Chapter 13 Introduction to polymer (edited).pptx

8/18/2019 Chapter 13 Introduction to polymer (edited).pptx

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CHAPTER 13

INTRODUCTION TO POLYMER


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At the end of this lecture,students should be able to:

Determine types of polymer Determine physical properties ofpolymer

Determine types of polymerization


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Introduction

Polymer is a macro moleculecomprised of repeating structuralunits joined by covalent bonds.

◦

Greek word: “ poly ”= many , “ mer ”= parts he repeating unit is a !roup ofatoms covalently bonded to!etherin a speci"c spatial arran!ement.

◦ Monomer : the building block or structuralunit of the polymer.


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Types o Polymers

PolymerInorganic Organic

Natural Synthetic Natural Synthetic

• clays (bricks,cement, pottery)

• sands (glass)

• fibres • polysaccharides(starch, cellulose)

• proteins(collagen, lignins)

• polyisoprene(rubbers)

• adhesives

• fibres•

coatings• plastics• rubber

s• resinsClassi!cation "ased on #ource


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Types o Polymers

T&ermoplastics T&ermosets

'i!h molar mass molecules (ow molar mass molecules

)o crosslinkin! *rosslinked

+often upon heatin! ecompose chemicallyupon heatin!

*an be remelted *annot remelt

-ecyclable )on recyclable

Classi!cation "ased on P&ysical


7/36Classi!cation "ased on t&e #tructure o t&e

Types o Polymers

here are three di erent types based on the structureof the polymers.

◦ Linear polymers on #tructure

◦ "ranc&ed c&ain polymers

◦ Cross lin'ed or Net$or' polymers


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Types o Polymers

POLYMER N(ME

#/* #oly$vinyl chloride%

#+ #oly$styrene%

+0- +tyrene1butadiene1rubber

#2 #oly$ethylene terephthalate%

#/Ac #oly$vinyl acetate%

#/A #oly$vinyl alcohol%

#A) #oly$acrylonitrile%

+A) +tyrene1acrylonitrile copolymer

A0+ Acrylonitrile1butadiene1styreneterpolymer


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Classi!cation o Polymers

#olymers can be classi"ed as:◦ Addition polymers◦ *ondensation polymers

)o$ever* some polymers are neit&ercondensation nor addition polymers .

herefore, polymers are classi"ed based onthe polymerisation mechanism:

◦ *hain reaction◦ +tep reaction


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Classi!cation o Polymers

)omopolymers 1 consist of chainswith identical bondin% lin'a%es toeach monomer unit.

his usually implies that the polymeris made from all identical monomermolecules .

hese may be represented as : 13A1A1A1

A1A1A41


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Mode o Polymerisation

(ddition polymerisation :◦ se,uential addition of one bifunctional5

polyfunctional monomer to !rowin! polymerchains $it&out t&e elimination of any

part of the monomer molecule.# n 6 7 → # n68


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(ddition Polymerisation

( simple representation is -.(-(-(-(--


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Mode o Polymerisation

Condensation polymerisation :◦ polymers formed from bifunctional

monomers with the elimination o a smallmolecule species $w%. he reaction can

occur between any two !rowin! polymermolecules.P m 1 P n P m1n 1 $


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Condensation Polymerisation

( simple representation is -.(-"-(-"-- -


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Types o Polymeri2ationReactions

C&ain reaction :◦ polymerisation process by repeated

addition of monomer molecules to!rowin! polymer chain without theelimination of low molar mass molecules.

9 → 91*' ; 1*'- →

91*' ; 1*'-1*' ; 1*'- etc.

where 9 is an initiator

*' ; =*'- 33

*' ; =*'-


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4ree Radical Mec&anism

Initiation : *l ; → ; *lPropa%ation : *l 6 *' > → '*l 6 *' ?*' ? 6 *l ; → *' ? *l 6 *lTermination $? types%

$i%dimerisation :*' ? 6 *' ? → *' ? 1*' ? $ii%disproportionation :

*' ? 1*' ; *' ; 6 *' ? $*' ; %; *' ; → *' ? *' = *' ; 6 *' ? $*' ; %; *' ?

$iii%c&ain trans er : a chain transfer a!entdeposits a hydro!en with one electron on theradical of a !rowin! polymer chain and thisprocess initiate another polymerisation process.

uv


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Molecular 5ei%&t Control

@n polymerisation process, the aim isto control the molecular wei!ht.

he followin! variables in uence themolecular wei!ht:

◦ Temperature : the hi!her $optimum% thetemperature, the shorter the time re


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Molecular 5ei%&t Control

◦ Concentration o initiator : Dor additionpolymerisation, hi!her concentration ofinitiator will result in lower molecularwei!ht polymer.

◦ Concentration o monomer :

◦ Type o initiator : the initiator forms

radicals by decomposition reaction whichhas a half life which is dependent ontemperature and type of initiator.


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Cationic Polymerisation

Monomer (pplication

@sobutylene *' ; =*$*' ? %; 2lastomer, adhesives

/inylethers *' ; =*'F-Adhesives, te&tileaids, platiciBers

Dormaldehyde *' ; =F 2n!ineerin! plastics

2thyleneimine *yclo1$)'*' ; *' ; %#aper additive,

occulant

etrahydrofuran *yclo1$F$*' ; %>%+oft se!ment forpolyurethanes


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Initiators : "ronsted acids $ perchloric acid,trichloroacetic acid, tri uoromethanesulfonic acid,etc. %CLe$is acids $ AlCl 3 , TiCl 4 , etc. %Coinitiators : water, carbenium salts $ acetyl

perchlorate %

he !rowin! polymer chain is positivelyc&ar%ed which stabilise itself by addition ofnucleophilic species.

/ery few monomers are polymerisedcationically on an industrial scale.


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(nionic Polymerisation

Anionic polymerisation are initiated bybases or Le$is bases such as alkalimetals, alko&ides, amines, phosphines,Gri!nard compounds and sodium

naphthalene. he type and proportion of the initiatin!species stron!ly a ect the polymerisationrates and the tacticity o t&e polymers$tacticity: refers to how the pendant groups arearranged in a polymeric strand isotactic,sindiotactic, atactic %

Tacticity $from Greek taktikos : of or relatin! to arran!ement or

order% is the relative stereochemistry of adjacent chiral centerswithin a macromolecule

http://en.wikipedia.org/wiki/Stereochemistryhttp://en.wikipedia.org/wiki/Chirality_(chemistry)http://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Macromoleculehttp://en.wikipedia.org/wiki/Chirality_(chemistry)http://en.wikipedia.org/wiki/Stereochemistry


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Tacticity o t&e polymers


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Narro$ molar mass distribution

2mployed for the production ot&ermoplastics especially blockcopolymers $syrene1butadiene1styrene type%


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P&ysical Properties

he physical properties of polymermaterial are lar!ely determined by:

◦ Molecular $ei%&t◦ #tren%t& o intermolecular orces◦ Re%ularity o t&e polymer structure◦ 4le9ibility o t&e polymer molecule

he physical properties includemeltin% point , %lass transitiontemperature , solubility , meltviscosity , tensile stren%t& .


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P&ysical Properties

Meltin% point :◦ a temperature ran!e in which the viscosity of the

polymer chan!es from a solid to a li


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P&ysical Properties

Tensile stren%t& :◦ measures how diHcult it is to break a substance

when stress is applied to pull it apart.◦ ensile stren!th !enerally increases with molecular

wei!ht.


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T)E END

Chapter 13 Introduction to polymer (edited).pptx

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