Vat photopolymerization 3D printing mainly uses acrylic or epoxy monomers, or a mixture of these monomers. Polymerization of hard and brittle acrylic monomers and flexible epoxy monomers forms an interpenetrating polymer network, resulting in a resin with fast curing speed and high toughness. However, phase separation occurs, and stress concentrated between the layers causes the cured resin to fracture. In this study, we synthesized acrylic monomers that have both rigid and flexible parts in a single molecule. By using this monomer in a photo-curable resin, we have developed resins that suppress phase separation and have excellent curing speed and toughness.