a water - swellable polymer product which may be physically bound to an open celled cellulosic sponge is produced by thermally induced amide - forming insolubilization of polyethyleneimine . the polymer product has high affinity for the absorption of transition metal ions . a cellulosic sponge containing a high add - on of the polymer product is permeable to water and substantially unaffected by water - borne suspended matter .