Polymer

 Polymers are large molecules made up of many smaller and identical repeating units joined together by covalent
bonds.
 The small molecules which combine with each other to form polymer molecules are termed monomer.
 There are some substances in which the molecules are also united together, but these are not called polymers. The
example of such substances are NaCl crystals, liquid water etc.
 In NaCl crystals, many molecules of NaCl are united together by ionic bond and in liquid water, many water
molecules are united together by hydrogen bond. But in polymers several units of a single molecule or two different
molecules are united together by covalent bond.
 The number of monomer units, which are united together to form a polymer molecule, is called degree of
polymerization.
 Polymers with a high degree of polymerization are called high polymers and high polymers have very high molecular
weight in which the repeating units are more than 100. Hence polymers are also called macromolecules.
 There are some substances whose molecules are also known as macromolecules but these are not polymers. Such as
carotene, vitamins etc.
 Hence, the basic difference is: polymers are composed of repeating units (monomer) but these macromolecules are
not composed of any repeating unit.

Acrylonitrile polyacrylonitrile
 Classification of Polymer
Based on degree of polymerization polymers are classified as:
(1) High polymer: Polymers with a high degree of polymerization are called high polymers. High polymers have
very high molecular weight in which the repeating units are more than 100. This polymer are also called
macromolecules.
(2) Low polymer: Polymers with a low degree of polymerization are called low polymers. low polymers have lower
molecular weight in which the repeating units are less than 100. this polymers are also called oligomers.

Depending upon the sources, the polymers are classified as:

(1) Natural polymer: Natural polymer is a polymer that results from only raw materials that are found in nature.
Example Proteins, Cellulose, Starch, Rubber.
(2) Semi-synthetic polymer: These are those polymers which are obtained by chemical modification of natural
polymers. Example cellulose derivatives - cellulose acetate (Rayon).
(3) Synthetic polymer: Synthetic polymers are derived from petroleum oil, and made by scientists and engineers.
Examples of synthetic polymers include nylon, polyethylene, polyester, Teflon, and epoxy.
Based on the structure of polymer, polymers are classified as:

 Linear chains: A polymer consisting of a single continuous chain of repeat units. Because of its linearity in
linear polymers, always exits flexibility in its chain. This is due to twisting of the single bond.
Branched chains: A polymer that includes side chains of repeat units connecting onto the main chain of repeat
units. In branched polymer, there is always side chain. The length of the side chain may be different in a branched
polymer.
Cross linked polymer: A polymer that includes interconnections between chains
Net work polymer: A cross linked polymer that includes numerous interconnections between chains

Linear Branched Cross-linked Network

 Organic and inorganic polymer
Organic polymer: Organic polymer are the polymer in which the backbone chain is essentially made up of carbon
and other valences of carbon atoms are satisfied with hydrogen, oxygen, nitrogen, sulfur, chlorine etc. All natural
polymers are organic polymers. Example Proteins, Cellulose, Starch, Rubber etc.

Starch
Inorganic polymer: An inorganic polymer may be defined as the polymer in which the backbone of the chain is
made up of atoms other than carbon atom. Examples glass, silicon rubber, poly phosphates, poly arsenates etc.

Silicon rubber Poly phosphate

Depending upon the mechanical properties, polymers are classified into two classes:
Thermoplastic polymer: Polymers that soften, without chemical change, and take new shapes by the application of
heat and pressure and harden when cooled. These polymer are able to retain their given shape on cooling. Thus the
softening on heating and stiffen on cooling can be repeated many times. Thermoplastic polymer may be recycled
several times. Thermoplastics have linear and branched chain having no cross-linking in its chain. Examples are
PP(polypropylene), PE(polyethylene), PVC and Nylon 66 etc.
Thermosetting polymer: The polymers which become soft on heating and can be given any desired shape and
retained its shape on cooling. But during heating the polymers undergo some chemical changes in their structure and
convert themselves into infusible and insoluble masses. As a result, on further heating they never be soft again and
cannot be recycled. These Polymers have heavily cross-linked to produce a strong three dimensional network
structure on heating. Examples are phenol formaldehyde resins, Melamine etc..

PVC

phenol formaldehyde resin

Depending on the ultimate form and use, polymers may be classified as plastic, elastomer, fiber and liquid resin.
(1) Plastic: These are polymers, which can be given shape of any hard and tough articles by the application of heat and
pressure. The examples of such polymer are poly vinyl chloride (PVC), Poly acryl amide (PAA), Poly methyl
methacrylate (PMMA).
(2) elastomer: These are rubber like substance, which deform on the application of load but come back to their original
shape on withdrawing load. That is, these polymers readily undergo reversible deformation and elongation. These are
mostly linear polymer having some degree of unsaturation in its backbone. As a result, these polymers lie in the form of
coil, which permits the polymers to be stretched under stress but regain its original shape when the stress is withdrawn.
Example natural rubber, synthetic rubber, silicon rubber etc.
(3) Fiber polymers: Polymer fibers may be defined as the polymer, which can be drawn into a long filament and whose
length will be at least 100 times larger of their diameter. Examples nylon, jute fiber. The special property of these
polymers is the inter particle forces in these polymers are quit strong.
(4) Liquid resin: These are the polymers, which are usually obtained, in liquid or semisolid form. These are used as
adhesive particularly in paint and vanish industry. Examples epoxy resin.

Based on composition, polymer are classified into two classes:

(1) Homo polymer: A polymer derived from only one type of repeat unit or monomer.
(2) Copolymer: When a polymer consists of two or more different monomer units then it is called co-polymer. In a co-
polymer molecules monomers arrange at random manner it is called random copolymer, but if monomers arrange in a
regular pattern, then it is called alternating copolymer.
 Random co-polymer
homopolymer
-(CH2 -CH2 )n- polyethylene Ethylene vinyl acetate
Alternating co-polymer

Classification based on polymerization

Addition polymers:
formed by the repeated addition of monomer molecules possessing double or triple bonds
n(CH2=CH2) -(CH2 -CH2 )n-
Ethylene polyethylene
Condensation polymers:
formed by repeated condensation reaction between two different bi-functional or tri-functional monomeric
units. eg. terylene (dacron), nylon 6:6, nylon 6.

n(H2N(CH2)6 NH2) + n(HOOC(CH2)4COOH) [-NH(CH2)6NHCO(CH2)4CO-]n + nH2O

(Nylon 6:6)
 Synthesis of polymer
Polymerization: A chemical reaction in which two or more molecules or monomer join to form a polymer is
called polymerization.
Polymer can be synthesized by four different methods:
(a) Addition polymerization
(b) Condensation polymerization
(c) Ring opening polymerization
(d) Oxidative polymerization
(a) Addition polymerization: Addition polymerization is a process in which polymer is formed from the
monomer, without the loss of any material, and the product is the exact multiple of the original monomeric
molecule. Addition polymerization proceeds by the initial formation of some reactive species such as free radicals
or ions and by the addition of the reactive species to the other molecule, with the regeneration of the reactive
feature.
Depending on the mechanism of addition polymerization is classified into three classes
(i) Free radical addition polymerization
(ii) Cationic addition polymerization
(iii) Anionic addition polymerization
(i) Free radical addition polymerization: In this process the initiation of the polymerization reaction is carried
by the formation of free radical. The transformation of the monomer into free radical is done by the action of light,
heat or ionizing radiation or by the addition of external substances which are readily decomposed into free radicals
such as H2O2, C6H5CO-O. etc. For example in chemical initiation method the polymerization is initiated by the
decomposition of some organic and inorganic peroxides, H2O2, diazo compounds. The decomposition is usually
 These radicals serve as the active centers and cause chain propagation by combining with monomer.
2RO• + CH2=CH2 → RO-CH2-CH2•
RO-CH2-CH2• + CH2=CH2 → RO-CH2-CH2-CH2-CH2• → → etc
In free radical polymerization the union of two free radicals terminates the chain propagation of reaction.
RO-CH2-CH2• + RO-CH2-CH2• → RO-CH2-CH2-CH2-CH2-RO
In free radical polymerization the chain termination is also occurred by the disproportionation reaction.
2 RO-CH2-CH2-CH2-CH2• → RO-CH2-CH2-CH2-CH3 + RO-CH2-CH2-CH=CH2

(ii) Ionic addition polymerization: In ionic addition polymerization reaction ions are formed by using different
types of initiators. Depending upon the nature of initiators, the polymerization may be carried out through the
formation of cation Ionic addition
or through thepolymerization: In ionicAccordingly,
formation of anion. addition polymerization reaction process
the polymerization ions are is
formed
calledbycationic
using different
Depending
polymerization and anionic upon the nature
polymerization, of initiators,
respectively. the polymerization
Lewis acid and base may be carried
are used out through
as initiator the formation
in cationic and of c
formation
anionic polymerization, of anion. Accordingly, the polymerization process if called cationic polymerization and anionic p
respectively.
respectively. Lewis acid and base are used as initiator in cationic and anionic polymerization, respectively.
(i) cationic polymerization:
+
Y (acid )+ CH2=CH2 → Y:CH2-CH2 ( a Carbonium ion)
+ +
Y:CH2-CH2 + CH2=CH2 → Y:CH2-CH2-CH2-CH2 → → → etc.
(ii) Anionic polymerization: _
..
Z (base )+ CH2=CH2 → Z:CH2-CH2 ( a Carbanium)
_ _
.. ..
Z:CH2-CH2 + CH2=CH2 → Z:CH2-CH2-CH2-CH2
_ _
.. ..
_ → → → etc.
Z:CH2-CH2-CH2-CH2 + CH2=CH2 → Z:CH2-CH2-CH2-CH2-CH2=CH 2
In the initiation step of cationic and anionic polymerization carbocation and carbanion forms, respectively, which
interacts with a monomer molecule thereby forms a bigger ion, which again interact with another monomer molecule
as a result chain growth starts.
In cationic polymerization, the chain termination takes place by the following processes:
(a) Mutual collision at the ends of growing ions
(b) Splitting of catalyst from the polymer chain.

In anionic polymerization initiator interacts with the monomer molecule and forms carbanion. The carbanion just like
to the carbonium ion of cationic polymerization interacts with another monomer molecule and forms a bigger
carbanion. In this way chain growth starts. This is accompanied with the communication of negative charge along the
chain. Thus the growth chain becomes a bigger carbanion and the molecular mass increase in the course of
polymerization.

In anionic polymerization chain termination occurs as result of collision between growing ions with a molecule of the
medium such as ammonia molecule.
Condensation polymerization: Condensation polymerization is the process in which many monomer molecules
unite together to form a big macromolecule with the loss of some simple molecules like water, CO2 etc. The most
common example of condensation polymerization is the formation of nylon 6 6 from adipic acid and hexamethyl
diamine.
Ring opening polymerization
Oxidative Polymerization
 Polymer processing
Polymers prepared by the different methods are generally obtained in the form of granules, powder or chips. To
convert these polymer into usable articles it must be processed. During processing the following substances are
added. These substance are known as additives.
(a) Binders
(b) Fillers
(c) Dyes or pigments
(d) plasticizer and
(e) Lubricants
(a) Binders: A binder is any material or substance that holds or draws other materials together to form a
cohesive whole mechanically, chemically, by adhesion or cohesion. The main function of binder is to hold
the other ingredients of the plastic together. It provides adhesion to a substrate, binds pigments and extenders
together, and determines important properties such as durability, flexibility and gloss. In most cases synthetic
resins, natural resins or cellulose derivatives are used as binders. Some examples of binders are shellac,
copal, gum arabic, epoxy resin, alkyd resin etc.

(b) Fillers: These are also called extenders. There are two important functions of the fillers, which are common
for all industrial products. (i) It reduces the cost of the product per unit weight, and (ii) It imparts certain
specific properties to the finished product. The commonly used binder are corn-husks, graphite, carbon
black, clay, paper pulp, wood flour, metallic oxides like ZnO, PbO, metal powder sush as Fe, Cu, Pb, Al etc.
The proportion of the fillers may be up to 50% of the plastic materials.
Some common examples of fillers with specific function:
 Barium salts are used to render the polymer impervious to X-rays.
 Quartz and mica are used to improve hardeness.
 Asbestos are added to improve heat resistence.
 Shredded textiles are used to increase impact strength.

(c) Dyes and pigments: The main function of dyes and pigments is to increase aesthetic appeal of the polymer
product. Both organic and inorganic substances are used as dyes and pigments. Some of these also work as
fillers.

(d) Plasticizer: The important function of the plasticizer is to improve the flexibility and plasticity of the
polymer so as to reduce the moulding temperature and pressure. The properties of the finished product are also
greatly influenced by the plasticizer. The proportion of plasticizer can be increase up to 60% of the polymer. A
variety of organic materials are used as plasticizer lie fish oil, castor oil, linseed oil,, tributyl phosphate, triphenyl
phosphate, camphor, ester of oleic acid, stearic acid, phthalic acid etc.

(e) Lubricants: Oils, waxes and soaps are usually used as lubricants. Their main function is to make the
moulding process easy and to impart elegant finish to the final product.
Polythene or polyethylene (PE):
Polythene is the most common plastic material used in making shopping bag. Polythene sheet is also used in
wrapping garments materials. It is the polymer of ethylene (CH2=CH2).Ethylene is the first member of olefins
(unsaturated hydrocarbon). The simplest unsaturated hydrocarbon, ethylene, id polymerized to form
polyethylene. Polyethylene is a thermo-plastic created from the polymerization of ethylene.

It is categories into two types:

Low Density Polyethylene (LDPE) High Density Polyethylene (HDPE)

LDPE (Low Density Polyethylene):
 LDPE has the most long- and short-chain branching of any form of PE, resulting in its lower density of 0.91–
0.94g/cm3.
 LDPE is partially crystalline substance. Its m.p is 115 oC. It is practically insoluble in any solvent at RT. But at
high temperature (100 oC) it is soluble in many solvents like CCl4, toluene, Xylene etc.
 However, strong oxidizing agents like concentrated nitric acid, K2Cr2O7 are able to oxidize LDPE. Oxidation
may takes place in air exposure to UV light and at elevated temperature.
Uses of LDPE:
Because of its inertness, LDPE is used for many purposes e.g. for packing and wrapping frozen food, textile
products etc. The branching keeps the molecular chains from packing tightly in its crystalline form, so LDPE has
less tensile strength but greater ductility. That exceptional “formability” makes LDPE particularly useful for a range
of applications, from rigid products like plastic bottles, buckets and bowls to filmy ones like plastic grocery bags
and plastic cling-wrap. LDPE is produced through free-radical polymerization. The non-polar nature of LDPE
makes it ideal for providing electric cable insulator.
The different steps involved in the synthesis of LDPE are
Initiation:
Free radical formation from initiator: I-I → 2I•
Reaction between monomer and initiator: I• + CH2=CH2 → I-CH2-CH 2•
Propagation:
Radicals interact with monomer to form a bigger radical.
I-CH2-CH2• +CH2=CH2 → I- CH2-CH2-CH2-CH2• → → I- (CH2-CH2)n-1-CH2-CH2•
Chain termination:
Chain termination is usually occurred by two different ways
(a) Mutual interaction
I- CH2-CH2-CH2-CH2• + I- CH2-CH2-CH2-CH2• → (-CH2-CH2-CH2-CH2-)n + I-I
(b) Disproportionation: It is a reaction where reduction and oxidation takes place simultaneously.
～CH2-CH2～ + ～CH2-CH2～ → CH3-(CH2-CH2)n-CH3 + CH3- CH=CH-(CH2-CH2)n-CH3
 Manufacturing procedure of LDPE
The raw material use for the manufacture of polyethylene is ethylene, which in turn prepared by the following
reactions.
(i) Dehydration of ethanol:- CH3-CH2OH → CH2=CH2 + H2O
(ii) Dehydro halogenations of ethyl chloride:- CH3-CH2Cl → CH2=CH2 + HCl
(iii) Hydrogenation of acetylene:- CH≡CH + H2 → CH2=CH2 etc.

LDPE is normally manufactured at high pressure

(-2000 atm) and high temperature ∼300oC. The
initiator used in this process are traces of oxygen,
benzoyl peroxide etc. When oxygen is used as
initiator, the operating pressure and temperature
for the polymerization are ∼1500 atm and
∼200oC respectively. Benzene and chlorobenzene
are used as solvents. The reaction is highly
exothermic. So the mechanism for heat
dissipation should be included in the
manufacturing process. In a typical process, 10-
30% of monomer is converted into polymer. The
rest of monomer is recycled. A flow char diagram
of manufacturing LDPE is shown in the figure.
Flow diagram for the manufacture of LDPE
HDPE (High Density Polyethylene):

 HDPE is well-defined by a density of larger or equal to 0.941 g/cm3. It has a liner polymer and lower degree of
branching.
 This results in molecules to be packed closer and intermolecular bonds are stronger than in highly
branched polymers such as LDPE. The absence of branching also results in a higher density and somewhat higher
chemical resistance than LDPE.
 With a high tensile strength, HDPE is used in products like garbage containers, baby toys, water pipes, jugs and
jars as well as packaging's such as milk jugs, butter tubs, and detergent bottles.
 HDPE is also more durable and more opaque and can tolerate higher temperatures mainly compared to LDPE.
Industrially, HDPE is synthesized from ethylene by a catalytic procedure.
 The high density polyethylene (HDPE) is linear and is manufactured at low pressure (2-4 atm) and at moderate
temperature in the range of 50-70 oC.
 Usually, the polymerization is carried out in an inert atmosphere and in the presence of Ziegler-Natta catalyst. This
catalyst is based on tri-alkyl-aluminium and titanium chloride. The solvents used in this polymerization process are
liquid hydrocarbons.

Initiation:

Propagation:

Chain termination:
(i) Internal transfer of hydride
Cat-CH2- CH2-CH2-CH2-CH2-CH3 → Cat-H + CH2=CH(-CH2-CH2-)n-CH2-CH3

(ii) Transfer to monomer

Cat-CH2-CH2(-CH2-CH2-)n-CH2-CH2 → Cat-CH2-CH3+ (-CH2-CH2-)n-CH2-CH3
 Manufacturing procedure of HDPE

Raw materials is mixed with 1-butene (co-monomer) and then

fed into a fluid bed reactor in which the temperature and
pressure are maintained at 100oC and 0.7-2.0 Mpa,
respectively. The reaction is carried out in the gass phase. The
unreacted ethylene flowing out from the top of the reactor is
passed through a compressor, cooling tower and then returned
to the reactor. The polyethylene is taken out from the bottom
of the reactor in the form of granules. These are then passed
through extruder, quench cooler separator and dryer. The
polymer in the form of pellet is then sent to the storage
chamber. A simple flow sheet diagram is presented in the
figure.
Flow diagram for the manufacture of HDPE
 Poly vinyl chloride (PVC)
Among all the plastic polymers PVC is most widely used as construction material. It is prepared from the monomer
vinyl chloride, which is commercially prepared by the catalytic addition of hydrogen chloride to acetylene.
HCl + CH≡CH Charcoal catalyst CH2=CHCl (vinyl chloride)
Hg
Polymerization of vinyl chloride is carried out by using hydrogen peroxide as the initiator.

Properties of PVC: PVC is a hard and amorphous powder. It is characterized by its excellent flame resistance and
low cost. PVC can be extruded to pipes of different dimensions . It can be compressed into thin sheet. PVC sheets
are used for manufacturing tank lining, safety helmet, trays, bicycles or motorcycle mudguards etc. To manufacture
flexible PVC plasticizers are added. The commonly used plasticizer are dioctyl phthalte, dibutyl phthalate, tricresyhl
phosphate etc. The plasticized PVC are used for wire coating, for sheathing of electric cable , film and tubing etc.
PVC containing low percentage of plasticizer are used in injection moulding for manufacturing household articles,
toys, tooth brash handles, etc.
 Nylon 6 6
Nylon 6 6 is copolymer obtained from the polymerization of two monomers (a) adipic acid and (HOOC(CH2)4COOH) (b)
hexamethylene diamine. (H2N(CH2)6NH2). tensile

Nylon 6 6 has characteristic properties of both plastic and fiber. It has high strength, elasticity, toughness and abrasive
resistances. It is insoluble in most common solvents. Strong acids degrade it to some extent. It does not absorbed moister.
Due to the presence of polar group in the molecule its use as electrical insulator are restricted to low frequency only.
The most important applications are manufacturing of tire, cords, ropes, threads etc. Cords have high tenacity and good
elasticity. Because of its high tensile and impact strength, high temperature stability, good abrasion resistance, self-
lubricating and ball bearing properties. It is also used as substitute of metal in ball bearing, gears etc.
 Bakelite
Bakelite is a phenol-formaldehyde resins formed by the condensation polymerization between phenol and formaldehyde. It
is a grafted copolymer and the nature and properties of the polymer depend on many factors such as (i) composition i.e.
molar ratio of the reactants, (ii) nature of the catalyst (acidic or basic), and (iii) temperature. If the ratio of phenol to
formaldehyde is greater than 1, the reaction proceeds in an almost linear fashion. If the ratio is less than 1 and alkaline
catalyst is used then a three-dimensional network structure is produced.
Bakelite has high stability and resistance to cold flow. These
are widely used because of their good dielectric properties.
Phenolic resins are used for impregnating paper, wood and other
substances as fillers for producing decorative laminates and wall
coverings.

It has wide applications such as water-soluble adhesives, laminating

adhesives, varnish, lacquer etc. Bekelite has excellent adhesive
properties and bonding strength and hence used as varnishes and
protective coatings. These are also used in the production of ion
exchange resins with variety of functional groups such as amines,
sulfonic acids, hydroxyls, phosphoric acids etc .
 Melamine
Melamine is a copolymer of formaldehyde. It is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton
structure. Urea-formaldehyde and melamine-formaldehyde resins are very much similar in their production and
applications. These are popularly known as melamine. It can be prepared from calcium carbide and nitrogen by the
following reactions.

Melamine can also be prepared from urea simply by heating in

the presence of ammonia.
 Melamine reacts with formaldehyde in slightly alkaline condition to yield methylol derivatives:

 The tensile strength and hardness of urea or melamine resins are somewhat better than those of phenolic resins.
 The melamine resins have better hardness, heat resistance and moister resistance than urea.
 Relatively more expensive.
 Melamine resins are extensively used for the production of decorative lamination, and for the production of
crockeries.
 Dacron or terylene
Dacron or terylene is a polyester fibre obtained by the condensation polymerization between dicarboxylic acid (terphthalic
acid) and a dihydric alcohol ( ethylene gycol).

260-300oC

 Dacron is heavier yarn. Its specific gravity is higher than that of nylon 6 6.
 It has good elasticity.
 It has good resistance to weak acids and bases but strong acids and bases readily attack it.
 It has moderate heat resistance and is attacked by any kinds of microorganism.
 It is flammable without spreading fire.
 It is attacked by UV or near ultraviolet regions of light.
 Dacron is used extensively as the materials of garments fabrics such as shirting, suiting, making shocks, blankets,
sweater etc.
 It is also used for making aeroplane tires, wire insulators, parachutes clothes etc.
 Teflon
Teflon is the polymer of tetra-fluro-ethylene. Polytetrafluroethylene is known as teflon. The monomer tetrafluroethylene is
prepared by pyrolysis (thermal cracking) using chloro-di-fluro-methane. Tetrafluoroethylene on emulsion polymerization
by oxygen gives a plastic material(Teflon) of exceptional characteristics.

 Teflon is a linear chain polymer.

 Teflon is a giant molecules having highly regular structure without
branching or crosslinking.
 As a result, teflon fibre has very high density (2.1-2.3).
 Teflon chains are crowded in the polymeric molecules.
 They have densely populate and strongly held fluorine atoms all
through the chains.
 As a result, teflon fibre has high chemical resistance, and exceptional
resistance to strong corrosive media such as acids, bases and oxidising
agents.
 Teflon is also thermally stable (325oC) and low water absorption
capacity.
Uses of Teflon:
Teflon is widely used in pump packing, shaft bearing, cable insulation etc. It is also used for insulation of motors,
generators, transformer coils, capacitors etc. small equipment such as gaskets, valve parts, mould release devices are
made of teflon. It is also used as coating materials in non-stick frying pan.
 Plastic polymer
Plastic polymers may be defined as the polymer, which can be moulded or given shape by applying heat and
pressure. Plastic of various properties are available nowadays. The following are the most important properties of
plastic polymer:-
 light weight
 low thermal and electrical conductance
 resistance to the action of water and acid etc.
 easy of fabrication
 high corrosion resistance
 resistance to the attack of small insects and microorganisms like fungi, moths etc .
 high resistance to the action of light, oils etc.
 high resistance to abrasion
 transparent as well as translucent
 low coefficient of thermal expansion
 law m.p. but high refractive index
 good shock absorber
 Impermeable to water and other liquids
 Low maintenance cost , do not require protective coating
 Good mechanical Properties
 good ability to mix with pigments and other additives