Synthesis and Chemical, Physical, and Optical Properties of 9,9-Diarylfluorene-Based Poly(ether−ether−ketone)

Abstract

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 (Mw > 270 000; Mn ∼ 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 °C and then 220 °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 Tg was confirmed in the DSC analysis. F-PEEK displayed a high storage modulus (E‘ = 2.93 GPa) and glass transition temperature (280 °C) in comparison with commercially available poly(ether−ether−ketone) (PEEK, E‘ = 1.73 GPa and Tg 169 °C). The high modulus of F-PEEK was derived unambiguously from both the fluorene and naphthalene skeletons.