Locally controlling dynamic exchange reactions in 3D printed thiol-acrylate vitrimers using dual-wavelength digital light processing†
Vitrimers are covalent adaptable polymer networks, which are able to rearrange their topology in response to an external stimulus. Below the topological freezing temperature (Tv) they behave like a classic thermoset, whilst above Tv, they become malleable, weldable and recyclable. However, vitrimers mainly rely on thermo-activated dynamic exchange reactions, which suffer from a lack in spatial control. Herein, we introduce triphenylsulfonium phosphate as a latent transesterification catalyst, which releases strong Brønsted acids upon UV exposure (365 nm). Once locally formed, the acids are able to efficiently catalyse thermo-activated transesterifications as confirmed by stress relaxation studies. The latent catalyst is introduced into visible light (405 nm) curable thiol-acrylate resins, whose fast curing kinetics enable the additive manufacturing of precise 3D objects. Due to the orthogonality between the curing reaction and the photo-activation of the catalyst, transesterifications can be selectively switched on in the photo-cured vitrimer simply by UV-light exposure. By using a dual-wavelength digital light processing 3D printer, operating at 405 and 365 nm, the catalyst is locally activated during the layer-by-layer build-up of the 3D structures. This enables the fabrication of soft active devices, which undergo locally controlled topology arrangements above the networks’ Tv.