ENGINEERING CHEMISTRY
Dr. Sarvajith M S, MSc, PhD
Assistant Professor GRADE-III
Department of Chemistry
NMAM Institute of Technology
NITTE.
10/19/2022
Sub code:20CY110
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POLYMERS
Introduction to Polymers
The word polymer is derived from the two Greek words Poly meros
Poly meros
poly = many
mers = units
Definition:
A polymer is a macromolecule (giant molecule of high molecular
mass) built-up by the linking together of a large number of simple
molecules (monomers).
Monomers
A monomer is a simple molecule having
two or more bonding sites through which
each can link to other monomers to form a
polymer chain.
Monomers = Building blocks of polymers
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POLYMERS
Examples:
Polythene or Polyethylene(PE)
Polyethene Bags
Pipes, Sheets
Polyvinyl chloride (PVC)
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Polypropylene (PP)
Plastic materials
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POLYMERS
Polymerization
Many Small Units or micro molecule)
(low molecular weight)
Monomers
macro molecule or Giant molecule
(High molecular weight)
Polymers
A monomer is a simple molecule having two or more bonding sites through which
each can link to other monomers to form a polymer chain.
The total number of functional groups or
bonding sites or reactive sites present in a monomer molecule is called
functionality of the monomer.
Functionality of Monomer:
Monomers = must contain at least 2 reactive sites or
bonding sites
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POLYMERS
Essential features of Monomers to form polymers
• It should be having low molecular weight
• It should contain at least 2 or more functional groups
• It should contain at double or triple bond
Example for Monomers
Some bi functional hydrocarbons
2-COOH groups
adipic acid
Ethylene glycol
2-OH groups
2-NH2 groups
1,6-hexanediamine
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POLYMERS
Example for Monomers
Some tri functional hydrocarbons
3-OH groups
Glycerol
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POLYMERS
Polymerization:
The chemical process by which the monomers
(low molecular weight) are converted into polymers (high molecular
weight).
Example:
Polyethylene or Polythene is formed by linking a large number of ethene molecules
Polystyrene is formed by linking styrene molecules
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POLYMERS
The number of repeating units (n) in the chain is known as the
Degree of polymerization (DP).
n
Degree of polymerization (DP).
Molecular weight of polymer = DP × Molecular weight of monomer
Molecular weight of Polyethylene having DP 1000
Molecular weight of Polyethylene = 1000 × Mol. wt of Ethylene
=1000 × 28
= 28000
Molecular weight of Polyethylene of DP 1000 is 28000
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POLYMERS
High Polymers
Polymers with high degree of polymerization (10,000-100,000) and
High molecular masses (10,000 to 10,00,000) are called
High polymers = High DP
Oligomers: Polymer whose molecules consist of
relatively few repeating units. (low mol wt. Polymers)
Polymers-High DP
Oligomers-Low DP
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POLYMERS
• Polymers are high molecular mass substances consisting of large
number of repeating structural units derived from simple
molecule.
• The simple molecules which combine to give polymers are called
monomers.
• The process by which the simple molecules are converted into
polymers are called polymerization.
• Example for polymers includes Polythene,
Polystyrene, Polyaniline, Polypropylene etc.
Polyvinyl
chloride,
• The number of repeating units (n) in the chain is known as the
Degree of polymerization (DP).
• Molecular weight of polymer varies from thousands to lakh based
on Degree of polymerization (DP).
• High polymers - Polymers with high DP
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POLYMERS
Classification of Polymers
Polymers can be classified in several ways,
➢ Based on Origin
➢ Based on Structure
➢ Based on Position of Substituent groups
➢ Based on Crystallinity
➢ Based on Thermal behavior
➢ Based on Methods of Formation
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POLYMERS
Classification of Polymers
➢ Based on Origin
➢ Natural polymers
➢ Synthetic polymers
Natural Polymers are those which are obtained naturally
E.g.: Cellulose, Silk, Starch, RNA, DNA, Proteins etc.,
Synthetic Polymers are those which are made by man
E.g.: polyethylene, polystyrene, PVC, polyester, etc.,
Semi-synthetic Polymers which are chemically modified
natural polymers
E.g.: cellulose acetate, cellulose nitrate, halogenated
rubbers etc.,
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POLYMERS
Classification of Polymers
➢ Based on Origin
• Natural polymers
• Synthetic polymers
POLYMERS
Classification of Polymers
➢ Based on Structure
➢ Linear Polymer
➢ Branched Polymer
➢ Cross-linked Polymer
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POLYMERS
Classification of Polymers
➢ Based on Structure
Linear Polymer
A linear polymer is simply a chain in which all the
carbon-carbon bonds exist in a single line.
The monomeric units combine linearly with each other
Example
Linear Polymer
Polyethylene
Example
Linear polymer
Polyvinyl Chloride
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POLYMERS
Classification of Polymers
➢ Based on Structure
Linear Polymer
Linear Homo-Polymer: Polymer containing same monomer unit
or identical monomer unit.
-M-M-M-M-M-M-M-M-
Linear Co-Polymer: Polymer chain containing more than one
type of monomer units.
-M1-M2-M1-M1-M2-M1-M1-M2-M1-M2
-M1-M2-M1-M2-M1-M2-M1
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-M1-M1-M1-M1-M2-M2-M2-M2-
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POLYMERS
Classification of Polymers
➢ Based on Structure
Linear Co-Polymer: Polymer containing monomer units arranged
randomly or alternatively or blocked.
-M1-M2-M1-M1-M2-M1-M1-M2-M1-M2
-M1-M2-M1-M2-M1-M2-M1
-M1-M1-M1-M1-M2-M2-M2-M2-
Examples
Nylon 6,6
Polycarbonate
Styrene-Butadiene Rubber
random polymer
POLYMERS
Classification of Polymers
➢ Based on Structure
Branched chain Polymer
Branched Chain Polymers have side chains or branches growing out
from the main chain. The side chains or branches are made of the
same repeating units as the main polymer chains. The branches
result from side reactions during polymerization.
Polyethylene
Graft Copolymer
One kind of monomers in their main chain
and another kind of monomers in their side
chain are called graft copolymers
POLYMERS
Classification of Polymers
➢ Based on Structure
Cross linked Polymer
Formed when linear molecules under certain conditions are linked to
neighbouring ones results in the formation of a three dimensional
structure of unlimited size.
Example: polybutadiene, ethylene propylene rubber, ethylene
propylene diene rubber, etc.
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POLYMERS
Classification of Polymers
➢ Based on Position of Substituent groups
(Stereo regular polymer or Tacticity (arrangement or order))
Isotactic
On same side
Syndiotactic
Alternating sides
Gutta percha (natural
organic polymers)
Atactic
Randomly placed
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POLYMERS
Classification of Polymers
➢ Based on Crystallinity
• Amorphous:
No Ordered arrangements of Molecules-Low degree of Crystallinity
Example: Poly(methyl methacrylate)
Polycarbonate
• Crystalline polymers:
Ordered arrangements of Molecules-High degree of Crystallinity
Example:
Nylon (polyamides)
Polypropylene
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POLYMERS
➢ Based on Thermal behavior
➢ Thermoplastics
➢ Thermosetting Polymers
Thermoplastics
Polymers which becomes soften on heating and can be converted into
any shape and can retain its shape on cooling.
Process can be repeated many times without affecting the chemical
properties. Example: Polyethylene, PVC, Teflon, etc.
Thermosetting polymers
Polymers undergo chemical changes and cross linking on
heating and becomes permanently hard and Infusible mass.
They will not soften on heating, once they are set.
Example: Epoxy resin, Phenyl formaldehyde resin, etc.
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POLYMERS
➢ Based on Thermal behavior
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POLYMERS
Classification of Polymers
➢ Based on Methods of Formation or Preparation
➢ Addition polymers
➢ Condensation polymers
Addition polymers are formed by self-addition of monomers
Without the formation of Co-product.
The molecular mass of a polymer is an integral multiple of
the molecular mass of a monomer
Example: Polyethene, Polypropylene
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Polypropylene (PP)
Polythene or Polyethylene(PE)
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POLYMERS
➢ Addition polymers:
Y=H, Polyethylene
(Chain growth polymerization)
n (H2C=CH)
Initiator
H
H
Y=CH3, Polypropylene
n (H2C=CH)
Initiator
Polystyrene
Y=Cl, Polyvinyl Chloride
n (H2C=CH)
n(H2C=CH)
Cl
( H2C-CH ) n
CH3
CH3
Y=
( H2C-CH ) n
Initiator
( H2C-CH ) n
Initiator
( H2C-CH ) n
Cl
POLYMERS
Classification of Polymers
➢ Based on Methods of Formation or Preparation
➢ Condensation polymers
Condensation polymers are formed by condensation reaction
i.e., reaction between two or more monomer molecules with
the elimination of simple molecules like water, ammonia,
HCl etc.,
Example: Polyamides,
n
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Polyesters
n
+ (2n-1) H2O
n
n
+ (2n-1) H2O
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POLYMERS
➢ Condensation polymers
(Step growth polymerization)
Example:
(n) HOOC
COOH + H2N
(n)
(CH2)4
Adipic acid
OH
(CH2)6
NH2
Hexamethylene diamine
O
O
C (CH2)4
C
H
HN
(CH2)6
N
H + (2n-1) H2O
n
Nylon-6,6
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POLYMERS
Classification of Polymers
DISTINGUISHING FEATURES OF
ADDITION AND CONDENSATION POLYMERISATION
ADDITION
CONDENSATION
Monomers undergo self addition to
each other without loss of by products
Monomers undergo intermolecular
condensation with continuous elimination
of by products such as H2O, NH3, HCl, etc.,
It follows chain mechanism
It follows step mechanism
Monomers are linked together
through C – C covalent linkages
Covalent linkages are through
their functional groups
High polymers are formed fast
The reaction is slow and the polymer
molecular weight increases steadily
throughout the reaction
Linear polymers are produced
with or without branching
Linear or cross-linked polymers
are produced
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e.g., Polypropylene, Polyethylene
e.g., Polyamide, Polyester
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Classification of Polymers
Based on
Origin
Based on
Structure
Based on Position of
Substituent groups
Based on
Crystallinity
Based on
Thermal behavior
Based on
Methods of Formation
Stereo regular or
Tacticity
Natural
polymers
Synthetic
polymers
Linear
Polymer
Isotactic
On same side
Amorphous
Polymers
Thermoplastics
Polymers
Addition
polymers
Branched
Polymer
Syndiotactic
Alternating sides
Crystalline
Polymers
Thermosetting
Polymers
Condensation
polymers
Cross-linked
Polymer
Atactic
Randomly placed
Linear
Homo-Polymer
Branched
Homo-Polymer
Linear
Co-Polymer
Branched
Co-Polymer
Graft
Co-Polymer
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POLYMERS
Addition polymerization- Mechanism
❖ Free Radical polymerization Mechanism
❖ Ionic polymerization Mechanism
Cationic
Anionic
❖ Co-ordination polymerization Mechanism
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POLYMERS
Free Radical polymerization
1) Generation of Free Radicals
2) Initiation
3) Propagation
4) Termination
Example
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POLYMERS
Free Radical polymerization- Polyvinyl Chloride
1) Generation of Free Radicals
Free Radicals
Molecule that contains at least one unpaired electron
Odd number of electron
Unstable and highly reactive species
Generation of Free Radicals by Initiator
R-R
Initiator
∆ or hv
Homolytic Cleavage
••
Initiator
∆ or hv
Homolytic Cleavage
•
2R
Free radicals
•
2R
Free radicals
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POLYMERS
Free Radical polymerization- Polyvinyl Chloride
1) Generation of Free Radicals
Commonly using Initiator: Dibenzoyl Peroxide
O
O
(C6H5-COO)2
(or)
C H -C-O-O-C-C H
6
5
6
5
Generation of Free Radicals by Initiator
O
O
O
∆ or hv
•
C6H5-C-O-O-C-C6H5
Homolytic Cleavage 2C6H5-C-O
Homolytic Cleavage
•
2R
•
∆ or hv
(or) 2C6H5 + 2CO2
Free radicals
POLYMERS
Free Radical polymerization- Polyvinyl Chloride
1) Generation of Free Radicals
Commonly using Initiator: Dibenzoyl Peroxide
O
O
(or) (C6H5COO)2
C H -C-O-O-C-C H
6
5
6
5
Generation of Free Radicals by Initiator
(C6H5COO)2
∆ or hv
Homolytic Cleavage
•
2C6H5 + 2CO2
Free radicals
(or)
•
2R
POLYMERS
Free Radical polymerization- Polyvinyl Chloride
2) Initiation
The free radicals generated initiate the chain process by
attacking the unsaturated monomer at the double bonds
generating new free radicals.
•
R +
••
(H2C=CH)
Cl
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∆ or hv
•
R-H2C-CH
Cl
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POLYMERS
Free Radical polymerization- Polyvinyl Chloride
3) Propagation
The new free radicals attack monomer molecules further in quick
succession leading to chain propagation.
•
••
R-H2C-CH + (H2C=CH)
Cl
(
)n-1
(
)
m-1
∆ or hv
•
-CH
R-H2C-CH-CH2
Cl
Cl
∆ or hv
∆ or hv
(
)
n
(
)
m
The values of n and m varies from several hundreds to several thousands.
Cl
POLYMERS
Free Radical polymerization- Polyvinyl Chloride
4) Termination
❖ Coupling
❖ Disproportionation
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POLYMERS
Free Radical polymerization- Polyvinyl Chloride
4) Termination
Coupling or combination
•
•
CH
-CH
+ HC-CH2-(CH-CH2)-R
R-H
)
( 2C-CH2
m
n
Cl
Cl
Cl
∆ or hv
Cl
Coupling
R-H
) CH2-CH- HC-CH2-(CH-CH2)-R
( 2C-CHm
n
Cl
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Cl
Cl
Cl
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POLYMERS
Free Radical polymerization- Polyvinyl Chloride
4) Termination
Disproportionation
•
∆ or hv
Disproportionation
R-H
) CH2-CH2 + HC=CH- (CH-CH2)-R
( 2C-CHm
n
Cl
Cl
Cl
Cl
POLYMERS
Free Radical polymerization- General mechanism
Glass Transition temperature (Tg.)
The temperature at which a polymer abruptly transforms from
The glassy (hard) to the rubbery state (soft).
• Polymers do not have sharp melting points
• At low temperature, polymers exist as glassy substances
• If the solid polymer is heated, eventually it softens and
becomes flexible
So, the glass transition temperature (Tg.) can be defined
as the temperature below which an amorphous polymer is
brittle, hard and glassy and above the temperature it
becomes flexible, soft and rubbery
Glass Transition temperature (Tg.)
• In the glassy state of the polymer, there is neither molecular
motion nor segmental motion.
Glassy state
(Hard and Brittle)
Tg.
Viscoelastic state
(Rubbery)
Segmental motion
Tm Viscofluid state
(Polymer melt)
Segmental motion &
Molecular motion
Tg. - Internal Brownian movement - Segmental motion
Tm.-
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Internal Brownian movement + External Brownian
movement - Segmental motion + molecular motion
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Glass Transition temperature (Tg.)
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Glass Transition temperature (Tg.)
Free Volume
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Glass Transition temperature (Tg.)
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Glass Transition temperature (Tg.)
PVC
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Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
1) Chain flexibility
2) Crystallinity
3) Branching and Cross linking
4) Intermolecular Forces
5) Molecular Mass
6) Stereoregularity of the polymer
7) Presence of plasticizers
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Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
1) Chain flexibility
•
A free rotational motion of the polymer chain imparts flexibility to the
polymer.
•
Linear polymer chains made of C-C, C-O and C-N single bonds have
a higher degree of freedom of rotation.
•
Presence of aromatic or cyclic structure or bulky side groups on the
backbone of C-atoms hinder the freedom of rotation thus lowering
the chain flexibility and increase in Tg.
Poly (ethylene adipate) Tg. = -70 °C
Poly (ethylene terephthalate) Tg. = 69 °C
Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
2) Crystallinity
Higher the crystallinity, larger is the Tg value of a polymer.
Ordered
Crystalline
region
Disorders
amorphous
region
Crystallinity = Close packing
More Crystalline = more strength = less mobility = Tg. increases
More Amorphous = less strength = high mobility = Tg. decreases
Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
3) Branching and Cross linking
•
A small amount of branching will tend to lower Tg..
•
High density of branching brings the polymer chains closer, lowers
the free volume thus reducing the chain mobility and resulting in
an increase in Tg.
Low density of branching = Increase in free Volume = High Chain mobility = Decrease in Tg.
High density of branching = Decrease in free Volume = Low chain mobility = Increase in Tg.
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Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
3) Branching and Cross linking
•
Cross linking of chains decreases the flexibility of the polymer chain
and, therefore, as the extent of cross linking increases, the Tg value
increases.
Cross linking = Decrease in free Volume = Low chain mobility = Increase in Tg.
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Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
4) Intermolecular Forces
• Due to the presence of polar groups in the polymer chain,
intermolecular bonding may be developed (hydrogen bonding).
• In the hydrogen bonding polymer chain will be closely packed and it
will restrict the segmental and rotational motion of polymer chain.
•
Due to which flexibility decreases and Tg increases
Tg. = -20 ° C
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PVC
Tg. = 80 ° C
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Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
5) Molecular Weight
• Tg. is directly proportional to the molecular weight of polymer.
• Short chains have more free volume. Tg. for shorter chains will be
lower than Tg. for longer chain.
• Generally
Tg
of
a
polymer
increases with molar mass upto a
particular value and beyond that
there is no change.
e.g.,
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PE (low Mw)
-110 °C
PE (high Mw)
- 90 °C
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Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
6) Stereoregularity of the polymer
A Syndiotactic polymer has a higher Tg. than atactic polymer which in
turn has higher Tg than its isotactic stereoisomer.
Tg.
Syndiotactic
Syndiotactic
Alternating sides
•
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>
Tg.
Atactic
Atactic
Randomly placed
>
Tg.
Isotactic
Isotactic
On same side
The bulky groups on chain, increases the Tg of the polymer
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Glass Transition temperature (Tg.)
Factors influencing the glass transition temperature (Tg.)
7) Presence of plasticizers (additives)
•
Addition of plasticizers reduces the Tg. value.
•
The plasticizers are usually dialkyl phthalate esters, such as dibutyl
phthalate, a high boiling liquid.
•
The plasticizer separates the individual polymer chains from one
another. It acts as a lubricant which reduces the attractions between
the polymer chains.
For example: addition of diisooctyl phthalate to PVC reduces its Tg. from 80
°C to below room temperature.
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Glass Transition temperature (Tg.)
Significance of glass transition temperature
(i) Tg can be used to evaluate the flexibility of a polymer
and predict its response to mechanical stress.
(ii) It helps to understand the usefulness of a polymer over
a temperature range.
(iii) The glass transition temperature helps in choosing the
right processing temperature
(iv) Predicting the re cyclability of polymer
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Polymers: Structure and Property Relationship
Macromolecules show a wide range of properties which are quite
different from those of respective monomers
They may be
Elastic or Rigid
Hard or Soft
Transparent or Opaque
Have strength of steel but can have very light weight
Soften on heating or
Can set to a hard mass on cooling the melt
These properties may vary from one type of polymer to another
and even among the same type
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Polymers: Structure and Property Relationship
The fundamental parameters which influence the structureproperty relationship are
Molecular mass
Polarity
Crystallinity
Molecular cohesion
The nature of polymeric chains and
Stereochemistry of the molecules
The properties like tensile strength, crystallinity, elasticity,
resistance to chemicals, wear and tear depend mostly on the
polymer structure
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Polymers: Structure and Property Relationship
Strength
This can be discussed based on
The forces of attraction
Based on forces of attraction
Strength of the polymer is mainly determined by the
magnitude and distribution of attraction forces between
the polymer chains
These attractive forces are of two different types
Covalent forces
Intermolecular forces
Polymers: Structure and Property Relationship
Linear polymer
•
In linear chain and branched chain polymers, the individual
chains are held together by weak intermolecular force of
attraction
•
These polymers exhibit mechanical strength only when
chain length is grater than 150 to 200 atoms.
• i.e., In case of Linear and branched polymers, strength
increases with increase in chain length (in turn increase in
molecular weight) as the longer chains are entangled
(anchored) better will be the strength.
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Polymers: Structure and Property Relationship
•
In cross-linked polymers, monomeric units
together only by means of covalent forces.
are
held
❑ Giant solid molecule
❑ Extending in three dimension
So the cross linked polymers are strong and tough
Since the movement of intermolecular chain is totally
restricted
•
Linear polymer
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Increase in Strength
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Polymers: Structure and Property Relationship
Examples:
Linear Polymers: Polyethylene, polyvinyl chloride (PVC),
polystyrene, polymethyl methacrylate (plexiglass), nylon,
fluorocarbons (teflon)
Branched Polymers: Many elastomers or polymeric rubbers
Cross-linked Polymers: Many elastomers or polymeric rubbers
are cross-linked (vulcanization process); most thermosetting
polymers
Network Polymers: Epoxies, phenol-formaldehydes.
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Polymers: Structure and Property Relationship
Molecular mass and the strength
•
High molecular weight polymers are tougher and more heat
resistant. High molecular masses of polymers account for their high
softening temperature and tensile strength.
The melt viscosity of a polymer at a given temperature is a measure
of the rate at which chains can move relative to each other.
•
Low melt viscosity and high tensile and impact strengths are
desirable properties for a polymer to be commercially useful.
Polymers: Structure and Property Relationship
Crystallinity
High Crystallinity
High Strength
High Density
High MP
crystalline
region
amorphous
region
• A linear polymer without branching and bulky groups will
have a high degree of crystallinity
• The “lumpier” and more branched polymer chain- less dense
and less crystalline polymer
• The chains of polymers are held together by secondary forces
such as Vander waal, hydrogen bonding, polar interaction, etc.
Such type of close packing imparts a high degree of crystallinity
Polymers: Structure and Property Relationship
Crystallinity
• The polymers such a HDPE, stereoregular isotactic and
syndiotactic isomers of poly propylene, PVC are highly
crystalline
• Atactic PVC, Polystyrene, Polypropylene in which bulky
pendant groups arranged randomly on the polymer backbone
are amorphous. LDP which has extensive branching is also
amorphous
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Polymers: Structure and Property Relationship
Elasticity
• Elasticity of the polymer is mainly because of the uncoiling
and recoiling of the molecular chains on the application of
force
• A polymer to show elasticity the individual chains should not
break on prolonged stretching
• Breaking takes place when the chains get separated
• So the factors which allows the breakage of the molecules
should be avoided to exhibit an elasticity
The elastic property can be improved by
• Introducing cross-linking at suitable molecular positions
• Avoiding bulky side groups such as aromatic and cyclic groups
on repeating units
• Introducing non-polar groups on the chains
Polymers: Structure and Property Relationship
• A polymer to show elasticity, the structure should be
amorphous
• By introducing a plasticizer, the elasticity of polymer can
enhance
• To get an elastic property, any factor that introduces
crystallinity should be avoided
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Polymers: Structure and Property Relationship
Plastic Deformation (Rheology of Polymer)
• Some polymers, on the application of heat and pressure,
initially become soft, flexible rubbery matter and undergo
deformation. On further heating beyond melting point, they
melt and flow. Such property is called as Plasticity.
Plasticity- Thermoplastics- Moulding operations
• Thermoplastics are linear, stereoregular polymers. The
polymer chains are closely packed and held by secondary
forces such as Vander Waal, hydrogen bonding and dipolar
interaction.
• Such polymers when heated, the chains acquire sufficient
energy and overcome these inter chain attractive forces. They
attain molecular mobility and flow like viscous fluid.
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Polymers: Structure and Property Relationship
• Thermosetting plastics do not exhibit plasticity.
• Moulded thermosetting have three dimensional structure. All
monomer units are held together through strong primary
covalent bonds throughout the structure.
• Primary covalent bonds are not easily broken by heat.
• On strong heating, charring occurs instead of deformation.
Therefore thermosetting do not undergo reversible plastic
deformation.
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Polymers: Structure and Property Relationship
Chemical Resistance
The chemical attack on polymers involves softening, swelling and
loss of strength of material.
•
The resistance to chemical attack of a polymer depends on several
factors such as
(a) The presence of polar or non-polar groups
(b) The degree of crystallinity and molecular mass, and
(c) Degree of crosslinking
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Polymers: Structure and Property Relationship
Chemical Resistance
(a) The presence of polar or non-polar groups
• Polymers containing polar groups like – OH, - COOH etc.,
usually dissolve in polar solvents like water, ketone, alcohol etc.,
but these are chemically resistant to non-polar solvents
• Similarly non-polar groups such as methyl, phenol dissolve
only in non-polar solvents like benzene, toluene, etc.,
• Polymers of more aliphatic character are more soluble in
aliphatic solvents, hence chemical resistance is less in
aliphatic solvents and more in aromatic solvents
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Polymers: Structure and Property Relationship
Chemical Resistance
(a) The presence of polar or non-polar groups
• Polymers with more aromatic groups dissolve more in
aromatic solvents, hence chemical resistance is less in
aromatic solvents and more in aliphatic solvents
• Polymers containing ester groups (e.g., polyesters) undergo
hydrolysis with strong alkalis at high temperature implies less
chemical resistance in alkalis
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Polymers: Structure and Property Relationship
(b) Degree of crystallinity and molecular mass:
• The swelling character of polymer decreases with the increase
in the molecular mass.
• For polymers having same chemical character, the chemical
resistance increases with increase in the degree of crystallinity.
(c) Degree of cross linking:
• Greater the degree of cross linking lesser is the solubility.
• Linear polymers readily dissolve in organic solvents and
readily melt on heating.
• On the other hand, branched chain and cross linked polymers
have very little solubility and may undergo rupture when
heated.
Commercial polymers
Polymethyl Methacrylate (Plexiglass, Leucite )
Prepared by radical polymerization of the methyl ester of methacrylic
acid.
Synthesis
Methyl methacrylate
Plexi glass is a highly transparent thermoplastic which softens at
120° C.
It is a hard solid which can be easily moulded and is resistant to the
action of organic solvents.
It has good mechanical properties and is a good substitute for glass
Commercial polymers
Acrylic polymers
Polymethyl Methacrylate
Transparency: Lenses, uses like glasses
Application
▪ For making lenses and optical fibers.
▪ Glass replacement.
▪ For making artificial eyes and TV screens
▪ Fibers- carpet industries, Blanket
▪ Good mouldability- desired shapes, different products.
▪Glazing automobiles and airplanes
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Commercial polymers
Polycarbonate (Lexan, Merlon) (repeating units of(-O-C=O-O-))
Polycarbonates (PC) are a group of polymers containing
carbonate groups in their chemical structures.
Polycarbonates used in engineering are
strong, tough materials, and some grades
are optically transparent. They are easily
worked, moulded, and thermoformed.
• The flexibility of the carbon-oxygen single bonds permits some
molecular flexibility in Polycarbonates
Commercial polymers
Polycarbonate
Synthesis
Condensation reaction
n
n
200 ˚C
200 °C
+ 2n
Commercial polymers
Polycarbonate
Commercial polymers
Polycarbonate
Properties
• Durable material has a Tg about 147 °C,
• It is a white transparent material.
• It has high melting point, tensile strength and impact resistance.
• It has excellent mechanical properties.
• However, it is soluble in acids and alkalis.
Commercial polymers
Polycarbonate
Carbonate interunit linkages (-O-CO-O-).
Application
PC roofing sheets
Water Bottle
Diffusion panel
Electric parts
Building materials
Film
Safety Goggles
Automobile part
Bullet proof glass
ELASTOMERS: SYNTHETIC RUBBERS
Organic polymers possessing the property of elasticity to the
extent of nearly 200-300% are known as Elastomers.
Elastomer is defined as a long chain polymer which under stress
undergoes elongation by several times and regains its original
shape when the stress is fully released.
Possesses the property of Elasticity.
Stretched
Returned to
randomization
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Elastic: Week Wander Walls force
ELASTOMERS: SYNTHETIC RUBBERS
Elastomers are high polymers, which have elastic properties in
excess of 300 %
The unstretched rubber will be in amorphous state
As stretching is done, the macromolecules get partially aligned
with respect to another, thereby causing crystallization
On releasing the deforming stress, the chains get reverted back
to their original coiled state and the material again becomes
amorphous
ELASTOMERS
NATURAL
RUBBER
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ELASTOMERS: NATURAL RUBBERS
Natural rubber consists of basic material latex, which is a
dispersion of isoprene, obtained from the tree havea brasillians
Addition between molecules of isoprene takes place by 1,4
addition and one double bond shifts between 2nd and 3rd
positions.
CH3
CH2=C-CH=CH2
Isoprene (2-methyl-1,3-butadiene)
During the treatment, these isoprene molecules polymerize
to form long-coiled chains of cis-polyisoprene
The mol. wt. of raw rubber is about 100,000 – 150,000
H3C H
n CH2=C-C=CH2
Polymerization
H3C H
-CH2-C=C-CH2n
Polyisoprene
H3C H
-CH2-C=C-CH2- CH2-C=C-CH2Cis-1,4-Polyisoprene
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H
H3C
H3C H
-CH2-C=C-CH2- CH2-C=C-CH2n
H
H3C
n
Trans-1,4-Polyisoprene
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ELASTOMERS: NATURAL RUBBERS
As each isoprene unit contains C = C bond, polyisoprene exists
in two isomeric forms
viz., cis and trans
Natural rubber contains the cis isomer while the gutta percha
contains the trans isomer
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ELASTOMERS: NATURAL RUBBERS
Gutta Percha is trans-polyisoprene and is obtained from the
mature leaves of dichopsis gutta and palagum gutta trees
(belonging to sapetaceae family)
These trees are grown mostly in Broneo, Malaya and Sumatra
Important Properties of Rubber
• Flexibility
• Strength
• Impermeability to water
• High resistance to abrasion
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ELASTOMERS: SYNTHETIC RUBBERS
Silicone rubber
Silicone rubbers are formed by the polymerization of dimethyl
silicone hydroxide
Silicone rubbers have different type of polymer structure
compared to any other synthetic rubbers.
Chain structure does not involve long chain of carbon atoms, but
a sequence of silicon and oxygen.
O
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H
H
H C H
H C H
Si
O
Si
H C H
H C H
H
H
Silicone rubber
O
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ELASTOMERS: SYNTHETIC RUBBERS
Dimethyl silicone dichloride is bifunctional and can yield very
long chain polymer.
Dimethyl silanol
CH3
n Cl
Si
CH3
H2O
Hydrolysis
Cl
- HCl
n HO
Si
CH3
CH3
unstable
Dimethyl dichlorosilane
Si
CH3
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H2O
CH3
CH3
O
OH
polymerization
O
n
( O
Si
O)
CH3
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ELASTOMERS: SILICONE RUBBERS
+
+
n
ELASTOMERS: SYNTHETIC RUBBERS
Properties
They possess exceptional resistance to
•
•
•
•
Prolonged exposure to sun light
Weathering
Most of the common oils
Boiling water
• Dilute acids and alkalies
• They remain flexible in the temp. range of 90 – 250 OC, hence,
find use in making tyres of fighter aircrafts
• Silicone rubber at very high temp decomposes; leaving behind
the non-conducting silica (SiO2), instead of carbon tar
ELASTOMERS: SYNTHETIC RUBBERS
Applications
• As a sealing material in search-lights and aircraft engines
• For manufacture of tyres for fighter aircrafts
• For insulating the electrical wiring in ships
• In making lubricants, paints and protective coatings for fabric
finishing and water proofing.
• As adhesive in electronics industry
• For making insulation for washing machines and electric
blankets for iron board covers
• For making artificial heart valves, transfusion tubing and
padding for plastic surgery
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ELASTOMERS: SYNTHETIC RUBBERS
BUTYL RUBBERS
• It is also known as polyisobutylene
• Co-Polymer of isobutylene monomer (95-99%) with small ratio
of (1-5%) of Isoprene monomer.
CH3
(95-99%)
+
nCH2=C
Isobutylene
CH3
Anh. AlCl3/CH3Cl
CH3
CH3
(1-5%)
nCH2=C-CH=CH2
Isoprene
Addition
co-polymerization
-95 °C
CH3
( CH2-C-CH2-C=CH-CH2 )
CH3
Butyl Rubber
n
ELASTOMERS: BUTYLE RUBBERS
+
Butyl Rubber
(
n
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)
+
(
n
)
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ELASTOMERS: SYNTHETIC RUBBERS
BUTYL RUBBERS
Properties:
• Low permeability to air, gas and moisture
• Low Glass transition temperature (Tg)
• Fast Cure rates: Toughening and hardening of polymer
material by cross linking of polymer chain.
• Wide vulcanization of versatility.
• High extensibility
Applications:
• For making cycle and flexible tubes, automobile parts, hoses,
conveyor belts for food and other materials, tank-linings,
insulation for high voltage wires and cables, etc.
ADHESIVES
Adhesive is defined as a polymeric substance used to bind
Together two or more similar or dissimilar materials so that
the resulting material can act as a single piece.
• The adhesive forces may be chemical or mechanical
in nature.
Chemical – Binding mainly by intermolecular forces of
attraction
Mechanical - Binding by Physical cementing (sticking together)
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ADHESIVES
Adhesives may be broadly classified into natural and synthetic
Natural Adhesives
Common gum and glues are
examples of natural adhesives
Thermosetting resins which include
Phenol-formaldehyde,
Synthetic Adhesives Urea-formaldehyde,
Resorcinol-formaldehyde,
Silicones and epoxides.
The effectiveness of and strength of an adhesive depends on
various factors• The materials bonded,
• The solvent used and
• The effect of external conditions such as heat, light and
environment.
ADHESIVES
• Epoxy resins serve as good adhesives in the case of metals,
wood, glass, concrete, ceramics and leather.
• Phenol-formaldehyde for rubber; urea-formaldehyde for wood.
• Resorcinol-formaldehyde for leather.
• Alkaline adhesives cannot be used for bonding the surfaces of
certain metals like aluminium
Surface cleaning of Materials
ADHESIVES
Epoxy resins (Araldite)
Epoxy resins are polymeric materials containing the epoxy
group.
Bisphenol-A
Epichlorohydrin
Produced from a reaction between epichlorohydrin and bisphenol-A
-n H2O
+
+ Na -O
O- Na+
O
Cl-CH2-CH-CH2 - NaCl
+
H2O
n
ADHESIVES
Properties
• It is a solid at higher mol. wt. with a melting range of
145 oC -155 oC.
• Molecular weight ranges from 350 to 8000
• It is a mobile and easy flowing liquid at a mol. Wt. of 350
• They have good resistance to chemicals
• They have less shrinkage during curing process
• They may be used in semisolid or liquid form
• They possess excellent electrical resistance
• Epoxy resins have ability of getting cured, without application
of heat
ADHESIVES
Applications
• Epoxy resins are mainly used as adhesives
• They are used for surface coatings
• Moulds are made with epoxy resins, which are used to produce
metallic components of aircrafts and automobiles
• They are used as laminating and casting materials
• Epoxy resins are used as potting compounds for electrical
equipment
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POLYMER COMPOSITES
Definition: A combination of two or more distinct components to form
a new class of material suitable for structural applications is referred to
as composite materials. When one of the component is a polymer, the
resulting composite is called a polymer composite.
• Polymer composites are generally made of two components,
namely (i) matrix and (ii) fibre.
• The matrix is usually a thermoset material such as epoxy
resin or a polyamide
• Fibre is most often glass but sometimes may be a carbon
fibre or Kevlar.
POLYMER COMPOSITES
A common fibre-reinforced composite is fiberglass. Its
matrix is made by mixing a polyester and a styrene
pouring the mixture over a mass of glass fibres.
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CARBON FIBER (wonder Polymer)
CARBON FIBER
Very thin strands of carbon
when bound together with
plastic polymer resin with heat,
pressure or vacuum
•
The strength of carbon fibre
depends on the weave.
• The more complex the weave - more durable the composite
CARBON FIBER
Preparation of Carbon Fiber
1. Polymerization of acrylonitrile to PAN.
2. Cyclization during low temperature process.
3. High temperature (600-700 °C) oxidative
treatment of carbonization (H2 is removed)
4. Graphitization where Nitrogen is removed
and chains are joined into graphite planes.
4
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CARBON FIBER
• Properties:
(i) Excellent strength but lighter than steel.
(ii) Good corrosion resistance.
(iii) Very low coefficient of thermal expansion.
(iv) Low impact resistance.
• Applications:
(i) In aerospace and automotive fields.
(ii) In modern bicycles and motorcycles.
(iii) In consumer goods such as laptops, tripods,
golf clubs, tennis rackets, etc.
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Conducting Polymers
Polymers (or plastics as they are also called) are
known to have good insulating properties.
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•
Polymers are one of the most used materials in the
modern world. Their uses and application range from
containers to clothing.
•
They are used to coat metal wires to prevent electric
shocks.
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Conducting Polymers
Yet Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa have
changed this view with their discovery that a polymer, polyacetylene,
can be made conductive almost like a metal.
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Conducting Polymers
Conducting
Polymers:
Polymers which
electricity is called Conducting polymers.
conduct
the
The conductivity of polymers is in between conductors
and insulators so it will call it as semiconducting
polymers
Clasification of Conducting Polymers
• Intrinsic conducting polymer
• Extrinsic conducting polymers
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Conducting Polymers
How polymer can become conductive?
Three conditions to become Conducting Polymer
1. Polymer should be linear
2. Polymer should consists of alternating single and double
bonds, called conjugated double bonds.
In conjugation, the bonds between the carbon atoms are alternately
single and double. Every bond contains a localised “sigma” (σ) bond
which forms a strong chemical bond. In addition, every double bond
also contains a less strongly localised “pi” (π) bond which is weaker.
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Conducting Polymers
3. Polymer has to be disturbed - either by removing electrons
from (oxidation), or inserting them into (reduction), the
material. The process is known as
Doping.
There are two types of doping:
1. Oxidation with halogen (or p-doping).
2. Reduction with alkali metal (called n-doping).
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Conducting Polymers
Example for Conducting Polymers
Polyacetylene
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Conducting Polymers
Mechanism of conduction in Polyacetylene
The oxidative doping of a Polyacetylene
New electronic state
Conducting Polymers
Polyaniline
It shows a conductivity of greater than 105s-1m-1. As a comparison Teflon
has a conductivity of 10-16s-1m-1 and that of copper is 108s-1m-1.
Properties
•
•
•
•
•
Highly conducting
High catalytic property
Easy of preparation
Stability under aqueous condition
Facility to fine tune the electrical optical and chemical properties
Conducting Polymers
Applications
Conducting polymers are highly promising materials to be used in
electric and electronic applications. Some of the applications are
(i) As electrode material for rechargeable batteries, for higher power to
weight ratio (coin type materials).
(ii) As conductive tracks on printed circuit boards.
(iii) As sensor- humidity sensor, gas sensor, radiation sensor,
biosensor for glucose, galactose etc.
(iv) In electrochromic display windows. (v) In information storage
devices.
(vi) As film membranes for gas separations. (vii) In light emitting
diodes.
(vii) In fuel cells as the electrocatalytic materials
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