Xiujie Li

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

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.

Preparation of HPEEK by Oligomer A2 + B3 Approach

A series of hyperbranched poly(ether ether ketones) with different chain length between branching point (L) were prepared using a A2+B3 methodology, in which the A2 is hydroxyl‐terminated PEEK oligomer. The L affects the properties of the polymers such as the inherent viscosity, the degree of crystallinity, the thermal properties of the polymers etc. The polymer with a L2≈8 had T g (122.4°C), T c (200.2°C), and broad T m (247.4°C). With the increment of L, up to the point L2≈20 and L2≈35, the polymers become semi‐crystalline, with a melting point of 300.9°C and 317.9°C, respectively. Their wide angle X‐ray scattering (WAXS) pattern indicated that their crystal structure is exactly the same as that of the linear homopolymer.