Multibenzocyclobutene Functionalized Silane for Low‑k Polyarylsilane Thermosets with Low Coefficient of Thermal Expansion and High Thermostability

Highly cross-linked thermosets have been extensively studied for their good thermostability and low coefficient of thermal expansion (CTE). Herein, multibenzocyclobutene (multi-BCB) functionalized silane monomers and the related thermosets as polyarylsilane are reported. These silane monomers can be cured at a high temperature above 200 °C. After curing, the corresponding transparent thermosets showed good thermal property. The results indicated that more benzocyclobutene (BCB) groups on the corresponding silane monomer induced a higher cross-linked structure, which contributes to improve heat resistance, glass transition temperature (T_g), and dimensional stability. Particularly, the cured tetra­(benzocyclobutene-4-yl) silane (SiB₄) showed extremely high T_g over 400 °C, high initial storage modulus, and good thermostability (T_d5 = 532 °C). The cured SiB₄ also showed excellent thermomechanical properties with a low CTE at 24 ppm/°C. These polymers also showed good dielectric properties with a low k below 2.70. The low-k material with a low CTE may be a good candidate for high-performance composite resin matrix and high-density substrates.