Abstract: A crystallizable thermoplastic aromatic polyetherketone, the polymeric chain of which contains the repeat unit--Ar.sub.1 --CO--Ar.sub.2 --O--where Ar.sub.1 and Ar.sub.2 are aromatic radicals which may be the same or different and comprise at least one aromatic ring, the polymeric chains having terminal ionic groups --A--X, where A is an anion and X is a metal cation. The anion is preferably selected from sulphonate, carboxylate, sulphinate, phosphonate, phosphate, phenate and thiophenate and the cation is preferably alkali metal or alkaline earth metal. The products may be used in blends with other polyetherketones as a nucleant for the other polyetherketones.

Abstract: Fast crystallizing polyester compositions obtained by reacting a polyester which comprises aromatic or cycloaliphatic residues obtained from diacids and/or hydroxyacids and aliphatic, aromatic or cycloaliphatic residues of diols with an ionizable metal salt of an organic compound having at least one acidic proton using sufficient of the ionizable metal salt to result in at least 4% of the end groups of the polyester being converted to carboxylate end groups but insufficient to result in the melt degradation performance of the polyester determined as hereinafter described being substantially inferior to that of the polyester in the absence of the salt. Preferred compositions contain a polyester comprising at least 90 mole % of ethylene terephthalate units and metal salts of substituted benzoic acids.