• BASICS OF CONDUCTIVITY
• MECHANISM OF CONDUCTION IN POLYMERS
• SOME CONDUCTING POLYMERS
• METAL CONJUGATED POLYMER
Polymers (or plastics as they are also called) are
known to have good insulating properties.
Polymers are one of the most used materials in the
modern world. Their uses and application range
from containers to clothing.
They are used to coat metal wires to prevent electric
4. Yet Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa have changed this view with their
discovery that a polymer, polyacetylene, can be made conductive almost like a metal.
5. What is conductivity?
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.
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.
7. What makes the material conductive?
Three simple carbon compounds are diamond, graphite and polyacetylene.
They may be regarded as three- two- and one-dimensional forms of carbon
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
8. 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)
9. Band structure is essentially rigid
Conventional Semiconductors at the atomic level
5 valence electrons
At room temperature electron is
delocalized in conduction band (CB)
0 E acceptor
hole in valence band
(hole in valence band)
An unbonded electron
At room temperature hole is
delocalized in valence band (VB)
Mobility is everything
12. Conformational structure impacts electronic properties
2. Conjugation yields an energy/unit length which is
minimized with increasing backbone planarity
3. Rotation breaks conjugation
C C CC C C
C C C
(after thermal conversion)
1. Cis and trans polyacetylene, according to the tight binding picture
just presented, should have the same band gap but they don’t!
Structural instabilities and disorder are extremely important (at all length scales)
13. Two conditions to become conductive:
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.
14. 2-The second condition is that the plastic has to be disturbed - either by removing electrons from
(oxidation), or inserting them into (reduction), the material. The process is known as Doping.
• There are two types of doping:
1-oxidation with halogen (or p-doping).
2- Reduction with alkali metal (called n-doping).
Polyacetylene consists of a long chain of carbon atoms with alternating single and double bonds between them, each with
one hydrogen atom. The double bonds can have either cis or trans geometry. The controlled synthesis of each isomer of
the polymer, cis-polyacetylene or trans-polyacetylene, can be achieved by changing the temperature at which the
reaction is conducted. The cis form of the polymer is thermodynamically less stable than the trans-isomer. Despite
the conjugated nature of the polyacetylene backbone, not all of the carbon–carbon bonds in the material are equal: a
distinct single/double alternation exists. Each hydrogen atom can be replaced by a functional group. Substituted
polyacetylene tend to be more rigid than saturated polymers.
16. • From acetylene:
• Polyacetylene can also be produced by radiation polymerization of acetylene. Glow discharge radiation, γ-
radiation, and ultraviolet irradiation have been used. These methods avoid the use of catalysts and solvent, but
they require low temperatures to produce regular polymers.
• Ring-opening metathesis polymerization:
• From precursor polymers:
Short, irregular segments of polyacetylene can be obtained by dehydrohalogenation of poly(vinyl chloride).Thermal
conversion of precursor polymers is a more effective method for synthesizing long polyacetylene chains.
Properties of Polyaniline:
• Polyaniline’s electrical properties can be reversibly controlled by charge-transfer doping and protonation.
• Polyaniline is environmentally stable and inert (noble) where stainless steel is corroded.
• Polyaniline is applicable to electrical, electrochemical, and optical applications. Polyaniline is currently used
in cell phones and calculators, and other LCD technology.
• Electrically and optically active polyaniline films doped with camphorsulfonic acid derivatives were
successfully deposited on non-conductive substrates via chemical vapour phase polymerization. The
polyaniline films grown by this method not only showed high electrochemical activity, but also
exhibited optical activity corresponding to the polymer chains.
• The corrosion inhibition properties of polished steel plates (low carbon) coated with a polyaniline
(emeraldine base form) blend with nylon 66 (termed PANi/Ny) via cast method with formic acid as the
solvent. Polyaniline (PANi) was prepared chemically from aqueous solution using aniline (0.2 M) as a
monomer and ammonium persulfate (0.2 M) as an oxidant. The polymer powder produced was
changed into emeraldine base (EB) form after treatment with dilute ammonia solution (0.5 M) in order
to do further processing.
20. • POLY-PYRROLES
• Poly-pyrrole films are formed by casting a pyrrole derivative (say, 3-hexadecyl pyrrole) in an organic solvent
on an air-water interface where the water subphase contains an oxidant (FeCl3). Free pyrrole as the vapour is
added to cause polymerization. They are excellent conductors.
The use of electrochemically synthesized polypyrrole film is investigated as a primer for protective coating on
carbon steel. It provides excellent adherence and corrosion resistance, and is more environment-friendly.
Polypyrrole was galvanostatically synthesized on carbon steel, and epoxy paint top coat was applied on it. The
corrosion performance was evaluated using salt spray test, and electrochemical impedance
spectroscopy. The performance was compared to that of a commercial zinc primer. These tests coherently
demonstrate that the use of polypyrrole film inhibits corrosion better than a zinc primer in salt and acid
21. • Other conducting polymers are polythiophenes, poly(p- phenylene
sulfide), Poly p- phenelynes etc.
23. Metal-containing conducting polymers can be divided into three types,
known as types I, II and III .These are tethered, coupled and incorporated
respectively. Type I polymers have the metal group tethered to the
conjugated backbone by a linker moiety such as an alkyl group. In these
Cases the polymer acts as a conductive electrolyte and the metal ions act in
similar way to an untethered group. Type II polymers have the metal
directly coupled to the polymer backbone or coupled to the backbone by a
conjugated linker group, which makes it easier for the polymer and the
metal group to affect each other's properties directly. The third type of polymer
has the metal group directly incorporated into the conjugated backbone. In this
type the metal group has the greatest influence on the properties of the
25. • Several methods of synthesizing this polymers are available. These include condensation, ROMP, electro
polymerization. Electro- polymerization is the most suitable process for the Type 1 and Type 2 as they form
the insoluble thin films which are difficult to cast by solution process. They include heterocyclic aromatic
compound like pyrrole, thiophenes.
• Most Type 3 can not be electro-polymerized except the thiophene based type 3 polymers. So the basically
or synthesized by condensation or ROMP process.Examples include ferrocene based polymers, polysilanes
and metal polychelates of bis-chelating ligands.
26. Shield for computer screen
Photographic Film Light-emitting diodes
• For conductance free electrons are needed.
• Conjugated polymers are semiconductor materials while doped
polymers are conductors.
• The conductivity of conductive polymers decreases with falling
temperature in contrast to the conductivities of typical metals, e.g.
silver, which increase with falling temperature.
• Today conductive plastics are being developed for many uses.
• H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang and A.J.
Heeger, J Chem Soc Chem Comm (1977).
• T. Ito, H. Shirakawa and S. Ikeda, J.Polym. Sci., Polym.Chem. Ed. 12
• Evaristo Riande and Ricardo Díaz-Calleja, Electrical Properties of
• POLYMER SCIENCE AND TECHNOLOGY-BY PREMAMOY GHOSH.