Low-κ, low CTE, high-temperature epoxy resin with high storage modulus based on spirobisindane for high-frequency electronic circuit field

High-temperature thermosetting resin with low dielectric constant (kappa), low thermal expansion coefficient (CTE), and high modulus are drawing more and more attention from scientists and engineers in the field of the high-frequency circuit, 5G and 6G communication networks to improve the signal transmission speed. Epoxy resin, as one of the important thermosetting resin members, possesses excellent properties such as heat resistance, cohesiveness, and reactivity. However, Epoxy resin was usually mixed with different inorganic fillers to meet the above requirements, especially to decrease the kappa and CTE. In this work, a new class of spirobisindane epoxy resin monomer (TSDEP) was synthesized by a classic two-step method based on 3,3,3 ',3 '-tetramethyl-1,1 '-spirobisindane-6,6 '-diol (TSD). Due to the highly distorted rigid structure of TSD, the movement of the TSDEP molecular segment is subject to more restrictions after being cured, and the free volume will increase. After cured by 4,4 '-diamino diphenyl sulfone (DDS), the TSDEP/DDS resin exhibited many desirable physical properties, e.g., low dielectric constant (similar to 3.45, 1 MHz), low dielectric loss (similar to 0.025, 1 MHz), low coefficient of thermal expansion (CTE, 72 ppm/ degrees C, 35-150 degrees C), high glass transition temperature (T-g > 241 degrees C) and high thermal stability (T-d5%similar to 400 degrees C). Furthermore, TSDEP/DDS exhibited excellent mechanical rigidity with a storage modulus of similar to 3.1 GPa. Compared with TSDEP/DDS, 4-methylhexahydrophthalic anhydride (MHHPA) cured TSDEP system showed lower kappa (similar to 3.09) and dielectric loss (0.015) due to weaker polar ester groups instead of more polar hydroxy groups.