Photoswitchable olefins as latent metathesis monomers for controlled polymerization.

Our understanding of polymers has given rise to fundamental changes in society. Nonetheless, there is much room to further develop and improve creative techniques to enable advanced materials. At the frontiers of this endeavour is the development of switchable catalysts aimed at providing spatiotemporal control over polymerization reactions. Here we present an alternative to the conventional catalyst-centred approach by using quadricyclane-norbornadiene isomerization as a switchable monomer for ring-opening metathesis polymerization. The on-demand polymerization of four norbornadiene derivatives was achieved using two different ruthenium-based olefin metathesis initiators. The latent quadricyclane isomer generated remarkably stable formulations upon mixing with ruthenium initiators, remaining unchanged for up to 7 weeks. In addition to conventional heating, the latent monomer could also be activated by the photothermal response of gold bipyramids, leading to highly efficient polymerization reactions amenable to 3D printing techniques. Finally, a one-pot diblock copolymerization strategy and sequential curing process inaccessible by traditional methodologies was developed, exploiting the exceptional latency of the monomers.