Bio-based Low‑<i>k</i> Polymers at High Frequency Derived from Anethole: Synthesis and the Relationship between the Structures and the Properties

Bio-based polymers have been widely investigated as sustainable low dielectric (low-<i>k</i>) materials in past decades. Nevertheless, a few of the polymers with excellent comprehensive properties have been achieved to satisfy the requirements of high-frequency communication application. In this paper, two fluorinated monomers (<b>BCB-F</b> and <b>2BCB-F</b>) have been designed and successfully prepared from biomass anethole. The thermal-cross-linkable benzocyclobutene and polyfluorobenzene groups were introduced in order to obtain low-<i>k</i> polymers with good comprehensive properties. A control monomer <b>C1</b> was prepared from the estragole, the isomer of anethole, to study intensively the effect of structures on properties. Among the thermally cured polymers, cured <b>BCB-F</b> with higher fluoride content shows a comparable dielectric constant (<i>D</i>_k) of 2.62 and lower dielectric loss (<i>D</i>_f) of 1.31 × 10^–3 at a frequency of 10 GHz, as well as better hydrophobic properties with a water uptake of 0.18%. Such good hydrophobic properties enable it to maintain the good dielectric properties even after being soaked in boiling water for 96 h. Cured <b>2BCB-F</b> with bifunctional benzocyclobutene groups displays excellent heat resistance with a high glass transition temperature (<i>T</i>_g) of 408 °C and a low coefficient of thermal expansion (CTE) of 52 ppm/°C in the temperature range 30–300 °C. Cured <b>2BCB-F</b> also shows good dielectric properties with a <i>D</i>_k of 2.61 and a <i>D</i>_f of 2.60 × 10^–3 at a frequency of 10 GHz. The good comprehensive properties reveal that the anethole-based polymers are suitable candidates as matrix or encapsulation resins for application in electronics and microelectric fields.