This document provides an overview of polymers including: 1. Polymers are composed of long molecules made by linking small repeating units called monomers through polymerization. Common examples are polyethylene, nylon, and polyvinyl chloride. 2. Polymers can be classified based on their source, structure, molecular forces, and synthesis method. Some key classifications include natural vs synthetic, linear vs branched structures, thermoplastics vs thermosets, and addition vs condensation polymerization. 3. Common polymer processing techniques include compression molding, injection molding, and extrusion. Polymers also exhibit viscoelastic behavior and properties that depend on factors like temperature. 4. Examples of polymer applications include

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Presented By
Shan Ali 18-MS-ME-012
Advanced Materials Sciences & Engineering

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INTRODUCTION
Polymers
 The word polymer ‘’poly’’ means many ‘’mers’’ means repeat unit or parts
 Polymer : is composed of very long molecules made by linking together small molecules called monomers
 Monomer: single unit
 Polymerization : Process by which simple molecules (monomers) converted to polymer.
Ethylene
(monomers)
Polymerization
Polyethylene
(Polymer)
Figure 1 Polymerization

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Homopolymers and Co-polymer
Homopolymer
When all of the repeating units along a chain are of the same type .
Ex: polyethylene
Ethylene + Ethylene =Polyethylene
Copolymer .
Two different types of repeating units combining to make polymer
Copolymer can have different structure (a)random(b)alternating(c)block
(d) Graft polymer
Ex: Nylon Hexamethylenediamine + adipic acid = Nylon
Figure 2 Homopolymer and Copolymer difference
Figure 3
Schematic
representations of (a)
random, (b) alternating,
(c) block, and (d) graft
copolymers

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Classification of Polymers
Based on source of
availability
Based on structure
Based on molecular
forces
Based on mode of
synthesis
Natural Polymers
Semi synthetic polymer
Synthetic polymer
Linear polymers
Branched chain
polymer
Cross-linked polymers
Elastomers
Fibers
Thermoplastics
Thermosetting polymer
Addition polymers
Condensation
polymers

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Based on source of availability (origin)
Natural Polymers
Naturally occurring polymers those derived from plants and animals.
Ex: wood, rubber, cotton, wool, leather, silk etc.
Semi-Synthetic Polymers
Synthetic Polymers
These polymers are derived from naturally occurring polymers by chemical modifications
Ex: Cellulose diacetate polymer , Vulcanized rubber etc.
The polymers which are prepared in laboratories are called synthetic polymer.
Ex : Polyethylene , PVC , Nylon , Teflon, Bake lite etc.
Classification of Polymers

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Based on Polymers based on structures
Linear Polymers
These are polymers in which monomeric units are linked together to form long linear chains
Ex : High density polyethylene PVC , Nylons , Polyesters etc.
Properties : High densities , high tensile strength , High melting points.
Branched chain Polymers
These are polymers in which monomers are joined to form long chains with side chains or branches of different
lengths.
Ex: Low density polyethylene , Starch etc.
Properties : low densities , low tensile strength , low melting points.
Cross-linked Polymers
In crosslinked polymers interconnections between chains are joined one to another at various positions .
Ex: Rubber etc.
Classification of Polymers

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Network Polymers
Based on Polymers based on structures
The polymer that is highly crosslinked may also be classified as a network polymer
.Ex: Bakelite etc.
Properties : Hard , Rigid , Brittle , Low melting points ,Higher tensile strength
Figure 4: Schematic representations of (a) linear, (b) branched, (c) crosslinked, and
(d) network (three-dimensional) molecular structures.
Classification of Polymers

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Classification of Polymers
Based on molecular forces
Elastomers
Elastomers is a type of polymer having specific characteristics feature of elastic deformation of greater than (200) %
Ex: Natural Rubber ,Buna S , Neoprene etc.
Properties : Flexibility , Strength , Impermeability to water, High resistance to abrasion
Fibers
These are polymers which have strong intermolecular forces between chain.
Ex: Nylon , Dacron , silk etc.
Properties : high tensile strength , sharp melting points , thin thread like structure etc.
Thermoplastics
These are polymers softened repeatedly when heating and hardened when cooled with a bit change in properties.
Ex: Polythene , Polystyrene ,PVC ,Teflon etc.
Properties: Intermediate between elastomers and fibers, linear structure.etc.

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Based on molecular forces
Thermosetting polymer
These are polymers become hard and get permanent deformation when heated .
Ex : Urea-formaldehyde resins , Bakelite etc.
Properties: Brittle ,insoluble in organic solvent, rigid etc.
Classification of Polymers

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Classification of Polymers
Based on mode of synthesis
Addition polymerization:
A polymer formed by direct addition of repeated monomers without the elimination of by product molecule is
called addition polymers
Ex: ethene + ethene + n
Monomer Monomer
Addition
polymerization
Polyethene
Condensation polymerization:
A polymer formed by the condensation of two or more than two monomers with the elimination of simple
molecule as by product .Ex: water, ammonia, HCl, alcohol etc.
Hexamethylenediamine + adipic acid Nylon
Condensation polymerization
-nH20
Figure 5 Addition Polymerization
Figure 6 Condensation Polymerization

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Degree of polymerization
The average number of repeating unit in chain is represented by the degree of
polymerization.
DP is related to average number of molecular weight
Number-average molecular weight
xi =fraction of total number of chain in a range i
Mi=Mean molecular weight of specific range
Weight-average molecular weight
wi =weight fraction of molecules within the same size interval
Mi=Mean molecular weight of specific range
Classification of Polymers
𝑀𝑛
m is number of repeat unit in molecular weight

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Classification of Polymers
Suppose we are taking PVC (C2H3Cl) and finding its degree of polymerization
m=2(12.01 g/mol)+3(1.01 g/mol)+35.45 g/mol = 62.5 g/mol.
DP=
𝑀𝑛
𝑚
DP=
21,150 g/mol
62.50 g/mol
DP=338

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Classification of Polymers
Mw is greater than Mn
Figure 7 Distribution of polymer

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Mechanical Behavior of Polymers
Stress-Strain Behavior of polymer
Figure 8 The stress–strain behavior for brittle (curve
A), plastic (curve B), and highly elastic (elastomeric) (curve C)
polymers.
Figure 9 The influence of temperature on the stress–strain characteristics of
poly(methyl methacrylate).

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Mechanical Behavior of Polymers
Figure 11 Specific volume versus temperature, upon
cooling from the liquid melt, for totally amorphous (curve
A), semi crystalline (curve B), and crystalline (curve C)
polymers
Figure 10 Melting and Glass Transition Temperatures for Some of the More Common
Polymeric Materials
A’
B’
Glass transition temperature

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Mechanical Behavior of PolymersModulusE(Mpa)
ModulusE(Psi)
Viscoelastic behavior of polymer Viscoelastic = (Viscous + elastic) Behaviour
Phase I : Glassy region
• Relatively high modulus
• Very hard
• High resistance to flow
Phase II : leathery /glass transition region
• Sharp decrease in elastic modulus
• Deformation not totally recoverable
Phase III : Rubbery region
Both elastic and viscous components present
Modulus falling rate stabilizes
Elastic –high strain rate
Phase IV : Rubbery flow region
• Viscosity starts dominating
• Modulus starts falling
Phase V : Viscous flow region
• Modulus drops steeply
Finally : Decomposition
Figure 10

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Polymer processing
1. Compression molding
FORMING TECHNIQUES FOR PLASTICS
Figure 12 Compression molding
2. Injection Molding
Figure 13 Injection Molding

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Polymer processing
FORMING TECHNIQUES FOR PLASTICS
3. Extrusion
Figure 14 Extrusion process

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DEFECTS IN POLYMERS
POLYMER DEFECTS
Figure 15 Representation of defects in polymer

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Characteristic of Polymer
Characteristics
 Low density
 Good corrosion resistance
 Good insulator
 Excellent surface finish
 Economical
Limitations
 Low melting point
 Low heat capacity
 Not suitable for heavy load
 Environment effected

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Polymer Properties Comparison
Electrical Conductivity
Ductility & malleability
Melting point
Conductivity
Chemical stability
Hardness
High
High
High
High
Poor
High
Low
Low
Low
Low
Poor
Low (Thermo plastic)
Medium (Thermo setting)
Low
Low
High
Low
Good
High
Property Metal Ceramics Polymer
General Comparison

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Polymer
Polyethylene
Polyvinyl chloride
Polypropylene
Polystyrene
Polyester
Polyphenylene
Polyimide
Nylon
Teflon
Application
Packing films ,wire insulation etc.
Pipe, valves, fitting etc.
Tanks , carpet fibers etc.
Insulation foams ,packaging etc.
Fibers , photographic film etc.
Coatings , Fluid-handling components
Electrical components etc.
Rope ,Fibers etc.
Seal, Valves etc.
POLYMER APPLICATIONS

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The End