Toughness and Low Dielectric Cyanate Ester Resin Modified with Polyethersulfones Containing Fluorene and Allyl Units

Cyanate resin is widely used in electronic packaging, printed circuit boards, radomes, and communication satellites for its excellent dielectric performance, heat resistance, and good flame retardancy, but its high brittleness is still a real challenge to be solved. In this paper, three poly(ether sulfone)s (PESs) were prepared from bis(4-fluorophenyl)sulfone with different bisphenol compounds, namely, bis(allyl)bisphenol A (DABPA, PES-a), bisphenol fluorene (BHF, PES-b), and the mixture of DABPA and BHF (PES-ab). Then, the effects of PESs on the mechanical, thermal, and dielectric properties of 2,2′-bis(4-cyanophenyl)propane cyanate (BADCy) resins were investigated. The bulky fluorene ring and its intrinsic low dipole moment make PES-b an effective modifier to reduce the dielectric constant (ε) and dielectric loss (tanδ), as well as to improve the toughness of BADCy resin composites. The allyl units in PES-a can efficiently react with BADCy monomers, leading to a highly improved interfacial compatibility. The impact strength of the PES-b/BADCy (10/90, wt/wt) composites was increased to 23.8 kJ/m2, which is 146% higher compared to the pure BADCy resin (9.7 kJ/m2), and the Tg was also increased slightly. More importantly, the ε and tanδ of PES-b/BADCy composites (7.5/92.5, wt/wt) are 2.51 and 0.0025, respectively, which are much lower than those of the pure BADCy (2.86 and 0.0054), at 106 Hz. In the Ku-band range (12–18 GHz), the wave transmittance of PES-b/BADCy (5/95, w/w) composites reaches up to 92.5%-86.1% (14–18 GHz) compared with pure BADCy resins (87.9%-81%). The low-k dielectric properties, excellent wave-transparent properties, and highly enhanced toughness of the PES/BADCy composites have great potential for applications in microelectronics and aerospace.