Tailoring the cage and functionality of POSS for scalable low-dielectric and tough cyanate ester hybrid resin

Although polyhedral oligomeric silsesquioxanes (POSSs) are ideal building blocks to reduce the dielectric constant and loss of cyanate ester (CE) resin, as well as enhancing its toughness, attention has been only focused on conventional ones with a cubic T₈ cage and a high functionality of eight. Herein, 2(or 4)EGEP-POSS with a DDSQ-type cage and 2/4epoxy-functionality was synthesized. Such a rational design not only endows the two POSSs with larger hollow structures to reduce the polarization of CE, but also confers them lower functionalities favorable for preventing over-crosslinking. Thus, the low-dielectric property and toughness of CE/2(or 4)EGEP-POSS hybrid resins are further optimized. Specifically, the hybrid resin containing 2 wt% 2EGEP-POSS possesses the lowest dielectric constant of 2.49 (10 GHz), the lowest dielectric loss of 0.008 (10 GHz), and a high impact strength of 27.4 MPa (increased by 114.1%). In addition, its excellent glass transition temperature is well maintained at 279.1 °C, and its power transmission coefficient predicated by finite element simulation is up to 94.2% as a radome working at 10 GHz, which is significantly higher than that of pure CE (85.7%). Overall, this work highlights a promising structure-tailored approach using POSSs for the fabrication of high performance hybrid resin materials for application in wave-transparent fields.