Synthesis of biphenylated cyanate esters: Thermomechanical resin comparisons within two isomeric series

Three isomeric tetraaryl cyanate esters containing biphenyl moieties {bis‐[4‐(4′‐cyanatophenyl)phenyl]propane, 2,2‐bis‐[4‐(3′‐cyanatophenyl)phenyl]propane, and 2,2‐bis‐[4‐(2′‐cyanatophenyl)phenyl]propane} and three isomeric triaryl cyanate esters {2‐(4′‐hydroxyphenyl)‐2‐[4′‐(4‐hydroxyphenyl)phenyl]propane, 2‐(4′‐hydroxyphenyl)‐2‐[4′‐(3‐hydroxyphenyl)phenyl]propane, and 2‐(4′‐hydroxyphenyl)‐2‐[4′‐(2‐hydroxyphenyl)phenyl]propane} were synthesized from their corresponding bisphenols. The structures of the monomers were confirmed with IR and 1 H‐NMR spectroscopy. The curing behavior was investigated with differential scanning calorimetry. Cyanate esters were cured thermally in the absence of a catalyst and were characterized by dynamic mechanical analysis. The results were compared to the properties of commercial bisphenol A polycyanurate. Of the three tetraaryl isomers, 2,2‐bis‐[4‐(2′‐cyanatophenyl)phenyl]propane had the highest melting point, and its corresponding resin had the lowest glass‐transition temperature ( T g ). The para isomer displayed the highest T g value of the three novel tetraaryl resins. The triaryl dicyanate isomers were low‐melting solids, with the ortho and meta isomers existing as liquids at room temperature. The T g value of the para ‐triaryl isomer was the highest of the three triaryl isomers and was about the same as that of bisphenol A polycyanurate.