Synthesis of eugenol-functionalized polyhedral oligomer silsesquioxane for low-k bismaleimide resin combined with excellent mechanical and thermal properties as well as its composite reinforced by silicon fiber

Introducing porous materials into resin matrix is effective to achieve low dielectric constant (low-k) value but challenge for simultaneously improving mechanical and thermal properties due to the heterogeneous dispersion of these fillers. Herein, a novel eugenol-functionalized cage-like (pore size, 1–2 nm) polyhedral oligomeric silsesquioxane (EG-POSS) was designed and synthesized, which exhibits excellent solubility and reactivity with BD-type bismaleimide resin. Thus, 4 wt% incorporated EG-POSS is uniformly dispersed in resin matrix and the resultant hybrid (BDEP-_0.04) shows outstanding comprehensive performance, especially on dielectric, mechanical and thermal properties. Specifically, the dielectric constant (k) and loss (tan δ) at 1 MHz are reduced to 2.88 and 0.010 from 3.33 and 0.013. Meanwhile, the corresponding impact strength and flexural strength are improved to 18.75 KJ/m² and 159.01 MPa, increased by 63.63 % and 27.29 %. In addition, BDEP_-0.04 also exhibits the excellent thermal stability with glass transition temperature (T_g) of 290 °C, which is 8 °C higher than BD resin. Based on the lower k and tanδ value of BDEP_-0.04 hybrid resin, as well as its better adhesion with silica fiber, the wave-transparent and mechanical properties of silica fiber reinforced composites (SF/BDEP_-0.04) are further improved, showing that the wave transmission efficiency (94.2%), flexural strength (309.99 MPa), flexural modulus (15.70 GPa) and interlaminar shear strength (35.41 MPa) are all greatly higher than those of SF/BD. It's concluded that EG-POSS is effective to optimize and balance the dielectric, mechanical and thermal properties of BD-type bismaleimide resin and SFs/BD composites, which is valuable for practical application in wave-transparent field.