The repeating units of structure B may alternatively be formed by the partial esterification or amidification of an already-polymerised olefinically unsaturated carboxylic acid (or an esterifiable or amidifiable derivative thereof such as an acid chloride or anhydride) using, preferably, an alcohol of formula HO--CHR1 CHR2 O)n R3 or an amine of formula H2 N--CHR1 CHR2 O)n R3.