Chemistry-R23

Unit-IV
Polymer Chemistry
Syllabus

UNIT-4: Polymer Chemistry

Introduction to polymers, functionality of monomers, chain growth and step growth
polymerization, coordination polymerization, with specific examples and mechanisms
of polymer formation.
Plastics –Thermo and Thermosetting plastics, Preparation, properties and applications
of – PVC, Teflon, Bakelite, Nylon-6,6, carbon fibres.
Elastomers–Buna-S, Buna-N–preparation, properties and applications.
Conducting polymers – polyacetylene, polyaniline, – mechanism of
conduction and applications. Bio-Degradable polymers - Poly Glycolic Acid
(PGA), Polyl Lactic Acid (PLA).

POLYMER CHEMISTRY
Introduction:

 Polymers are the macromolecules which are formed by the combination of

many smaller molecules called monomers.
 Polymerization is the process of forming a polymer by using number of
repeating units.

Degree of polymerization:

 It is defined as the number of monomers units in a homo polymer.

 Most of the polymers are in the molecular mass range of 5,000 – 2, 00,000.
 But in case of hetero polymer, degree of polymerization (D.P) is defined as the
ratio of total molecular weight of a polymer to molecular weight of each
repeating unit.
 In the above equation, ‘n’ is the degree of polymerization.

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Functionality:

 The number of active bonding sites of a monomer is referred to as its

functionality.

Number of Active Name of the

Example
sites in monomer monomer
2 Bi Functional Monomer Ethylene
3 Tri Functional Monomer Phenol
Poly Functional
>= 4 Novalac
Monomer

CLASSIFICATION OF POLYMERS

Based On the Origin

 Natural polymers: Polymers from natural materials or biological origin are
called natural polymers.
Ex: Cellulose, Starch, Protiens, Natural rubber etc.

 Synthetic polymers: Polymers synthesized in the laboratories are called

synthetic polymers.
Ex: Polyethylene, PVC, Nylon, Polyester etc.

Based On the Chemical Composition

 Organic polymers: A polymers whose backbone chain is made of carbon
atoms is termed as organic polymers.
Ex: poly ethylene, polystyrene etc.

 Inorganic polymers: A polymers whose backbone chain is made of other

than carbon atom is termed as Inorganic polymers.
Ex: poly silanes, poly germanes etc.

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Based On Monomeric Units
 Homopolymers: A polymer having identical monomers is known as
homopolymer.
Ex: -A-A-A-A-

 Co-polymers or Hetero polymers: A polymer having different monomeric

units is known as hetero (or) co-polymer.
Ex: -A-B-A-A-B-

Based on the arrangement of monomer copolymer is classified as four types

Random Co-polymer: Monomers are randomly distributed along the

polymer chain.

Alternative Co-polymer:Monomers are arranged alternatively.

Block Co-polymer: A block of repeating unit of one kind of monomer is

followed by block of another kind of monomer.

Graft Co-polymer: Polymer backbone and branches are formed from

different monomers.

Based On Chain Structure

 Linear chain polymer:
 Linear or straight chain molecules are formed by the combination of
bifunctional monomers which contain two reactive sites.
 Linear polymers are obtained by strong covalent bonds. But different
chains are held together by secondary weak vanderwaal’s forces.
 Branched chain polymer:

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  Branched chain polymers are obtained by the combination of
trifunctional monomer and bifunctional monomers.
 Cross linked polymer:
 Three dimensional network polymers are obtained by the combination of
poly functional monomers.
 In such polymeric molecules, the movement of monomer units is
prevented by strong cross links.

Based On Molecular Forces

 Thermosetting polymers:
 These polymers undergo permanent change on heating i.e., once they
have solidified, they cannot be softened during moulding process.
 These are hard infusible and insoluble products in all solvents.
 These polymers are having permanent rigidity.
 Ex: Bakelite

 Thermoplastics:
 These are linear, long chain polymers that turn to a liquid (soft) when
heated and freezes (hard) with little change when cooled.
 Their hardness is a temporary property.
 When heated, they melt to form a fluid which can be moulded into any
desired shape and then cooled to get the desired product.
 Ex: PE, PS, PVC etc.
 Elastomers:
 The polymers which behave visco elasticity like rubber are called
elastomers.
 These can be stretched to at least thrice of its length due to weak inter
molecular forces between the polymer chains.
 When stretching force is released, they return to their original shape due
to cross linkages in the polymer chains.
 Ex: Natural rubber

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  Fibres:
 These have strong intermolecular forces between the chains due to
hydrogen bonds or dipole – dipole interaction.
 These have sharp melting points and are used for making fibers.
 Ex: Nylon, poly esters etc.

Based On Their Methods of Synthesis or Polymerization

 Addition polymerization:
 Polymer is formed by addition of monomers without elimination of small
molecules.
 No by-products are formed.
 Monomer with unsaturation undergoes addition polymerisation
 Ex: PS, PVC etc.

 Condensation polymerization:
 Polymer is formed by two or more monomers by the elimination of small
molecules.
 By products are formed like H2O,NH3
 Monomers with functional group undergo condensation polymerisation.
 Ex: Nylon-6, Terylene etc.

Based On Tacticity
 The stereo chemical placement of the asymmetric carbons in the polymer chain
is called tacticity.
 Based on the stereo chemical orientation of atoms or groups at asymmetric
carbons, the polymers can be classified as
a) Atactic b) Syndiotactic (Syntactic) c) Isotactic

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  Atactic polymer:
 In these polymers, the substituents of asymmetric carbons are placed
randomly along the polymer chain.
 Substituent’s arranged in disorder manner.

 Syndiotactic polymers:
 In these polymers, the substituents of asymmetric carbon are placed in
alternative positions along the polymer chain
 Substituent’s arranged in order manner.

 Isotactic polymer:
 In these polymers, the substituents of asymmetric carbon on the same
side of the polymer chain.
 Substituent’s arranged in order manner.

 The polymers which are having tacticity and regular order of arrangement are
called stereo regular polymers.
 Syndiotactic and isotactic polymers are stereo regular polymers.
 The polymers which are having only tacticity are called stereo specific
polymers.
POLYMERIZATION
 Polymerization is the process of creating polymers.
 The process through which large chains of monomer molecules combine
together to form the polymer is called polymerization.

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Polymerization Mechanism
Polymerization consists of three steps that include,
1. Initiation

2. Propagation

3. Termination

Broadly polymerization can be classified into two categories,

 Chain-Growth or Addition Polymerization
 Step-Growth or Condensation Polymerization
CHAIN-GROWTH OR ADDITION POLYMERIZATION
 Polymer is formed by addition of monomers without elimination of small
molecules.
 No by-products are formed.
 Again, there are four types of addition polymerizations which are

1. Free Radical Polymerization: A free Radical Polymerization is a polymerizing

approach by which successive addition of free radicals takes place to form a

polymer unit.

2. Cationic polymerization: polymerization mechanism in which the formation

of a carbocation intermediate initiates the polymerization reaction.

3. Anionic Polymerization:polymerization process that is dependent on the

reactivity of anions to initiate and propagate the polymerization reaction.

4. Coordination Polymerization: This method was invented by two scientists

Ziegler and Natta who won a Nobel Prize for their work.
o They developed a catalyst which let us control the free radical
polymerization.
o It produces a polymer which has more density and strength.
o Coordination polymerization is a form of polymerization that is catalyzed
by transition metal salts and complexes.
FREE RADICAL POLYMERIZATION

In this type of polymerization monomer is activated to free radical by any one of the
following methods.

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 Mechanism of free radical polymerization involves three steps.

1. Chain initiation

It involves two steps.

a) Formation of free radicals from the initiator.

b) Addition of free radicals to monomer to form a free radical intermediate.

2. Chain propagation

Here addition of monomer molecules to the intermediate takes place one by

one leads to the formation of macro-radicals.

3. Chain termination

The growing polymer chain is terminated by many ways.

a) Recombination

Combination of two free radicals leads to termination.

At 60oC poly styrene or Acrylonitrile chains terminate mainly by recombination.

b) Disproportionation

Transfer of ‘H’ atom from one radical to another leads to formation of two
macro molecules, one of them with a double bond.

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 IONIC POLYMERIZATION

CATIONIC POLYMERIZATION

Monomers with electron releasing groups (-OCH3, -OC2H5& -C6H5 etc)

undergo cationic polymerization in the presence of Lewis acids like AlCl3, BF3, SnCl4
etc. Cationic polymerization takes place with higher rates even at low temperature.

Mechanism of cationic polymerization

It involves three steps.

1. Initiation
H+ ion is produced from Lewis acid and it forms cation with monomer.

Where, X is electron releasing group.

2. Propagation
Monomers are added to monomer cation in a sequence and length of
polymer chain increases gradually.

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 3. Termination
Growing polymer chain is stopped by removing H+ ion from the chain.

ANIONIC POLYMERIZATION

Monomers with electron withdrawing groups (-CN, CH3COO- and

C6H5etc) undergo anionic polymerization in presence of sodium or potassium amide.

Mechanism of anionic polymerization

It involves 3 stages.

1. Initiation

Anion is generated on reaction of potassium amide with monomer.

X = electron withdrawing group.

2. Propagation

Monomer units are added to anion one after the another and growth of
polymer chain is continued.

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 3. Termination

Growing polymer chain is stopped by neutralizing the negative charge on

growing chain.

ZIEGLER – NATTA CATALYSIS (OR) CO-ORDINATION POLYMERIZATION

 Ziegler Natta catalyst is useful in synthesizing stereo regular polymers

commercially.
 This catalyst is a co-ordination catalyst, consists of two components of catalyst
and co-catalyst.
MECHANISM

 Preparation:
 The active Ziegler – Natta catalyst is formed by chemisorption of aluminium
alkyl on TiCl4 crystal.
 Heating the monomers at 100oC at 10atm in presence of Ziegler Natta catalyst
forms stereo regular polymers.

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 1. Initiation
 Monomer forms -complex with active catalyst by co-ordination bond and with
empty orbital of titanium.

2. Propagation

 In this step monomers are added one after another in between the metal and
ethyl group in the same manner as in initiation step. Chain growth is continued.

3. Termination
 The polymer chain is separated from the catalyst by the addition of molecules
containing active hydrogen (HX). Chain growth is stopped.

APPLICATIONS

 Ziegler Natta catalyst is used for synthesizing the Syndiotactic and Isotactic
polymers.
 Co-polymers, like ethylene and propylene are obtained by using Ziegler Natta
catalysts, which are excellent elastomers.
 It is used for synthesizing the cis-1,4 poly isoprene which is identical to natural
rubber.

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STEP-GROWTH POLYMERIZATION OR CONDENSATION POLYMERIZATION

1. In this polymerization, Polymersare formed by the condensation of two or more

monomers with the elimination of small molecules like H2O,NH3.
2. By products are formed.
3. Monomers with functional groups undergo condensation polymerization.
4. The polymers are formed by step wise reactions.
5. It is also known as Step growth polymerization.
6. The molecular weight of polymer is not equal to the sum of molecular weights
of monomers.

Example-Preparation Of Nylon6,6

Monomers are adipic acid, hexamethylene diamine

Preparation Of Polyester

 Momomers are1,4-benzenedicarboxylic (terephthalic acid) and 1,2-ethanediol

(ethylene glycol)

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Preparation Of Polyamide

Differences between Addition (Chain Growth) & Condensation (Step Growth)

Polymerization

Chain Growth Polymerisation Step Growth Polymerisation

(Addition) (Condensation)
Polymer is formed by addition of Polymer is formed by combination of two or
monomers without elimination of more monomers with elimination of small
small molecules. molecules like HCl, H2O, NH3 etc.
No by-products are formed. By products are formed.
Monomers with unsaturation undergo Monomers with functional groups undergo
addition polymerization. condensation Polymerisation.
It requires Initiator. It requires Catalyst.
Chain reaction takes place. No chain reaction takes place.
Homo chain polymers, generally Hetero chain polymer either thermo plastic
thermo plastic is obtained. or thermo setting can be obtained.
Proceeds by chain growth mechanism. Proceeds by step growth mechanism.
Molecular Weight of polymer is equal Molecular Weight of polymer is not equal to
to the sum of the monomers. the sum of the monomers.

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 PLASTICS

Introduction:
 The Word Plastics is derived from Greek Word ‘Plastikos’ meaning capable of
being moulded [or] shaped.
 Plastics can be moulded [or] pressed [or] casted [or] extruded into various
shapes like plates, tubes, bottle, boxes, fibers etc.
 Plastics materials have
 Sufficient rigidity
 Mechanical strength
 Insulation Property
 Low density
 Low cost
 Light weight
 Resistance to chemicals, corrosion, insect abrasion etc to shape them into
desired article.

Depending on physical properties, plastics are divided into two types

1. Thermoplastic
2. Thermosetting
THERMOPLASTICS
1. Thermoplastic can be synthesized by the process called addition polymerization
2. They are linear (or) branched linked structures.
3. Polymers chains are held together by weak attractive forces.
4. They soften on heating and stiffen on cooling.
5. They have low melting point
6. They have low tensile strength
7. These types of plastics are low in molecular weight.
8. They are soluble
9. Here monomer is generally bifunctional
10.They can be remolded, reshaped and reused.
11.They can be recycled.
12.They are tough.
13.Example: polyvinyl chloride, polyethylene.
THERMOSETTING
1. Thermosetting plastic is formed by the process of condensation polymerization.
2. They are cross linked (or) three dimensional structures.
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 3. Polymers chains are held together by covalent cross links.
4. They don’t soften on heating.
5. These types of plastics have more melting point
6. These types of plastics have more tensile strength.
7. These are higher in molecular weight compared to thermoplastic.
8. They are not soluble.
9. The monomer is generally polyfunctional.
10.They cannot be remoulded.
11.They cannot be recycled.
12.They are brittle.
13.Example: urea formaldehyde, melamine formaldehyde.

POLY VINYL CHLORIDE(PVC)

Preparation:
Polyvinyl chloride is prepared by heating a water emulsion of vinyl chloride in
presence of benzyl peroxide or hydrogen peroxide in autoclave under pressure.

Properties: Polyvinyl chloride is

1. Colourless
2. Odourless
3. Non-inflammable
4. Chemically inert
5. Soluble in hot ethyl chloride
Uses: Used for the preparation of
1. Safety helmets
2. Light fittings
3. Tyres
4. Refrigerator components
5. Piping
6. credit cards
7. Medical devices and wire & cable insulation.
8. Window profiles, flooring and roofing

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 TEFLON (POLY TETRA FLOURO ETHYLENE ,PTFE) OR FLUON
Preparation:
Poly tetra flouro ethylene is prepared by polymerization of a water emulsion of
tetra flouro ethylene in presence of Benzoyl peroxide under pressure.

Properties:
1. Due to presence of highly electro negative fluorine atom, very strong attractive
forces between different chains.
2. Due to strong attractive forces
a) Teflon is extreme tough
b) High softening point ( >3500 )
c) High chemical resistance towards all chemicals except hot alkali metal
and hot fluorine
Uses: Used as
1. Insulating material for motors, cables
2. It is used in making waterproof fabric.
3. It is used in making non-stick cookware.
4. It is used in making an anti-friction device.
5. It is used for coating medical appliances (surgical devices).
6. Due to its high resistance to corrosion, it is used for coating the lining of
laboratory appliances.
7. Personal care products
8. Making artificial body parts

PHENOL FORMALDEHYDE RESINS: BAKELITE

Preparation:
 These are formed by the poly condensation between phenol and formaldehyde.
 The reaction is catalysed by acid or base.
Step I:- Formation of ortho and para hydroxy benzyl alcohols from phenol
and formaldehyde

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Step II:- Formation of Novalac from ortho-hydroxy,benzyl alcohol

Step III:- Formation of Bakelite from Novalac

Properties: These are

1. Rigid
2. Hard , resistant to heat
3. With stand to high temperature
4. Good insulator
5. Low electrical conductivity
6. Scratch-resistant.
Uses: Used for the preparation of
Electrical insulator parts like
1. Switches
2. Plugs

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 3. Handles
4. Manufacture of clocks
5. Buttons
6. Washing machines
7. Toy
8. Kitchenware
9. Moulded articles like
a. Telephone parts
b. Cabinets for T.V
c. Cabinets for radio

NYLON-6,6

 The monomers used to prepare Nylon-6,6 are adipic acid and

hexamethylenediamine.
 Nylon-6,6 is prepared by condensation polymerization of hexamethylene
diamine with adipic acid at high temperature and pressure.
The preparation of Nylon-6,6 is as follows.

Properties:
1. High melting point
2. Good strength
3. These are light and tough.
4. Flexible
5. High abrasion resistance
6. Lustrous
7. Elastic and are very strong
8. Nylons dry quickly.
9. High resistance to fungi, insects, animals

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Uses: Used for making of
1. Socks
2. Undergarments Dresses
3. Carpets
4. Filaments For Ropes
5. Bristles For Toothbrushes
6. Swimwear Due toWaterProff
7. Fishnet.
8. Conveyor And Seat Belts
9. Airbags, Nets & Ropes
10.Raincoats And Cycle Wear.

CARBON FIBERS
 The raw material used to make carbon fibre is called the precursor.
 About 90% of the carbon fibers produced are made from polyacrylonitrile(PAN).
 The remaining 10% are made from rayon or petroleum pitch.
Preparation:
 There are three successive stages in the conversion of PAN into high-
performance carbon fibers.
Step-1: Oxidative stabilization:
 Polyacrylonitrile is oxidized in a temperature range of 200-300°C.
 This treatment converts thermoplastic PAN to a non-plastic cyclic compound.
Step-2: Carbonization:
 After oxidation, the fibers are carbonized at about 1000°C in an inert
atmosphere (normally nitrogen) for a few hours.
 During this process the non-carbon elements are removed as volatiles to give
carbon fibers with a yield of about 50%.
Step-3: Graphitization:
 The fibers are treated at temperatures between 1500-3000 °C, which improves
the ordering, and orientation of the crystallites in the direction of the fiber axis.

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Properties:

1. Light weight

2. High strength-to-weight ratio

3. Very High modulus elasticity-to-weight ratio

4. High Fatigue strength

5. Good corrosion resistance

6. Very low coefficient of thermal expansion

7. Low impact resistance

8. High electric conductivity

9. High cost

10. Biologically inert

11. X-ray permeable

12. Self Lubricating

Disadvantages:
 Relatively expensive
 It causes lung cancer
Uses:
1. Airspace and aircraft industries
2. Automotive body parts
3. Mobile cases
4. Musical instruments
5. Badminton racket
6. Golf stick

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 7. construction industry
8. Wind mill and turbine blades
9. Helmets
ELASTOMERS (RUBBERS)

 Rubber is an elastomer.
 A polymer which regains its original shape after removing applied force is called
elastomer.
 Natural rubber, Thiokol, neoprene etc.
Characteristics of Elastomers
 Elastomers regain original shape after removing stress.
 Elastomers are sticky at higher temperatures.
 Elastomers exist at above glass transition (Tg) temperature.
 Elastomers absorb moisture.
 Elastomers have less chemical resistance.
 Elastomers have weak intermolecular attractions.
 Elastomers have coiled structures.

Buna –S (or) SBR (styrene butadiene rubber):

 It is prepared by free radical polymerization in the presence of free
radical initiator cumene hydrogen peroxide.
 It is a copolymer consists of 75% butadiene and 25% styrene.

Properties:
 Excellent abrasion resistance.
 Very tough.
 high load bearing capacity
 Sensitive to oil, waste water and ozone.
 Good electrical properties.
 Poorer resilience than that of natural rubber.
Uses:
 Used for the manufacture of
o Tyres

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 o Shoes heels
o Shoe soles
o Gaskets
o Chewing gums
o Electrical insulation
o Floor tiles
o Foot wear components
Buna –N (or) Nitrile butadiene rubber (NBR):

 It is prepared by free radical polymerization in the presence of free

radical initiator cumene hydrogen peroxide.
 It is a copolymer of 75% butadiene and 25% acrylonitrile.

Properties:
1. It is oil resistance. If the content of acrylonitrile more than 40%
then it is extremely oil resistance.
2. Resistant to heat, light and acids.
3. High load bearing capacity.
4. It has good tensile strength
5. It has good abrasion resistance.
6. It is less resilient than natural rubber.

Applications:
Used for the manufacture of
1. Oils Hoses
2. Floor mats
3. Conveyer belts
4. Printing rollers
5. Tank lining
6. Disposable non-latex gloves,
7. Conveyor belts
8. Used as latex in textile and cloth.
9. Oil seals, adhesives

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 CONDUCTING POLYMERS

 The Polymers which conduct electricity are called conducting polymers.

Ex: Poly acetylene, poly aniline, poly pyrrole, poly thiophene, poly quinoline etc.
Based on their conduction properties conducting polymers are classified into two
types
 Intrinsically Conducting Polymers
 Extrinsically Conducting Polymers

INTRINSICALLY CONDUCTING POLYMERS

Conjugation
 These polymers contain conjugated or delocalized  - e- pairs in the backbone
responsible for conduction.

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Explanation:
 When the electron enters the chain, breakage of  - bond takes place and a
new  -bond is formed.
  -bond between 2&3 is broken and a new  - bond is formed between 1&2.
 Similarly,  -bond between 4&5 is broken and a new  -bond is formed between
3&4.
 If current flows into the polymer this process is continued and thereby a
conducting path is created in the polymer.

Doped conducting polymers:

 The conductance of the Polymers can be improved by doping process.
 Doping of conducting polymers can be two types.
o p-Doping (or) Oxidative Doping
o n-Doping (or) Reductive Doping
p-Doping (or) Oxidative Doping:
o In this method the polymer is treated with an oxidizing agent like Lewis acid
which acts as a dopant.
o Examples of dopants used: FeCl3, I2 etc.

Mechanism of p-Doping:
 During this process, oxidation of polymer takes place and forms a cation
called Polaron.
 Further oxidation of polymer results in the formation of a dication or
bipolaron.
 The charges get separated by forming a soliton pair.

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  Thus, facilitates the jumping of electrons from valency band to conduction
band and improves the conductance.

n-Doping (or) Reductive Doping:

 In this method, the polymer is treated with a reducing agent like a Lewis base
which acts as a dopant.
 Ex; Sodium Naphthalide Na+ (C10H8)-

Mechanism of n-doping:
 During this process, reduction of polymer takes place and forms an anion
called Polaron.
 Further reduction of polymer results in the formation of a dianion or bipolaron.
 The charges get separated to form a soliton pair.
 Thus, facilitates the jumping of electrons from valency band to conduction
band and improves the conductance.

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 Extrinsically Conducting Polymers
 The conductivity of these polymers is due to the presence of externally added
ingredients.
 There are two types.
o Conductive Element Filled Polymers
o Blended Conducting Polymers
Conductive Element Filled Polymers
 The polymer acts as a ‘binder’ to hold the conducting element such as carbon
black, metallic fibers, metallic oxides etc.
 It improves the conductivity of polymers.
 Advantages: Low Cost Easy to Fabricate into any design Light weight
Mechanical Durability
 Applications: They are used in hospitals and operation theatres.

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Blended conducting polymers:
 The polymers are blended with a conducting polymer to improve physical,
chemical, electrical and mechanical properties.
 Eg; 40% pyrrole blended with a polymer gives conducting polymer with good
impact strength.
 Applications: They are used for making analytical sensors, ion exchangers,
optical fibers, photovoltaic devices etc.

Applications of Conducting Polymers in Biomedical Devices

Conducting polymers are used
1. As artificial devices like Heart valves, kidneys, and lungs.
2. As bone cement used for some fracture repairs.
3. As artificial teeth.
4. In the preparation other medical devices include sutures, pins, screws used
during surgery on bones, ankles, hands etc.
5. To prepare contact lenses which permit O2 to the eyes.
6. In rechargeable batteries.
7. In analytical sensors of pH, O2, NO2, SO2, NH3 etc.
8. In photo voltaic cells. Ex; Al/polymer/Au.
9. In telecommunication systems.
10. In transistors and diodes.
11. In solar cells.
12. As wiring in aircraft and aerospace parts.
BIODEGRADABLE POLYMERS
 Biodegradation is the chemical breakdown of materials by physiological
environment.
 Some polymers undergo degradation when exposed to moisture, heat, oxygen,
ozone and microorganisms.
 During biodegradation, microorganism secrets biosurfactant which facilitate
degradation easily.
 These organic materials can be degraded either aerobically or anaerobically.
 These agents change the chemical structure of the polymer and lead to
changes in properties of polymer.
 The activity of aerobic bacteria is measured by the amount of O2 consumed or
the amount of CO2 produced.
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  The activity of anaerobic bacteria is measured by the amount of CH4 gas
produced.

Properties:

 These are non – toxic.

 They can maintain good mechanical integrity until degrade.

 Capable of controlled rates of degradation.

Applications:
 It is used in drug delivery systems.
 It is used to coat a stent and release drugs in a controlled way.
 It is used in dental devices and orthopedic fixation devices.
Poly Lactic Acid (PLA):
It is a biodegradable thermoplastic polyester belonging to the class of poly hydroxy
alkanoates, derived from renewable sources such as starch, sugarcane etc.
The structure of Poly Lactic Acid is as follows.

Properties:
1. It is a chiral compound existing as l – lactic acid (PLLA).
2. The Glass transition temperature is 60 – 65OC.
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 3. The melting point is 173 – 178OC.
4. High grease and oil resistance
5. Good biocompatibility
6. High strength and modulus.
Applications:
1. It is widely used for making medical implants like anchors, screws, pins, mesh
etc.
2. It is also used for making compostable packing material, disposal garments,
diapers, food packing, 3D printers etc.

Poly Glycolic Acid (PGA):

 It is a biodegradable thermoplastic polyester which is prepared
from glycolic acid by polycondensation.
 The structure of Poly Glycolic Acid is as follows.

Properties:
1. The glass transition temperature is 36 – 40OC.
2. The melting point is 224 – 230OC.
3. High tensile strength
4. High resistance to common organic solvents
5. High heat distortion temperature
6. High stiffness
7. Fast biodegradability and Compostability
Applications:
1. It is widely used for making absorbable sutures which are used in general
surgery and gynecological procedures.
2. It is also used in the food packaging industry.

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Dhanekula Institute of Engineering &Technology
 QUESTION BANK

1. Explain the following terms with examples

a. Polymer
b. Degree of polymerization
c. Functionality
2. Explain coordination polymerization mechanism with example
3. Explain chain growth polymerization mechanism with example
4. Explain step growth polymerization mechanism with example
5. List the differences between the following with suitable examples.
a. Thermosetting resins from thermoplastics resins
b. Homo polymer from co-polymer
6. Give an account of preparation, properties and uses of the following
a. Bakelite
b. PVC
7. Give an account of preparation, properties and uses of the following
a. Teflon
b. Nylon6,6
8. write preparation, properties and uses of Carbon fibres
9. Give an account of preparation, properties and uses of the following
a. Buna-N
b. Buna-S
10.What are biodegradable polymers write examples and their significance?
11.What are conducting polymers? How are they classified?
12.Write the mechanism of conduction in conducting polymers and their
engineering applications.

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Dhanekula Institute of Engineering &Technology