chain grwth polymerizatin

8/12/2019 Chain Grwth Polymerizatin

1/63

ChainGrowthPolymerizationGeneralProcessrequires3stepstodescribethereactionprocess,i.e.radical,ionic,etc

(1) InitiationbyareactivespeciesR*

,

cation,anion,etc

(2) Propagation ReactivespeciesR*addstomonomerbyopeningpibondtoform

newreactivecenter

(3) Termination reactionendingevents

(DeadPolymer)


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ChainGrowthMonomers

ny onomers

Radicaland/orIonic

Ionic,typicallynotpronetoradicalpzn


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ChainGrowthMonomers

Monomer Radical Cationic Anionic

Ethylene + +

1,3dienes + + +

St renes + + +

Halogenated alkenes +

Acrylates + +

cry on tr e + +

Vinylether +

Ingeneral,thenatureoftheYgrouphelpsdeterminepzn mechanism

Substituenteffects:inductiveorresonancecharacteristicsofYalters

electrondensity,thusalteringabilitytostabilize,+,

e donatingsubstituents

facilitatecationic

mec an sm a oxy,a y ,

alkenyl,phenyl


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ChainGrowthMonomers

, , ,Decreasee densityofdoublebond

Stablilize propagationofanionicspeciesbyresonance

Highselectivityforcationic,anionicmechanisms

Radicalinitiatorpolymerizealmostanyvinylmonomers

radicalspeciesareneutral,lessstringentrequirementsforinitiation,stabilization


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ComparisonofStepandChainGrowth

Maindifferencesresultfrom2factors:

1. Rapidrxn rateforchaingrowthleadstoHIGHMWearlyintherxn

2. OnlyM*canreact

HighMWathighconversion HighMWinitially andcontinually

ChainGrowth StepGrowth

Mn w/conversion

Any2speciescanreact

Mnunaffectedbyconversion

Monomerspeciesonlyreactw/

initiatedspecies

Rxn mixturecontainsarangeof

differentsizes

[M]continuosly

OnlyhighMWpolymer,

intherxn misture


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RadicalChainPolymerization

1 Initiation

(a) DecompositionofInitiator

kd=rateconstantforinitiator

(b) Additionofprimaryradicaltomonomer

ssoc at on

ki=rateconstantforinitiation

step

kp=rateconstantfor

102 104 Lmols1

Veryfastprocess


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Structuralconsiderations

Expect:(H/T) highlyfavored,canstabilizeradicalbyresonancew/Y, alsolesssterically

hindered

Observe: Mostly(H/T)

ifYissmallorhaslittleresonanceeffect,H/H

AsTemp,H/H (overcomeshigheractivationbarrier)EA

H/H

T

H/T


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RadicalChainPolymerization:Termination(3) Termination

(a) Combination(coupling)

**mostcommonrouteto

termination

(b) Disproportionation hydrogenbetatoradicalcenteristransferredtoanotherradicalcenter **** formationoftwomolecules,1saturatedand1unsaturated

Typicallykt=106 106 Lmols1

kt >>kp ,butpropagationcontinuesdueto

8 . , . . n

likelytofind[M]ratherthan[Mm]

Later,wellseethatRp dependantonlyto

powero t


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KineticsofRadicalChainGrowthPzn

tionpolymerizaofrate,initiationofratewhere

:EquationRate

pi

pi

RR

RRdt

**Rigoroustreatmentoftheradicalmechanismwouldleadtoimmensecomplexities

1. kpindependentofDP

2. Kineticchainlengthsverylarge

Longpolymerchains,monomersconsumedonlyinpropagationstep,monomerconsumpt on n n t at on sneg g e

3. Only1typeofactivesite(i.e.onlyH/Treactions)

4. SteadyStateApproximation


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Simplifyingassumptions:

4. SteadyStateApproximation

Concentrationradicalsincreaseinitiallybutinstantaneouslyreachconstant

steadystatevalue

[M]=constant

=

Thisrequires Ri=Rt (initiationrate=terminationrate)

MMkRdt

Mdpp

][

Insuchform,thisequationisnotdirectlyuseablesinceitcontains[M];8


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2 tt

22:SSAthefrom k

2/1

2

so

n osu

2 pp

tk

2/112/1

,toalproportionrate2

i

t

ipp RM

k

RMkR

**

i.e.,doublingrateofinitiationdoesnotdoublepolymerizationrate

Rateincreasesonlybyafactorof asaresultofbimolecularterminationofradicals2

MethodstodetermineRp: separationandisolation,spectroscopy(NMR,FTIR,etcto

followdisappearanceofmonomer,dilatometry


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RadicalInitiators

Thermaldecomposition(homolytic dissociation)

(A) Peroxides

t1/2 @100C 30min

Id ][

Decompositionrates

expressedintermsofhalflife(B) Azo Compounds

tk

o eII

dtd][][

t1/2 @70C 4hrs

o

d

II

In

**AlsoAIBNdecompositionbyUVlight

dkt

2ln2/1

,

Initiatorsmustbeintherangeof100170kJ/mol,

Otherwisedissociationtoofastortooslow


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PhotochemicalRadicalInitiators

(1) PureMonomer

**

adsorptionoccursinUV,i.e.styrene,methacrylatesPracticallimitations:

1)quartzreactionvessels

2) quantumyieldslow

(2) PhotochemicalInitiators

a) Aliphatic/aromaticketones

b) Organometallic compounds


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RadicalInitiators(cont.)Rateofphotochemicalinitiation

LawLambert-Beerbyobtainedlightadsorbedofintensitywhere A

Ai

I

][ DAoA

eII

coeff.absorptionmolar

systemreactiontheintoDdistanceatintensitylight

o

AI

PIofconc.molar[A]

AdvantagesofPI

1. Pzn canbespatiallydirected(patterns,basisforphotoresist andlithography,etc)

2. TurnedONandOFF3. Initiationratescanbeveryfastandcontrolledbysourceofradicals,lightsource,

temperature

t

App

k

IMkR


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Redox InitiatorsManytypesofREDOXreactionscanproduceradicalstoinitiate

Polymerization

1) Peroxidescombinedwithareducingagentareacommonsourceof

radical

2) OrganicReagents AmineReductants/Acyl Peroxides


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Redox InitiatorsRateofredox initiation

2/1

ox anre uc an di

2xe

M

t

d

pp kkR

1. Radicalproductionoccursatreasonableratesoverwiderangeoftemperatures Canbe0 50Cdependingonthesystem

2. Rateofinitiationcanbehigherthanthermal

Example:

Benzoyl peroxideinstyreneat90 C

kd=1.33x104 L(mols)1

Benzoyl peroxide/Ndiethylaniline

@60 C1.25x102

L(mols)1

and @30C2.29x103

L(mols)1


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KineticsofRadical

Polymerization

ThermalInitiation


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1 Initiation Ste 1

(a) DecompositionofInitiator

kd=rateconstantforinitiator

ssoc at on

2 IfkR dd

radicalsoffractionorefficiencyinitiatorwhere f

iondecompositinitiatorofrate

growthchaininitiatethathomolysisfromproduced

etcevents,transferreaction,sidetodue

1usuallyiondecompositthermalfromradicalsunreactive1)

(2) Propagation


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ThermalInitiation:RadicalChainPolymerization

(1) Initiation(Step2)

Additionofprimaryradicaltomonomer

ki=rateconstantforinitiation

step

AdditionofprimaryradicaltoMisveryfastcomparedtoinitiatordecompostion (Step1),

2

expressiongeneralintosub

21/

ippp

k

RMkRR

21/

IkDescribesthemost

t

ppk

commoncaseofradicalchainpzn


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1Rate

2

M

Iate

1st orderdependenceofRp

on[M]Rpdependent[I]0.5


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0.5 1

(1)Terminationbyprimaryradicals

22

andRate MIk

MkkRtp

ip

p

(2) Initiatorefficiency(f)dependson[M]

2/3' MRMff p

(3) DecompositionofIpromotedmyM

2/3MR

(4) Tromsdorff polymerizationregion,radicalsdonotundergotermination(orlimits

termination

i.e.homolysis tbutylhydroperoxide occursfasterinpresenceofstyrenethanwithout

1/2angreater thondependance IRp


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Ma beevaluatedb substitutin theinte ratedformoftheinitiator

Variationof[M]withtime

decompositionrateexpressionintoRpexpression

tkId d

p

od

R

dt

intosub

t/ko

t

dpdteI

k

kfk

dt

Mdd

2

2

t/keI

fk

Md

121lnln

integrate

2

2/1

dto

p

conversionmonomerwhere

o

o

Mp


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MWinChainGrowthPzn

= average#ofmonomerspolymerizedperradicalthatinitiateschaingrowthORrate

ofpolymerizationperunitrateofinitiation

ip

ti

p

RRRRrateInitiation

andofsdefinitionpreviousthefrom

tp

t

p

R

Mk

k

Mk

k

222

pp

p

pp

MkMk

Mksou

22

pt

p

pt

Mkk2

Wecana so e inespeci ica y orpzn initiate

bythermaldecompositionofinitiator


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KineticChainLengthforThermalInitiatorDecomposition

Quantitativerelationship

k

IfkMkR

/

dpp

21

e weenra eso rxn an s zeo

molecules

k22

k

IfkMkk

/

t

dpt

21

2

Mk

p Kineticchainlengthforthecaseof

Ikfk td2

,increasesIasso1

erma n a or ecompos on

moleculessmaller


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EffectofterminationmodeonMW

22

kk

kkDP tdtcn

then

i.e.n,combinatiobyelypredominatoccursonterminatiif kk tdtc

2DPn

then

i.e.ionation,disproportbyelypredominatonterminatiif kk tctd

In absence of other

chainol merinmonomersof#avDPsince

DPn

processes,DPwillbe

betweenand2

monomerofMWwhere oo MDPMM nn


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MWDinRadicalPzn

Disproportionation Combination

11

pDPn

1

2

p

DPn

1

p

DPw 1

2

p

DPw

1 pDP

DP

n

w

2

2

p

DP

DP

n

w

1as2MWD p 1as1.5MWD p


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ChainTransferReactions

sometimesmuchlessthanandcannotbeexplainedonbasisofexperimentally

observedextentsofterminationbycouplinganddisproportionation.

2) PrematureterminationofPbytransfertomonomer,solvent,initiator,

impurities,etc

Mn + XA Mn-X + Aktr

transfer agent

constantratesferchain tranwhere

XAM

tr

trtr

k

kRrate

+ka

Amayreinitiatepolymerization


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polymerchainsize,moresubtleeffectonRp

EffectofchaintransferonRpisdependentonwhethertherateofreinitiation

a scompara etot ato t eor g na propagat ngspec es

SummaryofeffectofchaintransferonRpandDPn

patrp kkkk ;)1(

Relativerates Type of transfer Rp DPn

Normalchain transfer None

patrp kkkk ;)2( Retardation

patrp kkkk ;)3( Degradative chaintransfer


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ConsiderCase(1):


patrp kkkk ;

Forcase1,kineticchainlengthunchanged,but#ofpolymermoleculesproduced

perkineticchainlengthisaltered

DPn nolongergivenbyor2fordisproportionation orcoupling

ustre e ne nas p v e yt esumo c a n rea ngreact ons

(normaltermination+chaintransferrxn)Ifweassumecouplingasmodeoftermination:

IMkSMkMMkRDP

ItrStrmtrt

pn

2,,,

Normalterm.,

coupling

Transferto

monomer

Transferto

CTAorsolvent

Transferto

initiator

RRDP

Note

ppn 2

22

:sferchain trannoif:

it


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Moreconvenienttotake thenseparatecommondenominator


DP

1

R

k

R

k

R

k

R

R

DP

ItrStrmtrt

n

IMSMMM

2

1 ,,,

MMkR pp

kk ptr toofratioC

(C)constantsferchain trandefinecanweNow

kC

kC

kC

Itr

I

Str

S

mtr

m ;;,,,

ISRi

ppp

1

now

YieldsquantitativemeasureofvarioustransferprocessesonMW

DP m

pn 2


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:ifnow

k

IfkMkR

/

t

dpp

21

RkRRk tit2

2

R

IIfkRi

MkRMk

id

ppp

i 2222

2ifand,

2

Mfkk

Rk

MMk

kRR

d

pttp

i

d

2

2

22

2I

and2

RkC

SCC

Rk ptpt2

1

Anotherformmoreusefulfordeterminingtransferconstants

fkkkDP dppn


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DeterminationofCmandCI

(1)Consideraneatpolymerization (nosolvent,Cs=0)

1 23222 p

tImp

t

n

Rkk

kCCRk

k

DP

2axbmxy

plotlinear0if*

w/r toquadratic*

I

p

C

R

fasterdropssincelinear0,as*2

pp RR

f d


33/63

DeterminationofCmandCI

(2)Plotof vs forstyrenepolymerizationnDP

1pR

Initialportionoftheplotslinear,

butathi her I thushi herR

plotsdeviatefromlinearityasCIcontributionincreases

nDP

1

, u I=

goodinitiator

pt

p

t

k

kobtain

Mk

kslope

:regionlinearIn the

222

pR

mCy int

D i i f C


34/63

DeterminationofCI

(3)TodetermineCI,wecanrearrangethe

equationfornDP

1

kk tt

11

C

MfkkMkRDP

m

p

dppp

mn

3222

:smallisif

MI

CMk

Rk

DP I

pt

n

22

1 Plot: Slope=CI


35/63

Cmgenerallysmallformostmonomers

Propagatingradicalsw/higherreactivities generallyhavehigherCm

Hi hCmvalueforVCattributedto:Intermolecular

migration

ofCl atom

Chaintransfer

LimitsMWto50K 100KforPVC


36/63

TypicalCIvalues

Azo initiators

Acyl peroxidesgenerallyhavehigherCI

thanalkylperoxidesduetoweakerOO

bondinacyl compounds

Determination of C


37/63

DeterminationofCs(4)Transfertosolvent(CS)orchaintransferagent

conditionseunder thes

pznsofseriesover[I]adjustingelyappropriat(byconstant[M]

keep**

neg g eecomes,owuse

2

p

I

R

MS11

o

Snn

CDPDP

a entsferchain tranofabsencein1ofvalue1

where

Slope=CS

o nn DPDP

Benzylic hydrogens morereadilyabstracted,followsorganicchem rules

Tert > secondar > rimar

WeakSSbondleadstohightransfer ea on ea s o g rans er

Typical CS Values


38/63

TypicalCSValues

Practical Use of Chain Transfer


39/63

PracticalUseofChainTransfer

ControlofMW

Example


40/63

ChainTransfertoPolymer

,atcompleteorhighconversions

Formationofradicalsiteonpolymerchain leadstobranchedpolymer

Chain Transfer to Polymer


41/63

ChainTransfertoPolymer

(B)Intermoleculartransfer long

CH2 C

Y

CH2 C

Y

Mn + Mn-H +

Mn M

Y

DeterminationofCpisdifficult

DoesnotnecessarilyleadtodecreaseinDP

CH2 C

Mn

branchedpolymeroflargersizethaninitiallypresent,plusprematurelyterminatesa

NeedtomeasureBranchingDensity()

Cptypically104

Branching Density ()


42/63

BranchingDensity()

dpolymerizemonomerperbranchesof#

1ln1

where

pp

Cp

DerivedbyFlory

Equationindicatesbranchingincreasesrapidlyatlaterstagesofpzn

reactionofextentp

ForExample,if

p=0.80 1branch/104 monomers

p= x = . .

p=0.95 2.2branch/104 monomers

Extentofbranchingisgreaterforpolymersthathaveveryreactive

propagatingradicals,i.e.vinylacetate,vinylchloride,ethylene

Inhibition and Retardation


43/63

InhibitionandRetardation

. uppress ono po ymer za on1. Radical(InitiatorofM)convertedtononreactivespecies,toolow

reactivitytoundergopropagation

. ,

consumed

3. Retarders: lessefficient,stoponlyaportionofradicals,slows

ol merization

Normal

Inhibition

Retardation

B. Inhibitoroftenaddedtocommercialmonomerto reventthermal zn i.e.

Time

styrene)Quinones,mustberemovedpriortopzn (distillationorcolumn

chromatography)



44/63

I 2Rkd

. ne cso n onR + M M1

ki

M + M Mkp

z

k

kz:ConstantInhibitorDefine

M2 + Z P + Z

kz

net css mp e weassume:

i) Zdoesnotreinitiatepolymerization

ii)ZdoesnotregenerateZupontermination

0]][[][2][ 2

MZkMkRdt

Mdzti

SteadyStateAssumptionfor

radicalconc.:

][2

]][[w/combine

2

kZRkR

MMkR

zt

pp

neglectedbecanfirst termand,negligibleisionr terminatbimoleculanormal,1

][][ 22

kp

kzif

MkMk i

pp



45/63

*rateofinhibitedpolymerizationdependsonR 1

Rpinverselydependenton[Z]

**inductionperiodobservedforinhibitedpolymerization

directlyproportionalto[Z]

0][

][ RMk

Zi

p

zp

Inhibitorconcentrationwilldecreasewithtime

[Z]givenatanytimeby: ][

][

Zk

RMkR

z

ipp

tRZZ i ][][ moleculeinitiator

dterminateradicalsof#

time

.

y

t

dt

Md

Zk

RMkR

k

kzif

y

ip

pz

][

][

][and

-dt

ztZz-dt o ][

grearranginand**withcombining[M]d

y

zslopehlinear wit

.ln

y[M] in

iR

z Z oint-y

Typical z values


46/63

Typicalzvalues

Temperature Dependence for Radical Pzn


47/63

TemperatureDependenceforRadicalPzn

ec o empera ureonra eo po ymer za onan s mpor an ordeterminingtheconditionsofpzn

IncreasingTusuallyincreases Rpanddecreases MW

p n d, p, t

Aek RTEa

factorfre .collisionwhere

TEa (K)Tempandenergyactivation

E

or

aRT



48/63


empera ure epen ence oreac s ep

EAk d ition)n/decompos(initiatiolnln

EpPlotlnkvs.1/T

=

E

RTp a

yint =A

RTt

2/12/1

onterm natnn

MIfkkkMkR td

p

t

dpp

2/1

Assumingthermal

decomposition

Pzn ratedependsonratioofthe3

rateconstants



49/63


empera ure epen enceo sra o so a ne ycom n ng reesepara eArrheniusequations:

EE td

RTA

A

Ak

k

k

p

t

d

pt

d

p

2121

22

lnln

EE td

pznofrateforenergyactivationoverall

Plot lnR vs. 1 T

Ifk

MkR dpp

pR

since

22

ObtainERfromtheslope

fromtheyint

2/1

dp

AA

t

2/1

:can writewe

t

fRTA

A R

t

dpp lnlnln


50/63

:valuestypicalSome

decominitiatoralfor thermkJ/mol145-125

kJ/mol20-8

kJ/mol40-20

t

p

E

E

E

kJ/mol90-80:pznsinitiatedalmost thermFor

ER

C10eachforRpinincreasefold3-2,as o TRp

kJ/mol60-40

InitiationRedox

dE kJ/mol0

InitiationcalPhotochemi

dE

J mo40RE

TemptoeinsensitivrelativelyRpkJ/mol20

RE


51/63

Sterics playanimportantroleindeterminingtheabsolute

valueofkp CompareApforMMAandMA



52/63

p p

ompar ng n pa wo empera ures

EE

122

1 1122

ln TTRR

R p

p

p

EffectofTemperatureDPn


53/63

p n

2/1sfer)chain tranno(assuming

2:recall

Ikfk

Mk

td

p

coupling)byonterminatiassuming(2DPn

2/12/1ln

)(

lnln

If

M

kk

kDP

td

pn

EE

E tdp

2/12/1

ln)(

lnlnIfRTAA

DPtd

pn


54/63

ComparingDPattwotemperatures

1122ln122

1

tdp

TTR

E

DPDP

kJ/mol60

:tionspolymerizainitiatedalmost thermFor

td EEE

nDP

TincreasinwithdecreasesDP

C/10increasefold-2

o


55/63

nDPpR

1 TlowTHigh

T


56/63

Ifchaintransferoccurs,temperaturedependenceonDPn becomescomplex

, , ,

:dominantisCTAorStotransferIf

lnln

11Mln-

,

,,

Strp

Str

p

Str

p

nn RT

EE

A

A

k

k

DPDPSo

TincreasingwithdecreasesMW

kJ/mol6520, Strp EE

LivingorControlledRadicalPzn


57/63

Controlledpolymerizationisachievedbyminimizingbimoleculartermination&prolongingthelifetimeofpropagatingpolymerchains

Requiresintroductionofadormantstateforpropagatingspecies

Reversibletermination

Reversibletransfer

RR Z Z+

Reactive Stable

M

RMn

Z

Propagating Radical

BimolecularTermination RMn Z Dormant species

LivingorControlledRadicalPzn


58/63

1) Requiressimultaneousinitiationofpolymerchainssothatthe#ofpropagatingchainsisconstantoverthecourseofthereaction

2) Fastinitiationrelativetopropagation

3) Fastestablishmentofequilibriumbetweenpropagatingradicalanddormantspecies

4) Buildupconcentrationofstableradicalinearlystagesofthereaction

1) Normalterminationofinitiating/propagatingradicalsearlyinreaction

2) Irreversibleadditionofmonomertoinitiatingradical

5 E uilibriumshiftedtowarddormants ecies

1) Favorsdormantspeciesbyseveralordersofmagnitude

6) Concentrationofpropagatingradicalsapprox.sameasorslightlylowerthanconventionalradicalpzn,BUTconcentrationofdormantspecies46ordersof

ma nitude reater1) Propagatingradicals:107 108 M

2) Dormantradicals:101 103 M

Atom Transfer Radical Pzn


59/63

AtomTransferRadicalPzn

ActivationinvolvesCuBr

meta centerun ergoingan

electrontransferwith

simultaneoushalogenatom

abstraction

CuBr2(L) persistentradical

reducessteadystate

concentrationofpropagationspecies

ATRPKinetics


60/63

:bygivenATRPinradicalsprop.ofionConcentrat

kkK

CuCuIKR

d

awhere][

]][[2

CuIMKk ]][][[

:npropagatioforexpressionrateourwithcombining

Cup

:with timeMinchangeasexpressedratepzn

][ 2

tCu

CuIMKkMM p

][]][][[ln

2

o

ATRPKinetics Assuming fast quantitative initiation rapid deactivation of propagating radicals


61/63

Assumingfast,quantitativeinitiation,rapiddeactivationofpropagatingradicals,

:thenDPn

. .

o

o

o

o

][

][

][

][][

I

MpI

MMDPn

1][conc.monomerindecrease M

ATRPKinetics

MW Distribution


62/63

MWDistribution

12

][

][1

pDk

kI

DP

DP

d

p

n

w o

CuBragent,ngdeactivatiDwhere

:equationofeConsequenc

pd kofeslower valuand[D]),k(greaterondeactivatirapidwithnarrowsMWD3)

increasesconversionasnarrowsMWD2)

[I]lowerithnarrower wMWD1)

nw DPDP

:ondistributiPoissonthefollowsMWDmet,areconditionswhen

n

n

DPDP

elyapproximator1

2

nn

w

DPDP1

ATRPKinetics

MW Distribution


63/63

MWDistribution

nn

w

PP

DP 11

Approaches1asDPincreases

ExceptforverylowMW,sizedistributionwillbenarrow,i.e.

n .

ManyATRPpolymerizationsyieldPDIof

chain grwth polymerizatin

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