2 ethyl 4 methylimidazole

Hexane-1,6-diamine (HMDA), vanillin, 4-hydroxylbenzaldehyde (HBA), and 2-ethyl-4-methylimidazole (EMI) as a catalyst were purchased from Sigma-Aldrich (Yong-In, Korea). A diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin with an epoxy equivalent weight of 187 g/eq (YD-128) was provided by Kukdo Chemical (Seoul, South Korea). Solvents used in this work include ethanol (EtOH), methanol (MeOH), toluene (Tol), dimethylformamide (DMF), and dimethylacetamide (DMAc), which were supplied by Samchun Pure Chemical (Pyeong-Taek, South Korea). All materials were used without further purification.

Bisphenol A type epoxy resin, YD-128, was obtained from Kukdo Chemical (Seoul, Korea). Hexahydro-4-methylphthalic anhydride (HMPA), as the hardener for epoxy resin, and 2-ethyl-4-methylimidazole (EMI), as the catalyst, were purchased from Sigma-Aldrich (Yong-In, Korea). Furthermore, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (KBM-303), a coupling agent, was provided by Shln-Etsu Chemical Co., Ltd. (Tokyo, Japan). Aluminum oxides of spherical shapes with a median diameter of 14.4 μm (Al₂O₃, DAB-10SI) were purchased from Denki Kagaku Kogyo Kabushiki Kasisha (Tokyo, Japan). Boron nitride filler in the shape of a single-crystal platelet, with a mean particle size of ~45 μm and a surface area of 0.6 m²·g⁻¹, was purchased from Momentive Performance Materials, Inc. (Waterford, NY, USA). All materials were directly used without purification or modification.