chap 11. non-radical addition polymerization

Hanyang Univ.Hanyang Univ.

Chap 11. 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


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


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




Characteristics of an Ideal Anionic Polymerization

Negative 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:

nn

w

xM

M 11

• 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

0

0

I

MKxn

• K=1 or 2 depending on initiator used.


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



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



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


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 that of polymerization.



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+-



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

CH2 C

H

:- + C2H5OHCH2 CH2

+ C2H5O-

Strong base is not enough for initiation.


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

a)

b) anionic species(active center) react with chain endsto 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 very unreactive, highly resonance stabilized


Anionic Polymerization Termination of polar monomer

In this case, although initiator or active center attack monomer, that means 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-


Anionic Polymerization Backbiting or intramolecular rexn

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 - - ̈



][

]][[]][[ 2

2

K

KNHMKkMHNkR i

ii

N H 2 - C H C H 2 +

ki H 2 N C H 2 C : -

H

][

]][[

2

2

KNH

NHKk

KNH2 K NH2

k

If [K+] , then Ri

Dissociation of initiator

Initiation step


Propagation


]][[ MMkR pp

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

- kp

Termination

][

][][

]][[

][][

3,

22

3,

22

NHk

NHMkk

NHKk

KNHMkkKR

str

pi

str

pip

][

][][

]][[

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).

Add KCl Rp slow down

[K+]=[NH2-]



][

][

][

][

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



1 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, we can obtain narrow MW distribution.

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

NO2 C O> > SO2 > CO2

>>> CH3CH CH2

C N > S O > C 2 H 5



6) Practical Comments

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

purity import!

7) Propagation Kinetics

]][[ MMkR pp

propagation is not so fast compared to radical polymerization

About many 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 ionCounter ion and active center can be separated by changing solvent then rxn rate increase

conc. of anion = conc. of initiaor


(1) Evaluatation 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

)])([(][

][][,

]][[

)]([1

K)( .

]][[][

)]([][

CPKP

CPionaddif

CP

CP

K

CPCPEqat

MMkRM

CPkPkk app

pppapp

p


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

][

log 0

MC

C

.apppkslope

appk

2

1

][ M

p

pp

kintercept

Kkkslope 2

1

)(

t



][

][][

C

MKP

][][

][CZ

MKP

Conc. of living and 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]

At high added salt conc.

Conc. of added salt is [CZ]

][

)(

CZ

Kkkkk pp

pappp

][

)]([][

M

CPkPkk

originally

pappp

apppk

][CZ

p

pp

k

Kkkslope

int

)(

Now

Then able to get kp-, kp

, K from two graphs.


Anionic PolymerizationEffect 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 not tend to be solvating it has reverse tendency compared to the case of THF. Solvation is not important in dioxane. Cs is too big that there is no difference. Explanation is that there is not so solvating power of Cs



]][[

]][:[

MRLikR

MLiMkR

ii

pp

Look at difference.Unassociated species

Li+ genenion in aromatic hydrocarbon

Let’s say we are using BuLi initiator.

solvation as well as is important!

Although 1,2 diethoxyethane reduce , 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.Depend on 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



6

1

6946

1

1 ])[(][ LiHCKRLi

rateinitiationinorder

Rtheinorder

LiMKLiM

R i

6

12

1

2

1

22

1

2

6

1

]):[(]:[

][

Evidence — 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 rexn in Aliphatic HC is lower than inaromatic HC.


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

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

Generally sodium is more ionic than lithium

Lenz P.437 Table 13-9



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)


Cationic InitiatorsProton acids with unreactive

counterions

Lewis acid + other reactive compound:

* To use Lewis acid effectively as initiators, use coinitiator.

B

F

F

F

C2H5Cl C2H5 [BF3Cl]+. .

. .: +

cationogen


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 most effective in initiating polymerization


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



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


Chain Transfer Reactions - Cationic vinyl polymerization is plagued by numerous side reactions,

most of which lead to chain transfer

• Difficult to achieve high MW because each initiator (*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)


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 ring which be cyclized easily are very reactive * 3,4 and 7-11 membered ring is the reactive ring

5,6 membered rings are stable and polymerize slowly, but, possible to polymerize

**3-membered ring most easily polymerize

O R CH2 OCH2

R

O

CH2

ROORCH2ORCH2

CH2

R

++

+. .. .


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

H2O which is role of cocatalyst increase polyerization rateIt is possible to occur living polymerization, but occur termination or transfer together.

O (CH2)4 O+

-A+ O

(CH2)4

(CH2)4


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 have a low activation energy and be rapid

or

Simple propagation reaction

Overall rate of polymerization may actually increase w/ decreasing temperature, means that termination has a high activation energy.

chap 11. non-radical addition polymerization

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