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

摘要

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-(2a′-cyanatophenyl)phenyl] propane} and three isomeric triaryl cyanate esters {2-(4a′-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 1H-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.