Amorphous Copolyester with Ultrahigh Glass Transition Temperatures Based on 2,6-Naphthalenedicarboxylic Acid and Bis[4-(2-Hydroxyethoxy) Phenyl] Sulfone-Derived Building Blocks

High performance copolyesters with ultrahigh glass transition temperature ( T g ) are crucial in emerging technology fields such as electronic devices, automotives, and coatings. In this paper, a series of poly(ethylene bis[4-(2-hydroxyethoxy) phenyl] sulfone 2,6-naphthalate) (PESNs) with high T g are synthesized by the copolymerization of 2,6-naphthalenedicarboxylic acid (2,6-NDA), bis[4-(2-hydroxyethoxy) phenyl] sulfone (BHEBS), and ethylene glycol (EG). The chemical structure and compositions of prepared copolymers are confirmed by hydrogen nuclear magnetic spectra ( 1 H NMR). T g of copolyesters (121.1–152.2 °C) depends on composition and is comparable to that of polyetheretherketone (PEEK: 143 °C), increasing as the amount of BHEBS units is increased. The Fox, Gordon–Taylor, and Kwei equations are employed to evaluate the variation of T g with respect to the composition of PESNs, respectively. In these three equations, the data calculated by Kwei equation fit the actual results best, attributed to the peculiar dielectric properties. In addition, PESNs show good solubility in 1,1,2,2-tetrachloroethane, DMF, and DMSO, which is conducive to meet the needs of polyester coating.