Methyltetrahydrophthalic Anhydride (MTHPA)

Methyltetrahydrophthalic Anhydride (MTHPA) is the most widely used liquid anhydride curing agent for epoxy resins in electrical insulation, casting, and structural composite applications. It is a low-viscosity, room-temperature-stable liquid anhydride that provides an excellent balance of processing convenience, electrical properties, and cured system performance. MTHPA requires an accelerator (typically BDMA or DMP-30 at 0.5–2%) to achieve practical cure at temperatures of 80–150°C. Cured MTHPA-epoxy systems exhibit high Tg (100–140°C with proper post-cure), excellent electrical insulation, low water absorption, good chemical resistance, and superior hot/wet mechanical retention compared to amine-cured equivalents. The anhydride equivalent weight (AEW) of MTHPA is approximately 166 g/eq, and the recommended stoichiometric ratio is approximately 0.85–1.0 mol anhydride per mol epoxy. MTHPA is the standard curing agent for epoxy glass fiber laminates (G10/FR4), transformer potting compounds, semiconductor encapsulants, LED encapsulants, and filament-wound epoxy pressure vessels. Its liquid form at room temperature enables easy pump metering in automated production systems.