The two different benzoxazine (Bz) monomers were synthesized from two different bisphenol-AF (BF)- and bisphenol-S (BS)-based diamines with cardanol (CL) precursor, whose molecular structures were confirmed using spectroscopy tools. Further, 2.5 wt%, 5 wt% and 7.5 wt% of phenol-3-aminopropyltriethoxysilane benzoxazine-functionalized MCM-41 (APMS) were reinforced with cardanol-bisphenol AF core diamine-based benzoxazine (BFCL-Bz) and cardanol-bisphenol-S core diamine-based benzoxazine (BSCL-Bz) and cured, which leads to increased thermal stability. Successfully developed polybenzoxazines (PBz) nanocomposites dielectric properties were studied. It was observed that the incorporation of 7.5 wt% of APMS into BFCL-PBz polybenzoxazine results an ultra-low dielectric constant value of about 1.78 at 1 MHz, whereas the APMS/BSCL-PBz composites showed 2.16 for the same weight % concentration of APMS. This may be attributed to the presence of fluorine moieties in APMS/BFCL-PBz system. Data resulted from different studies, and it is concluded that the hybrid composites developed in the present work can conveniently be used in the form of adhesives, sealants and encapsulants for low k interlayer dielectric materials for high-performance microelectronics applications.