Dielectric and Mechanical Properties of Cyanate Ester-Based Composites Embedded with Different Glass Powders

Cyanate ester resins are widely recognized for their excellent thermal stability, low dielectric loss, and high glass transition temperature, making them attractive for advanced electronic and communication applications. However, their inherent brittleness and limited filler compatibility restricts broader use. In this study, cyanate ester composites were developed by incorporating transparent and opaque borosilicate glass powders modified with silane coupling agents-3-Triethoxysilylpropyl isocyanate (TESPI) and 3-Isocyana-topropyl trimethoxysilane (IPTMS)-to enhance interfacial adhesion and crosslink density. The transparent (CTF) and opaque (COF) composite systems were fabricated with varying filler contents (5-20 wt%), and their structural, mechanical, and dielectric performances were systematically characterized through X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy (EDX) and dielectric performance analyses. The results revealed that both filler types enhanced the dielectric and mechanical stability of the cyanate ester matrix; however, the COF-15 composite, containing 15 wt% opaque glass, exhibited the highest tensile strength of approximately 125.70 ± 1.50 MPa, and the dielectric constant increased from 2.86 ± 0.1 (neat matrix) to about 5.0 ± 0.1 while maintaining a low loss tangent (0.007@1 MHz). These improvements were attributed to the zirconium-enriched opaque glass phase, which promoted strong interfacial bonding, compact microstructure, and effective polarization control.