Polyacetylene. Polyacetylene is an organic polymer with -( C 2 H 2 )n repeating monomer. Structure. carbon atoms with alternating single and double bonds between them
Polyacetylene is an organic polymer with -(C2H2)n repeating monomer
Natta Routes (1958)
Also called Ziegler- Natta Scheme
uses titanium and aluminum catalysts
control over the structure and properties of the final polymer by varying temperature and catalyst loading
Yet Alan J. Heeger, Alan G. MacDiarmid and HidekiShirakawahavechangedthisviewwiththeirdiscoverythat a polymer, polyacetylene, can bemadeconductivealmostlike a metal.
(via the metal-carbene
Conductivity can be defined simply by Ohms Law.
Where R is the resistance,I the current and V the voltage present in the material.
The conductivity depends on the number of charge carriers (number of electrons) in the material and their mobility.In a metal it is assumed that all the outer electrons are free to carry charge and the impedance to flow of charge is mainly due to the electrons "bumping" in to each other.
Insulators however have tightly bound electrons so that nearly no electron flow occurs so they offer high resistance to charge flow. So for conductance free electrons are needed.
Three simple carbon compounds are diamond, graphite and polyacetylene. They may be regarded as three- two- and one-dimensional forms of carbon materials .
Diamond, which contains only σ bonds, is an insulator and its high symmetry gives it isotropic properties.
Graphite and acetylene both have mobile π electrons and are, when doped, highly anisotropic metallic
Images from Wikipedia
Nobel lecture December 8, 2000. Shirakawa at University of Tuskuba
(after thermal conversion)
Polyacetylene (PA) or (CH)x is chemically the simplest
A semiconductor in which chain conformation (structure) impacts band gap
Image from 1
Polyacetylene (After doping!)
(A “highly” crystalline polymer host)
Even when doped to a highly conductive state most p-conjugated polymers behave as classic semiconductors (VRH-variable range hoping is the standard proposed mechanism)
5 valence electrons
An unbonded electron
(hole in valence band)
hole in valence band
At room temperature electron is delocalized in conduction band (CB)
At room temperature hole is delocalized in valence band (VB)
Band structure is essentially rigid
Mobility is everything
1-The first condition for this is that the polymer consists of alternating single and double bonds, called conjugated double bonds.
In conjugation, the bonds between the carbon atoms are alternately single and double. Every bond contains a localised “sigma” (σ) bond which forms a strong chemical bond. In addition, every double bond also contains a less strongly localised “pi” (π) bond which is weaker.
Electronic states are split off from the valence and conduction bands
All charge excitations involve local self-consistent structural distortions of the lattice
From a tight-binding perspective:
EA is the energy of a single atomic orbital
A(R) is an overlap integral
is the key for
Oxidation with iodine causes the electrons to be jerked out of the polymer, leaving "holes" in the form of positive charges that can move along the chain.
Nobel Lecture 2000
Conducting polymers have many uses. The most documented are as follows:
A second generation of conducting polymers have been developed these have industrial uses like:
1. Floyd, L.K.; Grubbs, R. H.; Polycyclooctatetraene (polyacetylene): synthesis and
propertiesJ. AM.Chem. Soc.,1988, 110(23),pp 7807-7813.
2. Saxon, A.; Leipins, F.; Aldissi, M. Polyacetylene: Its Synthesis, Doping and
Structure. Prog. Polym. Sci: 11 57
3. Nobel lecture December 8, 2000. Shirakawa at University of Tuskuba
4. H. Shirakawa, E. J. Louis, A. G. MacDiarmid, C. K. Chiang and A. J. Heeger,
J. Chem. Soc., Chem. Commun.1977, 578
5.Evaristo Riande and Ricardo Díaz-Calleja, Electrical Properties of