Monomethyl maleate, also known as maleic acid monomethyl ester, is an unsaturated monomer that belongs to the glycol ether group. It is used in the production of polyvinyl alcohol with strong resistance to water vapor. It can also function as a solvent for tiglic acid and for copolymerization with other monomers, such as citric acid and maleate or ethylene. Additionally, it can be used as an anhydride in the manufacturing of glycol ethers.