DE2120232B2 - Process for the production of a block polymer - Google Patents

Description

The invention relates to a process for the production of a block copolymer with a central copolymer block of a conjugated diene and a vinyl aromatic compound and with two terminal ones Homopolymer blocks, the frequency of the structural units formed by the conjugated diene decreases from the middle of the middle copolymer block to its ends, by a one-step Polymerization of a mixture of the conjugated diene and the vinyl aromatic compound in one non-polar solvent, with no more than% by weight of a polar solvent being present in Presence of a catalyst, which is obtained by reacting a conjugated diene with a reaction product of metallic lithium with an aromatic hydrocarbon in a polar ether solvent has been made.

Various methods of making block copolymers of this type have been described. So describes e.g. B. Japanese Patent Application No. 798/1965 teaches the preparation of a block copolymer in a multi-step reaction using a lithium compound as an initiator. Thereby the method applied to the "living" polymerization. Block copolymers are obtained in which one successively 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 one described non-elastomeric block are linked together.

From Japanese Patent Application No. 19 286/1961, block copolymers are known which have a have central elastomeric block and two terminal non-elastomeric blocks. Even with this one known processes, the reaction is carried out in several stages. An aromatic starter is used Compound with two lithium atoms is used and the polymerization proceeds at both ends.

GB-PS 9 64 478 also discloses a process for the production of a block copolymer of this type with

ίο a middle copolymer block from a conjugated diene and a vinyl aromatic compound and with two terminal homopolymer blocks from the vinyl aromatic compound known. B. naphthalene used. However, the products obtained have insufficient impact strength and insufficient elongation. These disadvantages are based on the fact that undesired homopolymers or copolymers composed of two blocks are contained in considerable amounts in the resulting block copolymer. This is due to an increase in the inactive end groups, which are gradually increased by impurities in the solvent or in the monomers. If the three-block copolymer contains a two-block copolymer, the clarity, the ductility, the tear resistance and especially the impact resistance are lowered

ίο It is therefore the object of the invention to provide a block copoly- ' To create meres of the type mentioned, which have excellent mechanical properties, in particular has high impact and tear resistance and excellent clarity.

• λ This object is achieved according to the invention by using a catalyst which, by reacting the conjugated diene with the reaction product of metallic lithium and a diphenyl hydrocarbon and / or a terphenyl carbon

to hydrogen in a cyclic ether or an aliphatic polyether has been produced.

The block copolymer obtained has a three-block structure in which an elastomeric Middle block on both sides with a non-elastomeric one

4 ^r j block is connected. 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 ⁰ 100 C, while the

M glass transition point of the elastomeric block (Tg) should be below -4O ⁰ C.

The 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

ho co-polymerization of only a small amount of the vinyl substituted aromatic hydrocarbon compound. The ratio of vinyl substituted aromatic hydrocarbon to conjugated diene from the center of the block formed

h5 increased towards the ends. After the whole conjugated diene along with the minor amount of the vinyl substituted aromatic hydrocarbon compound is polymerized, only the polymer

ization of the vinyl-substituted aromatic hydrocarbon controlled to a significant 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.

During the preparation of the starter, the reaction temperature should generally be between -78.degree. C. and + 30.degree. C., preferably between -40.degree. C. and 0.degree. If more than 3O ⁰ C, the conjugated diene polymerizes. The reaction time can be selected depending on the reaction temperature. However, it is not subject to any restrictions.

The polar medium used to prepare the starter can e.g. B. tetrahydrofuran, tetrahydropyran, 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 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 starter and is mixed in an amount with the monomers, which exceeds the value of 2% by weight, only a random copolymer 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-trimethylstyrene and 3-methyl-5-n-hexyl-styrene. In the following the invention is based on styrene as Examples of the vinyl-substituted aromatic hydrocarbon will be described. As conjugated Serves can be used, for example, 13-butadiene and isoprene. It is preferable to use styrene in one Amount of 60 to 95% by weight, in particular 75 to 85% by weight, based on the total monomers, the remainder being conjugated dienes.

You can use inert hydrocarbon solvents

aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene; aliphatic hydrocarbons, z. B. use n-hexane and cyclohexane and mixtures thereof.

It is preferable to remove any impurities in advance remove which can decompose the initiator or the monomers used for the invention, e.g. B.

r> moisture, oxygen, carbon dioxide, certain Sulfur compounds or acetylene.

The block copolymerization of styrene and des conjugated diene is usually used at about -20 ° C to 100 ° C, preferably at about 20 ° C to 65 ° C carried out The block copolymerization time 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 of the block copolymerization, methanol or isopropyl alcohol was added. Furthermore, a low Amount of an antioxidant added, e.g. B. 4-hydroxymethyl-2,6-di-t-butyl-phenol and thereafter the block polymer obtained is precipitated out 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 high 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 1-1 flask is fitted with a tight stirrer, a

^r ) 0 reflux condenser, a gas inlet tube, an inlet for the reactants, a funnel and a thermometer. 250 ml of ethylene glycol dimethyl ether, in which 7.7 g of diphenyl have been dissolved, are added to this flask. Furthermore, 1.7 g of lithium, which is dispersed in an amount of 30 percent by weight in solid paraffin, are added to the flask, whereby the solution of a deep green colored complex is formed.

The flask is then placed in a dry ice-methanol

bo bad given to the contents to a temperature of to cool below -40 ° C and then 50 g of butadiene are slowly introduced. The initiation of the Butadiene occurs so slowly that the deep green color of the contents does not turn into a reddish brown color

b5 converts. After introducing the butadiene what takes about 1 hour, the reaction product is allowed to stand at room temperature. Included the color of the reaction product changes

Example 2

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

Table I.

15 reaction viscosity yield period (* 1) (* 2)

Styrene content of the polymer (* 3)

(Wt .-%)

10 190 11 30th 20th 340 19th 34 20 30 500 25th 37 40 1500 99 79 50 1450 98 81

reddish brown.

The reaction product is heated to the boiling point of the solvent and for several minutes on Maintained reflux, and then the solvent is distilled off and the product is in vacuo dried After sufficient drying, 300 ml of benzene are 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 to give 500 ml of a reddish brown solution.

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

b) block copolymerization

30 ml of the catalyst solution are placed in a Atoklav which is equipped with a stirrer and maintained at 50 ⁰ C. 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. Here, the viscosity of the solution of about 500OcP reduced down to about 2500 cP at 50 ⁰ 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 H.

Weight ratio of inserted
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) (* 5)
Turbidity (%) (* 6)

(* 1) The block copolymer was dissolved in CS2 and dried by an air 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 is measured with an Emiller viscometer 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.

35

40

65/35

70/30

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 o-terphenyl and 1.7 g lithium are in 250 ml of tetrahydrofuran according to Example 1 reacted. Butadiene then becomes the reaction product given and the existing tetrahydrofuran solvent is replaced by benzene, with 500 ml a blackish reddish brown reaction mixture can be obtained. When titrating the product with HCl results in a concentration of 0.39 n / l.

Table III

c) bulk polymerization

According to the procedure of Example 1 is repeated, the block copolymerization of styrene and butadiene ^r> using this catalyst solution, wherein in each case the total amount of styrene and butadiene is 500 g and the ratio of styrene to butadiene is between 70/30 to 90/10.

The physical properties of the ι ο block polymers obtained are summarized in Table HI.

Weight ratio of used 63/35 70/30 75/25 80/20 85/15 90 /: Styrene to butadiene Styrene / butadiene weight ratio 64.5 / 35.5 69/31 74.5 / 25.5 80/20 85/15 89 /: in block copolymers Molecular weight (■ 10 ⁴ ) 10.5 9.9 11.1 9.5 8.9 10.1 Tensile strength (kg / cm ² ) 175 200 225 197 282 370 Strain (%) 385 272 170 102 94 40 Dynstat impact strength (kg / m / cm ² ) - - - 104 64.5 20th Rockwell hardness (M scale 1/4) - - - 8th 21 39 Turbidity (%) 23.0 18.0 17.0 12.6 5.0 4.5

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 the vessel is removed 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 summarized in Table IV.

63/35

Table IV

Weight ratio of monomers
Styrene / butadiene

Styrene / butadiene weight ratio
in block polymer

Molecular weight (· 10 ⁴ )
Tensile strength (kg / cm ² )
Strain (%)

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

It is found that the block copolymers prepared in two stages according to this comparative example 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 L flask is attached to a sealed stirrer, a reflux condenser, a gas inlet, an inlet for the reactants, a funnel and a Equipped with a thermometer. 300 ml of tetrahydrofuran, which on a sodium-potassium alloy on Was refluxed and then distilled, are filled. 1 g diphenyl, which is made from hexane recrystallized and dried is also introduced and dissolved in the tetrahydrofuran. I ml of styrene are also added.

70/30

75/25

80/20

85/15

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

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

30 l of argon gas are then passed into the reaction vessel over a period of 30 minutes. The argon gas was for dehydration through a layer of titanium sponge heated to 800 ° C and through a molecular sieve then about 0.3 mmol of sec-butyl lithium added to the content, whereupon it takes on a pale yellow color. Next will be 101 Argon gas introduced for 10 minutes. 70 mg lithium, which in a concentration of 30 Weight percent dispersed in solid paraffin is 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, 1.5 1 of benzene and 400 g of styrene are added, which before 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 increased to 70 ° C to 80 ⁰ C and a plurality of bubbles is 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% of 4-hydroxymethyl-2,6-di-t-butyl-phenol are 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 molded 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.

From the granules obtained, test specimens of dumbbell shape or are made by an injection molding process Rod shape formed, which has a thickness of 2 mm, a width of 10 mm and a length of 80 mm exhibit. The physical properties of the product obtained are summarized in Table VI.

Table VI

Weight ratio used

Styrene / butadiene 85/15

Molecular weight (χ 10 ⁴ ) 12.5

Tensile strength (kg / cm ² ) 320

Elongation (%) 70

Dynstat impact strength (kg cm / cm ² ) 107

Rockwell hardness (M scale 1/4) 23

Haze (%) 7.0

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. 1.51 g 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 begins, whereby the Temperature of the contents of the reaction vessel increased to about 100 ° C.

After the polymerization, the block copolymer is separated off. It is obtained in an amount of 495 g. 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 using an extruder.

Example 7

10 g of diphenyl and 2.5 g of lithium are reacted in 250 ml of tetrahydrofuran according to Example 1. 80 g

2 ¹ ") butadiene are added and then the tetrahydrofuran is replaced by benzene, giving 600 ml of a blackish-reddish-brown reaction solution. A concentration of 0.45 n / l is determined by titration with hydrochloric acid.

jo game 1 is 400 g of styrene and 100 g of isoprene in benzene reacted at 35 ° C., 20 ml of the catalyst solution being used.

After 40 minutes, the contents of the reaction vessel turn red and the polymerization of the

Γ) Styrene starts at a temperature above 100 ° C. After the reaction has ended, the copolymer obtained is precipitated by methanol and in vacuo dried. There is 1% 4-hydroxymethyl-2,6-di-t-butyl-phenol added and the copoly-

4 (kidney is granulated with the help of an extruder The resulting granules are made into test specimens of a rod shape or a dumbbell shape by injection molding shaped. The test specimens have a thickness of 2 mm, a width of 10 mm and a length of 80 mm. the

v> Physical properties of the product obtained are summarized in Table VII.

Table VII

^r M weight ratio of used

Styrofoam / isoprene 80/20

Molecular weight (χ 10 ⁴ ) 8.5

Tensile strength (kg / cm ² ) 320

Elongation (%) 60

T> Dynstat impact strength (kg cm / cm ² ) 35

Rockwell hardness (M scale 1/4) 29

Haze (%) 5.0

Example! 8th

The polymerization experiments according to the preceding examples are repeated, but the total amount of styrene and isoprene in each case being 500 gh ^r i and the ratio of styrene to isoprene being selected in the range from 70/30 to 90/10. The properties of the block copolymer obtained are shown in Table VIII.

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 (%)

75/25

80/20

85/15

90/10

10.1 9.5 7.9 9.0 8.5 280 290 330 370 420 105 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 2t. 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

Table IX

and then cooled ^{to 25 ° C.} Then styrene is added and polymerized for 30 minutes. The ratio of styrene to isoprene is selected in the range from 70/30 to 90/10. Each of the treated and dried copolymers obtained is mixed with 1% of 4-hydroxymethyl-2,6-di-t-butylphenol and processed into test specimens. The physical properties of the copolymer obtained are shown in Table IX.

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 (%)

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 64 478 was compared to 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 ml (0.4 mol) 56 ml (0.4 mol) 14 g (0.45 mol) 300 ml

In a 2-liter flask equipped with a stirrer 300 ml of the dried ether were added and a stream of nitrogen was initiated. Then were 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, 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 1.31 n / l (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 2 l of toluene were added, a brown-colored solution being obtained. One measurement of active lithium shows that the yield of effective polymerization starer 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.

Molecu
lar
weight 13th strain 21 20 232 mole
kular
weight 14th strain Dynstat-
ScHag-
strength Table 1 (Enamel
index) (%) Table 2 (Enamel
index) (%) (kg / cm ² ) Styrene /
Butadiene 10.5
13.5
9.1 Tensile strength
speed 25th
65
800 Dynstat-
Impact
strength ^r > Styrene /
Butadiene 10.0
12.3
7.2 Tensile strength
speed 80
132
1080 58
96 (kg / cm ² ) (kg / cm ² ) (kg / cm ² ) 85/15
80/20
40/60 330
251
35 fs « 85/15
80/20
40/60 350
260
164 (Note 1) Attempt 3

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 procedure 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 mole)
7.8 g (0.05 mol)
250 nil
81g

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 is added slowly so that the color is maintained. The polymerization initiator according to the invention is obtained in this way. 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, π styrene and butadiene are copolymerized according to Experiment 1. The results are shown in Table 2.

In the case of the polymerization initiators according to Experiments 1 and 2, the polar solvent is used against benzene exchanged. Styrene is polymerized in the presence of the initiator obtained and the average number of lithium atoms at 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. A molecular weight of 15,600 is achieved with the starter according to experiment 1 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 (δ). The protons of the -Si- (CH ₃ J ₃ Hegen at 0 ppm (<5). From the results of the measurement η is calculated according to the following formula:

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 specification 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 has been prepared using a monofunctional starter are significantly worse than when a bifunctional starter is used. 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. Process for the preparation of a block copolymer with a medium conjugated diene copolymer block and a small amount a vinyl aromatic compound and two terminal homopolymer blocks, the Frequency of structural units formed by the conjugated diene from the middle of the middle Copolymer block decreases towards the ends of which by a one-stage polymerization of a mixture 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 one Catalyst, which by reacting a conjugated diene with a reaction product of metallic lithium with an aromatic hydrocarbon in a polar ether solvent has been manufactured, characterized in that that one uses a catalyst which by reaction of 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 has been made. 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.