Maleic Anhydride (MA)

Maleic Anhydride (MA) is one of the two primary raw materials used in the synthesis of unsaturated polyester resins (UPR), where it provides the reactive double bonds that crosslink with styrene monomer during curing. MA reacts with glycols (typically propylene glycol, ethylene glycol, or neopentyl glycol) and phthalic or isophthalic anhydride to form the UPR prepolymer backbone. The maleate double bonds are cis-configured and isomerize to the more reactive fumarate form during polyester condensation, providing the reactivity needed for free-radical co-polymerization with styrene. MA is a white crystalline solid with a melting point of 52–54°C and is handled as a melt or dissolved in glycol for UPR production. In direct applications, MA can also be used as a curing agent for certain polymer systems and as a chemical intermediate for maleic anhydride adducts. Industrial grade MA for UPR production requires high purity (≥99.5%) to ensure consistent resin reactivity and color. Maleic anhydride content in UPR typically ranges from 30–50 mol% of total diacid content, balancing reactivity and mechanical properties.