Dialkylaminoalkyllithium initiator solutions and processes for the preparation of dialkylaminoalkyllithium initiators

Abstract

The invention relates to concentrated dialkylaminoalkyllithium initiator solutions suitable for use as anionic polymerization initiators for olefin-containing monomers and in which the initiator concentration is at least 0.3 mol / L.

Description

[0001] The present invention relates to concentrated solutions of dialkylaminoalkyllithium initiators and processes for the production of dialkylaminoalkyllithium initiators for use as polymerization initiators for olefin-containing monomers. background

[0002] The living anionic polymerization of vinyl monomers is a key process for the industrial production of elastomers and rubbers such as polybutadiene, polyisoprene, styrene-butadiene rubber (SSBR), styrene-diene-styrene triblock copolymers, and liquid rubbers. On an industrial scale, organometallic compounds, particularly organolithium compounds such as n-butyllithium and sec-butyllithium, are typically used as initiators (R. Quirk, Anionic Polymerization, Chap. 7, 127, in: Handbook of Polymer Synthesis, Characterization, and Processing. 1). st(ed. By E. Saldivar-Guerra and E. Vivaldo-Lima, 2013, J. Wiley & Sons). These compounds are characterized by their strong basicity, as their conjugate acids have very high pKa values. S -values ​​typically of around 50

[0003] Butyllithium-initiated polymer chains can be hydrolyzed, end-functionalized with various compounds such as electrophiles, or coupled, depending on the intended application. Hydrolysis yields polymers with pure hydrocarbon chain ends. End-group functionalization allows the terminal C-Li bond to be treated with electrophiles such as carbonyl compounds, halogenated silanes, or amines to introduce a polar functional group at one end of the polymer molecule. Reaction with multifunctional coupling reagents such as SiCl₄ or SnCl₄ results in cross-linked or star-shaped polymers with improved solubility and reduced solution viscosity.

[0004] Polymers functionalized with polar end groups are characterized by enhanced interactions with and improved adhesion to polar filler particles, typically highly dispersed silica. These altered properties lead to improved vulcanization characteristics and, in particular, reduced hysteresis of the vulcanizate. The interactions between fillers and rubber can be further enhanced by functionalizing the polymer backbone with so-called backbone modifiers, usually sulfur-containing molecules. Suitable backbone modifiers and backbone modification methods are known, for example, from CG Robertson, Rubber Chem. Technol. 84, 4, 507-519, 2011. Polymers with this additional backbone modification exhibit improved tensile strength and improved rolling resistance properties, measured as tan δ at 60°C (SKH Thiele et al., KGKrubber November / December 2011).The loss factor tan δ characterizes the damping behavior of a polymer material.

[0005] When using non-functionalized monolithium initiators such as butyllithium, only one of the polymer ends can be functionalized, namely the end with the C-Li bond. Therefore, only α-functionalized polymer chains can be produced. The other polymer end, the ω-position, consists of an unfunctionalized hydrocarbon residue, such as a butyl group if butyllithium is used as the initiator. This end is therefore freely mobile and does not adhere, or only weakly adheres, to fillers. It thus contributes significantly to the undesirable hysteresis of the polymer material.

[0006] When using rubber in the manufacture of automotive tires, minimal hysteresis is desirable. The undirected movement of free polymer chain ends causes the release of frictional heat, thus increasing rolling resistance. The material behavior can be improved by fixing both polymer chain ends to the filler materials. Such α,ω-functionalized polymers contribute significantly to reducing rolling resistance and, consequently, specific fuel consumption. By using double-sided functionalized polymers, also known as telechelic polymers, in so-called "green tires" (environmentally friendly tires), fuel consumption can be reduced by approximately 6-8% (X. Na, Transportation Research Part D 113 (2022) 103501).

[0007] Several methods are known for producing α,ω-functionalized rubbers via anionically initiated polymerization. One method involves the use of dilithiated or multilithiated initiators. A suitable dilithiated initiator, for example, is the addition product of two moles of sec-butyllithium and one mole of 1,3-diisopropenylbenzene. Such dilithium compounds are typically characterized by strong aggregation phenomena, which results in low solubility in systems consisting solely of saturated hydrocarbon solvents and leads to the precipitation of three-dimensionally cross-linked species. Such initiator systems yield undesirably broad molecular weight distributions (J. Hofmans, M. van Beylen, Polymer 46 (2005) 303-318).

[0008] Another method for producing α,ω-functionalized rubbers via anionically initiated polymerization involves using a monolithium initiator system that already contains a polar function. Due to the high reactivity of organolithium compounds, only a few functional groups are compatible with the lithium-bound carbanionic function. Functionalized monolithium initiators can, for example, feature tertiary amine, ether, or siloxy groups, whereas hydroxyl, carboxyl, carbonyl, and primary amine groups are unsuitable. Due to their thermal stability, initiators functionalized with tertiary amine groups are particularly suitable for industrial applications.

[0009] A well-known amino-functionalized initiator is dimethylaminopropyllithium (DMAPLi), which can be prepared from dimethylaminopropyl chloride and lithium powder (NS Davidson et al., Macromolecules 21, 1, 1988). However, DMAPLi is practically insoluble in hexane, as described, for example, by Stewart et al. (British Polymer Journal 22 (1990) 319-325). US 5,527,753 A specifies the solubility of the group of amino-functionalized initiators in aliphatic and cycloaliphatic solvents, such as hexane, as less than 0.3 M. Due to this very low solubility, the transport of such solutions has been considered very costly. A higher concentration of the initiator in the solution can also be advantageous for its intended use in polymerization reactions. US 5,550,203 A describes the improvement of solubility through so-called "seeding technology." In this process, a specific amount of diene monomers, e.g., is added to the synthesis solution.Isoprene, given. A DMAPLi solution chain-extended in this manner with 2 mol of isoprene can be concentrated to a concentration of 1.36 M (US9,085,653 B2, Example 1).

[0010] However, a disadvantage of such diene-chain-extended DMAPLi solutions is their lack of configurational stability. They do not exhibit a defined structure; instead, intermolecular exchange reactions form di- and polylithiated initiation-active compounds. These multiply lithiated molecules lead to living polymers with two or more C-Li bonds. This, in turn, results in poorly defined, hyperbranched polymer structures and undesirable gel formation during subsequent polymer workup using coupling reagents.

[0011] US patent US 9,085,653 B2 describes the synthesis of telechelic diene polymers using amine-functionalized initiators. An example of these initiators is a structure of formula R. 1 R 2 NR 3 Li, where R 1 and R 2 These can be independent alkyl groups with 1 to 12 carbon atoms and may optionally form a cyclic structure. R 3 This can be, among other things, an alkylene group with 1 to 20 carbon atoms. The preparation of this initiator takes place in three steps. In the first step, a secondary amine of the formula R is prepared according to the reaction shown below [1]. 1 R 2 NH with an organolithium compound R 3 Li to a lithium amide compound of the formula R 1 R 2 NLi implemented.

[0012] This lithium amide compound is then reacted in the second step with an alkyl dihalide of formula XR according to reaction [2]. 4X', where X and X' are different halogens from the group of I, Br and Cl, to form the halogen compound R 1 R 2 NR 4 X' implemented.

[0013] By reacting with 2 equivalents of another organolithium compound of formula R 5 In the third step, according to reaction [3], Li finally becomes the initiator of type R. 1 R 2 NR 4 Li in a mixture with the Wurtz coupling product R 5 R 5 and receive LiX'.

[0014] The synthesis takes place in a hydrocarbon solvent, and a polar compound can be added to accelerate the production of the lithium compound and to achieve a solubilizing effect, thus improving its solubility in the hydrocarbon solvent. Examples of suitable polar compounds include tertiary monoamines, tertiary diamines, and open and cyclic ethers, such as tetrahydrofuran (THF).

[0015] Examples 3 and 4 of US 9,085,653 B2 describe the preparation of the initiators 3-(dibutylamino)propyllithium and 3-(hexamethyleneiminyl)propyllithium. In both examples, the secondary amine starting materials were lithiated using n-butyllithium in a solvent mixture of THF and hexane. In the next step, they were treated with 1-chloro-3-bromopropane at a temperature of -25°C and then stirred for 1 h at 0°C. The mixture was then cooled again to -25°C and a solution of tert-butyllithium in pentane was added, forming the respective initiators. The prepared initiators were thus present as a solution in a solvent mixture consisting of saturated aliphatic hydrocarbons and the donor solvent THF.

[0016] Solutions of organolithium compounds in ethereal solvents are unstable and decompose rapidly, forming ethylene and lithiated acetaldehyde enolate (TL Rathman et al., Org. Process Res. Dev. 2014, 18, 1192-1210). Furthermore, the synthesis of the amine-containing initiator described in US 9,085,653 B2 is problematic for safety reasons, particularly due to the pyrophoricity of tert-butyllithium, and also for commercial reasons due to the high cost of tert-butyllithium. Contamination of the product solutions by byproducts is also to be expected. In addition to the decomposition products of THF, these include the Wurtz coupling products of the reaction between the halogenalkane R, formed intermediately by halogen / metal exchange. 5 X' and the lithium alkyl R 5 Li, also R 5 R 5, in the third step of the synthesis. The THF cannot be removed from the finished reaction solutions without completely decomposing the synthesized initiator. Task

[0017] The present invention is therefore based on the objective of providing improved solutions of dialkylaminoalkyllithium initiators. A key aspect of the improvement is that the solutions should exhibit high initiator concentrations. An additional aspect of the improvement can consist of particularly high storage stability of the solutions. Furthermore, a cost-effective and safe process for the production of the dialkylaminoalkyllithium initiators is to be provided. Solution to the task

[0018] The stated problem is solved by the dialkylaminoalkyllithium initiator solutions according to claims 1 to 7 and the method according to claims 8 to 13. The invention is further directed to the use according to claim 14 and the method according to claim 15.

[0019] The dialkylaminoalkyllithium initiator solution according to the invention is characterized in that it contains a dialkylaminoalkyllithium initiator of formula (I) in a hydrocarbon solvent, RR'N(CH2) n Li (I), where R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, preferably at least 6, in particular at least 7 and especially preferably at least 8, and n = 2 to 10, and wherein the concentration of the dialkylaminoalkyllithium initiator is at least 0.3 mol / L.

[0020] It was surprisingly found that solutions of dialkylaminoalkyllithium initiators with concentrations exceeding 0.3 mol / L, such as 0.5 mol / L and higher, can be produced. These highly concentrated solutions can significantly reduce transportation costs and also offer advantages for their intended use as polymerization initiators. The initiator concentration in the solutions according to the invention is thus high enough that the "seeding" process known from US 5,550,203 is unnecessary. The initiator solutions produced by the inventive process exhibit well-defined compositions and therefore reproducible application properties. This contrasts with initiators produced using "seeding technology," which have a statistically determined ratio of seeding agent to initiator and a correspondingly undefined composition with a multitude of isomeric components and unsaturated C-C bonds.Furthermore, such compounds are not configurationally stable and can change during storage under lithium transfer. This has a detrimental effect on the properties of the elastomers produced with them.

[0021] Preferably, the concentration of the dialkylaminoalkyllithium initiator in the solution according to the invention is at least 0.4 mol / L, in particular at least 0.5 mol / L, more preferably at least 0.6 mol / L and particularly preferably at least 0.7 mol / L.

[0022] In a particularly preferred embodiment, the concentration of the dialkylaminoalkyllithium initiator in the solution according to the invention is 0.3 to 1.5 mol / L, preferably 0.4 to 1.3 mol / L, in particular 0.5 to 1.1 mol / L, more preferably 0.6 to 1.0 mol / L and particularly preferably at least 0.7 to 0.8 mol / L.

[0023] It is further preferred that the hydrocarbon solvent contains at most 0.05 wt% donor solvent based on the total weight of the solution and, in particular, is essentially free of donor solvents. For the purposes of the present invention, the term "donor solvent" refers to solvents that, due to their molecular structure, are capable of providing electron pairs. Such donor solvents are, in particular, ethers, amines, alcohols, and carbonyl compounds.

[0024] In a preferred embodiment, the hydrocarbon solvent contains, based on the total weight of the solution, at most 0.05 wt% ethereal solvents and, in particular, at most 0.05 wt% THF. In particular, the hydrocarbon solvent is substantially free of ethereal solvents and, in particular, substantially free of THF.

[0025] In a preferred embodiment, the hydrocarbon solvent of the dialkylaminoalkyllithium initiator solution contains one or more hydrocarbons with a boiling point in the range of 35 to 250°C. It is further preferred that the hydrocarbon solvent consists of one or more hydrocarbons with a boiling point in the range of 35 to 250°C.

[0026] It is preferred that the hydrocarbon solvent contains, and in particular consists of, one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons with 5 to 12 carbon atoms and aromatic hydrocarbons with 6 to 14 carbon atoms.

[0027] It is further preferred that the hydrocarbon solvent contains, and in particular consists of, one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons with 6 to 8 carbon atoms, toluene, ethylbenzene, cumene, and xylenes. Particularly preferably, the hydrocarbon solvent consists of one or more hydrocarbons selected from the group consisting of hexanes and heptanes.

[0028] The solution according to the invention contains a dialkylaminoalkyllithium initiator of formula (I), RR'N(CH2) n Li (I), where R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, preferably at least 6, in particular at least 7 and especially preferably at least 8, and n = 2 to 10.

[0029] Preferably, R and R' are independent alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of R and R' is at least 5, preferably at least 6, particularly at least 7, and most preferably at least 8. In particular, at least one of the R and R' groups has 4 to 12 carbon atoms. It is particularly preferred that R and R' each have 4 to 12 carbon atoms.

[0030] In a preferred embodiment, R and R' are alkyl groups, each selected from the group consisting of ethyl, propyl, butyl, pentyl, and hexyl, wherein the sum of the carbon atoms of R and R' is at least 5. In particular, R and R' are independently selected from propyl, butyl, and pentyl, and it is especially preferred that both R and R' are butyl.

[0031] In another preferred embodiment, R and R' together form an alkylene group, which in particular contains 4 to 6 CH2 groups.

[0032] In a particularly preferred embodiment, the dialkylamino group RR'N- of the initiator is selected from the group consisting of ethylbutylamino, dipropylamino, dibutylamino, dihexylamino, dioctylamino, and piperidinyl. The dialkylamino group RR'N- of the initiator dibutylamino- is particularly preferred.

[0033] The dialkylaminoalkyllithium initiator in the solution according to the invention has a structure of formula (I), wherein preferably n=3 to 6.

[0034] In a further particularly preferred embodiment, the dialkylaminoalkyllithium initiator in the solution according to the invention is selected from the group consisting of 3-(ethylbutylamino)propyllithium, 3-(dipropylamino)propyllithium, 3-(dibutylamino)propyllithium, 3-(dihexylamino)propyllithium; 4-(ethylbutylamino)butyllithium, 4-(dipropylamino)butyllithium, 4-(dibutylamino)butyllithium, 5-(dihexylamino)butyllithium, 6-(dibutylamino)hexyllithium, 3-(piperidinyl)propyllithium; 4-(piperidinyl)butyllithium. Of these dialkylaminoalkyllithium initiators, 3-(dibutylamino)propyllithium is particularly preferred.

[0035] The dialkylaminoalkyllithium initiator solution according to the invention is characterized by particularly high storage stability. Preferably, the dialkylaminoalkyllithium initiator solution is characterized in that the content of dialkylaminoalkyllithium initiator after 6 weeks of storage at 25 °C, determined by thermometry as active base content, is at least 70%, in particular at least 80%, more preferably at least 90%, and most preferably at least 95% of the content before the start of storage.

[0036] It is also preferred that the dialkylaminoalkyllithium initiator in the solution according to the invention is present in a purity of at least 80 mol%, in particular at least 90 mol% and especially preferably at least 95 mol%.

[0037] In a second aspect, the invention relates to a process for producing the dialkylaminoalkyllithium initiators contained in the solutions described above.

[0038] This process according to the invention for the preparation of a dialkylaminoalkyllithium initiator of formula (I) RR'N(CH2) n Li (I), where R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, preferably at least 6, in particular at least 7 and especially preferably at least 8, and n = 2 to 10, is characterized by the fact that (a) an aminohaloalkane of formula (II), RRN(CH2) n Hal (II) where Hal is selected from Cl, Br and I, and preferably from Cl and Br; R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, preferably at least 6, in particular at least 7 and especially preferably at least 8, and n = 2 to 10, in a hydrocarbon solvent under inert conditions, reacts with elemental lithium to give a dialkylaminoalkyllithium initiator of formula (I), wherein the molar ratio of aminohaloalkane:lithium is 1:2 to 1:5.4, preferably 1:2.2 to 1:5 or 1:2.2 to 1:4, to obtain a solution of the dialkylaminoalkyllithium initiator of formula (I) in the hydrocarbon solvent, and (b) any solids that may be present are separated by a solid / liquid separation operation.

[0039] The preferred embodiments of the initiators and hydrocarbon solvents described in connection with the dialkylaminoalkyllithium initiator solution according to the invention are also correspondingly preferred for the process according to the invention.

[0040] It was surprisingly found that, using the process according to the invention, under the conditions defined in the process, dialkylaminoalkyllithium initiators can be produced according to reaction [4] which are present in high concentrations in a hydrocarbon solution.

[0041] In the structures of reaction [4], Hal is selected from Cl, Br and I and preferably from Cl and Br. In addition, R and R' together form an alkylene group or R and R' are independently alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least 8.

[0042] In the process according to the invention, therefore, in step (a) an aminohaloalkane of formula (II) is used, RR'N(CH2) n Hal (II) where Hal is selected from Cl, Br and I and preferably is selected from Cl and Br; R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least 8, and n = 2 to 10 is, reacted with elemental lithium to form a dialkylaminoalkyllithium initiator of formula (I).

[0043] Preferably, R and R' in the aminohaloalkane of formula (II) are independent alkyl groups with up to 12 carbon atoms, preferably 2 to 12 carbon atoms, wherein the sum of the carbon atoms of R and R' is at least 5, preferably at least 6, particularly at least 7, and most preferably at least 8. In particular, at least one of the R and R' groups in the aminohaloalkane of formula (II) has 4 to 12 carbon atoms. It is particularly preferred that R and R' each have 4 to 12 carbon atoms.

[0044] In a preferred embodiment, R and R' in the aminohaloalkane of formula (II) are alkyl groups, each selected from the group consisting of ethyl, propyl, butyl, pentyl, and hexyl, wherein the sum of the carbon atoms of R and R' is at least 5. In particular, R and R' are each selected from propyl, butyl, and pentyl, and it is especially preferred that R and R' are both butyl.

[0045] In a further preferred embodiment, R and R' together form an alkylene group in the aminohaloalkane of formula (II), which in particular contains 4 to 6 CH2 groups.

[0046] In a particularly preferred embodiment, the dialkylamino group RR'N- in the aminohaloalkane of formula (II) is selected from the group consisting of ethylbutylamino, dipropylamino, dibutylamino, dihexylamino, dioctylamino and piperidinyl.

[0047] The aminohaloalkane has a structure of formula (II), where preferably n = 3 to 6.

[0048] In the process according to the invention for the preparation of a dialkylaminoalkyllithium initiator of formula (I), an aminohaloalkane of formula (II) is particularly preferably used. RR'N(CH2) n Hal (II) where Hal Cl is and / or, R and R' are independently alkyl groups with 3 to 6 carbon atoms and / or n = 3 to 6 is, reacted with elemental lithium to form a dialkylaminoalkyllithium initiator of formula (I).

[0049] An aminohaloalkane of formula (II) is particularly preferred. RR'N(CH2) n Hal (II) where Hal Cl is, R and R' are independent alkyl groups with 3 to 6 carbon atoms and n = 3 to 6, reacted with elemental lithium to form a dialkylaminoalkyllithium initiator of formula (I).

[0050] In a further particularly preferred embodiment, the aminohaloalkane of formula (II) is selected from the group consisting of 3-(ethyl butylamino)propyl chloride, 3-(dipropylamino)propyl chloride, 3-(dibutylamino)propyl chloride, 3-(dihexylamino)propyl chloride; 4-(ethyl butylamino)butyl chloride, 4-(dipropylamino)butyl chloride, 4-(dibutylamino)butyl chloride, 5-(dihexylamino)butyl chloride, 6-(dibutylamino)hexyl chloride, 3-(piperidinyl)propyl chloride; 4-(piperidinyl)butyl chloride.

[0051] The hydrocarbon solvent used in step (a) preferably contains, based on the total weight of the solution, at most 0.05 wt% donor solvent and is in particular essentially free of donor solvents.

[0052] In a further preferred embodiment, the hydrocarbon solvent used in step (a) contains at most 0.05 wt% ethereal solvents. In particular, the hydrocarbon solvent is essentially free of ethereal solvents.

[0053] In a preferred embodiment, the hydrocarbon solvent used in step (a) contains one or more hydrocarbons with a boiling point in the range of 35 to 250°C. It is further preferred that the hydrocarbon solvent consists of one or more hydrocarbons with a boiling point in the range of 35 to 250°C.

[0054] It is preferred that the hydrocarbon solvent used in step (a) contains, and in particular consists of, one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons with 5 to 12 carbon atoms and aromatic hydrocarbons with 6 to 14 carbon atoms.

[0055] It is further preferred that the hydrocarbon solvent used in step (a) contains, and in particular consists of, one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons with 6 to 8 carbon atoms, toluene, ethylbenzene, cumene and xylenes. Particularly preferably, the hydrocarbon solvent consists of one or more hydrocarbons selected from the group consisting of hexanes and heptanes.

[0056] Step (a) of the process according to the invention comprises reacting an aminohaloalkane of formula (II) with elemental lithium.

[0057] The reaction takes place "under inert conditions," which, in the context of the present invention, means that the reaction occurs in an environment where the presence of ambient air and moisture, in particular oxygen, water, and water vapor, is largely and preferably substantially completely prevented by measures commonly used for this purpose. These measures include, for example, the use of inert gases such as argon or nitrogen and the use of reaction vessels sealed from the environment. Such measures for ensuring inert conditions in the synthesis of organolithium compounds are generally known to those skilled in the art (B.J. Wakefield: The Chemistry of Organolithium Compounds, Pergamon Press, Oxford 1974).

[0058] The elemental lithium used in step (a) is preferably in particulate form. It is preferred that these lithium particles have an average size in the range of 1 µm to 10 mm. In a particularly preferred embodiment, the particles have an average particle size in the range of 2 to 8 mm. Such particles can be lithium metal castings such as granules. In another particularly preferred embodiment, the lithium particles are powder particles with an average size of less than 100 µm. The particle sizes given refer to the volume-weighted average particle size D. 50 , wherein the size determination of submillimeter particles according to ISO 13320 is carried out by means of static laser scattering using the Mie model in heptane as a dispersant.

[0059] The shape of the lithium particles is preferably spherical or angular, such as cuboid or prism-shaped.

[0060] It is further preferred that the elemental lithium has a sodium content of at least 0.1 wt.%, in particular at least 0.3 wt.%, and especially preferably at least 0.5 wt.%, based on the total weight of the elemental lithium. It is also preferred that the elemental lithium has a sodium content of less than 10 wt.%, and in particular less than 5 wt.%, based on the total weight of the elemental lithium. In a particularly preferred embodiment, the elemental lithium has a sodium content in the range of 0.3 to 10 wt.%, in particular 0.5 to 5 wt.%, based on the total weight of the elemental lithium.

[0061] The reaction of the aminohaloalkane of formula (II) with the elemental lithium in step (a) of the process according to the invention preferably takes place at a temperature of 0 to 110°C and particularly at 10 to 80°C.

[0062] In another preferred embodiment, the conversion in step (a) of the process takes place under boiling conditions.

[0063] It is further preferred that the reaction of the aminohaloalkane of formula (II) in step (a) takes place at a pressure that is reduced compared to atmospheric pressure and in particular at a pressure of 50 to 900 mbar.

[0064] In step (b), solids that may be present in the dialkylaminoalkyllithium initiator solution after the reaction of step (a) can be separated by a solid / liquid separation operation. These solids may be, for example, lithium halides formed as a byproduct of the reaction or excess elemental lithium. The solid / liquid separation operation is preferably filtration, sedimentation, or centrifugation, and in particular filtration.

[0065] After the implementation of step (a) the concentration of the dialkylaminoalkyllithium initiator in the solution is preferably at least 0.3 mol / L, particularly at least 0.4 mol / L, more preferably at least 0.5 mol / L, particularly preferably at least 0.6 mol / L and most preferably at least 0.7 mol / L.

[0066] In a particularly preferred embodiment, the concentration of the dialkylaminoalkyllithium initiator after the reaction of step (a) is 0.3 to 1.5 mol / L, preferably 0.4 to 1.3 mol / L, in particular 0.5 to 1.1 mol / L, more preferably 0.6 to 1.0 mol / L and particularly preferably at least 0.7 to 0.8 mol / L.

[0067] In a further aspect, the invention relates to a method for producing the dialkylaminoalkyllithium initiator solution according to the first aspect of the invention, wherein the method is carried out in accordance with the method described in the second aspect of the invention.

[0068] The embodiments described as suitable and preferred in connection with the above solution according to the invention and with the above process according to the invention for the preparation of a dialkylaminoalkyllithium initiator of formula (I) are also suitably suitable or preferred for the process according to the invention for the preparation of a solution of a dialkylaminoalkyllithium initiator of formula (I).

[0069] Another aspect of the invention relates to a solution of a dialkylaminoalkyllithium initiator of formula (I) in a hydrocarbon solvent, obtainable by the process according to the second aspect of the invention.

[0070] The embodiments described as suitable and preferred in connection with the above process according to the invention for the preparation of a dialkylaminoalkyllithium initiator of formula (I) are also suitably suitable or preferred for the solution of a dialkylaminoalkyllithium initiator of formula (I) obtainable by the process.

[0071] In a further aspect, the invention relates to the use of the dialkylaminoalkyllithium initiator solution according to the invention in the anionic polymerization of 1,3-dienes and aryl-substituted olefins, in particular styrene and methylstyrene, for the production of synthetic elastomers and liquid rubbers. Preferred liquid rubbers are rubbers based on isoprene, butadiene, or styrene-butadiene monomer units.

[0072] In the production of such synthetic elastomers and liquid rubbers, such as polybutadienes, polyisoprenes, or styrene-butadiene polymers, using the initiators according to the invention, adhesion promoters are preferably employed to improve the interactions between polymer chain ends and the fillers used in the production. Silica particles are preferred fillers.

[0073] In a preferred embodiment, the adhesion promoters are functionalized silanes. Such silane adhesion promoters are bifunctional compounds with two functionally active end groups. The first end group is an alkoxy group, which is preferably readily hydrolyzable. The alkoxy group can react with the silanol groups on the silica surface, forming stable siloxane bonds. The second end group is a nonpolar organofunctional group, which is therefore compatible with the also nonpolar rubber molecules. To participate in the sulfur vulcanization that typically occurs during production, the nonpolar organofunctional group of the adhesion promoters preferably has unsaturated carbon-carbon bonds. This allows it to form covalent sulfide groups with the polymer chains.

[0074] The silane adhesion promoter can thus act as a bonding element or “bridge” between silica and rubber to enhance the rubber-filler interaction and thereby achieve a further improvement in properties. Particularly preferred adhesion promoters are bis[3-(triethoxysilyl)propyl]disulfide (TESPD), 3,3'-bis(trimethoxysilylpropyl) disulfides (TMSPD), 3,3'-bis(dimethoxymethylsilylpropyl) disulfides (DMSPD), etc. (Lee et al., Polymers 2020, 12, 3058).

[0075] Furthermore, in the invention for the production of synthetic elastomers and liquid rubbers, coupling agents can be used to couple polydiene rubbers. During coupling, polymer chains are linked together, preferably to create branched, especially multi-armed or star-shaped, polymer structures. It is preferred that the coupling agent contains at least one vinyl group. Particularly preferred coupling agents are polyunsaturated siloxanes or titanates.

[0076] In a further aspect, the invention is directed to processes for the production of synthetic elastomers and liquid rubbers in which 1,3-dienes or aryl-substituted olefins are polymerized using the dialkylaminoalkyllithium initiator solution according to the invention.

[0077] The embodiments described as suitable and preferred in connection with the aforementioned use of the inventive dialkylaminoalkyllithium initiator solution in the anionic polymerization of 1,3-dienes and aryl-substituted olefins are also suitably suitable or preferred for the inventive process for the production of synthetic elastomers and liquid rubbers.

[0078] The subject matter of the invention is explained below by means of examples and comparative examples. Examples Example 1: Preparation of a 3-(Dibutylamino)propyllithium (DBAPLi) solution

[0079] In an inertized, i.e., dry, argon-filled 2 L double-jacketed reactor equipped with an internal thermometer, reflux condenser, and mechanical stirrer, 986 g of hexane and 42.3 g (6.08 mol) of lithium powder were placed. The mixture was heated to 50 °C, and then N,N-dibutylamino-3-chloropropane (313 g, 1.52 mol) was continuously added over a period of two hours. The internal temperature of the reactor was maintained between 50 and 55 °C.

[0080] After complete addition of the N,N-dibutylamino-3-chloropropane, the mixture was stirred for another hour at a jacket temperature of 50 °C and then cooled to room temperature. It was then poured onto a glass frit covered with a polypropylene filter cloth, and the filtrate was collected in a glass bottle filled with argon. The filter residue was washed twice with 50 mL of hexane each time, and the filtrates were combined. Since only hexane was used as the solvent, the resulting solution contained no donor solvent. Weighed: 1.280 g of a clear, light yellow solution, density = 0.68 g / mL

[0081] The active base content, determined by thermometric titration (titration solution is a 1 molar solution of sec-butanol in xylene), was 1.13 mol / kg or 0.775 mol / L (corresponding to 20.2 wt% DBAPLi). The titration was performed using a type 859 Titrotherm (Metrohm) thermometric titrator with the "Thermoprobe" temperature sensor. Yield: 95.2% of theory. Example 2: Storage stability of the DBAPLi solution from Example 1

[0082] A solution of the DBAPLi solution from Example 1, diluted with hexane to 17 wt% active base content, was placed in gas chromatography vials inertized by evacuation and argon filling and stored at 40°C. To investigate storage stability, the active base content of the samples was determined by thermometry at the time points specified in Table 1, as described in Example 1. Table 1: Storage time (days) at 40°C 0 13 18 28 41 52 69 Active base content (wt% as DBAPLi) 17,0 16,9 16,6 16,4 16,1 15,3 15,2

[0083] Based on the temporal profile of the active base content, and assuming first-order kinetics, a product decomposition rate of 0.16% per day is calculated.

[0084] In a further experiment, a solution of the DBAPLi solution from Example 1, diluted with hexane to 17 wt% active base content, was stored in airtight, inerted glass bottles at room temperature. The active base content was determined after 6 weeks. No significant loss of activity was observed. Comparative Example 1: Preparation of 3-(Dibutylamino)propyllithium according to the process described in US 9,085,653 B1 (Example 3) without the use of a donor solvent

[0085] In a 0.5 L double-jacketed reactor inertized by evacuation and argon filling, 85.5 g of N,N-dibutylamino-3-chloropropane (415 mmol, 1.0 eq.) were placed and heated to 20 °C. At this temperature, 295.5 g of an 18.0% solution of tert-butyllithium in hexane (830 mmol, 2.0 eq.) were added over 30 minutes. After complete addition, the solution was heated to room temperature and stirred for a further 16 hours at room temperature. The solution was transferred under argon pressure through tubing to a glass frit and filtered to separate the LiCl produced. The filter residue was washed with 30 mL of hexane, and the filtrates were combined. A pale yellow, clear product solution was obtained. Weight: 312 g pale yellow, clear product solution

[0086] The active base content was determined by thermometric titration as described in Example 1.

[0087] Active base content: 0.91 mmol / g, this would correspond to 16.2 wt% DBAPLi (74% of the theoretical active base content of 1.23 mmol / g).

[0088] GC / MS measurements revealed that the measured active base content was not solely attributable to the desired product DBAPLi, but rather to a mixture of various organolithium compounds. In addition to approximately 47 mol% DBAPLi, 34 mol% unchanged tert-butyllithium and approximately 19 mol% of other components were identified. To prepare for the measurements, an aliquot of the filtrate was derivatized with diphenyl disulfide (DPDS), and the relative contents of tert-butyllithium and DBAPLi were subsequently determined. The yield of the desired product DBAPLi was therefore only about 35%.

[0089] To investigate storage stability, the product solution was stored at room temperature for 48 hours. It was observed that the solution became cloudy. A sample of the solution was taken and filtered to clear. The active base content, determined according to the method described in Example 1, had dropped to 0.62 mmol / g. Therefore, the solution is not storage-stable but decomposes at a rate of approximately 16% per day. Comparative Example 2: Preparation of 3-(Dibutylamino)propyllithium according to the process described in US9,085,653 B1 (Example 3) using a donor solvent

[0090] In an inertized 0.5 L double-jacketed reactor, a mixture of N,N-dibutylamino-3-chloropropane (85.5 g, 415 mM, 1.0 eq.) and tetrahydrofuran (THF, 59.9 g, 830 mM, 2.0 eq.) was placed and cooled to -25 °C. At this temperature, 295.5 g of an 18.0% solution of tert-butyllithium in hexane (830 mM, 2.0 eq.) was added over 30 minutes. After complete addition, the solution was slowly warmed to room temperature and stirred for a further 16 hours. The solution was transferred under argon pressure through tubing to a glass frit and filtered to remove any LiCl formed. A pale yellow, clear product solution was obtained. Weight: 359 g pale yellow, initially clear product solution

[0091] The active base content, determined by thermometric titration according to the procedure described for Example 1 (titration solution is a 1 molar solution of sec-butanol in xylene), is 0.78 mol / kg. This corresponds to a DBAPLi concentration of 13.8 wt%. The theoretical product concentration, in contrast, is 1.10 mmol / g (19.6 wt%).

[0092] The isolated yield is calculated to be 280 / 415*100 = 67% of the theoretical yield.

[0093] The initially clear filtrate showed significant turbidity after just one day of storage at room temperature. The active base content after one day of storage, determined by thermometric titration using the method described for Example 1, had fallen to 0.45 mol / kg (corresponding to 8.0 wt%). This results in a product decomposition rate of 42% per day. Summary of the results of the examples

[0094] A comparison of Examples 1 and 2 according to the invention with comparative examples 1 and 2 reveals the advantages of the process according to the invention. According to the process according to the invention, in the case of Example 1 using lithium metal powder, a chloroalkylamine of the formula Bu₂N(CH₂)₃Cl, and a donor-free solvent (hexane), the desired organolithium compound can be produced in a high yield of approximately 95% of theory in the form of a 20% solution. This solution is very stable. Under suitable storage conditions (such as room temperature or below), it can be stored for a long period, for example, several months or longer, without significant decomposition. Even at an elevated storage temperature of 40°C, it decomposes at a very low rate of 0.16% per day.

[0095] In contrast, the methods described in US9,085,653 B1 are not suitable for providing a concentrated, storage-stable product solution.

[0096] When using a donor-free solvent (hexane, comparative example 1), a relatively high active base concentration is obtained, but only a portion (approximately 50%) of this is attributable to the desired product. The other half consists of unreacted tert-butyllithium and other decomposition products. The yield of the desired product DBAPLi in the fresh product solution is only about 34% of the theoretical yield. After only two days of room temperature storage, the active base concentration was reduced by 32%. This corresponds to a decomposition rate of 16% per day.

[0097] Even using a donor solvent (THF), it was not possible to obtain solutions with the advantageous properties of the solutions according to the invention. While an improved product yield was observed in the fresh filtrate when using 2 equivalents of THF (13.8 wt%), corresponding to 71% of the theoretical value, this solution was not stable. Turbidity was observed after only a short time. After one day of storage at room temperature, the active base content had already been reduced by 42%, corresponding to a DBAPLi content of only 8.0 wt% DBAPLi. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Zitierte Patentliteratur

[0000] US 5,527,753 A

[0009] US 5,550,203 A

[0009] US 9,085,653 B2 [0009, 0011, 0015, 0016] US 5,550,203

[0020] US 9,085,653 B1

[0095] Zitierte Nicht-Patentliteratur

[0000] R. Quirk, Anionic Polymerization, Chap. 7, 127, in: Handbook of Polymer Synthesis, Characterization, and Processing. 1 st ed. Ed. By E. Saldivar-Guerra and E. Vivaldo-Lima, 2013, J. Wiley & Sons

[0002] C. G. Robertson, Rubber Chem. Technol. 84, 4, 507-519, 2011

[0004] S.K.H. Thiele et al., KGKrubber November / Dezember 2011

[0004] X. Na, Transportation Research Part D 113 (2022) 103501

[0006] J. Hofmans, M. van Beylen, Polymer 46 (2005) 303-318

[0007] N.S. Davidson et al., Macromolecules 21, 1, 1988

[0009] Stewart et al. (British Polymer Journal 22 (1990) 319-325

[0009] T.L. Rathman et al., Org. Process Res. Dev. 2014, 18, 1192-1210

[0016] B.J. Wakefield: The Chemistry of Organolithium Compounds, Pergamon Press, Oxford 1974

[0057] Lee et al., Polymers 2020, 12, 3058

[0074]

Claims

[1] Dialkylaminoalkyllithium initiator solution containing a dialkylaminoalkyllithium initiator of formula (I) in a hydrocarbon solvent, RR'N(CH2) n Li (I), where R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, and n = 2 to 10 is, characterized by that the concentration of the dialkylaminoalkyllithium initiator is at least 0.3 mol / L. [2] Dialkylaminoalkyllithium initiator solution according to claim 1, characterized by that the hydrocarbon solvent, based on the total weight of the solution, contains at most 0.05 wt% donor solvent and preferably essentially no donor solvent. [3] Dialkylaminoalkyllithium initiator solution according to claim 1 or 2, characterized by, that the hydrocarbon solvent contains one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons with 5 to 12 carbon atoms and aromatic hydrocarbons with 6 to 14 carbon atoms, and preferably selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons with 6 to 8 carbon atoms, toluene, ethylbenzene, cumene and xylenes. [4] Dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 3, characterized by , that R and R' together form an alkylene group with 4 to 6 CH2 groups or are each selected from the group consisting of ethyl, propyl, butyl, pentyl and hexyl, wherein R and R' are preferably each selected from propyl, butyl and pentyl and in particular both are butyl. [5] Dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 4, characterized by , that n = 3 to 6. [6] Dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 5, characterized by that the concentration of the dialkylaminoalkyllithium initiator is at least 0.4 mol / L, preferably at least 0.5 mol / L, in particular at least 0.6 mol / L and most preferably at least 0.7 mol / L. [7] Dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 6, characterized by , that the content of dialkylaminoalkyllithium initiator after 6 weeks of storage at 25°C, determined by thermometry as active base content, is at least 70%, preferably at least 80%, in particular at least 90% of the content before the start of storage. [8] Method for the preparation of a dialkylaminoalkyllithium initiator of formula (I) RR'N(CH2) n Li (I), where R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, and n = 2 to 10 is, characterized by , that (a) an aminohaloalkane of formula (II), RR'N(CH2) n Hal (II) where Hal is selected from Cl, Br and I; R and R' together form an alkylene group or are independently alkyl groups with up to 12 carbon atoms, wherein the sum of the carbon atoms of the alkyl groups R and R' is at least 5, and n = 2 to 10 is, in a hydrocarbon solvent under inert conditions, reacts with elemental lithium to give a dialkylaminoalkyllithium initiator of formula (I), wherein the molar ratio of aminohaloalkane:lithium is 1:2 to 1:5.4, preferably 1:2.2 to 1:5 or 1:2.2 to 1:4, to obtain a solution of the dialkylaminoalkyllithium initiator of formula (I) in the hydrocarbon solvent, and (b) any solids that may be present are separated by a solid / liquid separation operation. [9] Method according to claim 8, characterized by , that the concentration of the dialkylaminoalkyllithium initiator in the solution after the reaction in step (a) is at least 0.3 mol / L, preferably at least 0.4 mol / L, in particular at least 0.5 mol / L and most preferably at least 0.6 mol / L. [10] Method according to claim 8 or 9, characterized by, that the reaction of the aminohaloalkane of formula (II) with the elemental lithium takes place at a temperature of 0 to 110°C, preferably 10 to 80°C. [11] Method according to one of claims 8 to 10, wherein the reaction of the aminohaloalkane of formula (II) with the elemental lithium is carried out under boiling conditions, wherein preferably the pressure is reduced compared to atmospheric pressure and in particular the pressure is 50 to 900 mbar. [12] Method according to any one of claims 8 to 11, characterized by , that in the case of the dialkylaminoalkane of formula (II) Hal Cl is, and / or R and R' are independently alkyl groups with 3 to 6 carbon atoms and / or n = 3 to 6, and preferably Hal Cl is, R and R' are independent alkyl groups with 3 to 6 carbon atoms and n = 3 to 6. [13] Method according to any one of claims 8 to 12, characterized bythat the hydrocarbon-containing solvent contains at least one saturated aliphatic or cycloaliphatic compound with 5 to 12, in particular 6 or 7, carbon atoms and preferably consists thereof. [14] Use of the dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 8 in the anionic polymerization of 1,3-dienes and aryl-substituted olefins for the production of synthetic elastomers and liquid rubbers. [15] Process for the production of synthetic elastomers and liquid rubbers in which 1,3-dienes or aryl-substituted olefins are polymerized using the dialkylaminoalkyllithium initiator solution according to the invention.