Coupling Reactions of Carbanionic Polymers by Elemental

31

Downloaded by UNIV OF TEXAS AT DALLAS on July 11, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch031

Coupling Reactions of Carbanionic Polymers by Elemental Compounds Such as Oxygen and Sulfur J. M. CATALA, J. F. BOSCATO, E. FRANTA, andJ.BROSSAS Universite Louis Pasteur, Centre de Recherches sur les Macromolecules (CNRS), 6 rue Boussingault, 67038 Strasbourg Cedex, France Synthesis of well defined functionalized (- telechelic or multifunctional-) macromolecules is an important task for polymer chemists. The polymers with PO(OR)2, - Si(OR)3, -OH, -OOH. . . functional groups1-8 are produced in limited quantities. The need for polymeric materials possessing specific properties has led to a renewed interest is functional polymers, especially if the initial material is a common hydrocarbon polymer. One of the techniques that we use in our laboratory to prepare these new molecules is based on anionic processes. This anionic technique is best suited to control the length of the chains prepared and to obtain samples with low polydispersity. Although the functionalization of carbanionic sites with various deactivating re agents is easier than with other methods because of the long lived species, it is still necessary to carefully control the de activation reaction to prevent secondary reactions. In this paper we describe the reaction between carbanionic ends of oligomers or polymers and elemental compounds such as oxygen and sulfur; we observe two sets of reactions: coupling and functionalization. If we can control the coupling reaction then one can effici ently functionalize polymers: on the other hand the coupling re action may often be a novel reaction. Reactions of Anionic Sites With Oxygen as a Deactivation Reagent The oxidation of living polymers by oxygen was first report ed by SZWARC9 who observed that the viscosity of the living mix ture increased when the oxygen was passed through a polystyrylsodium solution. Indeed, the ω-anionic polymers81,0 deactivated with oxygen exhibit a shoulder on the GPC chroraatogram. The molecular weight of the macromolecules corresponding to the shoulder, is double that of the Initial aliquot sample deactivated with methanol. A 0097-6156/81/0166-0483$05.00/0 © 1981 American Chemical Society

McGrath; Anionic Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

484

ANIONIC

POLYMERIZATION

coupling r e a c t i o n has obviously taken p l a c e . We have s t u d i e d the mechanism of t h i s r e a c t i o n and have d e s c r i b e d our r e s u l t s below. Mechanism of the r e a c t i o n The r e a c t i o n between carbanion and oxygen Is not a usual one because the oxygen molecule is a paramagnetic, with two s i n g l e e l e c t r o n s in the π l e v e l s . When oxygen r e a c t s with a carbanion, the most probable r e a c t i o n which is permitted is the e l e c t r o n t r a n s f e r r e a c t i o n from the carbanion to the oxygen according to the f o l l o w i n g schemes Downloaded by UNIV OF TEXAS AT DALLAS on July 11, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch031

χ

R~ + 0

R* +

2

0

(I)

2

T h i s mechanism was suggested f o r the first time by R u s s e l l l i f o r the o x i d a t i o n of 2-nitropropane in b a s i c medium. LambU: in the case of G r i g n a r d compounds has a l s o shown the e x i s t e n c e of a r a d i c a l intermediate. The high r e a c t i v i t y of organolithium com pounds has probably prevented the e a r l y study of t h i s r e a c t i o n . When we c a r r y out the o x i d a t i o n of the d i a n i o n i c dimers of v i n y l i c monomers, the first generation of compounds which is expected is the r a d i c a l anion B:

(ID

T h i s s p e c i e s can undergo two

reactions:

The second e l e c t r o n i c t r a n s f e r to the oxygen produces the d i r a d i c a l (C...) which evolves i n t o monomer formation. The l a t t e r p o s s i b i l i t y (IV) is a homolytic cleavage g i v i n g another anion r a d i c a l . I f the process f o l l o w s scheme I I I or IV, we must o b t a i n monomer formation a f t e r the o x i d a t i o n r e a c t i o n in all cases. We have c a r r i e d out the o x i d a t i o n of c a r b a n i o n i c dimers d e r i v e d from: isoprene, α-methylstyrene, styrene, 1,1-diphenylethylene. We have used two o x i d a t i o n procedures: •

d i r e c t o x i d a t i o n : the the l i v i n g s o l u t i o n

oxygen

is

directly

passed


through

31.

CATALA E T A L .

Carbanionic

Polymers

485

•

i n v e r s e o x i d a t i o n : the a n i o n i c s o l u t i o n is d e a c t i v a t e d by adding it dropwise i n t o a s o l u t i o n of THF c o o l e d t o -50°C... and s a t u r a t e d w i t h oxygen. The d i f f e r e n t r e s u l t s are c o l l e c t e d in the T a b l e I . Table I Y i e l d of Monomer Obtained


d i a n i o n i c dimers

by A c t i o n o f Oxygen on D i a n i o n i c Dimers

+2

10 [C...-],M

T

a

Tb

cation

c

a

c

b

α-methylstyrene

2 2

67 68

38 37.5

Na Na

0 0

10 10

1,1-diphenylethylene

2

64

66

Na

0

0

isoprene

2 2

0 0

0 0

Na Na

30 30

30 30

styrene

2 2

36 41

3 3.5

Na Na

10 10

30 30

1,1-diphenylethylene

2

57.5

52

Li

0

0

isoprene

5 5

0 0

0 0

Li Li

30 30

30 30

styrene

5

34.5

7

Li

10

10

τ: monomer y i e l d C...: c o u p l i n g r e a c t i o n y i e l d

a) " i n v e r s e o x i d a t i o n " b) " d i r e c t o x i d a t i o n "

We observe the presence of monomer formation f o r every o x i d a t i o n of carbanions in the b e n z y l i c p o s i t i o n . T h i s first o b s e r v a t i o n is the proof that a r a d i c a l mechanism takes place during the o x i d a t i o n of o r g a n o l i t h i u m . The second remark, concerns the c o u p l i n g r e a c t i o n : there is none f o r the diphenylmethyl carbanion: t h i s can be r e l a t e d to the Important s t e r i c hindrance of the l a t t e r . The t h i r d o b s e r v a t i o n concerns the monomer y i e l d , which depends on the o x i d a t i o n mode. With " i n v e r s e o x i d a t i o n " we o b t a i n a high y i e l d - between 40 and 70% - w i t h styrene, diphenylethylene and α-methylstyrene. In these cases, the funct i o n a l i z a t i o n r e a c t i o n and the e l e c t r o n i c t r a n s f e r from the carbanion t o the oxygen a r e competitive, and the c o u p l i n g reac t i o n (VI) is minimized.


486

ANIONIC POLYMERIZATION

L

functionalization reaction

\ •

(V)

coupling reaction


(VI)

With " d i r e c t o x i d a t i o n " there is a low amount of oxygen in the mixture and the c o u p l i n g r e a c t i o n and the a l c o h o l a t e formation are favoured. T h i s sequence prevents the monomer formation by the disappearance of the r a d i c a l . The l a s t observation concerns the o x i d a t i o n of the isoprene c a r b a n i o n i c dimers.ÎL We do not observe the monomer formation, but the presence of monoalcohols with a high y i e l d . In "inverse o x i d a t i o n " we o b t a i n 52% of monoalcohol and 80% in " d i r e c t o x i d a t i o n " . These monoalcohols have been i s o l a t e d and c h a r a c t e r i z e d ( F i g . 1 ) . They come from the t r a n s f e r r e a c t i o n from the primary r a d i c a l to the s o l v e n t . The high y i e l d of monoalcohol shows that the hydrogen t r a n s f e r from the solvent is a competitive r e a c t i o n towards f u n c t i o n a l i z a t i o n . T h i s f a c t is confirmed by the s i m i l a r values of the two rate constants (k 1 0 M . S - l ) 13,14. To summarize we can say that the first step of the r e a c t i o n of oxygen onto carbanion is of r a d i c a l nature. 2 - O x i d a t i o n of a n i o n i c polymers in s o l u t i o n By e x t r a p o l a t i o n of these r e s u l t s to the monocarbanionic polymers, it is p o s s i b l e to p r e d i c t the s y n t h e s i s of the f o l l o w i n g compounds: 8

(I)

00*

(V)

(VI)

00*

Dot, i

(VI)



CATALA ET AL. Carbanionic Polymers


487


488

To o b t a i n w e l l d e f i n e d f u n c t i o n a l i z e d macromolecules, it is necessary t o check the c o u p l i n g r e a c t i o n s (VI) which is inherent to the nature of the r e a c t i o n as we have shown before. We have s t u d i e d s e v e r a l parameters: • the oxygen c o n c e n t r a t i o n • the l i v i n g end concentrations • the s o l v e n t p o l a r i t y • the temperature • the s t r u c t u r e of the c a r b a n i o n i c end groups We have d e f i n e d the c o u p l i n g y i e l d as the ratio of the number of l i v i n g chains (2N ) which have p a r t i c i p a t e d to the c o u p l i n g r e a c t i o n s over the t o t a l number of i n i t i a l l i v i n g chains (Νχ + 2N ) 2N N]: non coupled macromolecules C... = Nl + 2N M : average number molecular weight of non coupled chains


2

2

2

2

n

Q

n,o andC..., 2

M

1 -

n

. .:

average number molecular weight of the f i n a l polymer

C... has been determined by deconvolution of the GPC curves. We have d e f i n e d a l s o , another parameter F, which corresponds to a t h e o r e t i c a l hydroperoxide y i e l d . F is the ratio of the number of non-coupled macromolecule (Νχ) t o the t o t a l number of macromolecules a f t e r r e a c t i o n : Nl F Νχ + N

M with

2

2

n

F , 2

= M

2 2-C...

n,o

We have determined the number of hydroperoxide groups per chain, analyzed by leucobase t i t r a t i o n . The comparison between the a n a l y t i c a l determination of hydroperoxide end groups f and the t h e o r e t i c a l values F, allows us to know whether all the non-coupled chains a r e f u n c t i o n a l i z e d by a hydroperoxide group. 2.1 - Influence of the o x i d a t i o n mode When the l i v i n g ends a r e d e a c t i v a t e d by " i n v e r s e o x i d a t i o n " we observe (Table I I ) a low amount of c o u p l i n g r e a c t i o n : 10% as opposed to the " d i r e c t o x i d a t i o n " mode (20%). T h i s d i f f e r e n c e comes from the oxygen c o n c e n t r a t i o n in the medium. In " i n v e r s e o x i d a t i o n " the oxygen c o n c e n t r a t i o n is in excess towards the l i v i n g ends c o n c e n t r a t i o n , the the secondary r e a c t i o n s VI and


31.

Carbanionic

CATALA ET AL.

Polymers

489

The s i m i l a r values of F and f confirm t h i s

V I I I a r e minimized, explanation.

Table I I Influence of the Oxygen Concentration ( O x i d a t i o n Mode) on the Hydroperoxide F u n c t i o n a l i t y and on the Coupling Y i e l d τ

3

10 . [PS*],M

lOxidat ion Mode


4|PS I PS I,

j jlnverse

IPSO I„ l o i r e c t PS I t

2.6 2.6

0.09

0.96

0,95

5 900

2,6

0.17

0.90

0.40

6 300

0,10

0.94

0.86

6 700

0,21

0.88

0.20

900

i

PSO I I , ίInverse 1

5 800

5 400

i .

PSO I I . D i r e c t 0

[pS ] : l i v i n g ends c o n c e n t r a t i o n PS : a n i o n i c r.h.iin d e a c t i v a t e d by a proton PSO : polymer chain which have undergone the o x i d a t i o n Deactivation Solvent

temperature : - 65°C... : THF

2.2 - Influence When the l i v i n g of c o l l i s i o n between c o u p l i n g r e a c t i o n is

o f the L i v i n g End Concentration end c o n c e n t r a t i o n i n c r e a s e s , the p r o b a b i l i t y two macroradicals increases and then the favoured (Table I I I ) .

Table I I I Influence of the L i v i n g Concentrations

M n o A

?S I

3

Ι Ο . [PS~],M

?S0 IT

7 100

lit,

4.6

7 200

0.96

0.95

0,13

0.90

0.85

6.1

0.23

0.87

0.81

16 7.8

6 300 2

0,08

*6.l

5 700

PSO IV,

f

4.6

6 300

PS IV

PSO i v

2,6

6 600

PS I I I

F

2.6 5 800

,S I I

C...

Reaction

η

5 500

,S0 I,

PSO

M

on the Coupling

16

6 700

D e a c t i v a t i o n mode:"inverse D e a c t i v a t i o n tern-* perature :- 65 C

0. 20

0.88

0.86

0.25

0.86

0.85

oxidation"

e



490


When low l i v i n g end c o n c e n t r a t i o n a r e used, we o b t a i n a good hydroperoxide f u n c t i o n a l i t y 0,95. 2.3 - Influence of the Solvent I f we i n v e s t i g a t e the i n f l u e n c e of the s o l v e n t , it is necessary t o take i n t o account the nature of the species in the medium. I n non-polar solvent we have aggregated s p e c i e s U i ; when we add tetramethylenediamine (TMEDA) we destroy the aggregates, and we have an e q u i l i b r i u m between i o n p a i r s and complexed s p e c i e s . l & I n p o l a r solvent, we have another e q u i l i b r i u m between the i o n p a i r s , the s o l v a t e d i o n p a i r s and loose i o n p a i r s . ϋ I f we compare the o x i d a t i o n r e s u l t s (Table I V ) , we observe that f o r s i m i l a r oxygen concentration, the coupling y i e l d and the hydroperoxide f u n c t i o n a l i t y increase l i k e the i o n i c i t y of the C...-LI l i n k a g e . Table IV Influence of the Solvent on the Coupling

So I v e n t

M

T'C...

η, ο PS

b e n z e n e / h e p Cane

I

PSO

I,

PSO

i

"

C...

f

F

η

7 000

30/70

benzene/heptane

2

η

Reaction

-18

7 000 0,03

0 .98 0.24

-18

7 600 0.16

0.91

0.24

TNfEBA

PS I I PSO n

tctrâhydrofurane

Living [PS~]

8 100

• 1

t

end c o n c e n t r a t i o n /

9 100 0 .20 0.89

-20 : 2.10

0. 50

M

[TMEDA] , 0,5

Deactivating

mode

: "inverse

oxidation"

The simultaneous increase of these two r a t i o s :C...and f , is due to the Increase of the macroradical c o n c e n t r a t i o n . Consequently t h i s phenomenon i m p l i e s that the e l e c t r o n i c t r a n s f e r to the oxygen ( r e a c t i o n I ) is e a s i e r with i o n i c s p e c i e s , than non i o n i c species. 2.4 -Influence of the Temperature The decrease of the temperature gives a f u n c t i o n a l i t y and a low amount of coupling r e a c t i o n s (Table V ) .


31.

CATALA

E T A L .

Carbanionic

491

Polymers

Table V I n f l u e n c e of the Temperature on the Coupling


Γ

T°C...

ι

ÎPSO

M η o A

l

IPSO 1 PSO

M

8 1 00

PS I

!

£

l

3

η

-6 5

8 600

-20

9 1 00

+ 20

9 I 00

I

Living Solvent

end c o n c e n t r a t i o n

j j, ι j j ι - 1ΐ° ii ° i j c

ΐ

LO

! °.20

s

!

0

0

i°-

20

91 i

95

89 !ο i

ο8 9

50

44

: 2.10

M

mode

j

j

: THF

De a c t i v a t i n t

Reaction

: "Inverse ο χ i ii a i: i o n "

i I

At low temperature the oxygen c o n c e n t r a t i o n in the medium is twice as high as that a t room temperature. In a d d i t i o n the low temperature i n c r e a s e s the viscositylâ. and the d i f f u s i o n of oxygen molecules is e a s i e r than the raacroradical which can e x p l a i n the r e s u l t s observed. 2.5 - I n f l u e n c e of the A n i o n i c Ends S t r u c t u r e s In adding d i f f e r e n t monomer u n i t s a t the end of monocarbani o n i c p o l y s t y r e n e s , we o b t a i n a s e t of c a r b a n i o n i c s t r u c t u r e s which habe been d e a c t i v a t e d in the same way. The r e s u l t s (Table VI) show that the terminal u n i t , which allows the more d e l o c a l i z e d anion o r r a d i c a l charge, and presents the more s t e r i c h i n drance, g i v e s the lower c o u p l i n g ratio, and the best f u n c t i o n ality.


492


Table VI Influence of the A n i o n i c Ends S t r u c t u r e s on the Coupling R e a c t i o n and on the F u n c t i o n a l i t y


Samples

3

PS"

. 10 ,M

M

PS

I

PSO

2,5

8 400.

2

6

PS I I PSO

9 100

0.14

0 92

0.89

9 800

0 29

0.83

0.40

7 300

0.24

0.86

0 .84

6 300

Ilj

PSDPEO I I

n

6 700

PSMMAO l l

3

6 700

PS I I I

7

PSMMAO l i t ,

Solvent

p.

0 .94

0 .92

11 0 .94

0 .90

0 .08

6 800

PSDPEOIIIj

PSI

f

I

η

1

PSIOI

C... ] F

M

η,ο

7 300

0.13

7 300

0 07

I j

0.93 0. 97

0.89

jO. 90

: THF

: anionic

polystyrene

with

isopreny/ termina I

units

PSDPE

: anionic

polystyrene

with

diphony Iethy I

PSMMA

: anionic

polystyrene

with

me t h y I me t l i n e r y I / I

Deactivating

temperature

: - 65°C...

Deactivating

mode

: "inverse

terminal

unit

terminal

unit

oxidation"

3 - O x i d a t i o n o f A n i o n i c Polymers in the S o l i d State The a b i l i t y of the macroradical and of the raacroions to d i f f u s e in the mixture, and to i n t e r r e a c t is r e s p o n s i b l e f o r the secondary products formation: coupling r e a c t i o n and a l c o h o l a t e s y n t h e s i s . To prevent the d i f f u s i o n phenomenon, we have c a r r i e d out the d e a c t i v a t i o n in the s o l i d s t a t e . The l i v i n g polymers have been prepared in benzene, with or without a s o l v a t i n g agent (THF o r TMEDA) and the s o l u t i o n has been freeze d r i e d before the oxygen i n t r o d u c t i o n . The experimental r e s u l t s a r e c o l l e c t e d in Table VII.


CATALA E T AL.

31.

Oxidation

Samp l e s

Carbanionic

1 ϋ \ [ P S "1


5

I

PSO I j

5

PS I I

5

PSO

11

5

1

M

! ."* , ο

! Add i t i v e s

i

ί

1

j ιο

ί ;

none

I

\ f"l η

η

500

1

: 1 2 500 1

none

9 5

I

j

PSO

9 5

1 ι

i

none

i 1 4 700

8 9Q0

i

PSO

n

5

!THF/R'-10)

111

9 5

!

2

j TUF/R'=20)

ί

PSO

111

3

9 .5

! TUF/R'=200)

PSO

i n

4

9 .5

j

5

j THF

PSO I I

TMEDA Vapor

j R' =

[T H

700

: 2 1

PSO

7

State

F

f

0.83

0 .23

0.82

0. 20

0 . 60 0 .57

0 .20

0. 1 2 0 93

0,87

c

!

i

!

\ 2 200

j

j î

PS I I I IIIj

493

Table V I I o f ω-Carbanionic Polymers in S o l i d

i .

PS

Polymers

1 3

I 0 .27 j 1 0.32 Î

300

0 20

0.39

0.87

: 9 600 ; 0 . 1 6 0.9 2 I i 9 300 j 0 .08 0.95

0. 90 0.96

! 1 2 500 " t o "

0.97

9 900

1

1

[ P S "•]

j

When the oxygen d e a c t i v a t e s the freeze d r i e d l i v i n g polymers without a d d i t i v e s , the coupling r e a c t i o n becomes predominant and can reach up t o 60%. We e x p l a i n t h i s r e s u l t by the a s s o c i a t i o n of the l i v i n g ends p r e e x i s t i n g in the s o l u t i o n , and kept in the s o l i d s t a t e . The proximity of these carbanions and consequently of the r a d i c a l a f t e r the e l e c t r o n i c t r a n s f e r favours the c o u p l i n g reactions. A l t e r n a t i v e l y , the disappearance of the aggregates by the a d d i t i o n of a s o l v a t i n g agent, allows us to o b t a i n a good hydro peroxide f u n c t i o n a l i t y and y i e l d s a low l e v e l of c o u p l i n g . F i n a l l y , is the s o l v a t i n g reagent is added in the vapor phase to the freeze d r i e d polymer, it is p o s s i b l e t o prevent the c o u p l i n g r e a c t i o n completely. We think that the THF molecules are p r e f e r e n t i a l l y l o c a t e d around the l i v i n g ends and t h i s h i n drance prevents the c o u p l i n g when the macroradicals a r e formed. In t h i s case, the hydroperoxide f u n c t i o n a l i t y is q u a n t i t a t i v e .



494


I I I - REACTION OF ANIONIC SITES WITH SUIFUR; Sfi, AS A DEACTIVATING REAGENT In a d d i t i o n to our i n v e s t i g a t i o n of oxygen r e a c t i o n s with carbanions, we have a l s o studied the r e a c t i o n of s u l f u r on carbanions. S u l f u r e x i s t s n a t u r a l l y under the form of an e i g h t raembered r i n g : S 3 . D i f f e r e n t authors have introduced s u l f u r in organic compounds v i a various methods. SchonberglS and Gilmanâû have reacted some carbanions with a l k y l g o l y s u l f i d e s and have obtained v a r i o u s s u l f i d e compounds. E l l e r U has reacted the 2,3,4,5 t e t r a f l u o r o p h e n y l l i t h i u m w i t h s u l f u r below stoichioraetry and obtained t h i o l a t e s . Hallensleben£2 has added some carbanions onto a e y e l o a l k y l p o l y s u l f i d e which causes the s u l f u r bridge to open. We have used monocarbanionic oligomers and c h a r a c t e r i z e d the d i f f e r e n t compounds which are formed a f t e r r e a c t i n g them onto The ratio of carbanion on s u l f u r is very important as f a r as the r e s u l t i n g compounds are concerned. We have i n v e s t i gated in d e t a i l the r e a c t i o n on a model molecule £.butyllithium in order to c h a r a c t e r i z e the d i f f e r e n t compounds "obtained. Table VII Nature and P r o p o r t i o n s of the Compounds Obtained When Sec.BuLi is Reacted on SQ

*

Χ:

7.

R - S, Ζ molar 2

κ

1

Wright

s

RSH

8

0

1

RSH+RSxR

8

ι

4

2 3

2 1

3 1

48

2

3 6

5

I I

36

0

t races

1

3 6

0

some

0, 5

3 6

0

some

I 00

Solvent :-Benzene, Κ , Çsec.BuLiJL

"

unreacted

46

t races

Temperature

60

No

30

Mo

: 25°C...

a

• F o r a ratio Κ 8 we o b t a i n only one coupled compound and a high y i e l d of s e c . b u t y l - t h i o l a t e (about 60% of the products formed). The coupled compound is w e l l defined and contains only one s u l f u r atom in the s u l f u r b r i d g e .


31.

CAT ALA ET

Carbanionic

AL.

Polymers

495

• When Κ = 4 we o b t a i n always the coupled compounds and only a small amount of t h i o l a t e . Let us remark that in both cases Κ « 8 and Κ 4, all the s u l f u r has been i n c o r p o r a t e d . The average number of s u l f u r atoms is about χ - 2.3 and we observe s u l f u r bridges c o n t a i n i n g 1, 2, and 3 atoms.


s

• For Κ = 2 we observe that there are t r a c e s of s u l f u r unreacted; we do not observe any t h i o l a t e formation but only coupled compounds with 3.6 average number of s u l f u r atoms in the bridge of the d i a l k y l p o l y s u l f i d e s . The number of s u l f u r atoms in the p o l y s u l f i d e s v a r i e s from 1 to 4, and one observes even traces of a higher polysulfide. • When Κ decreases down to 0.5 there is a l a r g e excess of s u l f u r and some is l e f t unreacted. There is no t h i o l a t e formed and the average number of s u l f u r per p o l y s u l f i d e does not change from the value obtained f o r Κ 2. This f a c t shows that the carbanion r e a c t i o n on the elemental s u l f u r is f a s t e r than those of the carbanion on the alkylpolysulf ides. s

A l l the c h a r a c t e r i z a t i o n s have been made by *H NMR. T h i s is p o s s i b l e because the protons l o c a t e d on the carbon α to the s u l f u r atom have d i f f e r e n t chemical s h i f t s , which depend on the number of s u l f u r atoms in the p o l y s u l f i d e (Table I X ) .

*H

NMR

Table IX Chemical S h i f t s of Disec.Butylpolysulfides

CH3-CH2

a

CH2-CH3

c \

/ CH-Sx-CH

CH3

• NMR apparatus Cameca 250 MHz

CH3

b X

solvent: réf.

TMS

COCI3 I

0.9

2

0.98

3

0.99

4

1

7

.00

! .

60

2 . 7 4

1.29

1 .

60

2 .

1 . 3 5

1 .

60

2

1 .

1 .

60

3.07

1

.25

39

74

. 98


ANIONIC


496

POLYMERIZATION

The a l k y l p o l y s u l f i d e s have been separated by vapor phase chroma tography. A l i n e a r r e l a t i o n s h i p is found between the logarithm of the r e t e n t i o n volume and the molecular weight of the d i a l k y l p o l y s u l f i d e ( F i g u r e 2) t h i s l i n e a r c o r r e l a t i o n is s i m i l a r to those observed by H i l l e n with v a r i o u s a l k y l s u l f i a e s . Z l The vapor phase chromatography was coupled with a mass spectrometer which enable us to determine the exact molecular weights, and the f r a g mentation of the d i f f e r e n t d i a l k y l p o l y s u l f i d e s . We c a r r i e d out the same i n v e s t i g a t i o n s using a s t a b l i z e d and s t e r i c a l l y hindered carbanion: the 3 - m e t h y l - l , l d i p h e n y l p e n t y l lithium. Table X Nature and P r o p e r t i e s of the Compounds Obtained When 3-Methyl-l,l-Diphenylpenthlithium is Reacted on Se

'λ w c i g h t

Sx

RSlfV

χ

R S H R-Sx-ÏÏ

unronrtea No

1. 2

66

4

2 . 5

33

2

3.4

1

4

some

4

some

8

0 .

.5|

No traces

We have not separated the i n d i v i d u a l p o l y s u l f i d e s . We can observe as before w i t h the secondary b u t y l l i t h i u m the predominant formation of a l k y l p o l y s u l f i d e R-Sx-R w i t h χ , 4, when Κ is below 2. T h i s average number decreases sharply when Κ reached 8. We can observe as w e l l that with Κ i n c r e a s i n g , the p r o p o r t i o n of t h i o l a t e increases also. We have not succeeded In s e p a r a t i n g the d i f f e r e n t p o l y s u l f i d e s with d i f f e r e n t s u l f u r atoms in the l i k a g e ( u s i n g vapor phase chromatography, or l i q u i d chromatography). The NMR spec trum has then been run on the mixture. Because there is no pro ton on the carbon α to the s u l f i d e , there is not c l e a r s e p a r a t i o n of the d i f f e r e n t compounds. The proton on the 3 p o s i t i o n is not s e n s i t i v e enough to achieve t h i s . The ΙΗ NMR spectrum shows that the methyl groups are strong l y s h i f t e d u p f i e l d . They appear at δ , 0.5 ppm from TMS as r e f erence. We can e x p l a i n t h i s by the s t r o n l y hindered p o l y s u l f i d e , which causes the methyl groups to be l o c a t e d in the s h i e l d i n g cone of the phenyl r i n g s . We have extended t h i s r e a c t i o n to o l i g o m e r i c carbanions (Table X I ) .


CATALA ET AL.

Carbanionic

Polymers

497


31.

Figure 2. Relationship between the logarithm of 1 VPC retention volume and the molecular weight of the Disec-butylpolysulfides: R = sec-BuLi; T = 150°C.; r = retention volume; column = 3% OV 171.2m. m



498

Table XI Molecular Weights of Oligomers A f t e r R e a c t i o n of Carbanions with Elemental S u l f u r

Li

compound

M

n

(H)

M

( S ) η found ( Λ ) caic .

'ield

R-Sx-R X

1 CH CII


3

1

7

fC H H C

CH,CH

2

\

3

-Ç

- ' J F.ιι '

/' .

H

l

214

554

520

79

176

446

420

77

3

1 94

4 32

4 50

82

3

5

0

1

2

1 Cll,

C H , C H ,

H C 3

f

\

CH.,

H c 3

CH.,)-U

1 ! ;

(a) : d e t e r m i n e d by c ryomet ry K. =2 Solvent

: benr.cno

The r e s u l t s obtained are q u i t e s i m i l a r to those described above. F o r Κ < 2, we observe high y i e l d s of coupled compounds (around 80%) and some t h i o l a t e formation. The number of s u l f u r atoms In the bridge are a l s o between 3 and 4. When any of these d i a l k y l p o l y s u l f i d e s are reacted w i t h carbanions such as secondary b u t y l l i t h i u m , in excess, one observes the gradual disappearance of the i n i t i a l compound and the formation of the d i s y m e t r i c d i a l k y l t h i o e t h e r r e s u l t i n g from a scrambling r e a c t i o n . Instead of monocarbanionic oligomers, we have used s i t e s c a r r i e d by polymers and observed the formation of t h i o l a t e s and c o u p l i n g r e a c t i o n s as described above. When d i c a r b a n i o n i c p o l y mers are used, if c o n d i t i o n s are chosen p r o p e r l y , a polycondens a t i o n type r e a c t i o n takes place between the c a r b a n i o n i c polymers and the s u l f u r . P o l y s t y r y l , p o l y i s o p r e n y l and p o l y - a - m e t h y l s t y r y l dianions have been used. In very good agreement with our expectation, we have observed an increase of the molecular weight by a f a c t o r of 2 to 5 depending on the c o n d i t i o n s . The number of s u l f u r atoms in the bridge v a r i e s from 1 to 3.


31.

CATALA E T A L .

Carbanionic

Polymers

499

To account f o r these r e s u l t s we can propose the f o l l o w i n g mechanism f o r the r e a c t i o n of carbanions onto elemental s u l f u r :

R - Li + S

8

> [R " S

8

- Li]

non i s o l a t e d (χ

[R-S -LiJ


8

+ RLi

-R + RLi

R-S χ

> R-S -

R + Li S

x

>

R - S

2

w

*

+ y = 8\

y

- R + R - ί· _ ν

1 j L 7

* >

z

"

IV - EXPERIMENTAL PART Experimental c o n d i t i o n s have been described elsewhere.2A2JL V -

CONCLUSION To conclude, we have been s u c c e s s f u l i n preventing the c o u p l i n g r e a c t i o n s when oxygen d e a c t i v a t e s freeze d r i e d l i v i n g polymers. Moreover, we have shown that o x i d a t i o n may be a general method to f u n c t i o n a l i z e l i v i n g polymers. With a small q u a n t i t y of d e a c t i v a t i n g reagent, the f u n c t i o n a l i t y i s q u a n t i t a t i v e , and one can prevent completely secondary r e a c t i o n s . In our i n v e s t i g a t i o n of d e a c t i v a t i n g l i v i n g polymers with s u l f u r , we o b t a i n t h i o l a t e s or p o l y d i a l k y l p o l y s u l f i d e s . F o r Κ 2 the polymers contain about 3 s u l f u r atoms i n the bridge. The technique of the s u l f u r coupling r e a c t i o n can be used a l s o to prepare m u l t i b l o c k polymers. The technique of d e a c t i v a t i o n of c a r b a n i o n i c polymer with oxygen or s u l f u r i s able to y i e l d numerous i n t e r e s t i n g organic compounds such as novel macroraolecular i n i t i a t o r s , new macromolecular a d d i t i v e s , and t e l e c h e l i c polymers. F i n a l l y , the coupling r e a c t i o n s can be used to b u i l d block polymers. β

Acknowledgments T h i s work was rendered p o s s i b l e thanks to the support of the Société N a t i o n a l E l f A q u i t a i n e (Polymères) t o one of us, J . F . Boscato.

Literature Cited 1. L. J . Fetters, J . Polym. Sci. 26, 1 (1969). 2. J . Brossas, G. Clouet, C. R. Acad. Sci. C-280, 1459 (1975). 3. J . Brossas, C. P. Pinazzi, G. Clouet, F. Clouet, Makroraol. Chera., 170, 105 (1973). 4. R. Rupprecht, J . Brossas, J . Polym. Sci. 52, 67 (1975). 5. J . Brossas, G. Clouet, Makromol. Chem. 175, 3067 (1974). 6. J . M. Catala, J . Brossas, Β. Ville, M. Fontanille, C. R. Acad. Sci., C-285, 417 (1977).




500

7. J. M. Catala, J. Brossas, Polym. Bull. 2, 137 (1980). 8. J. M. Catala, G. Reiss, J. Brossas, Makromol. Chem. 178, 1249 (1977). 9. M. Szwarc, Nature, 178, 1168 (1956). 10. L. J. Fetters, E. R. Firer, Polym., 18, 306 (1977). 11. G. A. Russel, J. Amer. Chem. Soc., 76, 1595 (1954). 12. R. C. Lamb, P. W. Ayers, M. K. Roney, J. F. Garst, J. Amer. Chem. Soc., 88, 4261 (1966). 13. J. K. Kochi, G. A. Olah, Free Radical, Ed. J. Wiley & Sons, 1, 66. 14. R. H. Gobran, M. B. Berenbaum, Α. V. Tobolsky, J. Polym. Sci., 46, 431 (1960). 15. M. Morton, L. J. Fetters, J. Polym. Sci., A-2, 2211 (1964). 16. G. Helary, M. Fontanille, 1st Europ. Disc. Meeting on Polymer Science, Strasbourg (1978). 17. S. Wenstein, G. C. Robinson, J. Amer. Chem. Soc., 80, 169 (1958). 18. C. Carbagal, K. J. Tolle, J. Smid, M. Szwarc, J. Amer. Chem. Soc., 87, 5548 (1965). 19. A. Schonberg, A. Stephen, H. Kaltschmitt, E. Petersen, H. Schulten, Ber. Deutsch. Chem. Gesell. 66 237 (1933). 20. H. Gilman, C. G. Stuckwisch, J. Amer. Chem. Soc. 65, 1461 (1943). 21. G. Eller, O. W. Meek, J. Org. Metal Chem. 22, 631 (1970). 22. M. Hallensleben, Makromol. Chem. 175, 3315 (1974). 23. J. F. Boscato, J. M. Catala, E. Franta, J. Brossas, Makromol. Chem. 180, 1571 (1979). 24. J. F. Boscato, J. M. Catala, E. Franta, J. Brossas, French Pat. 78.31.819 (1978). 25. L. W. Hillen, R. L. Werner, J. Chromatogr. 79, 318 (1973). Received May 5, 1981.


Coupling Reactions of Carbanionic Polymers by Elemental

Recommend Documents