Preparation and application of water-soluble polymer-metal complexes

Abstract

A series of water-soluble polymers and derivatives with chelating groups has been prepared and investigated for the complex formation with various metals. The complexation of basis polymers, such as poly(ethyleneiruine) , poly(vinylamine) , and poly(acrylic acid), as well as copolymers was carried out in homogeneous phase. Membrane filtration allowed continuous or discontinuous separation of the polymer chelates from metallic ions not bound to the polymer. The polymer complexes remained water-soluble independent of the chelated metal and the polymeric ligand. Studies on the dependency of the capacities of the polymers upon various parairters and methods for regenerating the polymeric ligands are described. The introduction of chelating groups, e.g. pyridine-2-aldimine, thiourea, iminodiacetic acid, 8-hydroxy quinoline, and hydroxyaniline, to the macromolecules by polymer-analogous reaction or by copolymerization improved significantly the selectivity for the metals cobalt, nickel, copper, cadmium, palladium, mercury, silver, gold, and platinum. By the use of membrane filtration in the preparation and application of water-soluble polymer—metal complexes it is possible to recover metal ions from solutions in a short time and in homogeneous phase. INTRODUCTION Water-soluble polymer complexes are. not only of theoretical importance but also of increasing practical interest, since they involve the potentiality of versatile applications in chemistry. Insoluble chelating resins, on the contrary, have considerable disadvantages, such as reaction in heterogeneous phase and long contact times. Up to present, many investigations have been carried out in this field, particularly on synthesis and properties of soluble polymer ligands and coordinating groups (Ref. 1-10). In general, there are three requirements with which polymers as chelating agents should comply: sufficient solubilizing power of the constitutional repeating unit which provides water-solubility of the polymer complexes, a great number of functional groups of the complexing agent for a high capacity, and a high molecular weight which allows an easy separation by usual methods from the metal not bound to the polymer. Preferable for these studies are molecular masses between 10 000 and 100 000. Molecular masses of polymers smaller than 10 000 are not suitable because of separation problems in membrane filtration. Therefore, all prepared macromolecular ligands consisted of molecular mass fractions greater than 10 000, which was verified by membrane filtration. Possibilities for the synthesis of polymer chelating agents are the following: 1) Preparation of polymers with chelating units, e.g. poly(vinylamine), poly (ethyleneimine). 2) Polymerization of monomers already bearing the complex forming group, e.g. acrylic acid, vinylmethyl ketone, vinylsulfonic acid. 3) Polymerization of monomers containing protected functional groups with following polymer-analogous deblocking reaction, e.g. poly(vinylalcohol) from poly(vinylacetate). 4) Conversion of side chains or functional units in order to form or to change complexing groups, e.g. hydrolysis of poly(1-vinyl-2-pyrrolidinone)