Building From the Ground Up: A Procedural Guide to Locally Controlling Bond Exchange Kinetics in Dynamic Thiol-Thioester Networks

Abstract

Covalent adaptable networks (CANs) are a new class of polymers possessing the structural robustness of classical thermosets and stimuli-dependent malleability of thermoplastics, imparting them with repairability, reprocessability, and recyclability potential. These CANs can even be tailored to have spatially controllable properties and enhanced functionality; however, the introduction of additional reactive moieties leads to inadvertent side reactions and deterioration of the desired performance. Herein, we present a comprehensive approach to the optimization of locally controllable CANs, relying on base catalyzed thiol-thioester exchange reactions. The network is formed by visible light (405/450 nm) induced radical thiol-ene polymerization, whilst local deactivation of the dynamic exchange reaction is achieved by neutralizing the basic catalyst with a photoacid generated upon UV-light (365 nm) exposure. The intricate interactions between the resin components were studied, and the factors affecting the network performance were investigated to provide a detailed account of the development process, from the rational selection of initial components to the systematic optimization of a locally controlled, photoswitchable CAN. Finally, its on-demand tunability is demonstrated by surface- and bulk shape reconfiguration through heat-assisted processes.