Fabrication and characterization of novel highly transparent and organo-soluble poly(ether imide)s thin film for gas separation

Abstract

A novel diamine with ether and phenyl linkages was prepared in two steps by the nucleophilic substitution reaction of 2-(2-hydroxy-5-methylphenylsulfinyl)-4-methylphenol and 1-chloro-4-nitrobenzene in N,N′-dimethylacetamide, followed by reduction with hydrazine monohydrate and Pd/C in ethanol. Four series of solution-processable aromatic poly(ether imide)s (PEI)s were prepared from the newly synthesized diamine and various dianhydrides via one-step high-temperature solution polymerization. The diamine monomer and PEIs were characterized by elemental analyses, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The inherent viscosities of the obtained poly(amic acid) (PAA) ranged from 1.09 to 1.93 dL g⁻¹ at a concentration of 0.5 g dL⁻¹ in N,N′-dimethylacetamide at 30 °C. All the obtained polymers were readily soluble in polar solvents and showed useful levels of thermal stability associated with high glass-transition temperatures (T_g, 279–303 °C) and high char yields (higher than 62% at 800 °C in nitrogen). Flexible and transparent films were obtained easily by solution casting. The cast films exhibited high optical transparency and almost no color with a UV-Vis absorption edge of 368–382 nm. These films also showed excellent mechanical properties with tensile strengths of 118–154 MPa and elongations at breakage of 11–15%. The combination of excellent solubility, film quality, and thermal stability makes these PEIs potential candidates for high-performance gas separation membrane applications by solution-casting processes. Permeability measurements were made for O₂, H₂, CO₂ and CH₄ at 35 °C.