Oxime ester photoinitiators

A compound of the formula Ia

• wherein
• M1 is a direct bond;
• M2 and M3 are no bond;
• R2 is C1-C20alkyl which C1-C20alkyl optionally contains one or more C—C multiple bonds;
• or R2 is C1-C20alkyl which is substituted by C1-C20heteroaryl or
• or R2 is phenyl or C1-C20heteroaryl, each of which optionally is substituted by one or more C1-C12alkyl, halogen, SR10 or OR11;
• or R2 is
• or R2 forms a ring with one of the C-atoms of the phenyl ring to which the group
• is attached, wherein said formed ring is unsubstituted or substituted;
• R″2 has one of the meanings given for R2;
• R3 and R4 independently of one another are hydrogen or are
• R′2 has one of the meanings given for R2;
• R′1 is C1-C20alkyl;
• R′3, R′4, R″3 and R″4 independently of one another have one of the meanings given for R3 and R4;
• R5 is hydrogen;
• R20 is (CO)R1;
• R21 is (CO)R1;
• R22 is C1-C20alkyl;
• R23 is C1-C20alkyl,
• wherein the group
• can be replaced with
• R10 and R11 are an unsubstituted or substituted C1-C20heteroaryl or C1-C20alkyl;
• Z is hydrogen COR1 or COR′1;
• provided that at least one radical Z in the compound of the formula Ia is hydrogen;
• and
• provided that at least two groups comprising the radical Z are present in the molecule;
• and provided that
• (i) at least one of R2 and R′2 in one of the substituents
• is
• or
• (ii) at least one of R2 and R′2 in one of the substituents
• forms a ring with one of the C-atoms of the phenyl ring to which the group
• is attached;
• or
• (iii) at least one of R2, R′2, and R″2 in one of the substituents
• is C1-C20alkyl contains one or more C—C multiple bonds;
• or
• (iv) at least one R2, R′2, and R″2, in one of the substituents
• is C1-C20alkyl which is substituted by one or more C1-C20heteroaryl, C1-C20heteroaryl-(CO)O, C1-C20heteroaryl-S or
• or at least one of R10 and R11 is C1-C20alkyl which is substituted by one or more C1-C20heteroaryl, or
• or
• (v) at least one of R10, R11 is an unsubstituted or substituted C1-C20heteroaryl.