Sustainable near UV-curable acrylates based on natural phenolics for stereolithography 3D printing

Photocured polymers have recently gained tremendous interest for a wide range of applications, such as industrial prototyping/additive manufacturing, electronics, medical/dental devices, and tissue engineering. However, current development of photoinitiated thermosetting formulations is mostly centered on commercial monomers/oligomers that are petroleum-derived and not environmentally friendly. This work aims to develop natural phenolic-based (meth) acrylates to expand the use of sustainable and mechanically robust 3D printable formulations. Utilizing thiol-ene chemistry, bifunctional 3,6-dioxa-1,8-octanedithiol eugenol acrylate (E) was synthesized through a highly efficient, scalable method. Real-time infrared spectra and photorheology studies revealed that E exhibits rapid photocuring kinetics and that the viscosity, glass transition temperature (T-g) and thermal properties of this material can be tuned by adding a sustainable reactive diluent, guaiacyl methacrylate (G). The effect of adding a crosslinker to binary GE monomers was further investigated by incorporating vanillyl alcohol dimethacrylate (V) or trimethylolpropane trimethacrylate (T). At 20 mol%, V showed a moderate improvement in curing rate and a lower degree of cross-linking than T due to the bifunctionality of V. However, the aromaticity of V provided more resistance to chain deformation and breakage within the network, demonstrating storage moduli and tensile strengths up to 3.4 GPa and 62 MPa, respectively. The distinct impact of the crosslinkers on the tensile behaviors of glassy terpolymers was correlated to the cohesive energy density. Ternary formulations GEV 60-20-20 by mol% with 2 wt% TPO photoinitiator were successfully printed using a commercial desktop stereolithographic 3D printer with 405 nm violet laser source. This work demonstrates a versatile, sustainable, and scalable synthetic strategy to design a class of natural phenolic acrylates for sustainable photocured formulations with potential translation to high performance 3D printing.