Synthetic Photoresist-Based Multifunctional Epoxy-methacrylate Macromers in 3D Printing Resin Formulations: Photocuring Kinetics and Properties

Macro-monomer (macromer) containing eight epoxy groups (SU-8), which is known as a photoresist for photolithography, was synthesized and subsequently converted into a series of epoxy-methacrylate macromers via epoxy ring opening with 2-hydroxyethyl methacrylate (HEMA). The resulting macromers were employed in 3D printing resin formulations. The epoxy to methacrylate conversion was confirmed using proton nuclear magnetic resonance (1HNMR) spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, and titration. The glass transition temperature (Tg) increased from −25.7 to 12.5 °C with increasing methacrylate content, as determined by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) demonstrated a decrease in thermal stability as the methacrylate functionality increased, with the fully methacrylated macromer (FA) losing up to 62% of its weight between 150 and 330 °C. For the study of the photocuring kinetics, ultraviolet (UV)-FTIR, along with the mechanical properties, demonstrated improved curing rate, higher volumetric shrinkage, and enhanced mechanical performance with increasing methacrylation, indicating optimized performance for vat photopolymerization-based 3D printing.