Development of an efficient route to hyperbranched poly(aryl ether ketone)s

Abstract

A two-step route to an AB₂ monomer that underwent polymerization via nucleophilic aromatic substitution to afford fluoro-terminated hyperbranched poly (aryl ether ketone)s (F-HPAEKs) was developed. The synthesis of 2,6-difluoro-4′-hydroxybenzophenone (AB₂ monomer) was accomplished by the reaction of 2,6-difuorbenzoyl chloride with anisole, followed by deprotection of the phenolgroup with hydrobromide (HBr) in acetic acid. The polymerization of AB₂ monomer in the presence of 4,4′-bis(2, 6-difluoro-benzoyl)diphenyl ether (B₄ monomer) as a core molecule afforded F-HPAEKs with number-average molecular weights ranging from 5081 to 9964 Da and polydispersity index values ranging from 2.89 to 3.76. The presence of cyclic oligomeric species, formed by an intramolecular cyclization process, was a contributing factor to the relatively low molecular weights. The degree of branching (DB) of the HPAEK samples was estimated by a comparison of the ¹⁹F-NMR spectra of the polymer samples with those of a series of model compounds, and DB values ranging from 0.54 to 0.58 were determined. The glass transition temperatures for HPAEK samples were in the range of 157–176°C, as determined by differential scanning calorimetry.