Cy consists of an n-alkyl moiety containing 18-24 carbon atoms, and b is a bond or a moiety which has a valence of at least 2 and which links the Cy moiety to the polymer backbone; (2) the polymer has a crystalline melting temperature, Tp, of at least 40??? C., an onset of melting temperature, To, such that the value of (Tp???To) is less than Tp0.7, and a heat of fusion of at least 5 J/g;