Knowing How to Make Molecular Glasses as Low Dielectric Materials at High Frequency

Two functional monomers containing thermo-crosslinkable benzocyclobutene and allyl groups and a bisphenol unit as a linker have been successfully synthesized. Powder X-ray diffraction indicates the monomers keep a complete amorphous state. DSC traces exhibit that the monomers have no melting point while display glass transition. Casting the solutions of the monomers in toluene into the surface of glass sheets forms smooth films. These data imply these monomers are molecular glasses due to their typical glass-forming behavior. Thermally cross-linked products based on the monomers exhibit good dielectric properties and low water uptake. Among these cross-linked monomers, the fluoro-containing resin displays better properties with a dielectric constant (D_k) of 2.74 and a dielectric loss (D_f) of 1.89×10^-3 at a frequency of 10 GHz, as well as exhibits a water uptake of 0.34 %. A control test indicates that the chemical structure of the bisphenol linker plays a crucial role for the formation of molecular glasses. When the linker is a rigid rod unit such as biphenyl group, the molecule does not exhibit molecular glass characteristics.