Highly Tunable Thiol‐Ene Photoresins for Volumetric Additive Manufacturing

Abstract

Volumetric additive manufacturing (VAM) is an emerging approach to photo polymerbased 3D printing that produces complex 3D structures in a single step, rather than from layer-by-layer assembly. [1] This paradigm holds promise because it overcomes many of the drawbacks of layerbased fabrication, such as long build times and rough surfaces. VAM also augurs a broadening of the materials available for photopolymer 3D printing, having fewer constraints on viscosity and reactivity compared to layerwise printing. Indeed, though VAM has been demonstrated with extremely soft hydrogels, [2,3] it has relied until now almost exclusively on acrylate-based chemistry. [4] This is natural, because the oxygen inhibition of acrylate polymerization provides the threshold behavior required for VAM. However, acrylate chemistry is in general limiting due to the brittle and glassy properties of the resulting materials. Accordingly, extensive efforts have been made to identify and target specific soft, elastic acrylate formulations. [5-9] Introducing alternative crosslinking chemistries to the VAM realm, as well as AM more broadly, is highly desirable as an alternative method to gain access to a wider range of mechanical, thermal, and optical performance. [10-14] Thiol-ene-based polymers are one class of materials that have drawn significant attention owing to their controllable, tunable mechanical properties. [15-17] This is generally attributed to more uniform molecular networks in thiol-ene materials, resulting from the step-growth mechanism of the polymerization reaction. [18,19] Thiol-ene materials have already shown promise for applications including use in adhesives, electronics, and as biomaterials. [20,21] This work expands the versatility of volumetric AM by introducing a new class of VAM-compatible thiol-ene resins. We demonstrate the formulation of thiol-ene resins with the nonlinear threshold-type kinetics required for VAM and show bulk-equivalent performance in the resulting 3D printed parts, confirming the advantage of the layerless whole-part process. In our volumetric AM system, a 3D distribution of light energy is delivered to the resin vat by superimposing exposures from multiple angles, a method termed computed axial litho graphy (CAL) (Figure 1a). [2] The exposures are a sequence of projections calculated from 3D CAD models using algorithms from computed Volumetric additive manufacturing (VAM) forms complete 3D objects in a single photocuring operation without layering defects, enabling 3D printed polymer parts with mechanical properties similar to their bulk material counterparts. This study presents the first report of VAM-printed thiol-ene resins. With well-ordered molecular networks, thiol-ene chemistry accesses polymer materials with a wide range of mechanical properties, moving VAM beyond the limitations of commonly used acrylate formulations. Since free-radical thiol-ene polymerization is not inhibited by oxygen, the nonlinear threshold response required in VAM is introduced by incorporating 2,2,6,6-tetrameth...

Three‐dimensional chemical reactors: in situ materials synthesis to advance vat photopolymerization

“…[172][173][174] During the curing of each new layer, the unreacted photopolymerizable groups in the previous layer can participate in the polymerization reactions with the monomers in the photoresin and form strong covalent bonds across the layer interface. [175][176][177] With more advanced VP techniques that utilize layerless continuous fabrication 6,178 or volumetric adsorption, 179 the issue of interlayer adhesion can even be completely circumvented. In contrast, the interlayer adhesion strength of polymeric parts made using techniques such as fused deposition modeling (FDM) and selective laser sintering (SLS) is based on the extent of diffusion and physical entanglement of polymer chains across the interface, without any covalent bonding.…”

Nanomaterials for 3D Printing of Polymers via Stereolithography: Concept, Technologies, and Applications

“…[ 75,76 ] Cook et al. [ 77 ] evaluated the mechanical properties of two thiol‐ene resins for the production of complex structures. The thiol‐ene resins showed a wide range of mechanical properties (from stiff to rubbery), and by changing its composition the modulus and toughness varied from 0.12 to 421 MPa, and 0.50 to 36 mJ m −3 , respectively.…”

“…The thiol‐ene resins showed a wide range of mechanical properties (from stiff to rubbery), and by changing its composition the modulus and toughness varied from 0.12 to 421 MPa, and 0.50 to 36 mJ m −3 , respectively. [ 77 ] Biobased and biocompatible thiol‐ene resins have been started to be developed as well. [ 75,76,78 ] Grauzeliene et al.…”

Additives for Ambient 3D Printing with Visible Light

“…Inspired by oxygen insensitive thiol-ene photopolymerizations, [26,27] we examined the use of thiols as additives to enable ambient 3D printing of acrylic resins with red light (~620 nm).…”