Water-containing ionically conducting polymers

This brief sampling of chemistries illustrates many of the approaches used to encompass the diverse range of performance requirements for this important class of materids. Upon review, the chemistry of water-containing, ionically conductive polymer systems reveals a variety of approaches that can be used to tailor the range of properties to a specific application. The commercial importance of water-containing ionically conductive polymer systems requires the continued development of new chemistries and processes to meet the ever increasing performance demands. 

Water-containing, ionicaUy conductive polymers are uniquely versatile and hold high economic value in industry. The patent Uterature contains a plethora of examples of novel chemistries and uses. Historically ionic conductivity was viewed as an undesirable property, which interfered with the intended insulating properties of polymers. As a consequence, the Uterature suffers from a relative paucity of informative articles or reviews (i). In this paper we review the chemistries, properties, and appUcations of several patentkl and commerciaUy available conductive polymer systems. 

Polymeric ion exchange membranes are a particular class of these ion-containing polymers. We have been interested in understanding their microstructure in order to explain membrane characteristics such as permselectivity, ionic conductivity, and water diffusion. 

Ionic conductivity in polymer-based, water-containing, solid systems has been with us for a long time. A review of that history, which is intimately associated with the history of analytical electrochemistry and the physical chemistry of electrolyte solutions, will help to put the present work into perspective. 

Water-soluble organic polymers are of considerable commercial importance, whereas few examples of water-soluble metal-containing polymers have been reported. Both cationic and anionic water-soluble polyferrocenylsilanes have been prepared by a variety of different synthetic methodologies [132-138]. These materials are of potential interest as electrode materials and as redox-active polymeric electrolytes, the ionic conductivity of which might be tuned by oxidation of the iron centers. Based on the potential formation of micellar aggregates, these materials may also prove useful as redox-active encapsulation agents [139]. Furthermore, various water-soluble ferrocenium salts have been shown to display anti-cancer activity [140]. 

Capacitive humidity sensors commonly contain layers of hydrophilic inorganic oxides which act as a dielectric. Absorption of polar water molecules has a strong effect on the dielectric constant of the material. The magnitude of this effect increases with a large inner surface which can accept large amounts of water. An example of this type of dielectric is porous j8-alumina. Colloidal ferric oxide, certain semiconductors, perowskites and certain polymers have also been used. /1-alumina is characterized by ionic conductance. Materials of this type can be characterized by a complex resistance composed of real (ohmic) as well as capacitive terms. The behaviour of such solids can be symbolized by a model and an associated equivalent circuit as given in Fig. 5.8. 

Ionic conduction occurs in polymers which contain kmic groups or to whidi ionic materials have been added. In these materials, dnorptioo of water plays a dominant role because water may act as a source of ions, as a dielectric impurity, or as a local structure modifier. In amorphous polymers, it can also occur due to the d of defects on application of an elec field In various polymers, particularly ptriymers with halogens in their molecular structure, as in poly(vinylcliloride). polyvinyl fluorideX and... 

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