A process for the preparation of an alkali metal salt of 4-chloro-4′-hydroxy benzophenone including the steps of (a) preparing purified 4-chloro-4′-hydroxy benzophenone by a process including distilling under reduced pressure a liquid containing 4-chloro-4′-hydroxy benzophenone and a solvent selected from diphenyl sulphone, diphenylene sulphone, benzophenone and dichlorobenzophenone, and then (b) preparing the alkali metal salt of thus purified 4-chloro-4′-hydroxy benzophenone by the reaction of the purified 4-chloro-4′-hydroxy benzophenone with a stoichiometric excess of at least one alkali metal base. There is also described a polymerization process using the alkali metal salt to yield PEK with high inherent viscosity and improved mechanical and thermal properties.