Abstractendo‐Dicyclopentadiene dioxide, a diepoxide melting at 185°C., reacts with polycarboxylic acid anhydrides, such as maleic anhydride, to give high softening, crosslinked resins. Polyhydric alcohols and phenols can be added to initiate the reaction and to modify the resin properties. The monomeric mixtures are mobile liquids at 35–50°C. for about 1 week. Partially cured resins, or B‐stage resins, are fusible and soluble for at least a year and are suitable for impregnating glass fibers in laminate applications. Crosslinking occurs at elevated temperatures by reaction of epoxide with carboxyl and hydroxyl groups and by reaction of maleate double bonds. In the optimum range of 0.3–0.5 mole of maleic anhydride for each epoxide equivalent, resins having an ultimate deflection temperature in excess of 300°C. and having excellent thermal stability are obtained. Vinyl monomers, such as styrene, can be used in the formulation to modify the reactivity and resin
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