Table VII.
Batch No. Filler Dielectric constant at 1 kc., 25 C. Dissipation factor at 1 kc.: 25 C. Dielectric strength (207& increases per 5 min.) (0.030 inch slab), volts per mil. Brittleness point, ’ C. (ASTM D 746-57T)
720 25 phr Cab-0-Si1 silica 3.44 0.010
Miscellaneous Properties 111 718 25 phr 25 phr Syloid 244 Alon C silica alumina 3.30 3.20 0.013 0.018
719 25 phr P-25 titanium dioxide 2.96 0.010
460
500
415
380
- 23
- 24
- 24
- 23
Acknowledgment
The authors thank C. M. Krutchen for carrying out much of the experimental work and the Rome Cable Division of Alcoa for permission to publish this report. literature Cited (1) Badische Anilin- und Soda-Fabrik A. G., Ger. Patent APPl. B 26959 (Februarv 1956). (2) Cabot ‘Corp., ‘Minerals and Chemicals Division, various technical releases (1958-1961). (3) Cole, H. M., Dannenberg, E. M., Jordon, M. E., J . Polymer Sci. 31, 127 (1958).
580 42 phr Mistron vapor talc 3.80 0.020 410 Not tested
(4) Hosmer, \Y. A,, Starke, A. C. (to General Aniline and Film Corp.), U. S. Patent 2,927,914 (1960). (5) Lamar, R. S., Warner, M. F., Mulryan, H. T., Rubber Age 89, 437 (1961). (6) Schildknecht, C. E. (to General Aniline and Film Corp.), U. S. Patent 2,429,587 (1947). (7) Studebaker. M. L.. Rubber Chem. Technol. 30. 1410 (1957). (8j Union Carbide Plastics Co., New York; “Bakklite ’Vinyl Ethyl Ether Resins,” Tech. Release 27 (revised June 1960). (9) wolf, R. F., Stueber, C. C., Rubber Age 86, 1009 (1960). RECEIVED for review May 4,1962 ACCEPTEDJuly 2, 1962 Division of Rubber Chemistry, ACS, Boston, Mass., April 1962.
ETHYLEN E-PROPYLEN E COPOLYMERS PRODUCED WITH SOLUBLE CATALYSTS R . J . K E L L Y , H . K . G A R N E R , H. E . H A X O , A N D W .
R. B I N G H A M
Research Center, United States Rubber Co., Wayne, N . J .
Soluble catalyst systems derived from alkyl aluminum halides in combination with vanadium oxytrichloride or tetrachloride produce highly random ethylene-propylene copolymers with high catalyst efficiency. By choice of the alkyl aluminum halide and molar ratio of aluminum to vanadium, polymerization efficiency and molecular weight may be varied. Copolymers prepared with these soluble catalysts have advantages in both processing and physical properties over those prepared with heterogeneous catalysts. Their vulcanizates have somewhat different accelerated aging properties, depending on the additive used with the peroxide. Low temperature properties of copolymers containing less than 70 weight propylene show a tendency for crystallization which i s not shown by x-ray diffraction. Over-all physical properties propylene copolymer over the 50% material. and tire tests show some preference for the 65 weight
70
yo
HE elastomers which can be obtained from ethylene and Tpropylene are of great interest, since they are derived from cheap, readily available monomers. Being essentially saturated rubbers, their air-aging properties and ozone resistance are excellent. I n this respect they resemble butyl rubber. However, in mechanical properties and air permeability they more closely resemble SBR, and they are intermediate between SBR and natural rubber in low temperature properties. With this rather unique combination of properties to recommend these elastomers, the acthiit). both in Europe and here is readily understood.
210
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
Natta and his coworkers a t the Milan Polytechnic Institute of Industrial Chemistry pioneered the preparation of ethylenepropylene copolymers, using coordination catalysts of the type discovered by Ziegler. These so-called heterogeneous Catalysts were formed by the interaction of an aluminum trialkyl with a transition metal halide (75). These investigators also showed that the product of the reactivity ratios of the individual monomers for this copolymerization was close to unity, indicating a nearly random copolymer (70, 77, 76, 77). Only recently three types of improved soluble catalyst
systems for producing these copolymers were disclosed. The first was prepared from tetraphenyltin, aluminum bromide, vanadium tetrachloride, and small amounts of oxygen. I t was reported to give crystalline copolymers of relatively low propylene content (78). The second was derived from dialkyl aluminum halides and vanadate esters ( 8 ) . The last was prepared from either trialkyl aluminum or dialkyl aluminum halides in combination with either vanadium oxytrichloride or tetrachloride ( 9 ) . The latter two soluble catalysts were reported to produce rubbery copolymers with 40 to 7070 propylene content. (The compositions of all ethylenepropylene copolymers in this paper are expressed in weight per cent of propylene. Monomer feeds are given in mole per cent.) Our work has led to the development of a group of soluble catalyst systems which are derived from alkyl aluminum halides and vanadium oxytrichloride or tetrachloride. R2AIX or RAlX?or
RIA
+ AlXx
Ii +
v 0 ( 2 l 3or VCla
+
pink to purple solution ( 6 )
J
The colors obtained are similar to those described by Carrick and coworkers (3, 4) from mixtures of aluminum halides, vanadium halides, and aluminum or tin alkyls. As indicated above, any mixture of trialkylaluminum and aluminum halide can be used, provided the stoichiometry is controlled so that only alkyl aluminum halides result from the equilibration. Excess aluminum halide is particularly had. It is preferable to use Al/V molar ratios in excess of 10 to 1 and to mix the catalyst components in the presence of monomers to prevent the formation of a solid catalyst phase. It is possible, however. to premix the catalyst components, centrifuge to separate the solid phase, and use the clear supernatant liquid to produce the copolymer. High purity monomers were used in all polymerizations. Ethylene was obtained from either the Phillips Petroleum Co. or Petroleum Chemicals, Inc. Propylene was 99+y0 purity obtained from Sinclair Petrochemicals, Inc. Heptane boiling a t 98-9OC. was obtained from Matheson Coleman & Bell and was purified using a chromatographic column packed with Davison activated silica gel (28- to 200-mesh) and coconut charcoal (50- to 200-mesh). The alkyl aluminum halides were purchased from either Texas Alkyls, Inc., or Ethyl Corp. and the VOCl, from the Anderson Chemical Co. Certain advantages are inherent in the use of a soluble catalyst. Higher efficiencies can be obtained, since the active catalyst site does not become coated with a layer of polymer. Catalyst efficiencies as high as 2000 grams of copolymer per gram of VOC13 have been obtained, and there is no reason to believe that this is the maximum possible. This in turn leads to lower catalyst residues in the rubber. The more random nature of the copolymer produced by these soluble catalysts is shown by their complete solubility in boiling n-hexane. \Ye have demonstrated this using copolymers containing both 50 and 657, propylene. As further evidence of their randomness, x-ray examination of 40y0 propylene copolymers has shown no crystallinity despite the high ethylene content. These soluble catalyst systems are not capable of producing isotactic polypropylene, so that copolymers very high in propylene do not show polypropylene-type crystallinity. Other advantages of using these soluble catalysts lie in the flexibility which they afford in the polymerization process. Although the materials selected for evaluation were prepared in autoclaves under pressure, our laboratory runs n e r e usually
conducted at atmospheric pressure and allowed to exotherm from ambient temperature. Certain polymerization variables were of special interest and were studied i n laboratory runs. For instance, as shown in Figure 1, it is possible to vary the viscosity-average molecular weight by varying the Al/V molar ratio when ethyl aluminum dichloride is used in the catalyst. A maximum in inrrinsic viscosity is observed a t a ratio of approximately 15 to 1. Beyond this point the intrinsic viscosity drops off. I t is this latter range: in which higher efficiencies are obtained. that is of particular interest because of the possible variations in molecular weight. The effect of AI/V ratio on molecular weight can also he coupled with total catalyst concentration to produce further variations. Figure 1 also illustrates the important relation of catalyst efficiency to the AI/V ratio. I t is possible to realize a sevenfold improvement in efficiency by increasing this ratio from 5 to 18. As shown in Figure 2, a similar relationship of catalyst efficiency to Al/V ratio is observed using ethyl aluminum sesquichloride in place of dichloride. The efficiency is increased by a factor of 3 by increasing the ratio from 10 to 20. The viscosity-average molecular weight remains almost constant over this range, however, in contrast to what was found using the ethyl aluminum dichloride. Our results with diethyl aluminum chloride, in general, parallel those described for the sesquichloride. I t is also possible, at a given Al/V ratio and VOCla concentration, to influence the polymerization by using various Et&lCl-EtAlC12 mixtures. T h e major result is that a mauimum in efficiency is found using a mixture consisting of 40 to 60 mole Yo Et41C12 (Figure 3). Efficiency is improved 40 to 100% by using a mixed halide catalyst in the optimum range. Furthermore, lower intrinsic biscosities obtained when EtzAlCl is mixed with the EtAlClz reflect a significant effect of this ratio on the copolymer molecular weight. These soluble catalysts are very sensitive to the presence of excess aluminum halide. I n Figure 4 it is shown that when a mixture of AIR3 and AlBr3 is used, as soon as the stoichiometric amount of AlBr3 necessary to produce the alkyl aluminum dibromide is exceeded, efficiency decreases sharply. M'ith a ratio of 3 moles of AIBr3 to 1 mole of A1R3 one obtains only a trace of polymer using a C2H4/C3H, feed of 50 mole % propylene. The latter condition is similar to that described by Carrick (3). Such catalysts are active for polymerizing
Y
-d 5
15
IO
20
AI/ V Figure 1. Variation of efficiency (grams EPR/gram VOCI, X lo-?) and intrinsic viscosity (cyclohexane a t 30" C.) with AI/V molar ratio Catalyst: EtAICly/VOCls 0.1 0 mmole of VOCII, 350 ml. of n-heptane, 1 to 1 molar feed of CrH,/C3H6 at 2 liters per minute, 30-minute reaction time
VOL.
1
NO. 3
SEPTEMBER 1 9 6 2
211
12
" 1 6
a
3
0
1
O
c
Figure 2.
20
Variation of efficiency (grams EPR/gram VOC13
X 1OP2) and intrinsic viscosity (cyclohexane a t 30" C.) with AI/V molar ratio Catalyst:
Et3AIf&/VOClj
0.05 mmole of VOCII, 350 ml. of n-heptane, 1 to 1 molar feed of C?Ha/CsHs a t 2 liters per minute, 30-minute reaction time
16
r
1 8
0 0
I
I
I
I
20
40
60
80
2 liters
0.12 90
290 66 0.4 0
Ii ~
15 AI/V
IO
Table 1. Variation of Feed Composition Catalyst EtzAIC1. Mole ratio Al/V = 20. Feed rate minute VOCla: millimole/liter n-heptane 0.06 0.12 C3H6in feed, mole % ' 50 70 G. EPRig. VOCl, 1300 1000 CsHs in copolymer, wt. 9?, 40 52 Intrinsic viscosity (Tetralin at 2.4 3 5 135' C . ) Crystallinity, % 0 0
,lo
