Weak-base anion exchange membranes by amination of chlorinated polypropylene with polyethyleneimine at low temperatures

Commercial chlorinated polypropylene (CPP) was aminated with polyethyleneimine (PEI) in a solvent mixture of acetone and toluene at low temperatures (30–55 °C), yielding colloidal PEI-aminated CPP suspensions and thus anion exchange membranes. The chemical structure, chemical composition, microstructure, and thermal stability of CPP and PEI-aminated CPP membranes were characterized by Fourier infrared spectroscopy (FT-IR), elemental analysis, scanning electron microscopy (SEM), thermogravimetric analysis (TG), respectively. The ion exchange capacity, water uptake, methanol uptake, and ionic conductivity of PEI-aminated CPP membranes were also determined. The PEI-CPP membranes exhibited high ionic conductivities ranging from 0.89 × 10−2 to 1.36 × 10−2 S/cm, and anion exchange capacities ranging from 7.38 to 9.33 mmol/g dry membrane while the degree of amination was raised from 50.2 to 65.3%. The water uptake of the PEI-CPP membrane increased whereas the methanol uptake dropped with the degree of amination increased. The PEI-CPP membranes developed here may be useful for a range of applications, and can be further converted into quaternary ammonium-based membranes for direct methanol alkaline fuel cells.