Chemical structure–property relationships of photocurable monomers/macromers: Potential binder candidates for ceramic/metal vat photopolymerization

Abstract

Successful ceramic/metal vat photopolymerization (VPP) depends on the precise optimization of photocurable polymers to achieve ideal component properties. Most photocurable polymers consist of binary systems with monomers/macromers of varying functionalities. Crosslinking polymerization in VPP, particularly concerning monomer/macromer chemical structure, has not been extensively researched. This study systematically investigates the effects of three difunctional monomers, three difunctional macromers, and three multifunctional monomers. 18 combinations were prepared using difunctional monomers/macromers and multifunctional monomers at a 50:50 ratio. The study examined how linker chain length, ethoxylation, functional groups, and functionality impact properties critical for VPP processes, including photocuring behavior, mechanical properties, and shrinkage. Curing depth measurements showed that resins with rigid monomers and longer chain lengths had a higher critical energy ($E_c$), while flexible monomers had a lower $E_c$. Methacrylate-containing formulations exhibited a higher $E_c$ than acrylates. Although resins with higher functionality ($f_{ave}$) generally showed higher $E_c$, this trend was not always consistent. Photo-DSC results showed that ethoxylated TMPTA slows down crosslinking polymerization in methacrylate-containing resins but accelerates it in acrylate formulations. Moreover, combining tetrafunctional monomer with methacrylate enhanced the polymerization rate of methacrylate. The compression tests showed that an excess of ethylene oxide groups in the chemical structure of used monomers introduces a higher degree of flexibility and softness to the cured structure, leading to a reduction in mechanical properties. Furthermore, it was observed that methacrylate-containing resins shrank more compared to their acrylate-containing counterparts. Finally, five potential candidates were proposed for ceramic/metal VPP.