Maleic anhydride

Maleic anhydride is one of the most important raw materials in the composites industry. It provides the reactive double bonds that allow unsaturated polyester resins to cure into strong, durable thermosets. AOC works with maleic anhydride every day in the production of its maleic resins and other polyester formulations, and also supplies it to customers.

Key properties of maleic anhydride

Maleic anhydride is a white crystalline solid with the formula C4H2O3. Commonly published reference values include:

• Molar mass (molecular weight): about 98 g/mol.
• Melting point (mp): around 53 °C.
• Density: roughly one and a half times that of water in solid form.

These are general literature values. For specification limits, purity and handling data of the material supplied by AOC, always refer to the product documentation.

Maleic anhydride vs maleic acid

When maleic anhydride comes into contact with water, it hydrolyses into maleic acid. Maleic acid has a much higher melting point, at roughly 130 to 135 °C, and behaves differently in production. This is one reason why maleic anhydride must be stored dry. Searches for malic anhydride usually refer to maleic anhydride as well. Malic acid is a different compound, found for example in fruit.

Role of maleic anhydride in polyester resins

In resin production, maleic anhydride reacts with glycols and other acids such as isophthalic or orthophthalic acid. The unsaturated groups it introduces later cross-link with a reactive monomer or styrene-free alternative during cure. The ratio of maleic anhydride to saturated acids controls reactivity, heat resistance and stiffness.

Pure maleic resins, such as Palapreg® P 14-01 and Palapreg® P 18-21, offer high reactivity and are used in low-shrinkage SMC and BMC, for example for headlamp reflectors.

Maleic anhydride SDS and safety information

Maleic anhydride requires careful handling, as it is a sensitising and corrosive substance. AOC does not publish the maleic anhydride SDS openly on its website. Customers can request the current safety data sheet, product specification and regulatory information through AOC Customer Service or their account manager.

Frequently asked questions about maleic anhydride

What is the molecular weight of maleic anhydride?

The molar mass, also called molecular weight or MW of maleic anhydride, is about 98 g/mol, based on the formula C4H2O3.

How do I get the maleic anhydride SDS from AOC?

The SDS is not published openly on our website. Request the current version through AOC Customer Service or your account manager, together with the product specification if needed.

Sourcing maleic anhydride from AOC

Do you need maleic anhydride, technical data or a resin based on it? Contact our sales team or reach out via the contact page. Our experts help you with documentation, logistics and the right maleic anhydride or maleic resin for your process.