A mixture according to claim 1, wherein the adduct (C) is derived from an epoxy resin containing on average more than one group of formula X ##STR55## wherein each of Q and Q is a hydrogen atom and Q' is a hydrogen atom or a methyl group or Q and Q together are --CH2 CH2 -- or --CH2 CH2 CH2 -- and Q' is a hydrogen atom, which group of formula II is attached to a sulfur, oxygen or nitrogen atom.