High molecular weight film-forming semicrystalline aromatic polyketones with a regular structure were obtained by precipitation electrophilic Friedel-Crafts polycondensation of 2,6-naphthalenedicarboxylic acid chloride with diphenyl ether, 1,4-bis(p-phenoxy)benzophenone and 1,4-bis(p-phenoxybenzoyl) benzene. Using H-1 and C-13 n.m.r. spectroscopy, the polyketones obtained were shown to be linear with para-substituted arylene fragments in the main chain. These polymers are soluble in strong protic acids and in common organic solvents, such as dichloroacetic acid and CHCl3/CF3CO2H mixtures. Depending on the chemical structure, these ’as-made’ polyketones were found to show multiple melting behaviour on heating.