chapter 7. ionic polymerization
DESCRIPTION
Chapter 7. Ionic polymerization. 7.1 Introduction. 7.2 Cationic polymerization. 7.3 Anionic polymerization. 7.4 Group transfer polymerization. counterion. ex). 7.1 Introduction. Presence of counterions (= gegenions) Influence of counterions Solvation effect. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 7. Ionic polymerization
7.1 Introduction
7.2 Cationic polymerization
7.3 Anionic polymerization
7.4 Group transfer polymerization
7.1 Introduction
Presence of counterions (= gegenions)
Influence of counterions
• Solvation effect
ex)
Cl C
CH3
CH3
C
CH3
CH3
Cl + BCl3 Cl C
CH3
CH3
C+
CH3
CH3
BCl4-
counterion
more complex than free radical polymerizations
but more versatile
7.1 Introduction
Application : in ring-opening polymerizations of cyclic ethers , lactams , lactones and in the polymerization of aldehydes , ketones
Commercial processes (Table 7.1) far fewer in number reflect a much narrower choice of monomers
O O
O
NH
O
C
O (CH2)m
O
RCR
O
'
RC
O
H
monomers must contain substituent groups
capable of stabilizing carbocations or carbanions
the necessity for solution polymerzation
TABLE 7.1. Commercially Important Polymers Prepared by Ionic Polymerization
Polymer or CopolymerCationica
Polyisobutylene and polybuteneb
(low and high molecular weight) Isobutylene-isoprene copolymerc
(“butyl rubber”)
Isobutylene-cyclopentadiene copolymer Hydrocarbond and polyterpene resins Coumarone-indene resinse
Poly(vinyl ether)s
Anionicf
cis-1,4-Polybutadiene cis-1,4-Polisoprene Styrene-butadiene rubber (SBR)g
Styrene-butadiene block and star copolymers ABA block copolymers (A= styrene, B=butadiene or isoprene) polycyanoacrylateh
Major Uses
Adhesives, sealants, insulating oils, lubricating oil and grease additives, moisture barriersInner tubes, engine mounts and springs, chemical tank linings, protective clothing, hoses, gaskets, electrical insulationOzone-resistant rubber
Inks, varnishes, paints, adhesives, sealantsFlooring, coatings, adhesivesPolymer modifiers, tackifiers, adhesives
TiresTires, footware, adhesives, coated fabricsTire treads, belting, hose, shoe soles, flooring, coated fabricsFlooring, shoe soles, artificial leather, wire and cable insulationThermoplastic elastomers
AdhesivesaAlCl3 and BF3 most frequently used coinitiators.b”Polybutenes” are copolymers based on C4 alkenes and lesser amounts of propylene and C5 and higher alkenes fromrefinery streams.cTerpolymers of isobutylene, isoprene, and divinylbenzene are also used in sealant and adhesive formulations.dAliphatic and aromatic refinery products.eCoumarone (benzofuran) and indene (benzocyclopentadiene) are products of coal tar.fn-Butyllithium most common initiator.gContains higher cis content than SBR prepared by free radical polymerization.hMonomer polymerized by adventitious water.
7.2.1 Cationic initiators
7.2.2 Mechanism, kinetics, and reactivity in cationic polymerization
7.2.3 Stereochemistry of cationic polymerization
7.2.4.Cationic copolymerization
7.2.5 Isomerization in cationic polymerization
7.2 Cationic polymerization
7.2.1 Cationic Initiators
The propagating species : carbocation
Initiation
E CH2 CR2 ECH2CR2++ + (7.1)
Initiator mineral acid : H2SO4, H3PO4
lewis acid : AlCl3, BF3, TiCl4, SnCl4
Coinitiator BF3 + H2O HOBF3-H+
AlCl3+ RCl AlCl4-R+
(C6H5)3CCl (C6H5)3C + Cl
Cl + Cl
(7.5)
(7.6)
(7.7)
(7.8)
Very active Lewis acid autoionization
2AlBr3 AlBr4-AlBr2
+
Other initiators
I2 + CH2 CR2 ICH2CIR2
ICH CR2 + HI
ICH2CR2I -+
7.2.1 Cationic Initiators
N
CH CH2
+ RNO2
N
CH CH
+ RNO
2
2
· ·
+
-
(7.9)
(7.10)
M + A M+
+ A -
Other initiators
7.2.1 Cationic Initiators
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
A. Carbocationic Initiation.
addition of the electrophilic species – the more stable carbocation
(Markovnikov’s rule) intermediate is formed.
C
H3C
H3C
CH2 + HCl C
H3C
H3C
CH3+
(CH3)2C CH2 > CH3CH CH2 > CH2 CH2
Stability of carbocation
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
A. Carbocationic Initiation.
For a series of para-substituted styrenes, the reactivity for substituent group
OCH3 > CH3 > H > Cl
Vinyl ethers
(7.11)CH2 CHORR'+
R'CH2 CH OR+
R'CH2 CH OR+
X CH2 CH
X
(Because of steric hindrance)
B. Propagation Step
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
Two Step
① -complex of chain end and approaching monomer
② formation of covalent bond
① ②
(7.12)+ + CH2 CR2slow
CH2
CR2
+ fast CH2CR2+
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
C. Influences polymerization rate
A + A- + A- + + A-
Covalent Intimateion pair
Solvent-separatedion pair
Solvated ions
(7.13)
① Solvent polarity
(polarity
② Degree of association between the cationic chain end and counterion (A-)
favors the initiation step)
D. Chain transfer reaction
1. With monomer :
2. By ring alkylation
CH2CH+HSO-4 + CH2 CH + CH3CH+HSO4CH CH
(7.14)
CH2 CH CH2 CH+HSO-4 + CH2 CH
CH2 + CH3 CH+HSO-4
(7.15)
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
D. Chain transfer reaction
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
3. By hydride abstraction from the chain to form a more stable ion :
4. With solvent-for example, benzene-by electrophilic substitution :
CH2CH+HSO-4 + CH2CHCH2 CH2CH2 + CH2CCH2
HSO-4+
(7.16)
CH2CH+HSO-4 + + CH2 CH
CH2CH + CH3CH+HSO-4
(7.17)
E. Termination reaction
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
Termination are the combination of chain end with counterion.
CH2CH+ -OCCF3
O
CH2CHOCCF3
O
CH2C+
CH3
CH3
BCl3OH-CH2C
CH3
Cl
CH3
+ BCl2OH
(7.18)
(7.19)
① styrene + CF3COOHinitiator
② Isobutylene + BCl3/H2o
F. Proton trap
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
It intercepts the proton before it transfers to monomer.
The result lower overall yield
higher molecular weight
lower polydispersity index.
(7.20)CH2CR2+
+
NCH CR2 +
N+
H
A:proton trap··B:monomer··
A
B
G. Telechelic Polymer
Cl C
CH3
CH3
C
CH3
CH3
Cl + BCl3 Cl C
CH3
CH3
C+
CH3
CH3
BCl4-
C
CH3
CH3
C+
CH3
CH3
Cl + CH2 C
CH3
CH3
Cl C
CH3
CH3
C
CH3
CH3
CH2C+
CH3
CH3
(7.21)
(7.22)
(7.23)
inifer
(bifunctionalcompound)
Cl C
CH3
CH3
C
CH3
CH3
C
CH3
CH3
C
CH3
CH3
Cl
CH2C+
CH3
CH3
+ C
CH3
CH3
C
CH3
CH3
ClCl
CH2C
CH3
CH3
Cl + C
CH3
CH3
C
CH3
CH3
Cl+
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
H. Pseudocationic Polymerization
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
(7.24)CH2CH OClO3
Ph
+ CH2 CH
Ph
CH2CHCH2CH
Ph Ph
OClO3
The reaction proceeds at a much slower compared with most cationic processes.
The propagating chain end is a covalently bonded perchlorate ester
I. To prepare living polymers under cationic conditions.
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
Tertiary ester + BCl3 / Isobutylene polymerization ① formation of tertiary carbocation-initiating species.
② Polymerization to yield polyisobutylene terminated
R3COCCH3
O
+ BCl3 R3C+ -OCCH3
O BCl3
(7.27)
–… (7.26)CH2 C(CH3)2
R3C CH2C
CH3
CH3
CH2C
CH3
CH3
OCCH3
O BCl3
: appearance of a very tightly bound – but still active – ion pair
(Termination or chain transfer reaction 없이 중합반응이 종결되는 예 )
ex1)
I. To prepare living polymers under cationic conditions.
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
I2 / HI or I2 / ZnI2 : vinyl ether propagation
CH2CH
OR
ICH2CH
OR
ZnI2
CH2CH
OR
CH2CH
I ZnI2
OR
(7.27)
Living Polymer
Termination 이 전체적으로 멈춘 곳에서 chain end 가 여전히 active 한 성질을 가지고 있는 polymer
Monomer 첨가 시 분자량이 증가하며 starting monomer 와 다를 경우 block copolymer 형성 매우 길고 anionic polymerization 에 많이 이용 대부분의 living polymer 는 낮은 온도에서 합성 Living polymer 란 용어는 정지 반응이 일어나지 않는 이온 중합에 이용
ex2)
(Termination or chain transfer reaction 없이 중합반응이 종결되는 예 )
J. Kinetics
Expression of general initiation, propagation, termination, and transfer rates
]][[
][
]][[
]][[
MMkR
MkR
MMkR
MIkR
trtr
tt
pp
ii
][
][
][
M
M
I : molar concentration of initiation
: molar concentration of monomer
: molar concentration of cationic chain end
As with free radical polymerization approximation to a steady state for the growing chain end.
ti RR
][]][[ MkMIk tit
i
k
MIkM
]][[][ or
thus
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
TABLE 7.2. Representative Cationic propagation Rate Constants,a
PR
Monomer
Styrene-Methylstyrenei-Butyl vinyl etheri-Butyl vinyl etheri-Butyl vinyl etherMethyl vinyl ether2-Chloroethyl vinyl ether
Solvent
NoneNoneNoneCH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Temperature (oC)
150300000
Initiator
RadiationRadiationRadiationC7H7
+SbCl6-
C7H7+SbCl6
-
C7H7+SbCl6
-
C7H7+SbCl6
-
kp (L/mol s)
3.5 106
4 106
3 105
5 103
3.5 103
1.4 102
2 102
aData from Ledwith and Sherrington.19
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
Substituting for ][ M in pR , one obtains
In the absence of any chain transfer, (the kinetic chain length = )
If transfer is the predominant mechanism controlling chain growth,
DP =
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
K. Difference between free radical and cationic processes.
free radical process cationic process
propagation rate (Rp)
DP ()
proportional to the square root of initiator concentration
dependent of initiator concentration
first-order dependence
independent of initiator concentration
Rp = dt-d[M] = kp[M]
t
d
k
Ifk ][Rp = dt
-d[M] = kp[M]t
d
k
Ifk ][Rp = dt
-d[M] = kp[M]t
d
k
Ifk ][Rp = dt
-d[M] = kp[M]t
d
k
Ifk ][
tr
p
tr
p
tr
p
t
p
t
p
t
p
t
ipp
t
i
ti
ti
k
k
MMk
MMk
R
RDP
k
Mk
Mk
MMk
R
RDP
k
MIkkR
k
MIkM
MkMIk
RR
M
M
I
]][[
]][[
][
][
]][[
]][[
]][[][
][]][[
][
][
][
2
tr
p
tr
p
tr
p
t
p
t
p
t
p
t
ipp
t
i
ti
ti
k
k
MMk
MMk
R
RDP
k
Mk
Mk
MMk
R
RDP
k
MIkkR
k
MIkM
MkMIk
RR
M
M
I
]][[
]][[
][
][
]][[
]][[
]][[][
][]][[
][
][
][
2
=
2kt[M·]2
kp[M][M·]=
2kt[M·]kp[M]
=kp[M]
][(2 Ikfk dt
=2kt[M·]2
kp[M][M·]=
2kt[M·]kp[M]
=kp[M]
][(2 Ikfk dt
tr
p
tr
p
tr
p
t
p
t
p
t
p
t
ipp
t
i
ti
ti
k
k
MMk
MMk
R
RDP
k
Mk
Mk
MMk
R
RDP
k
MIkkR
k
MIkM
MkMIk
RR
M
M
I
]][[
]][[
][
][
]][[
]][[
]][[][
][]][[
][
][
][
2
L. Nonconjugation diene – Cationic cyclopolymerization
C6H5 C6H5
R+R
C6H5 C6H5
+
R
C6H5C6H5
+monomer
R
C6H5 C6H5
(7.28)
7.2.2 Mechanism, Kinetics, and Reactivity in Cationic Polymerization
Cationic Polymerization lead to stereoregular structures.
ex) vinyl ether - methylstyrene
Vinyl ether observation resulting
(1) greater stereoregularity is achieved at lower temperatures
(2) the degree of stereoregularity can vary with initiator
(3) the degree and type of stereoregularity (isotactic or syndiotactic)
vary with solvent polarity.
7.2.3 Stereochemistry of Cationic Polymerization
R O CH CH2
CH2 C CH3
EX) t-butyl vinyl ether forms isotactic polymer in nonpolar solvents. forms mainly syndiotactic polymer in polar solvents.
( cationic chain end and the counterion are associated )
7.2.3 Stereochemistry of Cationic Polymerization
Solvent effect
In polar solvents both ions 1) be strongly solvated 2) the chain end – exist as a free carbocation surrounded by solvent molecules
In nonpolar solvents 1) association between carbocation chain end and counterion would be strong 2) counterion could influence the course of steric control.
7.2.3 Stereochemistry of Cationic Polymerization
Solvent effect
CCH2
RO HC
CH2
RO H
CH2C+
RO H
6 45 3
21 X
-CH2
C
H
CH2
C
OR
H
CH2C
H
ORR O
X-
65
43
1 2
+
(7.29)
CCH2
RO HC
CH2
RO H
CH2C
HRO
CH2CH+
OR
X-
CH2C
H
CH2
C
OR
H
CH2C
H
ORR O
X-+
ROCH CH2
(7.30)
Models proposed for vinyl ether polymerization
X-
CCH2
RO HC+
RO H
CH2 CH2 CHORC
CH2
RO HC+
RO H
CH2C
HOR
C
HH
-X
CCH2
RO H
CH2C
RO H
X-
ORH
CCH2
+
CCH2
RO HC+
RO H
CH2-
XC
RO H
CH2
(7.31)
CH2C
CH2C
R R' RR'
+ X-
+ C
H
HC
R'
R
front
(syndiotactic)
X-CH2
CCH2
C
R' R R'R
C
R R'
CH2+
back sideback(isotactic)
CH2C
R R'
CH2C
R'R
CH2 CR
R'
X-+
CH2C
CH2C
R R'RR'
C
R R'
CH2X-
+
(7.32)
(7.33)
front side
7.2.4 Cationic Copolymerization
A. Copolymerization equation - the situation is complication by counterion effects.
B. Reactivity ratios vary with initiator type and solvent polarity.
C. Temperature – unpredictable effect
D. Steric effects (Table 7.3)
E. commercial cationic copolymers – butyl rubber (prepared from isobutylene and isoprene.)
protective clothing tire inner tubes
TABLE 7.3. Representative Cationic Reactivity Rations (r)a
Monomer 1 Monomer 2 Coinitiatorb SolventbTemperature
(oC) r1 r2
1,3-Butadiene1,3-ButadieneIsopreneCyclopentadieneStyreneStyrene-Methylstyrene-Methylstyrenep-Methylstyrenetrans--Methyl- styrenecis--Methyl- styrenetrans--Methyl- styrenei-Butyl vinyl ether-Methylstyrene
AlEtCl2
AlCl3
AlCl3
BF3·OEt2
SnCl4
AlCl3
TiCl4
SnCl4
SnCl4
SnCl4
SnCl4
SnCl4
BF3
BF3
CH3ClCH3ClCH3ClPhCH3
EtClCH3ClPhCH3
EtClCCl4
CH2Cl2
CCl4/PhNO2(1:1)
CCl4/PhNO2(1:1)
CH2Cl2
CH2Cl2
-100-103-103-780
-92-780
-780
0
0
-78
-23
431152.5
0.601.609.021.2
0.050.331.80
1.0
0.74
1.30
6.02
00
0.44.5
1.171.995.5
2.901.741.10
0.32
0.32
0.92
0.42
Isobutylene
Styrene
p-Chlorostyrene
Ethyl vinyl ether
2-Chloroethyl vinyl ether
aData from Kennedy and Marechal.5
bEt = C2H5, Ph = phenyl.
7.2.5 Isomerization in Cationic Polymerization
XCH2 CH2 C+
CH3
CH3
monomer CH2 CH2 C
CH3
CH3
CH2 CH CH
CH3
CH3X+
XCH2 CH CH
CH3
CH3
H:shift
(7.34)
R+
R R
+
+ (7.35)
7.3 Anionic Polymerization
7.3.1 Anionic initiators
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
7.3.3 Stereochemistry of anionic polymerization
7.3.4 Anionic copolymerization
Nu- + CH2 CHR NuCH2 CH-
R(7.36)
Propagating chain - carbanion
Examples – nitro, cyano, carboxyl, vinyl, and phenyl.
Monomers having substituent group – stabilizing a carbanion
resonance or induction
7.3.1 Anionic Initiators
CH2 C
CH3
NO2
KHCO3 CH2 C
CH3
NO2
(7.37)
CH2 C
CN
CN
H2O CH2 C
CN
CN
(7.38)
The strength of the base necessary to initiate polymerization depends in large measure on monomer structure
cyanoacrylate adhesives
high reactivity
7.3.1 Anionic Initiators
Two basic types
that react by addition of a negative ion
that undergo electron transfer.
① The most common initiators that react by addition of a negative ion
simple organometallic compounds of the alkali metals
For example : butyllithium
Character of organolithium compounds - low melting - soluble in inert organic solvents.
Organometallic compounds of the higher alkali metals - more ionic character - generally insoluble
7.3.1 Anionic Initiators
7.3.1 Anionic Initiators
② Electron transfer (charge transfer)
by free alkali metal : solutions in liquid ammonia or ether solvents suspensions in inert solvents
by addition complex of alkali metal and unsaturated or aromatic compounds.
Electron transfer processes (involving metal donor D· , monomer M)
D + M D+ + M_
Na + Na+
Na + Ph CH CH Ph [Ph CH CH Ph] Na+
D + M D + M__
Na + PhCPh
O
PhCPh
O
Na+
2 PhCPh
O
Na+ Ph2C
O
CPh2
Na ONa
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
A. Mechanism 을 변화시킬 수 있는 요인a. solvent polarity
R metal R-Me+ R- Me+ R- + Me+
ion pair solvent separatedion pair
solvated ion
Degree of association of ioncounterion 의 역할
polar solvent : solvated ion 우세
X- + CH2 CH R XCH2 CH R-
non polar solvent : 이온들간의 association 우세 - complex 형성
R Li + CH2 CH
R'
R LiCHR'
CH2
RCH2CHLi
R'
b. Type of cation (counterion)
c. Temperature
B. The rate of initiation - initiator 와 monomer 의 structure 에 의존
C. Initiation by electron transfer dianion 생성
2 CH2 C
R
Na+Na+CHCH2CH2CHNa+
R R
Na + CH2 CH
R
CH2 CH
R
Na+
(7.46)
(7.47)
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
D. Kinetic
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
KNH2 K+ + NH2-
NH2-
+ M H2N M-
H2N(M)n- + NH3 H2N(M)nMH + NH2
-
]][[ 2 MNHkR ii
]][[ MMkR pp
]][[ 3NHMkR trtr
DPBecause the second step is slow relative to the first,
Chain termination is known to result primarily by transfer to solvent:
Rate expressions for propagation and transfer may be written in the conventional way:
][
][
]][[
]][[
33 NHk
Mk
NHMk
MMk
R
R
tr
p
tr
p
tr
p
][
]][[
3
22
NHk
MNHkkR
tr
ipp
Substituting in Rp we obtain
The average kinetic chain length, is expressed as
tri RR
]][[]][[ 32 NHMkMNHk tri
][
]][[][
3
2
NHk
MNHkM
tr
i
Assuming a steady state whereby
and
D. Kinetic
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
E. Other types of transfer reactions
CH2CH
CN
+ CH2 CH
CN
CH2CH2
CN
+ CH2 C
CN
CH2 C
CN
+ CH2 CH
CN
CH2 C
CN
CH2CH
CN
CH2 C
CH3
C
CH2 C
CH3
CH2
CO2CH3
O
OCH3
OCH3
H3C
O
H2C
C
CH3
CH2
C CH2
O
H3C CO2CH3
CO2CH3
CH3
+ OCH3
_
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
living anionic polymers can be made
When impurities are rigorously excluded
When the polymerization temperature is kept low
pi RR In Living PolymerizationF.
][][][
MIkdt
Mdop
tIko eMM ][][][
o
o
I
MM
][
][][
o
o
I
M
][
][
all chains begin to grow simultaneously.
No termination, no chain transfer reaction.
as monomer is completely consumed.
DP
electron transfer initiators
2DP
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
G. Important factor in propagation rate.
a. Association between counterion and terminal carbanion
2 CH2CHLi
R
CH2CH
R
Li
Li
CHCH2
R
(7.54)
TABLE 7.4. Representative Anionic PropagationRate Constants, kp, for Polystyrenea
Counterion Solvent kp (L/mol s)b
Na+
Na+
Li+
Li+
Li+
Tetrahydrofuran1,2-DimethoxyethaneTetrahydrofuranBenzeneCyclohexane
803600160
10-3-10-1c
(5-100)10-5c
aData from Morton.30
Bat 25oC unless otherwise noted.cVariable temperature.
7.3.2 Mechanism, kinetics, and reactivity in anionic polymerization
G. Important factor in propagation rate.
b. Monomer structure
CH2 CHCN CH2 CCO2CH3
CH3
CH2 CH CH CH2CH2 CHC6H5> >>
CH2 CHCN > CH2 CCN
CH3
> CH2 CHCO2CH3 > CH2 CCO2CH3
CH3
steric effect
inductive destabilization of the carbanion
7.3.3 Stereochemistry of anionic polymerization
A. Stereochemical of nondiene vinyl monomer
With soluble anionic initiators (homogeneous conditions) at low temperatures,
polar solvents favor syndiotactic placement
nonpolar solvents favor isotactic placement.
(stereochemistry depends in large measure on the degree of association with counterion, as it does in cationic polymerization)
(7.55)
7.3.3 Stereochemistry of anionic polymerization
A. Stereochemical of nondiene vinyl monomer
CH3
CCH2
C
CCH3
COCH3O
OH3C
O Li+
_ CH2 C
CH3
COCH3
O
C
CH2
C
CH2
C
CH3
C
O OCH3_Li+
CH3CH3
CO2 CH
3
CO2 CH
3
(7.56)
level of isotactic placement decreases –as the solvent polarity is increased or as lithium is replaced with the less strongly coordinating higher alkali metal ions.
level of isotactic placement decreases –as the solvent polarity is increased or as lithium is replaced with the less strongly coordinating higher alkali metal ions.
7.3.3 Stereochemistry of anionic polymerization
A. Stereochemical of nondiene vinyl monomer
RO
R R
COR
O
CO
Li
OC
RO
HH
R
R R
C
OORC
RO O
LiO O
RH
HC
OOR
(a) (b)SCHEME 7.1. (a) Isotactic approach of methyl methacrylate in a nonpolar solvent(b) Syndiotactic approach of methyl methacrylate in tetrahydrofuran.(Circles represent backbone or incipient backbone carbons: R=methyl. Backbone hydrogens omitted.)
Effect of solvent
B. Stereochemical of Dienes
H2C C
CH3
HC CH2
H2C CHHC CH2
7.3.3 Stereochemistry of anionic polymerization
catalyst, solvent 의 영향
isoprene 1,3-butadiene
Li-based initiator/nonpolar solventscis-1,4 polymer 의 생성이 증가
ex) Isoprene/BuLi/pentane or hexane cis-1,4 polyisoprene
(7.57)CH2Li + CH2 C
CH3
CH CH2CH2Li
C
CCH2 CH3
CH2H
formation of cis-polyisoprene – lithium’s ability
CH2C
HC
CH2
CH3
+ CH2 CH C CH2
CH3
CH2C C
H
CH2
CH3
LiCH2
CCHCH2
CH3
Li+-
(7.58)
forming a six-membered ring transition state – “lock” the isoprene into a cis-configuration
s-cis comformation by pi complexation – hold isoprene
CH
CCH2
CH2
CH3
CH
C
CH2
CH2CH3
(7.59)steric effect
7.3.3 Stereochemistry of anionic polymerization
7.3.4 Anionic Copolymerization
Complicating factors of counterion.
① solvating polar of the solvent
② temperature effect
③ electron transfer initiator 사용
Table 7.5
④ contrasts between homogeneous and heterogeneous polymerization systems.
relatively few reactivity ratios
free radical polymerizationAnionic polymerization
competition
Li+CHCH2CH2CHLi+ + Cl R Cl CHCH2CH2CH R
X X
- -
X X(7.60)
TABLE 7.5. Representative Anionic Reactivity Ratios (r)a
Monomer 1 Monomer 2 Initiatorb Solventc Temperatured
(oC)r1 r2
Nan-BuLin-BuLin-BuLin-BuLin-BuLin-BuLiEtNan-BuLiRLiNan-BuLiNaNH2
RLiNaNH2
NH3
NoneNoneHexaneHexaneTHFTHFBenzeneCyclohexaneNoneNH3
HexaneNH3
NoneNH3
25255025-78
40
50
0.12e
0.040.030.044.0
11.00.96
0.0460.120.013.380.250.343.2
6.4e
11.212.511.80.30.41.6
16.612.50.010.477.96.70.4
Methyl methacrylate
Butadiene
IsopreneAcrylonitrileVinyl acetateIsopreneAcrylonitrile
Vinyl acetate
Styrene
ButadieneMethyl methacrylate
aData from Morton.30
bBu=butyl, Et=ethyl, R=alkyl.cTHF=tetrahydrofuran.dTemperature cot specified in some instances.eNo detectable styrene in polymer.
(7.61)
7.3.4 Anionic Copolymerization
formation of block copolymers by the living polymer method.
B initiator B:- combination -:BB:- B -:BBBBBBBBBB:- S
-:SSSSSBBBBBBBBBBSSSSS:-(7.62)
ABA triblock polymers – Greatest commercial successex) styrene-butadiene-styrene
star-block (radial) – much lower melt viscosities, even at very high molecular weights
ex) silicon tetrachloride
Commercial block copolymers
4 + SiCl4 Si:- (7.63)
7.3.4 Anionic Copolymerization
7.4 Group Transfer Polymerization (GTP)
(In the 1980s a new method for polymerizing acrylic-type monomers)
GTP 의 특성
① Anionic polymerization 에서 흔히 사용되는 monomer 를 사용 Living polymer 로 전환
② Propagating chain Covalent character
③ Organosilicon 이 개시제로 사용
C COR
OSiR3
R
R+ CH2 C
CH3
CO2CH3
HF2-
RO2C C
R
R
CH2C
CH3
COSiR3
OCH3
(R CH3)
n CH2 C
CH3
CO2CH3
RO2C C
R
R
CH2C
CH3
CO2CH3
CH2C
CH3
COSiR3
OCH3n
(7.64)
living polyme
rOrganosilicon 에서 SiR3 가 transfer되어 중합을 형성 (GTP)
TABLE 7.6. Representative Compounds Used in Group Transfer Polymerization
Monomersa Initiatorsa Catalystsa Solvents
HF2-
CN-
N3-
Me3SiF2
Lewis acidc
ZnX2
R2AlCl
(R2Al)2O
CH2 CHCO2R
CH2 CCO2R
Me
CH2 CHCONR2
CH2 CHCN
CH2 CCN
Me
CH2 CHCR
O
Me2C COMe
OSiMe3
Me3SiCH2CO2Me
Me3SiCN
RSSiMe3
ArSSiMe3
Anionicb Acetonitrile1,2-Dichloroethaned
Dichloromethaned
N,N-DimethylacetamideN,N-DimethylformamideEthyl acetatePropylene carbonateTetrahydrofuranToluened
aR=alkyl, Ar=aryl, Me=methyl, X=halogen.b0.1 mol% relative to initiator.c10-20 mol% relative to monomer.dPreferred with Lewis acid catalysts.
7.4 Group Transfer Polymerization (GTP)
R2CHCO2RR'2N-Li+
R2CCO2R R2C CO-
OR
R3SiClR2C C
OSiR3
OR
* Synthesis of initiator
CH2SSiMe3
CH2SSiMe3+ CH2 CHCO2R
ZnI2CH2S
CH2S
CH2CH
CO2R
CH2CH C
OSiMe3
OR
CH2CH
CO2R
CH2CH C
OSiMe3
OR(7.65)
두 개의 작용기를 갖는 개시제 사용 사슬의 양끝에서 성장
7.4 Group Transfer Polymerization (GTP)
CH2C
CH3
COCH3
OSiR3
CH3OH
C6H5CH2Br
CH2CH
CH3
CO2CH3
CH2CCH2C6H5
CH3
CO2CH3
(7.66)
(7.67)
Speciality
① Once the monomer is consumed, a different monomer may be added
② chain can be terminated by removal of catalyst.
③ chain can be terminated by removal by protonation or alkylation.
7.4 Group Transfer Polymerization (GTP)
C COR
OSiR3
R
R
Nu-
CR
R
CH2
C C
O
COR
O SiR3
Nu
OCH3CH3
-
R
CR COR
OCH2 C
CH3
COSiR3
OCH3
(7.68)
GPT mecahanism
7.4 Group Transfer Polymerization (GTP)
CH2C C
OSiR3
CH3 OCH3+ C C
CH2
CH3
-O
CH3O
CH2C C
O Si (R3) O
CH3 OCH3
C C
CH3O CH3
CH2
(7.69)
Chain transfer of GPT