Crosslinking Poly(Tetrazine) Decorated Single‐Walled Carbon Nanotubes via Inverse Electron Demand Diels‐Alder Reaction for Film Fabrication

Thin films of single‐walled carbon nanotubes (SWNTs) were produced by first dispersing them using a conjugated poly(tetrazine) polymer wrapper, followed by filtration through a teflon membrane. The tetrazine units of the polymer wrapper are highly reactive toward trans‐cyclooctene (TCO) via the inverse‐electron‐demand Diels‐Alder (IEDDA) reaction. This reactivity allows crosslinking of the SWNT film post‐fabrication by using a crosslinker bearing multiple TCO groups. A series of polyethylene glycol (PEG) crosslinkers of different lengths with trans‐cyclooctene (TCO) end‐groups was synthesized and used to crosslink the SWNT films. Characterization of the crosslinking chemistry was carried out using scanning electron microscopy as well as FTIR and Raman spectroscopy, providing evidence for crosslink formation. Bulk and surface mechanical properties of the resulting films were studied using a home‐built mechanical analyzer as well as quantitative nanomechanical mapping using an atomic force microscope. These studies showed that crosslinked films exhibit a lower modulus, indicating a reduction in film stiffness post‐crosslinking. Overall, these studies demonstrate the utility of the IEDDA reaction in forming free‐standing, crosslinked films of polymer‐decorated SWNTs.