A New Silicon-Containing Bis(cyanate) Ester Resin with Improved Thermal Oxidation and Moisture Resistance

• Published in: Macromolecules Vol. 39; no. 18; pp. 6046 - 6053
• Main Authors: Guenthner, Andrew J, Yandek, Gregory R, Wright, Michael E, Petteys, Brian J, Quintana, Roxanne, Connor, Dan, Gilardi, Richard D, Marchant, Darrell
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 05-09-2006
• Subjects: Applied sciences; Chemical properties; Exact sciences and technology; Polymer industry, paints, wood; Properties and testing; Technology of polymers; Cyanate resin; Curing(plastics); Preparation; Mechanical properties; Organic silane; Water absorption; Experimental study; Lattice parameters; Chemical reactivity; Silicon polymer; Thermal stability; Crystalline structure
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma060991m

A new cyanate ester monomer was prepared from bis(4-cyanatophenyl)dimethylsilane (SiMCy) and fully characterized by analytical and spectroscopic techniques. The monomer was found to have a melting point about 20 °C lower than that of the commercial bis(4-cyanatophenyl)dimethylmethane (BADCy) with similar melt viscosity, curing kinetics, and postcure glass transition temperature. Analysis of the single-crystal molecular structure by X-ray diffraction showed that intermolecular packing was dominated by weak hydrogen-bonding attractions between the aromatic rings and the −OCN nitrogen atoms. In contrast, the packing interactions found in BADCy are dominated by dipole−dipole interactions of the OCN groups. These differences may explain the 50% reduction in moisture uptake observed in SiMCy as compared to BADCy during exposure to boiling water. In addition, thermogravimetric analysis revealed that SiMCy exhibited a significantly higher char yield in air than BADCy, presumably due to the formation of silicates at high temperature. The combination of improved thermooxidative stability and reduced moisture absorption without significant loss in ease of processing or mechanical properties makes SiMCy an important potential “drop in” replacement for BADCy and demonstrates the power of the molecular level approach to designing new high-temperature polymer materials.