JOURNAL OF POLYMER SCIENCE: Polymer Chemistry Edition VOL. 11, 2999-3004 (1973)

Alternating Copolymerization of Dienes with a-Olefins

JUNJI FURUIiAWA, SHIGENORI TSURUKI, and JITSUO KIJI, Department of Synthetic Chemistry, Kyoto University, Kyoto 606, J a p a n

synopsis

Alternating copolymerization of butadiene with several a-olefins and of isoprene with propylene were investigated by using a mixture of VO(Acac),, Et3A1, and Et2AlCl as catalyst. The alternating copolymerization ability of the olefins decreases in the order, propylene > 1-butene > 4-methyl-I-pentene > 3-methyl-1-butene. The study on the sequence of the copolymer of isoprene with propylene by ozonolysis reveals that the polymer chain is reasonably expressed by the sequence +CHz-CH=C(CH3)-CHz- CH(CH3)-CHz+,. NMR and infrared spectra indicate that the chain is terminated with propylene unit, forming a structure of =C(CH~)-CH~-C(CH~)==CHZ involving a vinylene group.

INTRODUCTION

The best catalyst for the alternating copolymerization of propylene with butadiene is prepared from organoaluminum and vanadium compounds. v 2

Essential features of the catalyst,3 the initiation r e a ~ t i o n , ~ and some pre- liminary exploratory studies5 on the copolymerization with olefins other than propylene have been recently reported. Until recently, however, alternating coordination of the monomers was proposed for the propagation me~hanism,~ but the regularity of the sequence remained obscure.

The present paper deals with the copolymerization of several a-olefins with butadiene and the alternating copolymerization of propylene with isoprene to elucidate the polymerization mechanism.

EXPERIMENTAL

Materials

Commercially available propylene, butadiene, isoprene, 1-butene, 3- methyl-1-butene, and 4-methyl-1-pentene were used after drying with 3A Molecular Sieves. Commercially available Et,3Al, EkAICI, and VO(Acac)z were used without further purification. Toluene was purified by drying over sodium metal and subsequently over calcium chloride, followed by distillation under an argon atmosphere.

2999

@ 1973 by John Wley & Sons, Inc.

3000 FURUKAWA, TSURUKI, KIJI

Polymerization Procedures and Measurements

The general polymerization procedure and the instrumental measure- ments were similar t o those previously r e p ~ r t e d . ~ The copolymer composi- tions were determined by the NMR study.

RESULTS AND DISCUSSION

General Survey of the Copolymerization

I n order to clarify the effect of the substituents of the a-olefins, a system- The results for the copolymers un- atic investigation was carried out.

fractionated are shown in Figure 1 and Table I.

I.l.rl.I.I 50 100

Mol % O O

DIENE IN MONOMER

Fig. 1. Copolymer composition curves: (0) butadiene-1-butene; (A) butadiene-4- methyl-1-butene; (a) butadiene-3-methyl-1-butene; (0) isoprene-propylene.

TABLE I Yields of Alternating Copolymers8

Olefin Diene Olefin in Concn, Concn, Yield, copolymer,

Type mmole/l. Type mmole/l. g % Propylene 75 Butadiene 60 3.57 50 1-Butene 80 Butadiene 20 1.87 51 4Methyl- 80 Butadiene 20 0.88 51

%Methyl- 80 Butadiene 20 0.75 41

Propylene 20 Isoprene 24 0.95 50

1-pentene

1-butene

a [Vo(A~ac)~] = 0.1 mmole/l., [Et3Al] = [EhAlCl] = 0.5 mmole/l.

4-Methyl-1-pentene entered into alternating copolymerization with buta- diene more facilely than 3-methyl-1-butene did. The yields of the alter- nating copolymers with butadiene decrease in the order, propylene > 1-

ALTERNATING COPOLYMERIZATION 3001

butene > 4-methyl-1-pentene > 3-methyl-l-butene, as shown in Table I. a-Olefins possessing a bulky group on the olefinic carbon atom give the corresponding alternating copolymer with butadiene only within a limited monomer ratio. These results show that a sterically bulky substituent on the olefinic carbon atom is unfavorable in the alternating copolymerization with butadiene, presumably in the coordination to vanadium. In the NMR spectra of all the 1 : 1 copolymers, the absorption at 7.96 T due to the butadiene-butadiene diad was negligibly small.

When isoprene was used instead of butadiene, the copolymerization ability of propylene was not altered, although the molecular weight was lower than that of the corresponding copolymer of butadiene formed under similar conditions. The composition of the copolymer was determined from the relative intensities of the NMR absorptions at 4.6-5.1 T [one ole- finic proton of isoprene -CH=C(CH3-+] and those higher than 9.0 T [methyl protons of propylene -CH,-CH(CH3+]. The infrared absorption spec- trum of the copolymer shows absorption at 890 cm-l due to the terminal methylene group. As described below, it was confirmed that this absorp- tion originates from the propylene endgroup and not from the isopropenyl group formed through 3,4-polymerization of isoprene. These observations lead to the conclusion that the propylene endgroup is vulnerable to hydro- gen transfer. The hydrogen is transferred through the form of a vanadium hydride to isoprene monomer to initiate the copolymerization.

1 I I I I I I I I . . . . , I _ _ , . . _ . I _ . . I . _ . I I . . . . , I . . . 4 5 6 7 8 9 ' 0 r

Fig. 2. 100 MHz NMR spectrum of isoprene-propylene alternating copolymer in CDCla.

W

Tab

le I1

Pr

oduc

ts o

f O

zono

lysi

s of

Cop

olym

era

Com

posi

- tio

n of

co-

po

lym

er

ratio

Pr:

IP

(mol

ar)

Ozo

noly

sis p

rodu

cts,

mg

H

CH

3 C

HI

I1

I11

A L

I

(4-M

e-)

(3-M

e-)

H

H

o= x"" -cH

2-

iiH3

=o o

=A-c

Hz-

cH2-

A =o

=o

O

=L

cHz-

CH

z-

=o

55 : 4

5 4.

0 2.

3 5

.8

trac

e 3.

8 94

-

R

CH

3 R

'

a C

opol

ymer

: 18

3mg;

O=C

.CH

2.

'A

H

.CH

z.C

Hz.

=O

; I,

R =

R'

= H

; 11

, R =

CH

3, R

' =

H;

111,

R =

H, R

' =

CH

o.

ALTERNATING COPOLYMERIZATION 3003

The typical copolymer was oxidized with ozone according to the method reported by Beroza,G followed by reduction with triphenylphosphine'. The major product was4-methylheptanal-6-one as shown in Table 11.

The yields of the products [O=C(CH3)-CH2-CH2CH0, O=CH- CH2CH2CH0, and O=C(CH3)CH2CH2C(CHs)=0 1 due to isoprene-iso- prene sequences were very low. If this copolymer were a random one, the sum of their yields should be 25 moleyo (12.5, 6.25, and 6.25 mole-%, respectively). If the head-tail orientation of propylene units in the alter- nating copolymer is random, I, 11, and I11 should each be obtained in 25 mole-% yield. The sharp singlet of the NMR spectrum (Fig. 2) a t 7.36 7

was assigned to the methylene protons attached to two olefinic carbon atoms, one of which is the terminal methylene. From these considerations it is highly probable that the copolymer chain has the structure:

CH3 CH, CH3 CH3 I I I I

w-CHz*CH = C--CH~-CH--CH~-CHZ--CH = C-CHz-C = CHI

This alternating copolymerization of isoprene with propylene can be explained by the alternating coordination mechanism (1).

R = H , E t

I I1 111

I V V

Unidentate propylene and bidentate isoprene coordinate alternatingly to the vanadium, when the available coordination sites for the monomers are one and two, respectively. If the number of available sites is two, iso- prene coordinates preferentially to the vanadium to give the intermediate I1 which then forms the *-ally1 complex (111). There are two possibilities when a ?r-ally1 complex is formed from isoprene. From the ozonolysis of the copolymer it can be concluded that I11 is exclusively formed. This is consistent with the general observation of ?r-ally1 metal complexes that the sterically hindered anti form is. unfavorable. The intermediate I11 has only one vacant coordination site which prefers the coordination of propyl- ene t o that of isoprene. Propylene reacts with the less crowded carbon atom of the ?r-ally1 intermediate to form V. The propagation is the repeti- tion of these reactions. The termination is caused by the elimination of vanadium hydride from V.

The mechanistic aspects of the alternating coordination of the monomers will be discussed in detail in a forthcoming paper.

3004 FURUKAWA, TSURUKI, KIJI

References 1. J. Furukawa, It . Hirai, and M. Nakaniwa, J . Polym. Sci. B, 7,671 (1969). 2. A. Kawasaki, 1. Mariiyama, M. Taniguchi, R. Hirai, and J. Furukawa, J. Polym.

3. J . Furukawa and R. Hirai, J. Polym. Sci. A-I, 10,2139 (1972). 4. J. Furukawa, Angew. Makromol. Chem., 23,189 (1972). 5. J. Furukawa, €I. Amario, and R. Hirai, J . Polym. Sci. A-I, 10,681 (1972). 6. M. Beroea and B. A. Bierl, Anal. Chem., 39,1131 (1967). 7. J. Furukawa, I<. Haga, E. Kohayashi, Y. Iseda, T. Yoshimoto, and K. Sakamoto,

Sci. B, 7,613 (1969).

Polym. J., 2,371 (1971).

Received April 23,1973 Revised May 8,1973