Copolymers of haemin and vinyl monomers as cyanide ion exchangers: Modifications of the ion exchange properties by introduction of acrylamide residues

Ternary copolymers of haemin (H) and styrene (St) with acrylamide (AAm), copoly(H, St, AAm), and with 1-vinyl-2-pyrrolidone (VP), copoly(H, St, VP), were synthesized by radical copolymerization. It was found that the H content of the resulting copolymer generally agrees with that of the corresponding monomer feed. Moreover, the yield and reduced viscosity decrease in proportion to the feed concentration of the H monomer. Each copolymer prepared showed hydrophilic character compared with the copolymer of H and St. The adsorption of cyanide ion onto the copolymer was investigated at different pHs to clarify the functional capability as cyanide ion exchanger. The amount of cyanide ion adsorbed on 1 g dry polymer (Acn in mg/g) was found to be dependent on the H content of the copolymer, thus indicating that the haem-iron is the adsorption site of the cyanide ion. From the curves of Acn against the AAm or VP content of the copolymer and against pH for copoly (H, St, AAm) and copoly(H, St, VP), it was observed that the adsorptive capacity of the cyanide ion is increased by the introduction of the AAm residue. The same result was obtained for column experiments. These results were discussed in connection with the reaction of a cyanide ligand with the haem-iron site in the copolymer.