CHD-1182-1.ppt

Course Code: CHD 1182
Title of the Course: Chemistry for Electrical and Electronic
Engineering
Department: Chemistry
Polymers for Electrical and Electronic Applications: Classification: source,
heat, composition – glass transition temperature – preparation, properties
and applications of polyethene (LDPE, HDPE), poly(vinyl chloride), PMMA,
polycarbonate, teflon, ABS, bakelite, urea-formaldehyde, epoxy resin -
conducting polymers: polyaniline, polyacetylene and poly(phenylene
vinylene), rubber-vulcanised rubber, ebonite, EPDM, polymer blends and
alloys - moulding techniques: injection moulding, compression moulding.
Module-I
1

What is the Polymer?
The word “Polymer” is derived from two Greek words, ‘Poly’ that
means many (numerous) and ‘Mer’ which means units.
2

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Classification of Polymers
1. Classification of polymers is based on their source of origin.
2. Classification of polymers based on their structure.
3. Based on Mode of Polymerisation.
4. Classification Based on Molecular Forces.

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1. The first classification of polymers is based on their source of origin
(i) Natural polymers
(ii) Synthetic polymers
(iii) Semi-Synthetic polymers

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(i) Natural Polymers
The easiest way to classify polymers is their source of origin.
Natural polymers are polymers which occur in nature and
are existing in natural sources like plants and animals.
Some common examples are proteins (which are found in
humans and animals alike), cellulose and starch (which are
found in plants) or rubber (which we harvest from the latex of
a tropical plant ).
The natural polymer polysaccharide cellulose

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(ii) Synthetic Polymers
Synthetic polymers are polymers which humans can
artificially create/synthesize in a lab.
These are commercially produced by industries for human
necessities.
Some commonly produced polymers which we use day to
day are polyethylene (a mass-produced plastic which we use in
packaging) or nylon fibers (commonly used in our clothes,
fishing nets etc.)

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(iii) Semi-synthetic Polymers
Semi-Synthetic polymers are polymers obtained by making
modification in natural polymers artificially in a lab.
These polymers formed by chemical reaction (in a controlled
environment) and are of commercial importance.
Example: Vulcanized Rubber ( Sulphur is used in cross
bonding the polymer chains found in natural rubber)
Cellulose acetate (rayon) etc.

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Classification Based on Structure of Polymers
2. Classification of polymers based on their structure can be of three
types:
(i) Linear polymers:
(ii) Branch chain polymers:
(iii) Cross-linked or Network polymers:

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(i) Linear Polymers:
These polymers are similar in structure to a long straight
chain which identical links connected to each other.
These polymers have high melting points and are of higher
density.
A common example of
this is PVC (Poly-vinyl
chloride).

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(ii) Branch Chain Polymers:
As the title describes, the structure of these polymers is like
branches originating at random points from a single linear
chain.
Monomers join together to form a long straight chain with
some branched chains of different lengths.
Low-density polyethylene
(LDPE) used in plastic bags and
general purpose containers is a
common example.

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(iii) Crosslinked or Network Polymers:
In this type of polymers, monomers are linked together to
form a three-dimensional network.
These polymers are brittle
and hard.
Ex:- Bakelite (used in
electrical insulators),
Melamine-formaldehyde
polymer etc.

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Classification Based on Mode of Polymerisation
3. Based on Mode of Polymerisation
i) Addition polymers.
ii) Condensation polymers.

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i) Addition Polymers:
These type of polymers are formed by the repeated addition of
monomer molecules.
The polymer is formed by polymerization of monomers with
double or triple bonds (unsaturated compounds).
Example: ethene
n(CH2=CH2) to polyethene -
(CH2-CH2)n-.

15
ii) Condensation Polymers:
These polymers are formed by the combination of monomers,
with the elimination of small molecules like water, alcohol etc.
A common example is
the polymerization of
Hexamethylenediamine
and adipic acid to give
Nylon–66 where
molecules of water are
eliminated in the
process.

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4. Classification Based on Heat
i. Thermoplastics.
ii. Thermosetting.
Classification Based on Heat

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Thermoplastics:
Thermoplastic polymers are long-chain polymers in which
inter-molecules forces (Van der Waal’s forces) hold the
polymer chains together.
These polymers when heated are softened (thick fluid like)
and hardened when they are allowed to cool down, forming
a hard mass.
They do not contain any cross bond and can easily be shaped
by heating and using moulds.
A common example is
Polystyrene or PVC
(which is used in
making pipes).

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Thermosetting:
Thermosetting are polymers which are semi-fluid in nature
with low molecular masses.
When heated, they start cross-linking between polymer
chains, hence becoming hard and infusible.
They form a three-
dimensional structure on the
application of heat. This
reaction is irreversible in
nature.
The most common example of
a thermosetting polymer is
that of Bakelite, which is used
in making electrical insulation.

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Glass Transition Temperature (Tg)
The glass transition temperature (Tg) of a polymer is the
temperature at which an amorphous polymer moves from a
hard or glassy state to a softer, often rubbery or viscous state.
Below Tg: Polymers are hard and brittle like glass, due to lack
of mobility.
Above Tg: Polymers
are soft and flexible
like rubber due to
some mobility.
Above Tg: the
physical and
mechanical properties
of polymer change.

21
Low Density Polyethene (LDPE)
Preparation:
The common method for the preparation of LDPE is polymerization
of ethylene monomer at high pressure (1000 - 4000 atm) and
temperature (2500C) in presence of oxygen/peroxide/hydro
peroxide(H2O2, free radical generator).
In this process huge branched chains are formed through out every
long back bone chain.

22
Properties of Low Density Polythene:
Low density polyethylene have density is low.
It is branched chain addition polymer.
Semi crystalline polymer having crystallinity 45-50 percent.
Chemically inert, nonpolar and having dielectric property
zero.
Tough but flexible.
Melting point 105- 110 0C.
Low Density Polythene (LDPE)

23
Applications of Low Density Polythene:
As LDPE is a good insulator they normally used for the
preparation of electrical wires and cables.
Pouch pack, squeeze bottles, delivery pipes are prepared
from LDPE.
Toys, refill for ball pen and ball pen also prepared from
LDPE.
Low Density Polythene (LDPE)

24
High density Polythene(HDPE)
Preparation:
The common method for the preparation of HDPE is by the
polymerization of ethylene monomer.
The high pressure (30 - 35 atm) and temperature (70-2000C) in
presence of metal oxide catalyst like CrO3 on silica alumina.
The low pressure (5 - 7 atm) and temperature (60-700C) in
presence of Zieglar Natta catalyst like triethyl aluminum and
titanium tetrachloride.

25

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Properties:
High density polyethylene have high density (0.95 to 0.97
gm/cc).
It is less branched.
Highly crystalline polymer having crystallinity 80-90 percent.
Chemically inert, nonpolar and having dielectric property
zero.
Highly tough but flexible.
Melting point 130-135 0C.

27
Applications:
As HDPE is a good insulator they normally used for the
preparation of high performance electrical cables.
Bucket, cup, toys are prepared from LDPE.
Due to inertness it is used for the storage of H2SO4, pipes for
LPG gas and water reserver also.

35
Phenol and Formadehyde: Bakelite
Phenol formaldehyde is an important polymer in making
different composite materials as well plywood.
It is a brown black color viscous liquid prepared from
phenol and formaldehyde at a temperature 140-145 0C in
presence of catalyst called resol.
At high temperature poly condensation takes place and it
becomes three dimensional cross linked, brittle and hard
mass solid called BAKELITE.
Bakelite is formed through methylol(-CH2OH formation
which ultimately converted to methylene(-CH2-) by removal
of water molecule.
Generally,phenol-formaldehyde polymer are two types-
1) Novoloc
2) Resol.

37

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Properties:
It is high thermal and electrical resistance.
It is malleable and liquefiable when heated and becomes
permanently hard after cooling.
 It is hard rigid and scratch proof.
It is resistant to many inorganic and base and many other
chemical actions.
It can be made into a variety of bright colors.
Bakelite can be quickly moulded or casted.
So it is also known as thermosetting plastic.

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Applications:
Bakelite is a good insulator used in non-conducting parts of
radio and electric devices like switches, automobile
distribution caps, insulation of wires, Sockets, etc.
It is used to make clocks, buttons, washing machines, toys,
kitchenware, etc.
It can be made into different colours so it is used in
producing vibrant and attractive products.

40
What is Poly(methyl methacrylate) (PMMA)?
PMMA-is the Poly(methyl methacrylate) (C5O2H8)n.
It is a thermoplastic and transparent plastic.
Chemically it is a synthetic polymer of methacrylate.

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Poly(methyl methacrylate) (PMMA)
Preparation of Poly(methyl methacrylate):
Materials Required:
Methyl methacrylate (MMA), N,N-dimethylaniline, benzoyl
peroxide, boiling chip, methanol, acetone, alumina.
Procedure:
1) 10 ml of MMA was added with 1 drop of N,N-
dimethylaniline and 0.1 g benzoyl peroxide. The mixture
was placed in boiling water bath.
2) At 3 minutes interval, 1 drop
of aliquot was transferred
into a test tube with
methanol. Observation was
recorded.
3) After 15 minutes, boiling tube was cooled and polymer was
dissolved in 10-15 ml of acetone.

43
4) While stirring vigorously, the polymer solution was poured
into a beaker containing 80-100 ml methanol.
5) Precipitated polymer was collected by vacuum filtration.
The percent conversion i.e., yield was determined.
Poly(methyl methacrylate) (PMMA)

44
PMMA is amorphous commodity thermoplastics of highly
transparent.
The poly(methyl methacrylate) (PMMA) also known as
Plexiglas, Lucite, Acrylite, and Altuglas.
It is a high volume amorphous thermoplastic with high Tg
(398 K), good mechanical properties and excellent
weatherability.
It is resistant to oils, alkanes and (diluted) acids but is not
resistant to many (polar) solvents such as alcohols, organic
acids and ketones.
It is also rather brittle and has low impact strength and
fatigue resistance.
It is transparent to visible light up to 97% (3-mm thickness).
Poly(methyl methacrylate) (PMMA): Properties

45
Exterior lights of automobiles.
Viewing dome in airbus, helicopters.
Poly(methyl methacrylate) (PMMA): Applications
Used in aquariums At Residents

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Helmets Visor Aircraft windows panes
Daylight redirection. In orthopaedics as bone cement

47
Used to affix implants and
remodel lost bones.
As paint: acrylic paint is the
PMMA suspension in water

48
Polytetrafluoroethylene (PTFE) or Teflon

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50

51

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Applications of PTFE
Because of its low coefficient of friction or non-adhesive characteristics
Coating other metal objects (for Non-stick equipment)
In clothing fabrics.

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Acrylonitrile Butadiene Styrene (ABS) Copolymer
These materials are complex blends and copolymers of
Acrylonitrile, butadiene and styrene.
In most types, Acrylonitrile and styrene are grafted onto a
polybutadiene backbone. The product also contain unreacted
polybutadiene and some acrylonitrile styrene copolymer.

57
ABS Car Dashboard ABS car interiors
ABS Car bumper ABS meter box
Applications of ABS

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Require Materials:
Paraformaldehyde, Urea and Potassium hydroxide (KOH).
Synthesis of UF Resin:
Paraformaldehyde, urea and potassium hydroxide were
milled by a grinder respectively and then were charged into a
reactor in the molar ratio of 1:4:0.8.
KOH dosage was used to adjust pH value of the reaction
mixture to 9.
Urea-formaldehyde Resin
Then, the reactor
was placed in an
oil bath at 60 °C
for 1.5 h under
stirring.

59
The reaction product was precipitated into dimethyl
sulfoxide and washed with ethanol several times to remove
unreacted paraformaldehyde and urea.
The precipitating–washing process was repeated three times.
After purification, the product was dried in a vacuum oven
at room temperature overnight.

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Properties:
Urea-formaldehyde (UF) products (also called aminoplasts or
carbamide-methanal) are highly crosslinked, semi-crystalline
thermosetting plastics.
The UF resins are noted for their high strength, rigidity, cost
effectiveness, and fast cure.
Has a property of high surface hardness.
Has the capacity of low water adsorption.

62
Applications
Electrical castings.
Tableware.
Decorative worktop laminates.
Plug and switches buttons.
Paints
Surface coating.
It is used as an adhesive for decorative laminate applications.

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Epoxy Resins
Reactive polymers/prepolymers which contain epoxide
groups.
Can undergo crosslinking reactions (referred to as curing)
with itself or amines, acids, phenols to give co-polymers.
Use as structural adhesives, metal coatings, electronic and
electrical components, electrical insulators, plasticizers of
vinyl polymers.

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Epoxy Resins
Require Materials
Epichlorohydrin, bisphenol-A, sodium hydroxide, and
dimethyl sulfide, toluene, methanol, and pyridine.
Synthesis of epoxy resin:
3.0 gram of bisphenol-A is added into a boiling tube
containing a solution of 15 ml water and 1.0 g NaOH.
The reaction mixture is heated to 45 °C under water bath.
Then, 2.0 g of epichlorohydrin is mixed into it. Temperature is
raised to 90 °C. Continuous stirring is done using a glass rod.
After 30-40 minutes of heating, solution mixture is cooled.
Aqueous layer is decanted.
20 ml of water is added to the mixture and again decanted.
After washing for 2-3 times, residue is filtered and dried.

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Epoxy Resins
Scheme for the synthesis of epoxy resin:

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Epoxy Resins
Properties
Chemical stability due to ether linkage.
High reactivity due to the epoxy/hydroxyl groups.
Excellent adhesion to the surfaces.
Low shrinkage.
Excellent weather/chemical resistance.
Outstanding electrical properties thus, industrial applications.
Ability to form copolymers with various applications.

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Epoxy Resins
Applications
Paints and coatings.
It is used as adhesives.
Industrial tooling and composites.
Electrical systems and electronics.
Petroleum and petrochemicals.
Consumer and marine applications.
Aerospace applications.
Biology.

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Books to consult
1. P. C. Jain and Renuka Jain, “Physical Chemistry for
Engineers”
2. A. Ravikrishnan, “Engineering Chemistry”

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