Repairable reinforced composites of 1D TiO2 lepidocrocite mesoparticles and thiol-yne click networks via alkylborane-initiated in situ polymerization

Synthesizing high-performance, multifunctional composites often entails poor filler dispersion, complex processes, or limited processing conditions. Hence, the advent of versatile syntheses employing simple conditions, inexpensive fillers, standard equipment, and robust reactions could expand attainable composites having enhanced performance, functionality, and customizability. We report on the synthesis of a novel multifunctional elastomeric composite from a new, reinforcing titania-based filler and a repairable, dynamic-covalent thiol-yne network or dissociative covalent adaptable network. Composites were processed by in situ polymerization via thiol-yne "click"chemistry initiated with a trialkylborane. Composite processing yields quantitative monomer conversion and uniform filler dispersion. The filler was a titania-based mesoparticle, self-assembled from 1D lepidocrocite nanofilaments through a recently discovered, scalable, and nearly universal route to wideranging nanostructures. A 47-fold enhancement in the modulus was achieved with 60 wt % filler versus the neat polymer, agreeing with theory. The reinforced, cross-linked composites were multifunctional, providing reprocessability over multiple damage-repair cycles with restoration of their mechanical properties.