Polymer chemistry

Dr. Damodar Koirala
Polymer Chemistry
Polymer Chemistry
Dr. Damodar Koirala | koirala2059@gmail.com
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Polymers: Terminologies
 The word polymer has a Greek origin, which means many
units (parts). Polymer is defined as a chemical substance of a
high molecular mass formed by the combination of a large
number of simple molecules, called monomers
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 The process by which the monomers get combined and
transformed into polymers. is known as polymerization

Classification of polymers
On the basis of origin
 Natural polymers: occur in nature (plants or
animals) eg: natural rubber
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 Synthetic polymers: prepared in the
laboratory e.g. polythene

On the basis of structure
 Linear polymers: monomers are linked to form long
linear chains. eg. High density polyethene
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 Branched chain: monomers are linked to form chains
with some branches.eg. Low density polyethene
 Cross-linked: monomer are linked to form three
dimensional network eg. bakellite

On the basis of monomers
 Homopolymer: the polymer which is formed by
combination of same monomer unit. eg: polyethene
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 Copolymer: the polymer which is formed by
combination of two or more different types of monomer
unit eg: nylon-66

On the basis of synthesis
 Condensation polymer: The polymers which are formed by
the combination of monomers with the elimination of small
molecules such as water, alcohol, hydrogen chloride. e.g., nylon-
6,6 is formed by the condensation of hexamethylene diamine with
adipic
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adipic
 Addition polymers: The polymers formed by the
polymerization of monomers containing double or triple bonds
(unsaturated compounds). Addition polymers have the same
empirical formula as their monomers. eg: polyethene, PVC

On the basis of molecular force
 Elastomers: polymer chains are held by weakest
intermolecular forces. eg: natural rubber
 Fibres: are thread-like and can be woven into fabrics.These
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 Fibres: are thread-like and can be woven into fabrics.These
are widely used for making clothes, nets, ropes

On the basis of action of heat
 Thermoplastics: melt on heating and set hard on cooling, thus,
they can be cast into different shapes using suitable moulds.These
are linear polymers and have weak van derWaals’ forces in chains.
eg: polyethene and polystyrene
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 Thermosetting plastics:When heated, they become hard and
infusible due to the cross-linking between the polymer chains.
Thus they can not be casted into different shapes. These are
normally semifluid substances with low molecular masses. eg:
bakelite

Important artificial polymer
Addition polymer (also homopolymer)
 Polyethene
 Polyvinyl chloride
 Teflon
 Rubber (natural rubber)
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Rubber (natural rubber)
 Silicon
Condensation polymer (copolymer)
 Polyester/Terylene / Dacron
 Nylon-6,6
 Bakelite
 Polyurethene

Polymers: polyethene
Preparation: heating ethylene in presence of organic peroxide catalyst
Polymerization
organic peroxide, Δ
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Properties: tough and flexible, chemically inert
Uses: for making film, for general packaging, for making moulded toys
Ethene
monomer
polyethene
polymer

Polymers: polyvinyl chloride (PVC)
Preparation: heating vinyl chloride with benzene peroxide as
catalyst
Polymerization
Cl Cl
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Properties: inflammable , excellent oil resistance, hard
Uses: in making sheet , for making pipes and bottles
Polymerization
Vinyl chloride
monomer
polyvinylchloride
polymer

Polymers: Teflon
Preparation: heating tetrafluoroethene with benzene peroxide as
catalyst
Polymerization
F F
F F
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Properties:Tough ,chemically inert, good electric insulator
Uses: making artificial limb, non-sticky coating on utensils
tetrafluoroethene
monomer
Polytetratfluoroethene (Teflon)
polymer
F F F
F

Preparation: heating 1,3-butadiene with benzene peroxide as
catalyst
Polymers: natural rubber
Polymerization
Properties: soft and sticky
Uses: not much used because at higher temperature, it becomes soft
and at low temperature, it becomes brittle.
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2-methyl-1,3-butadiene
or isoprene
monomer
rubber
polyisoprene
polymer

Polymers: polystyrene
Preparation: heating styrene with benzene peroxide as catalyst
Polymerization
Ph Ph
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Uses: in making disposable cups, food containers and in insulation
styrene
monomer
polystyrene
polymer

Polymers: orlon
 Preparation : heating vinyl cyanide with FeSO4 as
catalyst
Polymerization
CN CN
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 Uses: in making sweater and bathing suits
Vinyl cyanide
monomer
orlon
polymer

Polymers: polyester / terylene / dacron
 Preparation: by the condensation polymerization of
ethylene glycol (1,2-Ethanediol) and dimethylterephthalate
+ n
n
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 Uses: in making ropes, nets with high tensile strength
Ethylene glycol terephthalic acid
Terylene or dacron
+
n

Polymers: benzene
 Preparation: by heating acetylene in red-hot Fe or red-hot Cu
tube
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 Uses: used to make plastics, resins, synthetic
fibers, rubber lubricants, dyes, detergents, drugs and pesticides
Acetylene
monomer
benzene
polymer

Polymers: nylon-6,6
Preparation: the condensation polymerisation of adipic acid with
hexamethylene diamine
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Properties: high elastic strength, good heat and chemical resistance
Uses: in making gear parts, combs, brushes, carpets

Polymers: nylon-6
Preparation: the condensation polymerisation of 6-aminohexanoic
acid
+
19

Polymers: nylon-6
Preparation from e-caprolactam
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oxime
cyclohexanone

Polymers: nylon-6
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Polymers: bakellite
Preparation: by the condensation reaction of phenol with
formaldehyde in the presence of acid or a base catalyst.
+ [OH-]
+
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+ +
o-hydroxy benzyl alcohol
p-hydroxy benzyl alcohol
Phenol formaldehyde
monomers
polymerization
Bakelite
polymer
Properties: hard, rigid, and strong
Uses: on door, switches, handle for cooker

Polyethene
 Low Density polyethene (LDPE)
 Preparation: By polymerization of ethylene at high pressure of 1000-
5000 atm and about 250C temperature in presence of organic peroxide
as catalyst
 Properties:
 It is tough and flexible even at low temperature
It is chemically inert and has good chemical resistance
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 It is chemically inert and has good chemical resistance
 It is non polar hence it is not excellent electric insulation properties
 During propagation step, large number of chain transfer reaction
occur and branch chained structure can be prepared
 Uses:
 LDP is used for making film, for general packaging and carrier bags
 For making molded toys, ink tubes in pen and mugs

Polyethene
 High Density polyethene (HDPE)
 Preparation: By polymerization of ethylene at pressure of 6-7 atm and
about 65C temperature in presence of Zeigler Natta Catalyst (TiCL4 +
Al(C2H5)3
 Properties:
The HDPE molecules are linear and their packing is easy
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The HDPE molecules are linear and their packing is easy
Softening temperature of HDPE is 135C, which is higher than LDPE
It is excellent chemical resistance material
It is free from order and toxicity
Better resistance to oxidation and UV rays
 Uses:
Domestic water pipes, making crates, food tubes, tanks milk bottle

PVC
 Rigid PVC
 Preparation: By heating vinyl chloride in presence of small amount of
benzene peroxide or hydrogen peroxide as catalyst under pressure.
 Properties:
It is inflammable in nature
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It is orderless, colorless powder
It is hard and resistant to heat and chemicals.
This increases the stiffness of molecule due to the presence of
chlorine atom on the alternate carbon atom
 Uses:
It is used in making sheet , pipes and bottles
It has greater potential importance to building industries

PVC
 Plasticized PVC
 Preparation: By heating vinyl chloride in presence of small amount of
plasticizer such as DOP (Di-octylphthalate)
 Properties:
It is good insulator for direct current and low frequency AC.
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It is orderless, colorless powder
It is hard and resistant to heat and chemicals.
 Uses:
It is used for making plastic rainware, plastic shoes, leather clothes

Silicon Rubber
 Preparation: By mixing linear di-methyl silicon polymer with
fillers (SiO2) and peroxide containing curing agent.
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Silicon Rubber
 Properties:
 They have resistance to prolongation to sunlight, heat, dilute acid and
alkali solution
 They remain flexible in the temperature range of 90 to 250 C, hence
used to make tyre of fighter air-crafts
 At high temperature it decompose leading behind non conducting
SiO2 instead of carbon
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SiO2 instead of carbon
 Uses:
 Used as sealing material in searchlight and in aircraft engine
 Used in making lubricant, protective coating, insulation for washing
machine and electrical equipment
 Used in making artificial valves of heart

Polyurethelene
 Preparation: By rearrangement polymerization of di-isocyanate with
dihydric alcohol. They contain urethane linkage (-NH-COO-)
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Polyurethene
 Properties:
 Less stable at elivated temperature
 Their saturated character make them highly resistance to oxidation
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 They are good resistance to many organic solvents and attracted by
hot and conc acid and alkali solution.
 Uses: For coating of gymnasium and dance floor, for enhancing the life
of tyre threads, in making car and furniture cushions.

Free Radical Mechanism
 It involves formation of free radical
 Step I Chain initiation step: In this step, peroxide undergoes homolytic
fission, e.g. benzoyl peroxide on heating produces phenyl initiator free
radical.
 Step II Chain propagation step: The new free radical adds to another
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 Step II Chain propagation step: The new free radical adds to another
molecules of monomer to form a larger free radical.
 Step III Chain termination step: Two radicals react and form stable
compound
 For: Polyethene, PVC, Teflon

 Step I Chain initiation step: In this step, peroxide undergoes
homolytic fission, e.g. benzoyl peroxide on heating produces
phenyl initiator free radical.
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Ph-CO-O-O-CO-Ph 2 Ph-CO-O.
Ph-CO-O. Ph. + CO2

 Step II Chain propagation step: The new free radical
adds to another molecules of monomer to form a larger
free radical.
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 Step III Chain termination step: Two radicals react and
form stable compound
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Polymer chemistry

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