Chain Grwth Polymerizatin
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Transcript of Chain Grwth Polymerizatin
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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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RadicalChainPolymerization
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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KineticsofRadicalChainGrowthPzn
Simplifyingassumptions:
4. SteadyStateApproximation
Concentrationradicalsincreaseinitiallybutinstantaneouslyreachconstant
steadystatevalue
[M]=constant
=
Thisrequires Ri=Rt (initiationrate=terminationrate)
MMkRdt
Mdpp
][
Insuchform,thisequationisnotdirectlyuseablesinceitcontains[M];8
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KineticsofRadicalChainGrowthPzn
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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RadicalChainPolymerization
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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ThermalInitiation:RadicalChainPolymerization
1Rate
2
M
Iate
1st orderdependenceofRp
on[M]Rpdependent[I]0.5
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ThermalInitiation:RadicalChainPolymerization
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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ChainTransferReactions
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):
ChainTransferReactions
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
ChainTransferReactions
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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ChainTransferReactions
: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
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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
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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
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Cmgenerallysmallformostmonomers
Propagatingradicalsw/higherreactivities generallyhavehigherCm
Hi hCmvalueforVCattributedto:Intermolecular
migration
ofCl atom
Chaintransfer
LimitsMWto50K 100KforPVC
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TypicalCIvalues
Azo initiators
Acyl peroxidesgenerallyhavehigherCI
thanalkylperoxidesduetoweakerOO
bondinacyl compounds
Determination of C
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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
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TypicalCSValues
Practical Use of Chain Transfer
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PracticalUseofChainTransfer
ControlofMW
Example
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ChainTransfertoPolymer
,atcompleteorhighconversions
Formationofradicalsiteonpolymerchain leadstobranchedpolymer
Chain Transfer to Polymer
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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 ()
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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
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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)
InhibitionandRetardation
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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
InhibitionandRetardation
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*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
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Typicalzvalues
Temperature Dependence for Radical Pzn
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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
Temperature Dependence for Radical Pzn
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TemperatureDependenceforRadicalPzn
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
Temperature Dependence for Radical Pzn
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TemperatureDependenceforRadicalPzn
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
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: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
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Sterics playanimportantroleindeterminingtheabsolute
valueofkp CompareApforMMAandMA
TemperatureDependenceforRadicalPzn
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p p
ompar ng n pa wo empera ures
EE
122
1 1122
ln TTRR
R p
p
p
EffectofTemperatureDPn
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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
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ComparingDPattwotemperatures
1122ln122
1
tdp
TTR
E
DPDP
kJ/mol60
:tionspolymerizainitiatedalmost thermFor
td EEE
nDP
TincreasinwithdecreasesDP
C/10increasefold-2
o
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nDPpR
1 TlowTHigh
T
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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
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Controlledpolymerizationisachievedbyminimizingbimoleculartermination&prolongingthelifetimeofpropagatingpolymerchains
Requiresintroductionofadormantstateforpropagatingspecies
Reversibletermination
Reversibletransfer
RR Z Z+
Reactive Stable
M
RMn
Z
Propagating Radical
BimolecularTermination RMn Z Dormant species
LivingorControlledRadicalPzn
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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
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AtomTransferRadicalPzn
ActivationinvolvesCuBr
meta centerun ergoingan
electrontransferwith
simultaneoushalogenatom
abstraction
CuBr2(L) persistentradical
reducessteadystate
concentrationofpropagationspecies
ATRPKinetics
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: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
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Assumingfast,quantitativeinitiation,rapiddeactivationofpropagatingradicals,
:thenDPn
. .
o
o
o
o
][
][
][
][][
I
MpI
MMDPn
1][conc.monomerindecrease M
ATRPKinetics
MW Distribution
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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
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MWDistribution
nn
w
PP
DP 11
Approaches1asDPincreases
ExceptforverylowMW,sizedistributionwillbenarrow,i.e.
n .
ManyATRPpolymerizationsyieldPDIof