Polymers are macromolecules formed by linking together small repeating units called monomers. There are two main types of polymerization: addition and condensation. Addition polymers are formed without the elimination of small molecules when monomers containing carbon-carbon double bonds polymerize via a chain reaction mechanism involving three steps: initiation, propagation, and termination. Condensation polymers are formed with the elimination of small molecules like water or ammonia when bifunctional monomers react. Common examples of addition polymerization include polyethylene formed from ethylene monomers using a free radical initiator like benzoyl peroxide.

1. POLYMERS
•POLYMERS
•INTRODUCTION & CLASSIFICATION OF
Introduction to Polymers
POLYMERS
•ADDITION & CONDENSATION – POLYMERIZATION
•FREE RADICAL REACTION MECHANISM
BY,
MOHAMMED MAAZ
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2. WHAT ARE POLYMERS, MONOMERS
AND
POLYMERIZATIONS?
Polymers are macromolecules built up by the linking
Introduction to Polymers
together of large numbers of much smaller molecules.
Polymerization : The process of linking the repeating
units (monomers) is termed as polymerization
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3. WHAT ARE POLYMERS, MONOMERS
AND
POLYMERIZATIONS?
The small molecules which combine with each other to
Introduction to Polymers
form polymer molecules are termed monomers.
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4. Introduction to Polymers
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5. HOW BIG ARE POLYMERS?
Ethylene Polyethylene
Introduction to Polymers
Let CH2-CH2 ≈ 1 inch
Consider only a 200
- mer, Mw ≈ 5600
This ends up with a chain of approximately 1/4 inch (6.4 mm)
in diameter and 1/2 mile (805 m) long. 5

6. CLASSIFICATION OF POLYMERS
DEPENDING ON THEIR STRUCTURE
Linear polymers
Introduction to Polymers
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7. CLASSIFICATION OF POLYMERS
DEPENDING ON THEIR STRUCTURE
Branched polymers
Introduction to Polymers
What is the effect of branching on polymer
Crystallinity
properties?
Is it branched polymer?!!! 7

8. Introduction to Polymers
LINEAR POLYMER
Branched polymer
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9. CLASSIFICATION OF POLYMERS
DEPENDING ON THEIR STRUCTURE
Cross-linked polymers
Crosslinked polymers do not dissolve but can be swelled
by liquids.
Introduction to Polymers
Light cross-linking improves elasticity properties
Using appropriate monomers
Chemical reactions
⇒ polymer is used as rubber
High degree of crosslinking gives high rigidity and
thermal stability (high melting point).
Polymer molecules are connected together at points
BOTHthan their ends
other CROSSLINKED POLYMERS CANNOT BE RECYLED
OR REPOROCESSED 9

10. TYPES OF POLYMERS &
POLYMERIZATIONS
Classification
of Polymers
Polymerization
Polymer Structure
Mechanism
Condensation Addition Step- Chain-
Polymers Polymers Polymerization Polymerization
Introduction to Polymers 10

11. TYPE OF POLYMERIZATION
 Monomers undergo polymerizaton by two types. They are:
Introduction to Polymers
• Addition or chAin polymerizAtion
• condensAtion or step polymerizAtion
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12. THE ADDITION-CONDENSATION
SYSTEM
What are addition polymers?
Introduction to Polymers
Addition polymers are those formed from monomers
without the loss of a small molecule.
Y Y
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13. Polymer Structure
The addition-condensation system
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.
-R-Z-R-Z-R-Z-R-Z-R-Z-
R is aliphatic or aromatic grouping and Z is functional unit. 13

14. Polymer Structure
The addition-condensation system
Introduction to Polymers
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.
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15. ADDITION POLMERIZATION
 Self addition of several bifunctional monomers to
each ohter takes place by chain reaction without
the elimination of any simple molecules.
Introduction to Polymers
 GENERAL REACTION:
n [CH2=CH]  [-CH2-CH-]n
| |
Y Y
Where Y=H,Ethylene,CH3,Propylene,Cl, Vinyl 15
Chloride, C6H5, Sterene, CN , Acrylonitrile

16.  Addition polymerization is initiated
by small qty of substance called
Introduction to Polymers
Initiators.
 E.g.-Zeigler-Natta catalyst,
potassium persulphate , dibenzoyl
sulphat e.
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17. CONDENSATION
POLYMERIZATION
• Self addition of several bifunctional monomer to
each other takes place accompanying elimination
of simple molecues like H2O,NH3 & HCL
Introduction to Polymers
• General reaction:
n[HOOC-X-COOH] + n[HO-Y-OH]
HO-[….OC-X-COO-Y-O]n-H + (2n-1)H20
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18. E.g..
 Terylene is obtained by condensing terpthalic
Introduction to Polymers
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]
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19. MECHANISM OF ADDITION POLYMERIZATION
{FREE RADICLE REACTION MECHANISM}
 Free Radical Mechanism of chain reaction
involves 3 stages namely
Introduction to Polymers
II. Initiation
III.Propagation
IV.Termination
 SCHEMATIC REPRESENTATION
[ R* - Free radical
M* - Unsaturated Monomer]
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20. • Generation of free radical :
I  2R E.g. I  CH2=CH2
• Initiation :
R + M  RM1
Introduction to Polymers
• 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) 20

21. MECHANISM OF ADDITION
POLYMERIZATION OF POLY-
ETHYLENE
Synthesis of poly-ethylene -(CH2-CH2)- n from
Ethylene, CH2=CH2 using di-benzoyl peroxide
Introduction to Polymers
(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
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R-(CH2-CH2)Y-CH2-CH2

22. Termination
 By coupling (by the combination of two radicals)
R-(CH2-CH2)X-CH2-CH2 + CH2-CH2-(CH2-CH2)Y-R
Introduction to Polymers
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
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