An oligomer or polymer substituted by one or more bisacylphosphine oxide moieties, characterized in that said bisacylphosphine oxide moiety is linked via the phosphorous atom, optionally via a spacer group, to the oligomer or polymer backbone, which oligomer or polymer comprises units of the formula Ia m is an integer equal or greater than 2; y and z i ndependently of each other are an integer 0-15000; A is or wherein the asterisk denotes the bond to X; B 1 and B 2 independently of each other are wherein A, B 1 and B 2 are incorporated into the same polymer backbone via random or block polymerization; X is a direct bond, C 1 -C 10 -alkylene, -(CH 2) o -NH-CO-O-(CH 2) p - *, -(CH 2) o -NH-CO-O-CH 2 -CHOH-CH 2 - *, -(CH 2) o -NH-CO-NH-(CH 2) p - *, -(CH 2) o -NH-CO-S-(CH 2) p - *, -(CH 2) o -O-CO-CHR 3 -CH 2 -NH-(CH 2) p - *, * -(CH 2) o -O-CO-CHR 3 -CH 2 -NH-(CH 2) p -, -(CH 2) o -CO-O-(CH 2) p-*, -(CH 2) o -O-CO-CH 3- CH 2 -S-(CH 2) p - *, * -(CH 2) o -O-CO-CHR 3 -CH 2 -S-(CH 2) p -, -(CH 2) o -O-CO-CH(COCH 3)-CH 2 -C(COOR 3)CH 2 - *, -(CH 2) o -NH-CH 2 -CH 2 -C(COOR 3)CH 2 - *, -(CH 2) o -S-(CH 2) o -C(COOR 3)CH 2 - *, -(CH 2) o -O-CO-CH(COCH 3)-CH 2 -CHR 3 -CO-O-(CH 2 -CH 2 -O) t CH 2 - *, -(CH 2) o -NH-CH 2 -CHR 3 -CO-O-(CH 2 -CH 2 -O)t CH 2 - *, - o -S-CH 2 -CHR 3 -CO-O-CH 2 -CH 2 - *, -(CH 2) o -S-CH 2 -CHR 3 -CO-O-(CH 2 -CH 2 -O) t CH 2 - *, -(CH 2) o -NH-CH 2 -CHR 3 -CO-CH 2 -CH 2 - *, -(CH 2) o -O-CO-CH(COCH 3)-CH 2 -CHR 3 -CO-O-CH 2 -CH 2 - *, -(CH 2) o -CO-O-CH 2 -CHOH-CH 2 - *, -(CH 2) o- O -CH 2 - *, -(CH 2 CH 2 O) t - -CH 2 - *, -(CH 2) o- CHOH-CH 2 -O -CH 2 - *, or wherein the asterisk denotes the bond to the bisacylphosphine oxide moiety; o, p and q independently of each other are an integer 1-4; r is an integer 0-2; s is 0 or 1; t is an integer 1 or 2; R 1 is C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy or Cl; and R 2 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy or Cl; R 3 is hydrogen or methyl; R 4 is C 1 -C 4 alkyl; R 5 is methyl, phenyl or ethoxy; R 6 is C 1 -C 10 alkyl or C 1 -C 9 perfluoroalkyl; R 7 is C 1 -C 10 alkyl, -CH 2 -O-C 1 -C 10 alkyl, -CH 2 -O-(CH 2) o -C 5 -C 8 cycloalkyl, -CH 2 -O-(CH 2) o -C 6 -C 10 aryl, C 1 -C 9 perfluoroalkyl, -CH 2 -O-C 1 -C 10 perfluoroalkyl, -CH 2 -O-C 6 -C 10 aryl which is unsubstituted or substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or by Cl; R 8 is hydrogen, C 1 -C 8 alkyl, O-R 15 or CN; R 9 is hydrogen, O-R 15; or R 8 and R 9 are together ―(CH 2) w -, ―CH=CH-CH 2 -, - -O- -, - -N(R 16)-CO- or R 10 is hydrogen, C 1 -C 8 -alkyl or ―SO 3 - E +; R 11 is hydrogen; or R 10 and R 11 together are -O-CH 2 CH 2 -O-; R 12 and R 13 independently of each other are C 1 -C 4 -alkyl, vinyl, phenyl or C 1 -C 4 alkoxy; R 14 is hydrogen, CH 2 Br, CH 2 Cl or I; R 15 is hydrogen, C 1 -C 4 -alkyl or benzyl; R 16 is C 1 -C 4 alkyl or phenyl; w is an integer 3-10; E is a cation; and Z is CH 2 or O. m is an integer equal or greater than 2; y and z i ndependently of each other are an integer 0-15000; A is or wherein the asterisk denotes the bond to X; B 1 and B 2 independently of each other are X is a direct bond, C 1 -C 10 -alkylene, -(CH 2) o -NH-CO-O-(CH 2) p - *, -(CH 2) o -NH-CO-O-CH 2 -CHOH-CH 2 - *, -(CH 2) o -NH-CO-NH-(CH 2) p - *, -(CH 2) o -NH-CO-S-(CH 2) p - *, -(CH 2) o -O-CO-CHR 3 -CH 2 -NH-(CH 2) p - *, * -(CH 2) o -O-CO-CHR 3 -CH 2 -NH-(CH 2) p -, -(CH 2) o -CO-O-(CH 2) p-*, -(CH 2) o -O-CO-CH 3- CH 2 -S-(CH 2) p - *, * -(CH 2) o -O-CO-CHR 3 -CH 2 -S-(CH 2) p -, -(CH 2) o -O-CO-CH(COCH 3)-CH 2 -C(COOR 3)CH 2 - *, -(CH 2) o -NH-CH 2 -CH 2 -C(COOR 3)CH 2 - *, -(CH 2) o -S-(CH 2) o -C(COOR 3)CH 2 - *, -(CH 2) o -O-CO-CH(COCH 3)-CH 2 -CHR 3 -CO-O-(CH 2 -CH 2 -O) t CH 2 - *, -(CH 2) o -NH-CH 2 -CHR 3 -CO-O-(CH 2 -CH 2 -O)t CH 2 - *, - o -S-CH 2 -CHR 3 -CO-O-CH 2 -CH 2 - *, -(CH 2) o -S-CH 2 -CHR 3 -CO-O-(CH 2 -CH 2 -O) t CH 2 - *, -(CH 2) o -NH-CH 2 -CHR 3 -CO-CH 2 -CH 2 - *, -(CH 2) o -O-CO-CH(COCH 3)-CH 2 -CHR 3 -CO-O-CH 2 -CH 2 - *, -(CH 2) o -CO-O-CH 2 -CHOH-CH 2 - *, -(CH 2) o- O -CH 2 - *, -(CH 2 CH 2 O) t - -CH 2 - *, -(CH 2) o- CHOH-CH 2 -O -CH 2 - *, or wherein the asterisk denotes the bond to the bisacylphosphine oxide moiety; o, p and q independently of each other are an integer 1-4; r is an integer 0-2; s is 0 or 1; t is an integer 1 or 2; R 1 is C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy or Cl; and R 2 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy or Cl; R 3 is hydrogen or methyl; R 4 is C 1 -C 4 alkyl; R 5 is methyl, phenyl or ethoxy; R 6 is C 1 -C 10 alkyl or C 1 -C 9 perfluoroalkyl; R 7 is C 1 -C 10 alkyl, -CH 2 -O-C 1 -C 10 alkyl, -CH 2 -O-(CH 2) o -C 5 -C 8 cycloalkyl, -CH 2 -O-(CH 2) o -C 6 -C 10 aryl, C 1 -C 9 perfluoroalkyl, -CH 2 -O-C 1 -C 10 perfluoroalkyl, -CH 2 -O-C 6 -C 10 aryl which is unsubstituted or substituted by C 1 -C 4 alkyl, C 1 -C 4 alkoxy or by Cl; R 8 is hydrogen, C 1 -C 8 alkyl, O-R 15 or CN; R 9 is hydrogen, O-R 15; or R 8 and R 9 are together ―(CH 2) w -, ―CH=CH-CH 2 -, - -O- -, - -N(R 16)-CO- or R 10 is hydrogen, C 1 -C 8 -alkyl or ―SO 3 - E +; R 11 is hydrogen; or R 10 and R 11 together are -O-CH 2 CH 2 -O-; R 12 and R 13 independently of each other are C 1 -C 4 -alkyl, vinyl, phenyl or C 1 -C 4 alkoxy; R 14 is hydrogen, CH 2 Br, CH 2 Cl or I; R 15 is hydrogen, C 1 -C 4 -alkyl or benzyl; R 16 is C 1 -C 4 alkyl or phenyl; w is an integer 3-10; E is a cation; and Z is CH 2 or O.