hanyang univ. spring 2008 chap 10. non-radical addition polymerization anionic polymerization -the...

Hanyang Univ.Hanyang Univ.

Spring 2008

Chap 10. Non-Radical Addition PolymerizationAnionic Polymerization -the growing chain end bears a negative charge

The mechanism of cationic polymerization is a kind of repetitive alkylation reaction.

The mechanism of anionic polymerization is a kind of repetitive conjugate addition reaction .(the "Michael reaction" in organic chemistry)

Cationic Polymerization -the growing chain end bears a positive charge


Spring 2008

B-Z + CH2=CHX B-CH2-CH- Z+

X

Initiation:

Propagation:

M- Z+ + M MM- Z+

Termination:

M- Z+ + HT MH + ZT

General Scheme

Anionic Polymerization


Spring 2008

CH LiCH3CH2

CH3

CH2 CH CHCH3CH2

CH3

CH2 CH Li

CH2 CH Li CH2 CH CH2 CH CH2CH Li

CH2 CH Li H OH CH2 CH2 Li OH

Initiation:

Propagation:

Termination:

+

+

+ +

Styrene Polymerization



Spring 2008


Characteristics of an Ideal Anionic PolymerizationNegative centers repel one another and thus termination by recombination is not possible. An ideal polymerization is “living”, which does not terminate until a terminator is added. Initiation is normally very fast relative to propagation and all chains grow simultaneously. This leads to polymers with low polydispersity or monodispersity.Theoretically:

The rate of polymerization for methacrylates and styrenes is high even at -78 oC. This is partly for the high concentration of the anion centers.The degree of polymerization

K=1 or 2 depending on initiator used.

nn

w

xM

M 11

0

0

I

MKxn


Spring 2008

Initiation by Electron Transfer

- .

- .

CH2 CH CH2 CH-.

CH2 CH-.

CH2 CHCH2CH--

+ KTHF

-78 oC

K +

K + + +

2

K +

K +K +K

+

0

02

I

Mxn

• Polymerization mostly done in THF and not nonpolar solvents like cyclohexane or benzene for the solubility the complex in THF.

• The degree of polymerization is given by



Spring 2008

Initiation by Nucleophilic Attack

CH2 CH CH3(CH2)4 CHCH3(CH2)2CH2 Li Li

COOCH3

CH2 C

CH3

N Li N

COOCH3

CH2 C

CH3

Li

THF

-78 oC+

++

THF

-78 oC+ +

0

0

I

Mxn

• Polymerization can be done in both polar and nonpolar solvents.• The degree of polymerization is given by



Spring 2008

Initiation by Living Polymer

CH2 CH Li CH2 C

CH3

COOCH3

CH2 CH CH2C

CH3

COOCH3

LiTHF

-78 oC++ +

CH2 CHLiCH2 C

CH3

COOCH3

++

Because the starting anion has to be a stronger Lewis base than the resulting anion.

But not


0

0

I

Mxn


Spring 2008

Propagation

M Z M M MZ+-Z+-

Z+- +CovalentBond

Contact IonPair

Solvent SeparatedIon Pair

Free ions

Solvent polarity increases

kP increases

Polymer tacticity decreases

• Kp can vary by orders of magnitude.

• The polydispersity remains low because the rate of inter-conversion between the different forms is much faster than the polymerization.



Spring 2008

Termination

M MH

M MCOO

MCH2Br CH2Br

MM

MCH2Br CH2Br

M Br

Z+-

By proton

H+

Z+ +

By CO2

Z+- CO2

Z+-

By using a limiting amount of 1,2-dibromoethane

Z+-2

K=2

By using a much excess of 1,2-dibromoethane

Z+-



Spring 2008

Anionic Polymerization (1) proton donor H2O or ethanol Strong base is not enough for initiation.

(2)

Ctr,s=10-3 (small chain transfer constant)

EtOH high MW product

ethoxide no longer living.

C H 2 C

H

: - + H 2 O C H 2 C H 2 + O H

-

H2O Ctr,s=10H2O low MW polymer No living polymer

Strong base is not enough for initiation.

CH2

H

+ C2H5OHC:- CH2 CH2 + C2H5O-


Spring 2008

Anionic Polymerization (3) Termination can occurred by hydride elimination without impurities.

a)

b) anionic species(active center) react with chain ends to form inactive allylic anion.

C H 2 C H C H 2 C H : - N a +

C H 2 C H C H C H

+ N a + H - :

C H C H C H 2 C H + C H 2 C H . . -

C H 2 C H 2 + C H C H C H 2 C H . . - 1,3 diphenylallyl anion is

very unreactive, highly resonance stabilized


Spring 2008

Anionic Polymerization Termination of polar monomer

In this case, although the initiator or active center attacks the monomer, that results the non-polymerization.

C H 2 C

C H 3

C O C H 3

O

+ R - L i + C H 2 C

C H 3

C R

O

+ C H 3 O - L i +

+ CH2 C

CH3

COOCH3

CH2 C:-CH3

COOCH3

Li+

CH2 C

CH3

COOCH3

C

O

C

CH3

CH2 + Li+CH3O-


Spring 2008

Anionic Polymerization Backbiting or intramolecular reaction

4) Hugginson-Wooding System

J.Chem. Soc. 1952

Polymerization of styrene conducted in liq. NH3 at bp -33C

(1) reaction rate ↑ as [I] and [M]2

I=K+NH2- rate ↑ as [NH2

-] ↑ but as [K+] ↓

(2) MW [K+] and [NH2-]

(3) Polymer is formed without unsaturation.

Cyclic trimer at the end of chain

C H 2 C C

O C H 3 O

C C H 3

C O O C H 3

C H 3 C O O C H 3

C H 2 C C

O

C C H 3

C O O C H 3

C H 3 C O O C H 3

+ C H 3 O - - ̈


Spring 2008


][

]][[]][[ 2

2

K

KNHMKkMHNkR i

ii

][

]][[

2

2

KNH

NHKk

KNH2 K NH2

k

If [K+] , then Ri If [K+] , then Ri

Dissociation of initiatorDissociation of initiator

Initiation step

NH2 + CH CH2 H2N CH2 C:-

Hk1


Spring 2008

Propagation


]][[ MMkR pp

H 2 N M n - + M H 2 N M n . M

- kp

Termination

][

][][

]][[

][][

3,

22

3,

22

p NHk

NHMkk

NHKk

KNHMkkKR

str

pi

str

pi

][

][][

]][[

3,

2

1

222

1

2

1

22

1

NHk

KNHMkKkR

KNHMKkR

str

pip

ii

H 2 N C H 2 C H C H 2 C : - H

+ N H 3 H 2 N C H 2 C H C H 2 C

H

H

: N H 2 - +

ktr,s

n n

Occurs by chain transfer

Rtr=ktr,s[M-][NH3+]Overall Rate using Steady state assumption. (RiRt).

If KCl is added Rp decreases

[K+]=[NH2-]


Spring 2008


][

][

][

][

33, NHC

M

NHk

MkX

sstr

pn

In dehydrate state,

Chain transfer constant for solvent

molekcalEEEE

rateoverall

RateDPtemp

molekcalEEE

trpiR

n

trpnx

/9

/4

Activation energy for Xn


Spring 2008


1 if 1

1 n

wn

nn

w

M

MX

XM

M

RONa + nCH2 CH2

O

CH2CH2O-Na+RO(CH2CH2O)n- 1

In Flory

If there is no termination rxn, the narrow MW distribution can be obtained.

5) Base Initiated Polymerization - a strong nucleophile is required as the initiator

NO2 > C O > SO2 > CO2

CH CH2 >>> CH3

CN > SO > C2H5


Spring 2008


6) Practical Comments

If we use metal as an initiator, the propagation rate is fast.

purity import!

7) Propagation Kinetics

]][[ MMkR pp

Comparing to the radical polymerization, the propagation doesn’t occur too fast

For most of the living polymers

[M:-] = [I][M] = is about 10-9 to 10-7 molar[M:-] = 10-3 to 10-2 molar

kp for free radical case is 5103 l/molesec

Kp : depends on solvent and counter ion

Counter ion and active center can be separated by changing the solvent then reaction rate increases

conc. of anion = conc. of initiator


Spring 2008

(1) Evaluation of Individual Propagation Rate Constants

Propagation rate constant for free ion and ion pair. [P-]: conc. of free ion [P-(C+)]: conc. of ion pair

])][([]][[ MCPkMPkR ppp


2

1

)])([(][

][][

,addedbeen have ions more if

]][[

)]([1

K)( .

]][[][

)]([][

CPKP

CP

CP

CP

K

CPCPEqat

MMkRM

CPkPkk app

pppapp

p


Spring 2008

Anionic Polymerization* How to measure kp, kp, K ?

][

log 0

MC

C

.apppkslope

appk

2

1

][ M

p

pp

kintercept

Kkkslope 2

1

)(

t


Spring 2008


][

][][

C

MKP

][][

][CZ

MKP

the conc. of living and the conc. of free ion

][][

][)]([CZ

MKMCP

A salt that must be soluble in THF with common ion to gegen ion is added to reaction mixture.

[C+][CZ]

The salt was added at high conc.

Conc. of the added salt is [CZ]

][

)(

CZ

Kkkkk pp

pappp

][

)]([][

M

CPkPkk

originally

pappp

apppk

][CZ

p

pp

k

Kkkslope

int

)(

Hence

Then able to get kp-, kp

, K from the two graphs.


Spring 2008


Effect of gegen ion on Anionic Polymerization of Styrene

THF Dioxane

kp K107 kp

- kp

Li+ 160 2.2 6.5104 0.94

Na+ 80 1.5 3.4

K+ 60~80 0.8 19.8

Rb+ 50~80 0.1 21.5

CS+ 22 0.02 24.5

- Why kp- is the same value?; kp- is much more larger than kp Thus we can say that reactivity of free ion is much greater than that of ion pairs.

- In the case of dioxane?;In dioxane which is tend not to be solvated, it has reverse tendency comparing to the case of THF. Solvation is not important in dioxane. Cs is too high and there is no difference.


Spring 2008


]][[

]][:[

MRLikR

MLiMkR

ii

pp

Look at difference.Unassociated species

Li+ genenion in aromatic hydrocarbon

Let’s say we are using the BuLi initiator.

solvation as well as is important!

Although, the 1,2 diethoxyethane reduce the , kp varies 1~1000 fold because of highly

solvating ether . Reactivity of free ion < Reacitivity of ion pair

In aromatic hydrocarbon, unassociated species dominate rate.Depends on the unassociated species in very low conc.

(nC4H9Li)6 C4H9Li6

K1

(R Mn-Li+)2 2C4H9 Mn-Li+K2

CH2 C

H

RLi

LiCH

RCH2 2 CH2 CLi

H

RCovalent character


Spring 2008


6

1

6946

1

1 ])[(][ LiHCKRLi

rateinitiationinorder

Rtheinorder

LiMKLiM

R i

6

12

1

2

1

22

1

2

6

1

]):[(]:[

][

Evidence — the viscosity measurement before and after term, we find that living

polymer is associated after termination, viscosity drops.

Because initiators and ion pairs are reduced,

Polymerization reaction in Aliphatic HC is lower than inaromatic HC.


Spring 2008

Effect of solvent and gengenion on Copolymerization of Styrene and isoprene at 25C

Solvent% Styrene in copolymer

Na+ counter ion Li+ counter ion

Nonsolvent 66 15

Benzene 66 15

Triethyl ether 77 59

Ethyl ether 75 68

THF(highly saturating solvent)

80 80

Lenz P.437 Table 13-9


Generally sodium is more ionic than lithium


Spring 2008

Cationic PolymerizationThe growing chain bears a positive charge. The active sites are either carbenium ions or oxonium ions.

Electron donating groups are needed as the R groups because these can stabilize the propagating species by resonance.

Ex)


Spring 2008

Cationic InitiatorsProton acids with unreactive counterions

Lewis acid + other reactive compound:

* To use Lewis acid effectively as initiators, use the co-initiator.

B

F

F

F

C2H5Cl C2H5 [BF3Cl]+. .

. .: +

cationogen


Spring 2008

Cationic Polymerization

OH

BF3OH H++ C C

C

C

CH3 C+

C

C

B F3OH

isobutylene

BF3 + OH2 BF3OH H+k e

CH3 C C C C+BF3O H + C C

C

C

kp

Typical Initiator Systems Co-initiator Initiator SnCl4 H2O

AlCl3 HCl

H2SO4 H2SO4

Order of reactivity AlCl3 > AlRCl2 > AlR2Cl >AlR3

HCl > CH3COOH > C6H5NO2 > > H2O >> CH3OH > CH3COCH3

Ex)

More acidic initiators are the most effective in initiating polymerization


Spring 2008

Termination

Kinetics


2 *

3

*

2t

eipp M BFOH

k

KkkR

C C C

C

B F3OH

C

C

C

+ HB-F3OH

H

32ei3ii BF OH MKkHOFBH MkR

OHBF MkR 3pp

S SRR ti 32ei3tt BF OH MKkOHBF kR

32t

ei3 BFOHM

k

KkOHBF

Problem : temination reactions occur randomly.

[ * ] can control rxn


Spring 2008


MXk

constXk

ntr

nt

0

,. 0

Mkk

MkX

trt

pn

C1

C3

C 6

C7

C8

C15

C16

B17

F3OHk tr

C21

C22

C27

C30 C 32

C33

C34

B F3OH+

M k k

M k

RR

RX

trt

p

trt

pn


Spring 2008

Chain Transfer Reactions -Cationic vinyl polymerization is plagued by numerous side reactions, which lead to chain transfer mostly.

• Difficult to achieve high MW (*initiator can give rise to many separate chains because of chain transfer)

• These side reactions can be minimized But ! not eliminated by running the reaction at low temperature

Ex)


Spring 2008

Cationic Polymerization1) Ring opening polymerization

(1) Mechanism

carbon type polymzn.

Example of ROR : cyclic amides, sulfides, acetals, esters, lactam, alkanes, …

(2) Polymerizability

- unstable ring or the ring which cannot be cyclized easily are very reactive * 3,4 and 7-11 membered ring is the most reactive ring

5,6 membered rings are stable and polymerize slowly, but, it still possible to be polymerized.

**3-membered ring is the most easiest to be polymerized

O R CH2 OCH2

R

O

CH2

ROORCH2ORCH2

CH2

R

++

+. .. .


Spring 2008

Cationic Polymerization(3) polymerization of THF(Polytetrahydrofuran)

PF52 PF4 (PF6)+ -

PF4 (PF6)+ - + O PF4 O

+PF6

-

gegenion

O(CH2)4O(CH2)4 O(CH2)4

(CH2)4

+-

AO

O(CH2)4O(CH2)4O(CH2)4

+O (CH2)4

+

-A

if H2O exist in the co-catalyst, the polymerization rate increases.

If the living polymerization is possible to occur, thus the termination or transfer also could be occurred.

O (CH2)4 O+

-A+ O

(CH2)4

(CH2)4


Spring 2008

Cationic Polymerization(4)Kinetics

I + ZY K Y+(IZ)

-

initiator coinitiator

Y+(IZ)

-+ M

ki YM+(IZ)

-

nM O+

+ O Mn O (CH2)4O

CH2 C+

H

R

[SnCl4OH]- + CH2 CH

Rstrong initiator

CH2CHCH2

R

]][][[]][)([ MZYIKkMIZYkR iii

]][[ MMkR pp

Initiation

ex) styrene, stannic-chloride-H2O System [SnCl4OH-]H+

Propagation – can has a low activation energy and can be polymerized rapidly

or

Simple propagation reaction

The total rate of polymerization may actually increases by decreasing the temperature, which means that the termination has a high activation energy.

hanyang univ. spring 2008 chap 10. non-radical addition polymerization anionic polymerization -the...

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