This document provides an introduction to polymers including their classification, structure, common types, and mechanisms of polymerization. Polymers are macromolecules composed of repeating structural units connected through polymerization reactions. They can be classified based on their structure as linear, branched, or cross-linked. Common addition polymers include polyethylene, polypropylene, polyvinyl chloride, and nylon. Condensation polymers include polyethylene terephthalate and polyamides. Polymerization occurs primarily through either addition or condensation reactions. Free radical addition polymerization follows initiation, propagation, and termination steps.

1. POLYMERS
•POLYMERS
• INTRODUCTION & CLASSIFICATION OF
POLYMERS
•ADDITION & CONDENSATION – POLYMERIZATION
•FREE RADICAL REACTION MECHANISM
BY,
Nilanjan, Manasi, Preyangsee
nilanjan_dey@ymail.com
Introduction to Polymers
1

2. ANCIENT POLYMER HISTORY
Originally many natural polymers were
used
Wood – Rubber
 Cotton – Wool
 Leather – Silk
Oldest known uses of “Modern Polymers”
 Rubber balls used by Incas
 Noah used pitch (a natural polymer)
for the ark – as had all ancient mariners!

3. 3
POLYMER
Poly mer
many repeat unit (building blocks)
H H H H H H
C C C C C C
H H H H H H
Polyethylene (PE)
H H H H H H
C C C C C C
H H H
Cl Cl Cl
Poly(vinyl chloride) (PVC)
H H H H
C C C C C C
H H
Polypropylene (PP)
CH3
H H
CH3 CH3H
repeat
unit
repeat
unit
repeat
unit
Carbon chain
backbone

4. WHAT ARE POLYMERS, MONOMERS
AND
POLYMERIZATIONS?
Polymers are macromolecules built up by the linking
together of large numbers of much smaller molecules.
Polymerization : The process of linking the repeating
units (monomers) is termed as polymerization
4
Introduction to Polymers

5. WHAT ARE POLYMERS, MONOMERS
AND
POLYMERIZATIONS?
The small molecules which combine with each other to
form polymer molecules are termed monomers.
5
Introduction to Polymers

6. 6
Introduction to Polymers

7. HOW BIG ARE POLYMERS?
Let CH2-CH2 ≈ 1 inch
7
Introduction to Polymers
Ethylene Polyethylene
CCoonnssiiddeerr oonnllyy aa 220000
-- mmeerr,, MMww ≈≈ 55660000
TThhiiss eennddss uupp wwiitthh aa cchhaaiinn ooff aapppprrooxxiimmaatteellyy 11//44 iinncchh ((66..44 mmmm))
iinn ddiiaammeetteerr aanndd 11//22 mmiillee ((880055 mm)) lloonngg..

9. CLASSIFICATION OF POLYMERS
DEPENDING ON THEIR STRUCTURE
Linear polymers
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Introduction to Polymers

10. CLASSIFICATION OF POLYMERS
DEPENDING ON THEIR STRUCTURE
Branched polymers
Introduction to Polymers
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What is the effect of branching on polymer
Cprroysptearltliiensit?y
Is it branched polymer?!!!

11. LINEAR POLYMER
Introduction to Polymers
11
BBrraanncchheedd ppoollyymmeerr

12. CLASSIFICATION OF POLYMERS
DEPENDING ON THEIR STRUCTURE
Cross-linked polymers
Crosslinked polymers do not dissolve but can be swelled
by liquids.
Light cross-linking improves elasticity properties
Introduction to Þ polymer is used as rubber
Polymers
High degree of crosslinking gives high rigidity and
thermal stability (high melting point).
12
Using appropriate monomers
Chemical reactions
Polymer molecules are connected together at points
other than their ends
BOTH CROSSLINKED POLYMERS CANNOT BE
RECYLED OR REPOROCESSED

13. TYPES OF POLYMERS &
POLYMERIZATIONS
Classification
of Polymers
Polymer Structure Polymerization
Mechanism
Step-
Polymerization
Chain-
Polymerization
Condensation
Polymers
Addition
Polymers
Introduction to Polymers 13

14. POLYMER TYPES: ELASTOMERS
Elastomers – rubber
Crosslinked materials
Natural rubber
Synthetic rubber and thermoplastic
elastomers
 SBR- styrene-butadiene rubber
styrene
– Silicone rubber
butadiene

15. POLYMER TYPES: FIBERS
Fibers - length/diameter >100
 Textiles are main use
Must have high tensile strength
Usually highly crystalline & highly polar
• Formed by spinning
– ex: extrude polymer through a spinnerette
• Pt plate with 1000’s of holes for nylon
• ex: rayon – dissolved in solvent then pumped through
die head to make fibers
– the fibers are drawn
– leads to highly aligned chains- fibrillar structure

16. PROCESSING OF PLASTICS
 Thermoplastic –
can be reversibly cooled & reheated, i.e. recycled
heat till soft, shape as desired, then cool
ex: polyethylene, polypropylene, polystyrene, etc.
• Thermoset
– when heated forms a network
– degrades (not melts) when heated
– mold the prepolymer then allow further reaction
– ex: urethane, epoxy

19. TYPE OF POLYMERISATION
 Monomers undergo polymerizaton by two types. They are:
• Addition or chAin polymerizAtion
• condensAtion or step polymerizAtion
Introduction to Polymers
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20. THE ADDITION-CONDENSATION
SYSTEM
Addition polymers are those formed from monomers
without the loss of a small molecule.
Introduction to Polymers
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WWhhaatt aarree aaddddiittiioonn ppoollyymmeerrss??
Y Y

21. PPoollyymmeerr SSttrruuccttuurree
TThhee aaddddiittiioonn--ccoonnddeennssaattiioonn ssyysstteemm
Condensation polymers (New definition)
Introduction to Polymers
Polymers whose repeating units are joined together
by functional units such as ester (-OCO-),
amide (-NHCO-), urethane (-OCONH-), sulfide (-
SO2-) and other linkages.
21
-R-Z-R-Z-R-Z-R-Z-R-Z-R
is aliphatic or aromatic grouping and Z is functional unit.

22.  It is addition of
tetrafluoroethene.obtained
by heating
tetrafluoroethene with a
free radicle or persulphate
catalyst.
 nF2C=CF2 _(F2C-CF2)
n_
 It is polymerised
product of vinyl
cyanide.it is obtained
by addition of
acrylonitrile in
presence of peroxide
catalyst.
 nCH2=CHCN _(CH2-
CHCN)n_

23. The major addition polymers are those formed by
polymerization of monomers containing carbon-carbon
double bond; such monomers are called vinyl
monomers or substituted ethylenes.
Introduction to Polymers
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PPoollyymmeerr SSttrruuccttuurree
TThhee aaddddiittiioonn--ccoonnddeennssaattiioonn ssyysstteemm

24. ADDITION POLMERIZATION
 Self addition of several bifunctional monomers to
each ohter takes place by chain reaction without
the elimination of any simple molecules.
 GENERAL REACTION:
n [CH2=CH]  [-CH2-CH-]n
| |
Y Y
Where Y=H,Ethylene,CH3,Propylene,Cl, Vinyl
Chloride, C6H5, Sterene, CN , Acrylonitrile
Introduction to Polymers
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25. Addition polymerization is initiated
by small qty of substance called
Initiators.
E.g.-Zeigler-Natta catalyst,
potassium persulphate , dibenzoyl
sulphat e.
Introduction to Polymers
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26. CONDENSATION
POLYMERIZATION
• Self addition of several bifunctional monomer to
each other takes place accompanying elimination
of simple molecues like H2O,NH3 & HCL
• General reaction:
n[HOOC-X-COOH] + n[HO-Y-OH]
HO-[….OC-X-COO-Y-O]n-H + (2n-1)H20
Introduction to Polymers
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27. E.g..
 Terylene is obtained by condensing terpthalic
acid [HOOC-C6H4-COOH] with ethylene glycol
[HO-C2H4-OH]
 Nylon is made by the condensation of adipic acid
[HOOC-(CH2)4-COOH] with hexamethylene
diamine [NH2-(CH2)6-NH2]
Introduction to Polymers
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28. BULK OR COMMODITY POLYMERS

29. SOME COMMON ADDITION
POLYMERS

30. MECHANISM OF ADDITION POLYMERIZATION
{FREE RADICLE REACTION MECHANISM}
 Free Radical Mechanism of chain reaction
involves 3 stages namely
I. Initiation
II.Propagation
III.Termination
 SCHEMATIC REPRESENTATION
[ R* - Free radical
M* - Unsaturated Monomer]
Introduction to Polymers
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31. • Generation of free radical :
I  2R E.g. I  CH2=CH2
• Initiation :
R + M  RM1
• Propagation :
RM1 + M  RM2
RM2 + M  RM3
RM( x – 1 ) + M  RM x
RM( y – 1 ) + M  RM y
• Termination :
RM x + RM y  RM x + y (COUPLING)
RM x + RM y  RM x + RM y (DISPROPORTIONATION)
Introduction to Polymers
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32. MECHANISM OF ADDITION
POLYMERIZATION OF POLY-ETHYLENE
Synthesis of poly-ethylene -(CH2-CH2)- n from
Ethylene, CH2=CH2 using di-benzoyl peroxide
(C6H5COO)2 as the indicator
n CH2=CH2  -(CH2-CH2)- n
(C6H5COO)2
Generation of free radical
(C6H5COO)2 2C6H5COO 2CO2 + 2C6H5 or (R)
Initiation
R + CH2=CH2 R-CH2-CH2
In General : R-(CH2-CH2)X-CH2-CH2
R-(CH2-CH2)Y-CH2-CH2
Introduction to Polymers
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33. Termination
 By coupling (by the combination of two radicals)
R-(CH2-CH2)X-CH2-CH2 + CH2-CH2-(CH2-CH2)Y-R
R-(CH2-CH2)X-CH2-CH2-CH2-CH2-(CH2-CH2)Y-R
 By disproportionation
R-(CH2-CH2)X-CH2-CH2 + R-(CH2-CH2)Y-CH2-CH2
R(CH2CH2)X-CH2-CH3 + R(CH2CH2)Y-CH=CH2
Introduction to Polymers
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34. SOME CONDENSATION
POLYMERS

35. 35
COPOLYMERS two or more monomers
polymerized together
 random – A and B
randomly positioned along
chain
 alternating – A and B
alternate in polymer chain
 block – large blocks of A
units alternate with large
blocks of B units
 graft – chains of B units
grafted onto A backbone
A – B –
random
alternating
block
graft

36. 1.8.3 Rubber (Elastomers)
1) Natural rubber :
cis-polyisoprene
2) Synthetic rubber :
Styrene-butadiene, Polybutadiene,
Ethylene-propylene(EPDM), Polychloroprene, Polyisoprene,
Nitrile, Butyl, Silicone, Urethane
3) Thermoplastic elastomer :
Styrene-butadiene block copolymer
(SB or SBS)
POLYMER CHEMISTRY

37. 37
MOLECULAR WEIGHT
• Molecular weight, M: Mass of a mole of chains.
Low M
• Polymers can havehi gvha Mrious lengths depending on
the number of repeat units.
• During the polymerization process not all chains in a
polymer grow to the same length, so there is a
distribution of molecular weights. There are several
ways of defining an average molecular weight.
• The molecular weight distribution in a polymer
describes the relationship between the number of
moles of each polymer species and the molar mass
of that species.

38. 38
Biopolymers
Nucleic acid polymers (DNA, RNA)
Amino acids polymers (Proteins)
Sugar polymers (Carbohydrates)
Genetic information for the cell: DNA
Structural strength and catalysis: Proteins
Energy source: Carbohydrates