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,N-dimethylformamide, 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 (T
g >
200
°C) but relatively low melting temperatures and isotropization
temperatures (T
m and T
i, <340 °C). The LCPEI prepared with 10 mol %
IA shows excellent combined properties, whose ηinh, M
n (GPC), T
g, T
m, T
i, T
d
5%, 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 °C, 268 °C, 330 °C,
458 °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.
