Thermoplastic aromatic polyetherketones

A process for the production of a tough crystalline thermoplastic polyetherketone containing the repeat unit I ##STR28## alone or in conjunction with other repeating units selected from the group consisting of the repeating units IV ##STR29## where A is a direct link, oxygen, sulphur, --SO.sub.2 --, --CO--, or a divalent hydrocarbon radical, the oxygen atoms in the sub-units ##STR30## are ortho or para to the groups Q and Q', Q and Q' which may be the same or different are --CO-- or --SO.sub.2 --, Ar' is a divalent aromatic radical, and n is 0, 1, 2 or 3, which process comprises polycondensing, under substantially anhydrous conditions, at least one bisphenol which is hydroquinone or hydroquinone and at least one other bisphenol of formula ##STR31## where A is as defined above and at least one aromatic dihalide which is 4,4'-difluorobenzophenone or 4,4'-difluorobenzophenone and at least one other aromatic dihalide of formula ##STR32## where X and X' which may be the same or different are halogen atoms and are ortho or para to the groups Q and Q', and Q, Q', Ar' and n are as defined above, there being substantially equimolar amounts of bisphenol and aromatic dihalide, in the presence of at least one alkali metal carbonate or bicarbonate used in an amount providing at least 2 gram atoms of alkali metal per mole of bisphenol, the alkali metal or metals being selected from sodium, potassium, rubidium, and caseium provided that the sole use of sodium carbonate and/or bicarbonate is excluded, and in the presence of a solvent having the formula ##STR33## where Y is a direct link, an oxygen atom or two hydrogen atoms (one attached to each benzene ring) and Z and Z' are hydrogen or phenyl groups, within the temperature range 150.degree. to 140.degree. C., the final temperature level during the polycondensation being sufficiently high to maintain the final polymer in solution, such that a polymer having IV of at least 0.7 (which corresponds to RV of at least 0.8) is obtained.