Oligofunctional photoinitiators

1. A compound of formula (1) or (1A)

wherein

R 1 and R 2 are methyl or together are —(CH 2 ) 5 —; and

n is 2 or 3 and the solvent in (1A) is water or an organic solvent.

2. A compound of the formula (1) or (1A) according to claim 1 , wherein R 1 and R 2 are methyl.

3. A photopolymerizable composition, comprising

(A) at least one ethylenically unsaturated photopolymerizable compound and

(B) at least one photoinitiator of the formula (1) or (1A) as defined in claim 1 .

4. A photopolymerizable composition according to claim 3 , which additionally comprises at least one further photoinitiator (C) and/or other customary additives (D).

5. A photopolymerizable composition according to claim 3 , comprising 0.05 to 15% by weight of the at least one photoinitiator (B), based on the composition.

6. A photopolymerizable composition according to claim 4 , comprising (D) a pigment or dye or a mixture of pigments or dyes.

7. A photopolymerizable composition according to claim 4 , comprising (D) a dispersant or a mixture of dispersants.

8. A photopolymerizable composition according to claim 3 additionally comprising a binder polymer (E).

9. A photopolymerizable composition according to claim 3 which is a printing ink.

10. Process for the preparation of a compound of the formula (1) or (1A) as defined in claim 1 , which comprises reacting n compounds of formula (2)

with an acid chloride of formula (3),

in the presence of a base, to give a compound of the formula (1);

and subsequent crystallization from a solvent to give a compound of the formula (1A),

wherein R 1 , R 2 and n are as defined in claim 1 .

11. Process for the preparation of a compound of formula (2),

in which process

step 1) a compound of formula (4)

is treated with bromine without irradiation with lamps or the need to add radical initiators to give a brominated compound of formula (5)

and

step 2) the compound of the formula (5) is transformed to the corresponding hydroxyl compound of formula (2) by treatment with a base,

wherein

R 1 and R 2 are methyl or together are —(CH 2 ) 5 —.

12. Process for the preparation of a compound of the formula (1) or (1A) as defined in claim 1 , in which process

step 1) a compound of formula (4)

is treated with bromine without irradiation with lamps to give a brominated compound of formula (5)

and

step 2) the compound of the formula (5) is transformed to the corresponding hydroxyl compound of formula (2) by treatment with a base; and

step 3) n compounds of the formula (2)

are reacted with an acid chloride of the formula (3),

in the presence of a base, to give a compound of the formula (1); and subsequent crystallization from a solvent to give the compound of the formula (1A),

wherein n, R 1 and R 2 are as defined claim 1 .

13. A process for the photopolymerization of compounds containing ethylenically unsaturated double bonds, which comprises irradiating a composition according to claim 3 with electromagnetic radiation in the range from 150 to 600 nm or with electron beam or with X-rays.

14. A process according to claim 13 for producing pigmented or nonpigmented paints or varnishes, powder coatings, printing inks, printing plates, adhesives, dental compositions, gel coats, photoresists for electronics, electroplating resists, etch resists, liquid or dry films, solder resists, resists to manufacture color filters for display applications, resists to generate structures in the manufacturing processes of plasma-display panels, electroluminescence displays, spacers for LCD, holographic data storage (HDS), compositions for encapsulating electrical or electronic components, magnetic recording materials, micromechanical parts, waveguides, optical switches, plating masks, etch masks, colour proofing systems, glass fibre cable coatings, screen printing stencils, three-dimensional objects by means of stereolithography, image recording materials, holographic recordings, microelectronic circuits, decolorizing materials, image recording materials using microcapsules, photoresist materials for UV or visible laser direct imaging systems or photoresist materials used for forming dielectric layers in a sequential build-up layer of a printed circuit board.

15. A coated substrate which is coated on at least one surface with a composition according to claim 3 .

16. A photopolymerizable composition according to claim 3 which is a surface coating for food packaging materials.