Introduction to polymers

1. Polymers
Polymers are molecules with large molecular masses obtained by the covalent
linkage of small repeating units
These small repeating units are called ‘monomers’, which can be same or different
Homo polymer: Formed from same type of monomers; Eg: Poleyethylene,
Polypropylene, PVC etc
Co-polymer: Formed from two or more different monomers; Eg: butadiene-styrene
(BS), Acrylonitrile butadiene-styrene (ABS) etc.
Degree of polymerization: The number of monomers (repeating units) are called
degree of polymerization

2. Classification based on Types of polymerization
Polymers
Addition Polymers Condensation Polymers
1,2-addition 1,4-addition
Polyesters
-COO-
Polyamides
-CO-NH-
Polycarbonates
-O-COO-
Polyethers
-O-

3. Addition Polymers
 Formed by the combination of simple unsaturated
molecules through addition reaction
 Conversion of C-C π-bonds to strong C-C sigma bond is the
driving force for the polymerization
 Addition polymerisation is brought about by small amount
of initiators which will generate free radicals, cations,
anions etc which helps to grow the polymer
 The monomers added to the free radicals or active species
and the chain growth takes place. So addition
polymerisation is also known as chain growth
polymerisation
 There are two types: 1,2-addition and 1,4-addition

4. 1,2-Addition Polymers
 Each monomer consists of a π bond and it is converted into
a sigma bond by joining 1,2 positions of each monomer unit
Eg: Polymerisation of ethylene, propene, polyvinyl
chloride, styrene etc
1
2

5. 1,4-Addition Polymers
 Each monomer consists of two π bond and new bond is
formed at the middle (2,3 positions) by joining 1,4 positions
of each monomer unit
Eg: Polymerisation of butadiene, isoprene, chloroprene etc
2
3
4 1
When X = H, it is called polybutadiene rubber
Rubbers
When X = CH3, it is called polyisoprene; cis form is called natural
rubber and trans form is known as synthetic rubber (Gutta-percha)
When X = Cl, it is called chloroprene rubber or “Neoprene”

6. Condensation Polymers
 Linking together monomer units accompanied by the
elimination of simple molecules like water, ammonia, HCl
etc.
 Monomer units are usually different in this case
 Degree of polymerisation depends on the availability of the
reactive groups at the end of growing chain
 It is also known as “step-growth polymerization” as the
process takes place in a step by step manner

7. Condensation Polymers
Formation of PET

8. Co-polymers
Polymerization of 2 or more different monomeric species
together
Eg: Acrylonitrile-vinyl chloride, Butadiene-Styrene (BS),
Acrylonitrile-Butadiene-Styrene (ABS)
1
2

9. Types of co-polymers
1. Random co-polymers
During co-polymerization, if a mixture of monomers are allowed to
polymerize, random co-polymer will be formed
Eg: A mixture of acrylonitrile (A) and vinylchloride (B) is allowed to
polymerize the resulting random polymer will be like,
-A-A-B-A-B-B-B-A-B-A-A-A-B-B-A-B-A-B-
2. Alternating co-polymers
Two types of monomeric units distributed in alternating sequence.
Eg: A mixture of Styrene (A) and butadiene (B) is allowed to
polymerize the resulting alternate polymer (AB)n will be like,
-A-B-A-B-A-B-A-B-A-B-A-B-A-B-

10. 3. Block co-polymers
This type can be synthesized by partially polymerizing each monomer
into a resin or semi polymer. Semipolymer obtained on further
combination results Block co-polymers
Here the monomers form long blocks
-A-A-A-A-A-A-A-A-B-B-B-B-B-B-A-A-A-A-A-A-A
4. Graft co-polymers
This is a type of Block co-polymer. Here the semipolymer of one
monomer (B) are grafted to the high main polymer chain (A)
The arrangement will be represented as
-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A
B
B
B
B
B
B
B
B

11. Acrylonitrile Butadiene Styrene (ABS)
Synthesis:
 It is a ter polymer (3 diff units), made by polymerising styrene (40-60%) and
acrylonitrile (15-35%) in presence of poly butadiene (5-30%).
 ABS is a long chain of polybutadiene criss-crossed with shorter chains of
poly(styrene-co-acrylonitrile).
 The nitrile groups from neighboring chains, being polar, attract each other and
bind the chains together, making ABS stronger than pure polystyrene.

12. Properties of ABS
1. The styrene gives the plastic a shiny, impervious
surface. The polybutadiene, a rubbery
substance, provides toughness even at low
temperatures.
2. ABS is an amorphous thermoplastic polymer
with glass transition temperature of
approximately 105 °C (221 °F)
3. It has the strength and rigidity of acrylonitrile
and styrene with an added toughness of poly
butadiene
4. It is considered as one of the best due to its
hardness, gloss, toughness and electrical
insulation properties
5. It is resistant to aqueous acids and alkalies
Characteristics
1. Medium strength
2. Tough, Hard and Rigid
3. Good Chemical
Resistance
4. Dimensional Stability
5. Creep Resistant
6. Electroplatable
7. Outstanding
formability
8. High impact strength
9. High Tensile strength
10. Excellent ductility

13. Applications of ABS
LEGO building blocks
Used for the manufacturing of
 TV cabin
 Computer Monitor Body, Keyboard body
 Mobile Phone Body
 Kitchen Appliances
 Musical Instruments
 Automotive trim components

14. Kevlar (Poly-paraphenylene terephthalamide)
Synthesis:
 Kevlar is synthesized in solution from the monomers para-phenylene diamine and
tetraphthaloyl chloride in a condensation reaction yielding HCl gas as biproduct
 The product is a polymeric aromatic amide with alternating benzene rings and
amide groups
 When they are produced the polymer strands are aligned randomly
• The high strength of the polymer may be due to the inter-molecular hydrogen
bonds form between the carbonyl groups and NH centers.
• Additional strength is derived from aromatic stacking interactions between
adjacent strands.

15. Molecular Structure of Kevlar
Dashed lines indicates
the H-Bonds
Applications
1. Often used in the field of Cryogenics due to its low thermal conductivity and
high strength at low temperature
2. Used in aerospace applications due to its high strength to weight ratio
3. Kevlar is well known for the manufacture of personal armor such as combat
helmets, ballistic facemasks, ballistic vests, special type of gloves etc
4. Since they are found to have good acoustic properties, they are also used in
loudspeaker cones for bass and midrange drive units
5. Used as strength member in fibre optic cables for audio data transmissions