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

Abstract

With the rapid advancement of 5G communication technology, much attention has been paid on high-performance polymers with a low dielectric constant (D k), a low dielectric loss (D f) 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 T g 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 D k of 2.60, while LCPEI-6FD shows the lowest D f of 0.0053 at 10 GHz. It is found that high fluorine content and large pendent group can reduce the D k, while the fluorinated group grafted close to the nitrogen atom and the LC rigid rod-like conformation lead to low D f. We devoutly expect that this research offers some reference for structure design of LCPEIs with both low D k and D f at high frequency.

High Thermally Stable Anthracene-Based Polyimides with Low Dielectric Constants and Dissipation Factors

“…According to the DFT calculations (Figures S1 and S2), the AnDS-PI film exhibits a more bent structure because both the DSDA and An-NH 2 monomers show bent-like structures, which may decrease the linearity and enhance the aggregation and intermolecular interactions compared with other An-based PIs. In addition, mechanical characteristics are strongly influenced by many factors such as molecular weights of polymers, crystallinity, and molecular interactions. ,, Therefore, due to the more flexible, linear, and non-rigid molecular packing, the ether-linked AnOD-PI and AnBPA-PI films exhibit higher tensile strengths compared with AnBT-PI and An6F-PI films. The tensile strengths of the AnOD-PI, AnBPA-PI, AnBT-PI, and An6F-PI films are 83.2, 91.2, 31.76, and 27.7 MPa, respectively.…”

“…In recent years, with the rapid development of the internet of things (IoT) and 5G communication technologies, the transmission rate, integrity, and distortion of the signals have become more important. To meet the requirements of IoT and microelectronic industries, polymers with low dielectric constants ( D k ) and dissipation factors ( D f ) at high frequencies (≥10 GHz) have attracted considerable attention. − Over the past 2 decades, many low D k and D f polymers have been reported, , such as liquid crystalline polyesters (LCP), , polyimides (PI), ,− poly­(phenyleneether) (PPE), − epoxy resins, , cyanate ester resins, , poly-(silsesquioxane), polynaphthalene, and benzocyclobutene (BCB) resins. − Among all of these polymers, PIs have attracted broad attention because of their excellent thermal stabilities, heat resistances, mechanical strengths, and dielectric properties. ,− Therefore, research on PIs with low D k and D f values is of great significance.…”

Synthesis and properties of modified thermoplastic polyimide films with good dielectric properties at high frequency and enhanced thermal stability via incorporation of rigid ester and biphenyl structural units

“…[23][24][25] In summary, the novel thermoplastic PI films with high glass transition temperatures (T g ), comparable linear coefficient of thermal expansion to copper foils ($17.0 Â 10 À6 /K), comparable D k (≤3.3 at 10 GHz) and D f (≤0.005 at 10 GHz) values to LCPs, 26 and low water absorptions have to be designed and developed. In the literature, various methodologies have been established to achieve the low-D k and low-D f features for PI films based on the Clausius-Mossotti equation, 27 including introduction of the substituents with low molar polarization, such as fluoro-containing and alicyclic groups, 28,29 or with high molar volumes, such as phenyl, sulphone and bulky alkyl groups, 30 or incorporation of air (D k ≈ 1.0) micropores. 31 However, most of the procedures mentioned above might sacrifice the thermal and high-temperature dimensional stability of the final PI films due to the mutually contradictory molecular designs between achieving low-D k and high thermal stability for the polymers.…”

Exploring the Cross-Linking Effect on Decreasing the Dielectric Constant and Dissipation Factor of Poly(ester imide)s at a High Frequency of 10–40 GHz

“…Polymeric materials developed in recent years are often used for low-dielectric (low-k) materials to replace traditional epoxy and phenolic resin substrates in printed circuit boards (PCB). , Because the D k is mostly greater than 3.5, epoxy and phenolic resins do not meet the standards for high-frequency transmission applications. In contrast, low-k polymers such as poly­(phenylene ether) (PPE), − polyethylene terephthalate (PET), , liquid crystal polymers (LCP), − polyimide (PI), − etc. are extensively developed.…”