Synthesis and characterization of novel polyimides from 4,4′-bis(5-amino-2-pyridinoxy)diphenyl ether, 4,4′-bis(5-amino-2-pyridinoxy)diphenyl thioether and 4,4′-bis(5-amino-2-pyridinoxy)diphenyl sulfone

Abstract

To investigate the difference of the –O–, –SO₂– and –S– groups affecting the thermal, mechanical, optical properties and water uptake of polyimides (PIs), we prepared 4,4′-bis(5-amino-2-pyridinoxy)diphenyl ether (BAPDE), 4,4′-bis(5-amino-2-pyridinoxy)diphenyl sulfone (BAPDS) and 4,4′-bis(5-amino-2-pyridinoxy)diphenyl thioether (BAPDT) with 2-chloro-5-nitropyridine and 4,4′-thiodiphenol, 4,4′-oxydiphenol, 4,4′-sulfonylbisphenol, respectively. Two series of novel PI-(1,3,5) and PI-(2,4,6) were synthesized from BAPDE, BAPDS and BAPDT with two aromatic dianhydrides: 4,4-oxydiphthalic anhydride (ODPA), and 3,3′,4,4′-thiodiphenyl tertracaboxylic dianhydride (TDPA), through a typical two-step polymerization method. The resulting polyimides exhibited solubility in polar solvents, such as DMAc, NMP, DMF, DMSO and m-cresol at room temperature. These polyimides with inherent viscosities of 0.84–1.26 dL g⁻¹ exhibited high enough molecular weight to give tough and flexible thin films by solution casting. The glass transition temperature (T_g) values measured by differential scanning calorimetric and thermal stabilities based on 5% weight loss temperature of PI films varied from 226 to 305 °C and from 453 to 483 °C, respectively. Interestingly, the influence of oxygen and sulfur-connected ether linkage in diamine and dianhydride on T_g exhibits the reverse order. The polyimides also have good mechanical properties, tensile strengths of 101–114 MPa, tensile modulus of 2.8–3.2 GPa, and elongations at break of 8.8–33.3%. The cutoff wavelengths and transparency of PI films were in the ranges of 338–400 nm and 72–84% at 500 nm, respectively. The water uptakes of the resulting PI films were in the range of 0.5–1.4%.