AbstractPolyethylenimine membranes consisting of linear polyethylenimine (PEI) and polyepichlorohydrin (PECH) were prepared by casting and heating anN,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 1NHCl, the PEI membrane crosslinked rather tightly showed a specific ion‐selective transfer character. For example, in Cu2+–Ca2+system the permeability ratioPcu/Pcawas about 3.8. The selectivity arises from the difference between affinities (extractabilities) of PEI toward metal ions. The selectivity was changed depending on the
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