Introduction To Polymer

O-34 NITESH GUPTAO-36 SAURABH CHAUHAN

Introduction to Polymers

Poly = many, mer = unit, many unitsPolymer science is relatively a new branch of science . It deals with chemistry physics and mechanical properties of macromolecule .

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

Classification schemesClassification by Origin

Synthetic organic polymers

Biopolymers (proteins, polypeptides, polynucleotide, polysaccharides, natural rubber)

Semi-synthetic polymers (chemically modified synthetic polymers)

Inorganic polymers (siloxanes, silanes, phosphazenes)

Classification by Monomer Composition

Homopolymer Copolymer

Block Graft Alternating Statistical

HomopolymerConsist of only one type of constitutional repeating unit (A)

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Copolymer Consists of two or more constitutional repeating units (A.B )

Statistical copolymer (Random) ABAABABBBAABAABBtwo or more different repeating unitare distributed randomly Alternating copolymer ABABABABABABABABare made of alternating sequencesof the different monomers Block copolymer AAAAAAAAABBBBBBBBBlong sequences of a monomer are

followed by long sequences of another monomer

Graft copolymer AAAAAAAAAAAAAAAAAA B B B B B B )d(

Several classes of copolymer are possible

Classification by Chain structure (molecular architecture)Linear chains :a polymer consisting of a single continuous chain of

repeat units Branched chains :a polymer that includes side chains of repeat

units connecting onto the main chain of repeat unitsHyper branched polymer :consist of a constitutional repeating unit

including a branching groupsCross linked polymer :a polymer that includes interconnections

between chainsNet work polymer :a cross linked polymer that includes numerous

interconnections between chains

Linear Branched Cross-linked Network

Direction of increasing strength

Classification by Thermal BehaviorThermoplastics - materials become fluid and processible upon heating, allowing them to be transformed into desired shapes that are stabilized by cooling.Thermosets - initial mixture of reactive, low molar mass compounds reacts upon heating in the mold to form an insoluble, infusible network

Classification by Application Plastics Fibers Elastomers Coatings Adhesives

Classification Based on Kinetics or MechanismStep-growth

Chain-growth

Polymerization mechanisms

- Step-growth polymerization

Stage 1

Consumptionof monomer

n n

Stage 2

Combinationof small fragments

Stage 3

Reaction of oligomers to give high molecular weight polymer

Step-Growth Polymerization

Polymerization mechanisms- Chain-growth polymerization

Chain polymerization

Radical polym.The C=C is prefer the Polym. by R.P.and also can be used in the steric hindrance of the substituent

Ionic polym.

Anionic polym. Cationic polym.

X X X

radical cationic anionic

Electron with drawingsubstituent decreasingthe electron density on the double bond and facilitate the attack ofanionic speciessuch as cyano and carbonyl δ+ δ- CH2=CH Y

Electron donatingsubstituent increasingthe electron density on

the double bond and facilitate the attack of

cationic speciessuch as alkoxy, alkyl, alkenyl, and phenyl

δ- δ+ CH2 =CH Y

Polymer Degradation

Polymer degradation is a change in the properties – tensile

strength, colour, shape, etc of a polymer or polymer based

product under the influence of one or more environmental

factors such as heat, light or chemicals.

The term 'biodegradation' is limited to the description of

chemical processes (chemical changes that alter either the

molecular weight or solubility of the polymer)

Degradation:CHEMICAL DEGRADATIONBIOLOGICAL DEGRADATIONMECHANICAL DEGRADATIONCHLORINE INDUCED CRACKINGTHERMAL DEGRADATIONPHOTO DEGRADATION

Biological DegradationBiodegradable plastics can be biologically

degraded by microorganisms to give lower molecular weight molecules.

Chlorine induced crackingAnother highly reactive gas is chlorine, which

will attack susceptible polymers such as acetal resin and polybutylene pipe work.

There have been many examples of such pipes and acetal fittings failing in properties in the US as a result of chlorine-induced cracking.

Chemical Degradation:

Polymers can be degraded by solvolysis and mainly hydrolysis to give lower molecular weight molecules. The hydrolysis takes place in the presence of water containing an acid or base.

Polymers are susceptible to attack by

atmospheric oxygen, especially at elevated temperatures encountered during processing to shape.

Thermal degradationThermal degradation of polymers is molecular

deterioration as a result of overheating. At high temperatures the components of the long chain backbone of the polymer can begin to separate (molecular scission) and react with one another to change the properties of the polymer. The chemical reactions involved in thermal degradation lead to physical and optical property changes relative to the initially specified properties.

Photo degradationOne of the disadvantages of using polymers in

high temperature conditions or in outdoor applications – degradation

environment negatively influences the service life.

This process is called weathering - ageing an irreversible chemical process,

undesired changes of properties of the polymers,discoloration and loss of mechanical properties

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