Silicon-Containing Trifunctional and Tetrafunctional Cyanate Esters: Synthesis, Cure Kinetics, and Network Properties

The synthesis and physical properties of new silicon-containing polyfunctional cyanate ester monomers methyl[tris(4-cyanatophenyl)]silane and tetrakis(4-cyanatophenyl)silane, as well as polycyanurate networks formed from these monomers are reported. The higher crosslinking functionality compared to di(cyanate ester) monomers enables much higher ultimate glass transition temperatures to be obtained as a result of thermal cyclotrimerization. The ability to reach complete conversion is greatly enhanced by cocure of the new monomers with di(cyanate ester) monomers such as 1,1-bis(4-cyanatophenyl)ethane. The presence of silicon in these polycyanurate networks imparts improved resistance to rapid oxidation at elevated temperatures, resulting in char yields as high as 70% under nitrogen and 56% in air in the best-performing networks. The water uptake in the silicon-containing networks examined is 4-6 wt % after 96 h of immersion at 85 degrees C, considerably higher than both carbon-containing and/or di(cyanate ester) analogs. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 767-779