PURPOSE: To prepare the title composition useful as a curing agent of epoxy resins, by heating 3-methyl-and 4-methyl-delta-4-tetrahydrophthalic anhydrides separately, at a relatively low temperature, in the presence of an acidic ion exchange resin, and mixing the products in a specific ratio.
CONSTITUTION: 3-Methyl-Δ 4 -tetrahydrophthalic anhydride and 4-methyl-Δ 4 -tetrahydrophthatlic anhydride are separately heat-treated at 50W95°C, pref. 70W95°C, in the presence of an acidic ion exchange resin. A liquid dibasic acid anhydride composition stable at 0°C, is prepared by mixing 60W20wt.%, pref. 55W25wt.%, of the former product and 40W80wt.%, pref. 45W75wt.% of the latter product.
EFFECT: Product with light color: stable catalytic activity: easy removal of the catalyst.