A NEW HYDROCARBON ELASTOMER Copolymerization of Olefins and JVoncoy-ugated Dienes E. K. GLADDING, B. S. FISHER, AND J . W. COLLETTE Elastomer Chemicals Department, E . I. du Pont de Nemours
Co., Inc., Wilmington, Del.
The composition of sulfur-curable elastomers derived from olefins and diolefins is described and methods are given for their synthesis using coordination catalysts. Certain factors that influence the laboratoryscale polymer synthesis are discussed and the effects of catalyst type, polymerization temperature, and diene structure on the rate of polymer formation and polymer composition are outlined. Polymer properties are discussed in general terms, with particular emphasis on oxidative stability.
the discovery that polymers and copolymers of a-olefins can be synthesized readily in great variety with the aid of coordination catalysts, there has been a widespread interest in adapting these polymers and copolymers to commercial uses. Potentially favorable economics, stemming from a large-volume, inexpensive raw material supply and also polymer physical and chemical properties not attainable heretofore, are the major driving forces for the large effort to commercialize such polymers. In the elastomer field, attention has been centered on copolymers of ethylene and propylene. Early publications ( 74, 75: 20) indicated that ethylene-propylene copolymers would combine adequate elastomeric properties with outstanding oxidation and ozone resistance. A problem involved in the practical utilization of these copolymers, however, relates to the specialized vulcanization procedures which are required. Free radical chemistry, based on the decomposition of peroxides with or without adjuvants (6),is used to cross-link the copolymer and this chemistry, as now understood, imposes more or less severe limitations on the rubber compounding agents which may be employed. For example, acidic clays and many of the commonly used antioxidants interfere with peroxide vulcanization. Various methods for circumventing these difficulties have been suggested (9, 72, 73). There are reports also that sulfur-curable copolymers can be synthesized by incorporating into the ethylene-propylene product appropriate amounts of dienes. Conjugated dienes have been mentioned as comonomers (77), as well as various nonconjugated dienes ( 7 ) . This paper describes a class of sulfur-curable elastomers of the latter type-copolymers of a-olefins and nonconjugated dienes. These copolymers, in general, utilize ethylene and another a-olefin as major components, and as a minor component, a nonconjugated diene which introduces carboncarbon unsaturation pendant to the copolymer chain in sufficient amounts to impart sulfur curability. The copolymers of present interest thus comprise flexible polymethylene chains having alkyl groups attached at frequent intervals and, much less frequently, pendant unsaturated hydrocarbon groups. These copolymers are synthesized with coordination catalysts in organic solvents. A variety of nonconjugated dienes may be used, including aliphatic, or straightchain, types and bicyclic compounds of the norbornene or norbornadiene series. Numerous a-olefins may be used, although for economic reasons propylene is preferred. INCE
Sulfur Curable Elastomers Monomers Structural Lrni/
Ethylme
- CH 2-CH2-
a-Olefin
-CH2-CH-
R
I
Nonconjugated diene
-CHz-CHI R-C=C’ I
R
R ‘R
-CH-CH-
WR R - C=C’ I
R
‘R
c?
-CH-CH-
R
R
A broad range of copolymer compositions is possible without loss of elastic character. While the Composition range is broad, practical considerations impose certain limitations. Elastomer Composition
Ethylene Weight 70 Mole 70 Nonconjugated diene Mole per kg.
25-75 33-80 0.10-1.0
Thus, there is a n upper limit to the ethylene content which, if exceeded, leads to the appearance of polyethylene crystallinity in the elastomer and this, in turn. leads to solvent insolubility as well as high power losses in certain dynamic tests (2). This upper limit on ethylene content is in the range of 80 mole %-that is, about four ethylene units (on the average) for each unit derived from either the a-olefin or the diolefin. T h e lower limit on ethylene content is imposed to a large extent by the choice of a-olefin comonomer. \Vith propylene comonomer, for example, about 33 mole yo of ethylene-one ethylene for every two units of propylene or diolefin-appears to be needed. Low temperature properties are adversely affected if the ethylene content is reduced too much below this value. The adverse influence of high propylene content on the low temperature behavior of ethylene-propylene copolymers has been noted by Natta and Crespi (76) and has VOL 1
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0
80
In this particular experiment, the yield of polymer was 14.2 grams. The iodine number of the product was 16.8 and its propylene content was 56y0by weight. Various alternatives to the procedure just described can be used. In general, hydrocarbons and inert halogenated hydroElastomer Synthesis, Alternatives
,
40 60 8 0 MOL% P
,
Solvents
100
Catalysts
Figure 1 . Glass transition temperatures of ethylenepropylene copolymer
been confirmed by data obtained in this laboratory (Figure 1): where an abrupt increase in the glass transition temperature has been observed a t the point where the copolymer comprises about 60 mole % propylene (7, 17, 78). The concentration of carbon-carbon double bonds in the elastomer is adjusted to provide for sulfur curability. A rather broad range can be used, from about 0.10 to 1.0 mole of unsaturation per kilogram of copolymer. Generally, about 0.3 to 0.6 mole per kilogram is preferred, as this level of unsaturation provides an adequate degree of sulfur curability.
Experimental The laboratory synthesis of these elastomers is straightforward, as is shown by this preparation of the interpolymer of ethylene, propylene, and 11-ethyl-1,ll -tridecadiene.
Solvent Catalyst
Elastomer Synthesis, laboratory Scale Tetrachloroethylene 400 ml.
voc1,
TIBA Monomers ll-Ethyl-l,lltridecadiene Ethylene Propylene Time Temp. Isolation Yield
0,0025 mole/liter 0,0050 mole/liter
0,025 mole
Isolation
carbons are suitable solvents for the polymerization reaction. Many of the catalyst systems commonly mentioned in the literature are active in promoting the terpolymerization. Systems based on combinations of vanadium compounds and aluminum alkyls appear, a t this time, to be preferred, as they show little, if any, tendency to promote the isotactic-type polymerization which introduces crystalline polymeric impurities. In the laboratory, the polymer can be isolated by evaporation, after an aqueous acid wash to remove catalyst, or the entire charge can be steam-distilled and the resulting wet polymer dried on a rubber mill. I n all cases, it is considered advisable to incorporate a small amount of an antioxidant to protect the elastomer against oxidative degradation during prolonged storage.
Results Many nonconjugated dienes, all of which are accessible through classical synthetic procedures, have been utilized in the preparation of these sulfur-curable interpolymers ( 4 , 5, 8, 79). Nonconjugated Dienes
1
c=c-c-c-c=c
1 c=c-c-c-c=c-
1 , O liter/min. 3 . 0 liter/min.
1
1
c=c-c-c=c-c I C
c
1
C=C-(C),
-c=c-c I c-c
21 min. 35-45 c. Pptd. with methanol 14.2 g. (11 NO. = 16.8. 'j" P = 56)
The solvent, in this case tetrachloroethylene, is thoroughly dried over silica gel. I t is then charged to the reactor, sparged with nitrogen, and agitated to remove dissolved oxygen. T h e reactor is a standard resin kettle equipped with an electrically driven propeller-type agitator, inlet tubes for introduction of gaseous monomers, an opening sealed with a rubber serum cap through which catalyst and diene may be introduced by means of hypodermic needles, and suitable traps to prevent backflow of air. The diene is introduced and then flow of gaseous monomers is started, in this case at a rate of 3 liters of propylene and 1 of ethylene per minute. After 10 to 15 minutes (to saturate the solution with ethylene and propylene), the catalyst components are added, first the aluminum triisobutyl, followed, after a minute or two, by the vanadium oxytrichloride. For convenience, the catalyst components are handled as 1M solutions in tetrachloroethylene. Reaction starts a t once when the vanadium catalyst component is added. The temperature rises and is maintained. by cooling with an external water bath, between 35' and 45' C. After approximately 20 minutes the reaction mass is too viscous to agitate and polymerization is interrupted, and the product is isolated. by drownins the charge in excess methanol. The precipitated, gummy polymer is recovered and washed in a Waring Blendor with additional methanol and then acetone. These washes remove imbibed tetrachloroethylene solvent and also most of the catalyst residues. The washed polymer is dried first in air and then on a warm rubber mill. 66
Benzene, cyclohexane, chlorobenzene, pentane, heptane TiCla, VCl,, VO(OR),, Li.U(C1OH21)4, LiAl(C&II)I, A ~ ( C , H S ) C ~ ~ Aqueous wash, evaporate solvent, steam distill
I L E C PRODUCT RESEARCH A N D DEVELOPMENT
1
C=C = P O L Y M E R I Z A B L E DOUBLE B O N D
The terminal double bond of the aliphatic dienes is active in the polymerization reaction. An internal double bond is inactive and appears in the interpolymer as a side-chain cure site. O n this basis dienes with only one terminal double bond are preferred. Dienes with two terminal double bonds, such as 1,5-hexadiene, have been used successfully, but a portion of the diene appears to be incorporated as a cyclized structure (70) with consequent loss of unsaturation and there is a tendency also, because of the bifunctional nature of this monomer. to contaminate the elastomer with an insoluble fraction of cross-linked material. With the cyclic dienes of the norbornene series, the double bond of the bicyclo ring system is active toward polymerization ( 3 ) . However, the polymerizability of such double bonds can be prevented, or a t least retarded very greatly, by having an alkyl group attached to one of the doubly bonded ring carbon atoms. Thus, the 2-alkyl norbornadienes can be used as monomer components.
The 1,2 double bond of dicyclopentadiene appears to be slightly active toward polymerization. This was demonstrated by interpolymerizing ethylene. propylene, and 9,l O-dideutero9,lO-dihydrodicyclopentadiene. When concentrations of the dideutero compound in the range of 0.2 to 0.5 mole per liter were present during polymerization, the resulting interpolymer exhibited an infrared adsorption a t 4.6 mp (C-D band) which could not be removed by exhaustive extraction of the interpolymer with alcohol and acetone. However, the 1,2 double bond is much less reactive than the one of the bicyclo ring system. Interpolymers of ethylene, propylene, and dicyclopentadiene (or 1,2-dihydrodicyclopentadiene) are prepared readily when the diene concentration during polymerization is only 0.01 to 0.02 mole per liter. Dienes differ considerably with respect to their ease of interpolymerization with ethylene and 0-olefins. \Vith catalyst
Table I.
Ethylene-Propylene-Diene Terpolymers
Diene
Diene
Terpolymer Propylene, molelkg. wt. 70
Diene,
Concn.,
MolelL.
C=C-(C),-C=C-C
I
c-c
0.015 0.020
0.65
65 66
0.010
0.76
57
0.060
0.66
56
0.40
Catalysts. (IsoBu),Al-VOCl, Solvent. Tetrachloroethylene
Terpolymerization, E/P/D' ienes
Diene Polymerization
(TIBA/VOCla)
Diene Dime
Incorporation
NORBORNENES
\
EASY
'\
c=c-(c)8-c=c-c
I
\ ENTERING MONOMER
c-c I
I
c=c-c-c-c=c-c
/ I
I C
c=c-c-c=c-c
c=c-c=c I
C
+
DIFFICULT
derived from aluminum alkyls and vanadium oxytrichloride, the norbornenes are most readily incorporated into the terpolymer. Aliphatic dienes with widely spaced double bonds are next, followed by dienes with double bonds located in the 1,4 or 1,5 positions. The 1,3 dienes, such as isoprene, verge on being inoperable, a t least under the polymerization conditions outlined above. Differences in diene reactivity, while strongly dependent on diene structure, are influenced also by the polymerization conditions. T h e nature of the catalyst is important, as is its manner of preparation-in the presence or absence of the monomers, for example. Polymerization temperature is an important variable and, generally, low temperatures facilitate terpolymerization of ethylene, 0-olefins, and dienes with closely spaced double bonds. Norbornenes and aliphatic dienes with widely separated double bonds have no major influence on the polymerization reaction when used in the concentrations needed to produce a polymer with 0.3 to 0.6 mole of unsaturation per kilogram. Neither polymerization rate nor product composition is affected in a gross way. The norbornenes are, however, more reactive monomers than the aliphatic dienes. Concentrations of 0.01 to 0.02 mole per liter of the norbornene during polymerization suffice to produce a polymer having the above level of unsaturation. Aliphatic dienes require a concentration three to six times greater (Table I). As the double bonds of the aliphatic diene are moved closer to one another, polymerization rates tend to decrease and there is a tendency also to repress polymerization of the a-olefin being used. Evidence now available suggests that dienes with
closely spaced double bonds (perhaps including 1,5-dienes) form a cyclic complex with the catalyst which makes the chain propagation reaction more difficult. Dicyclopentadiene, 2-methylenenorbornenej and 11-ethyl1,ll-tridecadiene have only a relatively small influence on polymerization rate-as compared to an ethylene-propylene copolymerization control-while 1,4-hexadiene reduces the rate markedly (Figure 2). T h e experiment with 1,4-hexadiene a t 25' C. represents a n extreme case of rate retardation and was chosen to illustrate the very considerable effect a 1,4-diene can exert. Altering the reaction conditions by reducing the polymerization temperature to 0' C. increases the
@C
c-c-(cl~-c=c-c c-c
Figure 2.
c-c-c-c
-
c-c
Ethylene-propylene-diene terpolymerization Catalysts. (IsoBu)~Al-VOCld Solvent. CI,C=CCI?
VOL.
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-
90;
eok
TERPOLYMER
-
E/P CONTROL
Table 111.
kM
p 650700-
’
c 403020-
lor I
0-
M
I
M
c=c-(c)e-c-c-c I c-c
WC Figure 3. Effect incorpora tion
of
diene
c=c-c-c=c-c
on
structure
propylene
Ethyl VI. Methyl Side Groups E/P/A E/B/A E/P/C E/B/’C
Olefin, wt. % 45 43 55 55 Diene, wt. % ’ 5-8 HAF black 50 50 40 40 Cure Accelerated sulfur, 1 hr. at 160 C. M-300, p.s.i. 1500 1400 2000 1800 T-B, p.s.i. 2300 2500 2200 2400 E-B, % 410 480 330 400 Shore hardness 70 69 70 75 Yerzley resilience, 7 0 57 56 53 53 Compression set, % 14 17 24 37 A. Aliphatic diene C. Cyclic diene
Catalysts. (ls~Bu)aAl-VOCla Solvent. CClz = CClz
Table IV.
Physical Properties
Solubility
Table II.
Propylene Incorporation
p,
Yield,
2-Hexene 1-Hexene 2-hexene 1,4-Hexadiene
+
wt.%
G./L. 58 51
57 57 25
18
rate considerably, but even here it is only about one third that of the control. A strong catalyst-diene interaction has been demonstrated also by comparing the behavior of a n ethylene-propylene11-ethyl-1,ll-tridecadieneterpolymerization with a similar experiment in which a 1,4-diene is used, the catalyst being prepared from an alkyl aluminum dichloride and vanadium oxytrichloride. I n the former case, the polymerization proceeds smoothly while, in the latter, the polymerization rate is almost nil. Polymerization of propylene is repressed by the presence of 1,4-dienes, as indicated by a change in terpolymer compositions relative to that of a n ethylene-propylene copolymer control (Figure 3). Norbornenes and aliphatic dienes with widely separated double bonds exert but little influence in this respect. T h e nonterminal double bond of 1,4-hexadiene is not, of itself, responsible for inhibition of propylene polymerization. Its location relative to the terminal double bond is critical. Thus, neither 2-hexene nor a n equimolar mixture of 1- and 2hexenes inhibits the incorporation of propylene (Table 11). I n addition to those already mentioned, various combinations of olefins and diolefins have been copolymerized to sulfurMonomer Combinations 01ejn.r
Diolefins C
c=c-c-c-c=c-c
c=c-c-c-c-c
c =c- c- c- c= c- c
c=c-c : c=c-c-c
c=c-(c)8-c=c-c I c-c
c=c
; c=c-c-c
c = c ; c=c-c-c
6a
I
c=c-c
C I
c=c- c-c=c- c
m
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Soluble in benzene, toluene, tetrachloroethylene, carbon tetrachloride, chlorobenzene Insoluble in acetone, butanol, methanol Density, g./cc. E/P/diene 0.85-0,86 E/B/diene 0.87 Refractive index 1.481-1.484 Glass trans. temp., O C. -50 to -60 Compositions. 30-60 wt. % E Dienes. 6-Me-1,5-heptadiene, 1,4-hexadiene Dicyclopentadiene. 11-Et-l,ll ddecadiene
curable elastomers. Investigations in this area are not yet complete, but thus far it appears that minor changes in polymer structure do not greatly alter the properties of the elastomer. Specifically, elastomers with side-chain ethyl groups (from 1butene) appear to be about equivalent to those with side-chain methyl groups (from propylene) (Table 111).
Discussion As a class, these terpolymer elastomers possess attributes which are indicative of their broad utility in commercial applications. Their low density, combined with the low cost of the major intermediates from which they are synthesized, is suggestive of an ultimately favorable economic position lvith respect to elastomers now in general use. Electrical properties are inherently excellent, and these can be retained in vulcanizates through appropriate compounding. High quality reinforced vulcanizates, as judged by high tensile strength, high resilience, and low compression set. can be obtained readily although, in common with other elastomers \\hich do not crystallize on elongation, these terpolymers give gum vulcanizates of rather low tensile. Heat aging and ozone resistance are outstanding. Accelerated air-oven aging, for example, is best carried out in the range of 150 O C. in order to differentiate various stocks under test within a reasonable time. The sulfur curing system used permits the expected degree of compounding flexibility and the terpolymer elastomers, unlike their copolymer counterparts, are not limited in this respect by the chemistry of peroxide curing systems. Basic physical properties of raw terpolymer elastomers are given in Table IV. I n accordance with their chemical makeup, the terpolymers are soluble in the common hydrocarbon and chlorinated hydrocarbon solvents. They are insoluble in the usual oxygenated solvents. Density is lower than that of other elastomers in general use. The low glass transition temperature is indicative of good low temperature flexibility. Permeability of the terpolymer elastomers to gases is about the same as that of natural rubber and, of course, much higher than that of butyl (Table V).
Table V.
Permeation of Gases at 30' C.
TRIDECAD I E N E
Terpolymer" N .R. Butyl Permeability, Q X 108 (Sq. Cm.)(Sec.)-' (Atm.)-'
6.4 19 82
0.35 1.3 5.2
8.7 23 123
DIENE
-
HEP rADlENE
PENTADIENE
0T - E
2 2000-
-s
E-E
-
4500
p'
;1000W
N2 0 2
coz
Diffusivity, D X 106 (Sq. 0.8 1.5 1.1
Nz
Cm.)(Sec.)-l 1.6 2.2 1.4
Solubility, h (Atm.) 0.08 0.06
2 0.13 0.10 COP 0.71 0.90 EIP/G-.hrie-1,5-heptadiene, gum stack.
Table VI.
0.11 0.08
0.06 0.12 0.65
0
0
0.06
0ORIG. M-300 T-E
E-E
Thermal conductivity, (cal.)(cm.)-' X (sec.)-l( O C.)-l X 103 Heat capacity, (cal.)(cm.)-i(3C.)-I
970 3100 540
1100
ANTIOXIDANT
-
1300 2300 4 20
3600 560
NEOZONE D
910 2000 500
Figure 4. Heat aging of ethylene-propylene-diene terpolymer black stocks at 12 1 ' C. for 14 days
Terpolymera
'V,R.
0.96
0.75
0.46 0 56
0.36 0.52
Thermal diffusivity, (sq. cm.)(sec.)- I X
a
c
8 DAYS II-ETHYL- 1 > 1 1 TRIDECA D I E N E
Thermal Properties
103
-400 300 d
z
IO DAYS 1.4-HEXADIENE
2000-
n
6-METHYL- 1.5HEPTADIENE
-
4 DAYS DICYCLOPENTADIENE
n
0T - B E-E
- 500
Gum s/ocX..
-400 8 -300 6 200
Both thermal diffusivity and thermal conductivity of the terpolymer types are perhaps 10 to 15% greater than those of natural rubber (Table VI). T o the extent that thermal diffusivity and conductivity are controlling factors, satisfactory behavior of the terpolymers is indicated for uses where heat conduction and dissipation are requirements, such as in the curing of thick sections or in constructions subjected to heat build-up through flexing. The DC resistivity of raw terpolymer is in the range of 10'6 ohms per cm. In certain insulation-type stocks this resistivity can be retained. The dielectric constant and the power factor, both at 1000 cps., are about 2.5 and O.27,, respectively. Dielectric strength is close to 800 volts per mil. T h e high degree of heat aging resistance of terpolymer elastomers from ethylene, propylene, and various nonconjugated dienes is illustrated in Figures 4, 5, and 6. Two structural features, common to all of these terpolymers. are very likely responsible for their stability toward oxidative degradation during heat aging. First? the fully saturated backbone chain is less susceptible to oxidative cleavage (or perhaps more efficiently protected by antioxidants) than polymers with unsaturated linkages in the main chain as, in the latter case, the resulting multiplicity of allylic hydrogens is known to sensitize the polymer to peroxidative attack. Second, the carboncarbon double bond cure site. and its accompanying allylic hydrogens, is pendant to, and therefore isolated from, the backbone chain. Thus, oxidative attack in the neighborhood of the sulfur-containing cross link, or at double bonds which have not been involved in the cross-linking reaction, is confined to a region sufficiently far removed from the backbone to avoid its destruction and the associated degradation of vulcanizate physical properties. Examination of the data, in fact, indicates that the terpolymer elastomers tend to cross-link further during severe heat aging rather than degrade. The chemistry of this crosslinking process is not clear at the moment. I t may represent a continuation of the sulfur cure or the terpolymer may undergo
ORIG. M-300 T-E E -E
1400 2700 510
1300 3500 540
1600
I800
I800
19W 320
300
5
Figure 5. Heat aging of ethylene-propylene-diene terpolymer black stocks at 150' C.
--
M-200 M-300 0T - B E-B
ILLm
n
n
1600
AGING 16 H R S AT 190.C.
Figure 6. Heat aging of ethylene-propylene-1 1-ethyl1 , l 1 -tridecadiene black stock at 175" and 190" C. S. Thiuram M. MBTS, 60 minutes a t 150' C. 50 HAF black
a slow oxidative cross-linking reaction. Either the tertiary hydrogens of the backbone chain or residual double bonds not used in the sulfur curing process could be involved. In any case, this cross-linking reaction is relatively slow and useful tensiles and elongations are retained even after extremely severe heat aging (Figures 5 and 6). Similar considerations apply to ozone resistance. These terpolymers, in static tests, are not affected by 100 p.p.m. of ozone during several hundred hours' exposure. Here also it seems likely that the absence of unsaturation in the main polymer chain is responsible for this behavior. VOL. 1
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Acknowledgment
The authors thank LV. F. Gresham and M. Hunt, who established the basis for much of the work reported herein (U. S. Patent 2,933,4801, S. W. Caywood, M . S. Fawcett, J. L. Nyce, J. R. Pailthorp, D. N. Robinson, C. A. Stewart, R. C. Thamm, and C . A. Young for their contributions to the polymerization studies; and H. K. Frensdorff, R. R. Garrett, and R. M . Tabibian for carrying out many of the physical meamrements reported.
(6) Goldberg, E. J. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2.958.672 (Nov. 1. 1960). (7) Gresham, 'W. $., Hunt, M.'(to E. I. du Pont de Nemours & Co.), Ibid., 2,933,480 (April 19, 1960). (8) Henne, A. L., Chanan, H. H., J . Am. Chem. SOL.66, 392 (1944). (9) Makowski, H. A., Seelbach, C. W. (to Esso Research and Engineering Co.), French Patent 1,220,970 (Jan. 13, 1959). (10) Marvel, C. S., Stille, J. K., J . Am. Chem. SOC.80, 1740 (1958). (1 1) Montecatini. S.u.a.. Australian Patent 29.377 (Julv 8. 1957). ' (l2j Montecatini, S.p.a., Belg. Patent 563,834 (Jan. 9,'1958). (13) Zbid., 573,161 (Nov. 20, 1958). (14) Natta, G., International Synthetic Rubber Symposium, >
L
,
London, 1957. (15) Satta. G., Rubber and Plastics Age 38, 495 (1957). (16) Natta, G., Crespi, G., Rubber Age87,459 (June 1960). (17) Natta, G., Oanusso, F., Moraglis, G.. J . Polymer Sci. 25,
literature Cited
(1) Dannis, M. L., J . Appl. PolymerSci. 1, 121 (1959). (2) Dingle, A. D., Rubber World 143, 93 (October 1960). (3) E. I. du Pont de Nemours & Co., Australian Patent 32,649 (May 8, 1958). (4) E. I. du Pont de Nemours & Co., Can. Patent 598,984 (Oct. 13, 1959). (5) Freireich, E., Hyman, J., Lidov, R. E. (to Julius Hyman and Co.), Belg. Patent 498,176 (Jan. 5, 1951).
119 (1957). (18) deding. E. P., Ibid.: 21, 547 (1956). (19) RiobC, O., Compt. rend. 226, 1625 (1948). (20) Rubber and Plastics Age 40, 437 (1959). RECEIVED for review September 25, 1961 ACCEPTED February 13, 1962 Division of Petroleum Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961.
A NEW HYDROCARBON ELASTOMER Properties ff an Ettylene-Propylene-Noncoyugated Diene Terpobmer J . J. VERBANC, M. S. FAWCETT, AND E. J . GOLDBERG Elastomer Chemicals Department, E. I. du Pont de h'emours & Co., Inc., Wilmington, Del.
A new hydrocarbon elastomer has been synthesized from petrochemical intermediates using coordination catalysis. This amorphous polymer resembles commercial diene elastomers in general appearance, is completely soluble in hydrocarbon and chlorinated hydrocarbon solvents, and is stable to prolonged storage. It can b e vulcanized effectively b y the use of accelerated sulfur systems and reinforced by numerous fillers such as carbon blacks, clays, and certain silicas. Reinforced vulcanizates are strong, resilient, and extremely resistant to oxygen, ozone, heat, light, and many chemical agents. Properly compounded vulcanizates exhibit excellent electrical and low temperature properties. Permeability to gases, specifically nitrogen, oxygen, and carbon dioxide, parallels natural rubber. Thermal diffusivity and thermal conductivity are
-15%
greater than polyisoprene.
The practical significance of the thermal data remains to be deter-
mined.
I N REcEN'r years, the synthesis of polymers from a-olefins via coordination catalysis has been studied extensively. Much of the early pioneering work of Ziegler (77) and Natta ( 8 ) involved the synthesis of linear high molecular weight polymers of ethylene and stereospecific polymers derived from other a-olefins useful as plastics or fibers. More recently (7, 7, 9, 70, 72) copolymers of ethylene and propylene which exhibit the viscoelastic behavior of polyisobutylene, natural rubber, etc., have been synthesized using the same general chemistry. Preliminary evaluation of such polymers in end-use items confirms their attractive vulcanizate properties, but their precise future is in doubt because of the limitation imposed by free radical or peroxide vulcanization. The product described in this report is a new hydrocarbon elastomer synthesized from petrochemical intermediates by means of modified coordination catalysis. This elastomer falls in the general category of those described by Gladding,
70
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
Fisher, and Collette (5). It is a terpolymer of ethylene, propylene, and a nonconjugated diene (6). The concentration of termonomer is adjusted to permit adequate sulfur vulcanization. I t is a distinctive polymer which combines in a single product the good properties exhibited by the currently available hydrocarbon elastomers including versatility of vulcanization. R a w Polymer
T h e raw polymer is a transparent white to amber-colored solid resembling commercial diene hydrocarbon rubbers in general appearance, I t is stable to storage and shows no tendency to freeze or crystallize even after prolonged exposure at subzero temperatures. Although the bulk viscosity of this experimental polymer is considerably higher than that of general-purpose rubbers such as SBR-1500, it can be milled and compounded readily. Unlike conventional elastomers,
