Metallopolymer materials

In Chapter 8, coauthored by Kelly and Vos, the electrochemical behavior of osmium and ruthenium poly(pyridyl) redox polymers is discussed in some detail. Vos has made significant contributions in this area. This chapter ties in well with the more general discussion presented by Lyons in Chapters 1 and 2, in that many of theoretical concepts addressed in the latter chapters are again discussed by Kelly and Vos with specific reference to redox-active metallopolymer materials. 

Owing to the intrinsic optical and photophysical features discussed for metallopolyynes, it is expected that they have great potential as active materials in optical and photonic devices. Over the years, numerous studies have shown that these metallopolymers can be exploited for a collection of electronic and optoelectronic applications. 

The example considered is the redox polymer, [Os(bpy)2(PVP)ioCl]Cl, where PVP is poly(4-vinylpyridine) and 10 signifies the ratio of pyridine monomer units to metal centers. Figure 5.66 illustrates the structure of this metallopolymer. As discussed previously in Chapter 4, thin films of this material on electrode surfaces can be prepared by solvent evaporation or spin-coating. The voltammetric properties of the polymer-modified electrodes made by using this material are well-defined and are consistent with electrochemically reversible processes [90,91]. The redox properties of these polymers are based on the presence of the pendent redox-active groups, typically those associated with the Os(n/m) couple, since the polymer backbone is not redox-active. In sensing applications, the redox-active site, the osmium complex in this present example, acts as a mediator between a redox-active substrate in solution and the electrode. In this way, such redox-active layers can be used as electrocatalysts, thus giving them widespread use in biosensors. 

More recently, there has been growing interest in a new type of redox polymer that is a hybrid of materials from PTs and will be referred to as conjugated metallopolymers. The key feature of this class of material is that the metal is coordinated directly to the conjugated backbone of the polymer, or forms a link in the backbone, such that there is an electronic interaction between the electroactive metal centers and the electroactive polymer backbone. This can enhance electron transport in the polymer, enhance its electrocatalytic activity, and lead to novel electronic and electrochemical properties <1999JMC1641>. 

Early studies of metallopolymers were frequently hampered by poor solubility and incomplete characterization. Although great strides have been made in the last 20 years on the efficient synthesis of soluble metallopolymers, as witnessed by the two excellent collections of expert reviews [16,17], the applications of such polymers as photoactive materials is only just beginning. 

Platinum polyynes represent one of the most interesting and well-studied classes of linear metallopolymers. Dendritic analogs of these materials have been prepared via a variety of methodologies. One example is the nonametallic dendrimer 248 that was prepared via a convergent route as illustrated in Equation (92). Dendrimers based on ruthenium polyyne architectures have also been prepared and promising NLO properties have been identified. ... 

Thermolysis is widely used in the synthesis of nano-sized metallopolymer composites. This is a result of the specifics of the preparation of such materials. In spite of a variety of the methods for the preparation of metallopolymer nanocomposites, there are two principal routes bottom-up and top-down. ... 

An original method of metallopolymer production by precursors thermal decomposition is to localize the particles being formed due to a fast monomol-ecular decay of the solutions containing the metal compounds in polymer melts—that is, in the natural voids of the polymer matrix (as PE, PP, PTFE, etc.). Such materials are called cluspol [30, 63-65], and for their production it is necessary to provide the most possible melt temperature, which must be considerably above the temperature of the carbonyl decay initiation. For this purpose the carbonyl dilute solutions are used under these conditions, providing the ultimately fast and complete removal of the split out ligand from the reaction system. Such an approach has many advantages because the temperature rise from one side promotes the metal-forming precursor decomposition and from other side decreases the by-products yield. Furthermore, in a melt (as... 

Probably, materials based on graft polymers should be related to the same type of metallopolymers. The properties of such double-layered macroporous materials (particularly block-copolymers) depends on the localization of a graft layer as a thin film on the support polymer surface (PE, PP PTFE, PS are best) or using highly dispersed powders. For this purpose a graft of small amounts of functionalized monomer (acrylic acid, allyl alcohol, methylmethacrylate. 

Thus, particles with a very narrow distribution were observed - in the case of a second generation dendrimer, nanoparticles with a monodisperse nucleus of 2.4 0.2 nm. It is important that not only individual dendrimers can be used for metallopolymer preparation, but also their dispersed mixtures with polymer matrices, which form new types of polymer-inorganic nanomaterials. For example, the highest poly(amidoamide) generations in water were put in swollen polymeric patterns of poly(2-hydroxyethylmethacrylate) Cu, Au or ions of a complex bound to dendrimer [90] were added to such a composition. Reduction of the metal ions resulted in new types of inorganic hybrid materials. 

This survey of synthetic routes to metallopolymers completes the discussion of introductory topics in this chapter. In the following chapters, the main classes of metal-containing polymers will be discussed, with emphasis not only on synthetic details, but also on their properties and applications. The general philosophy will be to focus on well-characterized and well-studied materials which are truly polymeric in nature (Mn> 10,000, see section 1.2.3) rather than to exhaustively discuss every metallopolymer mentioned in the literature. Particular attention is given to examples where studies of properties and potential functions have been performed. 

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