Carvacrol-Derived Polyarylates with Low Dielectric Constant, High Glass Transition Temperature, and Optical Transparency

The growing demand for low-dielectric aromatic polyesters in 5G/6G communications is intrinsically limited by dense aromatic packing. Herein, a molecular-level strategy is employed to regulate chain packing and free volume by copolymerizing bulky side-group monomers. A carvacrol-derived bisphenol monomer, 4,4’-(phenylmethylene)bis(2-isopropyl-5-methylphenol) (PMBIMP), featuring bulky isopropyl and phenyl moieties, was successfully synthesized via a straightforward one-step condensation. By copolymerizing PMBIMP with bisphenol A (BPA) and terephthaloyl chloride (TPC)/isophthaloyl chloride (IPC), a series of copolyarylates (PMB-x) with high fractional free volume were prepared. Positron annihilation lifetime spectroscopy (PALS) and molecular dynamics (MD) simulations confirmed that the bulky PMBIMP units significantly hindered efficient chain packing, thereby expanding the fractional free volume. As the PMBIMP content increased, the copolyarylates exhibited enhanced thermal performance, with Tg increasing to 228.4 °C, and the dielectric constant decreased from 3.226 to 2.434 at 1 MHz and from 2.863 to 2.398 at 10 GHz relative to U-100, while the dissipation factors remained relatively low. The copolymers displayed high optical transparency and superior mechanical performance (tensile strength: 58.9–78.0 MPa; modulus: 1.6–2.7 GPa). These findings identify carvacrol-derived PMBIMP as an effective bulky bisphenol comonomer for regulating chain packing and balancing low dielectric constant, high Tg, optical transparency, and mechanical performance in polyarylates.