Polycondensation normally proceeds in a step-growth reaction manner to give polymers with a wide range of molecular weights. However, the polycondensation of potassium 5-cyano-4-fluoro-2-propylphenolate (1) proceeded at 150 degreesC in a chain polymerization manner from an initiator, 4-fluoro-4'-trifluoromethylbenzophenone (2a), to give aromatic polyethers having controlled molecular weights and low polydispersities (M-w/M-n less than or equal to 1.1). The resulting polycondensation of 1 had all of the characteristics of living polymerization and displayed a linear correlation between molecular weight and monomer conversion, maintaining low polydispersities. The MALDI-TOF mass spectrum of poly1 revealed that this polycondensation did not include conventional step-growth polycondensation which gave the polymer without initiation unit and macrocycles. The poly1 with low polydispersity showed higher crystallinity than that with broad molecular weight distribution, obtained by the conventional polycondensation of 1 without 2a.