Solvent-Gated Reaction Pathway Selection for Thiol-Maleimide Polymer Networks Programming

Thiol-maleimide click chemistry is widely employed across diverse fields for its rapid kinetics and mild reaction conditions, whose reversible bond exchange feature additionally imparts reprocessability and recyclability to polymer networks. Despite its widespread use, the influence of the reaction environment on the resulting network architecture has remained largely unexplored. Here, we demonstrate that solvent choice gates competing reaction pathways during thiol-maleimide network formation. From an identical precursor formation, protic solvents direct network formation predominantly through thiol-maleimide Michael addition, whereas aprotic solvents enable a dual pathway in which maleimide homopolymerization proceeds alongside thiol addition. This solvent-controlled pathway selection alters the effective cross-linking density and thereby modulates the mechanical and thermal properties of the resultant thiol-maleimide polymer networks, as well as the network dynamic ability, as revealed by the distinct stress relaxation kinetics and recycling efficiency. These results indicate that the stoichiometry of thiol and maleimide alone does not define the final network, whereas the reaction environment determines whether maleimide functions exclusively as a Michael acceptor or additionally as a chain growth monomer. By converting maleimide homopolymerization from a side reaction into a programmable structural handle, this work establishes solvent-gated pathway selection as a simple, formulation-invariant strategy for designing tunable thiol-maleimide polymer networks.