A composition comprising (a) an ethylenically unsaturated, polymerizable monomer or oligomer and (b) as radical generating compound an iminoxytriazine compound of the formula I n is 1 or 2; R 1 and R 2 independently of each other are hydrogen, NH 2, NHR 5, NR 5 R 6, COR 5, COOR 5, CONH 2, CONHR 5, CONR 5 R 6, CN, SR 5, OR 5, C 1 -C 18 alkyl, C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl, wherein said C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl is unsubstituted or substituted by one or more radicals selected from the group consisting of C 1 -C 12 alkyl, C 3 -C 12 -cycloalkyl, phenyl, halogen and C 1 -C 12 alkoxy, or R 1 and R 2 together with the C atom to which they are linked form a 4 to 12 membered carbocyclic or heterocyclic saturated or unsaturated ring which is unsubstituted or substituted by one or more radicals selected from the group consisting of C 1 -C 12 alkyl, C 3 -C 12 -cycloalkyl, phenyl, halogen and C 1 -C 12 alkoxy; R 3 is F, Cl, OH, OR 5, SH, SR 5, NH 2, NHR 5, NR 5 R 6 or R 1 R 2 C=N-O-; wherein R 1 and R 2 in all groups R 1 R 2 C=N-O- in the compound of the formula I are identical or different; if n is 1, R 4 is F, Cl, OH, OR 5, SH, SR 5, NH 2, NHR 5, NR 5 R 6 or R 1 R 2 C=N-O-; wherein R 1 and R 2 in all groups R 1 R 2 C=N-O- in the compound of the formula I are identical or different; if n is 2, R 4 is a difunctional group derived from a diol, diamine, aminoalcohol or mercaptoalcohol; R 5 and R 6 independently of each other are C 1 -C 18 alkyl, C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl. (a) an ethylenically unsaturated, polymerizable monomer or oligomer and (b) as radical generating compound an iminoxytriazine compound of the formula I n is 1 or 2; R 1 and R 2 independently of each other are hydrogen, NH 2, NHR 5, NR 5 R 6, COR 5, COOR 5, CONH 2, CONHR 5, CONR 5 R 6, CN, SR 5, OR 5, C 1 -C 18 alkyl, C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl, wherein said C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl is unsubstituted or substituted by one or more radicals selected from the group consisting of C 1 -C 12 alkyl, C 3 -C 12 -cycloalkyl, phenyl, halogen and C 1 -C 12 alkoxy, or R 1 and R 2 together with the C atom to which they are linked form a 4 to 12 membered carbocyclic or heterocyclic saturated or unsaturated ring which is unsubstituted or substituted by one or more radicals selected from the group consisting of C 1 -C 12 alkyl, C 3 -C 12 -cycloalkyl, phenyl, halogen and C 1 -C 12 alkoxy; R 3 is F, Cl, OH, OR 5, SH, SR 5, NH 2, NHR 5, NR 5 R 6 or R 1 R 2 C=N-O-; wherein R 1 and R 2 in all groups R 1 R 2 C=N-O- in the compound of the formula I are identical or different; if n is 1, R 4 is F, Cl, OH, OR 5, SH, SR 5, NH 2, NHR 5, NR 5 R 6 or R 1 R 2 C=N-O-; wherein R 1 and R 2 in all groups R 1 R 2 C=N-O- in the compound of the formula I are identical or different; if n is 2, R 4 is a difunctional group derived from a diol, diamine, aminoalcohol or mercaptoalcohol; R 5 and R 6 independently of each other are C 1 -C 18 alkyl, C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl. n is 1 or 2; R 1 and R 2 independently of each other are hydrogen, NH 2, NHR 5, NR 5 R 6, COR 5, COOR 5, CONH 2, CONHR 5, CONR 5 R 6, CN, SR 5, OR 5, C 1 -C 18 alkyl, C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl, wherein said C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl is unsubstituted or substituted by one or more radicals selected from the group consisting of C 1 -C 12 alkyl, C 3 -C 12 -cycloalkyl, phenyl, halogen and C 1 -C 12 alkoxy, or R 1 and R 2 together with the C atom to which they are linked form a 4 to 12 membered carbocyclic or heterocyclic saturated or unsaturated ring which is unsubstituted or substituted by one or more radicals selected from the group consisting of C 1 -C 12 alkyl, C 3 -C 12 -cycloalkyl, phenyl, halogen and C 1 -C 12 alkoxy; R 3 is F, Cl, OH, OR 5, SH, SR 5, NH 2, NHR 5, NR 5 R 6 or R 1 R 2 C=N-O-; wherein R 1 and R 2 in all groups R 1 R 2 C=N-O- in the compound of the formula I are identical or different; if n is 1, R 4 is F, Cl, OH, OR 5, SH, SR 5, NH 2, NHR 5, NR 5 R 6 or R 1 R 2 C=N-O-; wherein R 1 and R 2 in all groups R 1 R 2 C=N-O- in the compound of the formula I are identical or different; if n is 2, R 4 is a difunctional group derived from a diol, diamine, aminoalcohol or mercaptoalcohol; R 5 and R 6 independently of each other are C 1 -C 18 alkyl, C 3 -C 12 cycloalkyl, C 6 -C 14 aryl or C 2 -C 14 heteroaryl.