Cleavable Strand-Fusing Cross-Linkers as Additives for Chemically Deconstructable Thermosets with Preserved Thermomechanical Properties.

Permanently cross-linked polymer networks-thermosets-are often difficult to chemically deconstruct. The installation of cleavable bonds into the strands of thermosets using cleavable comonomers as additives can facilitate thermoset deconstruction without replacement of permanent cross-links, but such monomers can lead to reduced thermomechanical properties and require high loadings to function effectively, motivating the design of new and optimal cleavable additives. Here, we introduce "strand-fusing cross-linkers" (SFCs), which fuse two network strands via a four-way cleavable cross-link. SFCs enable deconstruction of model polydicyclopentadiene (pDCPD) thermosets with as little as one-fifth of the molar loading needed to achieve deconstruction using traditional cleavable comonomers. SFCs function under traditional oven curing as well as low-energy frontal ring-opening metathesis polymerization (FROMP) conditions and lead to improved thermomechanical properties, for example, glass transition temperatures, compared to prior cleavable comonomer designs. This work motivates the development of increasingly improved cleavable additives to enable thermoset deconstruction without compromising material performance.