Abstract: Protonation is one of the major factors for poly(aryl ether ketone)_s (PAED_s) molecules polarized in H₂SO₄. Results from UV and calculation show that degree of polarization of PAEK_s by H₂SO₄ increases with the ketone content or molecular chain regidity in polymer chains. This has been further proved by the experimental results, such as, larger λ_max (UV), more intense absorption at λ_max and greater deviatiou between experimental and practical viscosity values in concentrated H₂SO₄ than in other solvents. Based on these, we firstly suggested that the molecular rigidity is an important factor tobe considered in measuring the PAEK_s molecularweights. While, ¹⁹F NMR is adopted to quantitatively measure the molecular weight of many synthesized oligomers aud polymers, which gives a number-average molecular weights without any correction.

Key words: Poly (aryl ether ketone)_s, Protonation, Molecular weight, Structure and Rigidity