CA1266493A - Low-molecular polyalkenamers and their use - Google Patents

Abstract

Abstract Low-molecular polyalkenamers having an average molecular weight (?n) of 500 - 6,000, produced by ring-opening polymerization of a cyclo-octadiene isomer mixture containing, besides cis,cis-1,5-cyclooctadiene, maximally 20% by weight of cis,cis-1,3-cyclooctadiene and 10-99% by weight of cis,cis-1,4-cyclooctadiene.
They are utilized, optionally after isomerization, as binders in coating compositions.

Description

3L;2~i~f~3 The present invention relates to low molecular weight polyalkenamers produced by ring-opening polymerization of cyclo-octadiene isomer mixtures and useful as binders of coating compo-sitions.
Low-molecular weight polymers of 1,3-dienes, primarily polybutadienes wherein the double bc,nds exhibit predominantly cis-1,4-configuration are conventionally utilized as binders in air- and oven-drying paints (German Patent 1,186,631 and German Auslegeschrift (DAS) 1,494,417).
It is furthermore known from German Auslegeschrift (DAS) 1,174,071 to rearrange isolated double bonds in polybutadienes to conjugated double bonds. As a result, starting with the rela-tively inert polybutadienes with extensively isolated double bonds, very reactive polybutadienes are obtained which can be used in the low-molecular range, inter alia, for the preparation of self-drying varnishes.
Besides isomerization of isolated double bonds to con-jugated double bonds particularly in low-molecular polybutadienes as disclosed, for example, in German Auslegeschrift (DAS~
1,174,071; German Patent 2,342,885; German Offenlegungsschrifts (DOS) 2,924,548, 2,924,598, and 2,924,577; as well as Published European Application (EP-A-0) 086 894, another conventional method for the production of polymeric compounds with conjugated double bonds is the copolymerization of 1,3-dienes with acetylene [J. Furukawa et a:l., Journ. Polym. Sci., Polym. Chem. Ed. 14 :
1213-19 (1976)].

~2~6~93 However, all of these prior art products, when used as binders in painting media, fail to attain air-drying properties of the especially quickly drying China wood oil (tung oil).
Consequently, it was surprising to find that the low-molecular weight polyalkenamers produced by ring-opening polymeri-zation of cyclooctadiene isomer mixtures, especially after iso merization from isolated double bonds to conjugated double bonds, reach or even surpass the level of ~hina wood oil with respect to dust drying and through drying when used as binders in painting media.
According to an aspect of the present invention, there is provided a low-molecular weight polyalkenamer having a number average molecular weight (Mn) of 500 to 6,000, produced by ring-opening polymerization of a cyclooctadiene isomer mixture con-taining at most 20% by weight of cis,cis-1,3-cyclooctadiene, 10 - 99~ by weight of cis,cis-1,4-cyclooctadiene, and substantially the balance of cis,cis-1,5-cyclooctadiene.
According to another aspect of the present invention, there is provided a process for producing a low molecular weight polyalkenamer having a number average molecular weight (Mn) of 500 to 6,000, which comprises: simultaneously ring-opening and polymerizing a cyclooctadiene isomer mixture containing 0.01 to 20% by weight of cis,cis-1,3-cyclooctadiene, 10 to 99% by weight of cis,cis-1,4-cyclooctadiene and 0.99 to 89,99~ by weight of cis,cis-1,5-cyclooctadiene, using a ring-opening polymerization catalyst containing (A) a metal belonging to Sub-Group 5 through 7 of the Periodic Table and (B) a metal belonging to Main Group 1 ~Z~ 3 through 4 of the Periodic Table, in a dry soLvent at a temperature of -50 to 80~C.
According to a still further aspect of the present invention, there is provided a coating composition comprising a painting medium and, as a binder, a low-molecular weight poly-alkenamer having a number average molecular weight (Mn) of 500 to 6,000, produced by ring-opening polymerization of a cycloocta-diene isomer mixture containing at most 20% by weight of cis,cis-1,3-cyclooctadiene, 10 - 99% by weight of cis,cis-1,4-cycloocta-diene, and substantially the balance of cis,cis-1,5-cycloocta-diene.
A characterizing feature of the polyalkenes of this invention with a number average molecular weight ~n) f 500 ~
6,000 is the composition of the cyclooctadiene isomer mixture used as a raw material of the ring-opening polymerization ~for details see monograph "Olefin Metathesis" by K.J. Ivin, ~cademic Press (1983)], which mixture contains, besides cis,cis-1,5-cyclo-octadiene, at most 20% by weight of cis,cis-1,3-cyclooctadiene and 10 - 99% by weight of cis,cis-1,4-cyclooctadiene.
In general, mixtures of cyclooctadiene isomers are employed as the starting material which contain 0.01 - 20% by weight of cis,cis-1,3-cyclooctadiene, 10 - 99% by weight of cis,cis-1,4-cyclooctadiene, and 0.99 - 89.99~ by weight of cis,cis-1,5-cyclooctadiene. Preferred are isomer mixtures with 0.1 - 10~ by weight of cis,cis-1,3-cyclooctadiene, 20 - 99% by weight of cis,cis-1,4-cyclooctadiene, and 0.9 - 79.9% by weight of cis,cis-1,5-cyclooctadiene. Especially preferred are isomer mix-3L~63~3 ~ 4 ~ 23443 ~23 tures with 30 - 60~ by weight of cis,cis-l,~-cyclooctadiene and up to 10~ by weight of cis,cis-1,3-cyclooctadiene.
The number average molecular weight of the polyalkenamer is preferably from about 1,000 to 3,000. Preferably, the polyalkenamer contains a substantial amount (e.g., 10 to 70 molar ~) of conju-gated (i.e., 1,3-) double bonds. The polyalkenarner may have an iodine number of 200 to 500. In the polyalkenamer, -the majority of the double bonds (i.e., more than 50 molar ~) is usually trans.
As is Xnown, cis,cis~l,5-cyclooctadiene can be obtained according to various methods with high selectivity and in high yields by dimerization of 1,3-butadiene (German Patents 1,140,569;
1,144,268; 1,244,172; 1,79~,718; and 1,804,017).
It is then possible, according to the process of German Offenlegungsschrift (DOS) 3,325,268, to produce, from cis,cis-1,5-cyclooctadiene, a mixture of isomers with up to 97% by weight o~
cis,cis-1,3-cyclooctadiene and up to almost 30% by weight of cis,cis-1,4-cyclooctadiene; from this mixture, by distillatory separation, it is also possible to obtain cis,cis-1,4-cyclo-octadiene, heretofore accessible only with difficulties, with a degree of purity of up to 99% by weight.
As for ring-opening polymerization of the individual cyclooctadiene isomers serving as the starting material for the polyalkenamers according to this invention, this reaction has been Xnown for a long time for cis,cis-1,5-cyclooctadiene. As for cis,cis~l,3-cyclooctadiene, though, the only known aspect was that it can be reacted to a rapidly crosslinking polymer with a catalyst based on tungsten hexachloride/diethylaluminum chloride/

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epichlorohydrin in a 40 - 50% yield; this polymer, on aeeounk of its strong erosslinking property, eannot be characterized in any more detail [Y.V. Korshak, J. Mol. Catal. 15 : 207 (1982)].
Finally, the above-cited monograph "Olefin Metathesis" by K.J.
Ivin mentions with respect to cis,cis-1,4-cyclooctadiene that it has thus far been impossihle to polymerize this monomer in a ring-opening mode [A.J. Amass et al., Eur. Pol. J. 12 : 93 (1976)].
It has furthermore been known that polymerization of eis,cis-1,5-cyclodecadiene, though initially yielding an expected alternating copolymer of eyelobutene (or butadiene) and cyclo-hexene, then progresses to decomposition into polybutene (= 1,4-polybutadiene) and cyclohexene [Hocks et al., J. Pol. Sci. Pol.
Lett. 13 : 391 (1975)].
In view of this state of the art, it eould not be expeeted that mixtures of eyclooctadiene isomers containing, besiaes eis,eis-1,5-eyelooetadiene, up to 20% by weight of eis,eis-1,3-eyelooetadiene and 10 - 99% by weight of cis,eis-1,4-eyelooetadiene ean be polymerized with ring opening without the oeeurrenee of the aforementioned complieations (minimum yields, six-membered ring eleavages).
It is especially surprising to note that the polymers formed from cis,cis-1,4-eyelooetadiene do not split off their =CH-CH2-CH= units as 1,4-cyelohexadiene although this reaetion was expeeted from the behavior of the linolic and linolenic aeid esters under metathesis eonditions (C. Boelhouver and E.
Verkuijlen, Chem. Comm. 1974 : 793).

ii64~33 It is furthermore remarkable that the ring-opening poly-merization of cis,cis-1,4-cyclooctadiene and cis,cis-1,5-cyclo-octadiene is by far not so strongly inhibited as, for example, that of cyclooctene by the presence of the 1,3-isomer.
The polyalkenamers of this invention can be produced according to any processes of the prior art which concern the ring-opening polymerization of cyclic olefins having at least one unsubstituted double bond (~erman Offenlegungsschrifts 1,570,940;
1,645,038; 1,720,798; 1,720,820; 1,770,143; and 1,805,158; German Auslegeschrift 1,299,868; British Patents 1,124,456; 1,194,013;
and 1,182,975). The catalysts utilized for this ring-opening polymerization contain, as is known, compounds of metals of Sub-groups 5 through 7 of the Periodic System of the Elements (PSE), primarily those of niobium, tantalum, molybdenum, tungsten,and rhenium, as well as metals of Main Groups 1 through 4 of the PSE, such as aluminum or their alkyls or hydrides derivatives, optionally with additional ligands, such as, for example, halogen, alkoxy or carboxylate, or Lewis acids in their place. Besides, these catalyst systems, also called metathetic catalysts, can contain further activating additives, such as, for example, alcohols, epoxides, hydroperoxides, vinyl ethers and esters, and allyl ethers and esters, vinyl halides, and aromatic nitro compounds.
Particularly preferred catalysts contain tungsten compounds, for example, tungsten halides (e.g. WC16) and aluminum compounds, for example, alXyl aluminum halides (e.g. EtAlC12 and iBuAlC12). These preferred catalysts may further contain ~. .

~L2~i~493 activating additives, such as, lower alCohols ~methanol, ethanol, etc.) and allyl ethers (allyl tribromophenyl ether, etc.).
The reaction can be conducted in any inert solvents known to be suitable in polymerization with the aid of Ziegler-Natta catalysts. Suitable are aliphatic, alicyclic, aromatic, and halogenated hydrocarbons, and particularly suitable are the following: pentane, hexane, heptane, n- and isooctane, isononane (hydrogenated trimer propene), n-decane, isododecane (hydrogenated tetramer propene), cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, ethylcyclohexane, isopropylcyclohexane, cyclo-octane, decahydronaphthalene, hydrogenated terpenes, such as pinane and camphane, cyclohex~ne and its substitution products, benzene, toluene, o-, m-, p-xylene, ethylbenzene, o-, m-, p-di-ethylbenzene, n-propylbenzene, isopropylben~ene and other mono- to polyalkylbenzenes, tetrahydronaphthalene, methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethylene, trichloro-ethylene, tetrachloroethylene, chlorobenzene, o-dichlorobenzene, trichlorobenzene (mixture of isomers), bromobenzene, fluoro-benzene, 1,2-dichloroethane.
It is extremely desirable to use solvents, completely or substantially freed of water and other ~-acidic compounds as well as compounds having donor functions (Lewis bases), by means of suitable purification. Except for very small amounts optionally added to obtain specific effects, such impurities generally impair catalyst activity.
The process of this invention is usually performed at temperatures of between -50 and +80C. The reaction temperature ~i64~3 - 7a - 23443-323 herein is limited in the upward direction by the thermal stability of the catalyst and in the downward direction by an excessively reduced reaction velocity. The process is advantageo-lsly con-ducted at temperatures of between -30 and +60C, but preferably in a range between 0 and ~50C that can be realized with special ease.
The polyalkenamers of this invention, on account of their molecular weight, are readily fluid to highly viscous liquids. In order to obtain them, it is usually necessary to add to the polymerization charge, so-called molecular weight modifiers which are optionally substituted open-chain olefins of 2 - 30 carbon atoms (German Offenlegungsschrift 2,922,335 and German Patents 1,919,047; 1,945,35S3; 2,027,905; 2,028,716; 2,028,935,

2,105,161; and 2,157,405). The amount of the modifier to be added depends on the desired molecular weight of the polyalkenamer and generally is 1 - 20, preferably 3 - 12 mole percent, based on the total cyclooctadiene isomer raw material.
In general, the procedure in preparing the polyalkenamers of the invention involves putting the cyclooctadiene isomers together with the modifier into the solvent, adding the individual catalyst components, and performing the polymerization under agitation and optionally with removal of heat of reaction. The polymerization can, of course, also be conducted in partial steps, i.e. monomers, modifiers and catalyst components can be repeatedly introduced subsequently in metered amounts. Once the desired or attainable conversion has been achieved, the catalyst is deactivated by addition of an alcohol, such as, for example, ~2~i6493 - 7b - 23443-323 methanol, or other H-acidic compounds, optionally in admixture with alkaline compounds, such as sodium hydroxide. Then the polymer-containing phase is washed with an aqueous, aqueous-alcoholic or alcoholic solution of agents having a dissolving effect on the catalyst residues which latter are present initially as alcoholates or compounds of the H-acidic materials. Such dissolution-promoting materials are, for example, acids, alkaline solutions, or complex-forming agents, such as citric or tartaric acid, methanolic potassium hydroxide solution, acetylace~one, ethylenediaminetetraacetic acid, and nitrilotriacetic acid.
Thereafter the polymers are separated by precipitation, for example by pouring into a precipitant, such as, for instance, methanol or isopropanol, or by removing the solvent by distilla-tion, e.g. by blowing in steam or by passing the polymer solution throuyh nozzles into hot water.
In order to protect the resulting polyalkenamers against oxidation, gelling and other aging phenomena, stabilizers, for example, aromatic amines or sterically hindered phenols, can be admixed to the polyalkenamers of this invention in various pro-cessing stages. It is likewise possible, if necessary, to effectfurther purification of the polymers by reprecipitation. After these operations, the polymers are dried as is conventional, for example in a vacuum drying cabinet or by means of a rotary evapor-ator.
The polyalkenamers of this invention are well suitable, as mentioned hereinabove, as binders in paint media, especially after previous isomerization, for example according to the method , . ~

- 7c -of DOS 3,003,894. They can be intermixed, within the scope of their compatibility, with other binders, e.g. the isomerized, low-molecular polybutadienes obtained according to the process of EP-A 0 086 894, to such an extent that the good properties in connection with varnishing technology are brought out.

' ~,, ' , 12~i6~93 The present invention is described in greater detail by the examples below. In the latter, the following terms are written as the abbreviations appearing below:
cis,cis-Cyclooctadiene = COD
Ethyl = Et Isobutyl = isu Allyltribromophenyl ether = ATBPE
Double bond(s) = DB
Iodine number [g iodine/100 g compound] =
IN
Number-average molecular weight (determined by vapor pressure osmosis) = Mn Infrared = IR
Ultraviolet = UV
Nuclear magnetic resonance = NMR

~266493 .
Example 1 In a 6-liter glass reactor with face ground lid, equipped with agitator, thermal probe, dropping funnel, as well as feed and discharge conduits for protective gas, 3 1 of hexane and the partial amount of 250 g of a mixture of 376 g of 1,4-COD (49.2% by weight), 376 g of 1,5-COD (49.2~ by weight), 12 g of 1,3-C~D (1.6% by weight), and 59 g of l-octene were combined under dry argon with 10 mmol of WC16 (in the form of a 0.1-molar solution in chloroben~ene), 10 mmol of EtOH (in the form of a 0.1-molar solution in chlorobenzene), 10 mmol of ATBPE (in the form of a 0.1-molar solution in chlorobenzene), and 70 mmol of EtAlC12 (in the fo~m of a l-molar solution in chloro-benzene), and, with e~ternal cooling, the remaindero~ the monomer/modifier mi~ture was added to the reaction mi~tu~e through the dropping funnel within 10 minutes, the temperature rising from 20 C to 46 C.
Thereafter, once more the same amount of catalyst was added to the reaction mixture, the latter polymerized for 15 minutes, and the reaction stopped with a solu-tion of 30 g o~ potassium hydroxide in 300 ml of methanol. The polymer was precipitated into 6 1 of methanol, washed twice with respectively 4 1 of methanol, dissolved in 2 1 of toluene, insoluble proportions were filtered off, precipitated into 4 1 of methanol, washed with 2 1 of methanol, and dried under vacuum at 70 C.
The result was 522 g of an oil having the following characteristic data:
DB Configuration [~ trans/vinyl/cis] as per IR analysis: 67/4~29.
DB Positioning [~ 1,4-/1,5- and more remote/
vinyl] by NMR analysis: 54/42/4.
3S IN: 392 ~n: 2,050 - .

~266493 -- 10 -- , Example 2 In a 2-liter glass reactor, equipped like the 6-liter glass reactor descxibed in Example 1, 54 g of 1,4-COD (45.5% by weight), 54 g of 1,5-COD
(45.5% by weight), 10.8 g of 1,3-COD (9~ by weight), and 11.2 g of l-octene in 500 ml of hexane were combined with 3 mmol of WC16 lin the form of a 0.1-molar solution in chlorobenzene), 3 mmol of EtOH (in the form of a 0.1-molar solution in chlorobenzene),

3 mmol of ATBPE (in the form of a 0.1-molar solution in chlorobenzene), and 21 mmol of EtAlC12 (in the form of a l-molar solution in chlorobenzene~, and the - mixture was polyme~ized under agitation for 15 min-utes, the temperature rising during this step from 21 ~ to 40 C. Thereafter polymerization was stopped by adding a solution of 4 ~ o~ potassium hydroxide in 100 ml o~ methanol. The polymer was precipitated into 1 liter o~ methanol, washed with 1 liter of methanol, dissolved in 50~ ml of toluene, a small amount o~ insoluble material was removed by filtration, and th~ product was reprecipitated as described above and washed under agitation. A~ter removal of the volatile proportions under vacuum on a rotary evaporator at 70 C, 78 g o~ an oil was obtained having the following characteristics:
DB Configuration [% trans/vinyl/cis] deter-mined by IR analysis: 64/4/32.
DB Positioning [% 1,4-/1,5- and more remote/1,3-/vinyl] determined by NMR analysis:
56/35/5/4.
Mn: 1,480 ~Z66493 Example 3 In the 2-liter glass reactor of Example 2, there were added to 100 ml of chlorobenzene first of all 0.5 mmol of WC16 (in the form of a 0.1-molar solution in chlorobenzene), O.5 mmol of EtOH (in the fo~m of a 0.l-molar solution . in chlorobenzene), O . 5 mmol of ATsPE (in the form of a 0.1-molar solution in chlorobenzene), and 3.5 mmol of iBuAlC12 (in the form of a l-molar solution in chlorobenzene), then a mixture o~ 10.8 g of 1,4-~OD (20% by weight), 35.1 g o~ 1~5-~0~ ~65% by weight~, ~.1 g o~ 1,3-COD
(15~o by weight~, and 2. a g of l-octene. The batch was polymerized un~e~ agitation fo~ 20 minute~, ths temperature rising ~rom 2~ C t~ 42 ~ ~herea~ter ; 2 g o~ potassium hydroxi~e in 50 ml o~ methanol wa~
added, the polyme~ was pre~ipitated by ad~ing 1 llter o~ methanol~ the precipitated produ~t was washed with 50Q ml o~ methanol, then ~issolved in 250 ml o~ he~ane, a small amount o~ insoluble mate~ial wa~ filteEe~ ~r an~ the he~ane wa~ removed on a rotary evaporatoE at a~o ~ thus obtaining 31 9 o~ an oil having the characteristic data set ~orth below:
DB ~on~iguration [~ trans/vinyl/cis] deter-mined by IR analysis: 67~1/32.
D~ Positioning [~ 1~4~ 5- and more remote/
1,3-/vinyl] determined by NMR analysis: 36/53/9/2.
Mn: 1,870 ' 6~ 3 Example 4 (a) Isomerization of a Po.lyalkenamer According to Invention ._______________________________ . Under a protective gas atmosphere (nitro-gen), a three- necked flask having a capacity of ~ liters and equipped with reflux condenser and thermometer was charged with 750 g of a pol~ner having the following characteristic data and having been prepared from equal parts of l,4-COD and 1,5-COD (49.2% by weight) as well as 1.6~ by weight of 1r3-COD~in 750 g of dry toluene:
DB Configuration [% transtvinyl/cis] deter-mined by IR analysi.s: 67/4/29.
DB Positioning [% 1,4-/1,5- and more remote~
15 vinyl] determined by NMR analysis: 58/38~4.
Conjugated DB [as % o~tadiene] determined by UV analysis: 1.1.
IN: 377 Mn: 1,850 .
After heating to 80 C, isomerization was performed with the catalyst according to ~xample 6 of DOS 3,003,894 by agitating the batch for 30 minutes at 80 C. Since the reaction was slightly exothermic, cooling had to provided at times. Subsequently the - 25 mixture was rapidly cooled down to room temperature (20 C) and the insoluble portions were separated by filtration under pressure. After removing the solvents : on a rotary evaporator in an oil pump vacuum, 675 g of a viscous, brownish oil was obtained having the following analytical data:
DB Configuration [% trans/vinyl/cis] deter-mined by IR analysis: 69/3/28.
DB Positioning [% 1,3-/1,4-/1,5- and more remote/vinyl] determined by NMR analysis: 44/-/53/3.

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~ 13 - , Conjugated DB [as % octadiene/-triene/-tetra-ene] determined by UV analysis: 21/1.6/0.48.
IN: 337 Mn: 1,870 (b) Testing of AiI-Drying Properties The specimens were applied to glass plates in the coating thickness indicated in the table by means of an applicator frame and stored horizontally in a climate 23/50 according to DIN 50 014, illumination: "Osram" daylight lamp. Siccative: 0.04% Co.
- The abbreviations in the table mean the following:
ST = dust drying time, drying stage 1, DIN 53 150, in hours (h) DT = complete drying time in hours ~h~, measured according to DE~ 1053, method 8, load 2.27 kg.

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Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A low-molecular weight polyalkenamer having a number average molecular weight (?n) of 500 to 6,000, produced by ring-opening polymerization of a cyclooctadiene isomer mixture con-taining at most 20% by weight of cis,cis-1,3-cyclooctadiene, 10 -99% by weight of cis,cis-1,4-cyclooctadiene, and substantially the balance of cis,cis-1,5-cyclooctadiene.

2. A polyalkenamer according to claim 1, which contains 10 to 70 molar % of conjugated double bonds based on the total double bonds.

3. A polyalkenamer according to claim 1, which has a number average molecular weight of 1,000 to 3,000.

4. A polyalkenamer according to claim 1, 2 or 3, wherein the mixture of cyclooctadiene isomers utilized as a raw material contains 20 - 99% by weight of cis,cis-1,4-cyclooctadiene.

5. A polyalkenamer according to claim 1, 2 or 3, wherein the mixture of cyclooctadiene isomers utilized as a raw material contains 0.01 - 20 % by weight of cis,cis-1,3-cyclooctadiene.

6. A polyalkenamer according to claim 1, 2 or 3, wherein the mixture of cyclooctadiene isomers utilized as a raw material contains 0.1 - 10% by weight of cis,cis-1,3-cyclooctadiene.

7. A polyalkenamer according to claim 1, 2 or 3, which have an iodine number of 200 to 500.

8. A process for producing a low molecular weight poly-alkenamer having a number average molecular weight (?n) of 500 to 6,000, which comprises:
simultaneously ring-opening and polymerizing a cyclooctadiene isomer mixture containing 0.01 to 20% by weight of cis,cis-1,3-cyclooctadiene, 10 to 99% by weight of cis,cis-1,4-cyclooctadiene and 0.99 to 89.99% by weight of cis,cis-1,5-cyclooctadiene, using a ring-opening polymerization catalyst containing (A) a metal belonging to Sub-Group 5 through 7 of the Periodic Table and (B) a metal belonging to Main Group 1 through 4 of the Periodic Table, in a dry solvent at a temperature of -50 to 80°C.

9. A process according to claim 8, wherein the metal belonging to Sub-Group 5 through 7 of the Periodic Table is niobium, tantalum, molybdenum, tungsten or rhenium and the metal belonging to Main Group 1 through 4 of the Periodic Table is aluminum.

10. A process according to claim 8 or 9, wherein the catalyst further contains one or more activating additives selected from the group consisting of alcohols, epoxides, hydro-peroxides, vinyl ethers, vinyl esters, allyl ethers, allyl esters, vinyl halides and aromatic nitro compounds.

11. A process for producing a low molecular weight poly-alkenamer having a number average molecular weight (?n) of 500 to 6,000, which comprises:
simultaneously ring-opening and polymerizing a cyclooctadiene isomer mixture containing 0.1 to 10% by weight of cis,cis-1,3-cyclooctadiene, 20 to 99% by weight of cis,cis-1,4-cyclooctadiene and 0.9 to 79.9% by weight of cis,cis-1,5-cyclooctadiene in the presence of an open-chain olefin having 2 to 30 carbon atoms as a molecular weight modifier using a catalyst system containing a tungsten, halide and an alkyl aluminium halide at a temperature of 0 to 50°C in a dry reaction inert solvent.

12. A process according to claim 11, wherein the tungsten halide is WC16 and the alkyl aluminum halide is EtA1C12 or iBuA1C12.

13. A process according to claim 11, wherein the catalyst system is composed of WC16/(EtA1C12 or iBuA1C12)/EtOH/ATBPE, wherein ATBPE is allyl tribromophenyl ether.

14. A process according to claim 11, 12 or 13, wherein l-octene is used as the molecular weight modifier.

15. A process according to claim 11, 12 or 13, wherein the ring-opening and polymerization reaction is terminated by adding methanol containing potassium hydroxide to the reaction mixture.

16. A process according to claim 11, 12 or 13, which further comprises separating the polyalkenamer from the reaction mixture and then subjecting the separated polyalkenamer to isomerization under such conditions that the amount of conjugated double bonds increases.

17. A process according to claim 11, 12 or 13, which further comprises separating the polyalkenamer from the reaction mixture and then subjecting the separated polyalkenamer to isomerization using potassium tert-butoxide catalyst under such conditions that the amount of conjugated double bond increases.

18. A coating composition comprising a painting medium and, as a binder, a low-molecular weight polyalkenamer having a number average molecular weight (?n) of 500 to 6,000, produced by ring-opening polymerization of a cyclooctadiene isomer mixture con-taining at most 20% by weight of cis,cis-1,3-cyclooctadiene, 10 -99% by weight of cis,cis-1,4-cyclooctadiene, and substantially the balance of cis,cis-1,5-cyclooctadiene.

19. A coating composition according to claim 18, wherein the polyalkenamer is as defined in claim 2.