Basic Terms : Macromolecule, Monomer , Repeat Unit, Classification of polymers based on Origin, thermal response Polymerisation , Addition and condensation , Degree of Polymerisation, Polymer Structures - Linear , Branched and Cross-linked. Molecular weight of Polymers: Definition and Formulae of Number Average Molecular Weight , Weight Average Molecular weight, Viscosity Average Molecular Weight , Z-average Molecular Weight. Polydispersity Index

1. 02/10/2023 SYBSc Sem III Paper II - Polymer Chemistry Dr. Aqeela Sattar, Royal College
POLYMER CHEMISTRY
✓ Macromolecules / Giant molecules
✓ Greek word – Poly (many) , mer (parts)
✓ Introduced by Berzelius (1833)
Polymers are giant molecules or macromolecules formed by several repeat units.
the term polymer is derived from the Greek words ‘poly’ (many) and mer (parts or
units) introduced by Berzelius (1833) to designate two or more molecules with
higher molecular weight the individual small molecules from which the polymer
is formed are known as ‘monomer’ and the process by which the monomer
molecules are linked to form a big polymer molecule is called ‘polymerisation’
Eg. Butadiene (gaseous) with a M.W = 54 , combines nearly 4000 times to give a
polymer called Polybutadiene with a M.W of about 2,00,000.
DEGREE OF POLYMERISATION : The size of the polymer molecule is decided by
the no.of repeating units present in it. This no. is termed as degree of
polymerisation (D.P)
CLASSIFICATION OF POLYMERS
Polymers have different chemical structures, physical, properties, mechanical
behaviour, thermal characteristics and can be classified in different ways.
1. Based on Origin:
a) Natural Polymer: Polymers which are available in nature or which can be
isolated from natural materials are called natural polymers. Eg. Cotton, silk,
wool , rubber.
b) Semi-synthetic polymers : These are chemically modified natural polymers
such as hydrogenated or halogenated or hydro halogenated natural rubber,
ethers and esters of cellulose such as cellulose nitrate etc.
c) Synthetic Polymers :
Polymer synthesised from low molecular weight compounds are called
synthetic polymers. Eg. Polyethylene , PVC , terylene.
2. BASED ON NATURE OF BACKBONE CHAIN :
a) Organic Polymers : A polymer whose backbone chain is essentially of
carbon atoms is termed as an organic polymer. The atoms attached to the C-
atoms are usually those of hydrogen, oxygen , nitrogen etc. The majority of
synthetic polymers are organic polymers.

2. 02/10/2023 SYBSc Sem III Paper II - Polymer Chemistry Dr. Aqeela Sattar, Royal College
b) Inorganic Polymers : These polymers do not contain C-atoms in their chain
backbone. Eg. Mg-oxide, silicon, germanium, glass etc.
BASED ON THERMAL RESPONSE:
1) Thermoplastic polymers –
▪ Some polymers soften on heating & can be converted into any shape
that they can retain on cooling
▪ The process of heating reshaping and retaining the same on the cooling
can be repeated several times
▪ Such polymers that soften on heating & stiffen on cooling are termed as
Thermoplastics polyethiene
▪ PVC, Nylon & sealing wax, poly vinyl resins are examples of
thermoplastic polymers
▪ In this polymer this is no chemical cross linking
▪ They are soluble in organic solvent
▪ They are expensive
2) Thermosetting polymers ;-
▪ These polymers undergo irreversible chemical change on heating they
are like the yolk of the egg which on heating sets into a mass & once set
called thermosetting polymers
▪ In these polymers generally cross linking takes place
▪ These polymers are very hard
▪ Examples of thermosetting polymers include epoxy-plastics, bakelight,
urea formaldehyde, phenol formaldehyde polymers
▪ They are insoluble in organic solvent
▪ Not very expensive

3. 02/10/2023 SYBSc Sem III Paper II - Polymer Chemistry Dr. Aqeela Sattar, Royal College
BASED ON APPLICATION AND PHYSICAL PROPERTIES:
Elastomers: An elastomer possess the high degree of elasticity. This is
characteristic of rubber. These polymers have flexible chains. When they
stretched, they get deformed in their original shape and when stretching force
is removed it returns to its original form. These polymers do not contain
highly polar groups or hydrogen bonding.
Natural rubber, synthetic rubber, silicon rubber are elastomer
Plastics: There are usually much stronger then elastomer or rubbers some of
them are hard, rigid, stiff and dimensionally stable, while others may be soft
and flexible. Example: PVC, polystyrene etc
Fibers: These polymers which can be drawn into long filaments like material
and whose length is at least 80 to 100 times its diameter are called fibers.
Natural fibres are cotton and wool. Synthetic fibers include polyester fiber ,
acrylic fibers nylon and terylene.
Liquid resins: The polymers which are used as adhesives or sealing agent in a
liquid form are called liquid resins Eg epoxy adhesives, polysulphide sealing
agent etc.
BASED ON MODE OF FORMATION :
Addition polymers: These polymers are formed by multiple addition of
olefinic monomers such as ethylene, vinyl chloride etc. These polymers are
formed without elimination of any simple molecules.
Condensation polymers: The polymers formed by a reaction in which
monomers react by the elimination of small molecules (like H2O,CO2 etc ) is
called condensation polymers.

4. 02/10/2023 SYBSc Sem III Paper II - Polymer Chemistry Dr. Aqeela Sattar, Royal College
Homopolymers:
When a polymer has identical repeating units, it is known as homopolymer.
Copolymer : When two or more different monomers are linked together then it
is known as Copolymer
- A – A – A – A – A - - A – B – A – B – B – A -
Homopolymer Copolymer
FORMS OF COPOLYMERS:
Regular or Alternating Copolymer : In a copolymer when the monomer
units are arranged in a chain in regular manner we get a regular or
alternating copolymer
Random or Irregular copolymers : When the monomer units are arranged in
an irregular manner the copolymer is called an irregular copolymer.
Block Copolymer : Linear copolymers in which like monomeric units occur in
relatively long sequence are known as block copolymer.
Graft Coplymers : These are branched chain structures in which monomer
segments on the branches and the backbone are different.

5. 02/10/2023 SYBSc Sem III Paper II - Polymer Chemistry Dr. Aqeela Sattar, Royal College
Molecular weights of polymers:
 All polymer molecules do not grow to the same extent or terminate
at the same time hence polymer molecules containing the same
monomer can have different molecular weights
 Example : Polyethylene – Here the monomer ethylene ( CH2=CH2 )
has M.W= 28 but polyethylene can have different degree of
polymerisation and hence different molecular weights
 It is therefore necessary to consider an average molecular weight in
such substances
𝑵𝒖𝒎𝒃𝒆𝒓 Average Molecular Weight (𝑴𝒏):
𝐶𝑜𝑛𝑠𝑖𝑑𝑒𝑟 a polymer sample in which n1, 𝑛2, 𝑛3, . . .
𝑎𝑟𝑒 the number of molecules with molecular weights
𝑀1, 𝑀2, 𝑀3, . . . . . 𝑟𝑒𝑠𝑝𝑒𝑐𝑡𝑖𝑣𝑒𝑙𝑦, 𝑡ℎ𝑒𝑛 the number average
Molecular weight can be expressed as
Mn =
𝑛1𝑀1 + 𝑛2𝑀2 + 𝑛3𝑀3+. . . . .
𝑛1 + 𝑛2 + 𝑛3+. . . .
Mn =
∑ 𝑛𝑖𝑀𝑖
∑ 𝑛𝑖

6. 02/10/2023 SYBSc Sem III Paper II - Polymer Chemistry Dr. Aqeela Sattar, Royal College
𝑤ℎ𝑒𝑟𝑒 'n𝑖′ is the number of molecules of the ith
type with molecular weight 'M𝑖′
 Number average molecular weight can be obtained by the
methods based on cryoscopy, ebuillioscopy or osmometry
which are colligative in nature
Weight Average Molecular Weight:
𝐶𝑜𝑛𝑠𝑖𝑑𝑒𝑟 a polymer sample in which m1, 𝑚2, 𝑚3, . . .
𝑎𝑟𝑒 the masses of molecules with molecular weights
𝑀1, 𝑀2, 𝑀3, . . . . . 𝑟𝑒𝑠𝑝𝑒𝑐𝑡𝑖𝑣𝑒𝑙𝑦, 𝑡ℎ𝑒𝑛 the weight average
Molecular weight can be expressed as
Mw =
𝒎𝟏𝑴𝟏 + 𝒎𝟐𝑴𝟐 + 𝒎𝟑𝑴𝟑+. . . . .
𝒎𝟏 + 𝒎𝟐 + 𝒎𝟑+. . . .
Mw =
∑ 𝒎𝒊𝑴𝒊
∑ 𝒎𝒊
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7. 02/10/2023 SYBSc Sem III Paper II - Polymer Chemistry Dr. Aqeela Sattar, Royal College
𝑉iscosity Average Molecular Weight (𝑀𝑣):
𝑀𝑒𝑎𝑠𝑢𝑟𝑒 of intrinsic viscosity gives the viscosity average
molecular weight. It can be calculated by the relation
Mv = [
∑ 𝑛𝑖𝑀𝑖
(1+𝛼)
∑ 𝑛𝑖𝑀𝑖
]
1
𝛼
⁄
𝑤ℎ𝑒𝑟𝑒 'n𝒊' is no. of molecules having molecular weight 'M𝒊'
present in the sample and '𝛼' is the exponent related to [𝜂] as
[𝜂] = K 𝑴𝒗
𝛼
𝑤ℎ𝑒𝑟𝑒 [𝜂] = intrinsic viscosity and 'K' is constant.
When 𝛼 = 1 , Mv = Mw
𝑉𝑎𝑙𝑢𝑒 of '𝛼' can vary from 0.5 to 1.0
𝒁 − Average Molecular Weight (𝑀𝒛):
Mz =
∑ 𝑛𝑖𝑀𝑖
𝟑
∑ 𝑛𝑖𝑀𝑖
𝟐 =
∑ 𝒘𝑖𝑀𝑖
𝟐
∑ 𝒘𝑖𝑴𝒊
𝑤ℎ𝑒𝑟𝑒 'n𝒊
′
is no. of molecules having molecular weight 'M𝒊
′
𝐓𝐡𝐞 𝐦𝐨𝐥𝐚𝐫 𝐦𝐚𝐬𝐬 𝐝𝐞𝐩𝐞𝐧𝐝𝐬 𝐨𝐧 𝐬𝐢𝐳𝐞 𝐚𝐧𝐝 𝐦𝐚𝐬𝐬 𝐨𝐟 𝐭𝐡𝐞 molecule. Ultra
centrifugation technique is used to determine Z-average molecular weight of
polymer.
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