Polycyanurate Networks with Enhanced Segmental Flexibility and Outstanding Thermochemical Stability

The synthesis and physical properties of cyanurate networks formed from two new tricyanate monomers, 1,3,5-tris[(4-cyanatophenylmethyl]benzene and 3,5-bis[(4-cyanatophenylmethyl)]phenylcyanate, are reported and compared to those of 1,1,1-tris[(4-cyanatophenyl)]ethane (also known as ESR-255). All three networks possessed somewhat different aromatic contents and cross-link densities; however, the thermochemical stability of these networks, as determined by TGA, was outstanding, with that of 1,3,5-tris[(4-cyanatophenylmethyl)]benzene being among the best known for organic cyanate esters despite its comparatively high segmental flexibility. Moreover, the moisture uptake of cured 1,3,5-tris[(4-cyanatophenylmethyl)]benzene, at 2.2% after 96 h immersed in 85 °C water, was comparatively low for a cyanate ester network with a glass transition temperature of 320 °C at full cure. When cured for 24 h at 210 °C, the dry glass transition temperatures of the networks ranged from 245 to 285 °C, while the wet glass transi...