Anisotropic melt forming polyesters and polyesteramides

A polyester or polyesteramide capable of forming an anisotropic melt prepared by reacting together dicarboxylic acids, dihydric phenols, hydroxyaromatic acids, aminophenols and their polyester and polyesteramide forming derivatives characterised in that the reactants include (A) at least 10 mole % of the total reactants used to form the polyester or polyesteramide of reactants selected from the group comprising fumaric acid and alkyl substituted fumaric acids wherein the alkyl group contains from 1 to 4 carbon atoms, and (B) at least 10 mole % of aromatic ring compounds containing asymmetrically disposed substituents on the artomatic ring compound, the substituents being chosen from the group comprising halogen, phenyl an alkyl groups containing from 1 to 4 carbon atoms and wherein at least 30 mole % of the aromatic reactants used have their chain extending bonds disposed on the aromatic nuclei so that the chain extending bonds are either coaxial or parallel and oppositely directed.