chap 9. chain-growth polymerization
DESCRIPTION
1. Free radical Initiation Processes. 2. Cationically Initiated Processes. 3. Anionically Initiated Processes. 4. Group Transfer Polymerization. 5. Coordination Polymerization. Chap 9. Chain-growth Polymerization. Chain-Growth Polymerization (Addition) Processes. - PowerPoint PPT PresentationTRANSCRIPT
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Chap 9. Chain-growth Polymerization
Chain-Growth Polymerization (Addition) Processes
1. Free radical Initiation Processes
2. Cationically Initiated Processes
3. Anionically Initiated Processes
4. Group Transfer Polymerization
5. Coordination Polymerization
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Chain-Growth Polymerization
Step-Growth Polymerization1. Molecular weight increases steadily.
2.2. High molecular weight polymers are found at the end.High molecular weight polymers are found at the end.
3. Long reaction time needs to synthesize high conversion and high molecular weight.
1. Only growth reaction adds repeating units one at a time to the chain
2.2. Monomer concentration decreases steadily throughout the reactionMonomer concentration decreases steadily throughout the reaction
3. High Molecular weight polymer is formed at once; polymer molecular weight changes little throughout the reaction.
4. Long reaction times give high yields but affect molecular weight little.
5.5. Reaction mixture contains only monomer, high polymer, and about 10Reaction mixture contains only monomer, high polymer, and about 10 -8-8 part of growing chains.part of growing chains.
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(1) Initiation(1) Initiation
kkdd : I : Initiator decomposition rate constant
: 10: 10-4-4 ~ 10 ~ 10-6-6 L/mole sec L/mole sec
Unstable radicalUnstable radical
Chain Growth Polymerization
Heat (60ºC)Heat (60ºC)
UV UV kkdd
Primary radicalPrimary radicalAIBNAIBN
Bond EnergyBond Energy = 46 kcal/mole= 46 kcal/mole
IMkR ii
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(2) Propagation (2) Propagation
kkpp : 10 : 1022 ~ 10 ~ 1044 L/mole sec (much faster than step-growth polymerization) L/mole sec (much faster than step-growth polymerization)
(Repetition of similar reaction)
Chain Growth Polymerization
MMkR pp
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(3) Termination(3) Termination
(a) Coupling or combination(a) Coupling or combination
Chain Growth Polymerization
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(b) Disproportionation(b) Disproportionation
kktt=k=ktctc+k+ktdtd 101066 ~ 10 ~ 1088 L/mole sec L/mole sec
(3) Termination(3) Termination
Chain Growth Polymerization
2 MRMMkR tkt
tdk
tdk
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(4) Chain Transfer(4) Chain Transfer
Kinetic chain length
Monomer, Polymer, Solvent or Chain transfer agent
Physical chain length
Chain Growth Polymerization
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Chain Growth Polymerization
Kinetic Chain Length : kinetic chain length υ of a radical chain polymerization is defined as the average number of monomer molecules consumed (polymerized) per each radical, which initiates a polymer chain.
ex) Monomer # 4000 Disproportionation
υ =4,000/4 =1,000Determined by steps 1, 2, 3. (Initiation, propagation, and
termination)(No chain transfer)
Physical Chain Length :This condition contains Step 1, 2, 3, 4.
Radical
1,2,3,4
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Non-Polymerization Reaction
Peroxide induced Bromination of Toluene
1) Initiation
Two types of reaction
R-O-O-R 2RO• (1)
R-O• + Br2 ROBr + Br• (2)
R-O• + ФCH3 ROH + ФCH2• (3)
Two radicals and two kinetic chains are formed by decomposition of each ROOR molecules
Kinetic Chain Reaction
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2) Propagation
Br• + ФCH3 HBr + ФCH2 (4)
ФCH2• + Br2 ФCH2Br + Br • (5)
Two special features
The number of active species is fixed.
Same reactions are repeated during the kinetic chain reaction.
Kinetic Chain Reaction
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3) Termination
2 Br• Br2
2ФCH2• ФCH2 CH2Ф
ФCH2• + Br • ФCH2Br + Br •
Net Effect of Kinetic Chain Reaction:
One ROOR molecule can cause formation of Br2, CH2CH2, CH2Br,HBr, .‥
Kinetic Chain Reaction
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Time
Reaction
Rate
Induction period
Steady state
Chain reaction Ri = Rt
In proportion to the O2 concentration
Comparison between Chain Polymerization & Chain Reaction
Kinetic Chain Reaction
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In the case of Chain reaction, there are induction periods, due to the existence of inhibitor.When an active center is formed, the reaction rate would be faster and then go to steady state. The whole reaction rate is reaching a plateau region.After that, reaction rate decreases due to a loss of monomers or initiators.
Linear Chain-Growth: Polymer of high DPn found easily in early reaction
Linear Step-Growth: high extent of reaction value required to obtain high DPn
Kinetic Chain Reaction
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Comparison Free Radical Reaction & Ionic Reaction
- Ionic Initiation – multiple bond addition, ring opening polymerization
- Radical Initiation – Ring-opening polymerization is not initiated.
CH3
CH3
CH2
R CH3
CH3
CH2H
CH2
CH3
CH2
CH2
CH3
CH2
+ +
For the cationic initiation, it will not be free radical.
Ex)
Because of resonance stability
Kinetic Chain Reaction
isobutylene
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Ionic Free Radical Anionic Cationic
Ring opening + - - End-groups Generally, combine with counter-ion or gegenion
E.g. R+ AlCl4―
Degree of association depends on below Solvent-system polarity Stability of end group Type & size of scounter-ion Temp. Degree of association influences: Reaction rates Termination rate Stereospecificity
Truly Free Radical (no association)
Termination Depend on monomer consumption, Living polymer or Block copolymer
unimolecular Combination or disproportionation reaction
Bimolecular combination or disproportionation
Comparison between Free Radical Reaction & Ionic Reaction
Kinetic Chain Reaction
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A) Free Radical Termination
CH2 CH
X
CH CH2
X
CH2 CH CH CH2
X X
CH CH
X
CHCH2X
CH CH
X
CH CH2
X
H
H
unsaturated group.
. . ....
ktc (coupling or combination)
ktd (disproportionation)
+
Comparison between Free Radical Reaction & Termination Step of Ionic Reaction
Two molecules involved = bimolecular reaction
Kinetic Chain Reaction
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B) Cationic Termination
Anionic capture is similar to combination of free radical reaction.
But, this reaction can’t include increasing of MW because of unimolecular reaction
CH2 CH
R
CH2 CH
R
X
AlCl4
AlCl3
[XY]
+ Y
EX) ÀÌ °æ¿ì
X= Cl Y=
+ -
-
-
Kinetic Chain Reaction
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C) Anionic Termination
Termination is rare but can occur by loss of a hydride ion
Unimolecular type termination occurs
CH2 CH
R
M-
-H-
+
CH CH
R
+ HM
CH
R
H
R[XY]
+ -
proton release+
..
+ HY + Y
The proton release is similar to disproportination of free radical.. But, one chain joins in the reaction unimolecular reaction
C) Anionic Termination
Kinetic Chain Reaction
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Anionic Cationic Termination Termination
Free Radical Termination
Reaction rate Unimolecular High concentration of growing chains 10-2~10-3molar Rates 104~105 times higher than free radical
Bimolecular Relativity low concentration 10-8~10-9
molar occurs at high Rates
E Activation Energies Similar Chain Transfer Negligible + + Disadvantage Rigorous Purity or precautions Polymer System Solution or Bulk Wide variety of
polymer systems, Gas, Solid, Solution, Bulk, Precipitation, Suspension, Emulsion
Kinetic Chain Reaction
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Free Radical Initiated Polymerization of Unsaturated monomers
Kinetic Scheme
InitiationTwo step sequence-Both enter into overall rate1. Initiator decomposition
I2 2I
2. Addition of Initiator fragment to the monomer, Initiation of Chain growth.
I+M IM
The efficiency of Initiator - Determined by competition of desired reaction and side reaction
Primary radical species
Generally, 0.5 << f << 1
kd
ki
Kinetic Chain Reaction
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A.Cage Effect –primary recombinationInitiator fragments surrounded by restricting cage of solvent
Ex)
(acetyl peroxide)
CH3 C O O C CH3
OO
Kinetic Chain Reaction
O
O CH3
CH3
O
O
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I) Recombination possible I2 2I
II) If elimination reaction occurs while the free radical in-cage,
Formation of stable molecules due to Radical combination.And formation of Inactive Species.
C H 3 C
O
O
.
C H 3
. + C O 2
C H 3 + C H 3
. . C H 3 C H 3
CH 3 + O
C C H 3
O .
. C H 3
O C H 3 C
O
Kinetic Chain Reaction
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B. Induced Decomposition –Secondary combination
I) Through Radical attack on peroxide molecules
R + R-O-O-R RH + ROOR R=O + RO
Finally, R + ROOR ROR+ RO
Total number of radical does not change, but among them half molecules were wasted.
II) Chain Transfer to Solvent
(In this case, since just one radical was obtained half molecules were wasted.)
I . + SH IH S.
S. + I2 SI + I .
Kinetic Chain Reaction
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III) Reaction with Chain Radical
Since not all Molecules participate in the initiation → Efficiency factor
f: Initiator Efficiency= mole fraction of initiator fragments that actually initiate polymer chains.
0.5 < f < 1.0
Kinetic Chain Reaction
I + M . IMn .
IMn . + I2 IMnI + I .
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C. Reaction Rate
If [M] is representative for the concentration of chain radical,
That is , M = IM or = I [M]
f 1 Ri is unrelated with [M] f=[M]
f < 1 Ri is related with [M]
[M] , f [I2] , f due to induced decomposition
by convention, two radical formation.
][2
]][[
][
2Ifk
MIkdtMd
R
d
i
i
Kinetic Chain Reaction
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D. Initiator
- containing compounds.
O O S S N N
OO
O
CCH3
O
CH3C
OO
O
C
O
C
OOC
CH3
CH3
C
CH3
CH3
Kinetic Chain Reaction
Acetyl peroxide 80~100C
Benzoyl peroxide 80~100C
Cumyl peroxide 120~140C
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NNC
CH3
CN
C
CN
CH3
CH3CH3 C
CH3
CN
CH3
. + N2250~70C
AIBN 2,2 azobisisobutyronitrile
Kinetic Chain Reaction
CH3 O O CH3
CH3
CH3
CH3
CH3
CH3 O OH
CH3
CH3
Hydroperoxides, cumyl or t-butyl80~100C
t-butyl peroxide
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Propagation
Termination
n
k
k
pp
IM
IMMI
MMkdt
MdR
p
p
2
]][[][
By conventionSince 2 radical elimination
2])[ (2][
Mkkdt
MdR tdtct
M . M.
ktc ktd
Kinetic Chain Reaction
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Overall Rate of Polymerzation
Radical concentration
• Difficulty of measurement, low concentration. (~10-8molar)
• Thus, it is impractical using this therm.
• [M] elimination is desirable.
]][[~
]][[]][[
MMkRR
MMkMIkR
ppo
pio
(# of propagation step >>> # of initiation step)
Kinetic Chain Reaction
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[M] elimination methods
Steady-State Assumption
Radical concentration increases at the start, comes to steady state simultaneously and then reaction rate change becomes 0. (active centers created and destroyed at the same time) Ri = Rt
2
1
2
1
22
1
22
]2
[
][)(][
])[(2][2
t
i
tdtc
d
tdtcd
R
Ror
Ikk
fkM
MkkIfk
2
1
2
1
2 )(]][[
]][[][
tdtc
d
kkfk
IMk
MMkdtMd
R
Kinetic Chain Reaction
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Mostly in case of f<1 system → [I2]1/2 (Square Root Dependence of [I2])
※ Odian Fig. 3-4 MMA using BPO
Vinyl Acetate using AIBN
Rp
[I2]1/2
OO
O
C
O
C
O
C O
NNC
CH3
CN
C
CN
CH3
CH3CH3 C
CH3
CN
CH3.2
BPO
-CO22
300C
+ N2
Azobisisobutyronitrile
Kinetic Chain Reaction
H
.
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+ BPO + system
In case f < 1, but SRD is not applicable,
][][ 2
1
2 MIRp
2
3
2
1
2 ][][ MIRp
Because f is ‘dependent’ on [M]
Why? Due to induced decomposition of toluene + [I2]
Kinetic Chain Reaction
+ BPO + CH3
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At S-S assumption
(1) Disproportionation
Knowing that
Kinetic Chain Length (KCL)
)(
chain)polymer a initiates( radicaleach
ed)(polymeriz consumed moleculesmonomer ofnumber average the
it
p
RR
R
KCL
dt
MdRRR tctdt
][
(2) Coupling or combination
termtc
tc
dt
MdR
k
][
chains)polymer 2 fromproduct polymer 1(2
1const. rate the
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(3) Both (1)+(2)
Kinetic Chain Length (KCL)
)1(
22
2
1
t
tdt
p
tdtctd
p
tctd
p
t
p
RR
R
R
RRR
R
RR
R
R
RKCL
)1(
2 case, in this
:
yR
RKCL
ionationdisproportbycausednterminatiooffractionR
Rydefine
t
p
t
td
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The more concentration of monomer, The less concentration of initiator,
(1) Dispropotionation
(2) Coupling
Degree of Polymerization
Kinetic Chain Length (KCL)
nDP
2nDP
dtPolymerd
dtMdDPn /][
/][
Monomer consumption rate
polymer formation rate
nDP
nDP
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)3(][2
)2(][][
1
2
)1()1(
2
2
1
2
1
2
2
1
2
IfkRR
MIfk
kkRthatknowing
yDP
R
Rywhere
yR
R
RR
RDP
R
RRPolymer
dit
t
dpp
n
t
td
t
p
tctd
pn
p
tctd
소비속도모노머
생성속도
(3) Dispropotionation & Coupling
Polymer formation rate
Monomer consumption rate
Kinetic Chain Length (KCL)
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From (1),(2),(3)
In case of no Chain transfer, and valid S-S assumption
)4(
][)1(
][
2
1
2
Ifkk
ky
MkDP
t
dt
pn
)5()1(
][ 22
pt
pn Rky
MkDPor
Kinetic Chain Length (KCL)
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M + XY MX + Y Chain transfer agent
If Chain transfer occurs Rp is unchangable but has an effect on DPn
( Since∵ Since∵ [Y] instead of Rp=kp[M][M] )
ex)
(1) Chain transfer occurs by solvents or additives In this case, High chain transfer coefficient.
(2) Transfer occurs by monomer or polymer
Chain Transfer
C C
H
X
H
H
R . + C C l 4
C C
H
X
H
H
R C l + C C l 3 .
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Inhibitor When Y take part in chain opening reaction, polymer moves from one site to another. In this case, hydroquinone etc. are used as inhibitor.
Retarder When the reactivity of Y is low, controlling the MW of the monomer including these two materials, Mercaptan etc. are used as Retarder.
Chain Transfer
Inhibitor and Retarder
2
1
2
2
]}[{][
][)1]([
][
]][[2)1(][2
]][[2
2)1(
2
][
2
1][
Ik
fkMthatKnowing
XYkyMk
Mk
XYMkyMk
MMk
RyR
R
dtPolymerd
RDP
RRRdt
Polymerd
t
d
trt
p
trt
p
trt
ppn
trtctd
Like this, when chain transfer condition arises
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][
][
][
][11
][
][
][
][11
][
][][
][
)1(1
][][)1(
][
0,
,,
0,
2
1
2
2
1
2
M
TC
M
SC
DPDP
Mk
Tk
Mk
Sk
DPDP
Mk
XYkIf
k
k
Mk
yk
DP
XYkIfk
kyk
MkDP
TS
nn
p
ttr
p
str
nn
p
tr
t
d
p
t
n
trt
dt
pn
From the slope of a graphChain transfer coefficient ‘Cs’
See Odian P.235
1
[5]/[M]
DPn
Chain Transfer
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Assume : no chain transfer
Temperature Dependence of Rp and DPn
molekcal Eekk
molekcal Eekk
molekcal Eekk
(1) Ifk
kkMR
MIfk
kkR
tRTE
tt
dRTE
dd
pRTE
pp
t
dpp
t
dpp
t
d
/5~2
/30
/8~5
]][ln[ln]ln[ln
][][
/
/
/
2
1
2
2
1
2
1
2
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slope of lnRp/T is ( + )
as T lnRp
but Rate of Increase as d lnRp/dT
Temperature Dependence of Rp and DPn
0152722
]ln[ln
.,][],[),1(
22
2
1
2
RTRT
EEE
dT
kk
kd
dT
Rd
ToftindependenfconstMIassumeandEqFrom
dtp
t
dp
p
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Temperature Dependence of Rp and DPn
n
np
n
dtp
i
p
t
p
t
pn
DPT
DPbutRI
DPTas
RTRT
EEE
dT
d
R
R
R
R
yR
RDP
][
ln,
0152722ln
,)1(
2
22
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ㆍㆍ Ceiling TemperatureCeiling Temperature
Polymerization and Depolymerization are in equilibrium
ΔGΔGpp = ΔH = ΔHpp – TΔS – TΔSpp
ΔHΔHpp : : HeatHeat of polymerizationof polymerization
ΔSΔSpp : : Molecular arrangement changes between monomer andMolecular arrangement changes between monomer and polymerpolymer
At eq. State ΔGAt eq. State ΔGpp=0=0
Monomers can no longer be persuaded to form polymers by chain polymerization aabove a certain temperature. ceiling Temperature(Tceiling Temperature(Tcc))
Ceiling Temperature Polymer-Depolymerization Equilibria
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Rate Eq. of Polymerization Reactions at Depolymerization prominent Temperature
If,If,
M TM Tcc
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ksec-1 kdp
kp[M]
kp[M]- kdp
300 400 500 Tc
Tc
: No reaction above Tc
Stable blow Tc
Ceiling Temperature Polymer-Depolymerization Equilibria
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Monomer -H kcal/g mole Tc C (bulk)
St 16 235
MMA 13 164
Ethylene 26 407
Propylene 21 300
-methyl St. 7 6
※Odian Fig 3-18
Entropy changes for all polymers are not so different.
Sp= Sp- Sm (–) value of Sp is higherHp= Hp- Hm if (–) , exothermic.
Ceiling Temperature Polymer-Depolymerization Equilibria
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Trommsdorff Effect or Gel Effect
restricted mobility of polymer radical restricted mobility of polymer radical
kkpp ( relative to [M] )( relative to [M] )
( k∵( k∵ pp const. in reaction progress, k const. in reaction progress, ktt drop off in reaction progressdrop off in reaction progress
))
→ → Autoaccerelation effectAutoaccerelation effect
The increasing viscosity limits the rate of termination because of diffusional limitations
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t
80%
60%
40%
10% autoacceleratioan
as [M0] drastic in .
Trommsdorff Effect or Gel Effect
kte 1 one would expect ξ as t But ξ as [[M0]