Electrical properties of polymer

Some of the electrical applications to which unreinforced and reinforced engineering plastics have been put are listed in Table 4.1 and Table 4.2, respectively. 

polydiallyl phthalate Wire covering electrical connectors, switchgear housing and bush holders 

PA 12 Electrical and electronic applications, cable and wire covering 

PA Capacitors, cable insulation and printed circuit boards 

Perfluoroalkoxyethylene, fluorinated ethylene-propylene Wire coatings and electrical components 

In 1972, the first stable organic conductor was reported, one of the forms of TCNQ, TetraCyaNo-Quinodimethane. Its room-temperature conductivity was 

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

About the time that synthetic metals reached their apogee, twenty years ago, research began on semiconducting polymers. Today, at the turn of the century, such polymers have taken the center of the stage, and indeed promise some of the most important applications of polymers. 

A completely separate family of conducting polymers is based on ionic conduction polymers of this kind (Section 11.3.1.2) are used to make solid electrolyte membranes for advanced batteries and some kinds of fuel cell. 

Most polymeric materials are poor conductors of electricity (Table 18.4) due to the ima-vailability of large numbers of free electrons to participate in the conduction process electrons in polymers are tightly bound in covalent bonds. The mechanism of electrical conduction in these materials is not well understood, but it is believed that conduction in polymers of high purity is electronic. 

Polymeric materials have been synthesized that have electrical conductivities on par with those of metallic conductors they are appropriately termed conducting polymers. Conductivities as high as 1.5 X 10 (n m) have been achieved in these materials on a volume basis, this value corresponds to one-fourth of the conductivity of copper, or twice its conductivity on the basis of weight. 

This phenomenon is observed in a dozen or so polymers, including polyacetylene, polyparaphenylene, polypyrrole, and poly aniline. Each of these polymers contains a system of alternating single and double bonds and/or aromatic units in the polymer chain. For example, the chain structure of polyacetylene is as follows  

The valence electrons associated with the alternating single and double chain-bonds are delocalized, which means they are shared among the backbone atoms in the polymer chain—similar to the way that electrons in a partially filled band for a metal are shared by the ion cores. In addition, the band structure of a conductive polymer is characteristic 

---

Antioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reaction can cause degradation of the mechanical, aesthetic, and electrical properties of polymers loss of flavor and development of rancidity ia foods and an iacrease ia the viscosity, acidity, and formation of iasolubles ia lubricants. The need for antioxidants depends upon the chemical composition of the substrate and the conditions of exposure. Relatively high concentrations of antioxidants are used to stabilize polymers such as natural mbber and polyunsaturated oils. Saturated polymers have greater oxidative stabiUty and require relatively low concentrations of stabilizers. Specialized antioxidants which have been commercialized meet the needs of the iadustry by extending the useflil Hves of the many substrates produced under anticipated conditions of exposure. The sales of antioxidants ia the United States were approximately 730 million ia 1990 (1,2). 

Blythe, A.R. (1979) Electrical Properties of Polymers (Cambridge University Press, Cambridge). 

Sazhin BI (ed) (1970) Electrical properties of polymers, Leningrad Chemistry (in Russian)... 

We can define the principal electrical properties of polymers in terms of four characteristics electrical resistance, capacitive properties, dielectric strength, and arc resistance. We can change the surface characteristics of a polymer by subjecting it to a corona discharge generated by a strong electrical field. Lastly, we must also consider the influence of other physical properties on the application of polymers in electrical applications. 

Alignment of CNTs markedly affects the electrical properties of polymer/CNT composites. For example, the nanocomposites of epoxy/MWCNTs with MWCNTs aligned under a 25 T magnetic field leads to a 35% increase in electric conductivity compared to those similar composites without magnetic aligned CNTs (Kilbride et al., 2002). Improvements on the dispersion and alignment of CNTs in a polymer matrix could markedly decrease the percolation threshold value. 

The electric properties of polymers are also related to their mechanical behavior. The dielectric constant and dielectric loss factor are analogous to the elastic compliance and mechanical loss factor. Electric resistivity is analogous to viscosity. Polar polymers, such as ionomers, possess permanent dipole moments. These polar materials are capable of storing... 

Following are some relationships that are generally pertinent to describing the electrical properties of polymers. 

Barford, W. 2005. Electronic Properties of Conjugated Polymers. Oxford University Press, Oxford. Blythe, T. and Bloor, D. 2005. Electrical Properties of Polymers. Cambridge University Press, Cambridge. Chiellini, E., Gil, H., Braunegg, G., Buchert, J., Gatenholm, P., and vander Aee, M. 2001. Biorelated Polymers. Kluwer, New York. 

K. C. Frisch and A. V. Patsis, Electrical Properties of Polymers, Technomic, Westport, Conn. (1972). 

As described in Chapter 6, Electric Properties of Polymers, there is a general relationship between the delocalization of electrons throughout a polymer chain or network and color so that the incidence of and darkness of color increases as electron delocalization increases. Thus polyethylene is colorless while polyacetylene is black. 

J. Mort and G. Pfister, Electrical Properties of Polymers, Wiley, New York (1982). 

C. C. Ku and R. Liepins, Electrical Properties of Polymers Chemical Principles, Hanser, Munich (1987). 

Murayama.N. Piezoelectric and pyroelectric effects of polymer electrets. Microsymposium on Electrical Properties of Polymers, Tokyo (Jan. 1972). 

Seanor DA (ed) (1983) Electrical properties of polymers Academic, New York, Chap 5... 

While the study of the conventional semiconducting materials has progressed rapidly, the study of organic materials has received much less attention until the past few years. In particular the electrical properties of polymers have been much neglected and little authoritative work exists in the literature. In view of current developments in theories of the electrical properties of organic molecular crystals, it seems profitable to take stock of the situation as far as charge transfer in polymers is concerned. 

Despite the volume of work which has appeared concerning the electrical properties of polymers and pyropolymers, the mechanism of charge transfer is much less well understood than that of organic mole-... 

Emerson JA, Torkelson JM (eds) (1991) Optical and electrical properties of polymers, vol 214. Materials Research Society, Pittsburgh... 

---