CH659076A5 - LINEAR STRUCTURE ETHYLENE POLYMERS AND PROCESSES FOR THEIR PREPARATION. - Google Patents

Description

The present invention relates to particular ethylene polymers with a linear structure (i.e. substantially free of long branches) having a density lower than 0.9450 g / cm3. More specifically, it refers to ethylene copolymers with alme-40 no an-olefin having densities in the range from 0.9150 to 0.9450 g / cm3; it also relates to the processes for preparing these polymers.

It is already known (for example, German patent application No. 2 609 889, English patent No. 1 131 528, U.S. patent 45 No. 4 067 822 and German patent application No. 2 014 172), the possibility of obtaining polyethylene linear low and medium density through low pressure polymerization processes, during which ethylene is polymerized with an a-olefin, butene-1 or octene-1 preferably, in the presence of catalyst-50 bulls like Ziegler or, in any case , in the presence of catalytic systems usually used in the preparation of poly-to-ole-end.

These linear low density copolymers differ from conventional low density polyethylene (obtained with radical 55 processes at high pressure) not only for the structure, linear rather than branched, but above all for the remarkable improvements of some properties such as modulus and elongation as shown in the following table:

d (g / cm3) MFI (9/10 ') Extension module. Flexural tensile strength (MPa)% (MPa)

Linear LDPE. 9213 2.0 278 617 14.9

Conventional LDPE .9230 2.0 214 545 10.0

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659 076

Linear low density polyethylene has a higher mechanical strength than conventional low density polyethylene and this fact, for example in the case of processing to obtain films, can allow to save up to 30% of the product; appreciable advantages are found in the injection molding and in the production of wires and cables for the best mechanical properties at low temperature such as impact, the properties of the copolymers depending on the distribution of the comonomer in the polymer chain.

The applicant has now found, what constitutes the object of the present invention, that it is possible to obtain polymers with differentiated comonomer distribution using "high yield" catalytic systems already known for the preparation of high and medium density polyethylene described in the Swiss patent N ° 628 597. By versifying the production process or by making changes within the same process.

The catalytic systems in question comprise constituents which are basically formed by an organometallic aluminum compound and by a second compound which can be constituted by the product of the reaction of metallic values with the titanium compound and by a halogen donor or by such modified compound by subsequent reaction with an organometallic aluminum compound or with an alcohol.

In the first case the catalyst can be represented by a formula TÌX3 • m 'MX ", in which X represents a halogen, M a metal chosen from Mg, Al, Ti, V, Mn, Cr, Mo, Ca, Zn, n la valence of M and m 'is equal to or greater than 1 / n. Such a formulation is obtained through a process which involves the vaporization under vacuum of at least one of the metals mentioned above and the reaction of the vapors thus obtained with the titanium compound in the presence of a compound capable of giving halogen atoms. As said this composition can be used as such or it can be modified by reaction with an organometallic aluminum compound thus obtaining a formulation of the type Ti X3 • m M 'Yn ■ q M "Y' p • c Al Y" 3 -sR 's in which X is halogen; M'M '' are different metals and chosen from those listed above; Y, Y 'Y ", equal or different from each other are halogens, and can be in turn; equal 0 different from X, mq can be 0 0 different from 0, but they cannot both be equal to 0 at the same time; there is always different from 0; np represent the valences, respectively, of M 'and M ", s can assume all the values from 0 to 3, R' is a hydrocarbon radical, preferably having a number of carbon atoms less than or equal to 10; alternatively the catalyst can be the reaction product between a titanium compound, selected from halides or alcoholates, vapors of an electropositive and reducing metal condensed at low temperature, an organic or inorganic halogenated compound and an alcohol. In any case, an aluminum derivative of formula Al R '' p 'X3.P' in which R "is a hydrocarbon radical, X is a halogen and p 'a number varying between 1 and 3, is used as cocatalyst. the catalytic system can be obtained starting from (a) the product of the reaction between a titanium compound selected from halides and alcoholates, low temperature condensed magnesium vapors, an organic or inorganic halogenated compound and an alcohol, (b ) a trialkyl aluminum and a halogen aluminum corresponding to the formula Al R "'SX3.S with X equal to Cl or Br and s between 0 and 2.

The use of the above catalytic compositions, as mentioned, allows to obtain low density polyethylene, particularly linear low density polyethylene, causing the polymerization of the ethylene to take place in the presence of at least a second a-olefin having a number of carbon atoms from 3 to 10; it has been noted that a-olefins, particularly butene-1, increase the efficiency of the catalytic systems used.

Particular advantages have been found using butene-1, hexene-1 and octene-1; the final crystalline copolymers have a comonomer content ranging from I to 7% mol., a melting point between 115 and 130 ° C, an X-ray crystallinity, in melting of the amount of comonomer present, variable between 39 and 55%, a Melt Flow Index (according to the ASTM D 1238 method) between 0.1 and 50 g / 10 minutes; the density is always lower than 0.9450 g / cm3 preferably in the range of 0.9150-0.9450 g / cm3.

The distribution of the comonomer in the polymer chain is differentiated according to the production process adopted, this fact is evidenced by the different content of extractable products in boiling heptane with the same density and Melt Flow Index of the products.

The polymerization can be indifferently carried out in suspension, in solution and in the gas phase and, when necessary, the reaction medium can consist of C4-C10 hydrocarbons, linear or branched, cyclic hydrocarbons, halogenated hydrocarbons, or C4 reforming cut , depending on the path followed.

Of course, the conditions also vary according to the process followed: thus the gas phase polymerization is carried out by feeding the catalytic system described above to a gas mixture consisting of ethylene, an a-olefin, preferably propylene or butene-1, and hydrogen as regulator of the molecular weight in variable proportions depending on the product to be obtained, at a temperature that can be chosen between 20 and 100 ° C, preferably between 60 and 90 ° C at a pressure between 5 and 50 bar, preferably from 10 to 30 bar. The products obtained are characterized by densities between 0.9150 and 0.9450 g / m3 and by a content of extractables in heptane at boiling which range, for products with the same Melt Flow Index, from 65 to 5.9%.

The suspension polymerization is carried out in C4 aliphatic hydrocarbon solvents. This is linear or branched preferably in butane or isobutane or halogenated hydrocarbons, using as a C3-C10 a-olefin comonomer preferably from C3 to C6 and one of the catalytic systems described above.

The polymerization is carried out at a temperature that can be chosen between 20 and 90 ° C, preferably between 50 and 80 ° C at a pressure between 1 and 60 bar, preferably between 13 and 30 bar. The polymerization can be carried out in a single stage 0 in several stages with reactors in series and with feeding of the gas phase with different composition.

The finishing of the product can be carried out either by evaporation of the solvent in the case of low-boiling solvents or by centrifugation and drying of the powder or by stripping.

The products obtained in a single stage with a density between 0.9150 and 0.9450 have a fraction of extractable in boiling heptane between 43% and 3% while in samples obtained in a two-stage they have a fraction of extractable between 50% and 3.5%.

For the solution process it is necessary to operate with solvents whose critical temperature is higher than the polymerization temperature, the latter selected in the range between 130 and 250 ° C; Cyclic hydrocarbons such as cyclohexane and methylcyclohexane, and mixtures of normal hydrocarbons and ISO whose boiling temperature is between 120 and 180 ° C have proved to be particularly suitable as they have a good solvent power with respect to the copolymers produced; the best results are obtained by keeping the concentration of the polymer in the reaction mixture below 40% by weight of the solvent.

The regulation of the molecular weights of the copolymers produced is carried out conventionally using hydrogen in an amount comprised between 0.003 and 0.5 moles per mole of ethylene.

The polymerization can be carried out by feeding ethylene, hydrogen, an a-olefin (C3-C10) preferably from Cr, linear or branched and one of the catalytic systems described above while keeping the reaction mixture under stirring in order to promote heat dispersion polymerization and

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659 076

4

to improve the homogeneity of the system; the residence times of the polymeric solution can vary according to the polymerization conditions from 1 minute to 24 h, preferably in the interval from 5 minutes to 4 hours, the polymerization pressures are relatively low and comprised between 5 and 100 bar. 5

The copolymers are recovered by removing the unreacted monomers and the solvent from the polymerization mixture and deactivating the catalytic system with suitable reagents. The products obtained with a density between 0.9150 and 0.9450 have a fraction of extractables in boiling heptane between 56% and 5%. 10

In support of the differentiation of the products obtainable with the different processes in tab. (1) data of extractables in C7 at boiling temperature and some technological properties of the corresponding films are reported.

ES-Nr. PROCESS HALF OF d Tm MFI EXTRACTABLE % COMON.

REACTION (g / cm3) (° C) (9/10 ') nC7 98 ° C by weight

%

2

SLURRY MONOST.

ISOBUTANE

.9210

122

1.2

33.8

6.8

5

SLURRY BISTAD.

ISOBUTANE

.9204

122

1.1

39

7.0

6

SLURRY MONOST.

n-hexane

.9213

122.5

0.9

50.1

6.2

9

GAS PHASE

=

.9198

121.5

1.3

58

6.9

10

SOLUTION

cyclohexane

.9210

124

1.0

44

6.0

These and other operating modes will become more evident from the reading of the following examples, to which a simple illustrative function must be attributed, without, however, having to be understood as limiting in any way the object of the present invention.

Example 1

Catalyst preparation.

A rotary evaporator is used in whose flask, in the center, there is a spiral wound tungsten filament connected to the power supply. A cold bath is placed under the ball, placed horizontally.

The equipment is connected via a three-way stopcock to the vacuum and nitrogen line.

On the suitably protected tungsten resistance, 1 g of magnesium is wrapped in wire and 250 cm3 of anhydrous and deaerated heptane are loaded under nitrogen, 15 cm3 of 1 chlorohexane equal to 105 mM and 0.23 cm3 of TÌCI4 equal to 2.1 mM.

The flask is cooled to -70 ° C, the vacuum is made at 1.33 Pa and the spiral is heated so as to vaporize the metal. At the end of the vaporization (about 20 minutes) nitrogen is introduced into the apparatus and the flask is brought back to room temperature keeping the suspension under stirring and then heated for 1 hour at 80 ° C (catalyst A).

70 g of polyethylene powder with controlled particle size are loaded into a 500 cm3 flask, dried under vacuum for 30 minutes, then the nitrogen flask is filled and, always in an inert atmosphere, the previously obtained suspension is charged. Under vigorous stirring, the solvent is removed under vacuum by heating the flask to 50-60 ° C.

When the elimination of the solvent is complete, the nitrogen flask is filled. The catalyst obtained (catalyst B) is presented as a hazelnut-colored flowing powder.

The analysis shows:

Ti = 1, 4mg / g Mg = 12.934 mg / g CI = 39.70 mg / g.

Example 2

1.3 liters of isobutane are added to a 5-liter autoclave with a still-air-stirred stirrer under vacuum and brought to 60 ° C, then 120 g of butene-1, 7 mM of aluminum triiso-30 butyl, hydrogen equal to 1 are added , 55 bar, ethylene up to a total pressure of 13 bar and 0.5 g of catalyst (B) equal to 0.6946 mg of Ti.

The temperature is maintained at 60 ° C and ethylene is sent keeping the total pressure constant.

After two hours of polymerization the reaction is stopped with 35 20 cm3 of ethanol then the solvent is evaporated. 310 g of polymer are obtained: equal to a yield of 430 kg of polymer / g Ti having the following characteristics:

Density

40 Butene content (n.m.r.) CH3 / IOO C (number)

melt flow index (M.F.I.) at 2.16 kg Melting point RX crystallinity

45 Average apparent density of the powder Extracted in C7 at boiling

0.9210 g / cm3 6.8% weight 1.70

1.2 g / 10 minutes

122 ° C

42%

0.33 g / cm3 350 m 33.8%

Example 3

The same apparatus and methods described in Example 2 are used with a different butene quantity, namely 80 g. 260 g of polymer equal to a yield of 360 kg polymer / g of Ti are obtained, having the following characteristics:

Density

Butene content CH3 / IOO C (number) MFI

60 Bulk density Melting point

0.9284 g / cm3 4.8% weight 1.1

0.4 g / 10 minutes 0.30 g / cm3 124.5 ° C

Example 4

One operates with the same apparatus and method described in Example 2 with a quantity of butene-1 equal to 140 g.

350 g of polymer equal to a yield of 480 kg polymer / g of titanium are obtained, having the following characteristics:

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659 076

Density

Butene content CHs / lOO C MFI (2.16 kg)

Bulk density m.p.

Extracted in C7 at boiling

0.9152 g / cm3 10.3% weight 2.5

1.2 g / 10 minutes 0.25 g / cm3 120 ° C 52%

The polymer obtained in the quantity of 280 g equal to a yield of 385 kg of polymer / g of Ti has the following characteristics:

Example 5

One operates with the same apparatus described in Example 2 by varying the operating modes as follows: 1.3 liters of isobutane are charged, brought to 60 ° C, 40 g of butene-1, 6 mM of triisobutyl aluminum are added, hydrogen equal to 1.70 bar, ethylene up to a total pressure of 14 bar and 0.5 g of catalyst (B) of example 1 equal to 0.6946 mg of Ti. The temperature is maintained at 60 ° C and ethylene is fed keeping the total pressure constant. After 15 minutes of polymerization (polymer produced about 30% of the total) 140 g of butene are loaded and polymerization is continued maintaining the total pressure at 14 bar by sending ethylene. After a total of two hours of polymerization, the polymerization is stopped with 19 cm3 of ethanol and the solvent is evaporated. 320 g of polymer equal to a yield of 445 kg of polymer / g of Ti having the following characteristics are obtained:

Density

Butene content Melt Flow Index Bulk density Melting point Extracted in C7 at boiling point

0.9204 g / cm3 7.0% weight 1.1 g / 10 minutes 0.33 g / cm3 122 ° C 39%

Example 6

In a 5-liter autoclave with anchor stirrer, deaerated under vacuum, 2 liters of anhydrous hexane are loaded and de-aerated and brought to 60 ° C, then 130 g of butene-1, 6 mM of triisobutyl aluminum, equal hydrogen are added at 2.2 bar, ethylene up to a total manometric pressure of 6 bar and 0.5 g of catalyst (B) of Example 1 equal to 0.06946 mg of Ti.

The temperature is maintained at 60 ° C and ethylene is sent keeping the total pressure constant. After two hours of polymerization the reaction is stopped with 10 cm3 of ethanol then the autoclave is cooled, the gases are vented and the polymer suspension is stripped.

The dried polymer, 250 g equal to a yield of 350 kg of polymer / g of Ti has a sliding powder appearance and has the following characteristics:

Density

Butene-1 content Melt Flow Index Bulk density Extracted in C7 at boiling

0.9213 g / cm3 6.2% weight 0.9 g / 10 minutes 0.23 g / cm3 50.1%

Density

Butene content CH3 / IOO C number Melt Flow Index Crystallinity at RX Bulk density

0.9215 g / cm3 6.5% weight 1.65

0.90 g / 10 min 41%

0.34 g / cm3

Example 8

The procedure is carried out with the same apparatus and method of example 6 using 300 g of anhydrous and deaerated hexene. 240 g of polymer are obtained having the following characteristics:

Density

CH3 / IOO C number Hexene content Melt Flow Index 20 Bulk density

0.9290 g / cm3 0.90

5.4% weight 1.1 g / 10 min 0.25 g / cm3

Example 9

2 g of catalyst B and 6 mgat of AÜBU3 diluted in 15 25 cm3 of hexane are loaded into a dried coded test-tube and in an inert atmosphere; it is stirred with a magnetic stirrer then, under stirring, the hexane is evaporated until the sample is dry.

1 g of catalyst equal to 0.013 mgat of Titanium is loaded under nitrogen in a 2 liter autoclave with a stirrer dried and maintained in an inert atmosphere. The vacuum is made in the autoclave 30 to eliminate the nitrogen, it is heated to 70 ° C and then loaded with a stream of gas having the following volumetric composition: ethylene 80%, butene 15% hydrogen 5% up to a pressure of 10 Cafe.

After 1 hour of polymerization, 100 g of poly-35 mere powder are obtained having the following characteristics:

Density

Butene-1 MFI content

40 Melting point

Extracted in C7 at boiling

0.9198 g / cm3 6.9% weight 1.30 g / 10 minutes 121.5 ° C 58%

Example 10

In a 5-liter autoclave with agitator, 2 liters of 45 anhydrous and deaerated cyclohexane containing 1 mmol of Al (nOctb, is brought to 150 ° C, then 100 g of octene-1, hydrogen equal to 0.5 bar are added , ethylene up to a total manometric pressure of 10 bar and 1.5 cm3 of catalyst type (A) of Example 1 equal to 0.5748 mg of titanium. The constant pressure is maintained keeping 50 by giving ethylene for 30 minutes. at the end of the polymerization the reaction is stopped, the autoclave is cooled and the gases are vented The product obtained is made up of 140 g of polymer equal to a yield of 230 kg of polymer / g of Ti.

The polymer obtained has the following characteristics:

Example 7

The operation is carried out with the apparatus and methods described in example 2, using as an anhydrous n-butane and all the same components the polymerization in the same quantity whereby the total manometric pressure reached with ethylene is 11.5 bar.

Density

Octene content

CH3 / IOOC

Fusion point

Melt Flow Index

Extracted in C7 at boiling

0.9210 g / cm3 7.2% weight 0.96 122 ° C

1.0 g / 10 minutes 44.5%

v

Claims (15)

659 076 2 1. Copolymers of ethylene with at least a second alpha-olefin having, depending on the amount of comonomer present, densities in the range from 0.9150 to 0.9450 g / cm3, a melting point between 115 and 130 ° C, an X-ray crystallinity varying between 39 and 55%, a Melt Flow Index, according to the ASTM D 1238 method, between 0.1 and 50 g / 10 'and a comonomer content variable from I to 7 molar%. Copolymers according to claim 1, wherein the second alpha-olefin is preferably selected from butene-1, hexene-1 and octene-1. Process for preparing ethylene copolymers according to one of claims 1 and 2, consisting of bringing ethylene into contact with at least a second alpha-olefin in the presence of a catalytic system comprising an organometallic aluminum compound and the reaction product of metallic vapors with a titanium compound and a halogen donor. 4. Process for the preparation of ethylene copolymers according to one of claims 1 and 2, consisting of bringing ethylene into contact with at least a second alpha-olefin in the presence of a catalytic system comprising an organometallic aluminum compound and the reaction product of metallic vapors with a titanium compound and a halogen donor modified for subsequent reaction with an organometallic aluminum compound. 5. Process for the preparation of ethylene copolymers according to one of claims 1 and 2, consisting of contrasting ethylene with at least a second alpha-olefin in the presence of a catalytic system comprising an organometallic aluminum compound and the product of the reaction of metallic vapors with a titanium compound and a halogen donor modified for subsequent reaction with an alcohol. Process according to one of claims 3, 4 and 5 in which the catalyst is constituted by a compound of formula TÌX3 - m 'MXn in which X represents a halogen, M a metal chosen from Mg, Al, Ti, V, Mn, Cr, Mo, Ca and Zn, n the valence of M and m 'is equal to or greater than 1 / n. Process according to one of claims 3, 4 and 5 in which the catalyst is constituted by a compound of formula TiX3 • m M 'Y "• q M" Y' p • c A1Y '' 3-sR 's in which X it is halogen; M 'and M "are different metals and selected from those listed in the preceding claim; Y, Y 'and Y ", equal or different from each other, are halogen and can be equal or different from X; meq can be 0 or different from 0, but not simultaneously both equal to 0; c is always different from zero np represent the valences, respectively of M 'and M "; s can take all values from 0 to 3; R 'is a hydrocarbon radical having a number of carbon atoms less than or equal to 10. Process according to one of claims 3, 4 and 5, characterized in that the polymerization is carried out by feeding a gaseous mixture comprising ethylene, at least a second alpha-olefin and hydrogen. 9. Process according to claim 8, characterized in that the reaction is carried out at temperatures between 20 and 100 ° C and at pressures between 5 and 50 bar. 10. Process according to claim 9, characterized in that the reaction is preferably carried out at temperatures between 60 and 90 ° C and at pressures between 10 and 30 bar. 5. Process according to one of claims 3, 4 and 5, characterized in that the polymerization reaction is carried out in suspension. 12. Process according to claim 11, characterized in that the reaction is carried out in the presence of a sol 10 chosen from among C4 aliphatic hydrocarbons - This or from halogenated hydrocarbons. 13. Process according to claim 12, characterized in that the reaction is carried out at temperatures between 20 and 90 ° C and at pressures between 1 and 60 bar. 2. Process according to claim 13, characterized in that the reaction is preferably carried out at temperatures of between 50 and 80 ° C and at pressures of between 13 and 30 bars. Process according to one of claims 3, 4 and 5, 20 characterized by the fact that the polymerization is carried out in solution. 16. Process according to claim 15, characterized in that the reaction is carried out at a temperature comprised between 130 and 250 ° C. 25 17. Process according to claim 16, characterized in that the reaction is carried out in the presence of a solvent having a critical temperature higher than the polymerization temperature. 18. Process according to claim 17, characterized 30 by the fact that the solvent is selected from cyclic hydrocarbons and mixtures of hydrocarbons.