MXPA00007222A - Method for the production of block copolymers by retarded anionic polymerization - Google Patents

Abstract

The invention relates to a method for the production of block copolymers from vinyl-aromatic monomers and dienes by polymerization in the presence of at least one alkali metal organyl or alkali metal alcoholate and at least one magnesium, aluminum or zinc organyl.

Description

PREPARATION OF BLOCK COPOLYMERS BY DELAYED ANIONIC POLYMERIZATION The present invention relates to a process for the preparation of block copolymers from vinylaromatic monomers and dienes. Anionic polymerizations proceed, typically, very quickly, so they are difficult to control on an industrial scale, due to the considerable amount of heat generated. The reduction of the polymerization temperature results in an excessive increase in viscosity, in particular with a concentrated solution. Reducing the concentration of the initiator increases the molecular weight of the polymer formed. The control of the reaction by the appropriate dilution of the monomers results in a higher requirement of solvents and lower space-time yields. Therefore, it has been proposed to include, in the initiators of the anionic polymerization, various additives that have an influence on the polymerization rate. The effect of Lewis acids and Lewis bases on the anionic polymerization regime of styrene was described by Welch, Journal of the American Chemical Society, 82 (1960), 6000-6005. For example, it has been found that small amounts of Lewis bases, such as ethers and amines, accelerate polymerization, initiated by n-butyllithium, of styrene at 30 ° C, in benzene, while Lewis acids, such such as zinc and aluminum alkyls, reduce the polymerization rate or, when used in super-stoichiometric amounts, completely stop the polymerization. In Macromolecules, 19 (1956), 299-304, Hsieh and Wang investigated the formation of dibutylmagnesium complexes with the alkyl lithium initiator, or the active polymer chain, respectively, in the presence or absence of tetrahydrofuran, and found that dibutylmagnesium reduces the polymerization rate of styrene and butadiene, without affecting the stoichiometry. US Patent No. 3 716 495 discloses initiator compositions for the polymerization of conjugated vinyl dienes and aromatics, where a more efficient lithium alkyl as initiator is achieved by the addition of a metal alkyl of a metal of the Group. 2a, 2b or 3a of the Periodic Table of the Elements, such as diethylzinc, and polar compounds, such as ethers or amines. Due to the relatively large quantities of the solvent, relatively low temperatures and large reaction times. in the region of several hours, the space-time yields are correspondingly low.

W097 / 33923 describes primer compositions which are useful for the anionic polymerization of vinyl monomers, which comprise an alkyl metal and magnesium compounds, which carry hydrocarbon radicals and have a molar ratio of [Mg] / [alkyl- metal] of at least 4. Previously, patent application PCR / EP97 / 04497, unpublished to the priority date of the present invention, describes continuous processes for the polymerization or anionic copolymerization of styrene or diene monomers using an alkali metal - alkyl as the initiator of the polymerization, in the presence of at least one bivalent element, as a retarder. The patent PCT / EP97 / 04498, which also is not published on the priority date of the present invention, describes processes for the anionic polymerization of dienes and / or vinylaromatic monomers in a vinylaromatic monomer of the monomer mixture, in the presence of a metal-alkyl or aryl of at least one bivalent element, without Lewis bases added. Various mixtures of initiators, which may comprise alkali metals, alkaline earth metals, aluminum, zinc or rare earth metals, are known, for example, from EP-A 0 234 512 for the polymerization of conjugated dienes, with a high degree of of 1,4-trans binding. The German patent application, open to the public, No. 25 28 380, teaches, for example, the use of alkaline earth aluminates as co-catalysts, in conjunction with an organolithium initiator, for the preparation of polymers or copolymers of conjugated dienes, having a high content of the trans-1,4 bond, and low content of 1,2-linkage or 3,4-bond. This is said to lead to an increase in the polymerization rate. It is an object of the present invention to provide a process for the preparation of block copolymers from vinylaromatic monomers and dienes, which do not have the aforementioned disadvantages and which can be carried out in a controlled manner, in particular at high concentrations of monomers. We have found that this object is achieved by a process for the preparation of block copolymers from vinylaromatic monomers and dienes, in which these monomers are polymerized, in the presence of at least one organole of an alkali metal or an alkoxide of a metal alkaline and at least one organole of magnesium, aluminum or zinc. The alkali metal organyls that may be used are the alkali, mono-, bi- or multi-functional alkyls, aryls or aralkyls customarily used as anionic polymerization initiators. It is advantageous to use the organolithium compounds, such as ethyl lithium, propyl-lithium, isopropyl-lithium, n-butyl-lithium, sec.-butyl-lithium, tert.-butyl-lithium, phenyllithium, diphenylhexyl-lithium. , hexamethylene-dilithium, butadiene-lithium, isoprenyl-lithium, polystyryl-lithium or the 1,4-dilithio-butane, 1,4-dilithio-2-butene or 1,4-dilithiobenzene mufifunctional compounds. The amount of the alkali metal organole required depends on the desired molecular weight, the type and amount of the other metal organyls used and the polymerization temperature and is typically in the range of 0.0001 to 5 mole percent, based on the total amount of monomers. The alkali metal alkoxides which may be used, alone or in admixture, are the aliphatic, aromatic or araliphatic alkoxides of lithium, sodium or potassium. Examples are methoxide, ethoxide, n-propoxide, isopropoxide, n-butoxide, sec.-butoxide, tere. -butoxide, n-pentoxide, isopentaxide, hexoxide, amyl-alkoxide, phenoxide, mentolate, 2,4-di-tert-butyl-phenoxide, 2,6-di-tert-butyl-phenoxide, 3,5-di-tert-butyl-phenoxide, 2, -di-tert-butyl-4-methylphenoxide and lithium, sodium or potassium trimethylsilanoate. Preference is given to the use of the methoxides, ethoxides, tert-butylsubstituted phenoxides or branched alkylalkoxides, in particular the tert-butoxide, amylate or 3,7-dimethyl-3-octoxide lithium.

Useful magnesium organls are those of the formula R? Mg, wherein the radicals R are each, independently of the other, hydrogen, halogen, or C1-C20 alkyl or C6-C20 aryl. Preference is given to the use of ethyl, propyl, butyl, hexyl or octyl compounds, which are commercially available. Particular preference is given to the use of (n-butyl) (s-butyl) -magnesium, which is soluble in hydrocarbons. Aluminum organls that can be used are those of the formula R3AI, where the radicals R with each, independently of each other, hydrogen, halogen or C1-C20 alkyl, or C6-C2o aryl. The preferred aluminum organyls are aluminum trialkyls. Particular preference is given to the use of triisobutyl aluminum. Zinc organils that can be used are those of the formula R2Zn, where the radials R with each, independently of each other, hydrogen, halogen or C1-C20 alkyl / or C6-C20 aryl. The preferred zinc organyls are zinc dialkyls. Particular preference is given to the use of diethyl zinc. The aluminum, magnesium or zinc alkyls may also be present in the hydrolyzed, alcoholized or aminolized form, partially or completely.

Particular preference is given to the use of sec-butyllithium together with dibutylmagnesium or triisobutyl-aluminum. The molar ratios of the metal organils, with respect to each other, can vary within wide limits, but it depends primarily on the desired retardation effect, the polymerization temperature, the monomer composition and the concentration and the desired molecular weight. The molar ratio of magnesium, aluminum or zinc, respectively, to the alkali metal, is preferably in the range of 0.1 to 100, preferably in the range of 1 to 10. In a preferred embodiment, the polymerization is carried out in the presence of an alkali metal organole, an aluminum organole and a magnesium organole. The molar ratio of magnesium to alkali metal is advantageously in the range of 0.2 to 3.8, the molar ratio of aluminum to alkali metal is in the range of 0.2 to 4. The molar ratio of magnesium to aluminum is preferably in the range of 0.005. to 8. In the process of the invention, use is made primarily of organils of alkali metals, organils of magnesium, aluminum and zinc. The barium, calcium or strontium organyls are preferably present only in effective amounts that do not have a significant effect on the polymerization rate or the copolymerization parameters. The transition metals or lanthanoids, especially titanium or zirconium, should not be present in significant quantities. The organils of alkali metals, magnesium, aluminum and zinc can be added to the monomer mixture together or separately, at different times or different locations. The alkali metal, magnesium and aluminum alkyls are preferably used in the form of a premixed initiator composition. The composition of the initiator can be prepared by dissolving the organils of alkali metals, organils of magnesium, aluminum and zinc, in an inert hydrocarbon solvent, for example n-hexane, cyclohexane, white paraffin or toluene and combinations thereof. The organyls of metals dissolved in hydrocarbons are preferably mixed in a homogeneous manner and are allowed to form > aging at a temperature in the range of 0 to 120 ° C for at least 2 minutes, preferably at least 20 minutes. A solubilizer, for example diphenylethylene, may be added, if necessary, to prevent precipitation of one of the components from this initiator solution. The initiator system can affect the parameters of the copolymerization of vinylaromatic monomers and dienes. Depending on the type and the relationships of the metal organils, soft blocks B or B / S, which have a relatively high or low vinylaromatic content, are thus obtained. For exampleWhen a s-butyl lithium and dibutylmagnesium are used at a molar ratio of Mg / Li of less than 2, the copolymerization of styrene and butadiene supplies butadiene blocks having a low styrene content. The Mg / Li ratios of 4 preferably produce a mild block B / S of random butadiene-styrene. Also, the random incorporation of styrene is favored using alkoxides, such as dialkylaluminum alkoxides or potassium alkoxides. The retardation does not significantly affect the relative polymerization rate of styrene and butadiene, ie the butadiene polymerizes much slower and, in the mixture with styrene, has a retarding effect in the general conversion rate. Preferred monomers are styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene or 1, 1-diphenylethylene, butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene, 1,3-hexadiene or piperylene, or its mixtures. The polymerization can be carried out in the presence of a solvent. Suitable solvents are aliphatic, cycloaliphatic or aromatic hydrocarbons, having from 4 to 12 carbon atoms, which are generally used for anionic polymerization, such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, isooctane, benzene, alkylbenzenes, such such as toluene, xylene, ethylbenzene or decalin or their suitable mixtures. Obviously, the solvent must have the high purity typically required for the process. Solvents can be dried on aluminum oxide or molecular sieves and distilled before use to remove protein substances. The process solvent is preferably reused after the aforementioned condensation and purification. It is possible to adjust the effects of the delay within wide temperature ranges by means of the composition and the amount of metal organils. Therefore, it is also possible to carry out the polymerization at the initial concentrations of monomers in the range of 50 to 100% by volume, particularly from 70 to 100 volume percent, which leads to highly viscous polymer solutions and require higher temperatures, at least in major conversions. The target products are the block copolymers of vinylaromatic monomers and dienes. The styrene-butadiene block copolymers are preferably obtained.

Preference is given to block copolymers comprising at least one hard block S, composed of vinylaromatic monomers, and at least one soft block B, composed of dienes or a soft block S / B, composed of vinylaromatic monomers and dienes, in a random sequence. The soft blocks can be formed essentially from dienes (soft blocks B) or from dienes and vinylaromatic monomers in a random sequence (blocks S / B). The individual blocks may also be of conical type and include, for example, a gradient B- > S / B, (S / B)? - > (S / B) 2, B- > S, (S / B) - > S. The soft blocks can also be composed of different soft blocks, arranged in any order and can occur repeatedly, for example, block B-S / B, block (S / B)? - (S / B) 2. Particular preference is given to the preparation of linear block copolymers comprising block structures S-B, S-B-S, S-S / B-S, S-B-S / B-S, S-S / B? -S / B2. The individual blocks can be of equal or different length, ie the three-block copolymers can be symmetrical or asymmetric. The block transmissions can be acute or conical, ie the S blocks contain a significant proportion of copolymerized diene monomers and the B blocks contain a significant proportion of copolymerized vinylaromatic monomers in the transition area. Block copolymers have different properties, depending on their structure and composition. Preferred block copolymers are those that have elastomeric properties. They comprise at least the structure unit S-B-S or S-S / B-S, in the form of a linear block or star copolymer. The soft phase, expressed by the sum of all the soft blocks, is in the range of 50 to 90 percent, by volume, preferably in the range of 60 to 80 percent by volume, particularly preferred in the range of 65 to 75 percent in volume. Additional preference is given to rigid block copolymers, which at the same time are transparent and impact resistant. They also comprise at least the structural unit S-B-S or S-S / B-S in the form of a linear block or star copolymer. The soft phase, expressed as the sum of all the soft blocks, is in the range of 5 to 50 volume percent, preferably in the range of 10 to 40 volume percent, particularly preferred in the range of 15 to 30 percent by volume. one hundred in volume. Particular preference is given to the block structure of S1-S / B-S2 or S_-B- > S2, with the conical transition and a length of the SI block in the range of 10,000 to 30,000 g / mol and a block length greater than 50,000 g / mol. The process of the invention can be carried out in any reactor resistant to pressure and temperature, it being possible, in principle, to use the rear mixing reactors or without further mixing (i.e., reactors having characteristics of a stirred tank or of a tubular reactor). Depending on the selection of the initiator concentration and composition, the particular process route applied and other parameters, such as the temperature and the profile of the possible temperature, the process of the present invention leads to polymers having high molecular weights or low. It is possible to use, for example, stirred tanks, tower reactors, cycle reactors and tubular rectors or reactors of groups of tubes, with or without internal parts. These internal parts can be static or mobile. The polymerization is preferably carried out continuously. Suitable reactors are, for example, tubular reactors or reactors of groups of tubes, with or without mixing elements, such as Sulzer mixers, stirred tank reactors or continuous stirred tank reactors, cycle or recycle reactors, tower reactors , sizing reactors (self-cleaning), extruders, etc. The reactors can be used individually or can be combined properly and can be equipped with one or more load lines, for example for monomers or initiators. A part of the conversion, preferably a conversion greater than 50%, in particular greater than 70%, based on the total amount of monomers, is carried out in a non-post-mixing reactor or a reactor section, in particular if little or no solvent is added. Suitable reactors are, for example, pipe reactors and tube groups, tower reactors or extruders. Preference is given to the use of an extruder, whose trees are sealed to the transmission. The composition of the initiator according to the invention makes it possible to significantly reduce the rate of reaction or increase in temperature, respectively, without affecting the properties of the polymer, in sympathy with the anionic polymerization using an alkali metal organyl; this makes it possible, on the one hand, to spread the heat generation of the polymerization over a longer period of time and thus control, in a continuous process, the temperature profile as a function of time or location, for example in the reactor tubular. It is possible, for example, to ensure that a high temperature does not occur in the monomer concentration, initially high, while, on the other hand, a problem-free polymerization is possible at the high temperature which is finally (ie the higher conversion) achieved while achieving high space-time performance at the same time. In a preferred process, the vinylaromatic monomer is polymerized in the presence of an alkali metal organyl and at least one organo magnesium, aluminum or zinc, without any additional solvent (apart from small amounts which can be used to dissolve the organyls of metal). After a conversion leading to the formation of a hard block S, having the desired block length, the diene is added to the solution of the resulting S block in the monomeric vinylaromatic monomer. If necessary with cooling. The diene can be added all at once or continuously over a relatively long period of time or in more than one portion. After the addition of the butadiene and, if necessary, the heating of the polymerization solution, a random S / B block having a vinylaromatic content which strongly depends on the system of the selected initiator is formed. The concentration of the diene decreases as the polymerization proceeds and a gradient towards the vinylaromatic monomer is obtained. When the diene is completely consumed, the remaining vinylaromatic monomer polymerizes to form another S block. The polymerization is preferably carried out in a tubular reactor or in an extruder, until the conversion of monomers is complete. Due to the increasing viscosity toward the end of the polymerization, the temperature of the polymer causes it to melt to form the last styrene block must advantageously be at least 20-30 ° C above the glass transition temperature of the vinylaromatic polymer, that is, in the case of styrene polymers above about 130 ° C. The melt is protonated and stabilized and can then be heated to usual process temperatures (180-240 ° C). This process supplies, for example, three-block, symmetric or asymmetric copolymers, S-S / B-S, having a central soft block and a conical transition of diene / vinylaromatic blocks. The process is particularly preferably used for the preparation of a three-block copolymer of styrene-butadiene-styrene, in which a block of polystyrene dissolved in monomeric styrene is prepared by the partial conversion of styrene, a soft block comprising the butadiene is added, by the addition of butadiene and the residual styrene monomer is polymerized at a temperature of at least 20 ° C above the glass transition temperature of the resulting block copolymer, until the conversion is complete.

The block copolymers can be polymerized in the presence of a multifunctional alkali metal organole or bonded in a star-like manner, after polymerization, using a multifunctional coupling agent, such as aldehydes, ketones, esters, anhydrides or epoxides polyfunctional The coupling of blocks, identical or different, can provide symmetrical and asymmetric star block copolymers, comprising arms having the aforementioned block structures. After the polymerization is complete, the chains of the active polymer can be topped with a chain terminator, instead of being coupled. Suitable chain terminators are protic substances or Lewis acids, such as water, alcohols, aliphatic or aromatic carboxylic acids and inorganic acids, such as carbonic acid or boric acid. The block copolymers are usually mixed with stabilizers. Examples of suitable stabilizers include sterically clogged phenols, such as Irganox® 1076 or Irganox® 3052 from Ciba-Geigy, Basel, Switzerland, or a-tocopherol (Vitamin E). The chain termination and stabilization can be performed in separate stages or in a single step. This can be achieved, for example, by using a solution of a carboxylic acid, such as formic acid or acetic acid, an alcohol, such as methanol, ethanol, butanol, propanol, and one of the above stabilizers, in a suitable solvent, such as ethylbenzene. In industrial-scale processes, it is advantageous to add the stabilizer in liquid form, free of solvent. In this case, the melt of the active polymer is first deactivated using 0.1 to 5% by weight of water, based on the block copolymer. Immediately after, for example 25.6 g of a mixture of the following composition, one can add per kilogram of the polymer melt: EXAMPLES Example 1 Preparation of a styrene-butadiene block copolymer 4500 g of styrene were placed in a stirred tank of 10 liters and cooled to 12 ° C. At this temperature, 68 ml of a 0.5 molar solution of dibutylmagnesium in white paraffin and 16 ml of a 1.6 molar solution of sec.-butyllithium in white paraffin were added successively, and the stirred tank was slowly heated to 30 ° C. ° C. 44 minutes after the addition of the initiator, the volumetric temperature was raised to 53 ° C. The solids content was 16.6% at this time. Polymerization of the styrene block was then stopped by cooling to 30 ° C and adding 1500 g of butadiene. The stirred tank was then slowly reheated to 70 ° C, an exothermic reaction being observed at significantly higher temperatures. A solids content of 35% and a mass temperature of 86 ° C was reached 75 minutes after the addition of the butadiene. The content of monomeric butadiene was 2-3%. The polymerization was then stopped by cooling to 15 ° C.

Example 2 Preparation of the styrene-butadiene-styrene three-block copolymer The styrene-butadiene active block copolymer solution in the styrene, obtained as described in Example 1, was processed in an extruder.

Extruder Design: An extruder W &P ZSK 25, L / D = 30, was used. The polymerization zone was equipped with kneading elements, followed by a blocking element and a transport element, each to add the terminator / stabilizer and for devolatilization / deodorization and discharge.

Extruder Conditioning: The extruder was flooded with a mixture of approximately 0.1 molar of sec.-butyllithium in white paraffin and about 0.5% by weight of diphenylethylene together with Luflexen HX (metallocene-catalyzed polyethylene, from BASF), to remove pollutants and humidity. Once the Luflexen / white paraffin cord had turned a permanent red color, the addition of the white paraffin / sec-butyl-lithium mixture was stopped and the addition of the Luflexen was reduced to an extent that the screw was just sealed towards the back.

Polymerization of the second block of styrene; The polymerization mixture obtained in the Example 1, then continuously dosed in the extruder at 1.5 kg / h, using a gear pump. The extruder was operated at 50 revolutions per minute. The temperature was set at 120 ° C at the dosing point of the active polymer solution, at 140 and 150 ° C in the polymerization zone, which includes the termination zone and at 210 ° C in the devolatilization section. The colorless cord that comes out was cooled in a water bath and formed into pellets. The residual styrene content was less than 100 ppm.

Stabilizer Solution: The completion, acidification and stabilization of the styrene-butadiene block copolymer was carried out in one step. This was achieved by adding 100 g per 1 kg of the polymer melt of a solution of the composition shown in Table 1, after the polymerization zone The example was repeated with a yield of 2 and 2.5 kg / h. The residual styrene contents were also below 100 ppm.

Claims (11)

1. A process for the preparation of block copolymers from vinylaromatic monomers and dienes, in the presence of at least one organole of an alkali metal or an alkali metal alkoxide, and at least one organo magnesium, aluminum or zinc, this The process comprises carrying out the polymerization with an initial concentration of the monomer in the range of 50 to 100 volume percent.

2. A process, as claimed in claim 1, wherein the organyl of an alkali metal used is a lithium organyl.

3. A process, as claimed in claim 1, wherein the molar ratio of magnesium, aluminum or zinc, respectively, to the alkali metal, is in the range of 0.1 to 100.

4. A process, as claimed in any of claims 1 to 3, wherein block copolymers are prepared, comprising at least one hard block S, composed of vinylaromatic monomers, and at least one soft block B, composed of dienes, or a soft block of S / B, composed of vinylaromatic monomers and dienes, in a random sequence ..

5. A process, as claimed in any of claims 1 to 4, wherein block copolymers are prepared which comprise S-B-S, S-S / B-S, S-B-S / B-S, S-S / B1-S / B2-S block structures.

6. A process, as claimed in claim 5, wherein linear or star block copolymers are prepared, having a soft phase content, expressed as the sum of all soft blocks, in the range of 50 to 90 percent in volume.

7. A process, as claimed in claim 5, wherein linear or star block copolymers are prepared, having a soft phase content, expressed as the sum of all soft blocks, in the range of 50 to 90 percent in volume, and different block lengths of the terminal hard blocks.

8. A process, as claimed in any of claims 1 to 7, wherein the block copolymers are polymerized in the presence of a multifunctional alkali metal organyl or bonded in a star-like manner, after polymerization, using an agent multifunctional coupler.

9. A process, as claimed in any of claims 1 to 8, for the preparation of a three-block copolymer of styrene-butadiene-styrene, in which the polystyrene block, dissolved in a monomeric styrene, is prepared by partial conversion of styrene, a soft block, comprising butadiene, is added, for the addition of butadiene, and the residual styrene monomer is polymerized at temperatures of at least 20 ° C above the glass transition temperature of the resulting block copolymer , until the conversion is complete.

10. A process, as claimed in any of claims 1 to 9, wherein the polymerization is carried out continuously.

11. A process, as claimed in any of claims 1 to 10, wherein, at least part of the conversion, is carried out in a non-post-mixing reactor or in a reactor section.