Group 8. Kekule Group
1.
2.
3.
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5.
Mr. R .R. Singh K.V. EME BARODA AHEMDABAD (Group Leader)
Mrs. Manisha Bisht K.V. AFS Ojhar Mumbai
Mr. K. OJha K.V. Muzaffarpur (ss) Patna
Mr.Sushil Gurjar K.V. Manendragarh Raipur
Mr. V. K. Meena K.V. 1 Bikaner Jaipur
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
(hexamethylenediamine)
- (2n-1) H2O
(Nylon-6, 6-polymer)
A. Classification based on sources
NATURAL
Found in nature in plants and
animals. e.g. proteins, natural
rubbers etc.
SEMISYNTHETIC
Polymers are prepared by
some modification in natural
polymers. E.g. nitrocellulose
etc.
SYNTHETIC
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
branches. E.g. low density
chain-having linear chains with some
polyethene, glycol etc.
3. Cross linked or Network polymer- Generally formed from bifunctional 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
(hexamethylenediamine)
- (2n-1) H2O
(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 resins etc.
THERMOPLASTIC
-These soften and melt on heating
THERMOSETTING
-Do not soften but become hard. On strong
heating it start to burn.
- Formed by condensation polymerization.
-Three dimensional cross-linked structures.
-No
-More brittle and insoluble in organic
solvents.
- Bakelite, urea formaldehyde refins etc.
-Formed by addition polymerization.
-Usually have linear structures.
-Can be remolded, recast, and reshaped.
-Less brittle and soluble in some organic
solvents
-Teflon , PVC ,nylon ,polyethylene
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. ethene
polythene
O
O
||
||
(C6H5CO)2O2
Or
C6H5-C-O-O-C-C6H5
Benzoyl peroxide
-2CO2
Phenyl radical
(Initiator)
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.
C6H5-(CH2-CH2)n-CH2-CH2 –CH2-CH2-(CH2-CH2-)n-C6H5
2C6H5-(CH2-CH2)n-CH2-CH2
Polythene (polymer)
CH2=CH
Cl
-(CH2-CH)n-
PVC Polymer (Repeating units)
Cl
Vinyl Chloride polymer
CH2=CH
CN
-(CH2-CH)n-
Poly Aerylo nitrile (PAN)
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 (10002000atm) 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
CN
Peroxide Catalyst
- (CH2-CH) n-
Poly Aerylo nitrile
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
(1,3-butadiene)
C6H5 (styrene)
- (CH2-CH=CH-CH2-CH-CH2)(co-polymer)
C6H5
Co-Polymers have different properties from homopolymers. E.g. polysterene, a homopolymer 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 diacids 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 properties1. 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 -  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
(glycolic acid)
OH
|
CH3 – CH – COOH
(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 , , , etc.]
It is also biodegradable.