The acid anhydrides are used primarily as curing agents for alkyl and epoxy resins. [Rom, p. 1213] They are also one of the basic building blocks of polyesters. [Sullivan, p. 473]
An acid anhydride is a chemical compound that can form the acid when united with a molecule of water, e.g., from phthalic anhydride to phthalic acid. [Hawley] Acid anhydrides cause immunologic, occupational contact urticaria. [Kanerva, p. 219] Phthalic anhydride and trimellitic anhydride are in the NIOSH Pocket Guide. Six other acid anhydrides are listed in "Agents Causing Occupational Asthma with Key References" by Chan-Yeung & Malo [Malo] These six are tetrachlorophthalic anhydride, pyromellitic dianhydride, methyl tetrahydrophthalic anhydride, himic anhydride, chlorendic anhydride, and maleic anhydride. See "Trimellitic anhydride."