Engineering Chemistry and Environmental Studies UNIT VIII

8. Polymers

1) Define Polymer?

Ans:

Polymer:

Many simple molecules combined with each other to give a high molecular weight compound. This high molecular weight compound is called polymer.

Eg: Polythene, TEFLON, and PVC

2) Define Polymerization?

Ans:

Polymerization:

The reaction in which many simple molecules react to form a high molecular weight product is called polymerization.

The smaller reacting molecules are called monomers.

3) What are Types of polymerization?

Ans:

Types of polymerization:

The polymerization reactions are 3 types.

They are 1) Addition polymerization (or) chain polymerization

2) Condensation polymerization (or) step polymerization

3) Co-polymerization.

4) Explain the Addition polymerization with examples?

Ans:

1) Additional polymerization:

The polymerization is which monomers add together to form a high molecular weight product is called addition polymerization.

It is also called chain polymerization.

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2500 c, O2

1000 – 2000 atm

Engineering Chemistry and Environmental Studies UNIT VIII

In this polymerization, the monomers combine in a linear manner.

So, the polymer formed in chain structure.

The molecular weight equal to the sum of molecular weight of monomers.

In this polymerization no elimination of simple molecules.

This type of polymers is called homo polymers.

Eg: Formation of polythene.

Ethylene is polymerized at 1000 – 2000 atmosphere pressure and 2500 c in the presence of O2 to form polythene.

H H

n CH2 = CH2 C C

EthyleneH H n

PolytheneUses of polythene:

1) It is used to prepare insulators, bottles, caps, tubes, cables, wires.

2) It is used for making domestic things, toys.

2) Formation of poly vinyl chloride (PVC):

It is prepared by the addition polymerization of vinyl chloride in the presence of H2O2 under

pressure.

H HH Cl

n C = C C C

H Cl H H n

Vinyl chloride PVC

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Benzoyl

Peroxide

Engineering Chemistry and Environmental Studies UNIT VIII

Uses of PVC:

1) It is used for making helmets, tires, rain coats,

2) It is also used in conveyor belts, chemical containers.

3) Formation of Teflon (or) PTFE:

It is prepared by the addition polymerization of tetra fluoro ethylene in the presence of benzoyl

peroxide under pressure.

H HH Cl

n C = C C C

H Cl H H n

Tetra fluoro ethylene Teflon

Uses of Teflon:

1) It is used in transformers, cables etc.

2) It is also used for making burettes, bearing etc.

4) Formation of polystyrene:

It is prepared by the addition polymerization of styrene in the presence of benzoyl peroxide.

CH = CH2 CH CH2

n

Styrene Polystyrene

Uses of polystyrene:

1) It is used for making toys, combs, and buttons.

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Benzoyl

Peroxide

H2SO4

Engineering Chemistry and Environmental Studies UNIT VIII

2) It is also used in optical and photographic equipment.

5) Explain the Condensation polymerization?

Ans:

Condensation polymerization:

The polymerization in which many, small, different molecules react to form in a polymer with

the elimination of simple molecules like H2O, NH3etc is called condensation polymerization.

This type of polymerization generally occurs between different types of monomers.

A cross – linked polymer is formed.

The reaction occurs in three dimensional manner.

Eg: Formation of Bakelite:

Bakelite is prepared by the condensation polymerization of formaldehyde and phenol with

hexamine in the presence of H2SO4

Phenol + Formaldehyde Ortho (or) Para hydroxyl methylol Benzene

+ HCHO

OH

CH2OH OH CH2OH

(or)

OH

Uses of Bakelite:

1) To prepare electric switch boards switches.

2) To prepare T.V., Radio parts.

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n

OH-

Hexamine

-H2O

Engineering Chemistry and Environmental Studies UNIT VIII

Formation of Urea – formaldehyde polymer:

It is prepared by the condensation polymerization of 2 parts of urea and one part of formaldehyde

at 500 C in a stainless steel vessel in the presence of hexamine.

O O O

NH2 – C – NH H + C + H HN – C – NH2

H H

Formaldehyde Urea

NH – C – NH – CH2 – NH – CO – NH

Uses of Urea – formaldehyde:

1) It is used to prepare decorative articles, plates.

2) It is used as adhesive.

6) What are differences between addition and condensation?

Ans:

Addition polymerization Condensation polymerization1) Monomers add in linear manner 1) Monomers react in three dimensional

manner2) Linear polymer is formed 2) Cross – linked polymer formed3) No elimination of simple molecules 3) H2O, NH3 like molecules elimination takes

place4) High molecular weight polymer formed at once

4) Molecular weight of the polymer rises steadily throughout the reaction.

7) Define Plastics?

Ans:

Plastics:

The high molecular weight organic polymers which can be molded into desired form by the application of heat and pressure are called plastics.

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Engineering Chemistry and Environmental Studies UNIT VIII

Plastic are two types. They are

1) Thermo plastics.

2) Thermo setting plastics.

8) Write differences between Thermo plastics and Thermo setting plastics?

Ans:

Thermo plastics Thermo setting plastics1) The plastics which can be softened on heating and hardened on cooling are called Thermo plastics.Eg: Polythene, PVC

1) The plastics which cannot be softened on heating and hardened on cooling are called Thermosetting plastics.Eg: Bakelite

2) These are formed by addition polymerization

2) These are formed by condensation polymerization

3) These are long chain polymers 3) These are cross – linked polymers4) These are in linear form 4) These are in three dimensional form5) These are soluble in some organic solvents 5) These are insoluble in some organic solvents6) These are weak, soft and less brittle 6) These are strong, hard and more brittle7) Neighboring polymer chains are held together by weak vanderwall forces.

7) Neighboring polymer chains are held together by strong covalent bonds.

8) These can be reshaped 8) These cannot be reshaped9) These can be reclaimed from wastes 9) These cannot be reclaimed from wastes9) Write the Characters of Plastics?

Ans:

Characters of Plastics

1) They are light in weight.

2) They are low thermal and electrical conductance.

3) They are resistant to corrosion.

4) They have high tensile strength.

5) They are impermeable to water.

6) They are not affected by insects fungi, virus etc.

7) They have low thermal expansion.

8) They are not bio degradable.

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Engineering Chemistry and Environmental Studies UNIT VIII

9) They are chemically inert.

10) Low fabrication cost.

10) Write the Disadvantages of plastics?

Ans:

Disadvantages of plastics:

1) They have combustibility.

2) They are poor in ductility.

3) They are soft and weak.

4) They have low heat resistance.

5) They undergo deformation when pressure is applied.

6) The plastics are non – biodegradable.

Hence, they cause high environmental pollution.

Rubber:

The high molecular weight organic polymers having elasticity property are called rubbers.

10) What is Natural Rubber? (or) Write the preparation of Natural Rubber ?

Ans:

Natural Rubber:

Preparation:

Milky liquid, called Latex is obtained when v-shaped cuts are made in the trunks of rubber trees (heaveabrasiliensis).

Latex is diluted to contain between 15 – 20% of rubber and preservations like NH3 are added.

The diluted latex is treated with HCOOH (or) CH3COOH, which coagulates the rubber.

It is obtained as white mass called as Coagulum.

It is then milled and sheeted.

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Water

Filter and RollingHCOOH/CH3COOH

Coagulants

Engineering Chemistry and Environmental Studies UNIT VIII

Latex 15 – 20% Latex Coagulum Raw rubber

11) Write the Disadvantages of Raw rubber?

Ans:

Disadvantages of Raw rubber:

1) High water absorption capacity.

2) It becomes soft at high temperature and brittle at low temperature.

3) Swells in organic solvents.

4) High Elasticity.

5) Oxidized easily in air.

6) Low tensile strength.

12) Write the Structure of Natural rubber?

Ans:

Structure of Natural rubber:

Rubber is an organic polymer.

Monomer in the rubber is Isoprene.

Formula: CH3

C5H8⟹ CH2 = C – CH = CH2

2 Methyl 1,3 – Butadiene.

Natural rubber has the cis – configuration at every double bond.

CH3 H

CH2 CH2 C = C CH2 CH2

C = C CH2 CH2 C = C

CH3 CH3 H

Fig. Natural Rubber

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Engineering Chemistry and Environmental Studies UNIT VIII

13) Write the Vulcanization of rubber?

Ans:

Vulcanization of rubber:

The process of heating the raw rubber with sulfur at 1100 – 1400 c is called vulcanization.

In the vulcanization process sulfur combines chemically at the double bonds.

So this process stiffen the materials and prevent intermolecular movement of rubber strings.

This process is proposed by charless good year.

The properties of vulcanized rubber depends upon

a) Amount of sulfur.

b) Temperature.

c) Duration.

CH3 CH3 CH3

– CH2 – C = CH – CH2 – CH2 – C = CH – CH2 – CH2 – C = CH – CH2 –

– CH2 – C = CH – CH2 – CH2 – C = CH – CH2 – CH2 – C = CH – CH2 –

CH3 CH3 CH3 Sulfur 1100 -1400 c

Raw Rubber

CH3 CH3 CH3

CH2 – C = CH – CH2 – CH2 – C = CH – CH2 – CH2 – C = CH – CH2

S S S

CH2 – C = CH – CH2 – CH2 – C = CH – CH2 – CH2 – C = CH – CH2

CH3 CH3 CH3 n

Vulcanized Rubber

The stiffness of vulcanized rubber depends on the amount of sulfur added.

Eg: Tyre rubber - 3 – 5% S

Battery case rubber – 30% S

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m

Engineering Chemistry and Environmental Studies UNIT VIII

Ebonite (or) hard rubber – 32%S

14) Write the Characters of vulcanized rubber (advantages)?

Ans:

Characters of vulcanized rubber (advantages):

1) Good tensile strength.

2) Low water absorption capacity.

3) High resistance to oxidation.

4) Low elasticity.

5) It is resistant to organic solvents.

6) Working temperature – 400 to 1000 C

7) Slight tackiness.

15) What is Synthetic Rubber (or) Elastomers?

Ans:

Synthetic Rubber (or) Elastomers:

An elastomer is vulcanisable man – made rubber.

An elastomer can be stretched to at least twice its length, but it returns to its original shape and

dimensions as soon as stretching force is released.

Eg: Buna – S (Styrene rubber (or) GR – S Rubber):

The name Buna – S is derived from ‘Bu’ for butadiene ‘na’ symbol of sodium and ‘S’ for

styrene.

Buna – S is prepared by the co – polymerization of butadiene and styrene.

Equation:

m CH2 = CH – CH = CH2 + n CH2 = CH CH2 – CH = CH – CH2 CH2 – CH

n

Butadiene Styrene Buna - S

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Engineering Chemistry and Environmental Studies UNIT VIII

Buna – S rubber have high abrasion – resistance, so it is used in the preparation of motor tyres.

2) Neoprene (or) GR – M Rubber:

It is prepared by the addition polymerization of chloroprene ( 2 – Chloro – 1,3 – butadiene).

Equation:

Cl Cl

n CH2 = C – CH = CH2 CH2 – C = CH – CH2

Chloroprene Neoprene

Neoprene is used in the preparation of aprons, adhesives, gaskets etc.

16) Write the General uses of rubber?

Ans:

General uses of rubber:

1) Electrical insulator.

2) For chemical resistance.

3) Rubber bands, tubes due to elasticity.

4) Tyres due to abrasive resistance.

5) Storage battery – hard rubber.

6) For sound absorption – sponge rubber.

7) Bed pillows, cushions – foam rubber.

8) In Medicine – heart values.

9) Toys, sport goods.

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n