the company Jan Dekker. (7) Polymers corresponding to the general formula (XI) as described, for example, in French patent 1 400 366: in which R29 represents a hydrogen atom, a CH3O, CH3CH2O or phenyl radical, R30 denotes hydrogen or a lower alkyl radical such as methyl or ethyl, R31 denotes hydrogen or a lower alkyl radical such as methyl or ethyl, R32 denotes a lower alkyl radical such as methyl