Light-Curing Anionic 3D Printing of Cyanoacrylates

Light-curing cyanoacrylates are originally proposed in order to build three-dimensional (3D) objects. Various printing techniques are shown in proof-of-concept experiments: digital light processing (DLP), anionic continuous liquid interface polymerization (ACLIP), and volumetric 3D printing. To the best of our knowledge, this is the first case of light-induced anionic 3D printing of cyanoacrylates. Key unique selling propositions of that choice of resin are outlined: (i) tack-free polymers (no oxygen inhibition), (ii) fast postprocessing with low irradiance LEDs, (iii) thermoplastic polymers vs usual thermosets, and (iv) extremely fast propagation constants. Downsides are that printers had to be customized in order to avoid reactivity in the VAT─highlighting the need for printer manufacturers’ collaboration. Resolutions of 500 μm on the z-scale have been observed without using opacifying dyes. This paper paves the way toward light-curing anionic 3D printing. Moreover, the associated chemical mechanisms were investigated by colorimetric and real-time FTIR experiments, as well as quantum mechanical calculations. A mechanism of conversion of radicals to anionic initiating species can be proposed: Free Radical-Promoted Anionic Polymerization (FRPAP) for a very efficient curing of cyanoacrylates upon mild conditions.