Oxime esters: Potential alternatives to phosphine oxides, for overcoming oxygen inhibition in material jetting applications

• A series of four oxime esters is studied here as Type I photoinitiators for high performance systems. • Some of these oxime esters can outperformed benchmark photoinitiators. • The oxime esters were tested in 3D-inkjet printing applications, displaying highly promising results. • These oxime esters exhibit a dual-curing behavior, especially interesting for thermal post-curing treatment. Material jetting technology is emerging as a prominent technique within the additive manufacturing domain for printing multi-material objects. Despite its various advantages, including high printing resolution, oxygen inhibition remains the main issue for UV-curable materials. Oxime esters are interesting photoinitiators for this application due to their ability to undergo a photocleavage reaction followed by decarboxylation, limiting the diffusion of oxygen. A series of four commercially available oxime esters were studied as Type I photoinitiators, with the photoinitiating ability and photochemical properties of two of them never having been investigated before. Initially, their UV–visible absorption properties were studied, revealing significant absorption up to 420 nm. Photopolymerization kinetic studies indicate that the oxime esters can outperformed benchmark photoinitiators such as phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) by reaching around 80 % of double bond conversion in 12 µm layer under air (for O-16) against 60 % for BAPO under the same conditions. Finally, the oxime esters were tested in 3D-inkjet printing applications, displaying highly promising results with tack-free surfaces.