Curable epoxy resins obtainable in the presence of specific lewis acids as catalyst

Curable epoxy resin compositions, which are obtainable by heating a composition containing at least one epoxy compound, which contains on average at least one, preferably more than one, 1,2-epoxy group and optionally also one or several hydroxyl groups in the molecule, in the presence of at least one Lewis acid as catalyst, wherein the Lewis acid is a salt of trifluoromethanesulfonic acid or of perchloric acid, the counterion of which carries a 2- to 6-fold positive charge, until the epoxy value, measured in equivalent epoxy/kg (Eq/kg) of the starting material, has been reduced by 1 to 60 percent, preferably by 5 to 50 percent; a process for their preparation, and their use for the preparation of fully cured moulded compositions or coatings. Claimed are, inter alia, also high molecular weight epoxy compounds of formula (lla), wherein A is a divalent aliphatic or aromatic radical, B is the radical of the dioxan, which is substituted either in 2- and 5-position or in 2- and 6-position and which may be in the cis- or trans-form, and n is an integer from 1 to 10, preferably from 1 to 5.