Conducting polymer composites drawbacks

One of the big drawbacks associated with the use of many conducting polymers as electrochromic materials is their low cycle life stability. To overcome this, and other electrochromic properties, many composite materials have been studied. These composites include mixtures with other optically complementary, conducting polymers and inorganic electrochromes, such as tungsten trioxide and Prussian Blue, and colour enhancing agents or redox indicators, exemplified by the inherently electrochromic indigo carmine (1.96). °... 

The addition of a comonomer to a semicrystalline polymer typically causes a loss in crystallinity, unless the second monomer crystallizes with the first. The decrease in crystallinity is very significant as small quantities of the comonomer are added, and it is accompanied by reductions in stiffness, hardness and melting point. Because vinyl polymers are thermoplastic and completely miscible with most organic solvents, copolymerization with vinyl monomers is a logical route to conventional processability and environmental stability. This route was pursued by polymer chemists who desired these properties in an electrically conductive material. But with the low percolation threshold observed in simple blends of vinyl polymers and conducting polymers, work on copolymerization has been abandoned in favor of composites. The two principal drawbacks of composites are incompatibility of the components and lack of genuine solution processability. What follows is a brief review of efforts to obtain electrically conducting and processable random vinyl copolymers of 3-methylthiophene. 

The most desirable properties for electrically conductive polymeric materials are film-forming ability and thermal and electrical properties. These properties are conveniently attained by chemical modification of polymers such as polycation-7, 7,8, 8-tetracyanoqninodimethane (TCNQ) radical anion salt formation (1-3). However, a major drawback of such a system is the brittle nature of the films and their poor stability (4,5) resulting from the polymeric ionicity. In recent years, polymeric composites (6-8) comprising TCNQ salt dispersions in non-ionic polymer matrices have been found to have better properties. In addition, the range of conductivities desired can be controlled by adjusting the TCNQ salt concentration, and other physical properties can be modified by choosing an appropriate polymer matrix. Thus, the composite systems are expected to have important advantages for use in electronic devices. 

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