Improved wave-transparent performances and enhanced mechanical properties for fluoride-containing PBO precursor modified cyanate ester resins and their PBO fibers/cyanate ester composites

Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers can be applied as reinforcement to fabricate PBO/cyanate ester (CE) resin laminated composites with light weight, high specific strength & modulus, excellent dielectric properties, and extraordinary excellent thermal & humidity resistance for radome application. However, the surface of PBO fibers is extremely inert, resulting in poor interfacial compatibility to CE matrix. Besides, the toughness and wave-transparent performances of the cured CE resins need to be further improved. In this work, 2, 2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) and terephthaloyl chloride (TPC) were performed to synthesize fluorine-containing epoxy-terminated PBO precursor (epoxy-preFPBO) via condensation reaction followed by end-group functionalization with glycidol. Afterwards, epoxy-preFPBO modified CE resins (FPBO-co-BADCy resins) were prepared by copolymerization of epoxy-preFPBO and bisphenol A cyanate ester (BADCy). FPBO-co-BADCy resins with 7 wt% epoxy-preFPBO displayed the optimal wave-transparent performances and mechanical properties. Dielectric constant (ε) and dielectric loss (tanδ) is respectively 2.48 and 0.0081, and the corresponding transmittance (|T|²) at 10 MHz is 94.9%, higher than that of pure BADCy (92.7%). The corresponding flexural and impact strength was enhanced to 119.9 MPa and 12.3 kJ/m², 21.4% and 24.5% higher than that of pure BADCy, respectively. In addition, FPBO-co-BADCy resins presented better interfacial bonding strength with PBO fibers than that of pure BADCy.