hydrogen atom or a methyl, ethyl or isopropyl radical, R3 is a hydrogen atom or a methyl or ethyl radical; monomers C having general formula 3: ##STR11## where R' is a hydrogen atom or a methyl group; monomers D containing a succinimide moiety on a side chain and having general formula 4: ##STR12## where R' is a hydrogen atom or a methyl group; monomers E having general formula 5: (CH2 ═CH--