Enabling Selective Mechanochemical Scission of Network Crosslinks by Exchanging Single Carbon Atoms for Silicon.

The tearing of a polymer network arises from mechanochemically coupled bond-breaking events in the backbone of a polymer chain. An emerging research area is the identification of molecular strategies for network toughening, such as the strategic placement of mechanochemically reactive groups (e.g., scissile mechanophores) in the crosslinks of a network instead of in the load-bearing primary strands. These mechanically labile crosslinkers have typically relied on release of ring strain or weak covalent bonds for selective covalent bond scission. Here, we report a novel chemical design for accelerated mechanochemical bond scission based on replacing a single carbon atom in a crosslinker with a silicon atom. This single-atom replacement affords up to a two-fold increase in the tearing energy. We suggest a mechanism, validated by computational modeling, for accelerated mechanochemical Si-C bond scission based on minimizing the energy required to distort the starting material toward the transition-state geometry. We demonstrated the seamless incorporation of these scissile carbosilanes to toughen 3D-printed networks, which demonstrates their suitability for additive manufacturing processes.