Poly(aryl ether ketone) (PAEK) with Both High Gel Content and High Crystallinity for High-Temperature Applications

Poly(ether ether ketone) (PEEK) is a semicrystalline engineering plastic with excellent characteristics. However, its modulus and dimensional stability decrease significantly above the glass transition temperature (T_g). In this paper, cross-linkable PAEK (DBPEEKs) with carbon–carbon double bonds was synthesized, and the majority of cross-linkable synthesis methods were determined by using the curing kinetics. By the introduction of biphenyl bisphenol (BP) as a rigid monomer unit, a series of cross-linkable crystalline PAEK (DPEDEKs) with strong cross-linking and crystallinity after curing were generated. DPEDEK-25% after the curing process (DPEDEK-25%-gradient curing) still maintained 24% crystallinity (X_c) at a gel content (f) of 96%. This coexistence of crystallization and cross-linking broadens the application range of PEEK at high temperatures. At 250 °C, DPEDEK-25%-gradient curing had a tensile strength of 42 MPa, which was higher than that of the PEEK composite material 450GL30 at 275 °C and similar to that of 450CA30 (VICTREX official website). DPEDEK-25%-gradient curing remained applicable at 300 °C, with a wear rate of 7.69 × 10^–7 mm³ N^–1 m^–1 and an average friction coefficient (COF) of 0.41. Whether at ambient or elevated temperatures, DPEDEK-25%-gradient curing had the same solvent resistance as PEEK. This work provides important guidance for expanding the application scope of PEEK at high temperatures.