Polymers
Introduction to
Polymers
Poly = many, mer = unit, many units
Polymer science is relatively a new branch of
science . It deals with chemistry physics and
mechanical properties of macromolecule .
A polymer is a large molecule which is
formed by repeated linking of the small
molecules called “monomers”.
OR
polymer is organic substance made up of many
repeating units or building blocks of molecules
called mers.
POLYMER
• Combine, many monomers to create a polymer.
• Polymer is often used as a synonym for ‘plastic’.
• All plastic are polymers, but not all polymers are
plastics.
Poly mers
↓
↓
Many Units
are made up of many
Mono mer
↓
One
↓
Unit
Monomer molecules joined in units of long
polymer.
It consist of large no. of repeating units known as
monomers
The no. of repeating units in a chain of
polymer is known as degree of
polymerization
POLYMER
a family of natural and synthetic materials made of repetition of high weight molecules
in a form of flexible chain
NATURAL POLYMER
• Collagen
• Gelatin
• Silk
• Wool
• Natural rubber
• DNA
SYNTHETIC POLYMER
• Polyethylene
terephthalate (PET)
• High Density
Polyethylene (HDPE)
• Polyvinyl Chloride (PVC)
• Low Density
Polyethylene (LPDE)
• Polypropylene (PP)
• Polystyrene (PS)
Examples Of Polymers
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Polypropylene (PP) - Carpet, upholstery
Polyethylene low density (LDPE) - Grocery bags
Polyethylene high density (HDPE) - Detergent bottles, toys
Poly(vinyl chloride) (PVC) - Piping, decking
Polystyrene (PS) - Toys, foam
Polytetrafluoroethylene (PTFE, Teflon) - non-stick pans, electrical insulation
Poly(methyl methacrylate) (PMMA, Lucite, Plexiglas) - Face shields,
skylights
• Poly(vinyl acetate) (PVAc) - Paints, adhesives
• Polychloroprene (cis + trans) (Neoprene) - Wetsuits
Characteristics of Polymers
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Low Density.
Low coefficient of friction.
Good corrosion resistance.
Good mould ability.
Excellent surface finish can be obtained.
Can be produced with close dimensional tolerances.
Economical.
Poor tensile strength.
Low mechanical properties.
Poor temperature resistance.
Can be produced transparent or in different colours.
Properties of Polymers
The physical properties of a polymer, such as its strength
and flexibility depend on:
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Chain length - in general, the longer the chains the stronger
the polymer;
Side groups - polar side groups give stronger attraction
between polymer chains, making the polymer stronger;
Branching - straight, un branched chains can pack together
more closely than highly branched chains, giving polymers
that are more crystalline and therefore stronger;
Cross-linking - if polymer chains are linked together
extensively by covalent bonds, the polymer is harder and
more difficult to melt.
Properties of Polymers
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Reflective
Impact resistant
Tough
Brittle
Translucent
Malleable
Soft
Elastic
Inelastic
Insulative
Classification
of Polymer is
based on
source
structure
Polymerization
Molecular force
Classification
based on Source
Natural polymers
Semi-synthesis
polymers
Synthesis
polymers
Natural polymers
• The definition of a natural polymer is a polymer that results from
only raw materials that are found in nature.
• Example:• Proteins,
• Cellulose,
• Starch,
• Rubber.
Semi-synthesis polymers
• chemically treated polymers of natural origin are quite common and
of great practical importance
• Cellulose, for example, is used in two different ways:
• it is dissolved using some special solvent and precipitated again in a
different physical shape, e.g.
• viscose silk (reyon)
chemically treated polymers, that are of natural origin termed as semi synthesis
• copper silk
Synthesis polymers
• 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
structure
Linear polymers
Branched chain
polymers
Cross linked
chain polymer
Linear polymers
• consists of a long string of carbon-carbon bonds
• misleading because the geometry around each carbon atom is
tetrahedral and the chain is neither linear nor straight
• As the polymer chain grows, it folds back on itself in a random fashion
• E.g
• Polyethylene
Branched chain polymers
• Polymers with branches at irregular intervals along
the polymer chain are called branched polymers
• difficult for the polymer molecules to pack in a
regular array
• less crystalline and less dense
• amount and type of branching also affects physical
properties such as viscosity and elasticity
• Branches often prevent chains from getting close
enough together for intermolecular forces to work
effectively.
• E.g. polyethylene
• PE is a relatively simple polymer, there are two
common forms of it (high and low-density,) each with
unique properties.
Cross linked chain polymers
• formed from bi-functional and trifunctional monomers and contain
strong covalent bonds
• contain short side chains (cross
links)
• connect different polymer chains
into a “network”
• adding cross-links between
polymer chains makes the polymer
more elastic (they can stretch and
return to their original form)
Cross links
between
chains
Based on
polymerization
additional
condensation
Addition polymers
• formed by the repeated addition of monomer molecules possessing
double or triple bonds
n(CH2=CH2)
-(CH2 -CH2 )Ethylene
polyethylene
Condensation polymers
• formed by repeated condensation reaction between two different bifunctional 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)
Based on
molecular force
nylon
thermoplastic
thermosetting
Nylon
• Nylon is used as general name for all synthetic fiber forming
polyamides, i.e., having a protein like structure.
• These are the condensation polymers of diamines and dibasic acids
• A number is usually suffixed with the Nylon which refers to the
number of carbon atoms present in the diamine and the dibasic acids
respectively.
• example: nylon 6,6
• nylon-6,6: Nylon-6,6 is obtained by the polymerisation of adipic acid
with hexamethylene diamine.
Thermoplastic polymers
• These are linear or slightly branched long chain polymers, which can
be softened on heating & reversibly hardened on cooling repeatedly.
• Their hardness is a temporary property & varies with temperature.
• Example:- polyvinyl chloride.
• Polyvinyl chloride:- It is a vinyl polymer constructed of repeating
vinyl groups (ethenyls) having one of their hydrogens replaced with a
chloride group.
Thermosetting polymers
• initial mixture of reactive, low molar mass compounds reacts upon
heating in the mold to form an insoluble, infusible network.
Example: bakelite
• bakelite: bakelite is formed of phenol and form-aldehyde
polymerization.
Applications of Polymers:
• Polymeric materials are used in and on soil to improve
aeration, provide mulch, and promote plant growth and
health.
Medicine
• Many biomaterials;
• heart valve replacements
• blood vessels, are made of polymers like Dacron, Teflon and
polyurethane.
Consumer Science
• Plastic containers of all shapes and sizes are light weight and
economically less expensive than the more traditional containers.
• Clothing
• floor coverings
• garbage disposal bags
• packaging are other polymer applications.
Industry
• Automobile parts
• windshields for fighter planes
• Pipes
• Tanks
• packing materials
• insulation, wood substitutes
• elastomers are all polymer applications used in the industrial market.
Sports
• Playground equipment
• various balls
• golf clubs
• swimming pools
• protective helmets are often produced from
polymers.
Strength of Polymers
In general, the longer the polymer chain, the stronger the
polymer. There are two reasons for this:
• longer chains are more tangled
• there are more intermolecular forces between the chains
because there are more points of contact. These forces,
however, are quite weak for polyethene.
• Areas in a polymer where the chains are closely packed in a
regular way are said to be crystalline. The percentage of
crystallinity in a polymer is very important in determining its
properties. The more crystalline the polymer, the stronger and
less flexible it becomes.
• When a polymer is stretched (cold-drawn), a neck forms. In
the neck the polymer chains line up producing a more
crystalline region. Cold-drawing leads to an increase in
strength.
• The first polyethene which was made contained many chains
which were branched. This resulted in a relatively
disorganised structure of low strength and density. This was
called low density polyethene (ldpe).
• In the crystalline form, the methyl groups all have the same
orientation along the chain. This is called the isotactic
form. In the amorphous form, the methyl groups are
randomly orientated. This is called the atactic form.
• Polymers with a regular structure are said to be
stereoregular.
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