CA1120911A

CA1120911A - Polymerization and copolymerization of trans-piperylene and isoprene

Info

Publication number: CA1120911A
Application number: CA000322362A
Authority: CA
Inventors: Morford C. Throckmorton
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1978-04-05
Filing date: 1979-02-27
Publication date: 1982-03-30
Also published as: US4148983A

Abstract

Abstract Of the Disclosure There is disclosed a method for the polymeriza-tion and copolymerization of diolefins selected from the group of monomers consisting of trans-1,3-pentadiene and isoprene employing as a catalyst a mixture of (A) an organometallic compound selected from the group consisting of aluminum trialkyls, magnesium dialkyls and zinc dialkyls, (B) a soluble chromium compound selected from the group consisting of chromium salts of organic acids containing from 2 to 20 carbon atoms, organic complex compounds of chromium containing tridentate ligands and .pi.-bonded organochromium compounds, and (C) a member selected from dialkyl hydrogen phosphites, diaryl hydrogen phosphites and tris(2-chloroethyl)phosphite.
There is also disclosed as a composition of matter a catalyst comprising a mixture of (A) an organometallic compound selected from the group consisting of aluminum trialkyls, magnesium dialkyls and zinc dialkyls, (B) a soluble chromium compound selected from the group con-sisting of chromium salts of organic acids containing from 2 to 20 carbon atoms, organic complex compounds of chromium containing tridentate ligands and .pi.-bonded organochromium compounds, and (C) a member selected from dialkyl hydrogen phosphites, diaryl hydrogen phosphites and tris(2-chloro-ethyl)phosphite.

Description

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BACKGROUND OF INVENTION
... . . . . . . .
This invention is directed to a method of polymerization and/or copolymerization of diolefins selected from the group of monomers consisting of -trans-1,3-pentadiene and isoprene. It is also direc-ted to ; catalyst sys-tems used in these polymerizations. The products of these polymerizations have properties ranging from rubbers to plastics and thereby find utility in the preparation of vulcanized rubber products and plastics.
The polymers which have glass transltion temperatures (Tg's) which are relatively low may be utilized in tire carcass s-tocks while those with high Tg's may be used in tread stocks.
More specifically, -this invention is directed -to the use of a tertiary catalyst system comprising (~) an organometalllc compound selected from the group consis-ting of trialkylaluminums, dialkylaluminum hydrides, dialkyl-magnesiums, and dialkylzincs, (B) a soluble chromium com~
pound selected from the group consisting of chromium salts of organic acids containing from 2 to 20 carbon atoms, organic complex compounds of chromium containing tridentate organic ligands, and ~r-bonded organochromium compounds, and (C) a member selected from tris(2-chloro-ethyl)phosphite, dialkyl hydrogen phosphites and diaryl hydrogen phosphi-tes, to polymerize and copolymerize diolefins selected from the group of trans-1,3-pentadiene and isoprene.
Belgian Patents 530,617 and 535,082 and U. S.
Patent 2,825,721 were among the first to describe a ' par-tially reduced or par-tially oxidized chromium oxide supported on silica alumina cracking catalys-t for -the polymerization of e-thylene.
U S Patent 3,114,743 reported that bu-tadiene was polymerized to a trans-1,4-polybutadiene using either CrC13 and diethylaluminum hydride or chromium acetyl-acetonate and trie-thylaluminum; -the same ca-talyst poly-merized isoprene but the polymer was not described~
However, Belgian Patent 543,292 indicates tha-t when diisobutylaluminum hydride-CrC13 were used to polymerize isoprene, a 1,4 polyisoprene was obtained.
I-talian Patent 538,453 and British Pa-ten-t 835,752 indicate tha-t a binary catalyst system of chromium acetylacetonate and triethylaluminum polymerizes buta-diene to a prevailingly 1,2-enchained linear polybuta-diene and isoprene to prevailingly 3,4-polyisoprene.
Polyisoprenes prepared with a binary catalys-t system such as chromium acetylacetona-te plus -trie-thyl-aluminum or tris(1r-allyl)chromium plus a Lewis acid were generally low molecular weight liquids which had in-trinsic viscosities of about 0.2 dl/g. This is reported in J. Polym. Sci., Chem. Ed ~L, 2489 (1973).
In Proc. Acad. Sci. USSR 169, 790 (1966) it is reported that -the presence of oxygen with tris(crotyl) chromium during the polymeriza-tion of bu-tadiene caused almost complete inversion of the polymer microstructure from normally about 83 percent 1,2- to about 95 percent trans-1,4-polybutadiene. It has been reported in Bull. Acad. Sci. USSR, Div. Chem. Sci., 2059 (1967) that trichloroacetic acid wi-th -tris(cro-tyl)chromium polyrnerized butadiene to 93 percent cis-1,4-polybutadiene.
Polymers having high 1,4-trans-enchainmen-ts of isoprene and butadiene have been prepared using a chromia supported on silica-alumina, as reported in Do~l. Akad.
Mau~. USSR 124, 595 (1959) and Polym. Sci. USSR 9, 1802 (1968).
Chem. Abs. 80, 109590 v (1974) reports the preparation of 1,2~polybutadiene by polymerizing butadiene in the presence of hydrogen using chromium acetylacetona-te, dibutylphosphonate and triisobutylaluminum.
; Chem. Abs. 80, 4644n. (197h) reports that a polymer analyzing 95 percent 1,2-polybu-tadiene was pre-pared using a chromium compound, an organoaluminum com-pound and phosphoric acid es-ter catalyst system.
It has been repor-ted in Kobunshi Ronbunshu 31, 754 (1974) that a binary catalyst system comprised of chromocene (dibenzene chromium) and an organic halide polymerized butadiene to a polymer having a microstruc~
ture very similar to that produced by radical inîtiators, that is, about 67% trans-1,4; 15% cis-1,4- and 18% 1,2-polybutadiene.
In U. S. Paten-ts 3 7 429,940 and 3,804,913 there is repor-ted -that a ternary ca-talyst sys-tem comprising chromium acetylacetona-te, -triethylaluminum and an ali-phatic halide~ such as t-butyl chloride, oligomerized conjugated diolefins such as butadiene, isoprene and piperylene, -to large ring cYclic trimers such as trimethyl cyclododecatriene.

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There is reported in U S Paten-t 3~75L~, oL~ -tha-t another ternary ca-talys-t system using chromium ace-tyl-acetonate, triethylaluminum and a nitrogen containing compound, such as a-(2-pyridyl)benzylidine-p~toluidine produced oligomers of butadiene, isoprene or piperylene.
It is reported therein that -the polybutadienes having molecular weights between about 300 and about 1~00 were prepared and recovered in about 90 percent yield; less than 10 percent of the polybutadiene had a molecular weight between 1400 and 5500.
Therefore, to summarize, there has been no catalyst system containing chromium which has been pre-viously used to prepare solid elastomers of -trans-1,3-pentadiene and isoprene.
SUMMARY OF THE INVENTION
The invention consists of the polymerization and copolymerization of at least one diolefin selected from the group consisting of trans-1,3-pentadiene and isoprene employing as a catalyst a mixture of (A) at least one organometallic compound selected from the group consis-: ting of aluminum trialkyls, magnesi~n dialkyls and zincdialkyls 9 (B) at least one soluble chromium compound selected from the group consisting of chromium salts of organic acids containing from 2 to 20 carbon atoms, organic complex compounds of chromium containing triden : tate ligands and 1r -bonded organo chromium compounds and (C) at least one member selec-ted from tris(2-chloro-ethyl)phosphite, dialkyl hydrogen phosphites and diaryl hydrogen phosphites.

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D~T~ILED DESCRIPTION OF_INVENTION
The soluble chromium compounds employed in -the practice of this invention may be chromium salts of carboxylic acids containing ~rom 2 to 20 carbon atoms.
The organic complex compounds of chromium containing tridentate organic ligands are also suitable. Triden-tate organic ligands have three positions to which a covalent or coordina-te bond with the metal may be formed.
Representative of such a chromlum containing tridenta-te compound is chromium acetylacetonate. m e ~r-bonded organochromium compounds may be represented by -tris (allyl)chromium, tris(me-thylallyl)chromium, tris(crotyl) chromium, ~r-cyclopentadiene chromium -tricarbonyl and ~r -phenyl chromlum tricarbonyl.
The preferred soluble chromium compounds useful in -this invention are the chromium sal-ts of organic acids and may be represented by chromium octanoa-te, chromium benzoate, chromium neo-decanoate, chromium benzoate, chromium neo-decanoate, chromium naphthenate, chromium oxalate and chromium stearate. Of all the soluble chromium compounds, the most preferred are chromium naphthenate, chromium neo-decanoa-te, and chromium octanoa-te.
The organometallic compounds employed in this invention are aluminum -trialkyls or dialkylaluminum hydrides, representative examples of which are aluminum trimethyl, aluminum triethyl, aluminum tri-n-propyl, aluminum tri-n-butyl, aluminum triisobutyl,-aluminum tripentyl, aluminum trihexyl, aluminum trioctyl, die-thyl-- ~lZ~

aluminum hydride and diisobutylaluminum hydride and the like.
The dialkyl magnesium compounds useful in this invention may be represen-ted by di-n-hexylmagnesium and n-butylethylmagnesi~n and the like.
The dialkyl zinc compounds may be represented by diethylzinc and dibutylzinc and the like.
The dialkyl hydrogen phosphites may be repre-sented by the tautomeric structures:
R - O~ ~ O ~ R - O
P _ __ P - OH
' R'- O H R'- O
where R and R' indicate alkyl groups which may or may not be identical. The dialkyl phosphi-tes exis-t subs-tan-tially in the keto form (shown on -the left) and are associated in dimeric or trimeric groupings by hydrogen bonding. The nomenclature dialkyl hydrogen phosphite, if applied strictly, descrlbes only the keto tautomer, but it commonly is applied to both tautomeric forms and that is the intent herein. The phosphites of this invention may be described ~urther as having at least one phosphinic hydrogen atom.
The dialkyl hydrogen phosphites useful in the preparation of the catalyst of this invention are those containing from 1 to 20 carbon atoms in the alkyl groups.
They may be represented by dimethyl hydrogen phosphite, die-thyl hydrogen phosphite, diisopropyl hydrogen phosphite, dibutyl hydrogen phosphi-te, bis~2-ethylhexyl)hydrogen phosphite or dioctyl hydrogen phosphite t didodecyl hydro~
gen phosphite, dioctadecyl hydrogen phosphite, ethyl butyl ~L~LZ~91~L

hydrogen phosphite, methyl hexyl hydrogen phosphi-te and the like.
Diaryl hydrogen phosphites containing ~rom 6 to 12 carbon a-toms in -the aryl groups may also be employed in the practice of this invention. They may be repre-sented by dibenzyl hydrogen phosphlte and diphenyl hydro-gen phosphite. Cycloalk~l hydrogen phosphites, such as dicyclohexyl hydrogen phosphite, also may be used; and a monoalkyl-, monoaryl hydrogen phosphite, such as ethyl phenyl hydrogen phosphite and butyl benzyl hydrogen phosphi-te may also be utilized.
Tris(2-chloroethyl)phosphi-te is also use~ul in the invention.
; The dialkyl hydrogen phosphites containing ~rom 1 to 8 carbon atoms per alkyl group are the preferred phosphite containing compounds. ~ `
The catalyst system o~ the present in~ention has polymerization ac-tivity o~er a wide range o~ -total catalys-t concentration and catalyst component ratios. Catalys-t components apparently interreact to ~orm the active catalyst species. As a result, the optimum concentration ~or any one catalyst component is dependent upon the concentra-tions of the other catalyst components. While polymerizations will occur over a wide range o~ catalyst concentrations and ratios, the polymers ha~ing the most desirable properties are obtained within a narrower mole ratios range.
The molar ratio of the organometallic compound to the chromium compound (Me/Cr) can be ~aried -~rom about 9il 20/l to about 2/1. However, a more preferred range of Me/~r ls from about 8/l to about 4/1.
The molar ratio of the tris(2-chloroethyl) phosphite, dialkyl or diaryl hydrogen phosphite to chromium compound (P/Cr) may be varied from about 0.2/l to about 10/l, with a more preferred range of P/Cr being from about 0.5/1 to about 3/1.
Catalyst components may be charged to the polymerization system as separate catalyst components in either a step-wise or simultaneous manner, usually called the in situ preparation. The catalyst components may also be preformed by premixing the three components outside of the polymerization system. The resulting premixed catalyst components then may be added to the polymerization systems.
The amount of total catalyst employed depends on such factors as purity of the components, polymeriza-tion rate desired, and the temperature. Therefore, specific total concentrations of catalyst cannot be set forth except to say that catalytic amounts should be employed. Successful polymerizations have been made using molar ratios of monomer to the chromium component in the ternary catalyst system ranging between about 300/l to about 4,000/1. The preferred monomer to chromium concen-tration generally is between 600/1 and 2,000/1. Certain specific total catalyst concentration and catalyst com-ponent ratios which produce polymers having desired properties are illustrated in the examples elsewhere in the specification.

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In general, the polymerizations of -this inven-tion are carried out in inert solvent sys-tems and are, thus, considered to be solution polymeriza-tions. By the -term "inert solvent" is meant the solvent or diluent employed does not en-ter into -the polymer structure nor does it have an adverse effect on the catalyst ac-tivity.
Examples of such solvents are usually aliphatic, aromatic or cycloaliphatic hydrocarbons. The preferred solvents are hexane, pentane, benzene, toluene and cyclohexane.
The solvent/monomer volume ratio may be varied over a wide range. Up to 20 or more/l volume ratio of solvent to monomer may be employed. It is usually preferred -to employ a solvent/monomer volume ra-tio of abou-t 3/1 -to about 6/1. It is possible to employ a suspension polymerization system in -the practice of this invention.
This may be done by choosing a solvent or diluent in which the polymer formed~is insoluble.
~ It is usually desirable for best results to ; conduct polymerizations of thls invention by employing air-free and moisture-free techniques.
Temperatures employed in the practice of this invention are no-t critical and may vary widely from a low temperature, for example, such as -10C. or below to a high tempera-ture of 100C. or above. However, it is usually desirable to employ a more convenient temperature between about 20C. and about 90C.
The practice of the invention is further illus-trated by reference to the following examples which are intended to be representative rather than restrictive of g~.

the s¢ope of the invention. Unless otherwise noted, all pa~ts and percentages are by weight~ The dilu-te solution viscosities (DSV) which are reported in decili-ter~ per gram were dstermined in -toluene a-t 30C. The glass transition temperatures (Tg) were determined using Du Pont's model 900 Differential Thermal Analyzer (DTA).
The microstruc-tures of the polypiperylenes were deter-mined by a combination of Nuclear Magnetic Resonance (NMR), using a ~arian A-60 spectrometer, and In~rared (IR) techniques, as described by D.H. Beebe, et al, in J. Polym. Sci., Part A-l (in press). The micros-tructures of other polymers were determined by ei-ther NMR or IR
methods.
EX~MPLE I
A premix containing a solution of trans-piperylene in hexane a-t a concentration of 10 grams of monomer per hundred milliliters of total solution was charged to a series of 4-oz bottles. The catalyst com-ponents were charged by -the in situ addition -technique in the following order: The organometallic compound was charged first 9 followed by the chromium compound, fol-lowed by a dialkyl phosphite compound. The specific catalyst compounds in millimoles per hundred grams of mono-mer (mhm) are identified in Table 1 below. The bo-ttles were placed in a water bath and main-tained at 50C. and -tumbled end-over-end to provide agitation. The polymeriza-tions were terminated by the addition of one milli-li-ter of methanol plus one part/100 g. monomer of dibutyl-para-cresol, and the polymers were isolated by d:rying ~26~9i~L

under vacuum. Additional polymerization condi-tions and results are set ~orth in Table 1. The X-ray dif~rac-tion spectra of the polymers prepared in Runs 1 and 4 showed dif~use scattering which indicated -that they were amor-phous. The polymers had excellent resistance to oxidation.
In an accelerated aging test in which the raw polymers are heated in a pure oxygen atmosphere at 90C., Polymer No. 6 absorbed one weigh-t percen-t of oxygen in 756 hours (anytime beyond 400 hours at 90C. is considered very good).

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EXAMPLE II
The procedure in this example was similar to that in Example I except that chromium sal-ts of differen-t carboxylic acids and chromium acetylace-tona-te were utilized as -the chromium ca-talys-t component. Resul-ts are shown in Table 2.

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EXAMPLE III
The procedure in this example was similar to that utilized in Æxample I excep-t that dif~erent organo-aluminum compo~mds were used, and in one instance, no phosphite compound was added in order -to illustrate i-ts importance to produce solid, moderately hlgh cis-1,4-polypiperylene elastomers. Results are presented in Table III.

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EXAMPLE IV
The procedure followed in -this example was the same as that used in Example I except tha-t differen-t amounts of triethylaluminum (TEAL) were added in each experiment. Results are shown in Table 4.
Table 4 Catal~s-t ? mhm _ _ Pzn.
Run 1 Time, Yield, DSV
~ TEAL CrNaph (R0)2 HP0 Hours Wt. % dl~
1 2Q 2 5 Me 5.0 99 2.5

2 15 2 2 Bu 0.5 100 3.4

3 12 2 2 Bu 0.5 100 ~.6

4 10 2 2 Bu 0.5 97 4.1 8 2 2 Bu 21.0 41 L~.2 Me = me-thyl Bu = but~l EXAMPLE V
The procedure used in this example was similar to that in Example I except that either two or all three of the catalyst componen-ts were premixed instead of addlng them "in situ" to the piperylene in hexane solution.
The premixed catalysts stood for 0.5 hour after mixing before injection into the premix. Results are illustrated in Table 5.

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A distillate analyzed as set for-th -- 68.5 percent -trans-piperylene; 15.4 percent cyclopentene, 7.6 percent 2-methyl-2-butene, 4.0 percen-t cis-pipel~ylene and about 5.5 percent of other olefinic hydrocarbons including 140 parts per million (ppm) of 1,3-cyclopen-ta~
diene and 240 ppm of 3-penten-1-yne. A solu-tion of 4,270 grams of this dis-tillate in 11,730 g of industrial grade hexane was passed through a silica gel column, and charged into a ten-gallon stirred reactor. Nitrogen was bubbled through the solution for two minutes and ven~ed -to remove any dissolved air. The temperature of -the premix was raised to 50C.
The ca-talys-t components were added "in si-tu"
as follows: a) injected 106 milliliters of 1.8 molar triethylaluminum solution, b) syringed in 40 mls of 0.75 M chromium naphthenate solution (=4 weigh-t percent Cr), and c) injected 32 ml of 1.2 ~ dibutyl hydrogen phosphite. There was a strong exotherm which raised the temperature in the reactor from 53 to 71C. within about seven minutes. The temperature was restored to 50C. after about 20 minutes with brine cooling in the jacket surrounding the reactor.
A sample of polymer cement was withdrawn from the reactor after one hour, and it had a solids content of 9.8 wt %, indicating about 54 percent conversion. After three hours, the solids content was 10.8 percent. The polymerization was terminated by adding 100 ml of a 34 percent aqueous solution of a 90 percent solution ~lZ~)9:~

of tetrasodium salt of ethylenediamine-te-tra-acetic acid and 23 grams of dibutyl-~ara-cresol dissolved in 400 mls benzene and 100 mls of me-t~anol. The polymer cement was dried in trays at ~0C. under ~acuum, and 1786 grams of dry polymer were recovered.
The microstructure o~ the polymer was 75 percent cis-1,4-, 21 percen-t trans-1,2- and 4 percen-t 3,4-polypiperylene. Its Mooney viscosity (ML-4 at 212F.) was 63 and its DSV was 2.8 dl/g. The Tg was -44~C.
Thirty par-ts of the polymer were blended with seventy parts of natural rubber and i-t was evaluated in a radial tire carcass formulation. Some o~ i-ts physical properties are as follows: --Tensile streng-th 15.4 MPa 300% Modulus 9.5 MPa Elongation 465 percent Hot Rebound 83 percent EXAMPLE VII
Seventy-five milliliters of a purified premix ~ 20 containing 20 volume percent of isoprene in hexane was : oharged to each of a series of 4-oz bo-ttles. The isoprene contained 197 ppm of 1-penten-4-yne and 32 ppm of 1-pentyne as impurities according -to gas-liquid chroma-to-graphic analysis. The catalyst components were charged by the in situ addition -technique in the following order:
The organometallic compound was charged first, followed by -the chromium compound, followed by the dialkyl phosphite compound. The specific catalys-t compounds in millimoles per hundred grams (mhm) of monomer are identified in Table VI:

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~ ~¦ r-l C~l ~ J ~1~ 1I m EX~MPLE VIII
A purified solu-tion of trans-piperylene in n-pentane containing 10 g of piperylene per 100 ml of solution was prepared. A second purified solu-tion in pentane con-taining 10 g of isoprene per 100 ml of solu-tion also was prepared. Aliquots o:E these solu-tions were measured into a series of 4-ounce bottles -to prepare premixes containing a to-tal of 10 grams of -the two mono-mers in various ratios ranging be-tween 90:10 and 25:75 trans-piperylene:isoprene. The monomers -then were copolymerized using the experimental procedure outlined in Example I. The catalyst charged -to each bot-tle in this series was TEAL:Cr Octoa-te:(BuO)2~PO = 10:2:2 millimoles/100 grams of total monomer. The results are summarized in Table 7.
Table 7 Pzn. Polymer 2 Run 1 Time Yield, DSV, Tg No. t-PD IP Hours wt. /0 dllg C.
1 100 0 1.5 100 3.8 -44 2 90 10 3 90 2.3 -42 3 75 25 3 73 1.6 -40 4 50 50 20 76 1~3 -37

5 25 '75 20 83 1.2 -30

6 0 100 20 93 2.8 -23 1 t-PD = trans-1,3-pentadiene IP = isoprene Tg's determined using a DuPont Model 990 Thermal analyzer.

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While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spiri-t or scope of -the invention.
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process comprising the polymerization of at least one diolefin selected from the group consisting of trans-piperylene and isoprene by subjecting said diolefins to a catalyst comprising (A) at least one organometallic compound selected from the group consisting of aluminum trialkyls, magnesium dialkyls and zinc dial-kyls, (B) at least one soluble chromium compound selected from the group consisting of chromium salts of organic acids containing from 2 to 20 carbon atoms, organic complex compounds of chromium containing tridentate ligands and .pi.-bonded organo chromium compounds and (C) at least one phosphite compound selected from tris (2-chloroethyl)phosphite, dialkyl hydrogen phosphites and diaryl hydrogen phosphites.

2. A process according to claim 1 wherein the organometallic compound is a trialkyl aluminum in which the alkyl groups contain at least 2 and not more than 6 carbon atoms.

3. A process according to claim 1 wherein the soluble chromium compound is selected from the group con-sisting of chromium salts of carboxylic acids and chromium acetylacetonate.

4. A process according to claim 1 in which the soluble chromium compound is selected from the group con-sisting of chromium decanoate, chromium naphthenate and chromium octanoate.

5, A process according to claim 1 wherein the phosphite member is a dialkyl hydrogen phosphite in which each alkyl group contains at least 2 and not more than 10 carbon atoms.

6. A process according to claim 5 in which the phosphite member is selected from the group consisting of diethylhydrogen phosphite, diisopropyl hydrogen phosphite, dibutyl hydrogen phosphite, dihexyl hydrogen phosphite and dioctyl hydrogen phosphite.

7. A process according to claim 1 in which the molar ratio of the organometallic compound to the chromium compound (Me/Cr) ranges from about 20/1 to about 2/1 and the phosphite member to the chromium compound (P/Cr) ranges from about 0.2/1 to about 10/1.

8. A process according to claim 1 wherein the organometallic compound is a trialkylaluminum wherein each alkyl group contains at least 2 and not more than 6 carbon atoms, the soluble chromium compound is selected from the group consisting of chromium salts of carboxylic acids and chromium acetylacetonate and the phosphite compound is a dialkyl hydrogen phosphite in which the mole ratio of the organometallic compound to the chromium compound is from about 4/1 to about 8/1 and the phosphite compound to the chromium compound is from about 0.5/1 to about 3/1.

9. A process according to claim 8 where the diolefin monomer polymerized is trans-1,3-pentadiene and where the polymer produced is a moderately stereoregular elas-tomer having a microstructure containing at least 70 per-cent isotactic cis-1,4-pentadiene.

10. A process according to claim 8 where the diolefin monomer is isoprene and wherein the polymer produced contains approximately equal amounts of 1,4- and 3,4-polyisoprene.

11. A process according to claim 1 wherein trans-1,3-pentadiene and isoprene are copolymerized to produce amorphous, elastomeric copolymers.

12. A catalyst composition comprising (A) at least one organometallic compound selected from the group consisting of aluminum trialkyls, magnesium dialkyls and zinc dialkyls, (B) at least one soluble chromium com-pound selected from the group consisting of chromium salts of organic acids containing from 2 to 20 carbon atoms, organic complex compounds of chromium containing tridentate ligands and .pi.-bonded organo chromium com-pounds and (C) at least one phosphite compound selected from tris(2-chloroethyl)phosphite, dialkyl hydrogen phos-phites and diaryl hydrogen phosphites.

13. A catalyst according to claim 12 wherein the soluble chromium compound is selected from the group con-sisting of chromium salts of carboxylic acids and chromium acetylacetonate.

14. A catalyst according to claim 12 in which the soluble chromium compound is selected from the group con-sisting of chromium decanoate, chromium naphthenate and chromium octanoate.

15. A catalyst according to claim 12 wherein the phosphite member is a dialkyl hydrogen phosphite in which each alkyl group contains at least 2 and not more than 10 carbon atoms.

16. A catalyst according to claim 15 in which the phosphite member is selected from the group consisting of diethylhydrogen phosphite, diisopropyl hydrogen phos-phite, dibutyl hydrogen phosphite, dihexyl hydrogen phosphite and dioctyl hydrogen phosphite.

17. A catalyst according to claim 12 in which the molar ratio of the organometallic compound to the chromium compound (Me/Cr) ranges from about 20/1 to about 2/1 and the phosphite member to the chromium compound (P/Cr3 ranges from about 0.2/1 to about 10/1.