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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

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    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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    Cationic Polymerisation

    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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    Cationic Polymerisation

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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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    (nionic Polymerisation

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    (nionic Polymerisation

    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