Hexahydrophthalic Anhydride (HHPA)

Hexahydrophthalic Anhydride (HHPA) is a fully saturated cycloaliphatic anhydride curing agent for epoxy resins, offering a unique combination of solid form at room temperature (melting point 34–36°C), high purity, and excellent electrical and mechanical properties in cured systems. Unlike the liquid MTHPA and MHHPA, HHPA is handled as a solid or low-melting-point liquid above 40°C, requiring heated mixing lines for large-scale production. Its anhydride equivalent weight (AEW) is approximately 154 g/eq, slightly lower than MTHPA. HHPA produces cured epoxy systems with very high Tg (100–140°C with post-cure), excellent electrical insulation properties, low ionic impurity, and good chemical resistance. It is used in epoxy glass fiber laminate systems (B-staged prepregs), electrical casting compounds where slow pour is required, and dry powder pre-mix systems for automated injection or transfer molding of epoxy. HHPA can also be blended with liquid anhydrides (MTHPA or DDSA) to adjust viscosity, pot life, and flexibility of the cured product. Accelerators (BDMA, DMP-30, or imidazoles) are required at 0.5–2% dosage.