Polymerization by Opening of Small Carbon Rings - Advances in

10

Polymerization by Opening of

Polymerization Reactions and New Polymers Downloaded from pubs.acs.org by UNIV OF AUCKLAND on 09/29/18. For personal use only.

Small Carbon Rings

C. P. PINAZZI, J. C. BROSSE, A. P L E U R D E A U , J. BROSSAS, G. LEGEAY, and J. C A T T I A U X Laboratoire de Chimie Organique Macromoléculaire, Equipe de Recherche Associée au Centre National de la Recherche Scientifique, Rte de Laval 72, Le Mans, France

Polymerization of cyclopropane and substituted cyclopropyl compounds was studied with cationic initiators and ZieglerNatta catalysts.

Cyclopropane, bicyclo[n.1.0]alkanes, spiro

[2.n]alkanes, bicyclopropyle, and two isomers of isoprene give rise, with Lewis acids as initiators, to oligomers whose structures generally present methyl groups in a side chain. These methyl groups stem from molecular involving

opening

of the cyclopropyl

shift during the polymerization

rearrangement

group and

step. With

hydride

Ziegler-Natta

catalysts, these monomers give oligomers whose structures are different from those observed with cationic catalysts. Dihalocyclopropyl

compounds give, with either cationic or

Ziegler-Natta catalysts, oligomers by opening of the three­ -carbon ring.

The structures of these polymers are the same

in both cases and are characterized by the loss of one molecule of HCl per monomer unit.

'""phis w o r k concerns the s t u d y of the p o l y m e r i z a t i o n of c y c l o p r o p a n e , s u b s t i t u t e d c y c l o p r o p a n e s , a n d conjugated c y c l o p r o p a n e s i n the presence of c a t i o n i c a n d Z i e g l e r - N a t t a p o l y m e r i z a t i o n .

T h e u n s a t u r a t i o n of

c y c l o p r o p a n e has b e e n d e s c r i b e d b y several w o r k e r s i n the s a m e w a y as unsaturated compounds.

T h e u n s a t u r a t i o n of c y c l o p r o p a n e c o m p o u n d s ,

w h i c h is the basis for the p o l y m e r i z a t i o n of these structures, c a n

be

e x p l a i n e d b y the electronic r e p a r t i t i o n o n the three c a r b o n atoms

of

the r i n g .

D e t e r m i n a t i o n of the d i p o l a r m o m e n t of c h l o r o c y c l o p r o p a n e

has s h o w n that the c a r b o n i u m i o n r e s u l t i n g f r o m the attack of the r i n g b y a c a r b o c a t i o n is s t a b i l i z e d i n a h o m o a l l y l i c structure. 141

142

POLYMERIZATION REACTIONS AND N E W POLYMERS

S e v e r a l hypotheses c o n c e r n i n g t h e electronic structure of c y c l o p r o ­ p a n e h a v e b e e n suggested. b y Bernett

(I).

T h i s t o p i c has b e e n i n t e r e s t i n g l y p i n p o i n t e d

A cyclopropane model proposed b y W a l s h ( 2 ) indi­

cates that C - C b o n d s o f t h e rings a r e c a u s e d b y a n o v e r l a p o f o n e o f the sp- h y b r i d i z e d orbitals of each c a r b o n a t o m a n d o f e a c h ( W a l s h p r o p o s e d , i n fact, a n sp

2

pane

orbital

h y b r i d i z a t i o n state f o r each c y c l o p r o ­

carbon). C o n s i d e r a t i o n o f t h e u n s a t u r a t i o n of c y c l o p r o p a n e l e d t h e a u t h o r

to c o m p a r e t h e attack o f a p r o t o n o n c y c l o p r o p a n e w i t h t h e f o r m a t i o n of a π c o m p l e x .

H i i c k e l ( 3 ) d e t e r m i n e d m a t h e m a t i c a l l y t h e most stable

structure f o r a p r o t o n a t e d c y c l o p r o p a n e .

T h e representation

g i v e n is

i m p e r f e c t since i t is c o n c e r n e d w i t h o n l y one resonant structure; there are three possibilities as o n e of the ρ orbitals is a n t i b o n d i n g .

I n fact,

i t has b e e n c a l c u l a t e d that t h e b o n d s f o r m e d b y t h e o v e r l a p o f t h e ρ orbitals are o c c u p i e d b y f o u r electrons, associated i n t h e o v e r l a p o f three sp

2

I n this representation,

w h i l e o n l y t w o electrons a r e

orbitals i n t h e center o f t h e r i n g .

t h e C - H b o n d s are represented

b y sp

2

hybrid

orbitals. A m o r e recent representation

o f c y c l o p r o p a n e has b e e n

proposed

b y C o u l s o n a n d M o f f i t t (4), w h o i n t r o d u c e d t h e n o t i o n o f a b e n t b o n d . T h i s representation has t h e a d v a n t a g e of m i n i m i z i n g t h e b o n d energies. T h e orbitals associated w i t h t h e C - C bonds w e r e c a l c u l a t e d as b e i n g sp '

h y b r i d i z e d , w h i l e those of t h e C - H b o n d s a r e sp '

(5).

U n d e r these c o n d i t i o n s , t h e v a l e n c e

4

12

2

responds to a b e n d i n g o f 2 2 ° .

28

hybridized

angle is 1 0 4 ° , w h i c h cor­

C o u l s o n a n d G o o d w i n r e c o n s i d e r e d this

p r o b l e m , a p p l y i n g t h e p r i n c i p l e of m a x i m u m o r b i t a l o v e r l a p ( 6 ) . T h e b e n d i n g t h e n assumes a v a l u e o f 2 1 ° 2 6 ' .

F i n a l l y , t h e w o r k of R a n d i c

a n d M a k s i c ( 7 ) gives a v a l u e o f 101 ° 3 2 ' f o r t h e C - C v a l e n c e w h i c h i n v o l v e s a b e n d i n g of 2 0 ° 4 6 . /

angle,

T h e o p t i m u m c o n f o r m a t i o n is t h e n

o b t a i n e d w h e n t h e C - C b o n d orbitals a r e sp

5

hybridized and the C - H

orbitals sp h y b r i d i z e d . 2

T h e u n s a t u r a t e d nature of c y c l o p r o p a n e a n d its derivatives suggests that they are a b l e to p o l y m e r i z e w i t h p a r t i c i p a t i o n o f t h e r i n g t h e same as C = C c o m p o u n d s . (8),

T h e first studies w e r e m a d e b y T i p p e r a n d W a l k e r

w h o u s e d a c a t i o n i c catalyst

(between 0 ° a n d - 7 8 ° ) .

( A l B r . , - H B r ) at l o w e r

temperature

T h e y s h o w e d that t h e m e c h a n i s m was s i m i ­

l a r to that of t h e p o l y m e r i z a t i o n of p r o p y l e n e a n d other olefins w i t h F r i e d e l - C r a f t s catalysts. A m o r e recent p a p e r ( 9 ) indicates t h e existence o f m e t h y l groups i n side chains i n c a t i o n i c p o l y m e r s of c y c l o p r o p a n e .

T h i s is n o t i n c o n ­

flict w i t h the existence of a IT c o m p l e x d u r i n g t h e i n i t i a t i o n step, b u t i t suggests that t h e p o l y m e r i z a t i o n m e c h a n i s m is m o r e c o m p l e x t h a n that proposed by Tipper and Walker.

10.

Opening of Carbon

PINAZZI E T A L .

Ketley

(JO)

has

same p o l y m e r b y

s h o w n that

cationic

methyl-l-butene.

143

Rings

1,1-dimethylcyclopropane

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

that

the

from

3-

H e assumed a π complex mechanism for initiation.

I s o p r o p y l c y c l o p r o p a n e treated

with

Lewis

p a r t i c i p a t i o n of the c y c l o p r o p y l g r o u p (11).

acids

polymerization mechanism.

polymerizes

by

I n this case n o e v i d e n c e

has b e e n f o u n d f o r a h y d r i d e shift o c c u r r i n g i n the

3-methyl-l-butene

P h e n y l c y c l o p r o p a n e has b e e n p o l y m e r i z e d

w i t h L e w i s - a c i d - t y p e initiators

(12)

and with Ziegler-Natta

catalysts

T h e p o l y m e r s h a v e a structure that i m p l i e s o p e n i n g of the three-

(13).

carbon ring.

N o r c a r a n e ( b i c y c l o [4.1.0] h e p t a n e ) reacts w i t h Z i e g l e r -

N a t t a catalysts the

gives

obtained

chain.

cyclohexane

(13)

a n d gives oligomers h a v i n g c y c l o h e x a n e units i n

It p o l y m e r i z e s b y o p e n i n g of the s m a l l r i n g , l e a v i n g the unchanged.

T h i s p a p e r deals w i t h the p o l y m e r i z a t i o n of several p u r e l y h y d r o carbonated

and gem-dihalocyclopropanic monomers.

T h e influence

of

c o n j u g a t i o n b e t w e e n a c y c l o p r o p a n e a n d one d o u b l e b o n d , a n d the i n f l u ­ ence of the c o n j u g a t i o n

between

t w o c y c l o p r o p a n i c groups is s h o w n

for several m o n o m e r s , s u c h as spiropentane, v i n y l g e m - d i h a l o c y c l o p r o pane, a n d b i c y c l o n o n e n e .

Polymerization

of Cyclopropanic

Systems

T i p p e r a n d W a l k e r (8)

h a v e a l r e a d y s t u d i e d the kinetics of

p o l y m e r i z a t i o n of c y c l o p r o p a n e 0° and - 7 8 ° C ,

and cyclobutane

i n heptane

u s i n g a A l B r - H B r catalyst system. > r

the

between

W e have studied

the s t r u c t u r a l aspects b y s u b j e c t i n g c y c l o p r o p a n e ( M i ) a n d c y c l o b u t a n e to different types of initiators.

U s i n g a c a t i o n i c process i n the presence

of S n C l , T i C l , E t 0 - B F , a n d A l B r , b e t w e e n - 3 0 ° a n d 1 0 0 ° p o l y m e r i ­ 4

4

2

3

z a t i o n of c y c l o p r o p a n e occurs, whereas the same initiators h a v e no effect on cyclobutane.

T h e m e c h a n i s m i n v o l v e s the f o r m a t i o n of a π c o m p l e x

w i t h one of the c y c l o p r o p a n e bonds f o l l o w e d b y a h y d r i d e shift, g i v i n g rise to structure Ρ . Λ

N M R a n d I R spectroscopy s h o w that the p o l y m e r

has a p o l y p r o p y l e n e structure. I n the presence of Z i e g l e r - N a t t a catalysts, phase, The

the

reactivities

of c y c l o p r o p a n e

c o n v e r s i o n degrees v a r y b e t w e e n CH;

i n the

and cyclobutane

heterogeneous are

1 a n d 5%, a n d the

similar.

molecular

POLYMERIZATION REACTIONS AND N E W

144

POLYMERS

w e i g h t s are 1 5 0 0 < M < 2 0 0 0 for the s o l u b l e f r a c t i o n of the p o l y m e r s . N

W i t h this k i n d of catalyst, the p o l y m e r s h a v e a p o l y e t h y l e n e s t r u c t u r e of t y p e Ρ

2

(Equation 1 ) .

Polymerization

of

GENERAL PREPARATION. methylene

to the

Bicyclo[n.l.O]alkanes

and

Spiro[2.n]alkanes.

T h e m o n o m e r s w e r e s y n t h e s i z e d b y a d d i t i o n of

d o u b l e b o n d of the

methylenecycloalkenes—Simmons

corresponding cycloalkenes

a n d S m i t h r e a c t i o n (14)—or

or

by addi­

t i o n of a d i h a l o c a r b e n e f o l l o w e d b y the r e d u c t i o n of the d i h a l o c y c l o p r o p a n e g r o u p b y a N a / h y d r a t e d m e t h a n o l system ( E q u a t i o n 2 ) (15,

16):

I n t h e first case, the m e t h y l e n e is o b t a i n e d b y r e a c t i o n of a Z n - C u complex on diodomethane. i n t h e heterogeneous on

T h e a d d i t i o n r e a c t i o n itself is c a r r i e d o u t

phase.

The yields i n bicyclo compounds depend

the c o n d i t i o n of a d d i t i o n to the c y c l o a l k e n e d o u b l e b o n d .

The in­

terest i n this m e t h o d lies i n the fact that the s t a r t i n g cycloolefins

are

c o m m e r c i a l l y a v a i l a b l e a n d that the y i e l d s i n b i c y c l o a l k a n e s are g o o d ( f r o m 3 0 to 8 0 % ) . are

relatively

A d i s a d v a n t a g e , h o w e v e r , is that t h e final p r o d u c t s

hard

to separate,

especially

the

high-molecular-weight

monomers. POLYMERIZATION

O F BiCYCLo[n.l.O]ALKANES.

b i c y c l o [ n . 1 . 0 ] a l k a n e series,

six w e r e

chosen

F r o m the

large-ring

b e c a u s e of t h e i r

relative

ease of synthesis: b i c y c l o [ 5 . 1 . 0 ] o c t a n e ( M ) , b i c y c l o [ 6 . 1 . 0 ] n o n a n e ( M ) , 2

bicyclo[10.1.0]tridecane ( M [n.l.OJalkanes

and

prepared

1-methylcyclqalkenes See

4

3

) , a n d the c o r r e s p o n d i n g 1 - m e t h y l b i c y c l o f r o m the

( cycloheptene,

corresponding cycloalkenes

cyclooctene,

and

or

cyclododecene).

Equation 4. C A T I O N I C P O L Y M E R I Z A T I O N O F BiCYCLo[n.l.O]ALKANES.

The

bicyclo

[n.l.0]alkanes were polymerized i n methylene chloride b y various L e w i s a c i d s : T i C l , B F < - E t 0 , a n d S n C l — w i t h c a t a l y s t / m o n o m e r m o l a r ratios 4

f r o m 4 to 15%.

2

4

T h e temperatures

A t the l o w e r temperatures

used were between 2 0 ° a n d

a n d f o r the concentrations

80°C.

u s e d , the d e g r e e

10.

Opening of Carbon

PINAZZI E T A L .

Rings

145

(R =

η = 5

H)

Mo (R = C H ) 3

(R = H ) η = 6

M

3

(3)

(R = C H ) 3

(CH ) 2

(R = H )

n

10

M

4

(R = C H ) 3

of c o n v e r s i o n to p o l y m e r s is v e r y l o w , suggesting that p o l y m e r i z a t i o n of these c o m p o u n d s necessitates r e l a t i v e l y h i g h temperatures.

T h e degrees

of p o l y m e r i z a t i o n are l o w a n d v a r y little w i t h the e x p e r i m e n t a l c o n d i ­ tions, a n d they decrease as the r i n g size increases. effects

are

therefore

probably

responsible

for

Steric

hindrance

oligomer production.

C o n v e r s i o n s v a r y f r o m 0 to 65%, a n d are l o w e r f o r b i c y c l o [10.1.0] t r i d e cane t h a n f o r the other t w o m o n o m e r s .

F o r a given monomer,

the

degree of c o n v e r s i o n d e p e n d s o n the a m o u n t of catalyst. T h e p o l y m e r structures w e r e s t u d i e d b y i n f r a r e d spectroscopy a n d NMR.

I n f r a r e d is ineffective i n d i s t i n g u i s h i n g b e t w e e n

these three types.

polymers

of

I n a l l three cases, C - H b o n d s signals are o b s e r v e d

at 2950, 2920, a n d 1450 c m " , a n d a b a n d at 1375 c m " m a y b e a t t r i b u t e d 1

1

to m e t h y l groups. N M R spectroscopy gives m o r e d e t a i l a n d distinguishes b e t w e e n the three types of p o l y m e r s .

T h e signals r e c o r d e d i n the r e g i o n of δ = 1.4

p p m are caused b y h y d r o g e n s c a r r i e d b y the r i n g carbons, whereas the signals s i t u a t e d at 0.8-1

p p m are those

η

with

' (CH ) 2

=

of m e t h y l g r o u p h y d r o g e n s R

= H

P a

R

= CH3

?2b

R

= Η

P

R

= CH3

P b

R

= Η

P a

R

= CH

2

5

3 a

η = 6 3

n

η

=

10

4

3

P

4 b

(4)

146

POLYMERIZATION REACTIONS AND N E W POLYMERS

c a r r i e d b y the saturated carbons.

It m u s t therefore b e a s s u m e d

that

p o l y m e r i z a t i o n proceeds b y o p e n i n g of the c y c l o p r o p a n e , f o l l o w e d b y a rearrangement l e a d i n g to the f o r m a t i o n of one m e t h y l g r o u p p e r " m o n o ­ m e r u n i t " a n d t w o i n the structures F

2 a

to P

4h

case of

l-methylbicyclo[n.l.O]alkanes;

see

( E q u a t i o n 4 ).

O f various mechanisms that m a y be p r o p o s e d , the o n l y a c c e p t a b l e one is that s u m m a r i z e d i n E q u a t i o n 5 .

It is assumed that the attack o n

the c y c l o p r o p a n e system b y the active site leads to the f o r m a t i o n of a π c o m p l e x , w h i c h later rearranges to a c a r b o c a t i o n .

T h e r u p t u r e of the

b o n d of carbons 1 a n d 2 a n d the r o t a t i o n b e t w e e n A a n d c a r b o n 2 i n ­ volves the appearance

of a p o s i t i v e charge o n c a r b o n 1.

The primary

c a r b o c a t i o n f o r m e d w i l l b e able to rearrange i n t o a m o r e stable tertiary c a r b o c a t i o n b y h y d r i d e shift.

T h e polymers obtained b y such a mecha­

n i s m w o u l d have structures Ρ> to P i , . Ά

4

T h e y are the o n l y ones h a v i n g

one m e t h y l g r o u p i n the side c h a i n p e r " m o n o m e r u n i t " a n d t w o i n the case of l - m e t h y l b i c y c l o [ n . l . O ] a l k a n e s .

It must, therefore,

be

assumed

that this is the m e c h a n i s m to b e c o n s i d e r e d , a n d that structures P P

4 b

2 a

to

are the o n l y ones that agree w i t h the d a t a .

(5)

10.

PINAZZI E T A L .

Opening of Carbon

147

Rings

T h e i n i t i a t i o n step m a y b e i n t e r p r e t e d b y a s s u m i n g that a p r o t o n gives rise to a π c o m p l e x w i t h the c y c l o p r o p a n e , w h i c h rearranges

by

h y d r i d e shift i n t o a c a r b o c a t i o n that w i l l b e the active site f o r the p o l y m ­ erization.

The

t e r m i n a t i o n step m a y b e c o n s i d e r e d as a d e p r o t o n i z a -

t i o n i n the a p o s i t i o n f r o m the a c t i v e site of the last u n i t i n the c h a i n . T h i s h y p o t h e s i s is c o n f i r m e d e x p e r i m e n t a l l y i n o l i g o m e r s h a v i n g a v e r y l o w d e g r e e of p o l y m e r i z a t i o n b y the p r e s e n c e of w e a k N M R signals at δ =5.2

p p m (characteristic

of v i n y l i c p r o t o n s ) a n d at a b o u t δ = 2

ppm

( m e t h y l groups c a r r i e d b y C = C ). T h e s e results agree w i t h those of v a r i o u s authors w h o h a v e d e m o n ­ strated the t r a n s f o r m a t i o n of b i c y c l o [ n . l . 0 ] a l k a n e t y p e structures u n d e r a c i d catalysis into c o m p o u n d s h a v i n g a m e t h y l g r o u p . not p o s s i b l e to v i s u a l i z e a p r i o r i s o m e r i z a t i o n i n t o f o l l o w e d b y its p o l y m e r i z a t i o n .

H o w e v e r , i t is

methylcycloalkenes

O n e m u s t c o n s i d e r that p o l y m e r i z a t i o n

occurs i n a single step b y t r a n s f o r m a t i o n i n t o the c a r b o c a t i o n .

E v e n so,

the presence of m o n o m e r units w i t h the m e t h y l g r o u p not i n the side c h a i n b u t c a r r i e d b y c a r b o n atoms i n the r i n g s h o u l d not b e e x c l u d e d . If s u c h units existed, t h e y w o u l d b e present i n a v e r y s m a l l p r o p o r t i o n w i t h respect to the m a i n m o n o m e r u n i t . P O L Y M E R I Z A T I O N OF BiCYCLo[n.l.O]ALKANES B Y M E T A L - H A L I D E

PLEXES.

Bicyclo[4.1.0]heptane

i z e d w i t h Z i e g l e r - N a t t a t y p e catalysts s t u d y of the reactivities nonane,

W e h a v e c o n t i n u e d the

bicyclo[5.1.0]octane,

a n d b i c y c l o [10.1.0] t r i d e c a n e , (M

(13).

of the h i g h e r h o m o l o g s of n o r c a r a n e

t r a n s i t i o n m e t a l c o m p l e x catalysts: bicyclo[n.l.0]alkane

2

to M ) . 4

a n d the c o r r e s p o n d i n g 1 - m e t h y l -

The

t i o n seems to o c c u r at l o w temperatures. titanium, v a n a d i u m , and tungsten

with trialkylaluminum ( E t A l , 3

toward

bicyclo[6.1.0]-

reactions

were carried out i n

sealed tubes i n hexane, u n d e r n i t r o g e n , at 8 0 ° C f o r 24 hours. used:

COM­

( n o r c a r a n e ) has a l r e a d y b e e n p o l y m e r ­

N o reac­

V a r i o u s catalyst systems w e r e halides

used i n

( i - B u ) A l , and B u A l ) . 3

3

conjunction

T h e best con­

versions w e r e o b t a i n e d w i t h the complexes of t r i e t h y l a l u m i n u m , t r i i s o b u t y l a l u m i n u m , or t r i b u t y l a l u m i n u m w i t h stannic c h l o r i d e . formed

with

titanium

tetrachloride

produce

no

Complexes

polymer.

Although

o l i g o m e r s are o b t a i n e d i n a l l cases, the average degrees of p o l y m e r i z a ­ t i o n are g e n e r a l l y h i g h e r t h a n w i t h c a t i o n i c p o l y m e r i z a t i o n s ( f r o m

five

to e i g h t o n a v e r a g e ) , a n d are n e a r l y i d e n t i c a l f o r a l l six m o n o m e r s . Structural

determination

of

the

polymers

because of the c o m p l e x i t y of the spectra.

obtained

was

difficult

I n f r a r e d spectra s h o w b a n d s

a l r e a d y o b s e r v e d i n c a t i o n i c p o l y m e r i z a t i o n at 2950, 2920, a n d 1450 T h e m e t h y l b a n d at 1375 c m is a p e a k at 1460

- 1

s t i l l exists, b u t its i n t e n s i t y is less.

c m , i n the - C H 1

2

cm . -1

There

- r e g i o n , w h i c h suggests that

the

p o l y m e r s possess m e t h y l e n e groups different f r o m the c y c l i c m e t h y l e n e s . NMR

shows a s i g n a l at a b o u t δ = 1.4 p p m , w h i c h m a y b e a t t r i b u t e d to

148

POLYMERIZATION REACTIONS A N D N E W POLYMERS

r i n g h y d r o g e n s , a n d a s i g n a l at 8 = 0 . 8 - 0 . 9 p p m , characteristic of m e t h y l groups o n saturated carbons.

T h e p r o p o r t i o n of methyls is f a r less t h a n H CH

P

2 c

P

3

td

H

P c 3

(6) CH

3

H CH

P;kl

P

3

4 c

P a 4

one per " m o n o m e r u n i t , " a n d less t h a n t w o w i t h p o l y m e r s of the 1 methylbicyclo[n.l.O]alkanes

group.

W h e n it is a s s u m e d that the c h a i n

ends are e t h y l , b u t y l , or i s o b u t y l residues catalyst),

( d e p e n d i n g o n the t y p e of

the m o n o m e r u n i t consists of a 7-, 8-, or 12-carbon r i n g , de­

p e n d i n g on the monomers c o n s i d e r e d , a n d that these rings are by

a methylene

group P

( t - B u ) A l , the CH3/CH0 3

2 c

to P .

connected

I n p a r t i c u l a r , f o r catalysts u s i n g

4d

r a t i o i n the p o l y m e r p r o d u c e d is greater t h a n

for the catalysts o b t a i n e d f r o m E t A l . 3

F o r p o l y m e r s of h i g h e r degrees

of p o l y m e r i z a t i o n , the m e t h y l peaks are n e g l i g i b l e , thus c o n f i r m i n g that they b e l o n g to c h a i n - e n d m e t h y l groups.

T h i s hypothesis is c o n f i r m e d

b y the presence of an N M R peak i n the r e g i o n of δ = 1.2 p p m that does not a p p e a r i n b i c y c l o a l k a n e c a t i o n i c p o l y m e r s ( E q u a t i o n The

polymerization mechanism

proposed

is b a s e d

olefin p o l y m e r i z a t i o n b y N a t t a a n d D a n u s s o ( 1 7 ) .

6). o n studies

of

It i n v o l v e s attack of

the c y c l o p r o p a n e b y the c o m p l e x Α,,,Μβ-ΑΊΑ'οΜβ', w h e r e M e = T i , S n , V , or W ; M e ' = A l ; A = C1, or A \ ; a n d A ' = E t , i B u , or sec-Bu ( E q u a t i o n 7 ) . 2

A

CH

3

(7)

10.

Opening of Carbon

PINAZZI E T A L .

149

Rings

S p i r o [ 2 . 6 ] n o n a n e ( M ) , spiro

Polymerization of Spiro[2.n]alkanes.

5

[2.7]decane ( M ) , a n d spiro[2.1 l ] t e t r a d e c a n e ( M ) w e r e p r e p a r e d f r o m ( i

7

the c o r r e s p o n d i n g m e t h y l e n e c y c l o a l k a n e s ylenecyclooctane,

and

S i m m o n s a n d S m i t h reaction (14);

N

(methylenecycloheptane,

methylenecyclododecane,

respectively)

methby

the

see E q u a t i o n 8.

η

=

.6

M

5

η

=

7

M

6

η

=

11

M

(8)

7

(CH ) ' 2

n

T h e y i e l d varies f r o m 40 to 60% no m a t t e r w h a t size the r i n g is. T h e separation of the alkenes a n d their derivatives is difficult because of

the

closeness

of

their

boiling

points.

Furthermore,

one

obtains,

p r o b a b l y as the result of p a r t i a l i s o m e r i z a t i o n d u r i n g r e a c t i o n of methylenecycloalkanes ondary

compounds,

to 1-methylcycloalkenes, such

as

the

s m a l l amounts

corresponding

the

of sec­

methylbicyclo[n.l.O]

alkanes. CATIONIC POLYMERIZATION OF SPIRO[2.n]ALKANES.

erization

Cationic polym­

of s p i r o [ 2 . 5 ] o c t a n e a n d s p i r o [ 2 . 4 ] h e p t a n e has

c o n s i d e r e d b y K e t l e y a n d E h r i g (18) p o l y m e r s o b t a i n e d b y means of A l B r

already

been

to c o m p a r e the structures of the 3

w i t h those of p o l y m e r s

f r o m the c o r r e s p o n d i n g v i n y l c y c l o a l k a n e s .

obtained

T h e s e authors h a v e f o u n d

that the t w o groups of p o l y m e r s have v e r y different structures a n d , w i t h ­ out g i v i n g definitive results, c o n c l u d e d that p o l y m e r i z a t i o n of

spiranes

p r o b a b l y occurs b y passing t h r o u g h a b i c y c l i c i n t e r m e d i a t e ; o n o p e n i n g , the i n t e r m e d i a t e gives c o m p l e x c o m p o u n d s . S p i r o [2.6]nonane, spiro [2.7] decane, a n d spiro [2.11] tetradecane h a v e b e e n p o l y m e r i z e d i n m e t h y l e n e c h l o r i d e i n the presence of F r i e d e l - C r a f t s catalysts w i t h this i n c r e a s i n g o r d e r of r e a c t i v i t y : V O C l , 3

E t 0 , T i C l , and A1C1 . 2

4

at 8 0 ° C .

3

SnCl , 4

BF 3

T h e reactions w e r e c a r r i e d out over 24 hours

P o l y m e r i z a t i o n , a l t h o u g h r e q u i r i n g rather h i g h

temperatures

( a b o v e 2 0 ° C ) c o u l d o c c u r at temperatures l o w e r t h a n those o b s e r v e d f o r the

corresponding

b i c y c l o [ n . 1.0]alkanes.

Conversions

h i g h e r t h a n for the c o r r e s p o n d i n g b i c y c l o a l k a n e s .

are

generally

The polymerization

degrees are l o w a n d v i r t u a l l y i d e n t i c a l for the same o p e r a t i n g c o n d i t i o n s ( f r o m 3 to 6 ) . The

i n f r a r e d spectra

1450 c m . - 1

of p o l y m e r s s h o w bands at 2950, 2920, a n d

T h e presence of a peak at 1375 c m

1

means that these p o l y -

150

POLYMERIZATION REACTIONS A N D N E W POLYMERS

mers h a v e a m e t h y l g r o u p , w h i c h confirms the results of K e t l e y a n d E h r i g a n d proves that the structure is different f r o m that of p o l y m e r s of v i n y l cycloalkanes.

N M R gives t w o massive peaks, one i n the r e g i o n of

δ = 1.4 p p m , c o r r e s p o n d i n g to h y d r o g e n s i n the r i n g s , a n d the other i n the r e g i o n of δ = 0.9 p p m , c o r r e s p o n d i n g to the h y d r o g e n s of a m e t h y l g r o u p o n a saturated c a r b o n .

I n t e g r a t i o n shows one m e t h y l g r o u p p e r

monomer unit (Equation 9). CH

3

T h e p r o p o s e d p o l y m e r i z a t i o n m e c h a n i s m suggests that a π c o m p l e x is f o r m e d f r o m the spirane c y c l o p r o p a n e a n d the c a r b o c a t i o n active site (Equation θ Α

10).

Φ

10.

Opening of Carbon

PINAZZI ET A L .

151

Rings

F r o m this c o m p l e x , the r u p t u r e of the b o n d b e t w e e n carbons 1 a n d 2 gives rise to the f o r m a t i o n of a p o s i t i v e c h a r g e a p p e a r i n g o n c a r b o n 2, w h i c h involves f o r m a t i o n of a p r i m a r y c a r b o c a t i o n that c a n

rearrange,

b y h y d r i d e shift, i n t o a m o r e stable secondary carbo c a t i o n o n c a r b o n 3, l e a d i n g to p o l y m e r s of structure P , Pea, a n d P . 5 a

T h e s e structures

7 a

are

the o n l y ones h a v i n g one m e t h y l i n the side c h a i n p e r m o n o m e r u n i t . T h e structure of c a t i o n i c p o l y m e r s of s p i r o [2.n]alkanes is too h i n ­ d e r e d to a l l o w the f o r m a t i o n of h i g h - m o l e c u l a r - w e i g h t p o l y m e r . t e r m i n a t i o n step occurs r a p i d l y , p r o b a b l y b y rearrangement,

The

loss of a

p r o t o n , a n d f o r m a t i o n of a d o u b l e b o n d , the existence of w h i c h is c o n ­ firmed b y a v i n y l h y d r o g e n N M R s i g n a l at about δ =5.2 p p m . P O L Y M E R I Z A T I O N O F S P I R O [2.n]

PLEXES.

ALKANES BY TRANSITION-METAL

P o l y m e r i z a t i o n of s p i r o [2.n] alkanes

COM­

b y transition-metal

plexes was c a r r i e d out i n hexane at 8 0 ° C over 24 hours.

The

com­

catalyst

systems w e r e : E t , A l / T i C l , E t A l / S n C l , E t A l / V O C l , a n d E t A l / W C l 4

3

4

3

f o r catalyst/monomer ratios of a b o u t 16%. to 90%)

were

obtained

with Et Al/SnCl , 3

4

degrees b e i n g o b s e r v e d w i t h E t A l / T i C l 3

4

3

the highest

c o u p l e (D

6

(80

polymerization

= 3).

p

is p r a c t i c a l l y w i t h o u t effect o n b i c y c l o [ n . 1 . 0 ] a l k a n e s [n.1.0]alkanes.

3

T h e highest conversions

T h i s catalyst

and on methylbicyclo-

It is possible that the m o r e o p e n structure of c y c l o p r o ­

p a n e i n the case of spirane-type c o m p o u n d s allows a n easier r e a c t i o n w i t h this catalyst.

I n f r a r e d spectroscopy indicates b a n d s at 2950, 2920, 1450, a n d cm

- 1

1375

already

observed

on cationic

polymers.

1375

H o w e v e r , the b a n d

at

c m , c o r r e s p o n d i n g to m e t h y l groups, decreases i n intensity a n d 1

c o m p l e t e l y disappears i n h i g h - m o l e c u l a r - w e i g h t p o l y m e r s . the b a n d at 1455 c m

1

Furthermore,

m a y b e a t t r i b u t e d to l i n e a r - C H - groups. N M R 2

confirms this a s s u m p t i o n , since the h y d r o g e n i n the rings appear i n the r e g i o n of δ = 1.4 p p m , whereas the s i g n a l o b s e r v e d at δ = 0.9 p p m o b ­ t a i n e d w i t h c a t i o n i c p o l y m e r s is p r a c t i c a l l y nonexistent.

It appears

at

l o w intensity w i t h l o w - m o l e c u l a r - w e i g h t oligomers, a n d c a n p r e s u m a b l y be

attributed

to

the

chain-end

structures P , P , a n d P 5 b

( i h

7 b

methyl

groups.

From

these

results,

m a y be assigned to c o m p o u n d s o b t a i n e d f r o m

spiroalkanes f o r this t y p e of p o l y m e r i z a t i o n ( E q u a t i o n

11).

152

POLYMERIZATION REACTIONS A N D N E W POLYMERS

It is possible to assume a p o l y m e r i z a t i o n m e c h a n i s m b a s e d o n that p r o p o s e d b y N a t t a a n d D a n u s s o ( E q u a t i o n 12)

(17):

Αχ R

Me

/

\

/

\

/

\

Polymerization of Spiropentane, Methylenecylobutane, and Bicyclopropyle.

O n e c o m p o u n d i n the spirane h y d r o c a r b o n series is e s p e c i a l l y

w o r t h y of a t t e n t i o n — n a m e l y s p i r o p e n t a n e ( M ) , w h i c h is a n isomer of s

b o t h isoprene a n d m e t h y l e n e c y c l o b u t a n e ( M ) ; see 9

E q u a t i o n 13.

From

a s t r u c t u r a l p o i n t of v i e w , if one considers that s p i r o p e n t a n e is the l i n e a r c o m b i n a t i o n of the ρ o r b i t a l a n d the sp o r b i t a l associated w i t h e a c h r i n g of spiropentane, f o u r e q u i v a l e n t sp

A

h y b r i d orbitals m a y b e f o r m e d .

U n d e r these c o n d i t i o n s , s p i r o p e n t a n e constitutes

a highly p-type un­

saturated entity that is thus especially suitable f o r p o l y m e r i z a t i o n . A s l i g h t l y different m o n o m e r has also b e e n s t u d i e d : b i c y c l o p r o p y l e , c o m p o s e d of t w o c y c l o p r o p a n e s l i n k e d b y a σ C - C b o n d (M ). 10

The

c o n j u g a t i o n b e t w e e n the t w o c y c l o p r o p a n e s of the m o n o m e r is s i m i l a r to that a p p e a r i n g b e t w e e n the b u t a d i e n e orbitals. CH

M

2

Afio

M

8

9

Syntheses of spiropentane, m e t h y l e n e c y c l o b u t a n e , a n d b i c y c l o p r o p y l e are d e s c r i b e d i n the a p p r o p r i a t e sections. POLYMERIZATION

tane (19)

OF SPIROPENTANE.

The

preparation

of

spiropen­

is i m p o r t a n t , since other c o m p o u n d s are f o r m e d ( f o r e x a m p l e ,

10.

Opening of Carbon

PINAZZI E TA L .

methylenecyclobutane, catalysis.

153

Rings

2 - m e t h y l - l - b u t e n e ) that are sensitive to c a t i o n i c

S p i r o p e n t a n e is s y n t h e s i z e d f r o m p e n t a e r y t h r i t y l t e t r a b r o m i d e ,

w h i c h itself is p r e p a r e d b y successive reactions of h y d r o b r o m i c a c i d a n d phosphorus tribromide o n commerical pentaerythritol.

Pentaerythrityl

t e t r a b r o m i d e is treated w i t h z i n c i n a l c o h o l i c m e d i u m i n presence o f s o d i u m e t h y l e n e d i a m i n e tetracetate ( E q u a t i o n 1 4 ) .

PBr

The

r e s i d u a l alkenes

(14)

3

are d e s t r o y e d b y b r o m i n e i n d i b r o m o m e t h a n e ,

w h i c h leaves p u r e spiropentane ( y i e l d 60%), t h e p u r i t y b e i n g c o n f i r m e d b y a single N M R p e a k at 0.72 p p m . CATIONIC

decreasing TiCl , 4

POLYMERIZATION

order

O F SPIROPENTANE.

These initiators,

of a c t i v i t y — A 1 C 1 , W C 1 , M o C l , 3

G

5

ZrCl , 4

in

BF -Et 0, 3

2

a n d S n C l — y i e l d p o l y m e r s f o r w h i c h t h e c o n v e r s i o n degree is 4

h i g h e r i n m e t h y l e n e c h l o r i d e t h a n i n n-hexane.

T h e temperature

is i m p o r t a n t , since n o r e a c t i o n o c c u r r e d b e l o w 2 0 ° C . c a r r i e d o u t at 8 0 ° C or, o c c a s i o n a l l y , at 1 0 0 ° C .

factor

A l l runs h a v e b e e n

T h e a m o u n t of i n i t i a t o r

r e q u i r e d is v e r y h i g h , t h e catalyst/monomer ratio b e i n g u p to 10%. T h e p o l y m e r s o b t a i n e d h a v e a n average m o l e c u l a r w e i g h t of a b o u t 1000,

t h e i r i n f r a r e d spectra h a v i n g b a n d s i d e n t i c a l to those d e s c r i b e d

for c y c l i z e d p o l y - l , 4 - i s o p r e n e s .

T h e peaks at 2960, 2925, a n d 2870 c m

c o r r e s p o n d to c y c l i c methylenes. 1700

cm

- 1

- 1

A w e a k b a n d l y i n g b e t w e e n 1650 a n d

, t h e intensity of w h i c h depends o n t h e c y c l i z a t i o n degree,

determines t h e p r o p o r t i o n of tetrasubstituted c y c l i c d o u b l e b o n d s ( P A n a b s o r p t i o n b a n d b e t w e e n 1450 a n d 1465 c m groups, a n d a p e a k at 1378 c m Attempts

- 1

1

8 A

is c a u s e d b y - C H

)· 2

characterizes t h e m e t h y l groups.

of c y c l i z a t i o n of h i g h - m o l e c u l a r - w e i g h t p o l y - c i 5 - l , 4 - i s o -

prene has a l r e a d y b e e n p u b l i s h e d (20-22).

T h e m a i n characteristics o f

these c o m p o u n d s are ( N M R ) n o s i g n a l f o r protons c a r r i e d b y a C ^ C d o u b l e b o n d , b u t a strong s i g n a l at δ = 0.9 p p m c o r r e s p o n d i n g t o protons f r o m m e t h y l groups o n saturated carbons, a n d a massive p e a k b e t w e e n

-

154

POLYMERIZATION REACTIONS A N D N E W POLYMERS

δ = 1.1 a n d δ = 1.7 p p m , w i t h m a x i m a at δ = 1.25 a n d 1.6 p p m , caused, respectively, b y r i n g protons a n d protons of m e t h y l groups o n d o u b l e b o n d s ( structure P

S a

)·

0=0

T h e r e l a t i v e size of these t w o m a x i m a is

a f u n c t i o n of the c y c l i z a t i o n degree, the p e a k at δ = 1.6 p p m b e c o m i n g s m a l l e r as the n u m b e r of rings increases.

H o w e v e r , it is d i f f i c u l t to

d e t e r m i n e this n u m b e r exactly. Cyclopolymers

of s p i r o p e n t a n e

those of c y c l o p o l y i s o p r e n e s .

have

the

same characteristics

as

W e c o n c l u d e they h a v e s i m i l a r structures

( P ) a n d ( P b ) i n E q u a t i o n 15. 8 a

8

8b

T h e m e c h a n i s m p r o p o s e d i n v o l v e s the f o r m a t i o n of a c o m p l e x ( 15i, E q u a t i o n 15a)

b e t w e e n the c a t i o n i c i n i t i a t o r a n d the h y d r o c a r b o n r i n g ,

f o l l o w e d b y its t r a n s f o r m a t i o n into a c a r b o c a t i o n ( 1 5 ) 2

s p i r o p e n t y l i u m i o n p r o p o s e d b y F a n ta ( 2 3 ) . ture ( 1 5 ) 3

rearranges

s i m i l a r to the

T h e i n t e r m e d i a t e struc­

b y c y c l i z a t i o n because of the presence of L e w i s

a c i d a n d the rather h i g h r e a c t i o n t e m p e r a t u r e .

1X1 -

E^^

Φ : "A

φ

A-

CH 15

2

2

15i

^/cyclization (15a)

15 POLYMERIZATION

OF

SPIROPENTANE

BY

3

METAL-HALIDE

COMPLEXES.

Heterogeneous-phase polymerization w i t h t r i a l k y l a l u m i n u m metal-halide

10.

155

Opening of Carbon Rings

PINAZZI E T A L .

complexes has also b e e n s t u d i e d , u s i n g n-hexane as solvent at t e m p e r a tures b e t w e e n 2 0 ° a n d 1 0 0 ° C ( t h e r e is n o r e a c t i o n b e l o w 2 0 ° C ) . catalysts

These

were used: T i C l / R A l , W C 1 / R A 1 , S n C l / R A l , a n d V O C l / 4

3

6

R A 1 , where R = E t , i - B u , or C I .

3

4

3

3

A s before, the p o l y m e r s o b t a i n e d a r e

3

s o l u b l e i n h y d r o c a r b o n s a n d h a l o g e n a t e d solvents except those p r o d u c e d b y t h e r e a c t i o n w i t h t h e S n C l / R A l c o u p l e , w h i c h gives i n s o l u b l e p r o d 4

ucts

with

3

c o n v e r s i o n degrees of about

weights were determined b y osmometry.

70%. T h e average

molecular

T h e y v a r y b e t w e e n 1000 a n d

5000, d e p e n d i n g o n t h e nature a n d a m o u n t of catalyst a n d temperature. A s t r u c t u r a l s t u d y confirms c y c l o p o l y m e r i z a t i o n .

I n f r a r e d b a n d s are

o b t a i n e d at 2960, 2925, a n d 2870 c m " , as w i t h p o l y m e r s o b t a i n e d b y 1

L e w i s acids.

T h e difference b e t w e e n this case a n d t h e p r e v i o u s o n e lies

i n t h e existence of a s h o u l d e r of v a r y i n g intensity o n t h e m e t h y l b a n d between

1360 a n d 1370 c m

( t h e m a i n p e a k is at 1380 c m " ) .

1

This

1

s p l i t t i n g corresponds to t h e presence of g e m - d i m e t h y l groups, t h e n u m b e r of w h i c h varies inversely w i t h t h e n u m b e r of consecutive f u s e d rings (structure P

8 B

).

It is i m p o s s i b l e to differentiate b y N M R b e t w e e n c y -

c l o p o l y - l , 4 - i s o p r e n e s a n d t h e 3,4 v a r i e t y , since t h e signals o b t a i n e d i n b o t h cases are i d e n t i c a l . In P

8 A

;

This

s u m m a r y , c a t i o n i c p o l y m e r i z a t i o n gives p o l y m e r s of structure

Z i e g l e r - N a t t a complexes study

gives

further

m a i n l y l e a d to b l o c k s

evidence

molecular-weight polyisoprenes.

of structure P

f o r c y c l i z a t i o n reactions

8

B

.

of h i g h -

T h i s p o i n t of v i e w has b e e n c o n f i r m e d

b y t h e s t u d y of t h e c y c l i z a t i o n of m o d e l p o l y i s o p r e n e molecules

with

t w o , three, or f o u r m o n o m e r units t o w a r d t h e catalysts able to i n i t i a t e s u c h a reaction

(24).

POLYMERIZATION

OF METHYLENECYCLOBUTANE .

M ethylenecyclobu-

tane w a s s y n t h e s i z e d b y r e a c t i o n of a Z n - C u c o u p l e o n p e n t a e r y t r i t y l tetrabromide

(Equation 16).

T h e y i e l d of t h e synthesis is a b o u t 65%

(9). CH

;

(16)

M

9

CATIONIC

POLYMERIZATION

OF METHYLENECYCLOBUTANE.

Attempts

w e r e m a d e to d i s c o v e r catalyst systems able to attack m e t h y l e n e c y c l o b u tane, a n d tests w e r e c a r r i e d o u t o n different classes of catalysts. was

n o detectable reaction

w h e n u s i n g either

a n i o n i c catalysts s u c h as s o d i u m n a p h t h a l e n e .

There

benzoyl peroxide, or

H o w e v e r , interesting re-

156

POLYMERIZATION REACTIONS A N DN E W POLYMERS

suits w e r e o b t a i n e d w i t h L e w i s acids, Z i e g l e r - N a t t a catalysts, a n d c o m plexes s u c h as t r a n s i t i o n - m e t a l a c e t y l

acetonates/alkylaluminum.

I n i o n i c p o l y m e r i z a t i o n , E q u a t i o n 17, it c a n be assumed that there is a first stage c o m p r i s i n g f o r m a t i o n of a n a l k y l b i c y c l o b u t o n i u m i o n , v e r y s i m i l a r to the c y c l o p r o p y l c a r b i n y l c a t i o n s t u d i e d b y R o b e r t s a n d M a z u r (25).

T h e u n u s u a l a l k y l b i c y c l o b u t o n i u m i o n is c o n s i d e r e d as a resonant

h y b r i d of p y r a m i d a l structure that interconverts at different rates.

CH

The

(17)

1 2

CH

3

9d

10.

Opening of Carbon

PINAZZI E T A L .

p o s i t i v e charge

157

Rings

derives f r o m r e l o c a l i z a t i o n of the π o r b i t a l , a n d

the

unstable c y c l o b u t y l i u m i o n rearranges to a n u n u s u a l i o n b y d e r e a l i z a ­ t i o n — f o r e x a m p l e , of the 3-4 covalence d o u b l e t b e t w e e n carbons 1-3-4. T h e substituent m a y s t a b i l i z e a resonant f o r m , thus f a v o r i n g p r o d u c t s derived

from

this f o r m .

Generally speaking, during polymerization,

r e l o c a l i z a t i o n of the electrons of the a l k y l b i c y c l o b u t o n i u m i o n c a n o c c u r b y three different processes.

I n r e l o c a l i z i n g , the charges g i v e , as possi­

b l e structures, P , Peb, a n d P . 9 a

ture P

9 b

I n the presence of a c i d catalysts, struc­

9 c

m a y i s o m e r i z e to structure P , w h e r e the d o u b l e b o n d s b e c o m e 9 d

trisubstituted. F i n a l l y , i t has b e e n p r o v e d that structure P easily to s t r u c t u r e P With

9 e

9 d

could cyclize quite

because of the a h y d r o g e n s f r o m the d o u b l e b o n d .

a l u m i n u m - c h l o r i d e catalysts,

the

p o l y m e r structure

is

80%

c y c l o b u t a n e units a n d a b o u t 5% c y c l o p r o p a n e units, the r e m a i n d e r b e i n g polyene units. pane

W i t h stannic c h l o r i d e , w e d o not observe a n y c y c l o p r o ­

u n i t s ; the p o l y m e r consists

m a i n l y of c y c l o b u t a n e units

T h e presence

of m e t h y l groups o n c y c l o h e x a n e shows that the

units

partially isomerized

possess

and

cyclized polyene

(75%). other

structures.

W h e n u s i n g t i t a n i u m c h l o r i d e or e t h y l a l u m i n u m c h l o r i d e w i t h traces of

water

as

cocatalyst,

the

p o l y m e r consists

m a i n l y of

u n i t s — t h a t is, 60%, the d e m a i n d e r b e i n g c y c l i z e d ; see POLYMERIZATION OF METHYLENECYCLOBUTANE BY

COMPLEXES.

cyclobutane

E q u a t i o n 17. TRANSITION-METAL

Various transition metal halides were used: T i C l , 4

W C l o , V C 1 , etc., 3

SnCl , 4

c o m p l e x e d w i t h o r g a n o m e t a l l i c c o m p o u n d s s u c h as

E t A l , E t A l C l , (wo-Bu)sAl, and B u S n H . 3

2

3

I n the presence of E t A l / T i C l , p o l y m e r i z a t i o n of m e t h y l e n e c y c l o 3

4

b u t a n e gives a p o l y m e r h a v i n g exomethylene units ( P b ) 9

representing

a b o u t 40% of the structure, 60% b e i n g p a r t i a l l y c y c l i z e d . W i t h E t A l C l / T i C l , the p o l y m e r structures are different, d e p e n d i n g 2

4

o n the r e a c t i o n t e m p e r a t u r e .

A t l o w temperatures,

m i x t u r e of structures P , P b, Pec, a n d P . 9 a

veals the presence of P cm .

9 a

9

9 d

structures b y v i b r a t i o n s at 920 c m

T h e h o m o a l l y l i c structure Pç

- 1

b a n d at 890 c m . - 1

the p o l y m e r is a

I n f r a r e d s p e c t r o g r a p h y re­

)b

- 1

and

T h i s p o l y e n e structure is not alone, since

character-

istic absorptions of t r i s u b s t i t u t e d d o u b l e b o n d s P , R R C = C H R , 9 d

v i s i b l e w i t h shoulders at 930

1240

is d e m o n s t r a t e d b y a n a b s o r p t i o n

a n d 835-840 c m

- 1

1

2

3

are

f o r the trans a n d cis

forms, r e s p e c t i v e l y . N M R spectra s h o w a massive p e a k at 8 = 4 . 8 p p m , characteristic of structure P . 9 d

The P

9 b

A t 8 = 5.2 p p m , a slight s i g n a l indicates structure P . 9 d

u n i t c a n b e c o m e p a r t i a l l y c y c l i z e d to g i v e structure P . S e

When

the p o l y m e r is p r e p a r e d at l o w temperature, its b r o m i n e i n d e x is a b o u t 54%, w h i c h corresponds to a m o n o c y c l i z e d structure P . 9 e

erization temperature

increases,

A s the p o l y m -

the intensity of the characteristic s i g -

158

POLYMERIZATION REACTIONS A N D N E W POLYMERS

nal

of m e t h y l groups o n saturated c a r b o n atoms goes u p , a n d that of

a protons f r o m the d o u b l e b o n d s d i m i n i s h e s i n the same p r o p o r t i o n . T h e p e a k at 8 = 1.5 p p m becomes the most i m p o r t a n t ( c y c l o h e x a n e p r o tons).

T h e s a t u r a t e d - c a r b o n m e t h y l p e a k at 8 = 0.9 p p m , v i r t u a l l y n o n -

existent for l o w - t e m p e r a t u r e p o l y m e r s , increases i n size. tion temperature

increases,

As polymeriza-

the c y c l i z a t i o n degree increases, w h i l e t h e

p r o p o r t i o n of c a r b o n - c a r b o n d o u b l e b o n d s decreases ( E q u a t i o n Various

acetylacetonates

have

been

17).

used w i t h d i e t h y l a l u m i n u m

c h l o r i d e as catalyst f o r the p o l y m e r i z a t i o n of m e t h y l e n e c y c l o b u t a n e . this case, the N M R spectra of the p o l y m e r s are v e r y s i m p l e .

In

Between

8 = 4 . 6 a n d 4.8 p p m lies a singlet c o r r e s p o n d i n g to the resonance v i n y l i d e n e protons.

of

B e t w e e n 8 = 1.85 a n d 2.10 p p m , a s i g n a l reveals the

protons of a m e t h y l e n e groups f r o m a d o u b l e b o n d , a n d at 8 = 1.25 p p m , a p e a k corresponds to protons of m e t h y l e n i c groups. shows no a b s o r p t i o n at 920 presence

of

a

cyclobutane

cm

1

a n d 1240

structure.

stretching vibrations.

The

structure

CH —CRiR 2

a n d 1640

A strong a b s o r p t i o n at 1450

sponds to s t r e t c h i n g v i b r a t i o n s of the C - H bonds of the groups. At

790

T h e a b s o r p t i o n of m e t h y l groups at 1370 c m c m , the C H 1

2

the

- 1

i n d i c a t e d b y v i b r a t i o n of the C - H b o n d s at 890 C=C

T h e IR spectrum

c m , w h i c h excludes cm

cm

is

2

for

- 1

corre-

- 1

methylene

is v e r y w e a k .

- 1

r o c k i n g v i b r a t i o n becomes apparent, thus c o n -

f i r m i n g the succession of three - C H - groups. 2

of c y c l o p r o p a n e structure appears.

N o characteristic s i g n a l

So it m a y b e c o n c l u d e d that p o l y m -

e r i z a t i o n b y this t y p e of c o m p l e x leads to the f o r m a t i o n of a p u r e " i s o p o l y i s o p r e n e " f o r m i n w h i c h the c a r b o n - c a r b o n d o u b l e b o n d is i n the exo p o s i t i o n w i t h respect to the c h a i n . Under

a

vanadium

triacetylacetonate

organoaluminum

catalyst

( C H C O C H = C O - C H ) 3 V - E t A l C l , m e t h y l e n e c y c l o b u t a n e gives a p o l y 3

3

2

m e r i n w h i c h the i s o p o l y i s o p r e n e structure ( P b ) is p r e d o m i n a n t — t h a t is, 9

85 to 95%.

H o w e v e r , N M R spectra s h o w characteristic signals of c y c l o -

p r o p a n e structures b e t w e e n 0 a n d 0.2 p p m . of 5 to 15% of this t y p e of structure.

Integration give a proportion

T h i s is c o n f i r m e d b y i n f r a r e d

b a n d s at 3080 a n d 1015 c m " . 1

T e r n a r y catalysts, s u c h as E t A l C l / T i C l / E t N or E t A l / T i C l / P h P 2

have been used.

4

3

3

nent of the ternary catalyst, p o l y m e r s of P , Pgd, a n d P 9 b

obtained.

4

3

A c c o r d i n g to the v a r i o u s p r o p o r t i o n s of e a c h c o m p o 9 e

structures are

H o w e v e r , i n some cases, especially w h e n the ratio P h P / 3

T i C l = 1, m e t h y l e n e c y c l o b u t a n e gives a p u r e a n d l i n e a r " i s o p o l y i s o p r e n e " 4

structure

(P ), 9 b

i n w h i c h c y c l i z e d t y p e structures

and cyclopropanic

groups are e x c l u d e d . POLYMERIZATION

OF BICYCLOPROPYLE.

Bicyclopropyle

has

already

been synthesized i n small yields f r o m butadiene w i t h a methylene iodide and

a z i n c - c o p p e r c o u p l e (26,

27),

a n d b y r e d u c t i o n of 2,2,2',2'-tetra-

10.

Opening of Carbon

PINAZZI E T A L .

h a l o b i c y c l o p r o p y l e (28,

29).

159

Rings

B i c y c l o p r o p y l e also has b e e n o b t a i n e d

via

a n e w route f r o m b u t a d i e n e b y successive carbenations a n d r e d u c t i o n s . The

dichlorocarbene

a d d e d to b u t a d i e n e

or v i n y l c y c l o p r o p a n e is

ob-

t a i n e d b y r e a c t i o n of a strong base ( s o d i u m t e r a m y l a t e ) w i t h c h l o r o f o r m , a n d r e d u c i n g the g e m - d i c h l o r o c y c l o p r o p y l b y a s o d i u m - h y d r a t e d m e t h a n o l system.

E q u a t i o n 18 depicts the synthesis.

T h e overall yield

of the synthesis f r o m b u t a d i e n e is a b o u t 20%.

ci CH //

CH

CC1

C l \ - _

\ /

2

CH

2

CI

C l - V ^

2

Na/CH OH

\7

3

CH

2

2

CC1

(18)

2

Na/CH OH 3

Mi, Electron

d i f f r a c t i o n studies

have

shown

(30)

that, i n its

vapor

phase, the b i c y c l o p r o p y l e m o l e c u l e possesses t w o i s o m e r i c

conformations:

a n o n r i g i d s-trans f o r m ( A ) a n d a n o n r i g i d left f o r m ( B )

(Equation

19)

a b l e to oscillate respectively f r o m ± 8 0 ° to ± 18° a r o u n d a n e q u i l i b r i u m position.

B We

have

c o n f i r m e d this p o i n t of v i e w b y testing

f r o m i n its l i q u i d p h a s e b y N M R .

bicyclopropyle

T h e existence of the t w o

conformers

160

POLYMERIZATION REACTIONS A N D N E W POLYMERS

is c o n f i r m e d b y a n i m p o r t a n t s p l i t t i n g of the characteristic signals of t h e f o u r h y d r o g e n s H„ (8 = (8

- 0 . 1 6 to 0.13 p p m ) ; t h e f o u r h y d r o g e n s H

= 0.17 to 0.49 p p m ) ; a n d the f o u r h y d r o g e n s H

c

f t

(8 = 0.57 to 0.95

ppm). W i t h s u i t a b l e initiators, the t w o conformers m a y y i e l d p o l y m e r s of different structures.

T h e existence of a p s e u d o c o n j u g a t i o n b e t w e e n t h e

t w o c y c l o p r o p a n e s , w h i c h m a y b e c o m p a r e d w i t h those of the b u t a d i e n e orbitals, t h e o r e t i c a l l y favors a p o l y m e r i z a t i o n b y s i m u l t a n e o u s o p e n i n g of t h e t w o c o n j u g a t e d orbitals. CATIONIC

POLYMERIZATION

OF BICYCLOPROPYLE.

Polymerization

of

b i c y c l o p r o p y l e b y v a r i o u s L e w i s acids w a s c a r r i e d o u t i n m e t h y l e n e c h l o r i d e w i t h a constant c a t a l y s t / m o n o m e r ratio to b r i n g o u t t h e effects of t h e other p a r a m e t e r s — n a m e l y , A1C1 ), 3

temperature

hours).

t h e n a t u r e of t h e catalyst

( - 7 8 ° to 1 2 0 ° C ) ,

(SnCl 4

a n d r e a c t i o n t i m e ( 3 t o 24

T h e h i g h e s t c o n v e r s i o n (85%) w a s o b t a i n e d at a t e m p e r a t u r e

b e t w e e n 7 0 ° a n d 80 ° C , w i t h a l u m i n u m c h l o r i d e as i n i t i a t o r .

Infrared

spectroscopy o f t h e p o l y m e r s o b t a i n e d shows n o characteristic s i g n a l f o r c y c l o p r o p a n e groups at 860, 1020, 1040, a n d 3080 c m , b u t gives a w e a k 1

broad band between tetra-substituted

1620 a n d 1700 c m , i n d i c a t i n g t h e presence of 1

C = C bonds.

N M R indicates

the existence

of t w o

m e t h y l s (signals at 8 = 0.90 p p m ) , three methylenes, a n d a t e r t i a r y h y d r o g e n (8 = 1.22 to 1.27 p p m ) situated i n the a p o s i t i o n f r o m a s a t u r a t e d carbon.

I t also indicates the presence of t w o methylenes (8 = 1.80 p p m )

a n d a m e t h y l (8 = 1.54 to 1.60 p p m ) s i t u a t e d i n t h e a p o s i t i o n f r o m tetrasubstituted d o u b l e b o n d s . T h e s e results s h o w that p o l y m e r i z a t i o n occurs b y o p e n i n g o f t h e t w o c y c l o p r o p y l groups, a n d the existence m o n o m e r units suggests a c y c l i z a t i o n r e a c t i o n .

of a C = C b o n d f o r t w o T h e s e l e a d to a p o l y m e r

structure c h a r a c t e r i z e d b y s u b s t i t u t e d cyclohexene groups i n t h e c h a i n . T w o i s o m e r i c structures agree w i t h these assignments Equation 20).

Structure ( P

1 0 a

(Pi

0 a

a n d P b of 10

) is the most l i k e l y , b e i n g s i m i l a r to those

o b t a i n e d b y i n t r a m o l e c u l a r c y c l i z a t i o n of p o l y - l , 4 - i s o p r e n e i n presence of Et AlCl-H 0. 2

2

CH

3

C H

3

10.

Opening of Carbon

PINAZZI E T A L .

161

Rings

O s m o m e t r i c d e t e r m i n a t i o n of m o l e c u l a r w e i g h t s was not p o s s i b l e because of the l o w s o l u b i l i t y of the p o l y m e r i n solvents at r o o m t e m p e r a ­ ture.

H o w e v e r , N M R spectra c o u l d b e o b t a i n e d b y s w e l l i n g the p o l y ­

mer i n carbon tetrachloride. POLYMERIZATION

OF BICYCLOPROPYLE

BY

TRANSITION

METAL

COM­

P L E X E S . Heterogeneous-phase p o l y m e r i z a t i o n of b i c y c l o p r o p y l e w i t h Z i e g ­ l e r - N a t t a catalysts was c a r r i e d out i n n-hexane b e t w e e n —30° a n d 1 2 0 ° C over 24 hours.

T h e s e systems, i n d e c r e a s i n g o r d e r of r e a c t i v i t y g i v e

p o l y m e r s h a v i n g spectral characteristic s i m i l a r to those of p o l y m e r s o b ­ tained b y cationic initiation: S n C l / E t A l C l , S n C l / E t A l C l , S n C l / E t A l , 4

TiCl /Et AlCl, WCl /Et Al. 4

2

G

2

4

2

4

3

T h e same structures of cyclohexene m o n o ­

3

m e r units separated b y three methylenes i n c h a i n are p r o p o s e d

(struc­

tures Pioa a n d P b of E q u a t i o n 2 0 ) . 10

B y contrast, w e c o u l d give e v i d e n c e f o r different structures w h e n the T i C l - E t A l c o m p l e x is u s e d ( T i / A l = l ) . 4

addition

I n f r a r e d spectra s h o w , i n

3

to the

peaks

already observed i n previous polymerizations,

a b s o r p t i o n bands at 860, 1020, 1040, 1780, a n d 3080 c m , 1

characteristic

of c y c l o p r o p a n i c groups, a n d b a n d s at 770 a n d 780 c m , w h i c h c a n b e 1

a t t r i b u t e d to b i m e t h y l e n i c b l o c k s - C H - C H 2

results.

N M R confirms these

2

T h e c y c l o p r o p a n e protons a p p e a r at δ = 0 . 0 2 a n d 0.44 p p m , a n d

m e t h y l e n i c h y d r o g e n s of a l i n e a r c h a i n are c h a r a c t e r i z e d b y a s i g n a l at δ = 1.27 p p m .

T h e s e s p e c t r o g r a p h i c d a t a a n d the s i m i l a r i t i e s w i t h those

of p o l y v i n y l c y c l o p r o p a n e (31)

suggest that the c h a i n structure is c o m ­

p o s e d of units of u n d e s c r i b e d l i n e a r structure consisting of m e t h y l e n e groups i n the m a i n c h a i n of c y c l o p r o p a n e groups i n side c h a i n ( structure Pioc).

A s t u d y of this t y p e of p o l y m e r i z a t i o n shows that over a w i d e

r a n g e of r e a c t i o n temperatures ( 2 0 ° to 1 2 0 ° C ) , the l i n e a r f o r m p r e d o m i ­ nates see

( f r o m 55 to 70%),

40 to 30% b e i n g c y c l i z e d ( P

1 0 a

, Pmb, P i o c ) ;

E q u a t i o n 20. C a t i o n i c i n i t i a t i o n thus opens the t w o c y c l o p r o p a n e structures

to

g i v e p o l y m e r s i n w h i c h the t r i m e t h y l c y c l o h e x e n e rings are separated b y three methylenes

i n the c h a i n .

W i t h T i C l - E t A l , the p o l y m e r i z a t i o n 4

3

process is different, a n d the r e a c t i o n i n v o l v e s the o p e n i n g of one of the m o n o m e r .

The

p o l y m e r o b t a i n e d has

ring

a m o l e c u l a r w e i g h t of

a b o u t 5000, a n d consists of b l o c k s i d e n t i c a l to the f o r e g o i n g structures (P

1 0 a

a n d Piob) a n d of b l o c k s f o r m e d of m o n o m e r units w i t h p e n d a n t

c y c l o p r o p a n e groups ( P

1 0 c

)·

T h e results o b t a i n e d w i t h b i c y c l o p r o p y l e are q u i t e different f r o m those o b t a i n e d w i t h spiropentane, w h i c h , w h a t e v e r the t y p e of catalyst used, y i e l d s c y c l i z e d b l o c k s s i m i l a r to those o b t a i n e d w i t h p o l y - 1 , 4 - or 3,4-isoprene.

162

POLYMERIZATION REACTIONS A N D N E W POLYMERS

Polymerization The

of gem-Dihalocyclopropanic

gem-dihalocyclopropane

Systems

t y p e of structure,

considered highly

stable, is a t t a c k e d b y c e r t a i n e l e c t r o p h i l i c reagents or s i m p l y b y h e a t i n g , and

rearranges

by ring opening.

T h u s , w i t h L e w i s - a c i d catalysts,

the

d i h a l o c y c l o p r o p a n e d e r i v a t i v e opens w i t h f o r m a t i o n of a h a l o a l l y l i c carb o c a t i o n (32)

w h i c h , i n presence of a n u c l e o p h i l i c i o n , gives either a

h a l o a l l y l i c d e r i v a t i v e or a 1,3-diene. P y r o l y s i s of d i h a l o c y c l o p r o p a n e s was s t u d i e d a l o n g w i t h the effects of e l e c t r o p h i l i c reagents, a n d confirms the f o r e g o i n g results (33-37).

In

m a n y cases, those authors o b s e r v e d that p o l y m e r i c residues, i n a d d i t i o n to a l l y l i c a n d d i e n e - t y p e p r o d u c t s , w e r e present at the e n d of p y r o l y s i s . T h e f o r m a t i o n of these p o l y m e r s confirms the hypothesis that the d i halocyclopropanes

are

monomers

that

can be

p o l y m e r i z e d either

by

c a t i o n i c processes or b y the a c t i o n of t r a n s i t i o n - m e t a l c o m p l e x catalysts.

(21)

X

X'

1, l - d i m e t h y l - 2 , 2 - d i c h l o r o c y c l o p r o p a n e ( M u ) ( R i = R2 = C H ; R3 = H ; X = X ' = CI) 3

1,1,3-trimethyl-2,2-dichlorocyclopropane (Ri

= R

2

= R

3

(M ) i 2

= C H ; X = X ' = CI) 3

1, l - d i m e t h y l - 2 - c h l o r o - 2 - b r o m o c y c l o p r o p a n e (R

1 =

R

2

= CH ; R 3

3

(M13)

= H ; X = Cl;X' =

Br) These

Polymerization of Alkyl gem-Dihalocyclopropanes. mers ( E q u a t i o n 21)

responding ethylenic compounds—that and

mono-

are p r e p a r e d b y a d d i n g dihalocarbenes to the cor-

2-methyl-2-butene

for M . 12

is, isobutene for M

X1

and M i , 3

T h e carbenes are p r o d u c e d b y

basic

a e l i m i n a t i o n of h a l o f o r m s i n the presence of a strong base s u c h s o d i u m teramylate esters.

(15),

or b y basic

a e l i m i n a t i o n of

I n f r a r e d d a t a of these c o m p o u n d s s h o w a b s o r p t i o n b a n d s

3040 c m a n d 1020 c m

1

for c y c l o p r o p y l groups.

as

trichloroacetic at

N M R gives signals at

1.2 a n d 1.3 p p m . M 13

were

treated w i t h L è w i s - a c i d catalysts s u c h as A1C1 , T i C l , a n d S n C l .

CATIONIC

POLYMERIZATION.

Monomers

M

The

3

n

,

M

1 2

, and

4

p o l y m e r s o b t a i n e d give a b s o r p t i o n b a n d s ( 1650 a n d 850 c m

4

- 1

) and N M R

10.

Opening of Carbon

PINAZZI E T A L .

163

Rings

peaks (1.1 a n d 5.5 p p m ) , i n d i c a t i n g the presence of a c h l o r i n a t e d d o u b l e b o n d a n d m e t h y l g r o u p protons o n a saturated c a r b o n a t o m , r e s p e c t i v e l y . T h e i n f r a r e d b a n d s c o r r e s p o n d i n g to c y c l o p r o p a n e have c o m p l e t e l y dis­ appeared.

M i c r o a n a l y t i c a l determinations

CI

give an empirical formula

CI

Mu

CH

3

Cl

H

CH




Φ

Η

3

Η

CH

CH

Cl

H

Cl

3

Η

3

Η

3

(22)

Cl

CH

3

Φ

H

CH

CH

3

1 H

Cl

CH

CH Pu

3

3

3

164

POLYMERIZATION REACTIONS A N D N E W POLYMERS

that indicates

e l i m i n a t i o n of one h y d r o h a l i d e m o l e c u l e p e r

u n i t of the c h a i n .

monomer

T h e s e results suggest the o p e n i n g of a t h r e e - c a r b o n

r i n g a n d a d e h y d r o h a l o g e n a t i o n ' s o c c u r r i n g d u r i n g the p o l y m e r i z a t i o n . T h e f o l l o w i n g m e c h a n i s m m a y be p r o p o s e d ( i n the case of

M ): lt

attack b y the c a t i o n i c i n i t i a t o r i n v o l v e s the t r i c e n t r i c r i n g o p e n i n g . c a r b o c a t i o n f o r m e d m a y b e d r a w n i n several resonant f o r m s .

The

Attack on

a f u r t h e r m o n o m e r m o l e c u l e gives a p o l y m e r of structure P n , h a v i n g a chlorinated double bond and a gem-dialkyl group.

T h i s s t r u c t u r e is i n

agreement w i t h the e x p e r i m e n t a l results ( E q u a t i o n 2 2 ) . H o w e v e r , the r e a c t i o n m a y d e v e l o p i n other w a y s .

F o r example,

d e p r o t o n a t i o n of a m e t h y l g r o u p i n the c h l o r o a l l y l i u m g r o u p c a n y i e l d 2-methyl-3-chloro-l,3-butadiene,

w h i c h , u n d e r the e x p e r i m e n t a l c o n d i -

tions u s e d , c a n easily p o l y m e r i z e to g i v e several structures

(Equation

2 3 ) , d e p e n d i n g o n w h e t h e r p o l y m e r i z a t i o n is of the 1,2,3,4, or 1,4 t y p e . N M R

s p e c t r o g r a p h y makes it possible to e l i m i n a t e this e v e n t u a l i t y be-

cause of the absence of peaks c o r r e s p o n d i n g to protons of an a m e t h y l g r o u p f r o m the d o u b l e b o n d a n d m e t h y l e n e g r o u p i n the c h a i n .

R

X

3

Ri

L R P\\ ( R i — R2 P u (Ri = R The

2

=

(23)

2

CH ; R 3

= CH ; R

reaction temperature

3

= H j X = X ' = CI)

3

3

= H ; X = CI)

is q u i t e i m p o r t a n t .

A t 20 ° C , there is

p r a c t i c a l l y n o r e a c t i o n ; at 8 0 ° C , the degree of c o n v e r s i o n is b e t w e e n 15 a n d 20%. POLYMERIZATION BY TRANSITION-METAL

M

1 2

, and M

1

3

COMPLEX

have been polymerized by E t A l / T i C l 3

4

CATALYSTS.

catalysts

M

1U

between

5 0 ° a n d 8 0 ° C i n n-hexane, the r e a c t i o n times r a n g i n g f r o m a f e w hours to several d a y s .

T h e p o l y m e r s o b t a i n e d h a v e the same structure

those o b t a i n e d b y c a t i o n i c p o l y m e r i z a t i o n . p r o p o s e d i n the literature (38, 39),

as

B y analogy w i t h mechanisms

the structure s h o w n i n E q u a t i o n 24

m a y b e p r o p o s e d for the a c t i v e center. T h e f o r m a t i o n of H X i n a s t o i c h i o m e t r i c a m o u n t w i t h respect to the m o n o m e r p r o b a b l y i n v o l v e s the d i s a p p e a r a n c e of m a n y a c t i v e centers.

T h i s explains the r e l a t i v e l y large a m o u n t of catalyst r e q u i r e d f o r

p o l y m e r i z a t i o n to take p l a c e .

F u r t h e r m o r e , the p o l y m e r i z a t i o n degree

remains l o w , a n d the p o l y m e r s o b t a i n e d h a v e l o w m o l e c u l a r w e i g h t s (for

example,

1000

to 3 0 0 0 ) .

Temperature

is s t i l l a d e c i s i v e

factor.

10.

piNAZZi E T A L .

Opening of Carbon

CH

R

CH

3

CI

(24)

CI

Ti

A

CI

165

3

CI CI

Rings

CI

C o n v e r s i o n degrees b e c o m e a p p r e c i a b l e a b o v e 5 0 ° C .

I n a d d i t i o n , the

c o n v e r s i o n degree increases as the a m o u n t of catalyst increases. I n s u m m a r y , the p o l y m e r i z a b i l i t y of g e r a - d i h a l o c y c l o p r o p a n e s

de-

creases f r o m M u to M i , a n d becomes zero i n t h e case of 1,1,2,2-tetra2

methyl-3,3-dichlorocyclopropane,

w h i c h does not react i n the presence

of the p o l y m e r i z a t i o n catalysts u s e d .

T h e t y p e of s u b s t i t u t i o n of c y c l o -

p r o p a n e therefore seems to b e a n i m p o r t a n t factor. e r i z a t i o n i m p l i e s o p e n i n g of the t h r e e - c a r b o n genation of each u n i t . b y h i g h temperatures,

I n a l l cases, p o l y m -

ring

and

dehydrohalo-

P o l y m e r i z a t i o n of these c o m p o u n d s is f a v o r e d above 2 0 ° C ,

a n d catalyst

h i g h e r t h a n i n olefin p o l y m e r i z a t i o n s .

concentrations

much

T h e m o l e c u l a r w e i g h t s are

of

the o r d e r of 1000 to 3000, a n d the oligomers, s o l u b l e i n the u s u a l o r g a n i c solvents, are w h i t e p o w d e r s m e l t i n g a b o v e 1 5 0 ° C . Polymerization of Group.

Dihalocyclopropane with an Adjacent Phenyl

T h e m o n o m e r s s h o w n i n E q u a t i o n 25 are p r e p a r a t e d b y adding

X

V

H

u

(25)

H

M M

CI

(R = H ; X = H )

M

1

1

5

6

(R = C H ; X = H ) 3

(R = C H ; X = CI) 3

CI

2 - p h e n y l - l , 1-dichlorocyclopropane

(M ) i 4

(R = H ; X =

H)

l-phenyl-l-methyl-2,2-dichlorocyclopropane (R = C H ; X 3

=

(Mi ) 5

H)

l-p-chlorophenyl-l-methyl-2,2-dichlorocyclopropane (R = C H ; X = 3

CI)

(Mi ) 6

166

POLYMERIZATION REACTIONS A N D N E W POLYMERS

dichlorocarbenes

to styrene, α-methylstyrene, a n d p - c h l o r o - a - m e t h y l s t y -

rene. CATIONIC POLYMERIZATION.

pseudoconjugation mum

between

I n the

c o m p o u n d s of E q u a t i o n 25,

the

the p h e n y l a n d the c y c l o p r o p a n e is m a x i ­

w h e n the t w o rings are p e r p e n d i c u l a r (40).

P o l y m e r i z a t i o n , ca­

t i o n i c or b y t r a n s i t i o n - m e t a l c o m p l e x catalysts, indicates the p a r t i c i p a t i o n of the p h e n y l g r o u p . C a t i o n i c p o l y m e r i z a t i o n y i e l d s oligomers that h a v e a structure s i m i ­ lar to that of the p o l y m e r s p r e v i o u s l y d e s c r i b e d .

S p e c t r o g r a p h i c studies

and

m i c r o a n a l y t i c a l results i n d i c a t e t h e d i s a p p e a r a n c e of the three-car­

bon

r i n g a n d e l i m i n a t i o n of one m o l e c u l e of H C 1 p e r m o l e c u l e of m o n o ­

mer.

T h e s e results

agree w i t h a structure that w o u l d result f r o m a

p o l y m e r i z a t i o n m e c h a n i s m s i m i l a r to that p r o p o s e d i n the p r e v i o u s case. H o w e v e r , the presence of a n N M R p e a k (1.6 p p m ) indicates p a r t i c i p a t i o n of the p h e n y l g r o u p d u r i n g p o l y m e r i z a t i o n i n p a r a p o s i t i o n , g i v i n g the structure d e s c r i b e d i n E q u a t i o n 25. as w i t h m o n o m e r s M

6

W i t h the same r e a c t i o n c o n d i t i o n s

and M , monomer M 7

8

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

is s u b s t i t u t e d b y a c h l o r i n e a t o m ) does not g i v e any p o l y m e r . POLYMERIZATION

BY

ZIEGLER-NATTA

CATALYSTS.

Under

heteroge­

neous Z i e g l e r - N a t t a t y p e catalysis w i t h E t A l - T i C l , E t , A l - S n C l , E t A l C l 3

4

4

2

T i C l , E t o A l C l - S n C L , E t A l C l - S n C l , E t A l C l - T i C l , i - B u A l - T i C l , and 4

2

i-Bu Al-SnCl 3

4

4

4

3

4

i n hexane, the p o l y m e r s h a v e the same characteristics

those o b t a i n e d w i t h c a t i o n i c catalysts. z a t i o n parameters temperature,

2

as

T h e effects of v a r i o u s p o l y m e r i ­

w e r e s t u d i e d , ( c o n c e n t r a t i o n of catalyst, A l / M r a t i o ,

p o l y m e r i z a t i o n t i m e , etc.)

Temperature

is a factor

that

favors a n increase i n the c o n v e r s i o n degree, w i t h a m a x i m u m at 8 0 ° C . T h e polymers obtained from M

l4

are o n l y s l i g h t l y s o l u b l e i n c o m m o n

o r g a n i c solvents, whereas p o l y m e r s o b t a i n e d f r o m M i n the same solvents.

linkages that cannot h a p p e n i n the case of M of m e t h y l groups. tion

1

are h i g h l y s o l u b l e

5

T h i s difference m a y b e a t t r i b u t e d to i n t e r c h a i n 7

b e c a u s e of the presence

T h e m o l e c u l a r w e i g h t s are l o w ; M

n

~

2000 ( E q u a ­

26).

R

R

(26) Pu

R

H

Pl5

R

CH

3

10.

Opening of Carbon

PINAZZI E T A L .

Polymerization

Rings

167

2-Methyl-2-vinyl-l,l-dichlorocyclopropane.

of

case of v i n y l c y c l o p r o p a n e c o m p o u n d s is of p a r t i c u l a r interest

The

because

of the c o n j u g a t i o n b e t w e e n the c y c l o p r o p a n e a n d the C = C d o u b l e b o n d , a n d the a n a l o g y b e t w e e n these c o m p o u n d s a n d 1,3-dienes (41, 42).

The

p o l y m e r i z a t i o n of 2 - m e t h y l - 2 - v i n y l - 1 , 1 - d i c h l o r o c y c l o p r o p a n e

was

therefore s t u d i e d .

(M ) 17

T h i s m o n o m e r is p r e p a r e d b y a d d i n g d i c h l o r o c a r b e n e

to isoprene.

(27)

CH

3

CI

ci

M

CATIONIC

1

7

POLYMERIZATION.

Use

of

TiCl , 4

SnCl , 4

and

WC1

6

as

catalysts y i e l d s oligomers w i t h average m o l e c u l a r w e i g h t s of a b o u t 5000. T h e c o n v e r s i o n degree is a f u n c t i o n of temperature, the m a x i m u m b e i n g at 8 0 ° C .

A n a l y s i s indicates a n e m p i r i c a l f o r m u l a c o r r e s p o n d i n g to the

r e m o v a l of one m o l e c u l e of H C 1 p e r m o n o m e r u n i t , as i n the p r e v i o u s cases.

I n f r a r e d spectroscopy

the c y c l o p r o p a n e g r o u p . eliminated.

a n d N M R c o n f i r m the d i s a p p e a r a n c e

A 1,5-type of p o l y m e r i z a t i o n (43-46)

of

can be

O n the other h a n d , a 1 , 2 - p o l y m e r i z a t i o n of the d o u b l e b o n d

alone cannot b e a s s u m e d since the g e m - d i c h l o r o c y c l o p r o p y l g r o u p has completely

disappeared.

T h i s is p r o v e d b y spectroscopic

data.

p o l y m e r s o b t a i n e d g i v e i n f r a r e d a b s o r p t i o n b a n d s at 1615 c m cm , - 1

- 1

The

a n d 890

a n d N M R peaks at 0.95 a n d 1.2 p p m . In

fact, a c y c l o p r o p y l c a r b i n y l i o n is f o r m e d as the result of

attack b y the c a t i o n i c i n i t i a t o r . intermediate binyl ion.

the

T h i s c a r b o c a t i o n m a y rearrange, t h r o u g h

b i c y c l o b u t o n i u m ions, to g i v e c y c l o b u t y l i u m or a l l y l c a r T h e basic units o b t a i n e d f r o m s u c h rearrangements

structure that is either c y c l o b u t e n i c or a l l y l i c . tures of the p o l y m e r s are Pn

a

have a

T h e p r e d o m i n a n t struc-

a n d Pub of E q u a t i o n s 28 a n d 29.

POLYMERIZATION BY ZIEGLER-NATTA CATALYSTS.

Polymerization

by

t r a n s i t i o n - m e t a l c o m p l e x catalysts gives oligomers of the same structures as those o b t a i n e d c a t i o n i c a l l y , w i t h d i s t i n c t l y h i g h e r c o n v e r s i o n degrees (Equation

29).

168

P O L Y M E R I Z A T I O N

R E A C T I O N S

A N D

N E W

P O L Y M E R S

10.

Opening of Carbon

PINAZZI E T A L .

Rings

169

T h e r e a c t i v i t y of this v i n y l c y c l o p r o p a n e c o m p o u n d t o w a r d c a t i o n i c or Z i e g l e r - N a t t a initiators is greater t h a n that of p u r e l y type monomers.

cyclopropane-

T h i s stems f r o m the c o n j u g a t i o n of the t w o u n s a t u r a t e d

systems; the results o b t a i n e d agree w i t h w o r k c a r r i e d out o n the p o l y m ­ e r i z a t i o n of v i n y l c y c l o p r o p a n e itself. Polymerization of cyclenes ( M

1 8

to M

2

5

These

gem-Dihalobicyclo[n.l.O]alkanes.

mers are p r e p a r e d b y a d d i t i o n of d i c h l o r o c a r b e n e to the of E q u a t i o n 3 0 ) .

mono­

corresponding

T h e t r i c e n t r i c r i n g - o p e n i n g reac­

tions of the g e m - d i h a l o b i c y c l i c c o m p o u n d s has b e e n s t u d i e d b o t h b y u s i n g e l e c t r o p h i l i c reactants a n d b y p y r o l y s i s .

I n a l l cases, o p e n i n g of

the

t h r e e - c a r b o n r i n g is m a d e b y r u p t u r e of the b o n d c o m m o n to b o t h r i n g s .

η

CI

=

4

CI η

=

5

Mis

(R =

Η)

Μ

1 9

(R = C H )

Μ

2 0

3

(R =

Η)

(R = C H )

Μ

3

Ά

(30) η

=

6

Μ

(R =

Μ

(R = C H )

η

3

η

(CH ), 2

η

CATIONIC A1C1

3

=

7

POLYMERIZATIONS.

Η)

Μ

2 4

(R =

Μ

2 5

(R = C H )

Η) 3

Catalysts

s u c h as T i C l , 4

SnCl , 4

and

g i v e p o l y m e r s w h o s e spectroscopic d a t a s h o w N M R signals at 0.9,

1.6, a n d 2.1 p p m , c o r r e s p o n d i n g r e s p e c t i v e l y to m e t h y l protons o n satu­ rated

carbon

atom,

to

methylene

protons

α-methylene g r o u p f r o m C ^ C d o u b l e b o n d . η η η

= 3 = 4

Pis Pu

= 5

P20 P21 Ρ22

k

(CH ) 2

η

=

6

η

=

9

η

=

10

n

Ρ23

o n the

ring,

a n d to

(R (R (R (R (R (R

= = = = = =

Η) CH ) Η) CH ) H) CH ) 3

3

3

(R = H ) ρ

2 5

one

T h e i n t e g r a t i o n ratio gives

(R = C H ) 3

(31)

170

a

POLYMERIZATION REACTIONS A N D N E W POLYMERS

p r o p o r t i o n of o n e m e t h y l

group

per monomer

unit of polymer.

M i c r o a n a l y t i c a l results g i v e e v i d e n c e o f t h e loss o f o n e H C 1 m o l e c u l e per monomer unit.

A c c o r d i n g t o these results, t h e s t r u c t u r e o f this

p o l y m e r is as s h o w n i n E q u a t i o n 3 1 . T h e i m p o r t a n c e of t h e size o f t h e r i n g f u s e d t o t h e c y c l o p r o p a n e is d e m o n s t r a t e d b y systematic studies c a r r i e d o u t w i t h a great n u m b e r of i n i t i a t o r s .

I n p a r t i c u l a r , a l t h o u g h t h e size o f t h e r i n g does n o t a p p e a r

to affect t h e c o n v e r s i o n degree, i t seems that t h e m o l e c u l a r w e i g h t o f the p o l y m e r o b t a i n e d increases as r i n g size decreases. POLYMERIZATION

catalysts above.

BY ZIEGLER-NATTA

CATALYSTS.

The

Ziegler-Natta

h a v e b e e n u s e d w i t h t h e s a m e c o n d i t i o n s as those d e s c r i b e d P o l y m e r s o b t a i n e d u n d e r s u c h c o n d i t i o n s present t h e same struc­

tures as those o f p o l y m e r s o b t a i n e d b y c a t i o n i c p o l y m e r i z a t i o n . Polymerization [6.1.0]non-4-ene. non-4-ene

of Bicyclo[6.1.0]non-4-ene Bicyclo[6.1.0]non-4-ene

a n d 9,9-Dihalobicyclo-

a n d 9 , 9 - d i h a l o b i c y c l o [6.1.0]-

( Λ ί , E q u a t i o n 3 2 ) h a v e t h e s p e c i a l feature o f h a v i n g t w o 26

u n s a t u r a t e d sites that c a n react separately o r s i m u l t a n e o u s l y — t h a t is, o n e C = C

double b o n d and a cyclopropane (47-50);

9,9-dihalobicyclo[6.1.0]-

non-4-ene was s y n t h e s i z e d b y a d d i n g d i h a l o c a r b e n e t o 1,5-cyclooctadiene ( y i e l d 56%).

R e d u c t i o n of t h e d i h a l o c y c l o p r o p a n e g r o u p w i t h a N a /

h y d r a t e d m e t h a n o l system y i e l d e d b i c y c l o [ 6 . 1 . 0 ] n o n - 4 - e n e

( y i e l d 85%).

I n t h e presence o f c a t i o n i c i n i t i a t o r s , these m o n o m e r s p o l y m e r i z e via P

2 6 B L

a t r a n s a n n u l a r m e c h a n i s m t o g i v e p o l y m e r s of structures P f o r t h e bicyclo[6.1.0]non-4-ene,

2 6 a

i and

a n d dihalo-9,9-bicyclo[6.1.0]non-4-

ene, r e s p e c t i v e l y ( E q u a t i o n 3 3 ) . I n t h e presence o f Z i e g l e r - N a t t a catalysts, t h e t w o sites p a r t i c i p a t e i n t h e r e a c t i o n , b u t t h e structures of t h e p o l y m e r s o b t a i n e d are s l i g h t l y different: P

2 6 a

2 and P b2, respectively. 2 6

H o w e v e r , i n presence o f W C l - E t A l C l 6

ture

( m o l a r r a t i o M / W = 800,

2

i n b e n z e n e at r o o m t e m p e r a ­

m o l a r r a t i o A l / W = 8 ) , 50% c o n v e r s i o n

p o l y m e r s h a v i n g m o l e c u l a r w e i g h t s b e t w e e n 2500 a n d 6500 w e r e o b ­ tained.

T h e N M R spectra of these p o l y m e r s s h o w some s i m i l a r i t y w i t h

those o f t h e m o n o m e r .

I n b o t h cases, t w o signals at δ = 5.35 p p m a n d

2.1 p p m i n d i c a t e that a d o u b l e b o n d is s i t u a t e d b e t w e e n t w o m e t h y l e n e g r o u p s : at 8 = 0.62 p p m a n d —0.26 p p m , t w o peaks a p p e a r c o r r e s p o n d ­ i n g to c y c l o p r o p a n e protons. b y methylene

T h e s i g n a l at 6 = 1.35 p p m c a n b e g i v e n

a protons f r o m t h e c y c l o p r o p a n e .

I n t h e case o f t h e

10.

Opening of Carbon

PINAZZI ET A L .

CH

Rings

171

3

(33)

CH

3

26b2

26bl

m o n o m e r , because of the effect of the r i n g , this p e a k is d i v i d e d i n t w o at 8 = 2 . 1

p p m a n d 1.30 p p m .

p o l y m e r spectra

suggest a

T h e s e results a n d the i n t e g r a t i o n of the

1,4-polybutadiene

type structure

Ρ α3, i n :26

w h i c h one o u t of t w o d o u b l e b o n d s is r e p l a c e d b y a c y c l o p r o p a n e g r o u p (Equation

34).

(34)

X

—

H

X

= CI, Br

P 6a3 2

PMW

172

POLYMERIZATION REACTIONS A N D N E W POLYMERS

I n f r a r e d spectroscopy confirms this hypothesis.

T h e cyclopropane

groups are c l e a r l y c h a r a c t e r i z e d b y peaks at 3070 c m a n d 1030 c m

- 1

, and

the 1,4-polybutadiene structure is v e r i f i e d b y bands at 1660, 1410, 1310, a n d 1080 c m " . 1

Polymerization

of 9,9-dichlorobicyclo[6.1.0]non-4-ene

gives

a 30%

c o n v e r s i o n p o l y m e r h a v i n g a m o l e c u l a r w e i g h t of 2000 ( c a t a l y s t : W C 1 6

E t A l C L ; s o l v e n t : benzene; m o l a r r a t i o M / W = 300, m o l a r r a t i o A l / W = 8 ) . T h e spectroscopic d a t a m a y b e c o m p a r e d w i t h those of the b i c y c l o [ 6 . 1 . 0 ] non-4-ene p o l y m e r s . and

T h e N M R spectra s h o w t w o peaks at δ = 5 . 4 5 p p m

2.2 p p m , i n d i c a t i n g the existence of a d o u b l e b o n d b e t w e e n t w o

m e t h y l e n e g r o u p s ; a peak at δ = 1.5 p p m m a y b e a t t r i b u t e d t o m e t h y l e n e a protons f r o m a g e m - d i h a l o c y c l o p r o p a n e

T h e tertiary

(51).

protons

c a r r i e d b y this g r o u p are c h a r a c t e r i z e d b y a s h o u l d e r at δ = 1.3 p p m . T h e s e results, together w i t h i n t e g r a t i o n of t h e spectra, suggest t h e exist­ ence of structure P b3 s i m i l a r to structure P 26

2Ga

3 i n E q u a t i o n 34.

F u r t h e r m o r e , m i c r o d e t e r m i n a t i o n s of c h l o r i n e ( C a l c d . , 37.12%; f o u n d , 35.26%)

a n d I R spectroscopy

groups at 3070 a n d 1030 c m

1

(characteristic

bands

for cyclopropane

a n d f o r C - C l at 805 c m " ) c o n f i r m these 1

conclusions. Polymerization

of b i c y c l o [ 6 . 1 . 0 ] n o n - 4 - e n e

[6.1.0]non-4-ene i n t h e presence of W C l - E t A l C l e

a n d 9,9-dichlorobicyclo 2

catalyst y i e l d s m a i n l y

p o l y m e r s of 1 , 4 - p o l y b u t a d i e n e - t y p e structures, w h o s e m o n o m e r units are rigorously

alternating, containing a double b o n d a n d a cyclopropane

g r o u p separated b y t w o m e t h y l e n e groups l i n k e d together. propanes,

w i t h o r w i t h o u t substituents,

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

T h e cyclo-

take v i r t u a l l y n o p a r t i n t h e

M o r e i n f o r m a t i o n has a l r e a d y b e e n p u b l i s h e d

(52-58).

Acknowledgment This work was done i n collaboration w i t h F . Clouet, G . Clouet, J . C . Soutif, a n d J . P . V i l l e t t e .

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10.

FINAZZI E T A L .

Opening of Carbon

Rings

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R E C E I V E D April 13, 1972.