Conducting

polymer
 The majority of polymers are insulators, due to an unavailability
of free electrons to create the conductivity. eg plastics, rubber
 Some polymers contains free electrons & conduct electricity.
 For a polymer to be electrically conductive it must "imitate" a
metal i.e. the electrons in the bonds must be free to move and not
bound to the atoms.
 Organic polymer (Long chain of carbon based repeating
units) having current flowing properties. eg. Polyacetylene

Polymerizatio
n

Polyacetylen
e
 Types of conducting polymer
 Two types conducting polymer
1. Conjugated conduction polymer
2. Doped conduction polymer
1. polymers having conjugated π-electrons in the backbone
o In these types of polymer, conduction of electricity takes
place by either π-electrons (double bond) or lone pair of
electrons. These polymers are consisting of carbon
atoms with alternating single and double bonds i.e.
conjugated double bonds. eg polyacetylene

polyacetylene

oThe π -electrons of π bonds delocalized over the entire

backbone results in the formation of valence bands as
well as conduction bands, which extend over the
complete polymer molecule.
The energy gap between
the valence and the conduction
Empty
band (band gap) is relatively band
small. The electrons from valence
band become excited up into
the conduction band through
thermal or photolytic activation.
The electrons are free to move Filled band
and propagate in the conduction
band which creates an electric
current e.g.

Polyacetylene

H
Polymerization
N
Polypyrrole n *
N N N
H n H
H
pyrrole Polypyrrole
 Only conjugated double bonds in polymers is not sufficient for
electrical conductivity. So the conductivity is enhanced by
oxidation or reduction. This process is known as doping. The
polymer are known as doped polymer.
Depending on dopant, they are of two types:
Oxidative doping (p-doping) and Reductive doping (n-doping)
 Oxidative doping (p-doping):
It involves the oxidation (removal of electrons) of polymer to form
charge carrier. Oxidising agents are Lewis acids such as FeCl3, I2,
Br2 etc.
(Oxidative process)
(Polymer)n + X (Lewis acid) - e- (Polymer) n+ + Xn-
oxidizing agent delocalized cation
(e-acceptor)
The delocalized cation travels along the polymer chain by
rearrangement of single and double bonds and
the polymer become conducting. eg.
(C2H2)n + I2 (C2H2)n+ + I3n-
Polyacetylene p-doped polyacetylene
 Reductive doping (n-doping):
It involves the reduction of conjugated polymer to form charge
carrier i.e. addition of electrons to polymer backbone. Reducing
agent used in this process are Lewis bases such as sodium,
potassium, lithium etc.
Reductive process
(Polymer)n + Y (Lewis base) + e-
(Polymer)n- + Yn+
Reducing agent
(e-donar) delocalized anion

The generated delocalized anion moves along the chain and the
polymer become conducting.

(C2H2)n + Na (C2H2)n - + Na+

polyacetylene
n-doped polymer
 Synthesis and Applications of conducting polymers:

Synthesis and Applications of PANI (Polyaniline)

• Originally known as “Aniline black” because of its dark pigment
color, which was used for dyeing of textile fabrics.
• It behaves as organic conductor & semi-flexible rod polymer.
• Prepared using low-cost material and easy preparation process so
it has received much attention among conductive polymers.

Oxidative
Polymerization

aniline

polyaniline conducting polymer

Semi flexible rod polymers: a kind of organic polymer which may be

converted to conductive polymers by appropriate oxidations or doping.
 Three different forms of PANI (Polyaniline) base

Fully reduced form (White or colorless)

Less conducting

Most stable form - Blue

Fully oxidized form ((blue/violet)

Emarldine base form of polyaniline is most stable form.
 Synthesis:
Oxidative polymerization of aniline under acidic condition
(HCl). The most common oxidant is ammonium persulphate
((NH4)2S2O8)–.
Here Ammonium persulphate ((NH4)2S2O8 )–Oxidant
HCl -Dopant

9
 Synthesis of polyaniline (Process)

Aniline
Ammonium persulphate HCl/ (NH4)2S2O8
((NH4)2S2O8 ) –Oxidant (Oxidative polymerization)
HCl -Dopant
Imine nitrogen

Emerldine base- stable and less conducting

Protonation
(+H+/HCl)

conducting
 Internal
oxidation/Reduction

Emerldine salt- conductor

 Applications of PANI (Polyaniline)
1. In the manufacture of printed circuit boards in the final finish,
for protecting copper from corrosion.
2. It can increase electronic conductivity and improve Li+ storage
capability.
3. The combination of PANI (conducting polymers) and carbon
materials shown superior performance in as supercapacitor.

printed circuit boards

Lithium battery
 Applications of PANI (Polyaniline)
4. They are able to protect steel from corrosion by formation of an
iron oxide layer with a high protection ability.
 Applications of PANI (Polyaniline)
6. Its thin films are suitable candidates for efficient electrodes for
high-performance solar cells.
7. It have been applied for developing electrically conductive
scaffolds for tissue engineering (TE) in recent years.

Scaffold: Porous polymeric biomaterials, provide the structural support

for cell attachment and subsequent tissue development.
 tissue engineering (TE)
Scaffold: Polymeric biomaterials, provide the structural support for cell
attachment and subsequent tissue development.
Tissue engineering is techniques to produce tissue for repair or improvement of body functions.
15
 Applications of PANI (Polyaniline)
8. Since, it is capable of changing color from blue to green and vice
versa through oxidation/reduction reactions, it is used in sensors.

It has been used as a sensing material for chemical/toxic gases,

volatile organic compounds and humidity. For example: chemical
sensor

The color change response of the Pani

sensor:
(a) represents the original blank color
of the unexposed film PANI
(b) represents blue color of film in
presence of NH3 gas
(c) H2S
(d) CO2
(e) phenol
17
Synthesis and Applications of PPY ( Polypyrrole)

Polypyrrole (Ppy)
• It is a conductive organic polymer.
• It is one of the attractive polymer with most interesting
electrical properties due to its:
• (High conductivity),
• (Environmental stability),
• (Low cost),
• (Easy synthesis)

Polymerize

Conducting polypyrrole
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Synthesis: Prepared by polymerization of pyrrole with oxidizing
agents e.g. ammonium persulphate or ferric chloride by
electrochemical or oxidative chemical polymerization methods.

FeCl3

Less conductive polymer

- 2e- (Electrochemical)
Released to anode

Conducting Polypyrrole
 Applications of polypyrrole
1. It is used in smart windows due to ability to change color in
response of electric stimulus.

2. In the field of energy storage, it has been used in super-

capacitors and batteries due to high electrical conductivity.

20
 Applications of Polypyrrole
3. As a catalyst support for fuel cells.

4. Used as polymeric containers for encapsulation and

delivery of drugs.

Encapsulation of drugs.
Fuel cell
 Applications of (contd.)
5. As light weight rechargeable batteries etc.
6. The blend of polypyrrole based polymer protects
corrosion of metals.
7. It is a highly biocompatible so used in tissue
engineering.

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