Olefin Terpolymerizations. 111. Symmetry, Sterics, and Monomer Structure in ansa-Zirconocenium Catalysis of EPDM Synthesis

ZHENCTIAN YU, MARIA MARQUES, MARVIN D. RAUSCH, and JAMES C. W. CHIEN*

Department of Chemistry, Department of Polymer Science and Engineering, Materials Research Laboratories, University of Massachusetts, Amherst, Massachusetts 01 003

SYNOPSIS

Ethylenebis(g5-fluoreny1)zirconium dichloride (1) and rac-dimethylsilylene bis(1-g5-in- deny1)zirconium dichloride (2) were activated with methylaluminoxane (MAO) to catalyze ethylene (E) propylene (P) copolymerizations. The former produces high MW copolymer a t 20°C rich in ethylene with reactivity ratio values of rE = 1.7 and rp < 0.01, whereas the latter produces lower MW random copolymers with r, = 1.32 and rp = 0.36. Ethylidene norbornene (ENB) complexes with l/MAO but does not undergo insertion in the presence of E and P. In contrast, 2/MAO catalyzes terpolymerization incorporating 9-15 mol % of ENB with slightly lower MW and activity than the corresponding copolymerizations. In comparison, 1,4-hexadiene was incorporated by 2/MAO with much lower A and MW. Terpolymerizations were also conducted with vinylcyclohexene using both catalyst systems. The steric and electronic effects in these processes were discussed. 0 1995 John Wiley & Sons, Inc. Keywords: Ziegler-Natta catalysis EPDM synthesis metallocene catalyst

INTRODUCTION

Nonbridged CSu symmetric Cp2MC12 ( M = group 4 metal) produces moderate molecular weight (MW) polyethylene,' but only very low MW polypropylene2 and ethylene/propylene copolymers?-6 The ethylene- propylene copolymerizations have a tendency to form alternating or block7 sequences which are associated with reactivity ratios rE b rp and rE * rp > l.6,7 Bridged and alkyl substituted-Cp2ZrC12 with CZu symmetry also produces low MW amorphous polypropylene,8 while C2 symmetric derivatives catalyze stereoselec- tive propylene polymerizations with high MW.'

The designing of a metallocene catalyst for EPDM (ethylene-propylene-diene terpolymer) ~ y n t h e s i s ~ ~ ~ ~ ~ ~ ~ " is a demanding task, more than it is for an ethylene or a-olefin homopolymerization catalyst. An EPDM catalyst is required to possess the following attri-

* To whom all correspondence should be addressed. Journal of Polymer Science: Part A Polymer Chemistry, Vol. 33,2795-2801 (1995) 0 1995 John Wiley & Sons, Inc. CCC 0881-624X/95/162195-01

butes. Firstly, it should homopolymerize propylene randomly to perfectly atactic polymer associated with 13C-NMR triad distributions of [mm] = [rr] = 0.25 and [mr] = 0.50. Secondly, it should co- polymerize ethylene and propylene with high ac- tivity and without blocking, i.e., the copolymer is devoid of crystallinity; and should have low Tg, and high molecular weight (MW > 2 X lo5). Finally, the catalyst should incorporate diene ef- ficiently without appreciable loss of either activity or MW.

Very recently, we have synthesized ethylene- bis(~5-fluorenyl)zirconium dichloride ( 1) having an ideally C2" symmetry.12 Precursor 1 activated by methylaluminoxane (MAO) catalyzes propylene polymerization with an activity of 4 X lo6 g/(mol Zr[C3H6] h) at 50°C; the activity for ethylene po- lymerization is 20 times higher. Both polymers have MW of ca. 2 X lo5. Activation of 1 with triphenyl- carbenium tetrakis(pentafluoropheny1)borate (3) produced in situ the "bare" zirconocenium cation (l+), which is more active than 1/MAO by about 10-fold and the formed polyolefins have higher MW

2795

2796 YU ETAL.

Table I. Terpolymerization Catalyzed by Et(Flu)2ZrC1,/MA0 System"

Polymer Diene

TP Ab X D E Run E/P ("C) Type (MI (g/mol[Zrlh) (mol %) (mol %) M , x 10-~

375 4 20 0.0 3.8 91.8 21.8 376 4 20 ENB 0.074 0.45 0.0 92.0 21.0 377 4 20 HD 0.166 1.4 5.5 94.0 17.8 378 4 20 VCH 0.767 2.1 1.5 84.4 18.2 391 4 70 0.0 19.6 76.6 10.4 392 4 70 ENB 0.074 2.5 0.0 73.1 8.2 393 4 70 HD 0.166 1.7 5.7 68.5 8.9 394 4 70 VCH 0.767 2.5 1.0 64.4 9.9 387 2/3 20 0.0 7.2 76.7 8.2 388 2/3 20 ENB 0.074 0.35 0.0 76.4 7.0 389 2/3 20 HD 0.166 0.66 4.4 69.0 6.1 390 2/3 20 VCH 0.767 2.6 0.3 56.2 7.7

a Experimental conditions: [Zr] = 25 p M , [Al]/[Zr] = 1500, 50 mL toluene. b A = activity.

of 5 X lo5. The polypropylenes are perfectly atactic (uide supra). No terpolymerization has been inves- tigated with this CZu catalyst.

A large number of C2 symmetric zirconocenes had been synthesized and investigated for isospecific pro- pylene polymerization. However, only rac-ethylene- bis( l-~~~-indenyl)zirconium dichloride (4) had been employed for terpolymerization?,lo~ll Kaminsky and Miri5 reported results of ethylene/propylene terpoly- merization with ethylidene norbornene (ENB), we have extended the investigation to 1,4-hexadiene (HD)13 and 4-vinylcyclohexene (VCH).14 A much more active and stereoselective Cz symmetric precursor is rac-dimethylsilylenebis(l-~5-indenyl)zirconium di- chloride (2),15 but this zirconocene has not been em- ployed for terpolymerization thus far.

The objective of this work is to compare the ter- polymerization behaviors of the catalysts derived from the Czu symmetric 1 and the C2 symmetric 2 using ENB, HD, and VCH as the termonomers.

EXPERIMENTAL

Compounds 1,2, and 3 were synthesized according to literature procedures.'2.16-'8 MA0 was purchased from Akzo Chemical Co. Matheson ethylene and propylene were purified by passage through two Matheson Gas Purifiers (Model 6406). 1,4-Hexadi- ene, 4-vinylcyclohexene, and 2-ethylidene norbor- nene were supplied by Aldrich. HD was dried by CaH2, and VCH and ENB were dried over Na then distilled under argon immediately before use.

Copolymerization and terpolymerization were conducted as previously described, 13,18~19 as are the procedures for work-up of products and character- ization by 13C-NMR, proton NMR, DSC, and vis- cometry. The reactivity ratios were determined by 13C-NMR (Brucker AMX 500) at 100°C using tet- rachloroethane-d2 as a solvent. The diene content in EPDM was calculated by proton NMR measure- ment (Brucker AC 200) using chloroform-d as the solvent.

RESULTS AND DISCUSSION

Et( Flu),ZrCI,/MAO

The results of ethylene-propylene copolymerization and terpolymerizations are given in Table I. At 20°C and E / P = 4 (run 375), copolymerization activity was 3.8 X lo6 g/( mol Zr h ) . The formed copolymer contains largely ethylene (92 mol % ) . Raising Tp to 70°C increased activity to 2 X l o7 g/( mol Zr h ) and lowered ethylene content to 77 mol %. At 70"C, the homopolymerization activity for ethylene and pro- pylene was - 10' and - lo7, respectively. The co- polymerization rates lie in between but closer to that of propylene as expected. The MW was lowered to about half as compared to homopolymerization of either ethylene or propylene. Runs 375, 391, and 387 in Table I are ethylene/propylene copolymeri- zations; the adjacent entries (runs 376,392, and 388) are ethylene / propylene / ENB terpolymerizations. These comparative experiments showed that the

OLEFIN TERPOLYMERIZATION. 111 2797

presence of ENB significantly reduces the polymer- ization activity by 10-20-fold. However, the products with and without ENB in the reaction mixture have the same ethylene/propylene composition and MW. In other words, ENB is complexed with 1 but does not undergo migratory insertion. The relevant ir- complexation equations are

Zr+- R + ENB "? ENB + Zr+- R (3 )

on polymerization activities. The results indicate that the bridged ligand with bulky electron donating fluorenyl rings can form strong *-complex with ENB in a certain conformation with large K E N *

value, which is, however, not along the pathway toward the transition state for migratory inser- tion.

The results of terpolymerization with VCH (runs 378, 394, and 390) are similar to these described above for ENB but differ in two respects: the re- duction of polymerization activity by VCH is smaller, and there is incorporation of 0.3 to 1.5 rnol % of VCH. VCH is probably a weaker ir donor than ENB ( K V C H < K E N B ) . The polymerization activities in the presence of HD lie in between those of ENB and VCH.

Our previous r e ~ u l t s ' ~ showed that the second double bond of HD may chelate to the metal center:

E F (4)

Migratory insertion can not occur for the chelated structure E but HD will insert in the case of structure F. Figures 1 and 2 show a proton NMR of E / P / H D terpolymer (run 393) and a typical "C-NMR of E / P / H D (run 387) , respectively. Chelation is unlikely for VCH because of low steric flexibility of the double bond in the cyclohexene ring, thus the activities of HD terpolymerization are smaller than those of VCH.14

f

J

393

6 6 4 a 2 1 PPll

Figure 1. Proton NMR of E/P/HD terpolymer (393; x denotes HD termonomer as compared to Figure 3. Protons d of HD in backbone are overlapped with methylene units of the terpolymer.)

Me,Si(Ind),ZrCI,/MAO

The homopolymerizations of ethylene and propylene by 2 /MA0 had been previously de~cribed.'~ The ac- tivities at Tp = 70, 50, 25, and 0°C are 3, 1.5, 0.2, and 0.07 X 10' g PE/(mol Zr [C,H,] h ) and 1.7, 0.52, 0.014, and 0.032 X 10' g PP/(mol Zr [C3H,] h ) , respectively. The MWs are of the order of l o5 for the polyethylene and lo4 for the polypropylene.

The copolymerizations of ethylene and propylene by 2/MAO (Table 11) have activities lying between those oft he homopolymerizations. The proton NMR spectra of E / P copolymer is shown in Figure 3. The most significant difference between 2 and 1 is the incorporation of ENB by the former but not the latter. Firstly, comparing terpolymerizations run 396 and run 395 at 20°C and E / P = 4, the incorporation of 8.7 rnol % of ENB lowers the contents of both ethylene and propylene by almost 4 rnol %. At 70°C (run 399 and 400), the composition of terpolymer (run 400) is 66.4 mol % for E, 18.9 mol % for P, and 14.7 mol % for ENB, it has 11.6% less E but only 3% less P than those of run 399 copolymer. We have reported that the increase of Tp raises rp but lowers rE in both copolymerizations and terpolymeriza- tions.13 This was attributed to the greater thermal stability of propylene x-complex of Zr+P than the ethylene r-complex of Zr+P. This could also explain the amount of ENB incorporated at 70°C in run 400, which is greater than the amount found in run

2798 YU ETAL.

I I - - 7 ' m T - pPn 46 44 42 4b 38 $6 3j4 26 24 22 20 18 16

Figure 2. I3C-NMR of' E /P copolymer catalyzed by 1/MAO (sample 387).

396 a t 20°C. Secondly, for reaction mixture rich in propylene (E/P = 2/3), the amount of propylene found is actually greater in terpolymer than in the copolymer (runs 403 and 404). This suggests that the propylene a-complex and ENB a-complex weaken the Zr- C bond more than the ethylene complex does. It is quite reasonable that the ter- polymerization differences between precursors 2 and 1 are largely due to steric effects. If electronic factors play an important role here, one might expect 1 to incorporate more ENB than 2 because the fluorenyl (Flu) ligand is more electron-donating which may

cause more weakening of the Zr - C bond than the indenyl ( Ind) ligand.

VCH was terpolymerized to 4-7% a t E/P feed ratio of 4 (runs 398 and 402) but much less at an E/P feed ratio of 2/3 (run 406). This and previous studies14 indicate that the VCH a-complex of Zr+R is more stable than ethylene a-complex of Zr'R but is comparable to propylene a-complex of Zr 'R.

The terpolymerization of HD is interesting. As much as 5 4 % of HD is found in the terpolymers (397, 401, and 405). The proton NMR of sample 405 is shown in Figure 4. At the 80 : 20 E/P feed

Table 11. Terpolymerization Catalyzed by (CH3)2Si(Ind)2ZrC12/MA0 Systema

Polymer Diene

T P Ab X D E Run E/P ("C) Type ( M ) (g/mol[Zrl h) (mol W) (mol W) M , x 10-4

395 396 397 398 399 400 401 402 403 404 405 406

4 4 4 4 4 4 4 4

2/3 2/3 2/3 2/3

20 20 20 20 70 70 70 70 20 20 20 20

ENB HD VCH

ENB HD VCH

ENB HD VCH

0.0 0.074 0.166 0.767 0.0 0.074 0.166 0.767 0.0 0.074 0.166 0.767

9.7 2.0 0.44 4.0

11.7 1.0 0.72 3.12 2.6 0.8 0.23 2.6

8.7 7.8 6.8

14.7 5.0 4.0

12.5 5.2 1.5

87.0 82.6 82.8 81.7 78.0 66.4 73.2 60.0 79.8 60.5 71.7 61.0

17.0 13.9 3.8 8.5 6.6 4.5 3.0 4.3 7.3 5.1 5.1 6.7

a Experimental conditions: same as Table I. b A = activity.

OLEFIN TERPOLYMERIZATION. I11 2799

r-r---r-r-r-l----1-,7-7-v~1-7-,-,-., -I--, -. T,-v7.-rl-,-I--, --7-~-7-----7 7 - ~ T 7 - T - r r - l - ~ 6 .0 5 . 5 6 .0 4 . 5 4 . 0 3 . 5 3 . 0 2 . 5 2 . 0 1.6 1.0 .5

i v n

Figure 3. Proton NMR of E/P (sample 399).

ratio (run 397), HD lowers activity by 20-fold and MW by 4.5 times as compared with the copolymer- izations. This is consistent with our proposal13 that both double bonds in HD can chelate to the metal center (cf. structure E ) .

Comparison of Catalysts

ruc-Ethylenebis ( l-q5-indenyl) zirconium dichloride ( 4) and ruc-ethylenebis ( 1-q5-tetrahydroindenyl) zirconium dichloride ( 5 ) are the earliest investigated C2 symmetric unsa-metallocene catalysts? The eth- ylene /propylene copolymerization reactivity ratios a t 50°C are rE = 2.57, rp = 0.39 for 4/MAO and rE = 2.90, rp = 0.28 for 5/MA0.7 "Bare" cation 4 + ' 7 3 1 8

was generated for copolymerization, and it has rE = 1.2 and r p = 0.54 a t 50°C.11 The value of r E in- creases with the decrease of Tp reaching a value of 3.8, while rp decreases to 0.22 a t -10°C. In the pre- vious work,15 we have found that rE = 1.32 and rp

= 0.36 at 20°C in the case of 2/MAO. All these catalysts copolymerize ethylene and propylene ran- domly because the reactivity ratios do not differ by more than a factor of 10 and the rErp values lie be-

tween 0.5 and 1.0. However, precursor 1 is signifi- cantly different.*' In fact, the ethylene and propylene copolymerization reactivity ratio using this catalyst ( 1 ) is found to be rE = 1.7 and rp < 0.01 a t Tp = 20°C (run 387).

The terpolymerization for ENB catalyzed by 4/ MAO" has an activity which is about 3.5 times smaller than the copolymerization. Up to 20.5 wt % of ENB was incorporated. In the case of 4+ the ac- tivity was hardly affected by ENB and the terpoly- mer contains up to 44 wt % of this monomer de- pending upon the quantity of ENB in the reactor." The terpolymerization was quenched within 15 min because of the high activity. In the case of terpoly- merization catalyzed by Cp2Zr ( CH3)2/MA05, up to 32 wt % of ENB was incorporated. Catalyst derived from 2 has less favorable geometry than 4 for ENB terpolymerization. The amount of ENB incorpo- rated is lower and the adverse effects on catalytic activity and MW are greater. In the case of precursor 1 , ENB was complexed without insertion.

HD caused a 5-20-fold decline of copolymeriza- tion activity catalyzed by 4/MAO with significant loss of MW. Up to 22 mol % of HD was incorporated

2800 YU ET AL.

405

x a a

~..'.~...'1'.'.I....,.,..,,...,...,I.'..',....,,.,.I, 0.5 5.0 4.6 4.0 3.8 3.0 2.5 2.0 1.5 1 .o .5

Figure 4. as Figure I).

PPn

Proton NMR E/P/HD terpolymer (sample 405; the assignments are the same

in this case.13 The HD terpolymerization catalyzed by 2/MAO and 1/MAO behave very similarly to that of 4/MAO except HD does not significantly affect the MW nor appreciably alter the E and P contents of the product. On the other hand, the ter- polymers produced by both 1/MAO and 2/MAO are very similar according to the comparison of their proton NMR spectra (Fig. 1 vs. Fig. 4). In the cat- alyst systems of 2/MAO and 4/MAO,l4 VCH is the poorest termonomer in the sense that the amount of incorporated VCH is the least among three dienes even with the highest concentration in the feed.

Catalyst precursor 1 was synthesized by Y.-X. Chen."

REFERENCES AND NOTES

1.

2.

3.

H. Sinn, W. Kaminsky, H.-J. Vclmer, and R. Woldt, Angew. Chem. Znt. Ed. Engl., 1 9 , 3 9 0 (1980). H. Sinn and W. Kaminsky, Adu. Organomet. Chem., 1 8 , 9 9 (1980). H. Drugemuller, K. Heiland, and W. Kaminsky, in Transition Metals and Organometallics as Catalyst for

Olefin Polymerization, W. Kaminsky and H. Sinn, Eds., Springer-Verlag, Berlin, 1988, p. 303.

4. J. A. Ewen, in Catalytic Polymerization of Olefins, T. Keii and K. Soga, Eds., Kodansha, Tokyo, 1986, p. 271.

5. W. Kaminsky and M. Miri, J. Polym. Sci. Part A: Polym. Chem., 23, 2151 (1985) .

6. A. Zambelli, A. Grassi, M. Galinberti, R. Mazzocchi, and F. Piemontesi, Makromol. Chem., Rapid Commun., 1 2 , 5 2 3 (1991).

7. J. C. W. Chien and D. He, J. Polym. Sci. Part A: Polym. Chem., 2 9 , 1585 (1991).

8. W. Roll, H. H. Brintzinger, B. Rieger, and R. Zolk, Angew. Chem. Znt. Ed. Engl., 2 9 , 279 (1990).

9. W. Kaminsky, K. Kulper, H. H. Brintzinger, and F. R. W. P. Wild, Angew. Chem. Znt. Ed. Engl., 2 4 , 507 (1985).

10. J. C. W. Chien and D. He, J. Polym. Sci. Part A: Polym. Chem., 29,1609 (1991) .

11. J. C. W. Chien and B.-P. Xu, Makromol. Chem., Rapid Commun., 1 4 , 1 0 9 ( 1993).

12. Y.-X. Chen, M. D. Rausch, and J. C. W. Chien, Mac- romolecules, submitted.

13. Z. Yu, M. Marques, M. D. Rausch, and J. C. W. Chien, J. Polym. Sci. Part A: Polym. Chem., 3 3 , 9 7 9 ( 1995).

14. M. Marques, Z. Yu, M. D. Rausch, and J. C. W. Chien, J. Polym. Sci. Part A: Polym. Chem., submitted.

OLEFIN TERPOLYMERIZATION. I11 2801

15. W.-M. Tsai and J. C. W. Chien, J. Polym. Sci. Part A: Polym. Chem., 32,149 (1994).

16. W. A. Hermann, J. Rohrmann, E. Herdfweek, W. Spaleck, and A. Winter, Angew. Chem., 28, 1511 (1989).

17. J. C. W. Chien, M.-M Tsai, and M. D. Rausch, J. Am. Chem. SOC., 113,8570 (1991).

18. ( a ) J. A. Ewen and M. J. Elder, Eur Patent Appl., D426637 (1991); ( b ) J. A. Ewen and M. J. Elder, Makromol. Chem. Symp., 66, 179 (1993).

19. J. C. W. Chien and B. P. Wang, J. Polym. Sci. Part A: Polym. Chem., 20, 3089 (1988).

20. The intrinsic activity of the catalyst shown" by the "bare" 1' in ethylene polymerization is 1.4 X 10'" g PE/(mol Zr [C,H,] h ) at -2O"C, decreasing to 2.4 X 10' g PP/(mol Zr [C,H,] h ) a t 70°C. It is nearly constant for propylene polymerization having values

of 6.26 (k1.63) X l o 7 independent of the temperature in the range of -20 and 70°C. If one assumes that chain propagation involves ?r-complexation and mi- gratory insertion, then AH, + AE, - AE, and AE, - 0 kcal/mol for propylene polymerization; it is about 7.4 kcal/mol for ethylene polymerization. If AEl is about the same for both monomers, then AH, is much more negative in the former case. Since the electron- donating effect of the fluorenyl ligand are same for both ethylene molecule and propylene molecule, their different polymerization behaviors may be attributed to the steric eff'ect. The two bulky fluorenyl ligands can act like a vice to hold onto the propylene molecule.

Received December 22, 1994 Accepted June 4, 1995