One-Step Fabrication of Polysiloxane with Simultaneously Low Dielectric Property, High Flame Retardancy, and High Heat Resistance

The development of polymer materials with simultaneously high flame retardancy, high heat resistance, and low dielectric property for high-frequency and high-speed communication applications remains a challenge. Herein, a phosphorus- and benzene-containing siloxane monomer (VDDP) featuring double bonds was synthesized through sol–gel polycondensation using methyl vinyldimethylsilane (VMS), diphenylsilanediol (DPSD), and diphenylphosphine oxide (DPO). Subsequently, polysiloxane composites (PVDDPs) were fabricated through a double-bond cross-linking reaction. The introduced benzene-functionalized siloxane structures endowed PVDDP composites with exceptional thermal stability, demonstrating an initial thermal decomposition temperature (T_5%) of 450 °C. The phosphorus–silicon synergistic effect imparted outstanding fire safety, achieving both a limiting oxygen index (LOI) of 30.8% and a V0 rating in the UL-94 test. Notably, the peak heat release rate (pHRR) and peak smoke production rate (pSPR) of PVDDP dramatically decreased to 238.9 kW/m² and 0.26 m²/s, respectively. Due to the introduction of DPO, the increase of the free volume fraction between polysiloxane molecules effectively lowered the dielectric constant (D_k) to 2.80. The PVDDP composites with high flame retardancy, low dielectric property, and high heat resistance display a good application prospect in the field of high-frequency and high-speed electronic communication.