The curing process of epoxy resin with maleic anhydride has been examined with infrared spectroscopy，by following the functional group changes occuring in different curing stages at different temperatures． It has been found that the increase of mole-cular weight and the formation of cross—linkages in the epoxy resin are attained primarily via the esterification reaction，that is，the anhydride first reacts with the hydroxyl group in the resin to form a mono—ester and the newly formed carboxylic group reacts with an epoxy group to give a diester and a new hydroxyl group which can itself react with the anhydride． Under the influence of heat，the maleate structure formed in the esterifica-tion tends to isomerize into fumarate．This cis．trans isomerization reaction is tempera-turc-sensitive

but the extent of reaction is not appreciable below 60℃． At a curing temperature of 180℃ or higher。the carbon-carbon doubl~bonds in the maleate structures may undergo addition polymerization and thermal oxidation，resulting in the formation of new carbonyl and hydroxyl groups．