Anionic Polymerization of Isoprene by the Complexes

29

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Anionic Polymerization of Isoprene by the Complexes Oligoisoprenyllithium/Tertiary Polyamines in Cyclohexane. I. Kinetic Study SYLVIANE DUMAS, JOSEPH SLEDZ, and FRANCOIS SCHUÉ Laboratoire de Chimie Macromeléculaire, Université des Sciences et Techniques du Languedoc,Place Bataillon, 34060 Montpellier Cedex, France The influence of two tertiary polyamines ontheamnionic polymerization of isoprene in cyclohexane has been studied. TMEDA (N,N,N',N'-tetramethylethylenediamine) and PMDT (pentamethyldiethylenetriamine) can increase or decrease the propagation rate, depending on the concentration range. The results are discussed on the basis of the nature of the living species. The kinetic of the anionic polymerization of dienes and styrene has been intensively investigated by many workers (1-10) mainly by BYWATER et al (1-6, 8, 10), but in absence of complexing agents like amines. Recently several studies have focused on the nature of the active species in the polymerization of ethylene and conjugated dienes initiated by the chelate of butyllithium and Ν,Ν,Ν',Ν'tetramethylethylenediamine (TMEDA). LANGER (11) has postulated the presence of a 1:1 chelate and at tributed its reactivity in polymerizing ethylene and butadiene to the absence of association of the metal alkyl and the increa sed polarization of the metal alkyl bond. Recent studies, however, suggest a more complicated mechanism. 0097-6156/81/0166-0463$05.00/0 © 1981 American Chemical Society In Anionic Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

464

ANIONIC POLYMERIZATION

HAY e t a l (12, 13) showed that the a d d i t i o n of TMEDA to b u t y l l i t h i u m (BuLi) produces a remarkable increase in r e a c t i v i t y t o ward the p o l y m e r i z a t i o n of butadiene. T h i s higher r e a c t i v i t y is a t t r i b u t e d to the absence of a s s o c i a t i o n of a l k y l l i t h i u m species and the presence according to the maximum rate of polymerizôrt i o n , of a separated

i o n p a i r during the p o l y m e r i z a t i o n .

ERUSSALIMSKY e t a l ( l 4 ) described the a n i o n i c p o l y m e r i z a t i o n of Downloaded by UNIV QUEENSLAND on October 14, 2014 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch029

isoprene in the presence of TMEDA. They showed that the t e r t i a r y diamine causes a s i g n i f i c a n t increase of the p o l y m e r i z a t i o n

rate

and of the content o f 3,4-links in the polymers formed, a p l a t e a u being reached

f o r r = TMEDA/living species = 4.

More r e c e n t l y ERUSSALIMSKY e t a l (15) i n v e s t i g a t e d the p o l y m e r i z a t i o n of 2,3-dimethylbutadiene induced by oligo-2,3 butadienyllithium/TMEDA.

Contrary to butadiene

dimethyl-

and isoprene, c a -

t a l y t i c amounts of TMEDA decrease the propagation

rate

of dime-

thylbutadiene. HELARY and FONTANILLE (16) have s t u d i e d the system p o l y s t y r y l l i thium/TMEDA in cyclohexane s o l u t i o n . The behaviour

depends on

the concentration range : f o r h i g h concentration of l i v i n g ends -3 -J (8.3 x 10 mole.l ) the a d d i t i o n o f TMEDA increases the o v e r a l l r e a c t i v i t y of the system, a t low c o n c e n t r a t i o n -4 -1 (9.2 χ 10

mole.l

) a s l i g h t decrease

of the r e a c t i v i t y is noted

upon a d d i t i o n o f TMEDA. So, it seems that there e x i s t s a discrepancy about the mechanism of p o l y m e r i z a t i o n . U n t i l t h i s is resolved the proposed mechanism of the r e a c t i o n must be in doubt. Therefore, we have r e a l i z e d a systematic study (UV, NMR, k i n e t i c ) of the i n f l u e n c e of s e v e r a l f a c t o r s determining the r e a c t i v i t y of a c t i v e centres in the case of the p o l y m e r i z a t i o n of isoprene (17, 18, 19). The purpose of t h i s paper is to present some k i n e t i c r e s u l t s r e l a t i v e to the propagation

r e a c t i o n in the p o l y m e r i z a t i o n of i s o

prene by o l i g o i s o p r e n y l l i t h i u m complexed with TMEDA o r PMDT (pentame t h y l d i e t h y l e n e t r i a m i n e ) in cyclohexane.

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

29.

DUMAS E T AL.

lsoprene

465

K i n e t i c s t u d y o f the p r o p a g a t i o n

r e a c t i o n by u l t r a v i o l e t

spec-

troscopy.

The

i n i t i a t i o n s t e p is f o l l o w e d b y u l t r a v i o l e t

spectroscopy

a t 273 nm ( p o l y i s o p r e n y l l i t h i u m a b s o r p t i o n ) . The f o l l o w i n g e x p e r i m e n t a l c o n d i t i o n s a r e choosen: 9

t e m p e r a t u r e : 18 C 4


t-BuLi isoprene

]

= 4 χ ίο" m o l e , l " " -4 - l = 7 χ 10 mole.l

A f t e r 4 o r 5 h o u r s the r e a c t i o n is c o m p l e t e and a sigmoïdal v i n g ends f o r m a t i o n c u r v e is o b s e r v e d

l i -

( 1 ) . The d e g r e e o f p o l y -

m e r i z a t i o n o f the o l i g o i s o p r e n y l l i t h i u m e q u a l s

a b o u t t e n . By

a d d i t i o n o f c a t a l y t i c amounts o f c o m p l e x i n g a g e n t (TMEDA o r PMDT) the r e m a r k a b l e i n c r e a s e o f the i n i t i a t i o n rate is n o t m e a s u r a b l e by u l t r a v i o l e t s p e c t r o s c o p y .

A l s o , o n l y the p r o p a g a t i o n

s t e p was

studied. We h a v e f o l l o w e d the p r o p a g a t i o n isoprene i n i t i a t e d by cyclohexane goisoprenyllithium/TMEDA

rate

o f the p o l y m e r i z a t i o n o f

s o l u t i o n s o f the c o m p l e x e s

oli-

and o l i g o i s o p r e n y l l i t h i u m / P M D T in two

v e r y d i f f e r e n t r a n g e s o f l i v i n g ends c o n c e n t r a t i o n . I n e a c h c a s e we h a v e d e t e r m i n e d the o r d e r o f the r e a c t i o n w i t h r e s p e c t t o the l i v i n g ends c o n c e n t r a t i o n . The

monomer c o n s u m p t i o n is f o l l o w e d a t 255 nm (ε i s o p r e n e = 39)

and the p r o p a g a t i n g

s p e c i e is an o l i g o i s o p r e n y l l i t h i u m w h i c h

p o l y m e r i z a t i o n degree equals

t e n . The i s o p r e n e c o n s u m p t i o n in

p r e s e n c e o f TMEDA o r PMDT is c h a r a c t e r i z e d b y two s t r a i g h t o w i n g f o r the f a c t t h a t the c o m p l e x e s l a t i n g agents present propagation

rate

v

lines

polyisoprenyHithium/che

a very high s t a b i l i t y

(figure

1) ;

the

= -d[M] / d t is g i v e n b y the s l o p e o f the

lines.


466


Variation of ν

in p „

Complexation

f u n c t i o n o f r = a m i n e / l i v i n g ends , , . , 2 w i t h TMEDA.

The k i n e t i c o f the polymeariza**

t i o n h a s b e e n s t u d i e d b y v a r y i n g the c o n c e n t r a t i o n o f l i v i n g ends and the m o l a r

ratio

r = [ T M E D A ] / [ l i v i n g ends*}*

F o r " l o w " and c o n s t a n t c o n c e n t r a t i o n s o f p o l y i s o p r e n y l l i t h i u m -4 -1


(3.5 χ 10 varying

mole.l

the

ratio

) TMEDA d e c r e a s e s the p r o p a g a t i o n

no s e n s i b l e v a r i a t i o n is o b s e r v e d rate

R

rate,

at least

(figure 2 ) . I n order to follow

a s a f u n c t i o n o f the c o n c e n t r a t i o n o f TMEDA,

we h a v e s t a n d a r d i z e d ν and p l o t t e d v

by

r f r o m 0 t o 0 . 5 ; f o r h i g h e r v a l u e s o f r the

t e r t i a r y d i a m i n e d o e s n o t a f f e c t the p o l y m e r i z a t i o n

the p r o p a g a t i o n

rate

w i t h r e s p e c t t o the monomer c o n c e n t r a t i o n

= ν / [ M ] v e r s u s r ( f i g u r e 2 ) . [MJ r e p r e s e n t s the

monomer c o n c e n t r a t i o n . F o r " h i g h " and c o n s t a n t c o n c e n t r a t i o n s o f p o l y i s o p r e n y l l i t h i u m -3 -] (5 χ 10 rate

mole.l

by v a r y i n g

) , TMEDA a f f e c t s d r a s t i c a l l y the p r o p a g a t i o n the

ratio

r f r o m 0 t o 1.0 ( f i g u r e 3 ) . However a

low i n c r e a s e o f the rate is o b s e r v e d Complexation

w i t h PMDT.

f o r r v a l u e s l e s s t h a n 0.5.

The s t u d y d e v e l o p e d

repeated using a t e r t i a r y triamine

above h a s b e e n

(PMDT).

For "low" concentration of p o l y i s o p r e n y l l i t h i u m -4 -1 (4.5 χ 10

mole.l

r y i n g the m o l a r

ratio

) PMDT d e c r e a s e s the p r o p a g a t i o n r = [PMDT] / [ l i v i n g

rate

by v a

ends] from 0 t o 1

( f i g u r e 4 ) ; the e f f e c t is v e r y s e n s i b l e b e t w e e n 0 a n d 0.5, a low d e c r e a s e

being observed

b e t w e e n 0.5 and 1. —2

For

"high" concentrations of p o l y i s o p r e n y l l i t h i u m

PMDT a f f e c t s the p r o p a g a t i o n and

rate

a h i g h i n c r e a s e a r e observed

—1

(10 m o l e . l

),

l i k e TMEDA. R e s p e c t i v e l y a l o w f o r r v a l u e s l e s s t h a n 0.5 and

r v a l u e s i n c l u d e d b e t w e e n 0.5 and 1 ( f i g u r e 5 ) . The p r e s e n c e of

of a plateau f o r r values

1 s u g g e s t s the e x i s t e n c e

a 1 : 1 a c t i v e c h e l a t e . T h i s c o m p l e x e j u s t i f i e s the m i c r o -


467

Isoprene

DUMAS ET A L .

Ve c o n v e r s i o n

(b)

Figure 1. Influence of the agent on the propagation rate in merization of isoprene at I8°C... hexane: (a) r = [TMEDA]/[PILi] PILi = 5.4 X 10~ mol . L" ; [PMDT]/[PILi] = 0.9; PILi mol . L . 3

1

chelating the polyin cyclo= 1.0; (b) r = = 10*


1

\ 4 - < i M i xio3 mn-1 :

=

"

x

d\

[M]

[TMEDA]

" Q5 Figure 2.

1.0

15

M

"

2.0

Influence of TMEDA on the propagation rate in the polymerization of isoprene in cyclohexane at low PILi concentration.

Figure 3. Influence of TMEDA on the propagation rate in the polymerization of isoprene in cyclohexane at high PILi concentration: [PILi] — 5 X 10~ mol . L' ; 18°C. 3


1


468


οι 0

.

.

.

-

05

1

15

2

Figure 4. Influence of PMDT on the propagation rate in the polymerization of isoprene in cyclohexane at low PILi concentration: [M] = 0.34 mol ; [PILi] = 4.5 X 10' mol . L ; 18°C. 1

4

1

[PMPfl [PILi]

0

0.5

1

1.5

2

Figure 5. Influence of PMDT on the propagation rate in the polymerization of isoprene in cyclohexane at high PILi concentration: [PILi] = 10~ mol . L' ; 18°C. 2

1


29.

DUMAS ET AL.

Isoprene

469

s t r u c t u r e of the polymers obtained by p o l y m e r i z i n g a n i o n i c a l l y isoprene in presence of t e r t i a r y polyamines u l t r a v i o l e t spectroscopy and c i e s take in account

the

*H NMR

(17, 19). Moreover,

s t u d i e s of the l i v i n g

spe-

1 : 1 c h e l a t e (17, 18). A c c o r d i n g to

some p u b l i s h e d r e s u l t s , it seems that the complexe is not

aggre-

gated. By determining the orders w i t h r e s p e c t to the complexes polyisoprenyllithium/TMEDA


new

informations may

and polyisoprenyllithium/PMDT some

be a v a i l a b l e about the aggregation when

r is equal to the u n i t y .

Determination of the orders

Order w i t h r e s p e c t to the p o l y i s o p r e n y l l i t h i u m concentration

[PILij

.

In the propagation r e a c t i o n we have

determined

the order with r e s p e c t to p o l y i s o p r e n y l l i t h i u m in absence of any c h e l a t i n g agent at 18°C... ( f i g u r e 6 ) . We may

be a s s i m i l a t e d to 0.25

— *

P I L i + monomer

value which

as g i v e n by BYWATER AND

The f o l l o w i n g mechanism is proposed

(PILi),

found 0.3,

Q)

WORSFOLD ( J ) .

:

4 PILi

,

propagation

The non aggregated monomeric p o l y i s o p r e n y l l i t h i u m is the a c t i v e specie;

Complexation

w i t h TMEDA.

The

f o l l o w i n g experimental

con-

d i t i o n s are r e q u i r e d : temperature

: 18°C...

r - 1 [ P I L i ] and [TMEDA] v a r y i n g from 3.10

to 10~

2

mole.l"

1

The r e s u l t s p l o t t e d on f i g u r e 6 show t h a t the order w i t h r e s p e c t to the a c t i v e species c o n c e n t r a t i o n is equal to 1.1 that the complex

presuming

P I L i / T M E D A is monomeric.



470


Figure 6. Influence of PILi concentration of the propagation rate in the polymerization of isoprene in cyclohexane without and with complexing agents (TMEDA and PMDT).


DUMAS E T A L .

29.

The

Isoprene

471

two s t r a i g h t l i n e s obtained in presence

and in absence of

TMEDA cross at a p o i n t corresponding to a p o l y i s o p r e n y l l i t h i u m -4 -1 c o n c e n t r a t i o n of 7.2 χ 10

mole.l

; f o r that value any a d d i

t i o n of TMEDA does not a f f e c t the propagation rate of the p o l y m e r i z a t i o n . Below t h i s p o i n t the rate decreases and above t h i s p o i n t the rate i n c r e a s e s in presence of c a t a l y t i c amounts o f


TMEDA. Complexation

with PMDT.

The study developed

above has been

repeated using the t e r t i a r y triamine PMDT. The r e s u l t s are ana logous t o those found in presence of TMEDA ( f i g u r e 6). A

first

order r e a c t i o n with r e s p e c t to the complexe PILi/PMDT is e v i d e n ced

: so it seems that the a c t i v e propagating species is the

1 : 1 chelate. The

two c r o s s i n g l i n e s obtained in presence

and in absence of -3 -1

PMDT ( f i g u r e 6) show a c r i t i c a l p o i n t a t 2.5 χ 10 4

(7.2 χ 10" m o l e . l "

1

f o r TMEDA).

Moreover, it is p o s s i b l e to determine of v

R

mole.l

from f i g u r e 6 the values

corresponding to the complexes PILi/TMEDA and PILi/PMDT.

Such i n v e s t i g a t i o n evidences the h i g h e r r e a c t i v i t y o f the 1 : 1 chelate PILi/TMEDA toward the 1 : 1 complexe PILi/PMDT. Discussion

The r e s u l t s obtained can be i n t e r p r e t e d by c o n s i d e r i n g the f o l l o w i n g e q u i l i b r i a a l s o proposed by HELARY and FONTANILLE in the case of p o l y s t y r y l l i t h i u m (16) :

(PILi), (PILi)

• ,• 4

+ 4 amine

4 PILi *

(a) 4 (PILi/amine)

(b)



472

HC 3

\ / . Ν

CH

3

H \ / C...— C...

+

PILi


V Ν H

j

C

/ \

H C

CH,

2

CH,

step 1

PILi/TMEDA

ISOPRENE

Ν

H

3

CH, ' * «ΝΓ PILi-* CH,

C

Transirion Complex

N

CH, H.C... 2

* C... Λ

/

\

C...

Η

CH, Is,*p2

HC 5

C H

\

2

/

CH. 3

Li*'**

/

4 C... -

\

CHj

CH.

/


29.

DUMAS E T A L .

Isoprene

473

The e q u i l i b r i u m (a) should be s t r o u n g l y d i s p l a c e d to the l e f t and e q u i l i b r i u m (b) to the r i g h t . At low concentrations range the species tend t o d i s s o c i a t e , i n c r e a s i n g the c o n c e n t r a t i o n of non aggregated P I L i , b u t the complexation

by means of the amine drops the r e a c t i v i t y . A t high

concentrations range, the enhanced r e a c t i v i t y is explained by a high c o n c e n t r a t i o n of complexed specie (PILi/amine)

d e s p i t e its


low r e a c t i v i t y compared to the non complexed s p e c i e . The

f o l l o w i n g r e a c t i v i t y order must be respected :

PILi

,

A two step

(PILi/amine)

mechanism can be developed.

Using the same scheme, PMDT leads to a complexe in which three n i t r o g e n atoms surround the l i t h i u m atom. In step 1 occurs a precomplexation propagating

of the monomer which is then i n s e r t e d in the

chain (step 2 ) .

In both cases, the p r o t o n i c nmr study o f the l i v i n g species (J8) shows the existence of the 1 : 1 c h e l a t e ; the s t r u c t u r a l

(19)

and the k i n e t i c s t u d i e s confirm that e x i s t e n c e . I t seems a l s o reasonable

to think that s u b s t i t u t i n g

TMEDA by

PMDT provokes a s t e r i c hindrance in the monomer i n s e r t i o n , inv o l v i n g a diminution of r e a c t i v i t y ;

t h i s p o i n t is more d e v e l o -

ped in a coming paper about the p o l y m e r i z a t i o n of isoprene with the complexe oligois©prenyllithium/hexamethy1triethylenetetramine.

Experimental

The p u r i f i c a t i o n of chemicals, the s y n t h e s i s and the study of the l i v i n g species u s i n g p r o t o n i c n u c l e a r magnetic resonance and u l t r a v i o l e t spectroscopy have been i n t e n s i v e l y described in other papers (18, 19) . The k i n e t i c s have been performed on a CARRY 118C...spectrometer.


474


Isoprene presents a maximum of absorption a t 223 nm but its mo l a r a b s o r p t i v i t y is very high

i

max

=

23,000 cm *.l.mole

J

) ;

f o r that reason and in order to f o l l o w the propagation rate, the consumption of isoprene has been s t u d i e d at 255 nm (ε - 39). O l i g o i s o p r e n y l l i t h i u m of p o l y m e r i z a t i o n degree equal to JO, uncomplexed or complexed (with TMEDA or PMDT), was the l i v i n g spe cie.: used to " i n i t i a t e " the propagation of the monomer. Downloaded by UNIV QUEENSLAND on October 14, 2014 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch029

A l l the experiments

e

were c a r r i e d out at 18 C under high vacuum

(10 *\nm of mercury) in sealed g l a s s v e s s e l s u p p l i e d with an u l t r a - v i o l e t c e l l . Before p o l y m e r i z a t i o n the apparatus is care** f u l l y and s u c c e s s i v e l y washed with a cyclohexane

s o l u t i o n of

b u t y l l i t h i u m and cyclohexane. The s t a b i l i t y of complexed p o l y i s o p r e n y l l i t h i u m has been v e r i f i e d by p r o t o n i c n u c l e a r magnetic resonance

and u l t r a v i o l e t spectroscopy (18)

Literature cited 1. 2. 3. 4. 5. 6.

Worsfold D.J. and Bywater S.. Can. J. Chem., 1964, 42, 1. Bywater S. and Worsfold D.J.. Adv. Chem. Sci., 1966, 52, 36 Roovers J.E.L. and Bywater S.. Macromolecules, 1968, 1, 328. Roovers J.E.L. and Bywater S. Macromolecules, 1973, 8 251 Worsfold D.J. and Bywater S.. Can. J. Chem., 1960, 38, 1891 Bywater S. and Worsfold D.J.. J. Organometal. Chem., 1967, 10, 1 7. Kropacheva E.N.. Dokl. Akad. Νauk; SSR, 1960, 130, 1253 8. Bywater S. and Worsfold D.J.. Can.J. Chem., 1962, 40, 1964. 9.Szwarc M. "Carbanions, living polymers and electron transfer processes"; Interscience : New York, 1968. 10. Bywater S. and Alexander I.J. J. Polym. Sci., part Al, 1968, 6, 3407 11. a) Langer, A.W. Trans N.Y. Acad. Sci., 1965, 27, 742 b) Langer A.W. Polym. Preprints, 1966, 7, 132.


29.

DUMAS E T A L .

Isoprene

475

12. Hay J.N. ; McCABE J.F. and Robb J.O. Faraday Trans. I, 1972, 68, 1. 13. Hay J.N. and McCABE J.F.. J. Polym. Sci., Chem. Ed., 1972 10, 3451 14. Davidjan A. ; Nikolaew N. ; Sgonnik V. ; Belenkii B. ; Nesterow V. and Erussalimsky B.. Makromol. Chem., 1976, 177, 2469. Downloaded by UNIV QUEENSLAND on October 14, 2014 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch029

15. Smirnowa N. ; Sgonnik V. ; Kalninsch K. and Erussalimsky B. Makromol. Chem., 1977, 178, 773. 16. a) Helary G. and Fontanille M. 1st European Discussion meeting on Polymer Science, Strasbourg (FRANCE), Feb. 27March 2, 1978 b) Helary G. and Fontanille M. Europ. Polym.J., 1978,

14(5)

345. 17. Dumas S. ; Marti V. ;

Sledz J. and Schué F. 1st European

Discussion meeting on Polymer Science, Strasbourg (FRANCE), Feb. 27-March 2, 1978. 18. Part II, Collet V. ; Dumas S. ; Sledz J. and Schué F. to be published. 19. Part III, Dumas S. ; Sledz J. and Schué F. to be published. RECEIVED March 24, 1981.


Anionic Polymerization of Isoprene by the Complexes

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