Polymers
POLYMERS
Polymer engineering is generally an engineering field that designs, analyses, and/or
modifies polymer materials.
Polymer: Polymer is a high molecular weight compound formed by joining of thousands of
smaller molecular units together by chemical bonds
Monomers: Repeated units of a polymer are known as monomers. Monomers are
micromolecules which combine with each other to form a polymer.
Eg-1: Ethylene molecules combine with each other to form polyethylene (Polythene)
nCH2=CH2
(-CH2-CH2-)n
Ethylene
Polyethylene
Monomer: Ethylene,
Polymer : Polythene
Eg-2: Styrene molecules combine with each other to form polystyrene (Polythene)
Monomer: Styrene,
Polymer: Polystyrene
Polymerization: The process in which large number of simpler molecules combines together
either by addition or condensation reaction to form a very large molecule having high molecular
weight is known as polymerization”. The molecule is known as polymer.
Degree of Polymerization: The number of repeating units (or) monomeric units present in the
polymer is known as degree of polymerization.
Degree of polymerization is related to the molecular weight of the polymer by the equation
M
Dp 
M= Molecular weight of the polymer
m
Dp= Degree of polymerization
 M  Dp  m
m = Molecular weight of the monomer
Polymers with low molecular weight are termed as oligomers and with high molecular weight
are known as high polymers. The molecular weight of the polymers ranges from 5000 to 200000
0
Polymers
NOMENCLATURE OF POLYMERS
Based on the monomer units present, polymers are named as homopolymers and copolymers.
 Polymers consisting of identical monomers are known as homopolymers.
Eg: Polythene, polystyrene, PVC etc…
These homopolymers may be linear, branched or crosslinked.
Linear homopolymers: Homopolymers in which all the monomers are joined in a in the form
of long straight (linear) chains.
Branched homopolymers: Homopolymers in which the monomers are present in branches
along the main (Linear) chain.
Cross linked homopolymers: Homopolymers in which the adjacent main (Linear) chains are
connected by covalent bonds (crosslink) are termed as cross linked homopolymers.
 Polymers having different types of monomers are termed as copolymers.
Eg: Nylon
These Copolymers may be linear, branched or crosslinked.
Linear copolymers: copolymers in which all the monomers are joined in a in the form of
long straight (linear) chains.
Branched copolymers: Copolymers in which the monomers are present in branches along the
main (Linear) chain.
Cross linked copolymers: Copolymers in which the adjacent main (Linear) chains are
connected by covalent bonds (crosslink) are termed as cross linked homopolymers.
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Polymers
Depending on the linkage of monomers, the following four types of copolymers are possible.
S.No.
Copolymer
Structure
Description
Monomers are arranged in
1
Alternate
-M1-M2-M1-M2-M1-M2regular alternate fashion
A block of repeating unit
of one kind of monomer is
2
Block
-M1-M1-M1-M2-M2-M2followed by block of
another kind of monomer
Distribution of monomers
3
Random
-M1-M2-M2-M1-M2-M1is random along the
polymer chain
4
Graft
Have branched structures
in which the monomer
segments on the back bone
and branches are different
Homo chain polymers: Polymers in which the main chain is made by the same atoms are
termed as homo chain polymers.
Hetero chain polymers: Polymers in which the main chain is made by different atoms are
termed as homo chain polymers.
Graft polymers: These are branched copolymers in which the monomers present in back bone
(main chain) and the branched chains are different. i.e Main chain is formed by one type of
monomers where as the branched chain is formed by another type of monomers.
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Polymers
Tacticity : Polymers with regular substituents on the polymer chain possess a property known
as tacticity.
The difference in the configuration because of orderly or disorderly orientation of
functional groups in polymer with respect to the main chain is known as tacticity.
The orientation of functional groups / substituents can take place in three ways….
i. All the functional groups / substituents may present on the same side of the polymer chain
ii. Arrangement of functional groups / substituents may be random along the polymer chain
iii. Arrangement of functional groups / substituents may be alternate along the polymer chain
Based on the above three possibilities, polymers are termed as
a. Isotactic: Polymers in which the functional groups / substituents are present on the same
side of the polymer chain are known as isotactic polymers.
b. Atactic: Polymers in which the arrangement functional groups / substituents is random
along the polymer chain are known as atactic polymers.
c. Syndiotactic: Polymers in which the arrangement functional groups / substituents is
alternate along the polymer chain are known as syndiotactic polymers.
Functionality: The number of bonding sites or reactive sites or functional groups present in the
molecule which participate in the polymerization is known as functionality.
The minimum functionality of the monomers to take part in polymerization is two. That
means every monomer must be minimum of bifunctional.
Depending on the functionality of monomers, we get linear, branched and cross linked
polymers.
 If the functionality of the monomer is two, it is bifunctional monomer. Polymerization of
bifunctional monomers forms linear polymers.
 If the functionality of the monomer is three, it is trifunctional monomer. Polymerization
of trifunctional monomers forms cross linked (three dimensional) polymers.
 Polymerization of mixture of both bifunctional and trifuinctional monomers gives
branched polymers.
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Polymers
CLASSIFICATION OF POLYMERS
 Polymers are classified into different types
Classification based on source:
a. Natural polymers: Polymers which are available in the nature in plant and animal kingdom.
Eg: Starch ( a polymer of α D- Glucose), Cellulose ( a polymer of β D- Glucose), Proteins.
Natural rubber- a polymer of cis-isoprene
b. Synthetic polymers : Polymers which are being synthesized.
Eg: Polythene (PE), Polystyrene, Poly vinyl chloride, Polystyrene, Nylon, Bkelite.
Classification based on structure:
a. Linear polymers: Polymers in which monomeric units are joined in the form of straight
chains.
Eg: High Density polythene (HDPE), Nylon, Polyster
b. Branched polymers: Polymers in which possess branches along the main chain.
Eg: Low density polythene (LDPE), glycogen.
c. Three dimensional network polymers: Polymers in which the monomeric units are
connected by only covalent bonds. In these the movement of monomeric units is prevented
by cross-links.
Eg: Bakelite, Urea-Formaldehyde, etc
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Polymers
Classification based on mode of polymerization:
a. Addition polymers: A polymer which is formed by an addition reaction, where
many monomers bond together via rearrangement of bonds without the loss of any atom or
molecule. The empirical formula of these polymers is same as their monomers
Eg: Polyethene, PVC, Polystyrene…
b. Condensation polymers: Polymers which are formed through a condensation reactionwhere molecules join together by losing a small molecule as by-product such as H2O, NH3,
HCl.
Eg: Nylon, Polyster…
Classification based on growth of polymer chain:
a. Chain growth polymers: Polymers formed by the successive addition of monomers to the
growing chain carrying a reactive site. (Or) Polymers which are formed by chain-growth
polymerization where unsaturated monomer molecules add onto the active site on a
growing polymer chain one at a time.
Eg: Polyethene, PVC, Polystyrene…
Mechanism
b. Step Growth polymers: Polymers formed by the step growth reaction i.e a series of
independent reactions involving the bond formation between two different monomers with
loss of small molecule as byproduct.
Eg: Nylon, polyster…
Mechanism:
Classification based on molecular forces: Depending on the presence of intermolecular forces
polymers are classified into four types
i. Thermoplastic polymers: Thermo plastics are the polymers that become soft on heating
and hard on cooling and the process can be repeated for a number of times. They undergo
reversible changes on heating.
Eg: Polythene (PE), polypropylene (PP), polyvinyl-chloride (PVC), polytetrafluoroethylene
(PTFE or Teflon), polystyrene (PS), nylons, polyesters.
ii. Thermosetting polymers: Thermosets are the polymers that undergo chemical changes on
heating and become permanently hard, rigid and infusible. They will not soften on heating,
once they are set.
Eg: Phenol-formaldehyde resin, urea-formaldehyde resin, epoxy resins (araldite), melamine,
bakelite
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Polymers
iii. Elastomers: Elastomers are high polymers that undergo very long elongation under stress,
and regain their original size fully on releasing the stress. The property of elastomers is
known as elasticity. This arises due to the coiled structure of elastomers.
Eg: Styrene-Butadiene rubber
iv. Fibres: Fibres are the polymers whose chains are held by strong intermolecular forces like
hydrogen bonding. They are crystalline with high tensile strength.
Classification based on chemical composition:
i. Organic Polymers: Polymers in which the main chain (back bone) contains carbon atoms
only or carbon along with other hetero atoms like oxygen, nitrogen and sulfur are known as
organic polymers.
Eg: Polythene, PVC…
ii. Elemento Organic Polymers: Polymers whose chains are composed by carbon atoms and
other hetero atoms except oxygen, nitrogen and sulfur are termed as elmento organic
polymers.
Polymers with carbon atoms only in main chain and other hetero atoms except oxygen,
nitrogen and sulfur in branched chain directly connecting to carbon atom are also element
organic polymers.
Eg: Polydimethylsiloxanes:
iii. Inorganic Polymers: Polymers with no carbon atom are termed as inorganic polymers. In
these polymers the main chain is composed by different atoms joined by chemical bonds.
Eg:
POLYMERIZATION
Polymerization is a chemical process in which large number of small molecules combines
together to form a big molecule of high molecular weight.
The different ways of doing polymerization are –
i). By opening a double bond:
ii). By using molecules having two functional groups:
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Polymers
Types of polymerization:
Polymers can be synthesized by the following polymerization processes.
I. Addition polymerization (or) chain polymerization (or) chain growth polymerization
II. Condensation (or) step (or) step growth polymerization
III. Copolymerisation
Addition polymerization:
Polymerization which involves the successive addition of monomeric units to each other
without evolving any by product is known as addition polymerization.
Polymer synthesized by addition polymerization has the same empirical formula as that
of monomer. No byproducts were formed during polymerisation and the molecular weight of
the polymer is an exact integral multiple of the original monomeric molecule.
Addition polymerization is usually induced by light, heat or, a catalyst for opening the
double bond of the monomer and creating the reactive sites.
Eg: If
R= H , Polymer is Polyhtene
R= Cl , Polymer is Polyvinyl chloride (PVC)
R= C6H5 , Polymer is Polystyrene
Condensation polymerization:
A chemical process, which involves the reaction between monomers having polar
functional groups to form a polymer by the elimination of simple molecules like H 2O, HCl etc is
known as condensation polymerization. It is an intermolecular reaction involving two different
bifunctional reactants with affinity for each other and taking place through repeated condensation
reaction is known as condensation polymerization.
Eg: Nylon-6,6
Polyster:
Copolymerization:
A reaction in which a mixture of two (or) more monomers are allowed to undergo
polymerisation is known as copolymerization. The polymer is known as copolymer.
Eg: Copolymerisation of styrene and 1,3 – buta diene.
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Polymers
Differences between addition polymerization and condensation polymerization
Addition Polymerization
Condensation Polymerization
1. It requires the presence of a double bond in 1. It requires two reactive functional groups
the monomer
to be present at both ends of the monomer.
2. In this reaction, no by product is formed
2. Generally a byproduct is formed in this
reaction.
3. Homo-chain
polymer
is
obtained. 3. Hetero-chain polymer is obtained (either
(generally thermoplastic)
thermoplastic or, thermostat)
4. The growth of chain is at one active centre. 4. The growth of chain occurs at minimum of
two active centres.
5. Number of units decreases steadily 5. Monomers disappear early in the reaction
throughout the reaction
6. Ex: Polythene, PVC, Polystyrene etc..
6. Ex: Nylon, Polyster etc..
Mechanism of Addition Polymerization or Chain Polymerization:
It involves three steps. a. Chain initiation
b. Chain propagation c. Chain termination
Depending on the initiation step, chain polymerization can be carried out in four ways.
1. Free radical polymerization mechanism: Chain initiation step involves free radicals.
a. Chain initiation: This involves two steps.
i. Dissociation of the initiator into free radicals: Initiator added to the monomer undergoes
hemolytic dissociation to form free radicals.
ii. Addition of the first monomer molecule to the free radical to form chain initiating species.
Thus the polymerization of monomer CH2=CHY takes in the form
b. Chain propagation: It involves the successive addition of monomers to the initiating
species.
c. Chain termination: Propagating polymer chain may terminate either by the combination
two radicals or by disproportionation process.
Coupling or combination: two reactive or free radical polymer chains combine together to
form a dead polymer.
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Polymers
The disproportionation reaction involves the transfer of a hydrogen atom from one of the
free radical polymer chain to another free radical giving rise to one saturated and one
unsaturated polymer molecules. Disproportionation also terminates the propagation or
growth of the polymer chain resulting in a dead polymer.
Dead Polymer represents the cessation (termination) of the growth of the polymer chain
2. Cationic mechanism of polymerization:
a. Chain initiation:
b. Chain propagation:
c. Chain termination:
3. Anionic mechanism of polymerization:
a. Chain initiation:
b. Chain propagation:
c. Chain termination:
Coordination polymerization (or) Ziegler-Natta polymerization:
Ziegler (1953) and Natta (1955) discovered that, the polymerization in presence of a
combination of transition metal halides (TiCl4, TiCl3, TiCl2, halides of V, Zr, Mo and W) with
organo metallic compounds (Triethylaluminium, trimethylaluminium) is stereo specific.
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Polymers
Mechanism:
Intiation:
Propogation:
Termination:
 Ziegler-Natta polymerization is used to prepare polypropylene, polyethylene, Polydiene etc.
 Stereo specific polymers can be prepared by using Ziegler-Natta polymerization.
 Normal polymerization using conventional catalysts leads to the formation of atactic
polymers.
 Ziegler-Natta polymerization is used to produce specifically desired polymers (atactic or
isotactic or syndiotactic).
 Atactic polymers are elastic and others are dense.
Condensation polymerization:
A chemical process, which involves the reaction between monomers having polar functional
groups to form a polymer by the elimination of simple molecules like H2O, HCl etc is known as
condensation polymerization.
 Monomers having polar functional groups (like –COOH and –OH or, -COOH and –NH2)
undergo condensation polymerization.
 The reaction always accompanies the elimination of simple molecules like H2O, HCl,
CH3OH, NH3 molecules.
 Condensation polymerization involving trifunctional monomers give rise to a cross– linked
three-dimensional polymer where as bifunctional monomers give rise to linear polymers.
 It is catalyzed by acids or alkali
Mechanism:
Monomers undergoing condensation polymerization are two types.
1. Monomer with two similar functional groups (A-A or B-B).
Eg: Hexamethylene diamine, adipic acid, ethylene glycol
2. Monomers with two different functional groups (A-B)
Eg: α-aminocaproic acid
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Polymers
Depending on the monomers involved, condensation polymerization is two types:
i. AA-BB type:
Eg: Formation of Nylon-6,6, terylene
ii. A-B type:
Eg: Formation of Nylon-6, Nylon-11.
PLASTOMERS
Plastics are the materials that show the property of plasticity and can be moulded into any
desired shape and dimensions by the application of heat and pressure.
Eg: PVC, Polythene, Polystyrene, nylon, teflon, bakelite etc.
Classification of plastics: Plastics are classified into two types
i. Thermoplastic polymers: Thermo plastics are the polymers that become soft on heating
and hard on cooling and the process can be repeated for a number of times. They undergo
reversible changes on heating. Their hardness is temporary property subjected to change
with heat.
Examples: Polythene (PE), polypropylene (PP), polyvinyl-chloride (PVC),
polytetrafluoroethylene (PTFE or Teflon), polystyrene (PS), nylons, polyesters.
Thermoplastics –
 are formed by addition polymerisation
 consists of linear polymer chains with negligible cross-linking
 are soft and less brittle.
 are soluble in organic solvents.
 soften on heating and hence are amenable for moulding into any shape in the hot condition,
on cooling the resin becomes hard and rigid and retains the moulded shape.
 can be reheated and moulded into any other shape reversibly any number of times without
any change in the chemical nature.
ii. Thermosetting polymers: Polymers which sets on heating and becomes rigid and infusible
are known as thermosetting plastics.
Thermosets are the polymers that undergo chemical changes on heating and become
permanently hard, rigid and infusible. They will not soften on heating, once they are set.
Examples: Phenol-formaldehyde resin, urea-formaldehyde resin, epoxy resins (araldite),
melamine, bakelite
Thermosets:
 are mostly formed by condensation polymerisation.
 are mostly branched polymer chains with potential to form a 3- dimensional structure.
 become hard and rigid on heating during moulding process.
 are not soluble in common organic solvents.
 cannot be softened, reformed, reshaped once they are set.
 cannot be reclaimed from wastes.
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Polymers
Differences between thermoplastics and thermosettings:
Thermoplastics
Thermosettingplastics
1. Formed either by addition or by
1. Formed by condensation polymerisation
condensation polymerization reactions
reactions.
2. They have either linear or branched
2. They have 3-dimensional, crosslinked
structures.
network structure.
3. Adjascent polymer chains are held together
3. Adjascent polymer chains are held
by either vanderwaals forces, or by dipoletogether by strong covalent bonds called
dipole forces or by hydrogen bonds.
crossed-links.
4. They soften on heating and stiffen on
4. They do not soften on heating.
cooling
5. Low molecular weight thermoplastics are
5. They are insoluble in any solvent.
soluble in their suitable solvents.
6. They can be remoulded, re-shaped and re6. They cannot be remoulded and hence
used.
cannot be used.
7. They can be reclaimed from waste i.e.,
7. They cannot be reclaimed from waste.
they can be recycled.
They cannot be recycled.
8. There is no change in chemical
8. They undergo chemical changes such as
composition and structure during moulding
further polymerisation and cross-linking
process.
during moulding process.
9. They undergo reversible changes, on the
9. They undergo irreversible changes on
application of heat.
the application of heat.
10. They are soft and flexible.
10. They are hard, rigid and infusible.
11. They swell or dissolve in organic solvents.
11. They neither dissolve nor swell in
organic solvents.
12. They are tough materials
12. They are brittle materials.
13. The moulded articles are to be cooled to
13. The moulded articles can be taken out
room temperature before taking out from
of the moulds even when they are still
the moulds to avoid deformation.
hot without any deformations.
Examples:Polyethylene(PE), Polyvinylchloride Examples: Phenol-formalde-hyde resin (PF),
(PVC), Polystyrene(PS), Teflon (PTFE), nylons. Bakelite, urea-formaldehyde resin (UF),
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Polymers
Compounding of plastics:
Compounding of the plastics may be defined as the mixing of different materials like
plasticizers, fillers of extenders, lubricants, dyes and pigments to the thermoplastic and
thermosetting plastics to increase their useful properties like strength, toughness, etc. Resins
have plasticity or binding property, but they need other ingredients to be mixed with them for
fabrication into useful shapes.
Ingredients used in compounding of plastics (or) Moulding constituents of plastics
Some of the ingredients used in compounding of plastics are as follows
i. Resins or binders: resins are the basc binding materials and hold the different constituents
together. They are the major portion of the plastics. Resins are further classifies into thermo
plastic resins and thermosetting resins.
ii. Plasticizers: They are added to resins to increase their plasticity and flexibility. They
neutralize the intermolecular forces of attraction between the polymer chains, these results
in greater freedom of movement of polymer chain thereby increasing the flexibility of
plastic.
Eg: Vegetable oils, camphor, Tricery phosphate, tetrabutyl phosphate.
iii. Filers: These are the substances added to impart special properties to the plastic and to
reduce the cost of the plastic.
Eg:
Carborundum, quartz:
To provide extra hardness
Barium salts:
To make the plastic impervious to X-rays
Asbestos:
To provide heat and corrosion resistance.
iv. Stabilizers: These are added to improve the thermal stability of the during processing.
Opaque moulding stabilizers: These are usedin opaque plastics.
Eg: Lead salts like lead chromate, white lead, lead silicate.
Transparent moulding stabilizers: These are used in transparent plastics.
Eg: Stearates of lead, cadmium and barium.
v. Catalysts or Accelerators: These are added only in the case of thermosetting plastics to
accelerate the polymerization of fusible resin into infusible cross-linked form during
moulding.
Eg: Hydrogen peroxide, benzoyl peroxide, metal oxides
vi. Lubricants: These are added to make the moulding process easy and to impart a flawless,
glossy finish to the products.
Eg: Waxes, oils, stearates, oleates and soaps.
vii. Dyes & Pigments: To provide attractive colours to the product.
Eg: Organic dyes, opaque inorganic pigments. Carbon black-black; Zinc oxide-white;
Fabrication of plastics:
Fabrication involves conversion of polymeric materials into desired shape. Many
methods are employed for the fabrication which depends on the types of plastics.
Moulding process:
The process involves fabrication of plastics materials into desired shape under the
influence of heat and pressure in closed chamber.
The different moulding methods used are – a) compression moulding b) Injection moulding
c) Transfer moulding d) Extrussion moulding
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Polymers
Polyvinyl chloride (PVC):
Preparation: Polyvinyl chloride is obtained by heating a water emulsion of the vinyl chloride in
an autoclave under pressure in the presence of benzoyl peroxide or hydrogen peroxide.
Properties:
 PVC is a colorless and odorless powder.
 It is chemically inert and non-inflammable and exhibits high resistance to light,
atmospheric oxygen, acids and alkalis.
 It is soluble in chlorinated hydrocarbons.
 Pure resin possesses a high softening point (148oC) and a greater stiffness and rigidity
compared to polyethylene, but is brittle.
 It is the most widely used synthetic plastic.
Applications:
 Rigid PVC or unplasticized PVC have superior chemical resistance and high rigidity but
is brittle. It is used for making sheets that are employed for tank – linings, light-fittings,
safety, helmets, refrigerator components, tyres, cycle and motor cycle mudguards. It is
also extruded in strip and tube form for use in the place of non-ferrous metals.
 Platicized PVC is used for making continuous sheets of different thicknesses from 0.1mm
to 8mm. It is employed for packing rain coats, table-clothes and curtains, electrical
insulation like coverings of electric cables, injection moulding of articles like toys, toolhandles, toiled-goods, radio-components, plastic-coated cloth, chemical containers,
thermal insulating foam, conveyor belts etc.,
Plasticized PVC is obtained by adding plasticizers like dibutyl phthalate, dioctyl
phthalate, tricresyl phosphate etc.
Polytetrafluoro ethylene (PTFE) or Teflon:
Teflon is the trade name for polytetrafluoro ethylene. The linear structure of Teflon is
(CF2– CF2)n. The monomer used is tetrafluoro ethylene which is a non-toxic gas. The monomer
is obtained by the following reactions:
Preparation:Teflon is usually prepared by emulsion polymerisation of tetrafluroethylene, under
pressure in the presence of benzoyl peroxide as catalyst.
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Polymers
Properties:
 Teflon is essentially a linear polymer with no branching It is a thermoplastic
 High degree of crystallinity (93-98%)
 High melting point (3500C) and high density (2.1-2.3g/cm3)
 Presence of highly electronegative fluorine atoms and its regular arrangement results
strong attractive forces between the polymer chains which results extreme toughness and
high softening points to PTFE.
 Excellent electrical insulation properties.
 Very-low coefficient of friction
 Excellent thermal stability.
Applications: Teflon is used for
 Wire and cable insulation
 Laminates for printed circuitry Coatings of frying pans.
 Non-lubricating bearings.
 Variety of seals, gaskets, packings valve and pump parts and stop-cocks for burettes.
 Insulators for motors, generators, coil transformers and capacitors.
NYLON
Synthetic fiber forming polyamides are termed as ‘Nylons’. These are named based on
the number of carbon atoms present in monomer unit.
Nylon-6,6 :
It is prepared by condensation polymerization of hexamethylene diamine with adipic acid in 1:1
ratio.
Nylon -6 is prepared by the self condensation of €-amino caproic acid.
Nylon -11 is prepared by the self condensation of ω-amino undecanoic acid.
Properties:
a. Nylons are translucent, whitest,horny and high melting polymers.
b. They are insoluble in common organic solvents and soluble in phenol and formic acid.
c. Resistant to abrasion
d. Flexible and absorb low moisture
Uses:
a. Nylon-6,6 is used in sockes, dresses, carpets garments etc
b. Nylon-6 and Nylon-11 are used in gears, bearings, electrical mountings
c. Also used in making filaments,ropes, bristles for tooth brushes etc
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Polymers
BAKELITE:
It is prepared by condensing phenol with formaldehyde in presence of acidic/alkaline
catalyst.
Preparation: It involves three steps
1. Intial step involves the formation of ortho and para hydroxyl methyl phenol
2. The above formed ortho and para reacts to form linear polymer
3. During moulding, hexamethylene tetramine are added to the novolac. It converts the
soluble, fusible novolac into into a hard, infusible Bakelite.
Properties:
o Phenolic resins are hard, rigid and strong materials
o They have excellent heat and moisture resistance.
o They have good chemical resitance.
o They have good abrasion resistance.
o They have electrical insulation characteristics
o They are usually dark coloured.
o Lower molecular weight grades have excellent bonding strength and adhesive properties.
Applications: Phenol formaldehyde resins are used for
 Domestic plugs and switches, Handles for cooker and saucepans.
 Distributor heads for cars, Adhesives for grinding wheels and brake linings.
 Varnishes, electrical insulation and protective coatings. The production of ion exchange
resins.
 Impregnated paper, wood and other fillers, for producing decorative laminates and wall
coverings and industrial laminates for electrical parts including printed circuits.
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Polymers
ELASTOMERS
An elastomer is a material (polymer) with the mechanical (or material) property that it can
undergo much more elastic deformation under stress and return to its previous size on releasing
the stress without permanent deformation.
NATURAL RUBBER
Rubbers also known as Elastomers, they are high polymers, which have elastic properties
in excess of 300%. (OR) Elastomers are the high polymers which can be stretched to 4-10 times
of its original length by the application of force and as soon as the force is released it comes to
original length.
The coiled structure of the elastomers is responsible for their elasticity. Their structure
simply resembles a spring.
Natural rubber is a dispersion of isoprene. Natural rubber is made from the saps of a wide
range of plants like Hevea brasillians and guayule. The milk coming from rubber trees is known
as latex. Latex: is a milky white fluid that comes out from the plant Hevea brasillians when a cut
is made on the steam of the plant.
Gutta-Percha rubber: Gutta-percha is a name for a set of trees, mostly of the genus Palaquium,
noted for their latex. Chemically, gutta-percha is a polyterpene, a polymer of isoprene especially
trans-polyisoprene.
Processing of natural rubber or latex:
Latex of the rubber is an aqueous dispersion of rubber containing 25-40% rubber
hydrocarbon (poly isoprene). It is diluted to contain 15-20% and filtered to remove any dirt
present in it. After filtration the latex is coagulated by adding 5% acetic acid or formic acid.
The coagulated soft white mass is known as coagulum. Coagulum is washed and dried, and
then it is processed by either of the following methods.
1. Crepe rubber: A small amount of sodium bisulfate is added to bleach the coagulum.
After bleaching coagulum is passed through a crepe machine consisting of two rollers.
The coagulum is then converted into sheets of about 1mm thickness. Water is sprayed
in it and is dried at a temperature of 500C. The formed rubber sheets possess a rough
surface as crepe paper.
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Polymers
2. Smoked rubber: Coagulation of latex is carried out in large tanks containing paddles
(cross plates). Diluted latex is poured into the tank by removing the cross plates from
the tank. Coagulants like acetic acid or formic acid are added to the tank and stirred
thoroughly. The cross plates are then inserted in to the coagulum and kept undisturbed
for few hours. The tough sheets of coagulum so formed between the plates were
collected and passed through rollers to convert into sheets. These sheets are then
hanged for 4 days in smoked houses by maintaining a temperature 40-500C.
Drawbacks of natural rubber
o Plastic in natuture: It is hard and brittle at low temperature and soft and sticky at high
temperature.
o It is weak: tensile strength is 200 Kg/cm2
o It has high water absorption power.
o Non resistant to non polar solvents
o Non resistant to oxidizing agents like nitric acid, Con. Sulfuric acid, chromic acid etc
o It perishes due to oxidation in air
o It has marked tackiness
o It suffers permanent defprmation on greater stretching.
o Little durability.
o Swells with organic solvents.
Vulcanization:
A compounding process used to improve the properties of rubber discovered by Charles
Good Yeaar in 1839.
Vulcanization is a process of heating the raw rubber with sulfur at 100 – 140oC. The
sulfur combines chemically at the double bonds of different rubber chains and provides crosslinking between the chains. Thus vulcanization stiffens the rubber by forming cross links
between the polymer chains and by restricting the intermolecular movement of rubber chains.
The stiffness of vulcanized rubber depends on the amount of sulfur used. Tyre industry uses 3 –
5% sulfur. If the amount of sulfur is increased to 30%, a hard and rigid rubber called “ebonite”
is produced.
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Polymers
Advantages of vulcanization:
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The tensile strength of vulcanized rubber is very good. It is 10 times the tensile
strength of raw rubber.
It has excellent resilience i.e., articles made from it returns to the original shape
when the deforming load is removed.
It has better resistance to moisture, oxidation, abrasion.
It has much higher resistance to wear and tear compared to raw rubber.
It has broader useful temperature range (-40 to 100oC) compared to raw rubber’s
useful temperature range (10 – 60oC).
It is a better electrical insulator Ex: Ebonite
It is resistant to i) Organic solvents like petrol, benzene, CCl4, ii) Fats and oils, but it
swells in them.
It has only slight tackiness.
It has low elasticity. They property depends on the extent of vulcanization. Ebonite
has practically no elasticity.
It is very easy to manipulate the vulcanized rubber to produce the desired shapes.
Comparison betwee raw rubber and vulcanized rubber
Property
Raw Rubber
1. Tensile strength
200 kg/cm2
2. Elongation at break
1200
3. Rapidity of retraction
Good
4. Water absorption
Large
5. Selling in organic solvents Infinite (soluble)
6. Tackiness
Marked
7. Useful Temp range
10 to 600C
8. Chemical resistance
Very poor
9. Elasticity
Very high (300 – 1000%)
Vulcanized rubber
2000 kg/cm2
800
Very good
Small
Large but limited
Slight
-40 to 1000C
Much better
Low (depends on vulcanization
Compounding ingredients of rubber:
The process of mixing raw rubber with other material to impart specific properties is
known as compounding of rubber. The compounding ingredients are as follows
1. Plasticizer & softners: These are added to impart greater tenacity and adhesion to the
rubber. Eg: vegetable oils, waxes, stearic acids etc
2. Vulcanizing agents: Process of heating natural rubber with sulfur at 100-1400CTo stiffen
the rubber by anchoring and restricting the intermolecular movement of rubber springs.
Eg: The major substance is sulfur, its percentage varies from 0.15 to 32%. Other
examples are hydrogen sulfide, sulfur monochloride, benzoyl chloride etc.
3. Accelerators: To catalyze the vulcanization process. Eg: 2-mercaptol benzothiazole, zinc
alky xanthates, guanidines etc.
4. Antioxidants: These are added to prevent the oxidation process of rubber in air.
Antioxidant prevents the deterioration of rubber by light and air. Eg: Phenyl naphthyl
amine, phosphites and phenolic substances
5. Reinforcing filers: To give extra strength and rigidity to the rubber. Eg: ZnO, CaCO3,
MgCO3, BaSO4.
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Polymers
6. Colouring agents: To impart desired colour to the rubber.
Eg:
Lead chromate
yellow
Ferric oxide
red
TiO2
white
Chromium trioxide green
Buna-S or Styrene rubber or GR-S:
Buna-S rubber is probably the most important type of synthetic rubber, which is produced by
copolymerization of butadiene (about 75% by weight) and styrene (25% by weight) in presence
of sodium catalyst.
Properties: Styrene rubber resembles natural rubber in processing characteristics as well as
quality of finished products.
 It possesses high abrasion-resistance, high load-bearing capacity and resilience.
 it gets readily oxidized, especially in presence of traces of ozone present in the atmosphere.
 It swells in oils and solvents.
 It can be vulcanized in the same way as natural rubber either by sulphur or sulphur
monochloride (S2Cl2).
Uses:
 Mainly used for the manufacture of motor tyres.
 In the manufacturing of floor tiles, shoe soles, gaskets, foot-wear components, wire and
cable insulations, carpet backing, adhesives, tank-linings, etc.
Nitrile Rubber or GR-A or Buna – N or NBR:
Preparation: It is prepared by the copolymerization of butadiene and acrylonitrile in emulsion
system.
Compounding and vulcanization methods are similar to those of natural rubber.
Properties:
 Due to the presence of cyano group, nitrile rubber is less resistance to alkalis than natural
rubber.
 Excellent resistance to oils, chemicals, aging (sun light).
 As the acrylonitrate percentage is increased in nitrile rubber, its resistance to acids, salts,
oils, solvents etc. increases. But the low temperature resilience suffers.
 Compared to natural rubber, nitrile rubber (vulcanized) has more heat resistance and it
may be exposed to high temperatures.
 It has good abrasion resistance, even after immersion in gasoline or oils.
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Polymers
Uses:
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For making Conveyor belts, Lining of tanks, Gaskets
Printing rollers , Oil-resistance foams
Automobile parts and high altitude air-craft components
Hoses and adhesives.
POLY URETHANES RUBBERS:
Polyurethane or isocyanate rubber is produced by reacting polyalcohol (Ethylene glycol) with diisocyanates (ethylene di isocyanate).
Properties:
 Polyurethanes are highly resistant to oxidation, because of their saturated character.
 Good resistance to many organic solvents, but are attacked by acids and alkalis,
especially concentrated and hot.
 The polyurethane foams are light, tought and resistant to heat, abrasion, chemicals and
weathering.
Uses: For surface coatings and manufacture of foams and spandex fibres.
Thiokol rubbers or Polysulfide rubbers
Preparation: Thiokol is prepared by the condensation polymerisation of sodium polysulfide
(Na2Sx) and ethylene dichloride (ClCH2CH2Cl). In these elastomers, sulfur forms a part of the
polymer chain.
Properties:
 They have excellent resistance to swelling and disintegration by organic solvents and
gasoline, kerosene, lubricating oils.
 Outstanding resistance to oxygen ozone, sun light.
 It undergoes swelling by benzene and derivatives of benzene.
 It has lower tensile strength and modulus than natural rubber. It tends to lose shape under
continuous pressure.
 It has offensive-mercaptan-like odour, that restricts its use.
Applications:
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 Manufacture of oil hoses, chemically resistant tubing and engine gaskets.
 Diaphragms and seals in contact with solvents.
 Printing rolls
 Containers for transporting solvents and Solid propellent fuels for rockets.
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Polymers
CONDUCTING POLYMERS
Definition: A polymer which conducts electricity as par with metallic conductors is known as
conducting polymer. (OR) An organic polymers with delocalized π electrons in its backbone
conducts electricity, these are termed as conducting polymers.
Classification: Conducting polymers can be classified as follows.
1. Intrinsically conducting polymers:
The polymers have extensive conjugation of π electrons or residual charge in the
backbone which is responsible for conductance. These are of two types.
Conducting polymers having conjugated – π electrons in the backbone: Such polymers
contain conjugated - π electrons in the back bone which increases their conductivity to a large
extent.
Overlapping of conjugated - π electron orbitals over the entire backbone results in the
formation of valence bands as well as conduction bands that extends over the entire polymer
molecule. These conjugated π electrons get excited in an electrical field and transported through
the polymeric material.Conductivity of these polymers having conjugated -electrons in the
backbone is not sufficient for their use in different applications.
Eg:
Polyacetylene
Polythiophene
polypyrrole
Polyphenylene
Polyaniline
2. Doped conducting polymers:
The conducting polymers having conjugated - π electrons in the backbone can be easily
oxidized or reduced as they have low ionization potentials and high electron affinities. The
conductivities of intrinsically conducting polymer (ICP) can be increased by creating positive or
negative charge on polymer backbone by oxidation or reduction. It is a referred to as doping.
This is of two types. a) P-doping or oxidative doping b) n-doping or, reductive doping.
a. p-doping or oxidative doping: P- doping involves treatment of an intrinsically
conducting polymer with a lewis acid (electron pair acceptor). As the lewis acids are
electron acceptors, they attract an electron from the polymer back bone and oxidizes the
ICP thereby creating a positive charge on the polymer. The oxidation process leads to the
formation of delocalized radical cation ion called ‘Polaron’. The common p-dopants used
22
Polymers
are I2,Br2,ASF5,PF6, naphthyl amine.
Eg: Polyacetylene
A-dopant
Polyaniline
(Emarolidine base)
(Emarolidine hydrochloride known as synthetic metal)
b.
n-doping:. N- doping invoves the treatment of an intrinsically conducting polymer with a
lewis base like sodium naphthalide. As the lewis bases are electron donors, they release
an electron to the polymer back bone and reduction takes place in the ICP thereby
creating a negative charge on the polymer backbone.
3. Extrinsically conducting polymers:
These are the polymers whose conductivities are due to the presence of externally added
ingredients in them. These are of two types.
i. Conductive element filled polymer: In this type, the polymer acts as the binder to hold the
conducting element such as carbon black, metallic fibres, metallic oxides together in the
solid entity.
Minimum concentration of conductive filler in the polymer to start conduction is
known as ‘percolation threshold’. Because at this concentration of filler, a conducting path
is formed in polymeric material. Generally special conducting grade C-black is used as filler
which has very high surface area, more porosity and more filamentous properties.
ii. Blended conducting polymers: These polymers are obtained by blending a
conventional polymer with a conducting polymer. These polymers possess better physical,
chemical, electrical and mechanical process and they can be easily processed.
4. Co-oridnation conducting polymer: A charge transfer complex containing polymer
obtained by the combining the polydentate ligand with a metal is known as co-ordinate
conducting polymer.
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Polymers
Preparation:
1. Polymerization acetylene over zeigler catalysts gives polyacetylene predominantly in cisform.
2. Reaction of aniline with ammonium persulphate in presence of aqueous HCl produces
polyaniline as dark blue powder.
Applications:
1. In rechargeable Light weight batteries based on perchlorate doped Polyacetylene-lithium
Systems: These are about 10 times lighter than conventional lead storage batteries. These
can produce current density up to 50mA/cm2.
2. In electronic displays and optical filters: ICP’s can absorb visible light to give coloured
products so can be useful for electrochromic displays and optical filters. Thus the conducting
polymers can be used as electro chromic materials i.e., the materials that change colour
reversibly during the electrochemical processes of charge and discharge.
3. In wiring in aircrafts and aerospace components.
4. For making sensors for pH, O2, NOx,SO2,NH3 and glucose.
5. In telecommunication systems.
6. In electromagnetic screening materials.
7. In electronic devices such as transistors and diodes.
8. In solar cells, drug delivery system for human body etc.,
9. In photovoltaic devices.
10. In non-linear optical materials.
INORGANIC POLYMERS
The macromolecules composed by the atoms other than carbon atoms are known as
inorganic polymers. OR The macromolecules whose backbone is formed without carbon-carbon
linkage carbon atoms are known as inorganic polymers. In these polymers the atoms are linked
by covalent bonds.
Inorganic homo chain polymers: Inorganic polymers whose backbone is made by same type
atoms are called as inorganic homo chain polymers.
Eg: Poly germanes
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Polymers
Inorganic hetero chain polymers: Inorganic polymers whose backbone is made by different
atoms are called as inorganic hetero chain polymers.
Eg: silicone rubber
SILICONES: A Silicone polymer contains alternate silicon – oxygen atoms in which alky
radical are attached to silicon atoms. Their general formula is as follows
Preparation:
1. Reaction of silicon with alkyl halides or silicon halides with Grignard reagents forms
organo silicon halides (halo silanes)
2. Monomethylsilicon trichloride is a trifunctional monomer and forms crosslinked
polymers.
3. Dimethylsilicon dichloride is a bifunctional monomer and forms linear polymers.
4. Trimethylsilicon chloride is a monofunctional monomer and forms polymer of limited
chain length.
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Polymers
.
Properties of silicones:
1. Silicones may be liquids, viscous liquids, semi solids (greases), rubber like and solids
2. Because of silicon-oxygen link, they exhibit outstanding stability at high temperatures.
3. They exhibit good water resistance, oxidation stability and poor chemical resistance.
4. They are non toxic
5. Their physical properties are much less effected by variation of temperature.
Applications of silicones:
1. Liquid silicones or silicone oils are used
a. As high temperature lubricants,
b. As antifoaming agents
c. As aater repellent finishes for textile and leather industries
d. In heat transfer media, cosmetics and polishes
2. Silicone greases: Addiotion of filers to silicone oils yields silicone greases. These are
used as lubricants at very high and very low temperatures
3. Silicone Rubber: These are formed by the addition of filers to high molecular weight
linear silicon polymers. Silicones react with peroxides and form a dimethyl bridge
between methyl groups of adjacent chains.
These are used
a. As a sealing material in search engines, aircrafts
b. For manufacture of tyres to fighter air crafts
c. For insulating the electrical wiring in ships
d. In making lubricants, paints and protective coatings
e. To manufacture the boots which are useful at very high and low temperatures
4. Solid Silicone resins: These are used
a. For making high voltage insulators
b. High temperature foams and moldings of high thermal stability
POLYPHOSPHAZINES:
Backbone comprises alternate P and N atoms. Side groups (R) can be organic, inorganic
or organometallic. Their general representation is as follows
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Polymers
Preparation:
1. Polyphosphonitrile chlorides:
Properties:
a. They exhibit high elasticity and are known as inorganic rubbers
b. Freseshly prepared samples are soluble in chloroform
c. On long storage they becomes gel and get cross linked
d. Interacts with moisture and forms oxygen bridge
e. Interacts with ammonia and forms amine bridge
2. Poly dimethoxy phosphazines and Polydiethoxy phosphazines: These are prepared by
treating the poly phosphonitriles with sodium methoxide and sodium ethoxide
respectively.
Properties:
a. Colour less, transparent film forming thermo plastics
b. Resistant to radiation
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Polymers
c. High refractive index
d. Foms cyclic polymers on heating above 1000C
Applications:
a. Used to impart the bioerodibility
b. In the fileld of high technology elastomers
c. In the development of fire resistant, theramal and sound proof applications
d. To develop polymer electrolytes and hydrogels
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