Temperable dynamic polymeric glasses as tunable and rebondable adhesives

Abstract

Dynamic covalent polymer networks offer a promising strategy for developing recyclable and stimuli-responsive adhesives. However, direct modulation of adhesive strength remains challenging. The focus of this work is on designing glassy dynamic networks that are capable of being tempered to access a range of mechanical properties dictated by the tempering temperature (T_t) they are exposed to and exploring their ability as glassy adhesives. To this end a series of thia-Michael (tM) dynamic networks constructed from rigid benzalcyanoacetate (BCA) and benzalcyanoacetamide (BCAm) ditopic acceptors crosslinked with a tetrathiol were prepared. The electronic nature of the β-phenyl moieties on the BCA and BCAm acceptors controls the amount of thia-Michael adduct formed resulting in materials with a range of crosslink densities and glass transition temperatures (T_g). All the resulting dynamic networks exhibit dynamic reaction-induced phase separation (DRIPS) to yield robust two-phase materials. Tempering within the thermal window between T_g and the upper transition temperature (T_UT) enables systematic tuning of network adduct fraction and crosslink density, leading to controllable changes in storage modulus, fracture toughness, and glass transition temperature within the same material. These thermomechanical variations translate directly to tunable adhesive performance, with lap shear strengths adjustable across multiple substrates, including aluminum and polyetherimide. The ability to modulate adhesive shear strength through thermal tempering highlights the potential of thia-Michael dynamic glasses as tunable structural adhesives for adaptive materials applications.