Abstract: Monomers of poly(aryl ether ketone)s famiy, such as,4,4'-hydroquinone(PD),4,4'-biphenol(S₃)and 4,4'-difluorine benzophenone have been researched by ab initio RHFmethod.Results obtained show that these monomers have different torques in their aromatic rings.S₃ has a dihedral angle of 51.8°,its reactivity is a bit stronger than that of PD, but it introduced more active branching points.Thus, polymer DPEEKfrom S₃ has more serious chain branching and is more difficult in crystallizing than PEEKfrom PD.And also, it is found that there is a kind of red negative ion in DPEEK solution of concentrated H₂SO₄.

Key words: Ab initio RHF calculation, Monomers of poly (aryl ether ketone)s, Dihedral angle, Chain branching