2 Structure&Properties

8/11/2019 2 Structure&Properties

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2.

Structures

and

Bulk

Properties

of

Objective Tounderstandthedifferentstructuresof polymers,

metals andceramicsandhowthestructuresare

relatedtotheirbulkproperties.

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TheFramework

BioMaterialsBioMaterials Ceramics

Polymer

Structure

Characterization Protein

Property BiologicalImmunityBlood

Pathogen 2


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2.1Polymers

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Whatispolymer?

POLY MER

POLY=MANY MEROS

=PARTS

polymer mer

RepeatunitMer(thesmallestbuildingblockofapolymer):a

structurethatisrepeatedoverandovertoformthepolymer.

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Polyvinylchloride(PVC) Polypropylene(PP)

er un t er un t

Monomer

structure

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Polyethylene Poly(tetrafluoroethylene) Polystyrene

(PE) (PTFE) (PS)

po y

y roxyet ymethacrylate) Poly(methylmethacrylate)(PMMA)ol lactide

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Howtodefinethestructureofpolymers?

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Polymers:MolecularWeight

Degreeof

Polymerization:numberofrepeatunitsinapolymer,indicatedby

thelettern inthechemicalformulaforthepolymer.

= DegreeofMolecularweight Molecularweight TheNumberof

Molecularweightofpolymershasa

distribution

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AverageMolecularWeight

nMNumberaveragemolecularweight( )

=

i i

i

Nxi xi:numberfraction

==i i

i ii

i iin

N

MxM

wMWeightaveragemolecularweight( )

i iiMN 2

W

iii NW =

==

i iii

iiw

MN

w

=

i iW

w wi:weightfraction

o y spers y n ex :sma es

possiblePIis1.00

nM

=

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Agivenpolymersampleisamixtureofthreesamples:

1 5,000 1,000

2 10,000 1,000

3 1,000,000 3

a Calculatethenumberavera emolecularwei htofthe ol mer

[ ] )310001000()10000003()100001000()50001000( ++++=nM

==

i i

i ii

i iin NNMxM]/11:[8987 molegDaNoteDa ==

(b)Calculatetheweightaveragemolecularweightofthepolymer

)]10000003()100001000()50001000[()1000000(3)10000(1000)5000(1000

222++++=

wM

==

ii

i ii

i iiw MN

MNMwM

2Da173611=

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Howtodeterminethemolecularweight

of

polymers?

Chromatographyisthecollective

termforasetoflaboratory

techniquesfortheseparationof

mixtures.Themixtureisdissolvedin

afluid

called

the

mobile

phase

,

whichcarriesitthroughastructuremobile

phase

stationaryphase.Thevarious

constituentsofthemixturetravelat

stationary

phase

,

separate.Theseparationisbasedon

differentialpartitioningbetween

effluent

t emo ean stat onaryp ases.

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SEC:SeparationMechanismSEC columns are filled with small diameter about 10 m orous beads

Moleculesareseparatedbasedonthedifferenceintheirretentiontimeinthe

porousstationaryphase:themoleculewiththelargestsizefirstexitthe

stationaryp ase,an t esma estmo ecu esexists ast

Retentiontime

Sizeofthe

polymerchain

Retentiontime(min)

Molecularweight

0

Retentiontimeisthetime

requiredforasoluteto

mi rate or elute from the

column(fromtheinstant

ofsampleinjectiontothe

ointatwhichthe eak

maximumoccurs).

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SEC:Instrumentation

Pumpdrivescirculationofthemobile

sampleintothemobilephase

o umnsepara es eren s ze

moleculesbasedonretention

Detectortranslatestheamountof

ana y e n emo ep ase oan

detectiblesignal(UVvis,Mass

,.

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SEC:Instrumentation

Detector1

mobile hase

Detector2

PhotoColumn

PumpInjector

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SEC:Measurement

MWof

the

unknownsample

ight(Da

calibrationcurve

ecularw

M

ol

Retentiontime(min)

1.Runpo ymerstan ar swit nownmo ecu arweig t MW

2.Createacalibrationcurve(MWofthepolymerstandardsagainsttheir

3.Run

the

unknown

sample

and

readout

its

MW

from

the

calibration

curve

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Indepthquestion:

one

s u en

a

a

ra n ng

o

measure

a

po ymer

samp e

withnarrow,symmetricmolecularweightdistribution.

. ,

measurementrightafterpreparingthepolymersolution.Beforethe

secondmeasurement,heleftthepolymersolutionmagneticallystirredn ume oo w t outcapp ngt eso ut onv a . ss gnt eposs e

curvesbelowtothetwomeasurementsandexplainyourassignments.


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Polymer:Tacticity .

Isotactic:TheRgroupsarearrangedonthesame

sideofthechain

R:sidegroup Syndiotactic:TheRgroupsalternatepositionson

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PolymerStructure

near

po ymer:t erepeat ngun tsare o ne nanen toen as on.

Branched

polymers

havechainsbranchingoffthemainchain.

Crosslinked polymers:

adjacentchainsare

o ne atcerta npo nts

viacovalentbonds,

dimensionalnetwork 19


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Copolymersinvolvetwoormorerepeatunittypes

Randomcopolymer

(twomer unitsaredistributedalongthechainwithnopattern)

Alternating

copolymer(mer typesalternatealongthechain)

Blockcopolymers(eachtypeofrepeatunitisclusteredinregionsalongthechain)

Graftcopolymer(homopolymerchainsareattachedtoadifferenthomopolymer

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PolymersSynthesis

Addition(chain

reaction)

polymerization

(e.g.,

free

radical

polymerization)

kdn a on ac va ono a

monomerthroughchemical

reactions) R + M M

kd

Propagation(monomers

continuetosuccessivelyjointhepolymerchainand

increase its molecular wei ht

Mn + M Mn+1p

kterm na on es ruc ono theactivesite:freeradical

coupling)

n m n+m

kt

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n

m n

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PolymersSynthesis

Pol eth lene

Leadin to ol merswitha

molecular

weight

distribution 22


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PolymersSynthesis

Condensation(step

reaction)

polymerization

Thepolymerizationoccursthrougheliminationofonemolecular

usua ywateroraci

Theproductdoesnothavethesamechemicalformulaaseithermer

Typicalpolymers:nylonsandpoly(carbonates)

+ HCl

23SynthesisofNylon6,10


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http://www.youtube.com/watch_popup?v=yFEHKRdXb9Y&vq=medium

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How

are

polymer

chains

organized

to

ormmacroscop cmater a s

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PolymerCrystalStructures:Percentcrystallinity

ChainFolded

Model

of

Crystallinity

Polymerchainscanfoldtoformlamella

structure,whichisthebasicunitof

ol mericcr stal.

chainfolded

crystallite

Lamellar

chainfolded

Becauseofthelargesizeandflexibilityof

ol merchains, ol mermaterialsarerarel

crystallite

Tiemolecule

100%crystalline,eithersemicrystalline

(containingbothcrystallineandamorphous

regions)oramorphous.

Amorphous

Insemicrystallinepolymer,multipleintermingled

chainswhicheachhascrystallineregionslocated

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insidethelamellarstructuresandamorphous

regionsfound

outside.


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PolymerCrystalStructures:Percentcrystallinity

Factorsaffectingcrystallinity(anythingpreventchainalignment

polymercrystallinity)

closeenoughtoformacrystallinestructure.)

Chainbranching(branchedpolymershavelowerpercentcrystallinity)

Tacticity(atactic polymershavelowerpossibilitytocrystallizethanisotactic

orsyndiotactic polymers)

copolymershaveahigherprobabilityoftheformationofcrystalline

regionsthanrandomcopolymers)

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Com are cr stallinit of the followin ol mers

(A)

B

(C)

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Polymer:ThermalTransition

Crystalline

polymers

undergomelting

at

Tm(meltingtemperature).BelowTm,thecrystallineregionsofthepolymersarehighlyordered,whileabove

it,polymerchainsshowrandomdistributionwithnolongrangeorder.

Meltingoccurswhen

thereareenoughatomsorc a nsegments

vibratingtoresultin

overallchainmotion.

Amorphouspolymerspossessglasstransitiontemperature(T ).Below

Tg,thepolymermaterialisglassyandbrittle,whileaboveit,thechains

aremobileenoughtoproducearubbery,elasticmaterial.

Glasstransitionoccurswhenthereisenoughenergytocausemolecular

motionaroundthepolymerbackbone.

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Stiffness

Temperature

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ac ors

a ec ng

m any ng

scourage

secon ary

bondingbetweenchainswilldecreaseTm)

Chainbranching(withmorebranchedchains,moleculesareless

denselypacked,leadingtopoorsecondarybonding

between

the

mo ecu es

MolecularWeight(Forpolymerswiththesamechemicalstructure,high

MWpolymershaveahigherTm)

PolymerswithlowerMWhavemorechainends.Becausechain

endsaremorefreetomovethanotherpartofthepolymer

molecule,itneedslessenergytoproducethemotionfor

ol merswithsmallerMW.

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m

(A)

(B)

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ac orsa ec ngg

any ng avorsc a nv ra onan

rotationwilldecreaseTg)

Chainflexibility(polymerwithmoreflexiblechainsrequireless

energytoachievetherequiredmotionaroundthebackboneandts gw e ower

Bulkysidegroup(reducesthemovementaroundthebackboneand

increaseTg)

MolecularWeight(highMWpolymershaveahigherTg)

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ThermalAnalysis:DifferentialScanning

a or me ry ,

referencesampleisrecordedasafunctionoftemperature

whilethetwoareex osedtoacontrolledtem erature

ramp.

,

referenceareheatedfromthesameheaterandthe

thetwocellsismeasured.The

temperaturedifferenceisthen

converte into eat ow.

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Tm

Tg

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