AbstractThe modification of epoxy resins by reactions involving their hydroxyl groups is described. For example, reactions with enol ethers, acrylonitrile, ethyl acetoacetate and certain other carboxylic esters, or triethyl orthoformate, gave products which had reduced reactivities towards various hardeners, and which therefore gave lower peak temperatures on cure and/or longer usable lives. Suitable modification of epoxy resins with various other reagents(certain acid anhydrides, epichlorohydrin, orN‐hydroxymethylacrylamide) introduces additional useful functional groups. The uses of a diisocyanate and of α‐naphthyl isocyanate to modify epoxy resins or their mixtures prior to GPC analysis are also menti