Soluble Liquid Crystalline Poly(ester imide)s with High Glass Transition Temperatures and Improved Dielectric Properties

At present, high-performance liquid crystalline polyesters with a good processability, low dielectric constant, and low dielectric loss at a high frequency (GHz) are in high demand ascribed to the rapid development of high-speed communication technology. Here, an imide dicarboxylic acid (IA) with a bulky phenyl side group is designed and synthesized. It is then copolymerized with 4-hydroxybenzoic acid (HBA), isophthalic acid (IPA), 4,4 '-dihydroxybipheny (BP), and 4,4 '-dihydroxydiphenyl ether (ODP) via solution polycondensation to obtain liquid crystalline poly(ester imide)s (LCPEIs). By controlling the feeding ratio of IA, the solubility, thermal stability, mechanical properties, and dielectric properties of the LCPEIs are tunable. When the molar fraction of IA reaches or exceeds 5%, the obtained LCPEIs are soluble in ordinary organic solvents, such as chloroform, N,Ndimethylformamide, N-methyl-2-pyrrolidinone, and so forth, which allows a simple solution casting to prepare isotropic LC films. The nematic LCPEIs show high glass transition temperatures (Tg > 200 degrees C) but relatively low melting temperatures and isotropization temperatures (Tm and Ti, <340 degrees C). The LCPEI prepared with 10 mol % IA shows excellent combined properties, whose eta inh, Mn (GPC), Tg, Tm, Ti, Td5%, tensile strength, tensile modulus, water uptake, dielectric constant, and dielectric loss (at 10 GHz) are 0.92 dL g-1, 20,900 g mol-1, 218 degrees C, 268 degrees C, 330 degrees C, 458 degrees C, 80.5 MPa, 4.0 GPa, 0.39%, 3.07, and 0.006, respectively. These LCPEIs can be promising candidates for flexible copper-clad laminate substrates.

Automated summary

In this study, high-performance liquid crystalline poly(ester imide)s (LCPEIs) were successfully synthesized with tunable solubility, thermal stability, mechanical properties, and dielectric properties through copolymerization of an imide dicarboxylic acid (IA) with other monomers. The LCPEI with 10 mol% IA showed excellent combined properties and could be a promising candidate for flexible copper-clad laminate substrates.