DE2120232C3 - Process for the production of a block polymer - Google Patents

Description

The invention relates to a method / for production a block copolymer having a central copolymer block of a conjugated diene and a vinyl aromatic compound and with two terminal homopolymer blocks, the frequency of structural units formed by the conjugated diene from the center of the central copolymer block to the amount of which decreases by a one-step polymerization of a mixture of the conjugated diene and the vinyl aromatic compound in a non-polar solvent, with no more than % By weight of a polar solvent are present, in the presence of a catalyst, which by reaction of a conjugated diene with a reaction product of metallic lithium with an aromatic one Hydrocarbon in a polar ether solvent.

Various methods of making block copolymers of this type have been described. For example, Japanese Patent Application No. 798/1965 describes the preparation of a block copolymer in a multi-stage reaction using a lithium compound as an initiator. The method of "living" polymerization is used for this. Block copolymers are obtained in which, in succession, a non-elastomeric block of an unsaturated compound, e.g. B. a vinyl-substituted aromatic compound, an elastomeric block made of a conjugated diene and then again the non-eiastotic block described are linked to one another.

From Japanese patent application No. 19 286/1961 block copolymers are known which have a central elastomeric block and two terminal non-elastomeric blocks. In this known method, too, the reaction is carried out in several stages. An aromatic compound having two lithium atoms is used as an initiator, and the polymerization proceeds at both ends.

GB-PS 9 64 478 also discloses a process for the preparation of a block copolymer of this type a middle copolymer block of a conjugated diene and a vinyl aromatic compound and with two terminal homopolymer blocks from the vinyl aromatic compound is known worked in one stage and a reaction product of lithium and a polynuclear aromatic compound, z. B. naphthalene, uses Die however, the products obtained have insufficient impact resistance and insufficient elongation. These disadvantages are due to the fact that undesirable homopolymers or two blocks Copolymers are contained in significant amounts in the resulting block copolymer. This is on a Increase in inactive end groups due to impurities in the solvent or are gradually increased in the monomers. If the three-block copolymer contains a two-block copolymer, the clarity, the ductility, the Tear resistance and in particular the impact resistance are reduced.

It is therefore the object of the invention to create a block copolymer of the type mentioned at the outset which has excellent mechanical properties, in particular high impact strength and tear resistance, and excellent clarity.

According to the invention, this object is achieved by using a catalyst which has been prepared by reacting the conjugated diene with the reaction product of metallic lithium and a diphenyl hydrocarbon and / or a terphenyl hydrocarbon in a cyclic ether or an aliphatic polyether.

The block copolymer obtained has a three-block structure in which an elastomeric central block is connected on both sides to a non-elastomeric block. There should preferably be a large difference between the glass transition point (Tg) of the two blocks. Preferably, the glass transition point of the non-elastomeric block (Tg) should be above 100 ⁰ C, while should be the glass transition point of the elastomeric block (Tg) below -40 ° C.

Your polymerization process of the present invention is one at both ends of the initiator "Living" polymerization. There is a notable difference in reaction rates of the two monomers in the non-polar solvent. Therefore, in the one-step according to the invention Polymerization in the first reaction phase in the main the conjugated diene polymerizes under Copolymerization of only a small amount of the vinyl-substituted aromatic hydrocarbon compound. At the same time, the ratio of vinyl-substituted aromatic hydrocarbon gradually increases conjugated diene increased from the center of the formed block to the ends. After the whole conjugated diene together with the small amount of vinylic aromatic hydrocarbon compound is polymerized, only the polymer

■ isation of the vinyl-substituted aromatic hydrocarbon controlled to an appreciable extent, whereby two terminal homopolymeric blocks are formed.

During the preparation of the starter, the reaction complex involves the conversion of lithium with added a small amount of conjugated diene to the diphenyl or terphenyl hydrocarbon, the Dianion of an oligomer of the hydrocarbon is formed. Then the polar medium turns against a non-polar solvent exchanged by distilling off the polar medium and non-polar Adding solvent. A homogeneous starter can be produced by this method.

When making the starter, at least one gram atom of lithium is used with one mole of not condensed aromatic hydrocarbon reacted Preferably should not be less than 1 gram atom Lithium can be used, otherwise the starter obtained has a low activity. On the other hand, it is also not preferred to use too large an excess of lithium in order to achieve the Keeping procedures economical. Preferably, 1 to 10 gram atom of lithium should not be used for 1 mole of the lithium condensed aromatic. Hydrocarbon grains.

In the preparation of the initiator, the reaction temperature is generally between -78 ° C and + 30 ° C should be preferably between -40 "C and 0 ⁰ C. With more than 30 ° C, the conjugated diene, in The reaction time may vary polymerized by the reaction temperature can be selected, but it is not subject to any restrictions.

The polar medium used to prepare the starter can e.g. B. tetrahydrofuran, tetrahydropyran, r> Ethylene glycol diethyl ether, ethylene glycol dimethyl ether or diethylene glycol dimethyl ether.

It is not advantageous to use an aliphatic monoether because the reaction rate in in this case would be quite small. On the other hand, the reaction speed is remarkably high when an aliphatic polyether or a cyclic ether is used. In the latter case, the result is a secondary advantage in that the ratio of uncondensed aromatic hydrocarbon is π can be reduced to lithium, so that the purity of the end product is increased.

The amount of the polar medium is not limited, but a substantial amount is required polar medium after the reaction of lithium and the uncondensed aromatic hydrocarbon to remove and against a non-polar solvent, e.g. B. to exchange a hydrocarbon. If the polar medium remains in the starler and is mixed in an amount with the monomers, which exceeds the value of 2% by weight, only a statistical polymer is obtained irregularly distributed monomers, and it is impossible to produce a block copolymer with excellent mechanical properties and excellent optical clarity.

You can z. B. use the following vinyl-substituted aromatic hydrocarbons: styrene, Λ-methyl styrene, p-methyl styrene, 3,5-diethyl styrene, 4-n-propyl-styrene, 2,4,6-trimethylstyrene, 4-n-propyl-styrene, 2,4,6-trimethylsyrene and S-methyl-S-n-hexyl-styrene. Crazy! following! so!! the invention based on styrene as Examples of the vinyl-substituted aromatic hydrocarbon will be described. As conjugated For example, 13-butadiene and isoprene can be used insert. Styrene is preferably used in an amount of from 60 to 95% by weight, in particular from 75 to 85% by weight, based on the total monomers, whereby the remainder can consist of conjugated dienes.

As inert hydrocarbon solvents, aromatic hydrocarbons, e.g. B. benzene, toluene, Xylene and ethylbenzene; aliphatic hydrocarbons, e.g. B. η-hexane and cyclohexane and mixtures use the same.

It is preferred to remove any impurities in advance which may affect the starter or which are essential for the invention can decompose monomers used, z. B. Moisture Oxygen, carbon dioxide, certain sulfur compounds or acetylene.

The block copolymerization of the styrene and the conjugated diene is usually conducted at about -20 ⁰ C to 100 ⁰ C, preferably at about 20 ° C to 65 ° C the Blockcopolymerisationsdauer depends on the polymerization conditions, and is usually up to 48 hours, preferably up to 24 hours.

To deactivate the starter and the active end groups of the block copolymer obtained after the end: block copolymerization, methanol or isopropyl alcohol added. Furthermore, a low Amount of an antioxidant added, e.g. B. 4-hydroxymethyl-2,6-di-t-butyI-phenol and thereafter the block polymer obtained is precipitated by adding an excess of methanol or isopropyl alcohol, filtered off and dried.

The block polymer obtained has remarkable mechanical properties, e.g. B. a high impact strength, a high yield point and a large tensile elongation. In addition, it has a notable one Clarity. The advantageous properties of the block copolymer obtained result from the novel structure, which consists of a three-block copolymer, the inner block of which one from the inside has outwardly decreasing content of conjugated diene.

In the following, the invention is to be explained in more detail with the aid of exemplary embodiments.

example 1
a) Preparation of the catalyst

A l-1 flask is fitted with a tight stirrer, a Reflux condenser, a gas inlet tube, an inlet for the reactants, a funnel and a Equipped with a thermometer. In this flask 250 ml of ethylene glycol dimethyl ether are added, in which 7.7 g of diphenyl were dissolved. In addition, 1.7 g of lithium, which is in an amount of 30 Percent by weight dispersed in solid paraffin is added to the flask, the solution being a deep green colored Complex arises.

Is then added to the flask in a dry ice-methanol to the contents to a temperature of less than - 40 ⁰ C to cool and then 50 g of butadiene are introduced slowly. The butadiene is introduced so slowly that the deep green color of the contents does not change to a reddish brown color. After the butadiene has been introduced, which takes about 1 hour, the reaction product is left to stand at room temperature. The color of the reaction product changes in the process

Example 2

The block copolymerization according to Example 1 is repeated, but with 50 ml of the solution of the reaction product removed in each reaction period will. A small amount of the benzene-methanol mixture is added to each sample. The viscosity, the The yield after precipitation in methanol and the styrene content of the polymer are measured. the The values obtained are summarized in Table I.

Table I. viscosity yield Styrene content of Reaction (*1) (* 2) Polymers (* 3) period (cP) ( ⁰ A) (Wt .-%) 190 11th 30th 10 340 19th 34 20th 500 25th 37 30th 1500 99 79 40 1450 98 81 50

reddish brown.

The reaction product is up to the boiling point of the The solvent is heated and refluxed for several minutes, after which the solvent is added distilled off, and the product is dried in vacuo after sufficient drying 300 ml of benzene added and again distilled off, so that a dry product is obtained. 400 ml of dry benzene are added again, and the solution is filtered, 500 m! a reddish brown solution

The product is treated with 0.1 N HCl in methanol-water titrated against Phenolphlhalein as an indicator, whereby gives a concentration of 0.36 n / l

b) block copolymerization

30 ml of the catalyst solution are placed in an atoclave which is equipped with a stirrer and is kept at 50.degree. 1.5 l of dehydrated and air-free benzene as well as 400 g of styrene and 100 g of butadiene were previously placed in the autoclave. When the catalyst solution is added, the color of the mixture changes to a reddish brown. As the butadiene content decreases, it turns yellow. The initial pressure of the butadiene is about 0.5 kg / cm ² . It assumes atmospheric pressure in the course of about 20 minutes. After about 30 minutes, the reaction solution turns red, and the polymerization of the styrene leads to an increase in temperature due to an exothermic reaction. After about 1 hour, from the start of the reaction, several milliliters of a mixture of benzene and methanol are added to the viscous reddish solution, a clear, colorless solution being obtained. The viscosity of the solution is reduced from around 500 ocP down to around 2500 cP at 50 ° C.

The product is precipitated with methanol and dried in vacuo, 495 g of block copolymer being obtained. The molecular weight of the block copolymer obtained is determined by the osmotic pressure method in toluene and is 125,000. The styrene content is measured by the refractive index method and is 79 percent by weight. The product has a tensile strength of 201 kg / cm ² , an elongation of 127% and a Dynstat impact strength of 130 kg cm / cm ² .

Table II

Weight ratio of used
Styrene to butadiene

Styrene / butadiene weight ratio
in block copolymers (* 1)

Molecular weight (· 10 ⁴ ) (* 2)
Tensile strength (kg / cm ² ) (* 3)
Elongation (%) (* 3)
Dynstat impact resistance
(kgcm / cm ² ) (* 4)

Rockwell hardness (M scale 1/4) (* S)
Turbidity (%) (* 6)

i * l) The block copolymer was dissolved in CS2 and dried by a Lull blower on an Abbe refractometer. That

The ratio of styrene to butadiene was measured by the index of refraction. (* 2) It was measured according to the method of osmotic pressure in methanol. (* 3) Dumbbell-shaped sticks 2 mm thick, 10 mm wide and 80 mm long are used.

(* 4) The Dynstat impact strength was measured according to DIN. Samples 2 mm thick and 10 mm wide were used. (• 5) It was measured according to ASTM D 785. (* 6) It was measured ^{according to ASTM D 100 3.}

The product with a styrene content of 81% by weight has a molecular weight of 119,000, a tensile strength of 214 kg / cm ² , an elongation of 105% and a Dynstat impact strength of 110 kg cm / cm ² .

(* 1) 50 ml of the reaction product are mixed with 3 ml of a Mixture of benzene and methanol in a volume ratio treated by 4: 1. The sample comes with a Emiller viscometer measured at 50 ° C.

(* 2) 10 ml of the reaction product are applied in vacuo dried an aluminum foil.

(* 3) The reaction product dried in vacuo is dissolved in CS2, and the solution is blown by an air blower dried on an Abbe refractometer. The styrene content is determined by the refractive index of the product measured.

Example 3

The bulk polymerization according to Example 1 is repeated, but using the total amount of styrene and butadiene is 500 g and the ratio of styrene to butadiene is in the range of 70/30 to 90/10.

The various properties of the block copolymer obtained are summarized in Table II.

65/35

75/25

63.5 / 36.5 71.5 / 28.5 74/26

80/20

78/22

85/15

86.5 / 13.5 93/7

10.1 10.6 10.8 11.0 12.1 11.0 185 187 198 217 305 385 350 275 172 126 104 67 - - - 130 110 26th - - 7th 11.0 24.5 32.5 21.0 17.0 15.0 11.0 6.8 4.6

Example 4
a) Preparation of the catalyst

11.5 g of o-terphenyl and 1.7 g of lithium are reacted in 250 ml of tetrahydrofuran according to Example 1. Butadiene is then added to the reaction product and that consisting of tetrahydrofuran Solvent is replaced by benzene, with 500 ml of a blackish reddish brown reaction mixture can be obtained. When the product is titrated with HCl, the concentration is 0.39 n / l.

c) bulk polymerization

The block copolymerization of styrene and butadiene is carried out in accordance with the process of Example 1 -, using this catalyst solution repeatedly, wherein in each case the total amount of styrene and butadiene is 500 g and wherein the ratio of Styrene to butadiene / between 70/30 and 90/10.

The physical properties of the κι block polymer obtained are summarized in Table III.

Table III

Weight ratio of used
Styrene to butadiene

Styrene / butadiene weight ratio
in block copolymers
Molecular weight (· 10 ⁴ )
Tensile strength (kg / cm ² )
Strain (%)

Dynstat impact strength (kg / m / cm ² )
Rockwell hardness (M scale 1/4)
Turbidity (%)

63/35 70/30

64.5 / 35.5 69/31

75/25

80/20

74.5 / 25.5 80/20

10.5

175
385

23.0

9.9
200

272

18.0

11.1
225
170

17.0

9.5

197

102

104

12.6

85/15
85/15

8.9

282

94

64.5

21

5.0

Comparative example 1

In the following, the difference between the invention is based on a comparative example Processes and the conventional preparation of block copolymers are illustrated. Under use the same catalyst solution as in Example 1, butadiene and styrene are polymerized in two stages, butadiene alone is initially polymerized and the air is removed after the butadiene pressure has been reduced is removed from the vessel and 0.1 ml of sec-butyl lithium in 11 benzene are added and then the vessel is charged with styrene. It was with the monomer ratios according to Examples 3 and 4 worked. The results of this comparative example are shown in Table IV.

Table IV

Weight ratio of monomers
Slyrol / Buladia

Styrene / butadiene weight ratio
in block polymer

Molecular Weight (· 10 ")
Tensile strength (kg / cm ² )
Strain (%)

Dynstat impact strength (kg m / cm ² )
Rockwell hardness (M scale 1/4)
Turbidity (%)

63/35 70/30 75/25 80/20

62.5 / 37.5 71.5 / 28.5 74.5 / 25.5 87/13

85/15

86.5 / 13.5 91/9

11.7 12.1 10.1 13.1 12.6 11.0 198 201 250 272 321 405 170 52.1 25.5 12.5 10 7th 70 35 32.5 21.0 11.5 12th 7th 22nd 25th 27 31 41 22.0 17.0 12.5 11.0 5.0 4.5

It is found that the block copolymers prepared in two stages according to this comparative example the block copolymers prepared by the one-step process according to the invention in relation to the Impact resistance and elongation are inferior.

Example 5

A 3-1 flask is fitted with a sealed stirrer, a reflux condenser, a gas inlet, an inlet for the reactants, a funnel and a Thermometer equipped 300 ml of tetrahydrofuran, which on a sodium-potassium alloy am Was refluxed and then distilled, 1 g of diphenyl, which is made from hexane, is introduced was recrystallized and dried, is also introduced and dissolved in the tetrahydrofuran. Further, 1 ml of styrene is added.

Then are introduced 30 l of argon gas into the reaction vessel over 30 minutes, the argon gas was bubbled for dehydration through a heated at 800 ⁰ C layer of titanium sponge and through a molecular sieve, are then about 0.3 mmol sea-butyl lithium added to the contents, whereupon this takes on a pale yellow color. 101 argon gas is passed in for 10 minutes 70 mg lithium, which is in a concentration of 30

Percent by weight is dispersed in solid paraffin

are added and the content increases after 2 to 3

Turns green in minutes.

The reaction flask is then placed in a dry ice-methanol bath given to cool the contents and 3 ml of isoprene are added and the contents become Stirred for 30 minutes. The flask is then removed from the dry ice-methanol bath and poured on

Set water bath with a temperature of 30 ° C. The tetrahydrofuran is removed in vacuo. Then 300 ml of benzene are added, which was previously freed from air by argon gas and by means of sec-butyl-lithium was dehydrated. This benzene is then distilled off again in vacuo.

b) high polymerization

To the mixture obtained, 1.51 of benzene and 400 g of styrene were added, which was previously added after dehydrated and de-aerated using the same procedure. 100 g of isoprene are also added, which was distilled off over sodium. The contents take on a pale yellow-reddish-brown color.

It is stirred and, during the reaction, the viscosity of the contents gradually increases. After about 50 minutes the contents will turn red and the styrene will start to polymerize. After about 10 minutes the temperature increases to 70 ^° C. to 80 ^° C. and a large number of bubbles are observed. After about 1.5 hours from the start of the polymerization, a small amount of a mixture of methanol and benzene is added and the reaction product is precipitated by adding methanol and dried in vacuo

1% 4-hydroxymethyl-2,6-di-t-butyl-phenol is added to the dried polymer, and the product is processed into granules with the aid of an extruder. The granules obtained become too Test specimens formed from dumbbell or rod shape, which are 2 mm thick, 10 mm wide and 8 mm long exhibit. These test specimens are produced by injection molding. The physical properties of the obtained product are summarized in Table V.

Table V

Weight ratio of used

Styrene / isoprene 80/20

Molecular weight (χ 10 ⁴ ) 8.9

Tensile strength (kg / cm ² ) 370

Elongation (%) 37

Dynstat impact strength (kg cm / cm ² ) 25

Rockwell hardness (M scale 1/4) 31

Haze (%) 7.5

Example 6

Ig para-terphenyl and 100 mg lithium are used implemented according to Example 5 in tetrahydrofuran. 5 g of butadiene are added, and the tetrahydrofuran is distilled off and replaced by benzene. 1.5 liters of benzene, 425 g of styrene and 75 g of butadiene will be added, and the whole is polymerized at 50 ° C. After the butadiene has polymerized with a small amount of styrene after about 35 minutes, the Polymerization of the styrene, the temperature of the contents of the reaction vessel being reduced to about 100 ° C increased

After the polymerization, the block copolymer is separated off. 495 g are obtained. That Molecular weight is determined by the osmotic pressure method in toluene. It is 125,000. 1% of 4-hydroxymethyl-2,6-di-t-butyl-phenol are added to the block copolymer and this is mixed with Processed into granules with the help of an extruder Injection molding test specimen formed from dumbbell shape or rod shape, which has a thickness of 2 now, have a width of 10 mm and a length of 80 mm. The physical properties of the obtained product are summarized in Table VI.

Table VI

Weight ratio used Example 7 85/15 Styrene / butadiene 12.5 Molecular weight (χ 10 ⁴ ) 320 Tensile strength (kg / cm ² ) 70 Strain(%) 107 Dynstat impact strength (kg cm / cm ² ) 23 Rockwell hardness (M scale 1/4) 7.0 Turbidity (%)

10 g of diphenyl and 2.5 g of lithium are reacted in 250 ml of tetrahydrofuran according to Example 1. 80 g Butadiene are added and then the tetrahydrofuran is replaced by benzene, whereby 600 ml of a blackish-reddish-brown reaction solution is obtained. By titration with hydrochloric acid, a Concentration of 0.45 n / l found. According to Example 1, 400 g of styrene and 100 g of isoprene are in benzene reacted at 35 ° C using 20 ml of the catalyst solution.

After 40 minutes, the contents of the reaction vessel turn red and the polymerization of the Styrene starts at a temperature above 100 ° C. After completion of the reaction, the copolymer obtained is precipitated by methanol and dried in vacuo. There is 1% 4-hydroxymethyl-2,6-di-t-butyl-phenol added and the copolymer obtained is granulated using an extruder The resulting granules are made into test specimens of a rod shape or a dumbbell shape by injection molding The test specimens have a thickness of 2 mm, a width of 10 mm and a length of 80 mm. the physical properties of the product obtained are shown in Table VII

Table VI

Weight ratio of used

Styrene / isoprene 80/20

Molecular weight (χ 10 ⁴ ) 8.5

Tensile strength (kg / cm ² ) 320

Elongation (%) 60

Dynstat impact strength (kg cm / cm ² ) 35

Rockwell hardness (M scale 1/4) 29

Haze (%) 5.0

Example 8

The polymerization experiments according to the preceding examples are repeated, but with the total amount of styrene and isoprene is 500 g each and the ratio of styrene to isoprene im Range from 70/30 to 90/10 is selected. The properties of the block copolymer obtained are in Table VIII compiled

Table VIII

Weight ratio of styrene / isoprene used

Molecular weight (■ 10 ⁴ )
Tensile strength (kg / cm ² )
Strain (%)
Dynstat impact resistance
(kg cm / cm ² )

Rockwell hardness (M scale 1/4) Turbidity (%)

70/30 75/25

80/20

85/15

90/10

10.1 9.5 7.9 9.0 8.5 280 2Q0 330 370 420 105 70 50 35 21 68 41 33 31 15th 17th 22nd 25th 31 41 6.8 7.0 5.5 5.0 3.3

Comparative example 2

To illustrate the differences between the method according to the invention and the conventional one Block copolymerization the following experiments are carried out using the same catalyst As in Example 7, isoprene and styrene are polymerized in two stages, with isoprene first is polymerized alone at 50 ° C for 30 minutes and then cooled to 25 ° C. Then will Added styrene and polymerized at 30 minutes. The ratio of styrene to isoprene is increased Range selected from 70/30 to 90/10. Each of the treated and dried copolymers obtained is mixed with 1% 4-hydroxymethyl-2,6-di-t-butylphenol and processed into test specimens physical properties of the copolymer obtained are shown in Table IX.

Table IX

Weight ratio of one- 70/30

used styrene / isoprene

Molecular weight (· 10 ⁴ >
Tensile strength (kg / cnv)
Strain(%)
Dynsiat impact resistance
(kg cm / cm ² )

Rockwell hardness (M scale 1/4) Turbidity (%)

75/25

80/20

85/15

90/10

8.5 7.5 9.0 10.1 10.5 310 300 350 390 440 50 20th 15th 17th 5 22nd 25th 18th 19th 15th 32 33 35 39 45 9.0 7.5 7.7 6.0 3.0

Comparative experiments

Example 3 of British Patent 9,644,478 compared with Example 1 of the invention.

Attempt 1

According to example 3 of British patent specification 64,478, the following reaction was carried out:

Composition:

lithium

Isoprene

Methylnaphthalene

Butadiene

Dimethyl ether

8g (l, 14Mol) 41 m! (0.4 mol) 56 ml (0.4 mol) 14 g (0.45 mol) 300 ml

Into a 2-1 flask equipped with a stirrer 300 ml of the dried ether were added and a stream of nitrogen was initiated ml of methylnaphthalene, 41 ml of isoprene and 8 g of lithium were added and the flask was turned on for 24 hours kept with stirring at a temperature of -26 ° C. The reaction mixture shows a pale yellow Coloring. It follows from this that no reaction has taken place. The HCl titration essentially gives the value zero. This also shows that no reaction has taken place. After stirring for 48 hours, it results a titration value of 1.52 n / l (Note 1). When the solution is reacted with benzyl chloride, it results a titration value of 0.21 n / l (Note 2). This gives a value for the active lithium of 131 n / I (Remark 2).

According to the calculation, the yield of effective polymerization initiator is 40.2%, calculated as Li. Then the temperature of the reaction mixture was increased to 5 ° C and 198 g of butadiene was added 10 ml added over 2 h. After this addition, the dimethyl ether was removed under reduced pressure distilled off and 21 toluene were added, with a brown-colored solution is obtained. A measurement of the active lithium shows that the yield is an indication effective polymerization initiator is 42%

Using the polymerization initiator thus prepared, styrene and butadiene become in proportion from 85/15; 80/20 and 40/60 copolymerized and the mechanical properties of the copolymer obtained are measured. The results are shown in Table 1

Table 1

Styrene /

Butadiene

Molecular
weight

tensile strenght

strain

ι- (kg / cm ² ) (%)

Dynstat-

Impact

strength

(kg / cm ² )

index)

10.5
13.5

330
251

25th

65

800

25 65

(Note 1)

The metallic lithium is removed and only that as lithium hydroxide. Lithium oxide and organic Lithium present in the reaction system is measured.

(Remark 2)

Total lithium other than organic lithium is measured.

(Remark 3)

The total lithium present as active organic lithium is calculated.

Attempt 2

The process according to Example 1 of the invention is repeated. A catalyst is used which was obtained according to the following approach:

lithium
Diphenyl
Tetrahydrofuran
Butadiene

3.5 g (0.5 mol) 7.8 g (0.05 mol) 250 ml 81 g

The lithium is reacted with the diphenyl in the presence of 250 ml of tetrahydrofuran at 4 ° C The reaction has suddenly ended and a deep blue color appears.

81 g of butadiene are added slowly so that the color is maintained Way the polymerization initiator according to the invention. The measurement of the active lithium shows that the Yield of active lithium is 95%, based on the metallic lithium used. This value is significantly higher than that according to experiment 1. Using this polymerization starter Styrene and butadiene copolymerized according to Experiment 1. The results are shown in Table 2

Table 2

Siyrol / Mole Ziigfcsiig- elongation

Butadiene clarity

weight

(Schmiss- (kg / cm ² ) (%) index)

10.0

12.3

7.2

350
260
164

Attempt j

80

132

.080

Dynstat-

Impact

strength

(kg / cm ² )

96

In the case of the polymerization initiators according to Experiments 1 and 2, the polar agent is used against benzene exchanged. Styrene is polymerized in the presence of the initiator obtained and the average number of lithium atoms ac the ends of the polymers is measured. The molecular weight of each obtained Polymers is determined on the basis of the osmotic pressure after reaction with trimethylmonochlorosilane With the starter according to Experiment 1, a molecular weight of 15,600 is achieved and with the starter according to Experiment 2 has a molecular weight of 17,500

300 mg of the polymer obtained are dissolved in 0.5 ml of orthodichlorobenzene and 20 mg of anisole are mixed in. The methyl groups of the product obtained are measured in the NMR spectrum. The protons of the methyl group of the anisole are at 3.8 ppm (ό). The protons of the -Si- (CH ₃ ) ₃ are at 0 ppm (δ). From the results of the measurement, π is calculated according to the following formula:

Il =

D. B.

where D is the number of lithium atoms in the sample and where B is the number of polymer molecules in the sample. For the sample obtained with the starter according to Experiment 1, η = 1.5 and for the sample obtained with the starter according to Experiment 2, η = 2.1. This shows that the polymer produced according to the invention consists essentially of a bifunctional polymer, while that according to British Patent 9 64 473 contains a large proportion of a monofunctional polymer. British Patent 9 64 473 states that the physical properties of a copolymer, which under Using a monofunctional starter was produced, are much worse than when using a bifunctional starter. The major differences in terms of physical properties are due to the different ways in which the starter is manufactured. The combination of the features according to the invention leads to a purely bifunctional starter and thus to an extremely high quality polymer.

Claims (3)

Patent claims: 1. A method for producing a block copolymer with a central copolymer block of a conjugated diene and a small amount of a vinyl aromatic compound and two terminal homopolymer blocks, the frequency of the structural units formed by the conjugated diene decreasing from the center of the central copolymer block to its ends, by a one-stage polymerization of a mixture of the conjugated diene and the vinyl aromatic compound in a non-polar solvent, with no more than 2% by weight of a polar solvent being present, in the presence of a catalyst which is produced by reacting a conjugated diene with a reaction product of metallic lithium prepared medium with an aromatic hydrocarbon in a polar ether solvent, characterized in that a catalyst is used which, by reacting the conjugated diene with the reaction product of metallic lithium and a Diphen yl hydrocarbon and / or a terphenyl hydrocarbon in a cyclic ether or an aliphatic polyether. 2. The method according to claim 1, characterized in that a catalyst is used in its preparation the polar solvent after the reaction against a non-polar solvent was exchanged. 3. The method according to any one of claims 1 or 2, characterized in that there is a catalyst used with a dilithium compound.