Synthesis and Properties of Novel 4,4′-Biphenylene-Bridged Flame-Retardant Cyanate Ester Resin

The bisphenol-containing 4,4'-biphenylene moiety was prepared by the reaction of 4,4'-bis(methoxymethyl) biphenyl with phenol in the presence of p-toluenesulfonic acid. The bisphenol was end-capped with the cyanate moiety by reacting with cyanogen chloride and triethylamine in dichloromethane. Their structures were confirmed by Fourier transform infrared spectroscopy, H-1-NMR, and elemental analysis. Thermal behaviors of cured resin were studied by differential scanning calorimetry, dynamic mechanical analysis, and TGA. The flame retardancy of cured resin was evaluated by limiting oxygen index (LOI) and vertical burning test (UL-94 test). Because of the incorporation of rigid 4,4'-biphenylene moiety, the cyanate ester (CE) resin shows good thermal stability (T-g is 256 degrees C, the 5% degradation temperature is 442 degrees C, and char yield at 800 degrees C is 64.4%). The LOI value of the CE resin is 42.5, and the UL-94 rating reaches V-0. Moreover, the CE resin shows excellent dielectric property (dielectric constant, 2.94 at 1 GHz and loss dissipation factor, 0.0037 at 1 GHz) and water resistance (1.08% immersed at boiling water for 100 h). (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2609-2615, 2011