Engineering Chemistry

Copyright  2012 Wiley India Pvt. Ltd. All rights reserved.

 POLYMERS
Large molecules made up of many smaller and identical
repeating units Called -> monomers
These repeating units joins together by covalent bonds
forming polymer.

monomers

polymer
A polymer is a large molecule made by linking together
repeating units of small molecules called monomers

Preapred by: Mr. Harminder Singh 3

Preapred by: Mr. Harminder Singh 4
 Some Important Terms

• Degree of polymerization: The number of repeating units

present in a polymer is called degree of polymerization.
• “n” is called degree of polymerization. When n is large,
the polymers are called high polymers. For low values of
n, less than 10, the polymers are called oligomers.
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Preapred by: Mr. Harminder Singh 7
Classification of Polymers :

 (A)Classification on the basis of occurance :

 (B)Classification of polymers on the basis of structure
 (C) Classification on the basis of mode of synthesis
 (D) Classification based on the type of monomers
 (E) Classification based on the stereochemistry or
tacticity
 (F) Classification on the basis of Organic and Inorganic
polymers
 (G)Elastomer , Fibers, resins and plastics
Classification of polymers

1. Natural and Synthetic Polymers:

Natural polymers: wood, cellulose,, jute, cotton, wool etc.
Synthetic polymers: PE, PVC, epoxy resin etc.

Engineering Chemistry
Copyright  2012 Wiley India Pvt. Ltd. All rights reserved.
2. Thermoplastic and thermosetting polymers
Thermoplastic polymers: The polymers that soften on
heating and which can be converted into any shape on
cooling are called thermoplastics. The process of heating,
reshaping, and retaining the shape on cooling can be
repeated several times without affecting their properties
much. Ex: PE, PolyCarbonate(PC), Polytetrafluoro ethylene
(PTEE) etc.
Thermosetting polymers: Polymers that undergo chemical
changes and cross-linking on heating and become
permanently hard, rigid and infusible on cooling, are called
thermosetting polymers. They do not soften on reheating;
instead they undergo degradation. Ex: phenol-formaldehyde
(bakelite), urea-formaldehyde etc.
3. Addition polymers
The polymers formed by self-addition of several monomers to
each other without elimination of byproducts are called
addition polymers. Ex: PVC, PE etc.

•Monomers add successively to a growing polymer chain

•Polyethylene and polystyrene are addition polymers.
•Only olefinic or vinyl compounds can undergo addition
polymerization.
•No elimination of byproducts.
•Double bond provides required bonding sites.
•The elemental composition of the polymer is the same as that of
monomer.
•The addition of monomers takes place rapidly.
•Polymerization is brought about by initiators like free radicals.
 Addition Polymerization Example

In this type of polymerization C=C bonds of monomers react to form larger

monomers until the unit is a larger polymer chain as seen here.

Table on the next slide shows ethylene monomer based polymers

Engineering Chemistry
Copyright  2012 Wiley India Pvt. Ltd. All rights reserved.
Fig. Examples of addition polymers.
 Condensation Polymer
The polymers formed by intermolecular condensation reaction by the
functional groups of monomers with continuous elimination of small
molecules such as ammonia, water etc. Ex: nylon-6,6; polyester etc.

•Polymer chain grows when monomers combine and split out water or other
small molecule.
•Nylon 6,6 and polyurethane are condensation polymers.
•The monomers having two or more reactive functional groups can undergo
condensation polymerization.
•There is continuous elimination of byproducts.
•Polymerization proceeds through intermolecular condensation.
•Polymerization is catalyzed by acids or alkali.
•The polymer chain built up is slow and stepwise.
•The elemental composition of the polymer is different from that of the
monomers.
Condensation Polymer Example
4. Classification on the basis of type of monomers
Homopolymers and copolymers

Fig. Homopolymers and Copolymers

 Homo Polymerization Example

In this type of polymerization C=C bonds of monomers react to form larger

monomers until the unit is a larger polymer chain as seen here.

Table on the next slide shows ethylene monomer based polymers

Engineering Chemistry
Copyright  2012 Wiley India Pvt. Ltd. All rights reserved.
Preapred by: Mr. Harminder Singh 18
 Copolymerization
The polymerization of two or more different monomers resulting in the
formation of a polymer containing both monomers linked in one chain is called
copolymerization. It is considered as a type of addition polymerization. The polymers
so formed are called copolymers.
A copolymer is a polymer that has two types of monomer units in its chain .
•Block copolymer: When repeating units of each kind appear in blocks, it is called a
block copolymer.
•Random copolymer: If the various repeating units occur randomly along the chain
structure, the polymer is called a random copolymer.
•Graft copolymers: They are formed when chains of one kind are attached to the
backbone of a different polymer.
5. Classification on the basis of stereochemistry
Atactic, isotactic and syndiotactic polymers

Side Group is random

Side Groups are on same side

Side Groups are on

alternating fashion
Fig. Atactic, isotactic and syndiotactic polymers.

Engineering Chemistry
Copyright  2012 Wiley India Pvt. Ltd. All rights reserved.
5. Classification on the basis of stereochemistry

isotactic – pendant methyl syndiotactic – pendant methyl

groups are on the same groups alternate sides of the polymer
side of the polymer backbone
backbone

atactic – pendant methyl groups are

randomly arranged along polymer
backbone
6. Organic and Inorganic polymers
A polymer whose backbone chain is essentially made up of carbon atoms is termed as
organic polymers. The atoms attached to the side valencies of the backbone carbon atoms
are hydrogen, oxygen, nitrogen etc. Ex. Majority of synthetic polymers are organic
polymers. E.g ., PE , PVC , PMMA
The polymers that do not contain a carbon atom in their backbone chain is called
inorganic polymers. E.g.,
CH3

Silicon polymers -(- Si –O--)n-

CH3

Polyboron nitride polymer -(--B N ---) n---

Engineering Chemistry
Copyright  2012 Wiley India Pvt. Ltd. All rights reserved.
 Elastomer , Fibers, resins and plastics
• Elastomer : The polymer which undergo very long elongation
when pulled apart and return to its original shape on release.
• Fibers : These are long thin and thread like polymer, whose
length is almost 100 times their diameter. They do not
undergo streaching and deformation like Elastomer .
Elastomer Fibers
Resin : These are low mol. Wt. polymers, used as adhesive. They can be in
the form of liquid , powder , or solid.
Plastic: They are polymers which can be molded into desired shapes by
the application of heat and pressure e.g., PVC, TEFLON and PE,
PLEXIGLASS
Plastic

Resin
 Structure-property relationship

The structure of the polymer depends on the

(a) Size and shape of the polymer chain and

(b) Chemical nature of the monomers.
The structure of the polymers further affects the
physical and mechanical properties of polymers

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The tensile strength of a material
quantifies how much stress the
material will endure before
suffering permanent deformation.
For example, a rubber band with
a higher tensile strength will hold
a greater weight before snapping 26
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 Crystallinity

Linear polymers have higher crystallinity, because the atoms along the chain
Permit closer approach, branched polymer will have low crystallinity.

Polymers containing polar groups can form H-bonding, so have higher

crystallinity.

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 Glass transition temperature and melting point

The temperature below which a polymer is hard, brittle and above which it is soft
and flexible, is called the transition temperature , and it is denoted by Tg.

The hard, brittle state is known as the glassy state and the soft flexible state is
called the rubbery state.

In the glassy state , there is no segmental and molecular motion .

On the other hand in the rubbery state, there is only segmental motion but no
molecular mobility.

Segmental motion in polymers refers to the movement of small

chain segments.

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 Factors Affecting Tg

1.Flexibility 2. Effect of side chain 3. Intermolecular forces

4. Branching and cross linking 5. Presence of plasticizer

6. Stereo regulatory 7. Molecular weight

Linear chain poly more flexible - lower Tg,

branched chain rigid in nature - higher Tg
Strong intermolecular forces - higher Tg
Branching - lower Tg
Branching and cross linking - higher Tg
Presence of plasticizer - lower Tg
Isotactic - higher Tg
Syndiotactic - lower Tg
Higher Molecular weight - higher Tg

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Advanced Polymeric Materials (plastic)

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Classification of plastic

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Mechanism of Injection molding

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Advantage of Injection molding

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USES

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 Polypropylene

Application:-
For making packaging container, furniture and toys.
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Adhesives

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Degradable polymers

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 Liquid Crystals
Liquid crystals (LCs) are matter in a state that has properties between those of
conventional liquid and those of solid crystal. For instance, an LC may flow like a
liquid, but its molecules may be oriented in a crystal-like way.

Nematic liquid crystal

The nematic liquid crystal phase is characterized by molecules that have no positional order
but tend to point in the same direction. In the following diagram, notice that the molecules
point vertically but are arranged with no particular order

Nematic liquid crystal

Smectic phases
The smectic phases, which are found at lower temperatures than the nematic, form well-
defined layers that can slide over one another in a manner similar to that of soap. In the
smectic state, the molecules not only maintain the general orientational order of nematics, but
also tend to align themselves in layers or planes.

Smectic phases

In the nematic phase the molecules of a liquid crystal are rod shaped and pack next to each
other. In the smectic phase basically the molecules are placed in layers that can slide past
each other.
 Dendrimers
• Dendrimers are repeatedly branched, roughly
spherical large molecules. The name comes from
the Greek word (pronounced dendron), which
translates to "tree”.

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Application of Composite