NO752704L - - Google Patents

Description

Process for the production of ethylene-butadiene copolymers.

The present invention relates to a method for the polymerization of ethylene and I,3-butadiene with a high yield for the formation of copolymers which are characterized by:

I) high chain linearity

II) narrow molecular weight range

III) almost complete 1,4-trans configuration of the butadiene units IV) statistical inter- and intramolecular distribution of the monomer units V) low content of residual vanadium, even without any form of

in cleaning stage,

in that these copolymers can be vulcanized using common sulfur-containing compositions to produce cross-linked products similar to high-density polyethylenes, but with improved mechanical, thermal and chemical properties..

Ethylene-butadiene copolymers are previously known, but no known products simultaneously have the above-mentioned properties.

These properties are considered indispensable when desired

a product with significant advantages compared to polyethylenes.

The chain linearity, i.e. the substantial absence of intermolecular ring closures, cross-links and cross-links, ensures a low flow of the molten polymer and improves its processability and extrudability.

The narrow molecular weight range, combined with the chain linearity, ensures that the copolymer has better mechanical properties, such as impact resistance, with the same molecular weight otherwise, and other properties.

The low-polydisperse polymers are the most suitable for use in conversion techniques based on centrifugal casting, injection molding

of large finished products, fiber spinning etc.

1,4-trans addition of butadiene units into a polyethylene chain

is the only one that does not significantly disturb the crystalline structure of the latter polymer, at least not particularly

high content of copolymerized butadiene. As a consequence, the physical properties (melting point, density, etc.) of the copolymers, which are nevertheless able to vulcanize at a high rate, are not very different from the physical properties of high density polyethylene.

The statistical distribution of the monomer units, both within the individual macromolecule and between one macromolecule and another, is a necessary feature for the entire polymer to undergo homogeneous cross-linking. Only such copolymers can be vulcanized with good yield to give products with physico-mechanical, thermal and chemical properties better than those of the best polyethylenes.

Finally, a low vanadium content is also an essential feature of ethylene-butadiene copolymers as, due to the presence of double bonds, oxidation reactions must be avoided as vanadium here acts as a catalyst. Furthermore, vanadium salt residues, if present in particular amounts, will give the copolymers undesirable color tones. The use of catalysts which produce high yields during the copolymerization allows, in addition to removing the above-mentioned disadvantages, that simple processes can be carried out from which the washing phase for the obtained polymer can be omitted.

All of the above is necessary for the production of ethylene-butadiene copolymers to be interesting from an industrial point of view.

The different behavior during the polymerization of the monomers used, namely ethylene and butadiene, explains the difficulties in obtaining copolymers with the above-mentioned properties directly from the polymerization of their mixtures.

The properties of ethylene-butadiene copolymers are strictly dependent on the manufacturing process and consequently on the particular catalyst used. The known catalyst systems which use compounds of titanium, vanadium or chromium as transition metal compounds, in addition to not ensuring the formation of copolymers with all the above-mentioned properties, will also not give sufficiently high yields during the polymerization.

It has previously been proposed to produce ethylene-butadiene copolymers which can be homogeneously cross-linked by means of sulphur-containing compositions, but the previously proposed catalysts are not particularly active when products with a relatively low molecular weight are desired.

It has now surprisingly been found that it is possible to achieve high polymerization yields of ethylene-butadiene copolymers, with high chain linearity, narrow molecular weight range, almost complete 1,4-trans-w configuration of the butadiene units, inter- and intra-molecular statistical distribution of the monomer units, and low vanadium content,

and this is achieved by the method according to the invention where mixtures of ethylene and butadiene are polymerized under specified conditions in the presence of one or more aromatic solvents, the catalyst system being prepared from. a) one or more vanadium compounds which are soluble in the above-mentioned solvents b) .one or more aluminum compounds of the general formula R-^R^AIX in which R, and R^ are the same or different and stand

for alkyl, cycloalkyl, alkaryl or aryl containing from 1 to 18 carbon atoms or represents hydrogen and X is chlorine

or bromine

c) one or more acidic compounds according to Lewis or

Brønsted

d) thionyl chloride and/or hexachlorocyclopentadiene.

The vanadium compounds referred to under point a) include 4- and 5-

valent and complexed trivalent vanadium halides, vanadium-

and vanadyl alcoholates, chelates and complexes.

The term "complexes" refers to all compounds containing bonds between organic mono- or bidentate ligands, where "gigand" means an ion or molecule bound to metal or considered to be bound to metal and the term "mono- and bidentate" means a molecule with a resp. two positions with which it can form covalent or coordinative bonds with

.metal et.

Examples of vanadium compounds that can be used are vanadium tetrachloride (preferably stabilized in SiCl^ solution), vanadyl trichloride, vanadium trichloride complexed with three molecules of tetrahydrofuran, vanadium triacetyl acetonate, vanadyTdiacetyl acetonate, vanadyl triisopropylate, tetradimethylamide vanadium, etc.

The components (b) in the catalyst system are aluminum dihydrocarbyl halides, of which diethyl monochloride and diisobutyl monochloride are preferred due to price and easy availability.

Similar results are obtained by using the corresponding bromine derivatives. Aluminum hydrocarbyl halide hydrides can also be used with advantage.

The components (c) of the catalyst system are all acidic<cN>compounds

according to Lewis or Brønsted and includes both polyhalogenated compounds of metals belonging to groups III or IV in the periodic table, bg compounds which are able to release H+<-> ions, i.e. organic acids, inorganic acids and water, on condition that they are sufficiently soluble in the hydrocarbon reaction medium or are made soluble when they react with the other components of the catalyst system.

Examples of these compounds are boron trichloride, aluminum trichloride, aluminum monoethyl chloride, aluminum monoisobutyl dichloride, aluminum tribromide, stannous tetrachloride, acetic acid, benzoic acid, water, etc.

The components (d) in the catalyst system are, as already mentioned, thionyl chloride or hexachlorocyclopentadiene.

The mole ratio between compounds (b) and (a) is usually high

as the vanadium compound is used in very small quantities. The ratio is higher than 10:1 and usually from 50:1 to 100:1. However, when the vanadium concentration is less than 5.10 mol/liter, the Al/V ratio is preferably from 100:1 to 500:1. The best amount of vanadium compound is from 1.10~ to 1.10" mol/liter, while aluminum-

_3

the compound amounts from 1 to 8.10 mol/liter.

The molar ratio between components (c) and (b) is critical. It may

when (c) is a multihalogenated inorganic■or organometallic1 compound, is distilled as the total ratio of gram atoms of halogen to gram atoms of aluminum contained in the reagents (b) and (c). The ratio X/Al must be from 1 to 1.25 or preferably between 1.05 and 1.15.

When (c) is a protonic acid or water, the ratio between (b) and (c) is from 1:10 to 1:1 and preferably between 4:1 and 2:1.

The molar ratio between components (d) and (b) of the catalyst can vary greatly, and also depending on the particular compound (d) and the reaction conditions. This molar ratio is generally lower than 1 and is preferably chosen in the range from 1:4 to 1:1.

All the above-mentioned reactions are carried out in the presence of a hydrocarbon which, according to a special feature of the present invention, is of the aromatic type. However, mixtures consisting of aromatic hydrocarbons with aliphatic and cycloaliphatic hydrocarbons, halogenated aromatic hydrocarbons or mixtures thereof with the above or with other hydrocarbons containing halogens can also be used. Therefore, although benzene or toluene is preferably used, it is possible to use chlorobenzene or mixtures consisting of benzenecyclohexane, toluene-n-heptane, chlorobenzenetetrachloroethylene, etc.

The polymerization temperature varies greatly. The process is usually carried out at a temperature higher than room temperature to prevent the use of expensive cooling steps.

The most suitable temperature range is from 50 to 100°C, though

a wider range can be used so that this will be from 0 to 120°C.

The polymerizations are carried out under high ethylene pressure (2 - 20 kg/cm).

If necessary, hydrogen is also added to regulate the molecular weights.

Ethylene-butadiene copolymers, which can be produced by the method described above, are free of gel content, branches and internal ring closures, which can be checked by infrared

and nuclear magnetic resonance spectra and from their complete solubility in the hot state in hydrocarbon and chlorohydrocarbon solvents. •

The narrow molecular weight range, together with the high chain linearity, is demonstrated by melt flow measurements, according to ASTM 1236-65T. The ratio between the melt flow indices measured using weights of 21.6 kg (MFI^-^ g) and 2.16 kg (MFI^ ^g) is termed "shear sensitivity" and is:' for the above copolymers between 10 and 50.

The lower the average molecular weight, the lower this ratio and for the same molecular weight value, the ratio is lower if the polymer is more monodisperse and free of branching (R. Martinovitch, P.J. Boche, R.A. McCord, SPE J. 16, 1335 (1971)) .

The molecular weight distribution of the copolymers produced by the method

according to the invention, expressed as Mw/M^ and determined by gel permeability chromatography (Polymer Fractionation, M.J.R. Cantow, Academic/Press N.Y., 1967) is from 2 to 3.

The butadiene unit amounts (mol of butadiene per 100 mol of both monomers) vary greatly, e.g. from 0.1 to more than 10, and is regulated taking into account the conditions.

The products have a great interest in a subsequent transformation

in cross-linked finished products, and containing 0.5 to 5 mole percent copolymerized butadiene.

Copolymers with less than 0.5 mole percent butadiene undergo a "degradation" in the presence of vulcanizing agents. Copolymers with more than 5 mole percent butadiene are interesting, in addition to their low cost, because of their compatibility with other highly unsaturated polymers.

The 1,4-trans-butadiene units make up, determined by infrared spectography, at least 98% of all copolymerized butadiene. Bands due to cis- or 1,2-type units are not significant. The quantitative determination of butadiene contained in the copolymer is therefore carried out based on the band at 965 cm 1 according to known techniques.

The inter- and intramolecular statistical distribution of the monomer units in the copolymer according to the invention is confirmed by the fact that the raw product from the polymerization can be cross-linked, regardless of the fraction considered, when it is subjected to vulcanization with the help of common sulfur or sulfur donors or quinone compound-containing compositions, with or without accelerators or inert fillers. The rate of crosslinking is measured by the value of maximum binding obtained in a patch vulcanizer or measurement of the insoluble portion, after 24 hours in boiling xylene, and is expressed as gel percentage. It is a function of average molecular weight, molecular weight distribution, unsaturation content of the copolymer, in addition to the vulcanization mixture used, and is usually from 30 to 90% relative to the final product.

With the method according to the invention, ethylene-butadiene copolymer is obtained with such high yields that it is possible to eliminate the washing phase for the raw product from the polymerization, as small catalyst residues can remain in the polymer itself. The residual vanadium content is usually lower than 50 ppm.

Ethylene-butadiene copolymers are highly crystalline by X-ray examination. Their crystallinity in the range of interest is that typical of high-density polyethylene. The lack of crystallinite typical of 1,4-trans-polybutadiene, also for contents higher than 10% of these structural units, is further evidence of the

statistical distribution of the ethylene and butadiene units.

Finally, the density of the copolymer is not very different from the density of linear polyethylenes and is from 0.950 to 0.960 g/ml (ASTM D 1505-68).

The cross-linked products that can be obtained from the ethylene-butadiene copolymers are interesting because of many practical applications.

It is mentioned i.a. production of rigid foam plastic materials (very good insulating properties) and sound-absorbing materials (which burn without emitting black smoke), rigid containers, pipelines, pipe linings, etc.

For practical application, they have cross-linked copolymers in ratio

to polyethylenes, better mechanical properties, such as optimal tensile strength and impact resistance (ASTM D 256/56), improved stress-crack resistance (ASTM D 1693), low reduction in flexural modulus (ASTM D 747) and is essentially inert to oils and solvents.

Ethylene-butadiene copolymers which are not cross-linked can be used

as intermediates in the preparation of bifunctional olefin monomers after a suitable cleavage of the unsaturated chain.

Certain data for the above-mentioned properties, as well as for vulcanization mixtures and conditions, are reproduced in the following examples of preferred embodiments of the invention.

EXAMPLE 1

A steel autoclave with enamelled inner walls was used

with a volume of 5 liters and equipped with a mechanical stirrer, a jacket for the circulation of thermostatic liquid and valves, one of which was submerged for use in supplying reagent. A solution consisting of:

After thermostatically setting the mixture at 60°C, ethylene was introduced up to a pressure of 14 kg/cm 2 and then hydrogen was added to a total pressure of 20 kg/cm 2 .

A toluene solution (100 cm 3 ) containing 52 mg of dissolved vanadium triacetylacetonate was introduced by means of a pump over a few minutes. A solution of 0.65 ml of SOC^ in 100 ml of toluene was then slowly introduced using the same pump over the course of 20 minutes.

During the polymerization, ethylene was added so that the total pressure at 60°C was kept constant at 20 kc/.cr;2.

The experiment was interrupted after 40 minutes by adding 200 ml of methyl alcohol. The polymer formed was filtered off, washed on the filter with additional methyl alcohol (2. liters) and dried in an oven at 50°C under vacuum.

115 g of dry product was obtained with (IR analysis) 1.6 mole percent 1,4-transbutadiene units, MFI2 ±& =1.3 g/10' and MFI21 g<=><5>1.1 g/10'

(shear sensitivity = 39).

The copolymer was formed with the following compounds (g per 100 g copolymer):

The mixture was then press-treated at 180°C for 30 minutes.

The resulting product showed a gel content of 65% and an impact resistance of 56 kg/cm 2 (compared to 9.4 kg/cm 2 for the copolymer as such).

EXAMPLE 2

An experiment similar to example 1 was carried out using the same apparatus and reaction components, but the amount of vanadium triacetylacetonate was reduced to 17.5 mg.

The experiment was carried out within 30 minutes. It was achieved

91 g of polymer (36,400 g per gram of metallic vanadium) with:

The product was cross-linked in the same way as in example 1 and in this way gave 63% gel.

EXAMPLE 3

An autoclave was used as described in example 1, in which a solution obtained from was introduced

The autoclave was thermostatically controlled at 60 C (internal temperature) and

ethylene was introduced up to a pressure of 16 kg/cm 2 and then hydrogen up to a total pressure of 20 kg/cm 2.

During 30 minutes, a solution containing

35 mg of vanadium triacetylacetonate and 0.86 ml of SOCl^ in 200 ml of toluene.

During the polymerization, consumed ethylene was replaced.

The test time was 40 minutes and 78 g of polymer were obtained.

IR analysis resulted in a content of 1,4-trans-butadiene units of 15%. MFI2 = 1.1 g/10', MFI21 6 = 40.5 g/10' (shear sensitivity = 37.1).

EXAMPLE 4

A 1 liter steel autoclave equipped with mechanical stirring, electrical temperature regulation and valves for supplying the reaction component was used. The following solution was introduced into the container:

The mixture was thermostatically controlled at 60°C and then added 0.45 ml of A1(C2H5^C1 diluted in 50 ml of anhydrous toluene. Then, with the help of a calibration pump, a solution formed of 10.5 mg of vanadium triacetylacetonate and 0.28 ml of hexachlorocyclopentadiene was introduced over the course of 25 minutes in 50 ml anhydrous toluene.

The test time was 100 minutes and the consumed ethylene was replaced.

The polymer, isolated in the manner described in Example 1, weighed 19.5 g and had the following properties:

The copolymer was crosslinked in the presence of sulfur and accelerators (composition and conditions corresponding to Example 1).

EXAMPLE 5

In the autoclave described in example 4, the following was reacted:

By keeping the working pressure at 20 kg/cm2 at 60°C, a toluene solution of hexachlorocyclopentadiene in toluene (0.28 ml' in 50 ml) was introduced with the aid of a piston pump and then over the course of 25 minutes a solution of vanadyl diacetylacetonate in toluene (8 mg in 50 ml).

The experiment was stopped after 60 minutes from the addition of the vanadyl compound. 17 g of polymer were obtained with:

The polymer was 78% cross-linked by means of sulfur and accelerators (conditions and composition according to example 1).

EXAMPLE 6

In the autoclave according to example 4, the following reaction components were introduced:

By keeping the autoclave at 60°C with stirring, a solution of 10.5 mg of vanadium triacetylacetonate and 0.28 ml of hexachlorocyclopentadiene in 100 ml of toluene was added slowly over approximately 25 minutes.

The polymerization took place during 2 hours, during which absorbed ethylene was replaced by renewed supply.

28 g of copolymer were obtained with a butadiene unit content (mol percent) corresponding to 1.5.

EXAMPLE 7

An experiment was carried out in the same autoclave as in example 4 at

to use the following reaction components:

The ethylene was introduced up to a pressure of 16 kg/cm 2 •and then hydrogen was introduced to a total pressure of 90 kg/cm<2>at 60°C.

The polymerization was initiated by the gradual addition of a solution of 10.5 mg of vanadium triacetylacetonate in 50 ml of cyclohexane over the course of 25 minutes.

The experiment was interrupted after 70 minutes and the polymer was isolated by the usual procedure, where 7.5 g of polymer with the following properties were obtained:

- butadiene units (mol percent) = 1.24,

--MFI2 g = 5.39 g/10',

- MFI2 6 = 98.058 g/10'' (sk jærkr of tf beer somthe = 18.2).

Claims (10)

1. Process for the production of ethylene-butadiene copolymers with a high yield, characterized in that the polymerization reaction is carried out in one or more hydrocarbon solvents in the presence of a catalytic system consisting of: a) one or more vanadium compounds which are soluble in the above-mentioned solvents selected from 4- and 5-valent and complex-forming 3-valent vanadium halides, vanadium alcoholates, vanadium and vanadyl chelates• b) one or more aluminum compounds of formula R^ R2 A1X in which R^ and R2 are the same or different and stand for alkyl, cycloalkyl, alkaryl or aryl containing 1 to 18 carbon atoms or hydrogen, and X is halogen, preferably selected from chlorine or bromine c) one or more acidic compounds according to Lewis or Brønsted d) thionyl chloride and/or hexachlorodicyclopentadiene. 2. Procedure as stated in claim 1, characterized in that component a) is used in amounts of from 10-4 to 10-^ mol/litre. 3. Method as stated in claim 1 or 2, characterized in that the compound (b) is used in amounts of from 1 to 8.10 — 3 mol/litre. 4. Method as stated in claims 1-3, characterized in that when c) is a polyhalogen compound the ratio between gram atoms of halogen and gram atoms of aluminum is from 1.00 to 1.25. 5. Method as stated in claims 1-3, characterized in that the molar ratio between b). and c) when c) is a protonic acid or water, is from 10:1 to IL r 1 , preferably from 4:1 to 2:1. 6. Method as stated in claims 1-5, characterized in that the molar ratio between d) and b) is from 1:4 to 1:1. 7. Process as stated in claims 1-6, characterized in that the reactions are carried out in the presence of a hydrocarbon solvent selected from aromatic hydrocarbons, mixtures of aromatic hydrocarbons with aliphatic, cycloaliphatic, halogen-containing aromatic hydrocarbons, or mixtures thereof with the above-mentioned hydrocarbons or with other halogen-containing hydrocarbons. 8. Method as stated in claims 1-7, characterized in that the reaction is carried out at temperatures from 0 to 120°C, preferably from 50 to 100°C. 9. Method - as stated in claims 1-8, characterized in that the reaction is carried out with ethylene pressure of from 2 to 20 kg/cm 2. 10. Ethylene-butadiene copolymers with a content of butadiene units of from 0.1 to 10%, a vanadium content lower than 50 ppm, narrow molecular weight range, high chain linearity, high X-ray crystallinity, no gel content and statistical distribution of the monomer units.