Enhancing the robustness of thiol–thioester covalent adaptable networks through reversible thiol–Michael masking

Abstract

Covalent adaptable networks (CANs) offer an appealing alternative to traditional thermosets by combining mechanical robustness with reprocessability through dynamic covalent chemistry. Thiol–thioester CANs are particularly promising, but their reliance on free thiols to enable network rearrangement also promotes creep and permanent deformation. Here, we present a simple reversible thiol-protection strategy to overcome this issue. Free thiols are temporarily “masked” via a reversible thiol–Michael reaction, limiting chain mobility and improving mechanical resistance while preserving network dynamics. To demonstrate this concept, we developed a thioester-based CAN in which thiols are masked as dithioacetal groups. Model studies confirmed that the masked thiols can be released on demand and participate in thiol–thioester exchanges, with both steps catalysed by TBD. A reference network with unprotected thiols (C-FT) was compared to the protected analogue (C-BT). Although thiol protection slowed down relaxation due to incomplete dissociation, increasing catalyst concentration compensated for this effect, enabling similar relaxation kinetics while preserving enhanced mechanical resistance. This reversible thiol-protection strategy provides a simple and effective approach to mitigate creep in thioester-based CANs without compromising reprocessability, and could be extended to other nucleophile-activated dynamic chemistries.