Macromolecular Metal Carboxylates and Their Nanocomposites

At present, there are three main ways of production of metal-containing polymers on the basis of carboxyl precursors [1]: (I) the interaction of metal compounds MXn with linear functionalized (carboxyl-containing) polymers, when the main polymer chain remains untouched (so called polymeranalogous transformations), (II) the polycondensation of proper precursors, when metal ions are incorporated into and removed from the main chain leading to polymer destruction, (III) the recently developed method, polymerization and copolymerization of metalcontaining monomers.

Our goal was not to analyze known unsaturated carboxylic acids (this problem itself is unrealizable), but only to give a general idea about unsaturated acids and their polymersmore often used for obtaining metal carboxylates.Basic attention was paid to those representatives which are a priori capable of polymerization. As data on unsaturated carboxylic acids are dispersed in numerous researches, directories, and catalogs, many of which are not always accessible, their most important characteristics are given below. Other unsaturated heteroacids and their polymers (for example, vinylsulfonic and vinylbenzoic sulfonic acids, thio-, phosphonic, amino-, and other acids) are not analyzed in this book. More detailed information can be found in other available literature.

Prospective metal carboxylates of this type as subjects of various investigations, especially as potential monomers for the preparation of metallopolymers, attract the attention of a large number of researchers to the development of methods for their synthesis. These efforts in particular are aimed at the design of geometrical, electronic, and other characteristics of the compounds to achieve the specified properties. The major distinctions between methods for the synthesis of unsaturated carboxylic acids salts are in the type of the precursor metal compound employed and the corresponding method for introduction of a ligand.

In most typical cases the carboxylate group RCOO_ is capable of coordinating with metals such as monodentate (syn- and anti- configuration) (I), bidentatecyclic (chelate) (II), bidentate-bridging (III), tridentate (IV), and tetradentate (V) ligands [1–3]:

The application of polymers in modern technology, of concentration and isolation of metal ions from solution, water preparation, water purification, processes of removal, concentration, and separation of metal ions (including heavy), and catalysis, is determined to a great extent by the ability of metal ions to form stable contacts with functional groups of macromolecules as sorbents. They appear as a result of the creation of a system of electrovalent and coordination bonds between metal ions and certain groups of polymers, with formation of new polymer systems – macromolecular metal complexes(MMC).

It is well known that properties of the polymeric materials based on (co)polymers depend strongly on the sequence in which units of different nature are distributed throughout a polymeric chain. Distinctions in the units’ distribution are displayed in the character of intermolecular interactions that finally causes the variety of supramolecular structures affecting the properties of the materials.

The properties of metal-containing (co)polymers and also of traditional polymers modified by them are determined in many respects by the potential ability of metal ions to form ionic and coordination cross-links, to realize electron transitions in metal atoms under both electric field effect and high-energy radiations, to show cohesive and adhesion interactions.

The interest in the metal-containing polymeric nanocomposites is caused by a unique combination of properties of metals nanoparticles, their oxides and chalcogenides, and by mechanical, film-forming and other characteristics of polymers with opportunities for their use as magnetic materials for record and storage of information, as catalysts and sensors, in medicine and biology [1]. Homo- and copolymers of acrylic and methacrylic acids and their salts are widely used for the stabilization of metal-containing dispersions. For example, nanocomposites of the PbS/copolymer of styrene-methacrylic acid [2], PbS/copolymer of ethylene-methacrylic acid [3], CuS/polyvinylalcohol-polyacrylicacid[4],Cu2C-polyacrylicacid/CdS[5],Co/PAAblock- PS[6]wereobtainedbyvariousmethods.HeterometallicZnS/CdSnanocrystals with luminescent propertieswere synthesized by the treatment of the triple copolymer of styrene-Zn diacrylate-Cd diacrylate by the general reagent H2S (MnD4:7_104, atomic ratio Zn=CdD3:3 W1) [7]. Such examples are very numerous. On the one hand, carboxylated compounds of a monomeric and polymeric structure can be molecular precursors of nanocomposite materials. On the other hand, carboxyl groups of macroligands are efficient stabilizers of nanoparticles; these functions are frequently developed together in one system. Amphiphilic character of carboxylated polymers and copolymers allows not only to encapsulate nanoparticles of metals or to combine them with polymeric and inorganic matrixes or biological objects, but also allows to give such properties as solubility in various mediums, ability to self-organization, etc., to nanoparticles.

As appears from the analysis of the subject considered in the book, monomer and polymer metal carboxylates belong to an entirely new interdisciplinary science at the junction where the organic, physical, coordination, and high molecular branches of chemistry intersect. It has become possible to speak about all the features typical of an independent branch of chemistry: an intrinsic scientific matter, methodology and abundant experimental materials. The progress in this field is very promising. Firstly, a large variety of synthetic approaches have been developed and optimized allowing the obtaining of certain unsaturated metal carboxylates practically with a quantitative yield. In high molecular compound chemistry problems of synthesis and purity of monomers are very important. From this point of view, one can assert the development of a new class of organometallic monomers. For their synthesis the approacheswhich prevent polymerization at this stage should be used (namely, inert atmosphere, nonaqueous or dysphasicmedium, hydrothermal synthesis, specific additives, low temperatures, and so on).