The invention relates to novel N-substituted imides and polymerizable compositions comprising these N-substituted imides. The invention further relates to the use of N-substituted imides as polymerization initiators. The imides are compounds of the formula (I) and (II) wherein n is 1 or 2; m is 1 or 2; R1 and R2 are each, independently of one another, hydrogen, C1-C18alkyl, C1-C18alkenyl C6-C14aryl, aralkyl, C5-C12cycloalkyl, each of which may be substituted by halogen, C1-C4-alkyl, hydroxy, C1-C6alkoxy, carbonyl, C1-C6alkoxycarbonyl; or R1 and R2 together with the adjacent —CO—N—CO— group may form a monocyclic, bicyclic or polycyclic ring, said ring having up to 50 non hydrogen atoms and wherein said ring may contain the structural element (formula III) more than once; R3 if n is 1, is C1-C18alkyl, C6-C14aryl, aralkyl, C5-C12cycloalkyl, OR10 or SR11, NR12R13; wherein R3 if n is 2, is C2-C12alkylene, C6-C14arylene, xylylene R4 and R5, correspond to R1 and R2; R6 if n is 1, is hydrogen, C1-C18alkyl, C6-C14aryl, aralkyl, C5-C12cycloalkyl, NR14R15; wherein R6 if n is 2, is C2-C12alkylene, C6-C14arylene, xylylene; R7 is hydrogen, C1-C18alkyl, C6-C14aryl, aralkyl, C5-C12cycloalkyl, each of which may be substituted by halogen, C1-C4-alkyl, hydroxy, C1-C6alkoxy, carbonyl, C1-C6alkoxy-carbonyl; or R7 and R14 or R7 and R15 form together with the N-atom attached to R7 a 5-6 membered ring, optionally interrupted by —NH—, —N(C1-C8alkyl)-, —O- and/or S-atoms.