Vitrimers exhibit unique circularity-related properties, including self-healing, reprocessability, shape memory, and chemical recyclability through dynamic covalent bond exchange reactions. However, achieving sufficient toughness has been a challenge while maintaining these functionalities. In this study, polyrotaxane (PR), a topological supramolecular compound characterized by the sliding motion of cyclic molecules, was homogeneously dispersed within a vitrimer network, successfully improving the elongation at break by up to 5.3 times and the fracture energy by approximately 3 times while maintaining the Young’s modulus. Furthermore, the introduction of PR promoted bond exchange reactions, enhancing the self-healing and chemical recycling rates by more than 10 times. In addition to exhibiting complex shape memory, re-memory functions, and high weldability, the PR-containing vitrimer also exhibited marine biodegradability, which has not been observed in conventional vitrimer systems. These findings demonstrate that PR is a promising modifier capable of simultaneously enhancing the toughness and circularity of vitrimer materials, offering significant potential for applications in structural materials, adhesives, and fiber-reinforced composite materials.

We developed a thermosetting resin with low density and high modulus using machine learning to meet the demand for lightweight materials in the mobility field. Conventionally, reducing resin density while increasing modulus has been a trade-off, making molecular design challenging. In this study, machine learning was applied to predict density, modulus, and specific modulus, enabling a workflow to propose promising molecular structures from a virtual molecule library. As a result, it was suggested that alicyclic and aniline moieties are effective for achieving high specific modulus. Based on these findings, we designed and synthesized a novel curing agent, ADF, which exhibited low density, high modulus, and a 23% improvement in specific modulus compared to conventional systems. Finally, we succeeded in developing a resin with lightweight, stiff, and easy to handle, making it suitable for composite materials in mobility applications. Furthermore, this information-science-driven development process has demonstrated the possibility of further improving the efficiency of materials development.

Poly(glycidyl methacrylate)s (PGMA) with low molecular weights was synthesized by radical polymerization of glycidyl methacrylate (GMA) in the presence of ethyl 3-mercaptopropionate (EMP) as a chain transfer agent. PGMA was further converted to poly methacrylate bearing a five-membered cyclic carbonate pendant group (PMA5CC) by CO2 incorporation reaction. PMA5CC thus obtained had low molecular weight and showed good solubility to polar aprotic solvents as well as less polar solvents such as CH2Cl2 and toluene. PMA5CC with low molecular weight was also synthesized directly by radical polymerization of methacrylate bearing a cyclic carbonate group (MA5CC) in the presence of EMP. PMA5CC obtained directly from MA5CC showed good solubility similar to that of PMA5CCs synthesized via PGMA. Copolymerization of GMA with allylic compounds also yielded low-molecular-weight copolymers. These copolymers were successfully incorporated with CO2 to form cyclic carbonate. PMA5CC and the copolymers were cross-linked with hexamethylenediamine (HMDA) or 1,3-bis(aminomethyl)cyclohexane (1,3-BAC) to form networked polymers through ring-opening reaction of the cyclic carbonate group.

Heat resistance, thermal conductivity, toughness, and adhesion properties of the cyanate ester with a mesogenic backbone (DPC-CN) were evaluated. During the curing process, DPC-CN formed liquid crystal domains through the local arrangement of mesogenic groups, achieving the thermal conductivity 1.6 times higher, the fracture toughness approximately 10 times greater, and the glass transition temperature (Tg) approximately 10°C higher than those of conventional cyanate ester (Bis A-CN). On the other hand, the liquid crystalline arrangement decreased the adhesion strength of the cyanate ester. The effect of epoxy modification on DPC-CN was also investigated. Although biphenyl epoxy (DGEBP) modification decreased the fracture toughness and Tg of the DPC-CN curing system, the adhesive strength was slightly improved. Furthermore, the adhesive strength was significantly improved by setting the curing condition of the DGEBP modified system to high temperature and making the adhesive layer isotropic.

The phase structure and fracture toughness of cured epoxy resins prepared by blending epoxy resin with reactive flexible oligomers consisting of long-chain aliphatic structures were investigated. Imide-terminated oligomers bearing imide rings at both chain ends exhibited higher compatibility with the epoxy resin than the corresponding oligomers before the introduction of imide rings. The cured epoxy resins were prepared by precuring at various temperatures followed by post-curing at the same temperature. The cured epoxy/reactive flexible oligomer blend the cured epoxy underwent polymerizationinduced phase separation, forming sea-island morphologies. In particular, the cured epoxy/imide-terminated reactive flexible oligomer blends formed relatively fine phase structures that were independent of the pre-curing temperature. The fracture toughness showed little dependence on the pre-curing temperature at a displacement rate of 10 mm/min; however, it was influenced by the pre-curing temperature at a under low displacement rate (0.5 mm/min). The dependence of fracture toughness on pre-curing temperature was discussed based on the results of dynamic mechanical analysis.