Dialkylaminoalkyl lithium initiator solutions and process for the preparation of dialkylaminoalkyl lithium initiators

Abstract

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

Description

[0001] Dialkylaminoalkyl lithium initiator solutions and process for the preparation of dialkylaminoalkyl lithium initiators

[0002] The present invention relates to concentrated solutions of dialkylaminoalkyllithium initiators and to processes for the preparation of dialkylaminoalkyllithium initiators for use as polymerization initiators for olefin-containing monomers.

[0003] Background

[0004] The living anionic polymerization of vinyl monomers is a central 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. Industrial-scale initiators are usually organometallic compounds, in particular organolithium compounds such as n-butyllithium and secbutyllithium (R. Quirk, Anionic Polymerization, Chap. 7, 127, in: Handbook of Polymer Synthesis, Characterization, and Processing. 1sted. Ed. By E. Saldivar-Guerra and E. Vivaldo-Lima, 2013, J. Wiley & Sons). These compounds are characterized by their strong basicity, as their corresponding acids have very high pKs values of typically about 50.

[0005] Depending on the intended application, polymer chains initiated with butyllithium can either only be hydrolyzed, end-functionalized with various compounds, such as electrophiles, or coupled. Hydrolysis produces polymers with pure hydrocarbon chain ends. In end group functionalization, the terminal C- Li bond can be used to introduce a polar functional group at one end of the polymer molecule by reaction with electrophiles such as carbonyl compounds, halogenated silanes or amines. Reaction with multifunctional coupling reagents such as SiCI4or SnCI4produces cross-linked or star-shaped polymers with improved solubility and reduced solution viscosity

[0006] Polymers that are functionalized with polar end groups are characterized by increased interactions with and better adhesion to polar filler particles, usually highly dispersed silica. These modified properties lead to improved vulcanization characteristics and, in particular, to 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 sulphur-containing molecules. Suitable backbone modifiers and processes for backbone modification are known, for example, from C. G. Robertson, Rubber Chem. Technol. 84, 4, 507-519, 2011. Polymers whose backbone is additionally modified in this way exhibit improved tear resistance and improved rolling resistance properties, measured as tan 8 at 60°C (S.K.H. Thiele et al., KGK-rubber November / December 2011). The loss factor tan 8 characterizes the damping behaviour of a polymer material.

[0007] 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 a-functionalized polymer chains can be produced. The other polymer end, the co-position, consists of an unfunctionalized hydrocarbon residue, such as a butyl group, if butyllithium is used as an initiator. This end is therefore freely movable and does not adhere to fillers, or at best only weakly. It therefore contributes significantly to the undesirable hysteresis of the polymer material.

[0008] When using rubber in the manufacture of automotive tires, the lowest possible hysteresis is desirable. The undirected movement of free polymer chain ends causes the release of frictional heat and thus increases rolling resistance. The material behavior can be improved by fixing both polymer chain ends to the filler materials. Such a, co-functionalized polymers contribute significantly to reducing the rolling resistance and thus also the specific fuel consumption. By using polymers functionalized on both sides, which are also known as telechelic polymers, in so-called "green tires" (environmentally friendly tires), fuel consumption can be reduced by approx. 6-8% (X. Na, Transportation Research Part D 113 (2022) 103501).

[0009] There are several known ways of producing a, co-functionalized rubbers using anionically initiated polymerization. A first possibility is the use of dual or multiple lithiated initiators. A suitable doubly lithiated initiator is, for example, the addition product of two moles of sec-butyllithium and 1 mole of 1,3-diisopropenylbenzene. Such dilithium compounds are typically characterized by strong aggregation phenomena, which results in low solubility in systems consisting only of saturated hydrocarbon solvents and leads to the precipitation of three-dimensionally cross-linked species. Such initiator systems result in undesirably broad molecular weight distributions (J. Hofmans, M. van Beylen, Polymer 46 (2005) 303-318).

[0010] Another possibility for producing a, co-functionalized rubbers by means of anionically initiated polymerization is to use 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, have tertiary amine, ether or siloxy groups, whereas hydroxyl, carboxyl, carbonyl and primary amine groups are not suitable. Due to their thermal stability, initiators that are functionalized with tertiary amine groups are particularly suitable for industrial use.

[0011] A well-known amino-functionalized initiator is dimethylaminopropyllithium (DMAPLi), which can be prepared from dimethylaminopropyl chloride and lithium powder (N.S. Davidson et al., Macromolecules 21, 1, 1988). However, DMAPLi is almost insoluble in hexane, as described, for example, by Stewart et al. (British Polymer Journal 22 (1990) 319-325). In US 5,527,753 A, the solubility of DMAPLi and various other amino-functionalized propyllithium compounds in aliphatic and cycloaliphatic solvents, such as hexane, is reported to be equal or less than 0.3 M for the group of amino-functionalized initiators (see Table in experimental section of US 5,527,753). Due to this very low solubility, the transportation of such solutions in particular has been considered very cost-intensive to date. A higher concentration of the initiator in the solution can also be advantageous for the intended use in polymerization reactions. US 5,550,203 A describes the improvement of solubility through so-called "seeding technology". In this process, a certain amount of diene monomers, e.g. isoprene, is added to the synthesis solution. A DMAPLi solution chain-extended in this way with 2 moles of isoprene can be obtained with a higher concentration of 1.36 M (US 5,527,753, Example 1).

[0012] However, one disadvantage of such diene chain-extended DMAPLi solutions is their lack of configurational stability. They do not have a defined structure, but form di- and polylithiated initiationactive compounds through intermolecular exchange reactions. These multiply lithiated molecules lead to living polymers with two or more C-Li bonds. This in turn leads to poorly defined, hyperbranched polymer structures and undesirable gel formation during subsequent polymer processing using coupling reagents.

[0013] A method to improve the stability of functionalized organolithium initiators has been described in US 2003 / 0114611 Al. This document teaches to use a functionalized alkyllithium composition having enhanced thermal stability, comprising: at least one functionalized alkyllithium compound; and at least one organometallic compound capable of forming an ate complex with said alkyllithium compound in an amount sufficient to impart thermal stability to the composition without significantly inhibiting the reactivity of the alkyllithium species. This ate-forming compound typically is a dialkylmagnesium compound like dibutylmagnesium. However, it is known from the art that using bimetallic initiators will have a significant and undesired impact on polymer synthesis, see H. L. Hsieh and R. P. Quirk, Anionic Polymerization, Marcel Dekker, Inc. , NewYork, 1996, pp 143-146 . For example, addition of increasing amounts of dibutylmagnesium to a constant amount of sec-butyllithium in cyclohexane was reported to reduce the rate of styrene or butadiene polymerization and decrease molecular weight without significantly broadening molecular weight distribution or changing the polybutadiene microstructure.

[0014] U.S. Patent US 9,085,653 B2 describes the preparation of telechelic diene polymers using amine- functionalized initiators. An example of these initiators is a structure of the formula R1R2NR3Li, wherein R1and R2may independently be alkyl groups having from 1 to 12 carbon atoms and optionally form a cyclic structure. R3can be an alkylene group with 1 to 20 carbon atoms, among other things. This initiator is prepared in three steps. In the first step, a secondary amine of the formula R3R2NH is reacted with an organolithium compound R3Li to form a lithium amide compound of the formula R1R2NLi according to the reaction [1] shown below.

[0015] This lithium amide compound is then reacted in the second step according to reaction [2] with an alkyl dihalide of the formula XR4X', where X and X' are different halogens from the group consisting of I, Br and Cl, to give the halogen compound R1R2NR4X'.

[0016] By reacting with 2 equivalents of another organolithium compound of the formula R5Li, the initiator of the type R1R2NR4Li is finally obtained in the third step according to reaction [3] in a mixture with the Wurtz coupling product R5R5and LiX'

[0017] Production takes place in a hydrocarbon solvent, whereby a polar compound can be added to accelerate the production of the lithium compound and to achieve a solubilization effect to improve solubility in the hydrocarbon solvent. Examples of suitable polar compounds are tertiary monoamines, tertiary diamines and open and cyclic ethers, such as tetra hydrofuran (THF).

[0018] Examples 3 and 4 of US 9,085,653 B2 describe the preparation of the initiators 3-(dibutylamino)propyl lithium and 3-(hexamethyleneimino)propyl lithium. In both examples, the secondary amine starting materials were lithiated using n-butyl lithium in a solvent mixture of THF and hexane. In the next step, they were mixed with l-chloro-3-bromopropane at a temperature of -25°C and then stirred at 0°C for 1 hour. They were then cooled again to -25°C and a solution of tert-butyllithium in pentane was added to form 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.

[0019] Solutions of organolithium compounds in donor solvents, like ethereal solvents, are unstable and decompose rapidly to form ethylene and lithiated acetaldehyde enolate (T.L. 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, in particular due to the pyrophoricity of tert-butyllithium, and additionally due to the high cost of tert-butyllithium for commercial reasons. It is also to be expected that contamination of the product solutions by by-products cannot be avoided. In addition to the cleavage products of THF, these include the Wurtz coupling products of the reaction between the haloalkane R5X' formed intermediately by halogen / metal exchange and the lithium alkyl R5Li, i.e. R5R5, in the third step of the synthesis. The THF cannot be removed from the finished reaction solutions without complete decomposition of the prepared initiator. Problem

[0020] Accordingly, the problem underlying the present invention is to provide improved solutions of dialkylaminoalkyllithium initiators. An essential aspect of the improvement is that the solutions should have high initiator concentrations. An additional aspect of the improvement may be a particularly high storage stability of the solutions. Furthermore, a cost-effective and safe process for producing the dialkylaminoalkyllithium initiators is to be provided.

[0021] Solution to the problem

[0022] The underlying problem is solved by the dialkylaminoalkyllithium initiator solutions according to claims 1 to 7 and the process 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.

[0023] The dialkylaminoalkyllithium initiator solution according to the invention is characterized in that it contains a dialkylaminoalkyllithium initiator of the formula (I) in a hydrocarbon solvent,

[0024] RR'N(CH2)nLi (I), wherein

[0025] R and R' are independently of one another alkyl groups having up to 12 carbon atoms, preferably 2 to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least 8, and n = 2 to 10, and wherein the concentration of the dialkylaminoalkyllithium initiator is at least 0.3 mol / L at room temperature.

[0026] It was surprisingly found that solutions of dialkylaminoalkyllithium initiators with concentrations above 0.3 mol / L, such as 0.5 mol / L and higher, can be prepared. These highly concentrated solutions can significantly reduce transport costs and also offer advantages in their intended use as polymerization initiators. The initiator concentration in the solutions according to the invention is thus high enough so that the "seeding" known from US 5,550,203 is not necessary. The initiator solutions produced by the method according to the invention have well-defined compositions and thus also reproducible application properties. This is in contrast to the initiators produced using the "seeding technology", which have a statistically determined ratio of "seeding agent" to initiator and a correspondingly undefined composition with a large number of isomeric components and unsaturated C-C bonds. Moreover, such compounds are not stable in configuration, but can change during storage under lithium transfer. This has a detrimental effect on the properties of the elastomers produced with them. 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 at room temperature.

[0027] 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 at room temperature.

[0028] As used herein, the term "room temperature" refers to a temperature in the range of from 20°C to 25°C, and preferably to a temperature of 20°C.

[0029] The solution according to the invention is particularly characterized in that the dialkylaminoalkyllithium initiator is in the form of a homogenous solution having a concentration as specified herein. In other words, the solution according to the invention is a homogenous solution wherein the dialkylaminoalkyllithium initiator is evenly distributed in dissolved form throughout the hydrocarbon solvent.

[0030] Furthermore, it was surprisingly found that the solution according to the invention is stable towards crystallization at room temperature. Even more surprisingly, it was found that the solution according to the invention does not crystallize at low temperatures like 0°C. Accordingly, the solution according to the invention is particularly characterized in that it has not only a high concentration, but also a high enduring stability, i.e. the high concentration of homogeneous solution is maintained during storage, as will be further discussed below.

[0031] It is further preferred that the hydrocarbon solvent contains at most 0.05% by weight of 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" relates to solvents which, due to their molecular structure, are capable of providing electron pairs. Such donor solvents are in particular ethers, amines, alcohols and carbonyl compounds.

[0032] In a preferred embodiment, the hydrocarbon solvent contains, based on the total weight of the solution, at most 0.05% by weight of ethereal solvents and in particular at most 0.05% by weight of THF. In particular, the hydrocarbon solvent is substantially free of ethereal solvents and in particular substantially free of THF.

[0033] In a preferred embodiment, the hydrocarbon solvent of the dialkylaminoalkyllithium initiator solution comprises one or more hydrocarbons having a boiling point in the range of 35 to 250°C. It is preferred that the hydrocarbon solvent comprises one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons having 5 to 12 carbon atoms and aromatic hydrocarbons having 6 to 14 carbon atoms, and in particular consists thereof.

[0034] It is further preferred that the hydrocarbon solvent comprises one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons having 6 to 8 carbon atoms, toluene, ethylbenzene, cumene and xylenes, and in particular consists thereof. Particularly preferably, the hydrocarbon solvent consists of one or more hydrocarbons selected from the group consisting of hexanes and heptanes, may they be aliphatic or cycloaliphatic.

[0035] The solution according to the invention contains a dialkylaminoalkyllithium initiator of the Formula (I), RR'N(CH2)nLi (I), wherein

[0036] R and R' are independently of one another alkyl groups having up to 12 carbon atoms, preferably 2 to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least 8, and n = 2 to 10.

[0037] Preferably, 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 R and R' is at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least 8. In particular, at least one of the radicals R and R' has 4 to 12 carbon atoms. Particularly preferably, R and R' each have 4 to 12 carbon atoms.

[0038] 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 particularly preferably R and R' are both butyl.

[0039] In a particularly preferred embodiment, the dialkylamino group RR'N- of the initiator is selected from the group consisting of ethylbutylamino-, dipropylamino-, dibutylamino-, dihexylamino-, and dioctylamino-. Particularly preferred the dialkylamino group RR'N- of the initiator is dibutylamino-.

[0040] The dialkylaminoalkyllithium initiator in the solution according to the invention has a structure of Formula (I), wherein preferably n=3 to 6.

[0041] In another particularly preferred embodiment, the dialkylaminoalkyllithium initiator in the solution according to the invention is selected from the group consisting of 3-(ethyl-butylamino)propyllithium, 3-(dipropylamino)propyllithium, 3-(dibutylamino)propyllithium, 3-(dihexylamino)propyllithium; 4- (ethylbutylamino)butyllithium, 4-(dipropylamino)butyllithium, 4-(dibutylamino)butyllithium, 5- (dihexylamino)butyllithium, and 6-(dibutylamino)hexyllithium,. Of these dialkylaminoalkyl lithium initiators, 3-(dibutylamino)propyllithium is particularly preferred.

[0042] The dialkylaminoalkyllithium initiator solution according to the invention is characterized by a particularly high storage stability. Preferably, the dialkylaminoalkyl lithium initiator solution is characterized in that the content of dialkylaminoalkyl lithium 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%, further preferably at least 90%, particularly preferably at least 95% of the content before the start of storage.

[0043] 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 particularly preferably at least 95 mol%, relative to the total amount of organolithium species, including those which might be formed by decomposition or isomerization of the target initiator molecule.

[0044] In particular, it was found that the high initiator concentration according to the invention as well as the advantageous high storage stability according to the invention could be achieved without the need for an organometallic additive as described in US 2003 / 0096952 Al or US 2003 / 0114611 Al. Thus, the disadvantages associated with such organometallic additives, as discussed above, can be avoided. Accordingly, in a preferred embodiment, the dialkylaminoalkyllithium initiator solution according to the present invention comprises less than 0.1 mol %, more preferably less than 0.05 or 0.01 mol%, of metals of Group IIA, Group II B, or Group I II B of the Periodic Table of Elements, relative to the total amount of lithium and Group IIA, Group 11 B, and Group 111 B metals, and more preferably is substantially free of metals of Group IIA, Group 11 B, or Group 111 B of the Periodic Table of Elements.

[0045] In a second aspect, the invention is directed to a process for preparing the dialkylaminoalkyllithium initiators contained in the solutions described above.

[0046] This process according to the invention for the preparation of a dialkylaminoalkyllithium initiator of the Formula (I)

[0047] RR'N(CH2)nLi (I), wherein

[0048] R and R' are independently of one another alkyl groups having up to 12 carbon atoms, preferably 2 to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least n = 2 to 10, is characterized in that

[0049] (a) an aminohaloalkane of formula (II),

[0050] RR'N(CH2)nHal (II) wherein

[0051] Hal is selected from Cl, Br and I and preferably from Cl and Br;

[0052] R and R' are independently of one another alkyl groups having up to 12 carbon atoms, preferably 2 to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least 8, and n = 2 to 10, is converted in a hydrocarbon solvent under inert conditions with elemental lithium to yield a dialkylaminoalkyllithium initiator of Formula (I), wherein the quantitative ratio of aminohaloalkanedithium is from 1:2 to 1:5.4, preferably from 1:2.2 to 1:5 or from 1:2.2 to 1:4, to obtain a solution of the dialkylaminoalkyllithium initiator of formula (I) in the hydrocarbon solvent, and

[0053] (b) any solids present are separated by a solid / liquid separation operation.

[0054] 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.

[0055] It was surprisingly found that dialkylaminoalkyllithium initiators present in high concentrations in a hydrocarbon solution can be produced by the process according to the invention pursuant to reaction [4] under the conditions defined in the process.

[0056] 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' are independently alkyl groups having 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. In the process according to the invention, an aminohaloalkane of Formula (II) is therefore converted in step (a),

[0057] RR'N(CH2)nHal (II) wherein

[0058] Hal is selected from Cl, Br and I and is preferably selected from Cl and Br;

[0059] R and R' are independently of one another alkyl groups having up to 12 carbon atoms, preferably 2 to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, preferably at least 6, in particular at least 7 and particularly preferably at least 8, and n = 2 to 10, with elemental lithium to form a dialkylaminoalkyllithium initiator of Formula (I).

[0060] Preferably, at least one of the radicals R and R' in the aminohaloalkane of formula (II) has 4 to 12 carbon atoms. Particularly preferably, R and R' each have 4 to 12 carbon atoms.

[0061] 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 particularly preferably R and R' are both butyl.

[0062] 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-, and dioctylamino-.

[0063] The aminohaloalkane has a structure of Formula (II), wherein preferably n is 3 to 6.

[0064] In the process according to the invention for the preparation of a dialkylaminoalkyllithium initiator of the Formula (I), it is particularly preferred that an aminohaloalkane of the Formula (II),

[0065] RR'N(CH2)nHal (II) wherein

[0066] Hal is Cl and / or

[0067] R and R' are independently of each other 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).

[0068] Particularly preferably, an aminohaloalkane of Formula (II), RR'N(CH2)nHal CD wherein

[0069] Hal Cl is

[0070] R and R' are independently alkyl groups having 3 to 6 carbon atoms and n = 3 to 6, is reacted with elemental lithium to form a dialkylaminoalkyllithium initiator of formula (I).

[0071] In another 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, and 6- (dibutylamino)hexyl chloride,.

[0072] The hydrocarbon solvent used in step (a) preferably contains, based on the total weight of the solution, not more than 0.05% by weight of donor solvent and in particular is substantially free of donor solvents.

[0073] In a further preferred embodiment, the hydrocarbon solvent used in step (a) contains at most 0.05% by weight of ethereal solvents. In particular, the hydrocarbon solvent is substantially free of ethereal solvents.

[0074] In a preferred embodiment, the hydrocarbon solvent used in step (a) comprises one or more hydrocarbons having a boiling point in the range of 35 to 250°C. It is further preferred that the hydrocarbon solvent comprises one or more hydrocarbons having a boiling point in the range of 35 to 250°C.

[0075] It is preferred that the hydrocarbon solvent used in step (a) comprises one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons having 5 to 12 carbon atoms and aromatic hydrocarbons having 6 to 14 carbon atoms, and in particular consists thereof.

[0076] It is further preferred that the hydrocarbon solvent used in step (a) comprises one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons having 6 to 8 carbon atoms, toluene, ethylbenzene, cumene and xylenes, and in particular consists thereof. Particularly preferably, the hydrocarbon solvent comprises one or more hydrocarbons selected from the group consisting of hexanes and heptanes, including aliphatic or cycloaliphatic hexanes and heptanes.

[0077] Step (a) of the process according to the invention comprises reacting an aminohaloalkane of Formula (II) with elemental lithium.

[0078] The reaction takes place "under inert conditions", which in the context of the present invention means that the reaction takes place in an environment in which the presence of ambient air and moisture, in particular oxygen, water and water vapor, is largely and preferably substantially completely prevented by measures normally 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 that are sealed off from the environment. Corresponding measures for ensuring inert conditions during the synthesis of organolithium compounds are generally known to the skilled person (BJ. Wakefield: The Chemistry of Organolithium Compounds, Pergamon Press, Oxford 1974).

[0079] The elemental lithium used in step (a) is preferably present in particulate form. It is preferred that these lithium particles have an average size in the range from 1 pm 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 may be lithium metal impressions such as granules. In another particularly preferred embodiment, the lithium particles are powder particles with an average size of less than 100 pm. The specification of the particle sizes relates to the volume-based average particle size D5o, whereby 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 dispersant.

[0080] The shape of the lithium particles is preferably spherical or angular, such as cuboidal or prismatic.

[0081] It is further preferred that the elemental lithium has a sodium content of at least 0.1% by weight, in particular at least 0.3% by weight and particularly preferably at least 0.5% by weight based on the total weight of the elemental lithium. Furthermore, it is preferred that the elemental lithium has a sodium content of less than 10% by weight and in particular less than 5% by weight, 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% by weight, in particular 0.5 to 5% by weight, based on the total weight of the elemental lithium.

[0082] The reaction of the aminohaloalkane of Formula (II) with the elemental lithium in step (a) of the process according to the invention is preferably carried out at a temperature of 0 to 110°C and in particular at 10 to 80°C.

[0083] In a further preferred embodiment, the reaction in step (a) of the process is carried out under boiling conditions.

[0084] It is further preferred that the reaction of the aminohaloalkane of Formula (II) in step (a) is carried out at a pressure which is reduced relative to atmospheric pressure and in particular at a pressure of from 50 to 900 mbar.

[0085] 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. The solids may be, for example, lithium halides formed as a by-product of the reaction and / or excess elemental lithium. The solid / liquid separation operation is preferably a filtration, sedimentation or centrifugation and in particular a filtration.

[0086] After the reaction of step (a), the concentration of the dialkylaminoalkyllithium initiator in the solution at room temperature is preferably at least 0.3 mol / L, in particular 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.

[0087] 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 at room temperature.

[0088] In a further aspect, the invention relates to a process for preparing the dialkylaminoalkyl lithium initiator solution according to the first aspect of the invention, wherein the process is carried out in accordance with the process described in the second aspect of the invention.

[0089] 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 preparing a dialkylaminoalkyl lithium initiator of the Formula (I) are also suitable or preferred accordingly for the process according to the invention for preparing a solution of a dialkylaminoalkyl lithium initiator of the Formula (I).

[0090] 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.

[0091] The embodiments described as suitable and preferred in connection with the above process according to the invention for preparing a dialkylaminoalkyllithium initiator of the formula (I) are also correspondingly suitable or preferred for the solution of a dialkylaminoalkyllithium initiator of the formula (I) obtainable by the process.

[0092] 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.

[0093] In the manufacture 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 used in order to improve the interactions between polymer chain ends and the fillers used in the manufacture of the polymer, especially a synthetic rubber. Preferred fillers are silica particles.

[0094] In a preferred embodiment, the adhesion promoters are functionalized silanes. Such silane adhesion promoters are bifunctional compounds that have two functionally active end groups. The first end group is an alkoxy group, which is preferably easily hydrolysable. The alkoxy group can react with the silanol groups on the silica surface to form stable siloxane bonds (-Si-O-polymer- bonds). The second end group is a non-polar organofunctional group, which is therefore compatible with the likewise nonpolar rubber molecules. In order to be able to participate in the sulphur vulcanization that usually takes place during a further process step of rubber production, the non-polar organofunctional group of the adhesion promoter preferably has unsaturated carbon-carbon bonds. This enables it to form covalent sulphide groups with the polymer chains.

[0095] The silane coupling agent can thus act as a connecting element or "bridge" between silica and rubber in order to strengthen the rubber-filler interaction and thereby achieve a further improvement in properties. Particularly preferred coupling agents 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).

[0096] Furthermore, in the use according to the invention for the production of synthetic rubbers, elastomers and liquid rubbers, coupling agents can be used to couple polydiene rubbers. During coupling, polymer chains are linked together, preferably to produce branched, in particular 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.

[0097] In a further aspect, the invention is directed to processes for the preparation of synthetic elastomers and liquid rubbers in which 1,3-dienes or aryl-substituted olefins are polymerized using dialkylaminoalkyllithium initiator solutions according to the invention.

[0098] The embodiments described as suitable and preferred in connection with the above use of the dialkylaminoalkyllithium initiator solution according to the invention in the anionic polymerization of 1,3-dienes and aryl-substituted olefins are also correspondingly suitable or preferred for the process according to the invention for the production of synthetic elastomers and liquid rubbers.

[0099] The object of the invention is explained below by means of examples and comparative examples. Examples

[0100] Example 1: Preparation of a 3-(dibutylamino)propyllithium (DBAPLi) solution

[0101] In an inertized, i.e. dry and argon-filled 2 L double-jacketed reactor with internal thermometer, reflux condenser and mechanical stirrer, 986 g hexane and 42.3 g (6.08 mol) lithium powder (particle size < 100 pm) were added. The mixture was heated to 50 °C and then N,N-dibutylamino-3-chloropropane (313 g, 1.52 mol) was added continuously over a period of two hours. Thus, the quantitative ratio of aminohaloalkane to lithium was 1:4. The internal temperature of the reactor was kept in the temperature range between 50 and 55°C.

[0102] After the complete addition of the N,N-dibutylamino-3-chloropropane, the reaction mixture was stirred at a jacket temperature of 50 °C for a further hour and then cooled to room temperature. It was then placed on a glass frit 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 hexane each time and the filtrates were combined. Since only hexane was used as the solvent, the solution prepared did not contain any donor solvent.

[0103] Balance: 1,280 g of a clear, light yellow solution, density = 0.68 g / mL

[0104] The active base content, determined by thermometric titration (titration solution is a 1-molar solution of sec-butanol in dry xylene), was 1.13 mol / kg or 0.775 mol / L (corresponding to 20.2 wt.% DBAPLi). The titration was carried out with a thermometric titrator type 859 Titrotherm (Metrohm) with the temperature probe "Thermoprobe".

[0105] Yield: 95.2 % of the theory

[0106] Example 2: Storage stability of the DBAPLi solution from Example 1

[0107] A solution of the DBAPLi solution from Example 1 diluted with hexane to 17 wt.% active base content was placed in gas chromatography vials inerted by evacuation and filling with argon and stored at 40°C. To investigate the storage stability, the active base content of the samples was determined by thermometry, as described in Example 1, at the times indicated in Table 1: Table 1:

[0108] Assuming 1st order kinetics, a product decomposition rate of 0.16 % per day is calculated from the time course of the active base content.

[0109] In a further experiment, a 22.6 wt.% solution of the DBAPLi solution was stored in airtight inert glass bottles at room temperature. As can be seen, after 6 months, no significant loss of the active base content was observed. The variation of values indicated in Table 2 reflects the accuracy of measurement, i.e. deviations are within the accuracy limit of detection

[0110] Table 2:

[0111] Comparative Example 1: Preparation of 3-(dibutylamino)propyllithium according to the process described in US 9,085,653 Bl (example 3) without using a donor solvent

[0112] In a 0.5 L double-jacketed reactor inerted by evacuation and filling with argon, 85.5 g of N,N- dibutylamino-3-chloropropane (415 mMol, 1.0 eq.) was introduced at room temperature (20°C). At this temperature, 295.5 g of an 18.0 % solution of tert-butyllithium in hexane (830 mMol, 2.0 eq.) was added within 30 minutes. After complete addition, the solution was stirred for a further 16 hours at room temperature. The solution was transferred through a tube to a glass frit using argon overpressure and filtered to remove any LiCI formed. The filter residue was washed with 30 mL hexane and the filtrates were combined. A pale yellow, clear product solution was obtained.

[0113] Balance: 312 g pale yellow, clear product solution

[0114] The active base content was determined by thermometric titration as described in Example 1. 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)

[0115] GC / MS measurements, however, showed that the measured active base content is not only due to the desired product DBAPLi, but that a mixture of various organolithium compounds is present. In addition to about 47 mol% DBAPLi, 34 mol% unchanged tert-butyllithium and about 19 mol% other components were identified. In preparation for the analytical measurements, an aliquot of the filtrate was derivatized with diphenyl disulfide (DPDS) and the relative contents of the thioethers of tert- butyllithium, DBAPLi and other components were then determined. The yield of the desired product DBAPLi was only about 34 %. Due to the presence of other organolithium species such a solution is not suitable for the desired applications described herein.

[0116] To investigate the storage stability, the product solution was stored for 48 h at room temperature. It was observed that the solution became cloudy. A sample of the solution was taken and filtered. The active base content, determined according to the method described in example 1, had fallen to 0.62 mMol / g. The solution is therefore not storage-stable at room temperature, but decomposes at a rate of approx. 16% per day.

[0117] Comparative Example 2: Preparation of 3-(dibutylamino)propyllithium according to the process described in US9,085,653 Bl (example 3) using a donor solvent

[0118] A mixture of N,N-dibutylamino-3-chloropropane (85.5 g, 415 mMol, 1.0 eq.) and tetrahydrofuran (THF, 59.9 g, 830 mMol, 2.0 eq.) was placed in an inertized 0.5 L double-jacketed reactor and cooled to -25 °C. At this temperature, 295.5 g of an 18.0 % solution of tert-butyllithium in hexane (830 mMol, 2.0 eq.) was added within 30 minutes. After complete addition, the solution was slowly warmed to room temperature and stirred for a further 16 hours. The solution was transferred through a tube to a glass frit using positive argon pressure and filtered to remove any LiCI formed. A pale yellow, clear product solution was obtained.

[0119] Balance: 359 g pale yellow, initially clear solution

[0120] The active base content, determined by thermometric titration according to the method 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% by weight. In contrast, the theoretical product concentration is 1.10 mMol / g (19.6 wt.%).

[0121] The isolated yield is calculated as 280 / 415*100 = 67 % of the total.

[0122] The initially clear filtrate exhibited a significant turbidity after just one day of storage at room temperature. The active base content after one day's storage, determined by thermometric titration using the method described for Example 1, had fallen to 0.45 mol / kg (equivalent to 8.0% by weight). This results in a product decomposition rate of 42% per day at room temperature. Summary of the results of the examples

[0123] A comparison of Examples 1 and 2 according to the invention with Comparative Examples 1 and 2 reveals the advantages of the method 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 BujNfCHjJaCI and a donor-free solvent (hexane), the desired organolithium compound can be prepared with a high yield of about 95% of the theory in the form of a 20% solution. This solution is very stable in storage. It can be stored under suitable storage conditions (such as room temperature or below) over a long period of time, 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.

[0124] In contrast, the processes described in US9,085,653 Bl are not suitable for providing a concentrated, storage-stable product solution.

[0125] When using a donor-free solvent (hexane, Comparative Example 1), a relatively high active base concentration is obtained, but this is only partially (about 50%) due to the desired product. The other half is formed by unreacted tert-butyl lithium and other decomposition products. The yield of the desired product DBAPLi in the fresh product solution is only about 34% of the theory. 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.

[0126] Even when using a donor-containing solvent (THF), it was not possible to obtain solutions with the advantageous properties of the solutions according to the invention. When using 2 equivalents of THF, an improved product yield was observed in the fresh filtrate (13.8% by weight), corresponding to 71% of the theoretical value. However, this solution was not stable. Turbidity was observed after a short time. After one day of storage at room temperature, the active base content was already reduced by 42 %, which corresponded to a DBAPLi content of only 8.0 wt.% DBAPLi. This has to be expected as solutions of organolithium compounds are not stable in THF or THF-containing solvent blends.

Claims

Claims:

1. A dialkylaminoalkyllithium initiator solution comprising a dialkylaminoalkyllithium initiator of Formula (I) in a hydrocarbon solvent,RR'N(CH2)nLi (I), whereinR and R' are independently from each other alkyl groups having up to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, and n = 2 to 10, characterized in that the concentration of the dialkylaminoalkyllithium initiator is at least 0.3 mol / L at room temperature.

2. The dialkylaminoalkyllithium initiator solution according to claim 1, characterized in that the hydrocarbon solvent contains, based on the total weight of the solution, at most 0.05% by weight of donor solvent and preferably essentially no donor solvent.

3. The dialkylaminoalkyllithium initiator solution according to claim 1 or 2, characterized in that the hydrocarbon solvent comprises one or more hydrocarbons selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons having 5 to 12 carbon atoms and aromatic hydrocarbons having 6 to 14 carbon atoms, and preferably selected from the group consisting of aliphatic and cycloaliphatic hydrocarbons having 6 to 8 carbon atoms, toluene, ethylbenzene, cumene and xylenes.

4. The dialkylaminoalkyl lithium initiator solution according to any one of claims 1 to 3, characterized in that R and R' together form an alkylene group having 4 to 6 CH2groups 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 more preferably are both butyl.

5. The dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 4, characterized in that n = 3 to 6 and more preferably n = 3.

6. The dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 5, characterized in that the concentration of the dialkylaminoalkyllithium initiator at room temperature is at least 0.4 mol / L, preferably at least 0.5 mol / L, in particular at least 0.6 mol / L and particularly preferably at least 0.7 mol / L.

7. The dialkylaminoalkyllithium initiator solution according to one of claims 1 to 6, 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%, preferably at least 80%, in particular at least 90% of the content before the start of storage.

8. A process for the preparation of a dialkylaminoalkyllithium initiator of Formula (I)RR'N(CH2)nLi (I), whereinR and R' are independently alkyl groups having up to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, and n = 2 to 10, characterized in that(a) an aminohaloalkane of Formula (II),RR'N(CH2)nHal (II) whereinHal is selected from Cl, Br and I;R and R' are independently from each other alkyl groups having up to 12 carbon atoms, the sum of the carbon atoms of the alkyl groups R and R' being at least 5, and n = 2 to 10, is reacted in a hydrocarbon solvent under inert conditions with elemental lithium to give a dialkylaminoalkyllithium initiator of Formula (I), wherein the quantitative ratio of aminohaloalkanedithium is from 1:2 to 1:5.4, preferably from 1:2.2 to 1:5 or from 1:2.2 to 1:4, to obtain a solution of the dialkylaminoalkyllithium initiator of Formula (I) in the hydrocarbon solvent, and(b) optionally any solids present are removed by a solid / liquid separation operation.

9. The process according to claim 8, characterized in that the concentration of the dialkylaminoalkyllithium initiator in the solution after the reaction in step (a) is at least 0.3 mol / L at room temperature, preferably at least 0.4 mol / L at room temperature, in particular at least 0.5 mol / L at room temperature and particularly preferably at least 0.6 mol / L at room temperature.

10. The process according to claim 8 or 9, characterized in 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. The process according to any one of claims 8 to 10, in which the reaction of the aminohaloalkane of Formula (II) with the elemental lithium is carried out under boiling conditions, the pressure preferably being reduced relative to atmospheric pressure and in particular the pressure being from 50 to 900 mbar.

12. The process according to one of claims 8 to 11, characterized in that in the dialkylaminoalkane of Formula (II)Hal is Cl, and / orR and R' are independently from each other alkyl groups with 3 to 6 carbon atoms and / or n = 3 to 6, and preferablyHal is Cl,R and R' are both butyl, and n=3.

13. The process according to one of claims 8 to 12, characterized in that the hydrocarbon-containing solvent contains at least one saturated aliphatic or cycloaliphatic compound having 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 7 in the anionic polymerization of 1,3-dienes and aryl-substituted olefins for the production of synthetic elastomers and liquid rubbers.

15. A process for the preparation of synthetic elastomers and liquid rubbers comprising polymerization of 1,3-dienes or aryl-substituted olefins using a dialkylaminoalkyllithium initiator solution according to any one of claims 1 to 7.

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