Abstract: Heat curable compositions comprising: (A) at least one compound which is capable of undergoing cationic polymerization; (B) at least one quaternary ammonium salt of an aromatic-N-heterocyclic cation and of a non-nucleophilic anion; (C) at least one 1,1,2,2-substituted-1,2-ethane-diol and/or a derivative thereof, and (D) optionally further additives; and wherein said component (C) is a compound of formula (I), wherein each of R1, R2, and R3 independently of the other is unsubstituted phenyl or has one of the meanings of R4; R4 is substituted phenyl optionally substituted &agr;-naphthyl or &bgr;-naphthyl, or an optionally substituted aromatic heterocyclic ring system or each of R1 and R2 and/or R3 and R4 independently of the other form a residue of formula (II), wherein each of R5 and R6 independently of the other is hydrogen or (C1-C4)alkyl; R7 is —(CH2)n— or —S— or —O—; and n is 0, 1, 2, or 3.