Semi-aromatic polyamides containing methylene and thioether units: synthesis and membrane properties

Abstract

A series of semi-aromatic diamines containing a different content of methylene and thioether units were synthesized via reaction with 4-aminobenzenethiol (4-ABT) and a semi-aromatic difluorobenzamide. They were then reacted with 4,4′-thiodibenzoyl chloride (TDC) to yield a series of semi-aromatic polyamides. Thermal property investigation confirmed a high glass transition temperature (T_g) of 163–203 °C and a good thermal stability with initial degradation temperatures (T_d) of 409 to 419 °C for the synthesized semi-aromatic polyamides, as determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) characterization. A water flux and retention rate for the resultant semi-aromatic polyamide membranes in the range of 89–371 L (m² h)⁻¹ was observed when measured by ultrafiltration cup experiments, which suggests that they are suitable for separation processes. The resultant semi-aromatic polyamides showed good corrosion resistance especially in a strong alkaline environment. It was found that they can withstand a solution of NaOH (2 mol L⁻¹) for nearly 6 months without loss of mechanical strength.