Synthesis and chemical, physical, and optical properties of 9,9-diarylfluorene-based poly(ether-ether-ketone)

Fluorene-based poly(ether-ether-ketone) (F-PEEK) was designed and synthesized by reacting a 9,9-diarylfluorene-containing biphenol and a naphthalene-containing dihaloarene. High molecular weight F-PEEK (M-w > 270 000; M-n similar to 55 000) was obtained in quantitative yields by the two-step polycondensation of 9,9-bis(4-hydroxy-3-methylphenyl)fluorene and 1,5-bis(4-fluorobenzoyl)-2,6-dimethylnaphthalene in the presence of cesium carbonate in diphenyl sulfone at 165 degrees C and then 220 degrees C. The chemical, physical, and optical properties of F-PEEK were evaluated. Good solubility of F-PEEK in ordinary organic solvents such as THF and chloroform was confirmed. F-PEEK exhibited a high refractive index of 1.64 at 589 nm, whereas it showed a much lower birefringence value than a polycarbonate or a polyester. F-PEEK was amorphous and transparent at room temperature. The transmittance of F-PEEK in film state was over 80% in the visible region. These optical properties were probably related to the cardo structure of the fluorene moiety placed on the main chain. No phase transition except for T-g was confirmed in the DSC analysis. F-PEEK displayed a high storage modulus (E' = 2.93 GPa) and glass transition temperature (280 degrees C) in comparison with commercially available poly(ether-ether-ketone) (PEEK, E' = 1.73 GPa and T-g 169 degrees C). The high modulus of F-PEEK was derived unambiguously from both the fluorene and naphthalene skeletons.