Amination of Poly(ether imide) Membranes Using Di- and Multivalent Amines
Covalently aminated polyimide membranes are prepared by wet chemistry using different amines as modifiers. During this synthesis process carbonyl groups of the imide ring react with amine groups forming amide groups maintaining the macromolecular structure and an additional amide group bearing free amine groups. The reaction sequence was verified by FTIR-ATR and XPS measurements. Using poly(ethylene imine)s, highly aminated polyimide membranes with amine contents higher than 500 nmol/cm2 membrane can be produced which can be used as basic functions for further modification. As a result of amination, the hydrophobic polyimide membranes were strongly hydrophilized. Depending on the process parameters for functionalization and the applied modifier, a symmetric or an asymmetric distribution of amine functions across the membrane was observed. The distributions of amine functions were determined by SEM microscopy (EDX mode) and by AR-XPS (take-off angle resolved XPS). Calculations suggest that in the case of an asymmetric distribution the pores of the surface layer are almost completely filled with a swollen network of the modifier, which allows the covalent binding of second modifiers in order to obtain new types of composite membranes.