This document provides an introduction to polymers. Polymers are macromolecules formed by linking many smaller molecules called monomers through a process called polymerization. Polymers can be classified based on their structure as linear, branched or cross-linked. Polymerization occurs through either addition or condensation reactions. Addition polymers are formed without the loss of small molecules, while condensation polymers are formed with the loss of small molecules like water or ammonia. Common examples of addition and condensation polymers are also provided.
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
6. How big are polymers?
Let CH2-CH2 ≈ 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.
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
⇒ 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
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12. Type of Polymerization
Monomers undergo polymerizaton by two types. They
are:
• Addition or chain polymerization
• Condensation or step polymerization
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13. The addition-condensation
system
Addition polymers are those formed from monomers
without the loss of a small molecule.
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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 (-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.
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.
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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 [CH2=CH] [-CH2-CH-]n
| |
Y Y
Where Y=H,Ethylene,CH3,Propylene,Cl, Vinyl
Chloride, C6H5, Sterene, CN , Acrylonitrile
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17. – Addition polymerization is initiated by small qty of
substance called Initiators.
– E.g.-Zeigler-Natta catalyst, potassium persulphate ,
dibenzoyl sulphat e.
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18. Condensation polymerization
• Self addition of several bifunctional monomer to each
other takes place accompanying elimination of simple
molecules like H2O,NH3 & HCL
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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]
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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]
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21. • 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)
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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
(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-CH2Introduction to Polymers 22
23. 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 23