polymer

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POLYMERPOLYMER

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Content:Content:• Historical development.• What is Polymer ?• Classification.• Polymerization.• Structure & Properties. - Crystallinity. - Bulk Properties. - Glass Transition Temperature.• References.

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Historical DevelopmentHistorical Development

• Henri Braconnot 1811

• Jons Jakob Berzelius 1833

• BAKELITE 1909

• Joseph Priestly

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What is Polymer?What is Polymer?• They are complex and giant molecules

and are different from low molecular weight compounds.

• `Macro-molecules’ are made up of much smaller molecule.

• Combination of two or more than two monomers is known as `POLYMER’

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Chains made of interlinked rings Chains made of interlinked rings (representing polymer molecules)(representing polymer molecules)

Rings of same size(representing molecules of same

chemical)

Rings of different sizes(representing molecules of

different chemicals)

Poly meaning `many’ and mer meaning `part ’( In Greek)Example:- Butadiene

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Classification of PolymersClassification of Polymers• Natural and Synthetic Polymers

Natural Polymers Synthetic Polymer

-Cotton -Polyethylene-silk -PVC-wool -Nylon-rubber

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Classification of Polymers continued………Classification of Polymers continued………

• Organic and Inorganic Polymers A Polymer whose backbone chain is essentially

made of carbon atoms is termed an Organic polymer.

A Polymer which does not have carbon atom in

their chain backbone is termed as Inorganic polymer.

Glass and silicone rubber are examples of

inorganic polymer.

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•Thermoplastic and Thermosetting Polymers

Some polymer are soften on heating and can be converted into any shape that they can retain on cooling.

Such polymer that soften on heating and stiffen

on cooling are termed as `thermoplastic’ polymer.

Ex. Polyethylene, PVC, nylon, sealing wax Polymer that become an infusible and insoluble

mass on heating are called `thermosetting’ polymers.

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• Plastic, Elastomers, Fibres and Liquid Resins

A polymer is shaped into hard and tough utility articles by application of heat and pressure, it is used as `plastic’. eg. PVC.

When vulcanised into rubbery products

exhibiting good strength and elongation, polymers are used as `elastomers’. eg. Natural rubber.

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Plastics, Elastomers, Fibres, and Liquid ResinsPlastics, Elastomers, Fibres, and Liquid Resins • If drawn into long filament-like

materials, whose length is at least 100 times its diameter, Polymer are known as `Fibres’. eg. Nylon.

• Polymers used as adhesives, potting compounds, sealants, etc., in a liquid from are described as `liquid resins’. eg. Polysulphide sealants.

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PolymerizationPolymerization• polymerization is a process of bonding monomer, or

"single units" together through a variety of reaction mechanisms to form longer chains named Polymer.

• As important as polymers are, they wouldn't exist without monomers, which are small, single molecules such as hydrocarbons and amino acids. These monomers bond together to form polymers. The process by which these monomers bond is called polymerization

• Polymers such as PVC are generally referred to as "singular" polymers as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one molecule are referred to as "co-polymers".

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PolymerizationPolymerization• Polymerization that is not sufficiently moderated and proceeds

at an undesirably fast rate can be very hazardous. This phenomenon is known as Hazardous polymerization and can cause fires and explosions.

• Chain polymerization It is characterized by a self-addition of the monomer molecules

to each other, very rapidly through a chain reaction

• Step polymerization The polymer build-up proceeds through a reaction between

functional groups of the monomers, the reaction take place in step wise manner hence it is known as step polymerization

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Polymer Structure & PropertiesPolymer Structure & Properties• The structural properties of a polymer relate to the

physical arrangement of monomers along the backbone of the chain.

• Structure has a strong influence on the other properties of a polymer.

• For example, a linear chain polymer may be soluble or insoluble in water depending on whether it is composed of polar monomers (such as ethylene oxide) or nonpolar monomers (such as styrene).

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Polymer Structure & PropertiesPolymer Structure & Properties

Monomer identity

• Polymers that contain only a single type of monomer are known as homopolymers.

• while polymers containing a mixture of monomers are known as copolymers.

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Crystallinity• Crystalline solids and their behaviour

towards X-rays * We known that solids are conventionally classified as

crystalline or amorphous, depending on whether they possess a `long-range order’

* The presence or absence of a long-range order makes different solids behave differently when exposed to X-rays.

* while crystalline substance give sharp and well-defined X-ray diffraction pattern

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•Polymers and X-ray diffraction

* Polymers diffract X-ray like are crystalline substance would on the other hand, many behave like amorphous materials giving very broad and diffuse X-ray diffraction patterns.

* Unlike simple inorganic compounds.

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• Effect of crystallinity on the properties of polymers

1. Density.

2. Hardness.

3. Tensile strength.

4. Permeability

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• Bulk properties• The bulk properties of a polymer are

those most often of end-use interest

• These are the properties that dictate how the polymer actually behaves on a macroscopic scale

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• Glass Transition Temperature• The glass transition temperature, Tg, is the

temperature at which a glass becomes brittle on cooling, or soft on heating.

• More specifically, it defines a pseudo second order phase transition in which a supercooled melt yields, on cooling, a glassy structure and properties similar to those of crystalline materials.

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Glass Transition Temperature• The hard, brittle state is known as the

glassy state and soft flexible state as the rubbery or viscoelastic state.

GLASSY STATE

(Brittle plastics)

RUBBERY

OR

VISCOELASTIC

STATE

(Tough plastic and

rubbers)

VISCO FLUID

STATE

(Polymer melts)

Tg Tf Temp.

Change of state with temperature in polymeric materials

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Transitions and Associated Properties

• When a Polymer passes from one state to another, there is a gradual change in many of its physical properties.

• When we take a sample of a crystalline solid in a dilatometer and measure its volume change with temperature.

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Transitions and Associated Properties

ACrystalline solid

C

B

Tm

Liqid

D

0

+

Temperature

Vol

umec

hang

e,

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Specific volume (V) vs Temperature (T)

• Three polymer sample of the same chemical structure but different crystallinity.

• Sample 1-Highly crystalline

• Sample 2-Amorphous

• Sample 3-Partially crystalline

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• Highly crystalline

A B

C

D

TmTemp

Crystalline solid

Polymer meltA

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• Amorphous

MN

Tg Temp

Polymer melt

Rubber

B

Spec

ific

volu

me

(V)

Glassy

solid

O

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• Partially crystalline

T

S

R

QP

Tg TmTemp

Glassy and

crystalline solidRubber and

crystalline solid

Polymer meltC

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Glass Transition Temperature and Plasticisers

• The Plasticiser substantially reduces the brittleness of many amorphous polymers because its addition even in small quantities markedly reduces the Tg of the polymer.

• Their is reduction in Tg with the addition of different Plasticiser to a polystyrene sample.

• Many Plasticiser such as dibutyl phthalate,dioctyl sebacate, are used to decrease the Tg value of PVC.

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Glass Transition Temperature and Melting Point

• Factors affecting Tg will also affect Tm based on experimental observation,Tg and Tm, have been shown to be interconnected as follow

Tg=1/2 Tm (for symmetrical polymer)

Tg=2/3 Tm (for unsymmetrical polymer)

• Since this relation gives a range for Tg/Tm, it may more realistically reflect the thermal behaviour of polymer

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Importance of Glass Transition Temperature

• Polymeric material• Used for measuring of evaluating the

flexibility of a polymer molecule.• Tg value indicate wheather polymer at

the `use temperature’ will behave like rubber or plastic

• Polymer above Tg will be soft and flexible and below Tg will hard and brittle.

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ReferencesReferences

• 1) Polymer science, by V. R. Gowariker, N. V. Viswanathan and Jayadev Sreedhar, new age international limited publication.

• 2) Pharmaceutical Dosage froms:Disperse system, volume-3, 2nd edition by Herbert A. Lieberman, Martin M. Rieger and Gilbert S. Banker. Page no:436-438.

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• 3)Biodegradable Polymers as drug delivery system, Dekker series, edited by Mark Chasin and Robert Langer. Page no:3-10,150-155.

THANK YOU

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polymer

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