Synthesis of novel Co(ii) complexed bipyrimidine polyimide and preparation of thin film composite membranes

Abstract

A new diamine monomer with a dioxinyl bipyrimidine group was synthesized. Polyimide containing a bipyrimidine group was successfully homopolymerized by chemical imidization. Analyses to determine the structure and properties of these polymers were conducted using ¹H NMR and FTIR spectroscopy and gel permeation chromatography (GPC). For the first time, cobalt acetate was incorporated into the synthesized polyimide to fabricate cobalt-complexed polyimide thin film composite membranes (TFCMs) by spin coating. To fully understand the behavior of cobalt complexed TFCMs, these membranes were synthesized and then characterized by FTIR spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) to survey the effects of cobalt acetate on polyimide. The morphologies of TFCMs were determined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Phase separations and defects were absent in all cobalt-complexed TFCMs; the average thickness of the films ranged from 550 to 600 nm. This strongly suggested that cobalt acetate has good compatibility with bipyrimidine polyimide. The gas separation performance for TFCMs was also determined with the following results: the CO₂ permeance of DMD-PI-3.0 (mixing 3.0 wt% cobalt acetate) TFCMs was 69.9 GPU at 35 °C and 1.5 bar while the selectivity of CO₂/CH₄ was 44.79 for DMD-PI-15 TFCMs. In short, this work reports a promising method to utilize the separation characteristics of polyimide TFCMs by incorporating cobalt ions.