Dr. Sunita Nair / CSE B & BME AUG 2015

Introduction to Polymer

Polymer is derived from Greek word (Poly = many & mers = Units)

• Polymers are macromolecules formed by the combination of large number small molecules known as monomers.

• Therefore a monomer is a micromolucule composed of a single unitLike H2O, CO2, H2O2 etc….Like H2O, CO2, H2O2 etc….

• Whereas polymer is a macromolecule composed of large number of repeating units called monomer.

n CH2 = CH2 → ( CH2 – CH2 ) nethylene (monomer) polythene or

polyetylene

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H H

H

C C

nH

H H

C = Cn

Styrene(monomer )

Polystyrene(Polymer)

POLYMERISATIONPOLYMERISATION

Definition : Polymerisation is a chemical process in which anumber of monomers are linked together to form a polymer.Polymerisation proceeds by the chemical combination of two or more identical or different monomers with or with out the elimination of small molecule like H2O, MeOH etc..

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Functionality

• Functionality of a monomer is no. of reactive sites or bonding sites or functional group present in the repeating units.

• For a substance to act as a monomer, it must have at least one double bond .

• Polymerisation proceeds with breaking of these double • Polymerisation proceeds with breaking of these double bonds.

• Functionality is also given by the no. of functional groups a molecule has.Example: In case of ethylene, a double bond is broken during homolytic cleavage in presence of uv light or heat and each carbon atom gets converted to free radical.

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• In ethylene now we have two reactive sites can undergo polymerisation.All monomers are molecules but all molecules are not monomersAll macromolecules need not be polymers. Carbon dioxide is a molecule but does not undergo polymerization. On the other hand ethylene molecule, which is a monomer, polymerizes to give molecule, which is a monomer, polymerizes to give polyethylene .

• In other words for a molecule to become monomer it should have at least two bonding sites .

CH2=CH 2 CH2 CH2٠

..٠Homolytic cleavage

hv

CH2 CH2 + CH2 CH2٠ ٠ ٠ ٠

CH2 CH22

CH2 CH2٠ ٠n CH2 CH2

nPE

Therefore ethylene is considered as bifunctional monomer.Depending upon the presence of no. of bonding site present in the Depending upon the presence of no. of bonding site present in the monomers , they are classified as

Functionality Bonding Sites ExampleMonofunctional One CH3OH, CH3COOHBifunctional Two (CH2)4(COOH)2 & (CH2)6(NH2)2Trifunctionl Three (CH2 OH)2CHOH, PhenolTetrafunctional Four Acetylene, Non functional Zero MethaneREFER CLASS NOTES FOR MORE EXAMPLES

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• When bi-functional (BF) monomers undergo polymerisation then linear polymers are formed.

• When bi-functional monomers mixed with trifunctional (TF) & if the ratio of bi-functional monomer is > than tri-functional monomers, then branched chain polymers are formed.

• During mixed polymerisation , when the ratio of trifunctional monomer is > than bi-functional ,then cross linked polymer could be

• During mixed polymerisation , when the ratio of trifunctional monomer is > than bi-functional ,then cross linked polymer could be formed.

• When the tri-functional monomer undergoes polymerisation then cross linked or three dimensional net work polymers are formed.

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Classification1) Based on origin:

The polymers obtained from nature (plants and animals) are called natural polymers. These polymers are very essential for life.

i) Natural : Known as Biopolymer: Examples are Cellulose( polymer of glucose), protein, starch, fibres, silk, wool etcsilk, wool etc

ii) Synthetic : Examples are polypropylene, polystyrene, polyethylene etc

iii) Semi synthetic : These polymers are mostly derived from naturally occurring polymers by chemical modifications. Examples are Cellulosics such as cellulose acetate, cellulose nitrate ( gun cotton), Rayon etc.

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2) Based on Degree of Polymerisation (DP)

The number of repeating (monomers) units present in polymer chain is known as DP.

i) Low DP : Known as Oligomers( Molecular weight 500 to 5000)( Molecular weight 500 to 5000)

ii) High DP : High Polymers( Molecular weight 104to106)

3) Based on Structurei) Linear Polymers : HDPE, Nylon, Polyester ii) Branched Polymers : LDPE, glycogeniii) Cross linked or three dimensional Polymers :Bakelite, urea

formaldehyde4) Based on monomers

A polymer may consists of identical (Homopolymer) or different monomers (Hetero polymer)

a) HomopolymerPolymer consists of identical monomerPolymer consists of identical monomer

- CH2 – (CH2 – CH2 ) – CH2 – CH2 - (polythene)Other Examples are PS, PVC, PTFE,Based on type of arrangements of identical monomers

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i) Linear homopolymer

M M MM M

ii) Branched homopolymer

M M MM M

M

M

iii) Cross linked homo chain polymer

M M MM M

M M MM M

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b) Hetero polymer / CopolymerPolymer is made up of different types of monomers

M1 M2 M1M1 M2

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Nylon 6:6Nylon 6:6 is prepared by the condensation polymerisation between

hexamethylene diamine and adipic acid.

N C N + C C C

H H H

H H H6 O

OH

H

H

H

OH

Hexamethylene diamine Adipic acid

n

4

condensation polymerisation

2n-1 H2O

N C N C C C

H O

H

H

H

H

H

O6 4 n

OH

Nylon 6:6

Based on arrangementsi) Linear heteropolymer

M1 M2 M1M1 M2

ii) Branched heteropolymer

M1 M2 M1M1 M2

M1

M2

iii) Cross linked hetero polymer

M1 M2 M1M1 M2

M1 M2 M1M1 M2

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iv) Graft hetero polymerBack bone of the polymer is made up of one kind of monomers & branches made up of another type

M2

M2

M2

M1 M1 M1M1 M1

M2

M2 M2

v) Block hetero polymer

A B BA A A B BB BA A A A A

Blocks of monomers arranging in orderly or disorder ly form in a polymer

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GRAFT POLYMER

BLOCK POLYMER

GRAFT POLYMER

RANDOM POLYMER

5) Based on main chain of the polymeri) Homochain polymerMain chain is made up of same atoms

-C-C-C-C-C-C-Example : Polyethylene, polystyrene etc

ii) Heterochain polymerMain chain is made up of different atoms

-C-C-C-O-C-C-O-C-Example : Polyamides, Nylon 6, Nylon 6:6 etc.Example : Polyamides, Nylon 6, Nylon 6:6 etc.

6) Based On Geometry ( Tacticity)The orientation of monomeric unit with respect to main chain can

either be an orderly or random manner. This is called as tacticity.If monomeric units are arranged in some regular order,then the

polymer is termed as Stereo Specific Polymer (SSP)

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i) Isotactic ; In this functional groups ( monomeric unit) are arranged in the same side

of the main chain

C C C C C C C

R

H H

R R R R R R

HH H HH

ii) Syndiotactic

C C C C C C C

R

H

R R R R R R

HH H HH

C C C C C C C

ii) SyndiotacticIn this functional groups ( monomeric unit) are arranged in the same side of the main chain

H

H

R R H R H R

HR R HR

C C C C C C C

H

H

H

R R H R H R

HR R HR

C C C C C C C

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iii) AtacticIn this functional group ( monomeric unit) are arranged at random

around the main chain.

C C C C C C

R H R RR HH

R

H RH H H H

7) Based on Thermal properties (or Molecular forces)Thermoplastics : Plastics that soften when heated and become firm again when cooled. This is

the more popular type of plastic because the heating and cooling may be repeated.

Ex : Poly ethylene, polypropylene, PVC, PTFE

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• Thermosetting plastics :

Plastics that soften when heated and can be molded, but harden permanently. They will decompose when reheated.

Ex. Bakelite, urea formaldehyde, polyesters etc.

8)Based on synthesis

i) Addition Polymers : Involves addition of monomers to one another to form a long polymer chain without forming any by product.

Example: PE,PP, PVC, TEFLON.

ii) Condensation polymersInvolves addition of identical or different monomers to

one another to form a long polymer chain with the elimination of by product.

Example: Bakelite, Nylon 6, Nylon11,Nylon6:6 etc.

Nylon 6:6Nylon 6:6 is prepared by the condensation polymerisation between

hexamethylene diamine and adipic acid.

N C N + C C C

H H H

H H H6 O

OH

H

H

H

OH

Hexamethylene diamine Adipic acid

n

4

condensation polymerisation

(2n -1)H2O

N C N C C C

H O

H

H

H

H

H

O6 4 n

OH

Nylon 6:6

9) Based on nature of polymeri) Organic: PP, PVC, PSii) Inorganic: Silicones, polysilanes,

polyphosphazene

10) Based on applicationPlastics : PVC, PPElastomers : RubberFibers : Nylon, terylene, DacronResin : epoxy resin sealing agents, polysulphide

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(11) Based on degradability of Polymers(i) Bio- degradable polymers

Natural Bio- degradable polymersEx. Collagen Synthetic Bio- degradable

Polymers. Ex: Aliphatic polyesters,polyanhidride, Polyphosphazene

(ii) Non -Bio- degradable polymers

Hydrophobic Polymers Hydrophilic polymersEx: HPMC (hydroxypropyl

methyl cellulose) Ex. Ethyl cellulose, silicones

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