the phenylene group may be substituted by a hydrocarbyl group or a functional group; and D is a hydrocarbyl group and the units E, E??? and S are derived from one or more 1-substituted piperidin-4-ol or 4-aminopiperidines of general structure wherein Z is OH or NHG, wherein G is H or C1-C12 alkyl, R1 is ???(CH2)s???OH or ???(CH2)s???NH2, wherein s is an integer from 1 to 10; R2 represents hydrogen