Polymer/salt complexes coordinated

Two general types of polymer electrolytes have been intensively investigated, polymer-salt complexes and polyelectrolytes. A typical polymer-salt complex consists of a coordinating polymer, usually a polyether, in which a salt, e.g. LiC104, is dissolved. Fig. 5.1(a). Both anions and cations can be mobile in these types of electrolytes. By contrast, polyelectrolytes contain charged groups, either cations or anions, covalently attached to the polymer. Fig. 5.1(h), so only the counterion is mobile. 

The structures of crystalline polymer-salt complexes provide insight into the structure of the more conducting amorphous materials. To date, large single crystals of polymer-salt complexes have not been prepared, but it has been possible to obtain structural information from single crystal X-ray diffraction applied to stretched oriented fibres in the PEO NaI and PEOiNaSCN systems (Chatani and Okamura, 1987 Chatani, Fujii, Takayanagi and Honma, 1990). One of the most detailed studies is of (PEO)3 NaI, Fig. 5.11(a). The sodium ion in this structure is coordinated to both the polymer and to the iodide ion and the polymer is coiled in the form of an extended helix. 

Unique combinations of properties continue to be discovered in inorganic and organometallic macromolecules and serve to continue a high level of interest with regard to potential applications. Thus, Allcock describes his collaborative work with Shriver (p. 250) that led to ionically conducting polyphosphazene/salt complexes with the highest ambient temperature ionic conductivities known for polymer/salt electrolytes. Electronic conductivity is found via the partial oxidation of unusual phthalocyanine siloxanes (Marks, p. 224) which contain six-coordinate rather than the usual four-coordinate Si. 

The recent example of the ab initio structure determination of the polymer electrolyte Poly (ethylene oxide)6 LiAsFe by Bruce et is a notable example of the complex structures that can be determined from powder diffraction on a pulsed neutron source. Polymer electrolytes consist of salts dissolved in solid high molecular weight polymers, and represent a unique class of solid coordination compounds. Their importance lies in their potential in the development of truly all-solid-state rechargeable batteries. The structure of the 6 1 complex is particularly important, as it is a region where the conductivity increases markedly. The structure of the complex is distinct from all known crystal structures of PEO salt complexes (see Figure 7). The Li-i- cations are arranged in rows, with each row located inside a cylindrical surface formed by two PEO chains, with the PEO chains adopting a previously unobserved conformation. Furthermore the anions are located outside the PEO cylinders and are not coordinated with the cations. 

Compared to block copolymers, there have been relatively fewer examples of using homopolymers for nanofabrication. Nevertheless, some polymers with amphiphilic properties were also used in the fabrication of nanostructures with various metal salts/complexes. For example, polyaniline (PANI) emeraldine base formed self-organized mesomorphic structures when mixed with Zn(DBS)2 by the coordination between Zn2+ and the imine nitrogen atoms on the polymer main chain.100 The resulting supramolecule PANI[Zn(DBS)2]0.5 had a comb-shaped... 

Table 19. Coordination environment around the cation and polymer conformation in PEO-metal salt complexes as determined from X-ray diffraction studies...

A macromolecule provides a suitable fimctional group for either complexation with metal ions of metal salts or attaching metal complexes into the macromolecular matrix through a coordination bond typical examples of the former are silver-polymer complexes, while cobalt porphyrins incorporated on a polymer backbone through coordination bonding are examples of the latter. 

PEO can coordinate alkali metal ions strongly and is used as a solid polymer electrolyte [20-22]. However, conventional PEO-Li salt complexes show conductivities of the order of 10 S/cm, which is not sufficient for battery, capacitor and fuel-cell applications. A high crystalline phase concentration limits the conductivity of PEO-based electrolytes. Apart from high crystallinity, PEO-based electrolytes suffer from low cation transport number (t ), ion-pair formation and inferior mechanical properties. Peter and co-workers [23] reported the modification of PEO with phenolic resin for improvement in mechanical properties and conductivity. 

Pramanick and Sankar [99] investigated the polymerization of methyl methacrylate polymerization initiated by only ceric ions and found that the mechanism of initiation depends strongly on the acidity of the medium and is independent of the nature of anion associated with the ceric ion. In a moderately acidic medium, the primary reaction is the formation of hydroxyl radical by ceric-ion oxidation of water. When ceric sulfate is used, the hydroxyl radicals initiate the polymerization and appear as end groups in the polymer molecule. If, on the other hand, ceric ammonium sulfate or a mixture of ceric sulfate and ammonium sulfate are used, some of the hydroxyl radicals react with the ammonium ion, producing ammonium radicals, and both radicals act as initiators, giving polymers with both hydroxyl and amino end groups. In the polymerization of acrylamide by ceric salt, the infrared (IR) spectra suggests the formation of monomer-ceric salt complexes in aqueous solution [98]. This coordination bond presumably consists of both... 

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