Maleic Anhydride (MA): Applications and Procurement for Unsaturated Polyester Resin (UPR) and Tartaric Acid

Maleic anhydride (MA) is produced by oxidation of n-butane or benzene. Its molecule contains a highly reactive cis double bond and an anhydride group, so it readily takes part in addition and polymerisation reactions, making it the largest single raw material for unsaturated polyester resin (UPR).

Core Application 1: Unsaturated Polyester Resin (UPR)

Maleic anhydride co-condenses with phthalic anhydride (PA) and diols, then crosslinks with styrene to give UPR — the matrix for FRP, engineered stone, sanitary ware, anti-corrosion piping and automotive parts. A higher maleic anhydride ratio improves resin stiffness and heat resistance but raises brittleness, so it must be balanced with phthalic anhydride. See Resin Selection for Coatings for reference.

Core Application 2: Alkyd Resins and Coatings

Maleic anhydride is used to modify alkyd resins, improving fast-drying and hardness, and is also used in waterborne acrylics and insulating varnishes. Its reactivity with polyols is higher than that of phthalic anhydride, so the process temperature window is narrower and temperature control is needed to prevent gelation.

Core Application 3: Tartaric Acid and Fine Chemicals

Hydration and isomerisation of maleic anhydride can produce tartaric acid (a food/pharmaceutical acidulant and chelating agent). It is also used in lubricant additives, succinic acid derivatives and paper sizing.

Key Procurement Indicators

Watch anhydride content, initial melting point, molten colour, iron content and thermal stability (prone to caking). Moisture absorption causes hydrolysis to maleic acid, which affects reactivity, so it must be sealed and stored in a cool, dry place. We recommend requesting a COA and retaining samples for comparison. Haiyu Zhonglong can provide specification sheets for maleic anhydride and other anhydride raw materials, with samples from 1kg/25kg. Please contact us via Online Inquiry or Contact Us, and see the full range in the Product Centre.