Isotactic Olefin Polymerization with Optically Active Catalysts

Chapter 4

Isotactic Olefin Polymerization with Optically Active Catalysts

Downloaded by NORTH CAROLINA STATE UNIV on October 11, 2012 | http://pubs.acs.org Publication Date: June 22, 1992 | doi: 10.1021/bk-1992-0496.ch004

W. Kaminsky, S. Niedoba, N. Möller-Lindenhof, and O. Rabe Institute for Technical and Macromolecular Chemistry, University of Hamburg, D—2000 Hamburg 13, Germany

With the homogeneous Ziegler-Natta catalyst based on c h i r a l metallocenes/methylalumoxane highly isotactic polypropylene could be prepared. The catalysts can be separated into the optical active enantiomers. Even longer chained α-olefins as butene-1, pentene-1, or hexene-1, give isotactic polymers. Among the polymer features molecular weight and molecular weight distribution, solubility in toluene, melting point, density, and x-ray c r y s t a l l i n i t y as well as macrotacticity have been examined. Except for polyhexene all polymers investigated arrange i n a stable h e l i c a l conformation. Oligomers of butene -1 and pentene-1 show an optical rotation.

Among the great number of Z i e g l e r - t y p e c a t a l y s t s , Vanden berg (1) examined a t a very e a r l y stage the heterogeneous t i t a n i u m t r i c h l o r i d e system, e s p e c i a l l y f o r s y n t h e s i z i n g i s o t a c t i c polypropylene. Homogeneous systems have been p r e f e r e n t i a l l y studied i n order t o understand the elementary steps of the p o l y m e r i z a t i o n which i s simpler i n s o l u b l e systems than i n heterogeneous ones. The s i t u a t i o n has changed s i n c e i n recent years a homogeneous c a t a l y s t based on metallocene and aluminoxane was discovered which i s very a c t i v e and a l s o i n t e r e s t i n g f o r i n d u s t r i a l uses (2-3). In some cases s p e c i a l polymers could be syn t h e s i z e d only with s o l u b l e c a t a l y s t s (4). Breslow (5) discovered t h a t b i s ( c y c l o p e n t a d i e n y l ) titanium(IV) compounds which a r e w e l l s o l u b l e i n aromatic hydrocarbons, could be used i n s t e a d of t i t a n i u m t e t r a c h l o r i d e as the t r a n s i t i o n metal compound together with aluminum a l k y l s f o r ethylene p o l y m e r i z a t i o n . Subsequent research on t h i s and other systems with v a r i o u s a l k y l

0097-6156/92/0496-0063$06.00/0 © 1992 American Chemical Society

In Catalysis in Polymer Synthesis; Vandenberg, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.


64

CATALYSIS IN POLYMER SYNTHESIS

groups has been conducted by many other research groups. With r e s p e c t to the k i n e t i c s of p o l y m e r i z a t i o n and s i d e r e a c t i o n s , t h i s s o l u b l e system i s probably the one t h a t i s best understood. The use of metallocenes and aluminoxane as cocatal y s t r e s u l t s i n extremely high p o l y m e r i z a t i o n a c t i v i t i e s . The a c t i v i t y i s higher than with heterogeneous c a t a l y s t s . T h i s system can e a s i l y be used on a l a b o r a t o r y s c a l e . The c h i r a l zirconocene ethylenebis(4,5,6,7-tetrahydroinden y l ) z i r c o n i u m d i c h l o r i d e ( ( S ) - ( + )-Et(IndH4)2~ZrCl2 was the f i r s t i n i t i a t o r found to g i v e h i g h l y i s o t a c t i c polypropylene i n a homogeneous system (6,7). This c a t a l y s t allows s e p a r a t i o n i n t o enantiomers by formation of diastereomers with S - ( - ) - l , l - b i - 2 - n a p h t h o l . The use of one enantiomer opens the opportunity to r a i s e the u n i f o r m i t y among the polymer products as compared to those produced by means of conventional methods. With hetero geneous c a t a l y s t s i t i s g e n e r a l l y not p o s s i b l e to get o n l y one type of i s o t a c t i c polymer chain (Figure 1). Pre suming t h a t there i s always a β-hydrogen t r a n s f e r to form a double bond chain end, there are two d i f f e r e n t s t r u c tures i n the F i s c h e r p r o j e c t i o n using heterogeneous c a t a l y s t s and one using the o p t i c a l l y a c t i v e homogeneous system. Isotactic Polyolefins The c a t a l y s t used was (S)-(+)-Et(IndH4)2-ZrCl2/MAO. Homopolymers from the p r o c h i r a l 1 - o l e f i n s propylene, 1butene, 1-pentene and 1-hexene have been synthesized. This i n v e s t i g a t i o n i s focused on the i n f l u e n c e exerted by the p o l y m e r i z a t i o n temperature and the a l k y l s i d e chain length of the o l e f i n s on the r e a c t i o n r a t e and the p o l ymer f e a t u r e s . The r e a c t i o n r a t e drops continuously from r a t h e r high i n i t i a l values, according to the monomer type used, to r a t h e r low, almost constant values a f t e r s e v e r a l min utes ( i n the case of propylene) or even days (1-pentene). The mean a c t i v i t y values c a l c u l a t e d over the whole p o l y m e r i z a t i o n p e r i o d i n c r e a s e s t e a d i l y with i n - c r e a s i n g tem peratures from -50 °C up to +85' °C ( i n the case of prop ylene) and are highest f o r propylene (2,000 kg/mol m t x h χ monomer) as compared to those of the other monomers (Table I ) . The most important r e s u l t of t h i s i n v e s t i g a t i o n was the f i n d i n g t h a t the s o l u b l e c a t a l y s t can polymerize even long-chain o l e f i n s l i k e 1-pentene and 1-hexene i n a h i g h l y i s o t a c t i c manner. Among the polymer f e a t u r e s , the mean molecular mass and i t s d i s t r i b u t i o n , the s o l u b i l i t y i n toluene at room temperature, the melting p o i n t , d e n s i t y and x-ray c r y s c a

c


KAMINSKY ET AJL

Polymerization with Optically Active Catalysts

Heterogeneous

Catalysts

50 %


50 %

Homogeneous O p t i c a l l y

Active

Catalysts

100 %

Figure 1. Stereochemistry of isotactic polypropylene chains.

Table I. Polymerization of Olefins with (S)-(+)-Et(IndH ) ZrCl /MAO in Toluene 4

Polymerization Temperature (°C)

Cat-Cone. Monomer ( 1 0 ~ m o l / l ) (mol/1) 6

2

2

Activity (kg/mol Zr χ h χ C m

Polypropylene

+ + + +

53 15 9 16 23 53 83

14,5 6,8 27,9 19,9 19,9 3,1 15,5

o, 0, 1, 1, 1, 1, o,

9 9 2 9 7 6 9

0,6 67,0 79,0 295,0 1154 , 0 1649, 0 2038,0

15,0 81,0 10,0 22,3 9,0

1, 8, o, o, o,

1 1 5 9 4

0,2 0,4 2,6 9,0 455,0

10,5 6,7 10,5 35,8 4,5

2, 3 3 3 7 3

Poly(1-butene)

+ + + +

15 10 20 48 60

Poly(1-pentene)

-

18 0 + 12 + 23 + 42 Poly(1-hexene)

9,9 10,5

+ 8 + 11 C

m

= Concentration

0,02 0,09 0,4 1,6 3,6

2, 2, 2, 2, 6 0, 2,9

o f t h e monomer

0,1 6,5 (mol/1)



66

CATALYSIS

IN POLYMER SYNTHESIS

t a l l i n i t y as w e l l as the m a c r o t a c t i c i t y (determined by IR-spectroscopy) have been examined. These f e a t u r e s are dependent on i n t e r m o l e c u l a r f o r ces. In a l l cases s t u d i e d , a strong i n f l u e n c e of the p o l y m e r i z a t i o n temperature on these p r o p e r t i e s i s observed and leads t o a decrease with r i s i n g temperature except f o r s o l u b i l i t y and molecular mass d i s t r i b u t i o n . With polypropylene (Table II) the mean molecular masses decrease i n the temperature range from -15 °C t o +83 °C from 200,000 g/mol down t o almost 1,300 g/mol ( f a c t o r of 140). The m e l t i n g p o i n t of 158 °C of a p o l y propylene prepared at -53 °C i s v e r y s i m i l a r t o t h a t of a commercial product (162 °C). The d e n s i t y i s even a l i t t l e higher, at 0.9150 (- 15°C) compared t o 0,9132. At h i g h e r p o l y m e r i z a t i o n temperatures the m e l t i n g p o i n t goes down from 152 °C to a g l a s s t r a n s i t i o n temperature of -35 ° C , x-ray c r y s t a l l i n i t y from 67,7 % down to 14,4 %, and IRs p e c t r o s c o p i c m a c r o t a c t i c i t y from 72 % down t o 29 %. In accordance with these values s o l u b i l i t y i n toluene a t room temperature increases and the molecular mass d i s t r i b u t i o n becomes even more narrow from Mw/Mn = 4,7 t o 1,5. The C-NMR measured i s o t a c t i c i t y (pentads) a t the lowest p o l y m e r i z a t i o n temperatures are much h i g h e r than t h a t of the commercial product (Table I I ) . The m e l t i n g p o i n t i s s t i l l lower, however, because there are some i r r e g u l a r i t i e s with the homogeneous c a t a l y s t (head t o head and 1,3-insertion) and the mistakes are random ( s t a t i s t i c a l l y ) d i s t r i b u t e d over the whole chain. Together with t h i s temperature i n f l u e n c e on i n t e r molecular c h a r a c t e r i s t i c s there i s another i n f l u e n c e working, i . e . the growing a l k y l s i d e chain length of the d i f f e r e n t monomers used. In both polybutene and polypentene, the i s o t a c t i c i t y a t low p r e p a r a t i o n temperatures i s very h i g h , decreases with i n c r e a s i n g p o l y m e r i z a t i o n temperature (Table I I I ) . The i n f l u e n c e of temperature i s higher a t the m e l t i n g p o i n t . The molecular weight of pol y (1-butene) goes down from 45 000 (prepared a t -15 °C) to 5 000 (prepared at 60 °C). Table IV d i s p l a y s s e l e c t e d f e a t u r e s of d i f f e r e n t p o l y o l e f i n s which have been synthes i z e d with the c h i r a l c a t a l y s t system at approx. 10 °C. With r e s p e c t to mean molecular masses - as observed over the whole temperature range s t u d i e d (Tables II and III) - the d i f f e r e n c e i s g r e a t e s t between polypropylene and polypentene. With respect to c r y s t a l l i n i t y , however, the d i f f e r e n c e i s most evident between polypentene and polyhexene. By means of SAXS-investigations and IR-spectroscopy data t h i s change of behaviour can be a s c r i b e d to the growing a l k y l s i d e chain length l e a d i n g to a p r e f e r e n t i a l formation of polymorphic m o d i f i c a t i o n s and a growing preponderance of the s i d e chain to determine the molecular 13


4. KAMINSKY ET


Table II. Isotacticity (I), Melting Point (mp), Molecular Weight (Μη) and Density of Polypropylenes Catalyzed with (S)-(+)Et(IndH ) ZrCl /MAO 4

2


Polymer ization Temp. (°C)

2

(I) (mmmm)

mp (°C)

Mw/Mn

Μη (g/mol)

3

(g/m )

- 53

99,7

- 15

99,4

152

200 000

0,9150

2,5

0

98,9

147

130 000

0,9075

4,3

158

15

97,7

148

60 000

0,9070

3,1

37

95,5

159

27 000

0,9056

2,7

53

91,5

95

10 500

0,9041

2,3

83

54,0

- 35

1 260

0,8700

1,5

(a)

95,8

162

350 000

0,9132

6,0

(a) = Commercial Product

Table III. Isotacticity (I), Melting Point (mp), Glass Transition Point (*), and Molecular Weight (Μη) of Polybutene, Polypentene, and Polyhexene Catalyzed with (S)-(+)-Et(IndH ) ZrCl /MAO 4

2

2

Polymerization Temperature (°C)

(I) (mmmm)

mp (°C)

Μη (g/mol)

Poly(i-butene) - 15 + 10 + 20 + 48 + 60

98,0 97,7 95,5 89,6 72,2

119 97 94 78

45 45 34 15 5

000 000 000 000 000

Poly(1-pentene) - 18 0 + 23 + 42

99,0 99,0 98,0 85,6

69 66 62 -61*

18 12 7 1

000 900 000 900

Poly(1-hexene) + 8

95,8

-48*

37 000

-


67

68

CATALYSIS IN

POLYMER SYNTHESIS

s t a t e of order. Except f o r polyhexene a l l polymers i n v e s t i g a t e d b u i l d up s t a b l e h e l i c a l conformations. In the case of polypropylene t h i s p r e f e r r e d conformation can be observed i n the IR-spectra f o r p o l y m e r i z a t i o n tempera t u r e s up to 66 °C. The lower l i m i t f o r the d e t e c t i o n of the h e l i c a l segment length i s 11 - 12 u n i t s . From the p o i n t of view along a s i n g l e polymer c h a i n , the i n t r a - m o l e c u l a r f e a t u r e s e x h i b i t e d were s t u d i e d . Here the u n i f o r m i t y of bond formation i s most important and was adequately i n v e s t i g a t e d by means of C-NMR-spectroscopy. Again a continuous d e c l i n e from h i g h l y r e g u l a r i l y attached u n i t s ( m i c r o i s o t a c t i c i t y > 99 %) at low polymer i z a t i o n temperatures down to predominantly a t a c t i c con f i g u r a t i o n s at high temperatures ( m i c r o i s o t a c t i c i t y < 50 %) i s observed. The i n f l u e n c e of the a l k y l s i d e chain, however, i s much smaller than i n the case of intermolec u l a r c h a r a c t e r i s t i c s . Even completely amorphous p o l y hexene (polymerized at + 11 °C) turns out to be s t i l l very i s o t a c t i c (> 95 % ) . The i n f l u e n c e of the a l k y l chain causes the β-hydrogen t r a n s f e r r e a c t i o n to be more pre f e r r e d so t h a t the chains become s h o r t e r . From these two conclusions the f o l l o w i n g may be deduced: the tendency of the c a t a l y s t to b u i l d up p o l y mers from 1 - o l e f i n s i n an i s o t a c t i c manner i s not s e r i o u s l y hindered by i n c r e a s i n g the a l k y l s i d e chain l e n g t h . On the other hand i t must be admitted t h a t very high r e g u l a r i t y i n the bond formation process does not per se lead to improved macroscopic f e a t u r e s . In c o n c l u s i o n , the p o l y m e r i z a t i o n of d i f f e r e n t o l e f i n s with o p t i c a l l y a c t i v e homogeneous c a t a l y s t gives polymers which are h i g h l y s t e r e o s p e c i f i c but with no spe c i a l p h y s i c a l p r o p e r t i e s . The polymers are not o p t i c a l l y a c t i v e . The e x i s t e n c e of o p t i c a l a c t i v i t y could happen o n l y i f there were formed a one-handed h e l i x s t r u c t u r e s t a b l e under c o n d i t i o n s at which o p t i c a l a c t i v i t y can be measured. This normally r e q u i r e s very bulky s i d e groups, as i n poly(tripehylmethy1 methacrylate) (8) or p o l y c h l o r a l (9). Such a c o n d i t i o n i s not found i n these p o l y olefins.


13

Oligomers S o l u t i o n s of high molecular weight i s o t a c t i c p o l y o l e f i n s produced with the o p t i c a l l y a c t i v e c a t a l y s t are expected to show no or o n l y very low o p t i c a l a c t i v i t y , because g e l i c e s of these polymers r a p i d l y change t h e i r screw sense i n s o l u t i o n (10). In c o n t r a s t to t h i s , s o l u t i o n s of oligomers or hydrooligomers should g i v e a measurable o p t i c a l r o t a t i o n (11,12). The oligomers can be synthe s i z e d at s i m i l a r temperatures and lower monomer concen t r a t i o n . Table V shows the s p e c i f i c r o t a t i o n f o r o l i gomers of 1-butene.


4. KAMINSKY ET AL.


Table VI. Molar Rotation of Pentene Oligomers. Catalyst: (S)-(+)Et(IndH ) ZrMe 4


r

u

i

y

u

i

e

i

i

2

2

Mol.Weight M e l t i n g (g/mol) Point °C

a

Isotacticity % mmmm Pen-" tads

Polypropylene

60 000

148

98,8

X-Ray, % Crystallinity 65,0

Poly(1-butene)

44 000

97

97,7

66,9

Poly(1-pentene)

10 000

66

98,3

37,9

Poly(1-hexene)

17 000

- 48

95,8

amorphous

Table V. Specific Optical Rotation at Different Wave Lengths of 1Butene Oligomers Prepared with (S)-(+)-Et(IndH ) ZrCl /MAO at 50 or 70 ° C 4

Wave Length:

2

2

Φ 589 nm

Φ 365 nm

0

0

Dimer Trimers (50 °C)

-

1,0

-

3,5

Trimers (70 °C)

-

0,3

-

0,8

Tetramers

(50 °C)

-

3,2

-

10,0

Tetramers

(70 °C) ^ ^ ^ ^ ^ ^ ^

-

1,2

-

3,4

As p r e d i c t e d , the dimer shows no o p t i c a l r o t a t i o n . The o p t i c a l r o t a t i o n of the higher oligomers decreases with i n c r e a s i n g o l i g o m e r i z a t i o n temperature. The r o t a t i o n of the tetramers i s higher than that of the t r i m e r s . The o p t i c a l p u r i t y (ee) of the oligomers i n c r e a s e s from 10 % by high o l i g o m e r i z a t i o n temperatures (60 °C) up t o 90 % by low temperatures (0 ° C ) . A l s o the next homologue, 1-pentene, c o u l d be o l i g o merized with the asymmetric ethylene-bridged ( S ) - E t (IndH4)2ZrMe2/MAO-system. The product mixtures, as w e l l as f r a c t i o n s of d e f i n e d degree of o l i g o m e r i z a t i o n , show measurable o p t i c a l a c t i v i t y . S p e c i f i c o p t i c a l r o t a t i o n values a r e of the same order of magnitude as i n the case of 1-butene oligomers. Table VI l i s t s molar o p t i c a l r o t a t i o n values f o r pentene oligomers s y n t h e s i z e d with the o p t i c a l l y a c t i v e (S)-Et(IndH4)2ZrMe2 catalyst.


69

70

CATALYSIS IN POLYMER SYNTHESIS

Table IV. Comparison of Properties of Polyolefins Prepared with (S)(+)-Et(IndH ) ZrCl /MAO at 10 ° C 4

Component

\

2

2

Wave length


Dimers

589 nm

546 nm

365 nm

-

Trimers

- 1,33

- 1,65

-

5,07

Tetramers

- 2,59

- 3,41

-

8,11

Product Mixture (M = 290 g/mol)

- 1,86

- 2,15

-

5,58

As expected, the o p t i c a l r o t a t i o n f i r s t i n c r e a s e s with i n c r e a s i n g number of c h i r a l centers i n the molecule and then d e c l i n e s again a f t e r going through a maximum. This behavior i s due t o the lower degree of asymmetry of the c h i r a l carbon atoms i n longer chained molecules. I t must be emphasized that the oligomers d e s c r i b e d above are, again, genuine o l e f i n s and s t i l l bear a term i n a l double bond. T h i s e x p l a i n s the absence of o p t i c a l a c t i v i t y f o r the dimers. Through t h i s f u n c t i o n a l i z a t i o n the oligomers become a v a i l a b l e f o r use i n f u r t h e r organic syntheses where o p t i c a l l y a c t i v e hydrocarbon groups a r e to be i n t r o d u c e d . The product molecular weights were confirmed by GC/MS and i s i n accord with the expected h i g h l y i s o s p e c i f i c 1 , 2 - i n s e r t i o n and t e r m i n a t i o n by β-hydride t r a n s f e r (Figure 2 ) .

Figure 2. Structure oligomerization.

of

1-pentene

oligomers;

n:

degree


of

4. KAMINSKY ET AL.



Literature Cited 1. Vandenberg, E . J . (1963) US Pat. 3 108 973 (to Her cules Incorporated, C.A. (1964) 60: 8155 C 2. Sinn, H . ; Kaminsky, W.; Advances in Organometallic Chemistry, V o l . 18, Acad. Press, New York, 1980, p. 99 3. Sinn, H . ; Kaminsky, W.; Vollmer, H.-J.; Woldt, R.; Angew.Chem.Int.Ed.Engl. 1980, 19, 390 4. Ewen, J . Α . ; Jones, R . L . ; Razari, Α . ; J.Am.Chem.Soc. 1988, 110, 6255 5. Breslow, D.S. (1958) U.S. Pat. 2 827 446 (to Hercules Incorporated) 6. Kaminsky, W.; Külper, K . ; Brintzinger, H . H . ; , Wild, F.R.W.P.; Angew.Chem.Int.Ed.Engl., 1985, 24, 507 7. Kaminsky, W.; Angew.Makromol. Chem., 1986, 145/146, 149 8. Okamoto, Y; Yashima, E; Prog.Polym.Sci., 1990, 15 (2), 263-298 9. Vogl, O.; Corley, L . S . ; Harris, W.J.; Taycox, G . D . ; Zhang, J.; Makromol. Chem. Suppl., 1985, 13, 1 10. Pino, P . ; Adv.Polym.Sci., 1966, 4, 393 11. Pino, P . ; Cioni, P . ; Wei, J.; J.Am.Chem.Soc., 1987, 109, 6189 12. Kaminsky, W.; Ahlers, Α . ; Möller-Lindenhof, Ν . ; Angew.Chem.Int.Ed.Eng., 1989, 28, 1216. RECEIVED

November 15, 1991


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Isotactic Olefin Polymerization with Optically Active Catalysts

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