New soluble polyamides with high transparence and improved gas separation properties

Abstract

Based on the aromatic diamine monomer containing di-tert-butylbenzene and methyl groups, this work proposes its polymerization with four different dicarboxylic acids. The prepared polyamides (PA 3a–3d) were characterized by GPC, FTIR, ¹H NMR, mechanical, thermal, optical and gas separated techniques. They exhibited high solubility and good optical transparency. Their optical transmittance at 450?nm wavelength was in the range of 81.4%–86.8%, and the cutoff wavelength was in the range of 327–352?nm. The membranes also had good mechanical properties with tensile strength of 79.7–91.4?MPa, elongations at breaks of 9.0–10.9% and initial modulus of 1.5–1.9?GPa. Meanwhile, these membranes possessed good thermal properties with glass transition temperature (T _g) values of 226–246?°C. The permeability of CH₄, N₂, and CO₂ for these membranes was tested by constant pressure-variable volume method. The PA 3d containing tert-butyl moiety in the diacid units exhibited highest permeability (P_CO2 = 31.4 and P_N2 = 1.9) whereas PA 3c containing hexafluoroisopropylidene moiety exhibited highest selectivity (CO₂/CH₄ = 22.2).