of the following formulas: in which the groups A and B are, independently of one another: a hydrogen atom,a linear, branched and/or cyclic, saturated or unsaturated, aliphatic or else aromatic carbon radical; comprising 1 to 16 carbon atoms, especially 2 to 10 carbon atoms, even 4 to 8 carbon atoms, especially methyl or ethyl;or else A and B taken together form a saturated or unsaturated, even ar