Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a heterocyclic ring containing oxygen (of cyclic esters of polyfunctional acids C08L31/00; of cyclic anhydrides of unsaturated acids C08L35/00); Compositions of derivatives of such polymers