Polymerization

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1. Introduction to Polymers 1

2. POLYMERS
Introduction to Polymers 2

3. Polymers and Polymerizations
Polymers are macromolecules built up by the linking
together of large numbers of much smaller molecules.
The process of linking the repeating units is termed as
polymerization .
Introduction to Polymers 3

4. Monomers
The small molecules which combine with each other to
form polymer molecules are termed monomers.
Introduction to Polymers 4

5. Introduction to Polymers 5

6. How big are polymers?
Let CH
2
-CH
2
≈ 1 inch
Introduction to Polymers 6
Ethylene Polyethylene
This ends up with a chain of approximately 1/4 inch (6.4 mm) This ends up with a chain of approximately 1/4 inch (6.4 mm)
in diameter and 1/2 mile (805 m) long.in diameter and 1/2 mile (805 m) long.

7. Classification of polymers
depending on their structure
Linear polymers
Introduction to Polymers 7

8. Classification of polymers
depending on their structure
Branched polymers
Introduction to Polymers 8
Is it branched polymer?!!!

9. Linear polymer
Introduction to Polymers 9
Branched polymerBranched polymer
Linear polymers

10. Classification of polymers
depending on their structure
Cross-linked polymers
Introduction to Polymers 10
Using appropriate monomers
Chemical reactions
Polymer molecules are connected together at points
other than their ends
Crosslinked polymers do not dissolve but can be swelled by
liquids.
Light cross-linking improves elasticity properties
Þ polymer is used as rubber
High degree of crosslinking gives high rigidity and thermal
stability (high melting point).
BOTH CROSSLINKED POLYMERS CANNOT BE RECYLED OR
REPOROCESSED

11. Types of polymers &
polymerizations
Classification
of Polymers
Polymer Structure
Polymerization
Mechanism
Step-
Polymerization
Chain-
Polymerization
Condensation
Polymers
Addition
Polymers
Introduction to Polymers 11

12. Type of Polymerization
Monomers undergo polymerizaton by two types. They
are:
•Addition or chain polymerization
• Condensation or step polymerization
Introduction to Polymers 12

13. The addition-condensation
system
Addition polymers are those formed from monomers
without the loss of a small molecule.
Introduction to Polymers 13
What are addition polymers?What are addition polymers?
Y Y

14. Condensation polymers
Introduction to Polymers 14
Polymers whose repeating units are joined together by
functional units such as ester (-OCO-), amide (-
NHCO-), urethane (-OCONH-), sulfide (-SO
2
-) and other
linkages.
-R-Z-R-Z-R-Z-R-Z-R-Z-
R is aliphatic or aromatic grouping and Z is functional unit.
Polymer StructurePolymer Structure
The addition-condensation systemThe addition-condensation system

15. 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 15
Polymer StructurePolymer Structure
The addition-condensation systemThe addition-condensation system

16. 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 [CH
2
=CH]  [-CH
2
-CH-]
n
| |
Y Y
Where Y=H,Ethylene,CH3,Propylene,Cl, Vinyl
Chloride, C6H5, Sterene, CN , Acrylonitrile
Introduction to Polymers 16

17. –Addition polymerization is initiated by small qty of
substance called Initiators.
–E.g.-Zeigler-Natta catalyst, potassium persulphate ,
dibenzoyl sulphat e.
Introduction to Polymers 17

18. Condensation polymerization
•Self addition of several bifunctional monomer to each
other takes place accompanying elimination of simple
molecules like H2O,NH3 & HCL
Introduction to Polymers 18

19. 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 19

20. 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 20

21. •Generation of free radical :
I  2R E.g. I  CH
2
=CH
2
•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)
21

22. 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
(C
6
H
5
COO)
2
Generation of free radical
(C
6
H
5
COO)
2
2C
6
H
5
COO 2CO
2
+ 2C
6
H
5
or (R)
Initiation
R + CH
2
=CH
2
R-CH
2
-CH
2
In General : R-(CH
2
-CH
2
)
X
-CH
2
-CH
2
R-(CH
2
-CH
2
)
Y
-CH
2
-CH
2
Introduction to Polymers 22

23. Termination
By coupling (by the combination of two radicals)
R-(CH
2
-CH
2
)
X
-CH
2
-CH
2
+ CH
2
-CH
2
-(CH
2
-CH
2
)
Y
-R
R-(CH
2
-CH
2
)
X
-CH
2
-CH
2
-CH
2
-CH
2
-(CH
2
-CH
2
)
Y
-R
By disproportionation
R-(CH
2-CH
2)
X-CH
2-CH
2 + R-(CH
2-CH
2)
Y-CH
2-CH
2
R(CH
2
CH
2
)
X
-CH
2
-CH
3
+ R(CH
2
CH
2
)
Y
-CH=CH
2
Introduction to Polymers 23

24. Introduction to Polymers 24