Polymer science deals with large macromolecules formed by bonding many small monomer units together. There are two main types of polymerization: addition polymerization and condensation polymerization. In addition polymerization, monomers add together through a chain reaction of initiation, propagation, and termination steps. Condensation polymers form when monomers bond together while releasing small molecules, like water. Polymers can be classified in various ways, including their source, monomer composition, chain structure, and properties like being thermoplastic or thermosetting. Common polymers have a wide range of applications as plastics, fibers, elastomers, and more.

1. Lecture 1

2. Introduction to Polymers
• Poly = many, mer = unit, many units
•Polymer science is relatively a new branch of science
•It deals with chemistry physics and mechanical
properties of macromolecule
•The small molecules which combine with each other
to form polymer molecules are termed monomers.
The dimmers trimmers are called oligomers.
Oligomers combine to produce polymer

3. DEFINITION
The word ‘polymer’ comes from the Greek
words poly (meaning ‘many’) and meros
(meaning ‘parts’).
Example: POLYBUTADIENE =
(BUTADIENE+ BUTADIENE+......)n
Where n = 4,000
Polymers are very large molecules made when hundreds of
monomers join together to form long chains.

4. POLYMERISATION
• The process by which the monomer molecules are linked
to form a big polymer molecule is called ‘polymerisation’.
• Polymerization is a process of bonding monomer, or
“single units” together through a variety of reaction
mechanisms to form longer chains named Polymer
• As important as polymers are, they exist with monomers,
which are small, single molecules such as hydrocarbons
and amino acids.

5. The no. of repeating units in a chain of polymer is known as
degree of polymerization
Degree of polymerization

6. 6 Introduction to Polymers
Common polymers used in Textile industry

7. Classification schemes
Classification by Origin
Synthetic organic polymers
 Biopolymers (proteins, polypeptides, polynucleotide,
polysaccharides, natural rubber)
 Semi-synthetic polymers (chemically modified synthetic
polymers)
 Inorganic polymers (siloxanes, silanes, phosphazenes)

8. Classification by Monomer Composition
Homopolymer Copolymer
Block Graft Alternating Statistical
Homopolymer
Consist of only one type of constitutional repeating unit (A)
AAAAAAAAAAAAAAA
Copolymer
Consists of two or more constitutional repeating units
(A.B )

9.  Statistical copolymer (Random)
ABAABABBBAABAABB
two or more different repeating unit
are distributed randomly
 Alternating copolymer
ABABABABABABABAB
are made of alternating sequences
of the different monomers
 Block copolymer
AAAAAAAAABBBBBBBBB
long sequences of a monomer are
followed by long sequences of another
monomer
 Graft copolymer
AAAAAAAAAAAAAAAAAA
B B B
B B B
(d)
Several classes of copolymer are possible

10. Classification by Chain structure (molecular architecture)
Linear chains :a polymer consisting of a single continuous
chain of repeat units
Branched chains :a polymer that includes side chains of
repeat units connecting onto the main chain of repeat units
Hyper branched polymer :consist of a constitutional
repeating unit including a branching groups
Cross linked polymer :a polymer that includes
interconnections between chains
Net work polymer :a cross linked polymer that includes
numerous interconnections between chains

11. Molecular Structure of Polymer
Linear
– High Density Polyethylene (HDPE), PVC, Nylon,
Cotton
Branched
– Low Density
- Polyethylene (LDPE)
Cross-linked
– Rubber
Network
– Kevlar, Epoxy

12. Thermoplastic and Thermosetting Polymer
 Some polymer are soften on heating and can be converted
into any shape that they can retain on cooling.
 Such polymer that soften on heating and stiffen on cooling are
termed as `thermoplastic’ polymers.
Ex. Polyethylene, PVC, nylon, sealing wax.
 Polymer that become an infusible and insoluble mass on
heating are called ‘thermosetting’ polymers. Plastics made of
these polymers cannot be stretched, are rigid and have a high
melting point.

13. Plastics, Elastomers, Fibres & Liquid resins
 Polymer is shaped into hard and tough utility articles by
application of heat and pressure, is known as ‘plastics’.
E.g. polysterene, PVC, polymethyl methacrylate.
 When plastics are vulcanised into rubbery products exhibiting
good strength and elongation, polymers are known as
‘elastomers’.
E.g. silicone rubber, natural rubber, synthetic rubber, etc.
 Long filament like material whose length is atleast 100 times it’s
diameter, polymers are said to be ‘fibres’.
E.g. Nylon, terylene.
 Polymers used as adhesives, potting compounds, sealants, etc.,
in a liquid form are described as ‘liquid resins’.
E.g. Epoxy adhesives and polysulphides sealants.

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

15. Stage 1
Consumption
of monomer
n n
Stage 2
Combination
of small fragments
Stage 3
Reaction of
oligomers to give
high molecular
weight polymer
Step-Growth Polymerization

16. Polymerization mechanisms
- Chain-growth polymerization

17. Chain polymerization
Radical polym.
The C=C is prefer the
Polym. by R.P.
and also can be used in
the steric hindrance of
the substituent
Ionic polym.
Anionic polym. Cationic polym.
X X X
radical cationic anionic
Electron with drawing
substituent decreasing
the electron density on
the double bond and
facilitate the attack of
anionic species
such as cyano and
carbonyl
δ+ δ-
CH2=CH Y
Electron donating
substituent increasing
the electron density on
the double bond and
facilitate the attack of
cationic species
such as alkoxy, alkyl,
alkenyl, and phenyl
δ- δ+
CH2 =CH Y

18. It is useful to distinguishfour polymerization procedures fitting this general
description.
• Radical Polymerization The initiator is a radical, and the
propagating site of reactivity (*) is a carbon radical.
• Cationic Polymerization The initiator is an acid, and the
propagating site of reactivity (*) is a carbocation.
• Anionic Polymerization The initiator is a nucleophile, and
the propagating site of reactivity (*) is a carbanion.

19. STEPS FOR SYNTHESIS OF
POLYMERS
There are three significant reactions that take place in addition
polymerization:
Initiation
(birth)
Propagation
(growth)
Termination
(death)

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]
20 Introduction to Polymers

21. 1. INITIATION
INITIATOR:
• A relatively unstable molecule that decomposes into a
free radical. Used to "initiate" a polymer growth reaction.
(A molecule with an unpaired electron, making it highly
reactive).
• The stability of a radical refers to the molecule's
tendency to react with other compounds. An unstable
radical will readily combine with many different
molecules. However a stable radical will not easily
interact with other chemical substances.

22. • 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  RMx
RM( y – 1 ) + M  RMy
• Termination :
RMx + RMy  RMx + y (COUPLING)
RMx + RMy  RMx + RMy (DISPROPORTIONATION)
22 Introduction to Polymers

23. 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 inicator
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-CH223 Introduction to Polymers

24. 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
24 Introduction to Polymers

25. LIVING POLYMERISATION
• There exists a type of addition polymerization that does
not undergo a termination reaction. This so-called "living
polymerization" continues until the monomer supply has
been exhausted. When this happens, the free radicals
become less active due to interactions with solvent
molecules. If more monomers are added to the solution,
the polymerization will resume.
• Uniform molecular weights (low polydispersity) are
characteristic of living polymerization. Because the
supply of monomers is controlled, the chain length can
be manipulated to serve the needs of a specific
application. This assumes that the initiator is 100%
efficient.

26. Condensation polymers (New definition)
26 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.

27. • General reaction:
n[HOOC-X-COOH] + n[HO-Y-OH]
HO-[….OC-X-COO-Y-O]n-H + (2n-1)H20
27 Introduction to Polymers

28. • In A. P. mol. weight of polymer is roughly equal to that of all
monomers, while in C. P. the mol. weight of polymer is lesser by the
weight of simple molecules eliminated during the condensation
process.
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]

29. 29 Introduction to Polymers