B.Sc. Engineering First Year First Semester Engineering Chemistry Course on Polymer & its Classifications

1. CH 1105
ENGINEERING CHEMISTRY
Akib Jabed Shovon
Department of Mechanical Engineering
Khulna University of Engineering & Technology
Khulna 9203
Roll: 1705006
POLYMER

2. Polymer
1 | P a g e
a k i b j a b e d s h o v o n @ g m a i l. c o m
Polymer: Polymer may be defined as a substance in which many units of a single or two different
molecules are united together by a covalent bond.
Sodium chloride crystals & liquid water are not polymer. In sodium chloride crystals many molecules of
sodium chloride are united by ionic bond & in liquid water many water molecules are united by hydrogen
bond.
Monomer: The starting molecule from which the polymer molecule is formed is called monomer.
Degree of Polymerization: The number of monomer units which are united together to form a polymer
molecule, is called degree of polymerization.
Degree of polymerization =
Moleculer weight of Polymer
Molecular weight of Monomer
Polymers with a high degree of polymerization is called high polymers & those with low degree of
polymerization is called low polymers/oligomers.
High polymer have very high molecular weight in which the repeating units are more than 100. Hence
high polymers are also called macromolecules. But all macromolecules are not polymers. Such as vitamins
& carotene. The main difference between polymers & macromolecules is polymers are composed of
repeating units but these macromolecules are not composed of any repeating units.
Oligomers/low polymers have repeating unit less than 100.
Classifications of Polymer:
Depending upon the source polymers may be classified as-
1. Natural Polymer:
These polymers are obtained from nature. Example: rubber.
2. Synthetic Polymer:
These are manmade polymers. Examples: polyethylene, nylon, terylene, styrene etc. Synthetic
polymers are divided into three types:
a) Linear Polymer
b) Branched Polymer
c) Cross Linked Polymer
Usually linear & non-cross linked polymers are thermoplastic & cross linked polymers are thermosetting
polymers.
Depending upon the backbone chain polymers may be classified as-
1. Organic Polymer:
Backbone chain is essentially made up of carbon atoms.
2. Inorganic Polymer:
Backbone chain is made up of atoms other than carbon atom.

3. Polymer
2 | P a g e
a k i b j a b e d s h o v o n @ g m a i l. c o m
Depending upon the monomers polymers may be classified as:
1. Homo-Polymer:
Polymer molecule consists of a monomer unit only.
−𝐴 − 𝐴 − 𝐴 − 𝐴 − 𝐴 − 𝐴 − 𝐴 −
2. Co-Polymer:
Polymer molecule consists of two or more different monomer units. Co-polymers are divided into
two types-
a) Random Co-polymer
𝐴 − 𝐴 − 𝐵 − 𝐴 − 𝐵 − 𝐵 − 𝐴
b) Alternating Co-polymer
−𝐴 − 𝐵 − 𝐴 − 𝐵 − 𝐴 − 𝐵 − 𝐴 − 𝐵 −
Depending upon the mechanical properties polymers may be classified as-
1. Thermoplastic Polymer:
Thermoplastic are those polymers, which become soft on heating & can be given any desired
shape. These polymers are able to retain that given shape on cooling. However, on further heating
they become soft again with deformation of given shape. Thus the softening on heating & stiffen
on cooling can be repeated many times. As a result, thermoplastic polymers may be recycled
several times.
Examples: polyvinyl chloride, polyethylene, polypropylene, nylon:6,6 etc.
2. Thermosetting Polymer:
Thermosetting polymers may be defined as the polymers, which become soft on heating & can
be given any desired shape. The shape is retained on cooling. But during heating these type of
polymers undergo some chemical changes in their structure & convert themselves into infusible
& in soluble masses. As a result, on further heating they never be soft again. Thus thermosetting
polymers can’t be recycled.
Examples: bakelite, melamine etc.
Difference between Thermoplastic & thermosetting polymers:
No. Thermoplastic Polymers Thermosetting Polymers
1. Soften & melt on heating & become hard on
cooling. The process is reversible.
Soften & melt on heating & become hard on
cooling. The process is irreversible.
2. Can be moulded, remoulded & reshaped. Can’t be moulded, remoulded & reshaped.
3. Formed by additional polymerization. Formed by condensation polymerization.
4. Structure is generally linear. Structure is generally cross linked.
5. Low molecular weight. High molecular weight.
6. Soft, weak & brittle. Hard, strong & more brittle.
7. Soluble in organic solvents. Insoluble in organic solvents.
8. Can be reclaimed from wastes. Can’t be reclaimed from wastes.
9. Monomers used in these polymers are
generally bi-functional.
Monomers used in these polymers are
generally poly-functional.
10. Example: nylon:6,6. Example: melamine.

4. Polymer
3 | P a g e
a k i b j a b e d s h o v o n @ g m a i l. c o m
Synthesis of Polymer:
Polymer molecules may be synthesized by four different methods:
1. Addition Polymerization.
2. Condensation Polymerization.
3. Ring Opening Polymerization.
4. Oxidative Polymerization.
1. Addition Polymerization:
Addition polymerization may be defined as the process in which monomer units are added together to
form a polymer molecule without losing any small molecules. For example: Conversion of ethylene to
polyethylene.
𝑛𝐶𝐻2 = 𝐶𝐻2 → (−𝐶𝐻2 − 𝐶𝐻2 −) 𝑛
Depending upon the mechanism addition polymerization may be classified into two classes. These are-
a) Free Radical Addition Polymerization.
b) Ionic Addition Polymerization.
Whatever the method, the addition polymerization consists of three steps.
1. Initiation.
2. Propagation.
3. Termination.
a) Free Radical Addition Polymerization:
In this process the initiation of the polymerization reaction is carried out by the formation of free radical.
The transformation of the monomer molecule into free radical is done by the action of light, heat or
ionizing radiation or by the addition of external substances which are readily decompose into free radicals.
Chain Initiation:
In chemical initiation method the polymer reaction is initiated by the decomposition of some
organic & inorganic peroxides such as benzoyl peroxide, hydrogen peroxide, diazo compound etc.
The decomposition is carried out by the application of heat.
Chain Propagation:
These radicals serve as the active centers & cause chain propagation by combining with
monomers.

5. Polymer
4 | P a g e
a k i b j a b e d s h o v o n @ g m a i l. c o m
Chain Termination:
1. Combination: The union of the two free radicals terminates the chain propagation of
reaction.
2. Disproportion: It is the transfer of hydrogen atom from one macro radical to another one
to form two macromolecules; one with a double bond at its end & other is a saturated
molecule.
b) Ionic Polymerization:
Addition polymerization can be carried through the formation of ions by using different types of initiators.
Depending upon the nature of initiators, ionic addition polymerization may be carried out through the
formation of cation or through the formation of anion. In cationic polymerization acids particularly Lewis
acids are used as initiators. On the other hand, in anion polymerization bases particularly Lewis bases are
used as initiators.
I. Cationic Polymerization:
Chain initiation:
𝐴(𝐿𝑒𝑤𝑖𝑠 𝐴𝑐𝑖𝑑) + 𝐶𝐻2 = 𝐶𝐻2 → 𝐴: 𝐶𝐻3 − 𝐶𝐻2
+
Chain Propagation:
𝐴: 𝐶𝐻3 − 𝐶𝐻2
+
+ 𝐶𝐻2 = 𝐶𝐻2 → 𝐴: 𝐶𝐻3 − 𝐶𝐻2 − 𝐶𝐻2 − 𝐶𝐻2
+
𝐴: 𝐶𝐻3 − 𝐶𝐻2 − 𝐶𝐻2 − 𝐶𝐻2
+
+ 𝑛𝐶𝐻2 = 𝐶𝐻2 → 𝐴: 𝐶𝐻3 − 𝐶𝐻2 − (𝐶𝐻2 − 𝐶𝐻2) 𝑛 − 𝐶𝐻2 − 𝐶𝐻2
+
Chain Termination:
𝐴: 𝐶𝐻3 − 𝐶𝐻2 − (𝐶𝐻2 − 𝐶𝐻2) 𝑛 − 𝐶𝐻2 − 𝐶𝐻2
+
→ 𝐶𝐻3 − 𝐶𝐻2 − (𝐶𝐻2 − 𝐶𝐻2) 𝑛 − 𝐶𝐻 = 𝐶𝐻2 + 𝐴
II. Anionic Polymerization:
Chain initiation:
𝐵(𝐿𝑒𝑤𝑖𝑠 𝐵𝑎𝑠𝑒) + 𝐶𝐻2 = 𝐶𝐻2 → 𝐵: 𝐶𝐻3 − 𝐶𝐻2
−
Chain Propagation:
𝐵: 𝐶𝐻3 − 𝐶𝐻2
−
+ 𝐶𝐻2 = 𝐶𝐻2 → 𝐵: 𝐶𝐻3 − 𝐶𝐻2 − 𝐶𝐻2 − 𝐶𝐻2
−
𝐵: 𝐶𝐻3 − 𝐶𝐻2 − 𝐶𝐻2 − 𝐶𝐻2
−
+ 𝑛𝐶𝐻2 = 𝐶𝐻2 → 𝐵: 𝐶𝐻3 − 𝐶𝐻2 − (𝐶𝐻2 − 𝐶𝐻2) 𝑛 − 𝐶𝐻2 − 𝐶𝐻2
−
Chain Termination:
𝐵: 𝐶𝐻3 − 𝐶𝐻2 − (𝐶𝐻2 − 𝐶𝐻2) 𝑛 − 𝐶𝐻2 − 𝐶𝐻2
−
→ 𝐶𝐻3 − 𝐶𝐻2 − (𝐶𝐻2 − 𝐶𝐻2) 𝑛 − 𝐶𝐻 = 𝐶𝐻2 + 𝐵

6. Polymer
5 | P a g e
a k i b j a b e d s h o v o n @ g m a i l. c o m
2. Condensation Polymerization:
Condensation polymerization is the process in which many monomer molecules unite together to form a
big macromolecule with the loss of some simple molecules, usually water, carbon dioxide etc.
 Preparation of Nylon:6,6:
 Preparation of Dacron:
Difference between Chain Growth Polymerization & Step Growth Polymerization:
No. Chain Growth Polymerization Step Growth Polymerization
1. CGP is the formation of polymers from
unsaturated monomers.
SGP is the formation of polymers from bi-
functional or multi-functional monomers.
2. A polymer chain is formed at the beginning by
the attachment.
Oligomers are formed at the beginning are
later combined together forming polymer
chain.
3. Unsaturated monomers are used in CGP. Bi-functional & multi-functional monomers are
used in SGP.
4. No rapid loss of monomers at beginning. A rapid of monomers at the beginning.
5. An active site can be observed at the end of the
polymer chain.
All monomers are active themselves.
6. Initiators requires to break the double bond in
monomer molecules.
Doesn’t require initiators.
7. CGP shows no growth of polymerization after
termination.
SGP doesn’t show termination.
8. Only monomers & polymers are observed in
CGP.
Any type of molecule such as dimers, trimers,
tetramers & oligomers can be observed in SGP.
Nylon 6,6

7. Polymer
6 | P a g e
a k i b j a b e d s h o v o n @ g m a i l. c o m
Conductive Polymer:
Conductive Polymers are those polymers which can conduct electricity.
Advantages of Conductive Polymers over Traditional Polymers:
 Can provide electromagnetic shielding of electronic circuits.
 Can be used as antistatic coating material to prevent electrical discharge exposure on
photographic emulsions.
 Can be used as hole injecting electrodes for OLEDs
 In use as emissive layer in full color video display.
 Usage on electro luminescent (mobile/telephones).
 Some are promising for field effect transistors.
 Some absorbs microwaves.
Difference between Polymers & Macromolecules:
 Macromolecules & polymers are giant molecules both. Some macromolecules are polymer, but
not all. Some of them can’t be divided into small unit.
 Polymers are macromolecules with a repeating unit called monomer throughout the molecular
structure. But not all macromolecules have a monomer in their structure.
 Macromolecules comprise of both polymeric & non polymeric molecules. But polymer include
only polymerized molecules.
Living Polymer:
A polymer that continues to grow without chain termination steps until either all of the monomers are
consumed or external agent is added to terminate the chain.
Chain Initiation:
𝑁𝑎 + 𝑁𝑎𝑝𝑡ℎ𝑎𝑙𝑒𝑛𝑒 ⇄ 𝑁𝑎+
+ 𝑁𝑎𝑝𝑡ℎ𝑎𝑙𝑛𝑒−
Chain Propagation:
𝑁𝑎𝑝𝑡ℎ𝑎𝑙𝑛𝑒−
+ 𝑃ℎ − 𝐶𝐻 = 𝐶𝐻2 → 𝑁𝑎𝑝𝑡ℎ𝑎𝑙𝑒𝑛𝑒 + 𝑃ℎ − 𝐶𝐻 − 𝐶𝐻2 −
Polymer Properties & Structure:
Isotactic & Syndiotactic polymers are ordered polymer (more crystaline).
Atactic polymers are non-crystaline polymers.
Natural Rubber – Non crystaline.
Gutta Percha – Crystaline.

8. Polymer
7 | P a g e
a k i b j a b e d s h o v o n @ g m a i l. c o m
Polymer Structure:
1. Primary Structure (Chemical
Composition).
2. Secondary Structure.
Polymers have high molecular weight, have
higher strength.