A1, R10 and R12 can form, with the two nitrogen atoms to which they are attached, a piperazine ring; in addition, if A1 is a linear or branched, saturated or unsaturated alkylene or hydroxyalkylene radical, B1 can also be chosen from a group ???(CH2)n-CO-D-OC???(CH2)n- wherein n is an integer ranging from 1 to 100 and for example from 1 to 50, and D is: