The invention relates to a compound of formula (I):wherein:ALK is a (C1-C6)alkylene group；X1 et X2 are each independently one of the following groups: —CH═CH—, —CO—, —CONR—, —NRCO—, —COO—, —OCO—, —OCONR—, —NRCOO—, —NRCONR′—, —NR—, —S(O)n (n=0, 1 or 2) or —O—；R and R′ are independently H or a (C1-C6)alkyl group；i is an integer of from 1 to 40, preferably from 1 to 20, and more preferably from 1 to 10；j is an integer corresponding to 1 when X2 is —CH═CH— and 2 when X2 is not —CH═CH—；Zb is a simple bond, —O— or —NH— and Rb is H or a (C1-C6)alkyl, (C3-C7)cycloalkyl, aryl, heteroaryl or (C3-C7)heterocycloalkyl group； or Zb is a single bond and Rb is Hal.
