cyclic S,O-acetal-based covalent adaptable networks

Abstract

New dynamic chemistry is nowadays sought to widen the library of accessible covalent adaptable networks (CANs). Here, we investigate the dynamic nature of CO₂-sourced cyclic S,O-acetal bonds under unexplored conditions. Model molecule studies were conducted on various compounds and supported by extensive DFT calculations to understand the required conditions for triggering exchange and the underlying reaction mechanisms. This is the first study to report dynamic S,O-acetal bonds with an unprecedented associative exchange mechanism occurring through nucleophilic attack onto a remote function from the exchanged site. Our findings were translated to macromolecular engineering with the successful production of CO₂-sourced CANs embedding cyclic S,O-acetal bonds from bifunctional alkylidene cyclic carbonates and polythiols. The polymer properties were tuned by the use of structurally divergent monomers, affording materials with distinct thermal and mechanical properties (e.g. T_g ranging from 2 to 51 °C). Complex relaxation behaviour was recorded by rheology experiments, suggesting concurrent exchange reactions to take place at elevated temperatures. The materials dynamics was leveraged through recycling by compression molding for over five cycles. Furthermore, a proof-of-concept coating application was developed, showcasing damage healing at high temperatures.