Conduction plane polyacetylene

FIGURE 5.8. Structures of some common doped conductive polymers, each projected on a plane normal to the direction of the polymer chains. Cross-hatched circles indicate dopant ions, (a) The square channel structure of potassium-doped polyacetylene (other alkali-doped PA lattices show similar structures),(b) lithium-doped polyparaphenylene, (c) potassium-doped ppp,(ii3) AsFs-doped PPR In (d) the dopant species, represented by x, are probably... 

In photo-conductors, the gap between the valence and conduction bands is small enough that electrons can be excited into the conduction band by absorption of a visible photon. Some polymers, such as polyacetylene, and covalent crystals, such as graphite, may also have accessible conduction bands if they have partly filled rr-bond systems. Graphite has a much lower electrical and thermal conductance along the axis perpendicular to the plane of the sheets in this direction the atoms are connected only by the weak van der Waals forces. 

Oriented polyacetylene films have been synthesized by using a nematic liquid crystal as a polymerization solvent. The maximum value of parallel electrical conductivity of the films doped with AsFs was 11,000 S cm [17]. The use of an aged mixture of Ti(OC4Hc,)4-A1(C2H0. in silicone oil that has been mixed with various quantities of n-butyllithium, as the catalyst for the polymerization of acetylene, yields polyacetylene that is highly regular, compact, and crystalline, in well-defined parallel planes. When it is stretched and doped, the polyacetylene film shows a dramatic increase in conductivity to a value greater than lO S cm [18]. 

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