Effect of Fluorinated Substituents on Solubility and Dielectric Properties of the Liquid Crystalline Poly(ester imides)

With the rapid advancement of 5G communication technology, much attention has been paid on high-performance polymers with a low dielectric constant (Dk), a low dielectric loss (Df) and good processability. In order to further research and improve dielectric properties of the liquid crystalline poly(ester imide)s (LCPEIs), four imide dicarboxylic acids (IAs) with fluorinated groups are designed and synthesized. They are then copolymerized with 1,3-phthalic acid (IPA), p-hydroxybenzoic acid (HBA), and bisphenol monomers via solution polycondensation to obtain fluorinated PEIs, whose fluorine content, position of the fluorinated group, and LC behavior are tunable by using different IAs and bisphenol monomers. These PEIs with the highest Tg of 238 °C are soluble in general organic solvents, such as m-cresol, N-methyl-2-pyrrolidone (NMP), chloroform, and so on. PEI-6F25AF exhibits the lowest Dk of 2.60, while LCPEI-6FD shows the lowest Df of 0.0053 at 10 GHz. It is found that high fluorine content and large pendent group can reduce the Dk, while the fluorinated group grafted close to the nitrogen atom and the LC rigid rod-like conformation lead to low Df. We devoutly expect that this research offers some reference for structure design of LCPEIs with both low Dk and Df at high frequency