Polyethylenimine–polyepichlorohydrin interpolymer for chelating ion-exchange membrane

Polyethylenimine membranes consisting of linear polyethylenimine (PEI) and polyepichlorohydrin (PECH) were prepared by casting and heating an N,N-dimethylformamide solution of the two polymers under nitrogen at 100°C for 60 min. The membrane was also prepared by a heat-press method in a conventional manner. The cast membrane obtained was transparent. The membrane has a crosslinked structure due to the reaction between the secondary amino groups in PEI and the chloromethyl groups in PECH. Although a larger feed ratio of PEI/PECH gave membranes with a larger adsorption capacity for Cu²⁺ ions, the optimum ratio was 40/100 with respect to mechanical properties. A belt conveyor system using the PEI membrane was able to transport Cu²⁺ ions from one bath to another. In a diffusion dialysis against 1N HCl, the PEI membrane crosslinked rather tightly showed a specific ion-selective transfer character. For example, in Cu²⁺–Ca²⁺ system the permeability ratio P_cu/P_ca was about 3.8. The selectivity arises from the difference between affinities (extractabilities) of PEI toward metal ions. The selectivity was changed depending on the pH value.