UNIT - 15 POLYMERS

Polymers are the compounds of higher molar mass formed by combination of large number of

simple molecules called monomers and the process is called polymerization.

350-570K

n CH2 = CH2 1000-2000 atm - ( CH2 = CH2 )n- (Polythene) (Homopolymer)

(Ethene)

Homopolymer –repeating structural units are derived from one type of monomer unit called

homopolymers .e.g. PVC, polyethene etc.

Co-polymers: - Structural unit derived from two or more types of monomers called co-polymers.

Polymerisation

nH2N-(CH2)6-NH2+nHOOC-(CH2)2-COOH - (2n-1) H2O

(hexamethylenediamine)

(Nylon-6, 6-polymer)

A. Classification based on sources

NATURAL SEMISYNTHETIC SYNTHETIC

Found in nature in plants

and animals. e.g.

proteins, natural rubbers

etc.

Polymers are prepared by

some modification in

natural polymers. E.g.

nitrocellulose etc.

Man-made in Lab. E.g.

nylon, polyethene etc.

A. Classification based on structure

1. Linear polymers-polymers having long chain and

straight chain. e.g.PVC, nylon etc.

2. Branched chain-having linear chains with some branches. E.g.

low density polyethene, glycol etc.

3. Cross linked or Network polymer- Generally formed from bi-functional or tri-functional

monomers and has strong covalent bonds between various linear polymer chains. E.g.

Bakelite, melamine etc. The polymers are hard, rigid and brittle.

A. Classification based on mode of polymerization

1. Addition polymers- These polymers are formed by the repeated addition of some or

different monomer molecules having double or triple bonds e.g. polyethene etc.

2. Condensation polymers and condensation polymerization-formed by repeated

condensation reaction between different bi-functional or tri-functional monomer units,

usually one small molecules like alcohol, HCl, H2O etc.

Polymerisation

nH2N-(CH2)6-NH2+nHOOC-(CH2)2-COOH - (2n-1) H2O

(hexamethylenediamine)

(Nylon-6, 6-polymer)

CLASSIFICATION BASED ON MOLECULAR FORCES:-

Elastomers- Polymers having weakest intermolecular forces of attraction between polymer

chains. Due to these weakest forces, polymers can be stretched. Low cross links are introduced

in between the chains, which help the polymers to retain its original position after force is

released. E.g. vulcanized rubber e.g. Buna-S-, Buna-H-, neoprene etc.

Fibres- They have the strongest intermolecular forces such as H-bond or dipole-dipole

interactions. These polymers can be used to make fibres as their molecules are long and thread

like. Nylon 6-6, terylener are common examples.

Thermoplastics-have intermolecular forces of attraction between elastomers and fibres. They are

linear or slightly branched chain polymers. They become soft on repeatedly heating and attain

hardness on further cooling. E.g. polyethene, polystyrene etc.

Thermosetting- These polymers are cross linked or heavily branched molecules, which on heating

undergo extensive cross linking in moulds and again become infusible. These polymers can’t be

reshaped e.g. Bakelite, urea formaldehyde refins etc.

THERMOPLASTIC THERMOSETTING

-These soften and melt on heating -Do not soften but become hard. On

strong heating it start to burn.

-Formed by addition polymerization. - Formed by condensation

polymerization.

-Usually have linear structures. -Three dimensional cross-linked

structures.

-Can be remolded, recast, and

reshaped.

-No

-Less brittle and soluble in some organic

solvents

-More brittle and insoluble in organic

solvents.

-Teflon , PVC ,nylon ,polyethylene - Bakelite, urea formaldehyde refins etc.

Types of Polymerisation Reactions

A. Addition polymerization or chain growth polymerization

Involve successive addition of monomer units to the growing chain carrying a reactive

intermediate such as free radical or anion.

Three types on the nature of reacting species

a. Free radical polymerization: - alkenes or dienes and their derivatives are polymerized in

presence of a free radical generating initiator (catalyst) like benzoyl peroxide. Acetyl

peroxide, tert butyl peroxide etc.

E.g. ethane polythene

O O

|| ||

(C6H5CO)2O2 Or C6H5-C-O-O-C-C6H5

Benzoyl peroxide

2C6H5 -2CO2

Phenyl radical

(Initiator)

Indicator Monomer

b. Chain propagation:-

C6H5-CH2-CH2+CH2=CH2 C6H5-CH2-CH2-CH2-CH2

C6H5-(CH2-CH2)n-CH2-CH2

(Intermediate)

c. Chain Termination:- Two molecules of intermediate combined together combine together

to give polymer.

2C6H5-(CH2-CH2)n-CH2-CH2 C6H5-(CH2-CH2)n-CH2-CH2 –CH2-CH2-

-(CH2-CH2-)n-C6H5

Polythene (polymer)

CH2=CH -(CH2-CH)n- PVC Polymer (Repeating units)

Cl Cl

Vinyl Chloride polymer

CH2=CH -(CH2-CH)n- Poly Aerylo nitrile (PAN)

CN CN

Aerylo nitrile

Preparation of some Important Addition Polymers :-

B. Polythene : (Polyethylene):-

a. Low density Polythene: - (LDP) - It is obtained by polymerization of ethene under high

pressure (1000-2000atm) temp 350 to 510K in presence of traces of O2 or any peroxide

intiator.LDP is obtained through free radical addition and H-atom abstraction is highly

branched structure.

350-570K and 1000-200 atm

n CH2 = CH2 traces of O2 - ( CH2 = CH2 )n- (LDP)

These are chemically inert, tough and flexible, poor conductors of electricity.

b. Prepared by co-ordination polymerization of ethene. Here ethene is heated to 333-

343K at 6-7 atm pressure in presence of catalyst i.e. Triethyl aluminium and TiCl4 or

TiCl3

333-343K and 6-7 atm

n CH2 = CH2 (C2H5)3Al / TiCl4 - ( CH2 = CH2 )n- (HDP)

It is translucent, chemically inert, highly tough, hard and high tensile strength. Used in,

manufacturing of container, house wires, pipes, bottles and toys.

Polypropene :-

Used in manufacturing of toys, ropes, pipes, carpet fibers etc.

Polystyrene or Styrone :-

Used as insulator, wrapping material, manufacture of toys, radio & TV cabinets.

Tetraflouroethene [Teflon]-

n CF2=CF2 Catalyst - (CF2-CF2) n- (Polytetra flouroethene)

(Terta fluoroethene)

It is very tough material and resistant towards heat action of acids or bases. It is bad

conductor of electricity.

Due to high chemical inertness and high thermal stability, Teflon is used for making

non-stick utensils, gaskets etc.

Poly Aerylonitrile (PAN)

CH2=CH Peroxide Catalyst - (CH2-CH) n- Poly Aerylo nitrile

CN CN

Aerylo nitrile

It is used as a substitute for wool in making fibres called Orlon or aerilan.

Co-Polymerisation:- More than 1-monomer is allowed to polymerize.

nCH2=CH-CH-CH2 + nCH2=CH2 - (CH2-CH=CH-CH2-CH-CH2)-

(1,3-butadiene) C6H5 (styrene) (co-polymer) C6H5

Co-Polymers have different properties from homopolymers. E.g. polysterene,a homopolymers of

styrene is a good insulator and is used for making toys, T.V cabinets etc.Whereas styrene-

butadiene rubber, a co-polymer of styrene and butadiene, is a good substitute for rubber and is

used for making automobile tyres,cable insulators etc.

Condensation polymerization or step growth polymerization

It involves repetitive condensation of different or same monomers having bi-functional group. At

every stage a small molecule like H2O is lost.

1. Polyamides polymers possessing amide linkage are called polyamides.

Prepared by condensation polymerization of dibasic acids with diamines or their

equivalents.

(a) Nylon 6,6 – prepared by condensation polymerisation of hexa methylenediamine with

Adipic Acid under high pressure and temperature.

nHOOC-(CH2)4-COOH + nH2N-(CH2)6-NH2

(2n-1)H2O +

Ques. Why it is called nylon-6, 6?

Ans. It is because both acid and amine contains 6C atoms.

- It is used in making sheets, bristles for brushes and in textile industry.

Nylon-6- (Terlon) :- prepared from single monomer having a potential amino group at one end

and potential carxyl group at the other.

- Used in manufacturing of tyre cords, fabrics and ropes.

Polyester: - having ester linkages are called polyesters and are prepared by condensation

polymerization of di-acids with di-oils.

1. Terylene or Decron

- Used to make wash and wear fabric tyre cords, sails and seatbelts.

2. Glyptal

Glyptal

Used in manufacturing of paints & lacquered.

Cross Linked Polymer: -

Phenol – formaldehyde polymer (Bakelite): - It is formed by condensation of phenol with formaldehyde in presence of an

acid or base.

Bakelite is hard, scratch resistant as well as water resistant polymer, insulator. Hence, it is used for making electrical goods

(switcher etc.) gramophone records, handler etc.

Melamine – formaldehyde Polymer: -

It is co-polymer of melamine and formaldehyde. It is formed by condensation, polymerization of Melamine and

formaldehyde.

Used to make unbreakable crockery.

Co – Polymerisation: -

Two or more different monomers are allowed to polymerise together, product is called co – polymer and process co –

polymerisation.

� Very tough and good substitute of natural Rubber.

� High Tensile strength, used to make automobile tiers.

� Used for making floor or tiles, footwear components, cable insulation etc.

Rubber: -

A. Natural Rubber – It is a natural polymer, has remarkable elasticity, reversible even after applying small force. It is

called elastomers.

Manufactured form rubber latex which is a colloidal dispersion rubber in water.

� Natural rubber is a linear polymer of Isoprene.

Natural Rubber

The cis – polyisoprene molecule consists of various chains held together by weak Van der Waal’s interaction and

has coiled structure. It can be stretched like a spring and exhibits elastic properties.

Trans – polyisoprene [Gutta Percha]

B. Vulcanised Rubber – Natural become soft at high temperature and brittle at low temperature. It is non – resistant

to polar solvents and is easily attacked by oxidizing agents. Addition of sulphur to heat rubber improves its

properties. This process is called Vulcanisation.

During vulcanisation, sulphur forms cross-links of the reactive sites (at allylic positions).

Vulcanised rubber shows improved properties-

1. Rubber gets stiffened.

2. Has a low H2O absorbtion property.

3. Resistant to oxidation & organic solvents.

4. It is hard, tough & has high tensile strength.

� Amount of sulphur decides the properties of vulcanised rubber.

5% sulphur contains vulcanised rubber used to make automobiles tiers.

30% used in battery case rubber.

C. Synthetic Rubber – Synthetic rubbers are either Homopolymers of 1, 3-butadiene derivatives with another

unsaturated monomer.

Neoprene:-

Used in the manufacturing conveyer belts gaskets and hoses.

Resistant to vegetables and mineral oils.

Buna – N:-

Co – Polymer of 1, 3-butadiene and Acrylonitrile in presence of peroxide catalyst.

Resistant to

the action of petrol, lubricating oil and used in making oil seals and for tank lining.

BIODEGRADABLE POLYMERS

Biodegradable Polymers are those which can be broken into small segments by enzyme catalyzed reaction. In biological

system polymers are degraded mainly by enzyme hydrolysis or sometimes by oxidation. Biodegradable synthetic polymers

have functional group similar to natural polymers. The C-C bonds of chain growth polymers (polymers etc.) are inter to

enzyme action. Therefore, they are non-biodegradable. Certain groups like easily hydrolysable ester group, etc. are

introduced which can be hydrolysed.

e.g.

i. PHBV [Poly hydroxyl butyrate – CO - β hydroxyl valerate]

It is a co-polymer of 3 –hydroxy butanoic acid and 3 – hydroxyl pentanoic acid

This is used for special packing, orthopaedic device and slow release in formulation of medicines.

ii. Polyglycolic Acid & Polyactic Acid

COOH

|

COOH

OH

|

CH3 – CH – COOH

(glycolic acid)

(Lactic acid)

They are used as Sutures (post – operative stiches).

iii. Nylon – 2 – Nylon – 6

It is an alternating poly – amide. It is a co-polymer of Glycene and ∈ - Amino Caproic acid.

[∈ - on 6th C – atom (like α, β, γ, etc.]

It is also biodegradable.

SOME COMMON IMPORTANT POLYMERS

ADDITION POLYMERS

1 POLYTHENE Ethene

CH2=CH2

i. as an insulator

ii. Packing material

iii. Containers

2 POLYPROPENE Propene

CH3-CH=CH2

Manufacture of ropes, toys, pipes,

fibers etc.

3 POLYSTYRENE Styrene

For making toys, TV cabinets as

insulator.

4 POLYVINYLCHLORIDE Vinyl chloride

CH2=CH-Cl

For making raincoats, pipes, vinyl

flooring etc.

5 TEFLON

Polytetrafluoroethene

Tetrafluoroethene

CF2=CF2

For making gaskets oil seals, non-stick

cookware etc.

6 NEOPRENE

Chloroprene

For making hoses, gaskets, conveyer

belts etc.

7 BUNA-S

SBR or Styrene – Butadiene Copolymer.

Butadiene

CH2=CH-CH=CH2

&

Styrene

For making automobile tiers water-

proof shoes, rubber soles etc.

8 BUNA-N

(nitrile rubber)

Butadiene

CH2=CH-CH=CH2

&

Acrylonitrile

CH2CH-CN

For making oil-seals, hoses, tank-linings.

9 PMMA – Polymethylmetacrylate Methyl methacrylate

Uses for making lenses, aircraft,

windows, transparent domes.

10 POLYACRYLONITRILE

(PAN)

ORLON ACRYLAN

Acrylonitrile

For making synthetic fibers & wool,

carpets and blankets.

CONDENSATION POLYMERS

(A) POLYSTERS

1 TERYLENE OR DACTRON

i. Ethylene glycol

HOCH2-CH2OH

ii. Terephthalic acid

For making crease-resistance fibers as

blend with cotton & wool for making seat

belts, sails.

2 GLYPTAL (Alkyd Resins)

i. Ethylene glycol

HOCH2-CH2OH

ii. Phthalic acid

Used in the manufacture of paints &

lacquers.

(B) POLYAMIDES

1 NYLON - 6,6

i. Adipic acid

HOOC-(CH2)4-COOH

ii. Hexamethylenediamine

H2N-(CH2)6-NH2

Used in manufacture of textile fabrics,

ropes, bristles for brushes.

2 NYLON – 6

Caprolactam

Used for making tyre cords.

THERMOSETTING POLYMERS -RESINS

1 Phenol – formaldehyde resin

i. Phenol

ii. Formaldehyde

HCHO

For making combs, phonograph

records, electrical switches & handles

for utensils.

2 Melamine – formaldehyde resin

i. Melamine

ii. Formaldehyde

HCHO

For making unbreakable cookware.

3 Urea – formaldehyde resin

i. Urea

H2N-CO-NH2

ii. Formaldehyde

HCHO

For making laminated sheets,

unbreakable cups.