Ultrafast Photo-Crosslinking of Thiol–Norbornene Opaque Silicone Elastomer Nanocomposites in Air

Photocured silicone elastomers have become increasingly popular in a variety of advanced materials applications including soft robotics, biomedical devices, microfabrication, functional coatings, and additive manufacturing. Oxygen inhibition, however, remains a major challenge for conventional photoradical curing, limiting applications and restricting processing. Here, we report a thiol–norbornene-based silicone system using a polydimethylsiloxane (PDMS) displaying terminal norbornene groups and a highly functionalized thiolated PDMS to achieve very fast curing speeds in an ambient atmosphere. Complete curing, without any unreacted oily residue on the surface of the silicone elastomer, was achieved in the absence of inert atmosphere protection. The impact of a formulation and photoinitiating system, including the use of visible-light initiators, on the kinetics and mechanical properties of the silicone networks was studied. Despite their opacity, nanocomposites incorporating fumed silica and graphene oxide (GO) retained fast cure rates (gelation times below 1 and 5 s for silica and GO composites, respectively) with tack-free surfaces. After thermal conversion, this afforded composites with conductivities above 0.1 S/m. Finally, combination with a conventional room-temperature vulcanization system enabled the formulation of effective dual-cure composites. The fast crosslinking thiol–norbornene silicones reported are attractive for a wide range of applications where ambient curing is required or where processing requires ultrafast reaction rates.