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A8008 – Polymeric Materials

POLYMERIC MATERIALS
Introduction:
Polymer is the word derived from two Greek words. poly and mers. “poly” means many and “meros”
means units or parts.

Definition: a polymer is a macromolecule formed by the repeated linking of large number of small
molecules.

Example: Polythene is a polymer of ethylene formed by the repeated linking of large number of small
ethylene molecules.

 The repeated unit of polymer is called a monomer.

 Polymers possess the desirable properties like high strength, good flexibility, special electrical
properties, resistance to chemicals and can fabricate into complex shapes in a wide variety of colors.

Polymerization:
The process of joining together of a large number of simple or small molecules to form a very big
molecule is termed as polymerization.

Small molecules that combine with each other to form a polymer are known as Monomers.

Ex: nCH2= CH2---------→ [-CH2-CH2-] n

Monomer Polymer

Degree of Polymerization (DP):

The number of repeating units (n) in a polymer chain is called “Degree of Polymerization (DP)”.
For example, if 100 molecules of ethylene are polymerized to give the polymer chain, i.e., polyethylene. The
degree of polymerization of polyethylene polymer is 100.

Classification of Polymers:

 Based on Degree of Polymerization: Depending on the degree of polymerization, there are two
types of polymers.

1. Oligo Polymers: those polymers whose degree of polymerization is less than 600 are called oligo
polymers. These polymers do not possess the Engineering properties.

2. High Polymers: When the Degree of polymerization of a polymerization of polymers more than 600 it is
called high polymers. High polymers possess the desired Engineering properties. Polymers posses the
desirable properties like high strength, light weight, good flexibility, special electrical properties like
resistance to chemicals and fabrication into complex shapes in a wide variety of colors.

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 Based on Functionality of Monomers:

For a substance to acts as a monomer, it must have at least two reactive sites (bonding sites).
The number of reactive sites or bonding sites in a monomer is called functionality of the monomer.
1. If two reactive sites are present in a monomer it is called Bi functional monomer and forms a linear
straight chain polymer.
2. If three reactive sites are present in a monomer it is called tri functional monomer and forms a branched
chain polymer.
3. Poly functional monomer contains more than three reactive sites. It forms 3 dimensional network of a
polymer.
The monomer molecule in a linear chain is linked by primary covalent bonds and the different chains are
held together by secondary Vander wall’s forces of molecular attractions.

 Based on Tacticity (Configuration):

There are three different types of polymers depending on the relative geometric arrangement of the
functional groups. Depending on the tacticity there are three different types of polymers

1. Isotactic Polymers: All functional groups are on the same side of the polymer chain (iso similar).

H H H H H H H H

3 C C C C C C C C

H Cl H Cl H Cl H Cl

2. Atactic Polymers: When there is no regular arrangement of functional groups on the backbone of the
polymer chain. Those polymers are called Atactic polymers.

3. Syndiotactic Polymers: The polymers with alternative arrangement of functional groups are called
syndiotactic polymers.

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 Based on Monomers:

1. Homo polymer: In this type, a single type of monomer unit is present. Example: Polyethene
2. Heteropolymer or co-polymer: It consists of different type of monomer units. Example: nylon -6, 6

 Based on The Synthesis:

On the basis of synthesis, polymers are of two types.

1. Addition Polymers: These are formed by the polymerization of monomers without the elimination
of atom (or) groups (bi products).

Monomer Polymer
Ethylene Polyethylene
Vinyl Chloride Poly vinyl chloride (PVC)
Tetra fluoro ethylene Teflon

2. Condensation Polymers: These are formed by the polymerization of monomers with the
elimination of small molecules NH3, H2O and CH3-OH.

Monomer Polymer
Caprolactum Nylon 6
Hexamethylene di amine and Adipic acid Nylon 6,6
Hexamethylene di amine and Sebasic acid Nylon 6,10

1. Addition Polymerization (Chain Growth Polymerization):

Addition (or) chin growth polymerization is the linking of molecules having multiple bonds. These
unsaturated monomers have extra internal bonds which are able to break and linkup with the other
monomers to form repeating chain. All the addition polymers are chain growth polymers, but few examples
of condensation polymers are also present whose mechanism proceeds through chain growth
polymerization.

Generally, Addition polymerization is having following characteristics;

1. The functionality of the monomer is a double bond and it is bifunctional.

2. The polymerization takes place by self-addition of the monomer molecules to each other through a
chain reaction.
3. No bi products like NH3, H2O, CH3-OH etc are produced.
4. The polymer has the same composition as that of a monomer.
5. The molecular weight of the polymer is the exact multiple of monomers.
6. The mechanism is carried out in three steps i.e. initiation, propagation, termination.

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7. The conversion of a ∏ bond to σ bond takes place during the polymerization, liberating 20 k.cal/mol
of energy. Hence these are highly exothermic reactions.
8. The mechanism is very fast.
9. An initiator required to start the mechanism.
Ex: 1. Olefines like CH2= CH2, CH3-CH= CH2
2. Vinyl compounds, CH2= CH-Cl, nCH2= CH-C6H5
3. Allyl compounds CH2= CH-CH2-Cl
4. Dienes CH2= CH-CH=CH2

2. Condensation Polymerization (Step Growth Polymerization):

Step growth polymerization is defined as the polymerization in which the polymers are formed by step
wise reaction between functional groups of monomers.
Generally, condensation polymerization is having following characteristics;
1. The monomers contain functional groups like –OH, -COOH, -NH2, -COOR, halides etc.
2. The functionality of the monomer must two or more than two. The monomer must be dibasic acid, di
amines or triols etc.
3. The polymer is built by a slow stepwise condensation reaction of the functional groups of monomers.
4. The polymerization reaction is accompanied by the elimination of byproducts like HCl, NH3, H2O, CH3-OH
etc.
5. The reactions are not exothermic.
6. The molecular weight of the polymer is not exact multiple of a monomer.
7. It does not follows the initiation, propagation, termination in mechanism.
8. The reactions are catalyzed by catalyst.
Ex: a) The polymerization of a diacid with diol produces polyester.
b) Nylon (6,6)

Differences between Addition and Condensation Polymerization:

Addition polymerization Condensation polymerization

1. Formed by addition reaction. 1. Formed by condensation process with

elimination of small molecules
like H2O,NH3,CH3OH e.t.c
2. Molecular mass is a whole number multiple of 2. Molecular mass is not whole number multiple
the monomer. of the monomer units.
3. Generally involve one monomer unit. 3. Generally involve more than one monomer
unit.
4. Monomers are unsaturated molecules. 4. Monomer units must have two active
functional groups.
5. They are generally chain growth polymers. 5. They are generally step growth polymers.
6. These are highly exothermic reactions. 6. The reactions are not exothermic.

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7. The mechanism is carried out in three steps i.e.

7. It does not follow the initiation, propagation,
initiation, propagation, termination. termination in mechanism.
8. An initiator required to start the mechanism. 8. The reactions are catalyzed by catalyst.
9. The functionality of the monomer is a double 9. The functionality of the monomer must two or
bond and it is bifunctional. more than two. The monomer must be dibasic
acid, di amines or triols etc.
10. The mechanism is very fast. 10. The polymer is built by a slow stepwise
condensation reaction.
Examples: Poly Ethylene,Poly Vinyl chloride,Poly Examples: Nylon 6,6….Nylon 6,10 and Ply Ester
Styrene etc. etc.

Plastics:
The term ‘Plastic’ was derived from the word ‘Plastikos’ which means ‘to mould’ in Greek, and it is
used to refer to a wide range of semi-synthetic or synthetic organic polymers. Different types of plastics
are known to possess different physical and chemical properties. Many articles like chairs, tables, buckets,
toys, balls, etc are made of plastic material.

Characteristics of Plastics

i. They are light in weight and are chemically stable.

ii. Easily moulded into different shapes and sizes.
iii. Good insulation and low thermal conductivity.
iv. Good impact resistance and they do not rust.
v. Good transparency and wear resistance.
vi. Poor dimensional stability and can be easily deformed.
vii. Low processing cost.

Plastic resins are classified into two types.

1. Thermoplastic Polymers: Thermoplastics are polymers that soften on heating and become hard on
cooling. These are the polymers in which intermolecular forces of attraction are moderate and there
are no cross-links between the chains. Ex: Polyethene, polypropylene, PVC, etc.

2. Thermosetting Polymers: On heating, extensive cross-linked is formed in these polymers between

the polymeric chains and thus they become hard. Ex: Bakelite, Urea-formaldehyde.

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Differences between Thermoplastic and Thermosetting Plastics:

Thermoplastic resins Thermosetting resins
1. These plastics (resins) soft on heating and rigid 1. These resins do not soften on heating, on
on cooling reversibly. prolonged heating these are burns.
2. These can be remolded or reshaped. 2. These cannot be reshaped or remolded.
3. These have linear structures. 3. These have 3D-cross linked structures.
4. These are less brittle, soft & weak. 4. They are more brittle, hard, and strong.
5. They are formed by the addition 5. Formed by the condensation polymerization.
polymerization.
6. These are soluble in organic solvents. 6. Insoluble in almost all organic solvents.
7. These plastics can reclaim from waste. 7. These plastics cannot reclaim from waste.
8. Low Melting Points. 8. High Melting Points.
9. Low Tensile strength. 9. High Tensile strength.
10. Chemical resistant 10. More resistant to high temperatures than
thermoplastics.
Ex: Polyethene, PVC Ex: Bakelite

1. Poly Vinyl Chloride (PVC):

It is produced by free radical chain polymerization of vinyl chloride in the presence of
benzoyl peroxide (or) hydrogen peroxide.

The parent compound vinyl may be prepared by the following method.

HCl
HC CH H2C CH Cl
Acetylene Hg+2 Vinyl Chloride
PVC is also known as KOROSEAL.

Properties:
1. PVC is colourless, chemically inert powder
2. It has specific gravity 1.33 and melting point 1480c
3. PVC is strong, brittle.
4. It is resistant to atmospheric conditions like O2, CO2, & moisture.
5. PVC is unstable to heat and UV radiation.

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Engineering Applications:
PVC treated with plasticizers is called plasticized PVC. It is used for electric insulators, injection molding
articles like tool handles, radio and telephone components.
Unplasticized PVC is rigid, highly resistant to chemicals and brittle. This PVC is used for making safety
helmets, refrigerator components, tires.

2. Teflon (Poly Tetra Fluoro Ethylene-PTFE):

It is prepared by the polymerization of tetra fluoro ethylene under pressure in the presence of free radical
initiator.

Tetra fluoro ethylene is produced by dechlorination of syn di chloro tetra fluoro ethane in the presence of
catalyst.

Teflon is also known as FLUON.

Due to the presence of highly electro negative fluorine atoms Teflon has strong attractive forces between
the different chains in the Teflon molecules.

This strong attractive force is responsible for high toughness and high chemical resistance towards all
chemicals except hot metal and hot fluorine.
Properties:
Due to the presence of high electro negative fluorine atoms it has
1. High melting point (>350oc).
2. High chemical resistance.
3. High density (2.1-2.3 gm/cc).
4. It is very strong, hard polymer.
Engineering Applications:
1. Teflon is a very good insulating material for motors, transformers etc.
2. Due to extreme chemical resistance, it is used for making chemical carry pipes.
3. It is used for making gaskets, pump parts.
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4. Non –lubricating bearings and non-stick stop cock for burettes are made from Teflon.
5. It also used for coating.

Fibers:
Those polymers which can be drawn in the form of long filaments with high tensile strength, high rigidity or
stiffness and irreversible deformation are called fibers.

Characteristics of Fibers:
i. These fibers possess high crystallisability and high melting points.
ii. High Strength - can withstand pulling and twisting
iii. Shrinkage - ability to maintain size
iv. Warmth - ability to maintain body temperature
v. Durability - the ability to hold up to repeated usage
vi. Absorbency - ability to take in moisture
vii. Wrinkle resistance - ability to resist creasing
viii. Resiliency - ability to spring back when crushed or wrinkled

Fibers are classified into

1. Natural fibers (Cotton, wool, silk etc).
2. Synthetic fibers (poly Ester, Nylons etc).

Poly Ester: The step polymerization of diacid and di alcohol produces poly Ester. The saturated poly
ester is formed by the condensation polymerization of ethylene glycol with Tere pthalic acid.

Synthesis of Dacron

Terepthalic acid. Ethylene glycol Polyethylene terephthalate

Terylene / Dacron

It can also prepared by the condensation polymerization of ethylene glycol with Dimethyl Terepthalate

Dimethyl Terepthalate Ethylene glycol Polyethylene terephthalate (Terylene)

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Properties:
1. They are highly resistance to mineral acid.
2. The fiber does not hold water.
3. The fibers are strong.
4. It is very easy to dye.
5. Good durability and
6. High color preservation.

Applications:
1. Polyester is used both as domestic fiber and industrial fiber.
2. Industrial application is to make tires.
3. Polyesters are widely used as a finish on first-class wood products such as guitars, pianos and
automobile/ship interiors.
4. Polyester thread or yarn is used expansively in apparel and home furnishing products. Those
products from shirts and pants to jackets and hats, bed sheets, blankets, upholstery furniture and
computer mouse mat.
5. Polyester fabrics are used for conveyor belts, safety belts, coated fabrics and plastic supporting with
high-energy absorption.

Nylon (Poly Amide):

Poly amides are polymers obtained by the condensation of acids, amines and contain amide[c]groups.
ex: Nylon-6,Nylon-(6,6), Nylon-(6,10), Nylon-11 etc.

Nylon-(6, 6):
The first number used in the suffix with the name of nylon represents the number of carbon atoms
present in the amine monomer and the second number represents the number of carbon atoms
present in acid monomer. It is obtained by the condensation of hexamethylene di amine & adipic
acid in 1:1 ratio.

O O

n H2 N  (CH2 )6  NH2  nHOOC  (CH2 )4  COOH 

2nH2O
[HN  (CH2 )6  NH  C(CH2 )4  C ]n 

Hexa methylene di amine Adipic acid Nylon (6,6)

Nylons are insoluble in common solvents and dissolve in phenols and formic acid.

Properties:
1. Nylons possess high strength, hardness and high M.P.

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The high melting point of the Nylons is due to the H-Bonding between the hydrogen atom of
the amine group (-NH) and oxygen atom of the C=O group.
2. Nylons possess high crystallinity.
3. Nylons possess good chemical resistance.
4. Good electrical insulators.
5. Good resistance to environmental conditions.

Engineering Applications:
1. Major application in textile industry.
2. Nylons are used as electrical insulators.
3. Nylon are also used for making tire cords.
4. Nylons are used in mobile industry and telecommunication industry for making
Radiator parts.
5. These are used in gears, bearing, machine parts etc.

Rubbers (Elastomers)
Rubbers are high polymers capable of returning to their original length, shape or size after being stretched
or deformed. Rubber is also known as elastomer. The rubber obtained from natural sources is called natural
rubber and the polymer prepared in the laboratory which are similar to natural rubber, are known as
synthetic rubber.

Characteristics of Rubbers:
i. High tear and tensile strength
ii. Resilience (ability to spring back when crushed or wrinkled) and resistance to abrasion, friction
and extreme temperatures (can stand at high temperatures)
iii. Resistant to water swell.

Natural Rubber:
 Natural rubber is obtained from nearly 500 different plants, but the main source from which
commercial natural rubber obtained is the Hevea Brasiliensis. The rubber is obtained from the latex
(milky sap) collected from cuts made in the bark of the tree.
 The obtained latex contains hydrocarbons with impurities such as fatty acids, proteins and resins in
an emulsified form.
 Small quantities of natural rubber are composed of 95% hydrocarbons, 4% protein and 1% of resins.
 Natural rubber is a polymer of isoprene units.

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 The X-ray diffraction studies have shown that in rubbers the isoprene units arranged in the cis form.
 Gutta percha rubber is also a natural rubber in which isoprene units arranged in Trans form.

Vulcanization of Natural Rubber:

The raw or crude rubber is of very little use because it has very undesirable properties such as
low tensile strength, elasticity only over a limited range of temperature and becomes softer, more
plastic and sticky on heating and brittle on cooling. It solubility in organic solvents (such as CHCl3,
benzene and petrol) is of advantage of preparing rubber derivatives.

In order to give more strength and more elasticity natural rubber is heated with sulpher or sulpher
compounds at 1500c temperature for few hours. The sulpher combines chemically at double bonds of
different rubber springs and a cross-linked network is formed. The process is known as vulcanization.

The vulcanization process can be enhanced in the presence of certain organic substances known as
accelerators. The common accelerators contain nitrogen & sulpher (or) both etc.

The main advantages of vulcanized rubber are as follows:

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1) Simple to use
2) Long shelf life
3) Low residual chemicals
4) Low toxicity
5) Vulcanized rubber has good tensile strength.
6) The working temperature of vulcanized rubber is enhanced up to 100°C. Temperature range of raw
rubber is 10–60°C.
7) It has good resistance to organic solvents.
Disadvantages:
Vulcanization" is more expensive than a "bound-rubber" process. However, vulcanized rubber
will remain softer, are self-healing, and are more durable.

Applications:
Vulcanized rubber has come to be used to make a wide variety of products. Among the most common of
these are automobile tires, rubber seals and gaskets, transmission belts, shoe soles and hockey pucks. In
each case, the results are exactly the same, creating new chemical bonds in the liquid rubber and making
a substance that is stronger and more rigid, which still retains the elasticity of pre-vulcanized rubber.

Synthetic Rubbers:

1. Buna-S (Styrene Butadiene Rubber-SBR):

B-butadiene-monomer S-styrene- monomer Na-sodium (catalyst)

Co-polymerization
CH2 = CH— CH = CH2 + n (CH2 = CH -Ph) [-CH2 - CH = CH—CH2—CH2—CH-Ph ]n
Butadiene Styrene Buna-s

 Buna-S is a co polymer of 75% butadiene (CH2=CH-CH=CH2) and 25% of styrene (C6H5-CH=CH2). The
polymerization is carried out at 500c in the presence of peroxide catalyst.
 It is introduced at the time of second world war by us in order to overcome the scarcity of natural
rubber.
Properties:
1. It is a strong and tough polymer.
2. It is vulcanized by similar to natural rubber using either sulpher (or) sulpher mono chloride.
3. Good electrical insulator.
4. Resistant to chemicals, but attacked by even traces of ozone, present in atmosphere.

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Applications:
Buna-S used for the manufacture of motor tires, the rubber can also used for foot wear soles,
gaskets, cable insulation etc.

2. Butyl Rubber:
It is formed with the combination of isoprene and isobutylene.
Another name for this rubber is IIR which means Isobutylene Isoprene Rubber.
Its commercialization took place in 1943, making it the first rubber that was synthesized.
CH 3 CH3
CH 3 CH 3

n C n C CH2
H 2C CH 3 H 2C C CH 3 n
H
Isobutylene Isoprene Butyl rubber
98% 2%

Properties:
1. It is a Flexibile polymer (Visco elastic)
2. Colorless to yellow
3. It is vulcanized by similar to natural rubber using either sulpher (or) sulpher mono chloride.
4. Good electrical insulator.
5. The usability temperature of the Butyl rubber is between -50 to 120 OC.

Applications:
 Adhesive
 Agrochemicals
 Chewing gums
 Tyre inner tubes
 Spekers
 It also serves the use as a sealant to insulate the windows
 The Butyl rubber strip is used for car and truck body mounts, suspension bushings, and others
 Making conveyor belts, aircraft components, gaskets, oil resistant foams, automobile parts etc.

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Conducting Polymers:
Generally, polymers are insulators i.e., they do not conduct electricity or heat and due to this property, the
most common use of these is as an insulator for electric wires.
However scientists have discovered that certain class of organic polymers called conjugated polymers,
which contain many double bonds in their structure and conduct electricity like semiconductors.

Conducting Polymers:
1. Intrinsic conducting polymers
2. Extrinsic conducting polymers

1. Intrinsic conducting polymers:

a. Conjugated p-electrons conducting polymers
b. Doped conducting polymers
a. Conjugated p-electrons conducting polymers: Conjugated conducting polymers have alternating
double and single bonds along the polymeric chain and each carbon atom is in sp2 hybridized state.
One valence electron (p) on each carbon is in a pz orbital, which is orthogonal to other three sigma
bonds. The orbitals of conjugated p-electrons, overlap the entire backbone of the polymer and result
the formation of valence band and conduction band. The valence band is filled band and conduction
band is empty. When the energy gap between these is low, the electrons from valence band are excited
to conduction band and become mobile throughout the polymer and show conductivity. The examples
of such type of conjugated polymers are:

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b. Doped conducting polymers: The conductivities of the polymers can be increased or decreased by
oxidation or reduction process. When the conducting polymers undergo oxidation process by adding
some alkali metal ion or an electron acceptor, the conductivity so enhanced is said to be due to ‘p-
doping’, on the other hand the enhancement of conductivity due to reduction process by adding an
electron donor is called ‘n-doping’.
(i) Oxidation process (p-doping): Conducting polymers are oxidisied by adding some oxidizing agents.
In this process, p-electrons are removed from conjugated double bonds and positive hole or radical
cation is cre- ated. The radical cation is called ‘polaron’ which stabilizes itself by pola- rising the
medium. The positive holes (polaron) are mobile (delocalised) and this delocalisation of positively
charged holes is responsible for the conduction of current in the polymers. The p-doping is generally
brought by adding Lewis acids (such as FeCl3), iodine, bromine, arsenic penta-fluoride (AsF5) etc.

I2
CCl4
Poly Acetylene Polaron

I2 CCl4

Bipolaron

Reduction process (n-doping): In this type of doping some electrons are introduced into the polymer
by reducing agent like sodium naphthalide or by adding Lewis base (electron donor).
The n-doping in less common because on earth, atmosphere is oxygen rich, which creates an oxidizing
environment. An electron rich ‘n-doped’ polymer will react immediately with oxygen and converts into
the neutral state by re-oxidizing. Thus in the research field, electrochemical ‘n-doping’ is more common

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because it is easier to exclude oxygen from a solvent in a sealed flask. However there are likely no
commercialized n-doped conducting polymers.

2. Extrinsic conducting polymers:

Conducting element filled polymers:
The polymer acting as a binder to hold the conducting element such as carbon black, metallic fibres,
metallic oxides etc. minimum concentration of conducting filler is added so that the polymer starts
conducting. The minimum concentration of conductive filler is called percolation threshold. At this
concentration of filler a conducting path is formed in polymeric material. The most preferred filler is c-
black has very high surface area, more porosity.
Blended Conducting Polymers: These are the polymers, which are obtained by mixing a non-
conducting polymer with a conduction polymer either by physically or chemically. These blended
conducting polymers have better physical, chemical and mechanical properties. Iodine and bromine
used as dopant produce high conductivities but they are unstable and slowly evaporate from the
material while organic acids, including trifluroacetic acid, propionic acids and sulphonic acids produce
doped conducting polymer with lower conductivities than iodine but with higher environmental
stabilities. The structure and conductivity of some conducting polymers are given with doping
materials.
Applications of conducting polymers:
1. Smart Windows: Smart windows are the windows which change colour in response to sunlight or
temperature changes. The smart windows are made of two glass panes which are laminated together
with a conducting polymer foil. The glass panes are coated with an electrochromic film. The conducting
polymers which used in smart window are polyaniline, polythiophene etc.
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2. Light Emitting Diodes (LED): Many outstanding properties of organic conducting polymers
compared to inorganic semiconductor, create new business opportunities in wide range of electronic
devices such as transistors, light emitting diodes etc. The conducting polymer which used in LED, in
‘bulky p-conjugated’ poly (phenylenevinylene).
3. Rechargeable Batteries: The conducting polymers are also used in re- chargeable dry cell battery
which is cheap, safe and compact in comparison to the conventional dry cell. The conducting polymer
based rechargeable batteries are highly useful for portable microelectronic devices and house- hold
appliances such as radio, transistors, tape recorders etc.
4. The conducting polymers are used in lasers, flat television and solar cells.
5. These are also used in electro luminance displays like in mobile phones etc.

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