Copolymerization of butadiene and isoprene with the aid of complex organometallic catalysts

COPOLYMERIZATION OF BUTADIENE AND ISOPRENE WITH THE AID OF COMPLEX ORGANOMETALLIC CATALYSTS* L . S. B R E S L E R , B . A . ] ) O L G O P L O S K , M . F . K O L E C t t K O V A

and YE. N. K R O P A C H E V A S. V. Lebedev Scientific Research Institute for Synthetic Rubber

(Received 13 August 1961) AS IS well known, the relative activity of the same pair of monomers differs markedly according to the mechanism by which polymerization takes place-radical, cationic, or anionic. On polymerization under the influence of catalytic complexes, the composition of the copolymers may also be determined by the chemical and physical nature of their components, regardless of whether the elementary acts of addition which take place are of a cationic or of an anionic type. While copolymerization under the influence of free radicals has been studied for a considerable number of pairs of monomers, relatively few investigations have been devoted to the analogous process under the influence of ionic catalysts. The investigation of copolymerization under the influence of complex organometallic catalysts is mainly carried out with a-oletins [1]. We have studied the copolymerization of isoprene and butadiene in the presence of two catalytic systems: a heterogeneous system I, formed by the reaction of tri-isobutylaluminium with titanium tetrachloride, and a homogeneous system II produced by the reaction of di-isobutylaluminium chloride with a complex of cobaltous chloride and ethyl alcohol. EXPERIMENTAL All the work was carried out in an atmosphere of argon with the careful exclusion of traces of oxygen and moisture from the reaction vessel, the reactants, and the solvent. Polymerization was carried out in a thermostated autoclave with a stirrer. The polymer was isolated by precipitation with ethyl"alcohol and was dried in vacuum to constant weight. The glass temperature of the polymers obtained was determined by Marei's method [2], their elasticity fl'om their recovery ill a KS elastometer [3], and their structure by I R spectroscopy. I n a study of the eopolymerization constants, the composition of the eopolymer was determined by the radioactivity of polymers obtained from mixtures of isoprene and butadieno labelled with 14C. The labelled butadiene was synthesized from a mixture of radioactive and inactive butadieno tetrabromide [4]. The activity of the monomerie butadieno was determined from the radioactivity of polybutadieno [5]. The measurements of the radioactivity of the polymers were carried out in films in a layer of complete absorption *Vysokomol. soyed. 5: No. 3, 357-362, 1963. 1012

Copolymerization of butadiene and isoprene with organometallic catalys~s

1013

of the radiation of the 1~C isotope using a BFL-25 erLd-window counter with a mica window with a thickness of 1.3 mg/cm ~ (statistical error of the measurements, 1%). The copolymerization of isoprene with the labelled butadiene was carried out in tubes with a dividing wall which was ruptured after the temperature had a t t a i n e d constancy. The catalyst and solvent were placed in one p a r t of the tube and the monomers were measured into the other through a distribution manifold with an accuracy of -4-2~/o (relative). I n the construction of curves of the composition of the copolymer as a function of the composition of the mixture of monomers, corrections were m a d e for those cases where the yield of monomer exceeded 10% [6]. The relative activity of the monomers was calculated b y the method of F i n e m a n and Ross [7].

DISCUSSION Catalytic systems of type I are extremely stereospecific in the polymerization o f i s o p r e n e ( t h e p o l y i s o p r e n e c o n t a i n s a b o u t 9 8 % o f cis-l,4-units [8]) b u t l e s s s t e r e o s p e c i f i c i n t h e c a s e o f p o l y b u t a d i e n e (70°/o o f cis-l,4- u n i t s , 2 5 % o f trans-l,4u n i t s , a n d 5 % o f 1 , 2 - u n i t s [9]). T h e c a t a l y t i c s y s t e m I I is m o s t s t e r e o s p e c i f i c for b u t a d i e n e ( t h e p o l y b u t a d i e n e c o n t a i n s a b o u t 9 5 % o f cis-l,4- u n i t s [10]); the polyisoprene which we obtained with this system contains more than 30% o f 3,4- u n i t s . When butadiene and isoprene were copolymerized with the aid of the catalytic system I, the structure of the resulting copolymer was practically the s a m e a s o n h o m o p o l y m e r i z a t i o n ( T a b l e 1). T h e b u l k o f t h e m o n o m e r i c u n i t s w e r e l i n k e d i n t h e 1,4- p o s i t i o n s , t h e r e l a t i v e p r o p o r t i o n s o f cis- a n d trans-l,4u n i t s in t h e b u t a d i e n e p a r t o f t h e c h a i n b e i n g p r e s e r v e d . TABLE 1. STRUCTURES OF POLYMERS OF BUTADIENE AND ISOPRENE FROY/THE RESULTS OF I R SPECTROSCOPY*

Catalyst system

Content of units in the polymer, °/o b y weight

Content of units in the polymer from the results of I R spectroscopy, °/o b y weight

Butadiene Isoprene I, 1,2Al(iso-CdHg)a ~- TiC14. System I ¢

100 72.2 44.3 22.6 --

Al(iso-C~H9),C1

--CoC]~ (complex with C2HsOH ). System II$

100 83 54.5 25 --

-27.8 55.7 77-4 100

-17 45.5 75 100

5 2 1 0.5

3,4-< 1 2 2

--

4 I4 23.6 9 2

2

-1 7 20 >31

1,4trans-l,4isoprene butadiene -30 55 82 98

-18 38 54.3 <67

25 16 6 4 --

70 45 24 10 --

4 6 2 0 --

cis.l,4butadiene

92 60 35 15 --

* Obtained b y L. S. Skripova. t Content of butadienc units in the copolymers d e t e r m i n e d f r o m the r a d i o a c t i v i t y of the samples. P o l y m e r i z a t i o n eonditions: total concentration of m o n o m e r s in solution in benzene 10% b y wt.; [TiCI,] = 0"1% b y weight; AI:Ti (molar) = 1"1:1; t e m p e r a t u r e 30 °. ++ Polymerization conditions: total concentration of m o n o m e r s in solution in benzene 10% b y wt.: [CoCiz] = 0"002% b y wt.; [ AI(iso-C,Hg)~CI] = 0"3 % b y wt.; t e m p e r a t u r e 30 °,

1014

L.S. BRESLER et al.

I n t h e presence of the c a t a l y t i c s y s t e m I I , a e o p o l y m e r w a s f o r m e d differing in the s t r u c t u r e o f the e l e m e n t a r y u n i t f r o m t h e corresponding h o m o p o l y m e r s , as was s h o w n b y the considerable increase in t h e c o n t e n t of 1,2- units. Since the t o t a l a m o u n t of 1,4- a n d 3,4- isoprene units in the p o l y m e r c o r r e s p o n d s a p p r o x i m a t e l y to t h e k n o w n t o t a l n u m b e r o f isoprene units, it m a y be a s s u m e d t h a t the 1,2- units are f o r m e d b y a d i s t u r b a n c e o f the r e g u l a r i t y o f t h e addition of b u t a d i e n e units in copolymerization, A m a r k e d change in the s t r u c t u r e o f t h e b u t a d i e n e p a r t of the chain t a k e s place w h e n a b o u t 30 m o l e s - % of isoprene is used a n d r e m a i n s a t a c o n s t a n t level w h e n t h e c o n c e n t r a t i o n o f isoprene is increased f u r t h e r u p to 80 m o l e s - % . A rise in the c o n t e n t of 1,2- units in t h e b u t a d i e n e p a r t of t h e chain h a d been n o t e d earlier b y P a s q u o n et al. [11] in the c o p o l y m e r i z a t i o n of b u t a d i e n e w i t h isoprene u n d e r t h e action o f cobalt d i a c e t y l a c e t o n a t e a n d d i e t h y l a l u m i n i u m chloride. I t was n e c e s s a r y to show t h a t the s y s t e m s considered f o r m c o p o l y m e r s a n d n o t m i x t u r e s of h o m o p o l y m e r s . F o r this purpose, a c o m p a r i s o n of s o m e p r o p e r t i e s of the c o p o l y m e r s which we h a d o b t a i n e d with those o f m i x t u r e s of h o m o p o l y m e r s p r e p a r e d b y m i x i n g t h e m on rolls or c o p r e c i p i t a t i n g t h e m f r o m solution. As follows f r o m T a b l e 2, t h e glass t e m p e r a t u r e (T~) of the c o p o l y m e r s changes m o n o t o n i c a l l y as a function of t h e c o n t e n t o f e a c h of t h e m o n o m e r s in t h e p o l y m e r i z e d m i x t u r e , while Tg of a m i x t u r e of h o m o p o l y m e r s corresponds to t h e Tg of one of the two h o m o p o l y m e r s c o m p o s i n g it. TABLE 2. GLASSTEMPERATUREOF COPOLYMERSAND MIXTURESOF HOMOPOLYMERSOF ISOPRENE AND BUTADIENE* Catalyst

Content of units in the copolymer, moles- %

system

Butadiene

Isoprene

Tg of the eopolyaner, °C

I

100 76 48 25

II

100 84 60 34

-24 52 75 100 -16 40 66 100

110 99 89 76 71 112 95 84 73 50

-

-

-

-

Content in the mixture moles- % Polybutadiene

Polyisoprene

100 70 -20

-30 -80 100

-

-

100 75 -30 -

-

-

-

25 -70 100

Tg of the mixture, °C 110 114 -73 71 112 106 -54 50

* The eopolymerswere comparedwith mixturesof homopolymersof butadiene and isopreneobtained using the same catalysts. I n view of t h e f a c t t h a t in c o p o l y m e r i z a t i o n w i t h t h e c a t a l y t i c s y s t e m I t h e m i c r o s t r u c t u r e o f t h e units in t h e chain r e m a i n s t h e s a m e as in t h e h o m o p o l y m e r s , it a p p e a r e d possible to s t u d y t h e connection b e t w e e n Tg a n d t h e com-

Copolymerization of butadiene and isoprene with organometallic catalysts

1015

position of the copolymer. In agreement with the relationships for other pairs of monomers established previously [12, 13], Tg for the eopolymer rises proportionally with the increase in the content of isoprene units in it (Fig. 1). This result agrees with those obtained earlier for trans-l,4-copolymers of isoprene and butadiene [13]. Tc,°C -70

Tc, oc -70

9 -0~ -llO0 100

40i

9 -0 80I

Butadiene units, % 80 20 I~oprene units, %

colIO 0

FIG 1. Glass temperature as a function of the content of butadiene units in 1,4-copolymers of butadiene with isoprene obtained on catalyst system I. Content of butadiene units determined from the radioactivity of the samples. Marei and Sidorovich have also studied the change in the elasticity of the rubbers and the dynamic modulus as functions of the temperature for the copolymers which we obtained. On the elasticity curves obtained in an investigation of the copolymers, as on the curves for the homopolymers, there is only one minimum and its position is displaced relative to the minima on the curves of the corresponding homopolymers (Fig. 2a and b). On the elasticity curves of mixtures of rubbers there are two minima, corresponding to the two minima of the homopolymers. On the curves of the dynamic modulus, the difference between the copolymers of butadiene and isoprene and mixtures of their homopolymers is also clearly shown (Fig. 3). The facts cited show that we did in fact obtain copolymers. The relative activities of the monomers studied in polymerization under the influence of the catalyst system I was close to 1, i.e. the composition of the copolymer does not change with the degree of polymerization. In the presence o f catalyst system II, the relative activity of butadiene was 2.3 and that of isoprene was 1.15 (Table 3, Fig. 4). Thus, the relative reactivities of isoprene and butadiene in the presence of complex organometallic catalysts are different from in cationic [I0] and ordinary anionic [15] polymerization. In accordance with the ideas of Mark, Natta, and other investigators [16], in catalytic polymerization, the growth of the chain takes place through the metal--carbon bond in a bimetallic organometallic complex, the insertion of the monomer being preceded b y the stage of the formation of a complex of the monomer with the positively charged metal atom.

1016

L.S. BRESLERet al. 7O

a

3o 20

50' 2 4O 3O 20 10 0

-100 -80

-60

-40

-20 0 20 Temper~fzme, °C

40

60

80

100

:FIG. 2. Elasticity as a function of the temperature for polymers: a - o b t a i n e d with the catalyst system I; b--obtained with the catalyst system II. a: / - - f o r polyisoprene; 2--for polybutadiene; 3--for a mixture of 80 moles-~o of polybutadiene and 20 moles-% of polyisoprene; 4--for a mixture of 55 moles-~o of polybutadiene and 45 moles-~o of polyisoprene; 5--for a copolymer containing 50~/o of polybutadiene units, b: / - - f o r polyisoprene; 2--for polybutadiene; 3--for an equimolar mixture of polybutadiene and polyisoprene; 4--for a copolymer obtained from an equimolar mixture of butadiene and isoprene. W h e n the electron d e n s i t y on the double b o n d s is increased (when electrond o n a t i n g substituents are present), the i~rst s t a g e - - t h e f o r m a t i o n of the c o m p l e x --is facilitated, b u t the second stage - - t h e addition of the m o n o m e r to the negatively polarized end of the c h a i n - is hindered. I f the two stages of the process take place with c o m m e n s u r a b l e velocities, t h e n the influence of the s u b s t i t u e n t

Copolymerization of butadiene and isoprene with organometallic catalysts kg/cm~

4

1017

1'

1 12

280

240

200

tO0F

IFO

"orl

80

"~ 40

0

I

-60

I

.40

t

I

-20 0 Tempepatu/~, °C

I

20

. I

40

0

2

I

I

I

I

20 40 60 80 Butadienein the mlxtupe ~ moles- %

FIG. 3 FIG. 4 FIG. 3. Dynamic modalus as a function of the temperature for polymers obtained using catalyst system II: 1--for polyisoprene; 2--for polybutadiene; 3--for a n equimolar mixture of polybutadigne and polyisoprene; g--for a copolymer obtained from a equimolar mixture of butadiene and isoprene. :FIG. 4. Composition of copolymers of butadiene and isoprene as a function of the composition of the mixture of monomers: / - - f o r the catalyst system I; 2--for the catalyst system II.

TABLE 3. C O M P O S I T I O N OF

T H E COPOLYMERS OF B U T A D I E N E AND I S O P R E N E AS A F U N C T I O N

OF T H E COMPOSITION OF T H E I~IIXTURE OF MONO~IERS

(Determined from the radioactivity of the polymers) Content of I butadiene in I Conversionl Catalyst the mixture of / °~o system monomers, b y weight moles- °~o I

II

25 50 75

6.3 10.7 15

25 31 50 74.5

" 9.3 12.5 2;10 10

Content of butadiene units in the copolymer 25 48 76 28.6 34.1 60; 61-5 84.5

rl (for butadiene)

r2 (for isoprene)

1-04-0.05

1.04-0.05

2.3±0.1

1.154-0.05

l

/00

1018

L.S. BRESLERet al.

is c o m p e n s a t e d a n d two m o n o m e r s such as isoprene a n d butadiene can p r o v e to be a l m o s t equally active in p o l y m e r i z a t i o n b y m e a n s of the catalysts considered. CONCLUSIONS (1) The copolymerization of butadiene with isoprene u n d e r the influence o f the following catalytic systems has been studied: t r i - i s o b u t y l a l u m i n i u m / t i t a n i u m tetrachloride, a n d di-isobutylaluminium chloride/complex of cobaltous chloride with e t h y l alcohol. (2) F r o m a s t u d y of the properties of the resulting p o l y m e r s a n d of m i x t u r e s of h o m o p o l y m e r s of b u t a d i e n e a n d isoprene, it has been established t h a t cop o l y m e r s are in fact formed from m i x t u r e s of isoprene a n d b u t a d i e n e in the presence of the catalysts mentioned. (3) The copolymerization c o n s t a n t s of b u t a d i e n e a n d isoprene in the presence of these catalysts have been d e t e r m i n e d b y using labelled atoms. T r a n s l a t e d by B. J. HAZZARD

REFERENCES 1. G. NATTA, J. Polymer Sci. 34: 88, 1959; N. M. YEGOROV et al., Plastich. massy, No. 1, 10, 1959 2. A. I. MAREI, Tr. VNIISK, No. 3, Leningrad and 1Koseow, p. 173, 1951 3. Ye. V. KUVSHINSKII and Ye. A. SIDOROVICH, Zh. tekh. fiz. 26: 878, 1956 4. I. A. VOLZHINSKII, V. N. L'VOV and V. O. REIKHSFEL'D, Rukovodstvo k prakticheskim zanyatiyam v laboratorii SK. (Handbook for Practical Work in the Synthetic Rubber Laboratory.) Leningrad, Goskhimizdat, p. 62, 1955 5. F. DANUSSO, G. PAJARO and D. SIANESI, J. Polymer Sci. 22: 179, 1956 6. C. G. OVERBERGER, D. TANNER and E. M. PEARCE, J. Amer. Chem. Soe. 80: 4566, 1958 7. M. FINEMAN and S. ROSS, J. Polymer Sei. 5: 259, 1950 8. I. I. BOLDYREVA, B. A. DOLGOPLOSK, V. A. KROL', V. N. REIKH et al., Khim. nauka i prom. 2: 391, 1957; V. N. REIKH, V. V. SAMOLETOVA, L. S. IVANOVA, D. P. FERINGER and V. A. KORMER, Kauchuk i rezina, No. 3, 1, 1960 9. D. D. BABITSKII, B. A. DOLGOPLOSK and V. A. KROL', Khim. nauka i prom. 2: 392, 1957 10. B. A. DOLGOPLOSK, Ye. N. KROPACHEVA, Ye. K. KHRENNIKOVA et a/.,Dokl. Akad. Nauk SSSR 135: 847, 1960 11. J. PASQUON, L. PORRI, A. ZAMBELLI and F. CIAMPELLI, Chim. Ind. 43: 509, 1961 12. A. I. MAREI, Kauehuk i rezina, No. 2, 1, 1960 13. Ye. I. TINYAKOVA, B. A. DOLGOPLOSK, R. N. KOVALEVSKAYA et al., Dokl. Akad. l~auk SSSR 129: 1306, 1959 14. F. R. MAYO and C. WALLING, Chem. Revs. 46: 191, 1950 15. G. V. RAKOVA and A. A. KOROTKOV, Dokl. Akad. Nauk SSSR 119: 982, 1958; Yu. L. SPIRIN, A. R. GANTMAKHER and S. S. MEDVEDEV, Vysokomol. soyed. 1: 1258, 1959 16. F. EIRICH andH. MARK, J. Colloid Sei. 11: 748, 1956; G. NATTA, Chim. Ind. 42: 1207. 1960; K. S. MINSKER and V. K. BYKHOVSKII, Vysokomol. soyed. 2: 535, 1960; M. I, MOSEVITSKII, Usp. khim. 28: 455, 1959