A functional polymer whose molecules have a main chain of carbon-carbon bonds and one or more pendant functional groups each appended to the main chain via a carbonyliminocarbonyl linkage, in which the or each functional group is chosen from fluorinated, aminotriazine, photosensitive, bicyclic and spiro structure-containing groups, and in which the content of the functional groups plus the carbonyliminocarbonyl linkages per molecule is from 0.1 to 99.9% by weight.