A new method for preparing commercially valuable polymeric ketones is described. The method employs an .alpha.-amiononitrile as a monomeric unit whereby an amorphous, soluble polymer having protected carbonyl moiety is obtained. Upon deprotecting the carbonyl moiety, a crystalline polymeric ketone is obtained. The method allows production of polymeric ketone materials having aromatic, aliphatic or mixed aromatic/aliphatic backbones.