Photopolymers share a significant portion of the market for 3D printing, which is expected to grow to at least 16 billion dollars in the next decade. Formulation of photocurable resins is integral to achieve the desired properties of 3D printed materials. Given the variety of new “lignin-first” catalytic technologies that produce high yields of phenolic monomers from lignin and biomass, our group has been investigating lignin-derived aromatic monomers to produce photocurable resins. Select phenolic compounds such as 4-ethylguaiacol and acetovanillone, which are commonly produced during lignin depolymerization, were modified via a methacrylation process using (hydroxyethyl)methacrylate (HEMA) or methyl methacrylate (MMA) and then cured under UV light (365-405 nm). Free radical polymerization of the synthesized resins was initiated with bisacylphosphine oxide, a common commercial photoinitiator. Real-time FTIR spectroscopy was used to quantify the amount of uncured resin at a specified time point and subsequently to calculate the reaction kinetics. We determined that HEMA-containing resins exhibited significantly higher curing rate (0.19 sec<sup>-1</sup>) when compared to MMA-containing resins (0.04 sec<sup>-1</sup>). We attribute this to the MMA-containing polymer network forming a denser network, thereby slowing the diffusion of macromonomer radicals and ultimately leading to the termination of polymer chains. In addition, we found the differences in curing rate affected the thermo-mechanical properties of photopolymers. For example, resins with faster curing rates produced photopolymers with higher thermal tolerance and resins with slower curing rates produced photopolymers with shorter branches and subsequently higher storage moduli. Thus, by altering the composition of photocurable resins, it is possible to tune the thermo-mechanical properties of the resulting photopolymer. These results and opportunities to use depolymerized “lignin-first” monomers for photocurable resin synthesis will be discussed.

Photopolymerization of acrylated lignin monomers: Implications for lignin utilization in additive manufacturing by stereolithography

2019 Spring National Meeting

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