Method for preparing organosiloxanes carrying higher molecular triorganylsilyl groups and having a low content of cyclosiloxanes

Abstract

The present invention relates to a method for preparing organosiloxanes (A) carrying SiR3 groups, wherein the radicals R are each independently selected from organic radicals, comprising the steps of: (i) reacting at least a portion of at least one silanol group-carrying organosiloxane (B) with at least one SiR3 group transfer agent (C) such that a portion of the silanol groups is converted into SiOSiR3 groups; (ii) condensing a portion of the silanol groups not reacted in step (i) with the elimination of water. The invention also relates to the correspondingly prepared SiR3 group-carrying organosiloxanes (A).

Description

[0001] Method for the production of higher molecular weight organosiloxanes bearing triorganylsilyl groups with a low cyclosiloxane content

[0002] The present invention relates to the production of organosiloxanes bearing higher molecular weight triorganylsilyl groups, in particular α,co-divinyl polydiorganylsiloxanes and α,co-dimethyl polydiorganylsiloxanes, which have a low cyclosiloxane content. The particular focus is on the production of α,co-divinyl polydimethylsiloxanes and α,co-dimethyl polydimethylsiloxanes which, in addition to a low cyclosiloxane content, also exhibit high viscosity.

[0003] In general, higher molecular weight polydiorganylsiloxanes are prepared by polymerization of lower molecular weight cyclosiloxanes or α,co-dihydroxy-polydiorganylsiloxanes using an acidic or basic catalyst. Sodium hydroxide, potassium hydroxide, and tetraalkylammonium hydroxide are typically used as basic catalysts, while hydrochloric acid and sulfuric acid are frequently used as acidic catalysts.

[0004] During polymerization using the aforementioned catalysts, equilibration typically occurs. An equilibrium is established between cyclosiloxanes, low-molecular-weight polydiorganylsiloxanes, and the desired higher-molecular-weight polydiorganylsiloxane. Thus, during polymerization, not only are the siloxane bonds of the cyclosiloxanes broken and / or higher-molecular-weight polydiorganylsiloxanes formed via low-molecular-weight polydiorganylsiloxanes, but siloxane bonds of the higher-molecular-weight polydiorganylsiloxane are also broken, resulting in the formation of cyclosiloxanes and low-molecular-weight polydiorganylsiloxanes. These low-molecular-weight compounds are now undesirable as residual components in the higher-molecular-weight polydiorganylsiloxane.Therefore, low-molecular-weight residual components in higher-molecular-weight organosiloxanes are usually removed by suitable separation methods, for example, using a thin-film evaporator. However, such methods have the disadvantage that an additional separation and purification step is required. An alternative approach is to suppress equilibration as much as possible during the production of the higher-molecular-weight polydiorganylsiloxanes in order to reduce the formation of low-molecular-weight components. Processes for the polycondensation of silanol-bearing, low-molecular-weight polydiorganylsiloxanes, or alternatively for the ring-opening polymerization of cyclosiloxanes in which equilibration is not catalyzed, are known from the prior art.

[0005] EP0693520A1 discloses a process for the production of organopolysiloxanes containing small amounts of a low molecular weight organosiloxane. In this process, a cyclic trisiloxane is polymerized with a specific lithium compound (a lithium silanolate) as a polymerization initiator in the presence of a nitrile compound. Specifically, the examples used either dilithiated diphenylsilanediol or, alternatively, the reaction product of an α,co-dihydroxyoligodimethylsiloxane and n-butyllithium as the lithium compound. Acetonitrile is used as the nitrile compound. It is further described that the lithium compounds used are intended to enable the non-equilibration polymerization of cyclic trisiloxane, and that the nitrile compound significantly inhibits the formation of low molecular weight organosiloxanes.The resulting higher molecular weight polydimethylsiloxanes exhibit a maximum dimethylsiloxane content of 742 ppm with a degree of polymerization of up to 25. If acetonitrile is omitted, the content increases to 2491 ppm. Further reactions of the silanol groups of the higher molecular weight α,co-dihydroxy-polydimethylsiloxanes are not described.

[0006] EP1020486A1 describes a process for the condensation of silanol-containing compounds using basic catalyst systems. The catalyst system comprises a catalyst selected from basic alkali and alkaline earth metal compounds and a specific chelating ligand as a cocatalyst. The examples include the reaction of a mixture of an α,co-OH-terminated siloxane and a trimethylsilyl-terminated siloxane with lithium hydroxide as the catalyst and diethylenetriamine as the cocatalyst. A bimodal molar mass distribution is observed, attributable on the one hand to the polycondensation product of the α,co-OH-terminated siloxane and on the other hand to the unreacted trimethylsilyl-terminated siloxane. It is described that the catalyst system used does not act as an equilibrator and that no octamethylcyclotrasiloxane (D4) is formed in the reaction.It is further revealed that without a cocatalyst, a multimodal distribution of low-molecular-weight organosiloxanes is observed and that a high molar mass is not achieved during polycondensation with LiOH. Further conversion of silanol groups after condensation is not described here either.

[0007] The aforementioned publications deal with the reduction of the residual content of cyclosiloxanes in the production of simple α,co-dihydroxy-polydimethylsiloxanes.

[0008] However, many applications require organosiloxanes with terminations other than silanol groups. Of particular importance are reactive, unsaturated organosiloxanes, especially those with alkenyl groups, such as vinyl groups. It is known to synthesize alkenyl groups by reacting silanol-functionalized organosiloxanes with alkenyl group transfer agents.

[0009] CN106065073A, for example, discloses a process for producing a vinyl silicone resin in which a compound bearing SiOH groups is first reacted with 1,3-divinyl-1,1,3,3-tetramethyldisiloxane in a solvent under heating, followed by a separation and purification step to obtain the vinyl silicone resin. The separation and purification are preferably carried out using a rotary evaporator at 120°C to 200°C and a vacuum of 10 mbar or less. Low-molecular-weight components such as solvent, silanol, divinyltetramethyldisiloxane, water, ammonia, unreacted silazane, and other small molecules are separated. The cyclosiloxane content is not disclosed. This process has the particular disadvantage that an additional separation and purification step is required.

[0010] JPH10195414A describes a silicone adhesive with components (A), (B), and (C). Component (A) is a reaction product containing alkenyl groups, which is formed by reacting polyorganosiloxanes bearing hydroxyl groups and other compounds with a silazane of formula R. 2 R 3 2SiNHSiR 3 2R 2 is obtained. R is involved. 2 for an alkenyl residue and R 3 for a monovalent hydrocarbon residue. Component (B) is a polyorganohydrogensiloxane with at least three hydrogen atoms bonded to silicon atoms. Component (C) is a platinum catalyst for catalyzing a hydrosilylation reaction between the SiH groups of component (A) and the alkenyl groups of component (B). The aim is not to reduce the cyclosiloxane content. Accordingly, the cyclosiloxane content is not disclosed.

[0011] EP0331753A1 relates to a process for the production of alkenyl-terminated organopolysiloxanes from cyclic trisiloxanes. In this process, an alkali salt of an organosiloxane is first prepared by reacting a corresponding silanol-functionalized organosiloxane with n-butyllithium. Using this alkali salt as a starter, hexamethylcyclotrisiloxane (D3) is then polymerized, and the open end of the intermediate is subsequently reacted further, if desired. The examples describe, among other things, the reaction of Me₂HexSi(OSiMe₂)OH (Hex = Vi(CH₂)₄⁻ with Vi = vinyl) with first n-butyllithium and then hexamethylcyclotrisiloxane (D3) to give Me₂HexSi(OSiMe₂)i₂eOH. The intermediate is then reacted with dimethylvinylchlorosilane to give Me₂HexSi(OSiMe₂)i₂7OSiMe₂Vi. The residual content of cyclosiloxanes is not disclosed.

[0012] However, methods for producing higher molecular weight polydiorganylsiloxanes with unsaturated groups are also known, which specifically aim to keep the residual content of cyclosiloxanes as low as possible.

[0013] CN113698605A, for example, describes a process in which low-molecular-weight components of a polysiloxane are removed using a thin-film evaporator. The proportion of low-molecular-weight components is intended to be less than 100 ppm. The examples specifically disclose the production of a high-purity vinyl silicone oil. First, octamethyltrisiloxane (D4) is reacted with vinylsiloxane and ammonium siliconate as a catalyst under heating. The catalyst is then deactivated by heating to over 150 °C. The product is subsequently purified using a special thin-film evaporator. This process has the particular disadvantage that an additional separation and purification step is required.

[0014] A process for the production of higher molecular weight polydiorganylsiloxanes with unsaturated groups, which specifically aims to keep the residual content of cyclosiloxanes as low as possible without requiring a further separation and purification step, is also known from the prior art.

[0015] JPH06329804A discloses a process for the production of polydiorganylsiloxanes in which, in a first step, an organosiloxane containing hydroxyl groups is polymerized using an acid with a pKa value <3 as a condensation catalyst, and the resulting polycondensation product is subsequently reacted with a compound of the formula RsSiNHSiRs, where R can be the same or different and represents an unsubstituted or substituted monovalent hydrocarbon group, thereby introducing the group R, more precisely the group SiRs, into the molecular chain end. The examples disclose the reaction of a low-viscosity α,co-dihydroxy-polydimethylsiloxane to a higher-viscosity α,co-dihydroxy-polydimethylsiloxane, using C3F7OCF(CF3)CF2OCF(CF3)COOH as the condensation catalyst.The resulting α,co-dihydroxy-polydimethylsiloxane is then reacted with hexamethyldisilazane, i.e., (H3C)3SiNHSi(CH3)2, or alternatively with 1,3-divinyl-1,1,3,3-tetramethyldisilazane, i.e., (H2C=CH)Si(CH3)2NHSi(CH3)2(CH=CH2). The content of cyclosiloxanes D3 to D20 ranges from 1030 ppm to 1100 ppm. This low content is attributed to the choice of catalyst, i.e., the use of an acid with a pKa value <3, as well as to the neutralization of the catalyst after the reaction with the compound of the formula RsSiNHSiRs, and to the substitution of the terminal hydroxy groups by SiRs groups. However, the inventors have now determined that the functionalization with SiRs groups is only partially successful. It is assumed that this is due to the high viscosity of the α,co-dihydroxy-polydimethylsiloxane used in the functionalization. Furthermore, the inventors have found that the cyclosiloxane content can also be higher.Furthermore, this process preferably uses per- and polyfluoroalkyl substances (PFAS). However, PFAS and their degradation products are very persistent in the environment and are therefore also referred to as "perpetual chemicals." Some PFAS are suspected of being carcinogenic. For this reason, the use of PFAS is generally undesirable, if not prohibited.

[0016] The objective was therefore to provide a process for the production of organosiloxanes bearing triorganylsilyl groups (SiRs) that offers advantages over the prior art. In particular, the objective was to provide a process by which organosiloxanes with high viscosity, a low cyclosiloxane content, and a high number of triorganylsilyl groups (SiRs) could be obtained.

[0017] Surprisingly, a method has now been found to solve this problem in which a low molecular weight organosiloxane bearing silanol groups (SiOH) is first reacted with a SiRs group transferor in such a way that only a portion of all available silanol groups are converted into SiOSiRs groups, and subsequently a higher molecular weight organosiloxane bearing triorganylsilyl groups is obtained by condensation of unreacted silanol groups.

[0018] This process has the advantage that higher molecular weight organosiloxanes with a higher average number of triorganylsilyl groups (SiRs) can be obtained. The prior art process, in which a higher molecular weight silanol-bearing organosiloxane is first produced from a low molecular weight silanol-bearing organosiloxane by condensation with dehydration, and this higher molecular weight silanol-bearing organosiloxane is then reacted with a SiRs group transfer agent, leads to poor conversion of the silanol groups. While not bound to any specific theory, it is assumed that this is due to the higher viscosity of the higher molecular weight silanol-bearing organosiloxane.

[0019] A further advantage of the process according to the invention is the low content of cyclosiloxanes in the final product. Without being bound to any theory, it is assumed that this is due to the fact that no equilibration takes place during the synthesis of the higher molecular weight organosiloxane.

[0020] A first object of the invention is therefore a process for the preparation of SiRs-group-bearing organosiloxanes (A), wherein the residues R are each selected independently of one another from organic residues, comprising the steps:

[0021] (i) Reaction of at least part of at least one silanol group-bearing organosiloxane (B) with at least one SiRs group carrier (C) such that some of the silanol groups are converted into SiOSiRs groups;

[0022] (ii) Condensation of a portion of the silanol groups not converted in step (i) with elimination of water.

[0023] Another object of the invention is an organosiloxane (A) containing SiRs groups, obtainable by the method according to the invention.

[0024] In connection with this invention, the designations M, D, T, and Q for organopolysiloxane building blocks are also used. For a reference to their meaning, see W. Noll, Chemie und Technologie der Silicones (Chemistry and Technology of Silicones), Verlag Chemie, Weinheim Bergstr., 1960, p. 2 ff.

[0025] Unless otherwise stated, where average values ​​are given below, they are numerical averages. Where measured values, parameters, or material properties determined by measurement are given below, they are measured values, parameters, or material properties at 25 °C and preferably at a pressure of 101,325 Pa (standard pressure), unless otherwise stated.

[0026] Advantageous embodiments of the subject matter of the invention can be found in the claims, the examples, and the description. Furthermore, it is expressly pointed out that the disclosure relating to the subject matter of the present invention includes all combinations of individual features of the present and subsequent description of the invention and the claims. In particular, embodiments of one subject matter according to the invention also apply mutatis mutandis to embodiments of the other subject matter according to the invention.

[0027] As explained above, the process according to the invention is a process for the preparation of SiRs-group-bearing organosiloxanes (A), wherein the residues R are each selected independently of one another from organic residues, comprising the steps:

[0028] (i) Reaction of at least part of at least one silanol group-bearing organosiloxane (B) with at least one SiRs group carrier (C) such that some of the silanol groups are converted into SiOSiRs groups;

[0029] (ii) Condensation of a portion of the silanol groups not converted in step (i) with elimination of water.

[0030] Steps (i) and (ii) are carried out in the specified order, i.e., first step (i) followed by step (ii). The process steps follow each other directly or indirectly. The process may include further upstream, intermediate, or downstream steps, such as purification of the reactants, intermediates, and / or final products, and / or conversion of the final products to derivative products.

[0031] As explained above, in step (i) of the process at least a part of at least one silanol group-bearing organosiloxane (B) is reacted with at least one SiRs group carrier (C).

[0032] It is preferred that the silanol group-bearing organosiloxane (B) has a viscosity of

[0033] The viscosity is preferably between 10 and 10,000 mPa s, preferably between 20 and 2,000 mPa s, and particularly between 50 and 500 mPa s. The viscosity is preferably determined according to DIN 53019-1 (publication date September 2008).

[0034] The silanol group-bearing organosiloxane (B) is usually subject to a molecular weight distribution.

[0035] It is further preferred that the silanol group-bearing organosiloxane (B) has, on average, 2 to 1000, preferably 5 to 500, and in particular 10 to 300, silicon atoms. This average value is the quotient of the number of silicon atoms of all molecules considered, neglecting the SiRs groups, divided by the total number of molecules considered.

[0036] It is also preferred that the silanol group-bearing organosiloxane (B) has a number-average molecular weight M n from 500 to 45,000 g / mol, preferably from 1,000 to 30,000 g / mol, in particular from 1,500 to 20,000 g / mol.

[0037] It is also preferred that the silanol group-bearing organosiloxane (B) has a weight-average molecular weight Mw of 1,000 to 70,000 g / mol, preferably of 2,000 to 45,000 g / mol, in particular of 2,500 to 30,000 g / mol.

[0038] It is still preferred that the silanol group-bearing organosiloxane (B) has a polydispersity M w / M n from 1.1 to 2.9, preferably from 1.4 to 2.5, in particular from 1.5 to 2.3.

[0039] The number-average molecular weight M n , the weight-mean molecular weight Mw and the polydispersity M w / M n are preferably determined in accordance with the standard DIN EN ISO 13885-1 (issue date November 2021), with the difference that toluene is used as the eluent instead of tetrahydrofuran (THF).

[0040] The silanol group-bearing organosiloxane (B) can be linear or branched with respect to the silox fraction. Preferably, the silanol group-bearing organosiloxane (B) is a linear organosiloxane with respect to the silox fraction.

[0041] It is preferred that the silanol group-bearing organosiloxane (B) is selected from α,co-dihydroxy-polydiorganylsiloxanes, preferably from α,co-dihydroxy-polydimethylsiloxanes.

[0042] It is still preferred that the silanol group-bearing organosiloxane (B) is selected from compounds of formula (I),

[0043] Formula (I); where:

[0044] R' is each independently selected from the group consisting of monovalent, substituted and unsubstituted hydrocarbon residues with 1 to 18 carbon atoms, preferably each independently selected from the group consisting of vinyl, methyl, ethyl, propyl and phenyl, in particular methyl; m is a number from 5 to 600, preferably from 10 to 400, in particular from 20 to 300.

[0045] The number m is preferably to be understood as the mean value (number mean) and then stands for the quotient of the number of all SiR'2 groups divided by the number of all polymer molecules in the silanol group-bearing organosiloxane (B) of formula (I) used, i.e., in short, for the mean number of silicon atoms per polymer molecule of the silanol group-bearing organosiloxane (B) used.

[0046] If R' is a substituted hydrocarbon residue, then R' can, for example, be selected from fluorine-substituted hydrocarbon residues, such as fluorine-substituted vinyl and alkyl residues. However, substituted hydrocarbon residues, and in particular fluorine-substituted hydrocarbon residues, are less preferred as R'.

[0047] As described in the introduction, the process according to the invention enables the production of highly viscous organosiloxanes bearing triorganylsilyl groups with a low content of cyclosiloxanes.

[0048] Cyclosiloxanes are siloxanes consisting exclusively of D-units. These are preferably siloxanes of the formula D₂. n with n > 3 with D = [R*2SiO2 / 2], where R* is an organic residue, preferably a hydrocarbon residue, in particular a methyl residue. The residues R* can be the same or different. Preferably, however, the residues R* are the same. Particularly preferably, all residues R* are methyl residues.

[0049] It is preferred that the sum of the mass fractions of Ü4, D5, and De, relative to the total mass of all silanol group-bearing organosiloxanes (B) used, is < 2500 ppm, preferably < 1500 ppm, and particularly < 900 ppm. Here, D4 ​​represents octamethylcyclotetrasiloxane, D5 represents decamethylcyclopentasiloxane, and De represents dodecamethylcyclohexasiloxane. It is even more preferred that the sum of the mass fractions of all cyclosiloxanes, relative to the total mass of all silanol group-bearing organosiloxanes (B) used, is < 2500 ppm, preferably < 1500 ppm, and particularly < 900 ppm.

[0050] It is particularly preferred that the entirety of all silanol group-bearing organosiloxanes (B) used is essentially free of cyclosiloxanes.

[0051] Without being bound to any theory, it is assumed that a low content of cyclosiloxanes in the silanol group-bearing organosiloxanes (B) used is advantageous in order to achieve a low content of cyclosiloxanes in the process product, i.e. the SiRs group-bearing organosiloxane (A), at least if no equilibration takes place during the process, which in turn can lead to the formation of cyclosiloxanes.

[0052] A preferred embodiment of the process is characterized in that impurities, such as water or volatile organosiloxanes, are distilled off from the silanol group-bearing organosiloxane (B) before the reaction in step (i). This has the advantage of improving the purity of the process product, i.e., the SiRs group-bearing organosiloxane (A).

[0053] It is preferred that the distillation takes place at a temperature of 85 °C to 180 °C, preferably from 90 °C to 130 °C, and in particular from 90 °C to 120 °C.

[0054] It is further preferred that the distillation takes place at a pressure of at most 70 mbar, preferably from 0.1 to 40 mbar, in particular from 0.001 to 5 mbar.

[0055] It is also preferred that the distillation takes place over a period of 10 h to 4 h, preferably from 8 h to 4 h, and in particular from 6 h to 4 h.

[0056] An alternative preferred embodiment of the process is characterized in that no impurities are distilled off from the silanol group-bearing organosiloxane (B) before its reaction in step (i). This has the advantage that the production costs can be reduced if a particularly high purity of the process product, i.e., the SiRs group-bearing organosiloxane (A), is not required.

[0057] As explained above, in step (i) of the process, at least a portion of at least one silanol group-bearing organosiloxane (B) is reacted with at least one SiRs group carrier (C). It is preferred that the residues R are each independently selected from the group consisting of substituted and unsubstituted hydrocarbon residues, preferably unsubstituted hydrocarbon residues.

[0058] It is further preferred that the R groups are each independently selected from the group consisting of alkyl groups and alkenyl groups. It is further preferred that the R groups are each independently selected from the group consisting of alkyl groups with 1 to 6 carbon atoms and alkenyl groups with 2 to 6 carbon atoms. The alkyl and alkenyl groups are substituted or unsubstituted, but preferably unsubstituted.

[0059] It is still preferred that the R residues are each independently selected from the group consisting of methyl and vinyl.

[0060] Preferably, the SiRs group carrier (C) is selected from the group consisting of 1,3-divinyl-1,1,3,3-tetramethyl-disilazane (CAS number: 7691-02-3), 1,3-divinyl-1,1,3,3-tetramethyl-disiloxane (CAS number: 2627-95-4), dimethyl(dimethylamino)vinylsilane (CAS number: 13391-72-5), methoxy(dimethyl)vinylsilane (CAS number: 16546-47-7),

[0061] Bis(dimethylamino)methylvinylsilane (CAS number: 13368-45-1), Chloro(dimethyl)vinylsilane (CAS number: 1719-58-0), 1,3-Bis(trimethylsilyl)urea (CAS number: 18297-63-7), Chloro(trimethyl)silane (CAS number: 75-77-4), (Dimethylamino)trimethylsilane (CAS number: 2083-91-2), N-(Trimethylsilyl)diethylamine (CAS number: 996-50-9), (Diethylamino)trimethylsilane (CAS number: 996-50-9), Methoxytrimethylsilane (CAS number: 1825-61-2);

[0062] Hexamethyldisilazane (CAS number: 999-97-3), hexamethyldisiloxane (CAS number: 107-46-0), 1-(trimethylsilyl)imidazole (CAS number: 18156-74-6), N,N-bis-(trimethylsilyl)methylamine (heptamethyldisilazane, CAS number: 920-68-3), N,O-Bis(trimethylsilyl)acetamide (CAS number: 10416-59-8).

[0063] Particularly preferred is the SiRs group carrier (C) selected from the group consisting of 1,3-Divinyl-1,1,3,3-tetramethyldisilazane (CAS number: 7691-02-3) and hexamethyldisilazane (CAS number: 999-97-3).

[0064] Among the SiRs group carriers (C) listed above, bis(dimethylamino)methylvinylsilane (CAS number: 13368-45-1) occupies a special position, as some of the SiOSiRs groups initially formed in step (i) can be directly reacted with further silanol groups to form SiOSiR2OSi groups. This compound therefore functions not only as a SiRs group carrier (C) but also as a SiR2 group carrier and thus as a chain extender. This can be adjusted, in particular, by the molar ratio of the silanol groups of the silanol-bearing organosiloxane (B) to the SiRs groups of the SiRs group carrier (C). The molecular weight, viscosity and SiRs group density of the process product, i.e. the SiRs group-bearing organosiloxane (A), depends significantly on the proportion of silanol groups that are not reacted in step (i), since only these can condense in step (ii) with the elimination of water.

[0065] It is therefore preferred that in step (i) the molar ratio of the silanol groups of the totality of all silanol group-bearing organosiloxanes (B) used to the SiRs groups of the totality of all SiRs group carriers (C) used is from 0.5:1 to 110:1, preferably from 0.6:1 to 100:1, in particular from 0.7:1 to 90:1.

[0066] The lower limit of 0.5:1 takes into account the fact that, particularly in the case of the especially preferred SiRs group transferors (C) 1,3-Divinyl-1,1,3,3-tetramethyl-disilazane (CAS number: 7691-02-3) and hexamethyldisilazane (CAS number: 999-97-3), usually only one of the two SiRs groups contained in the molecule is actually transferred.

[0067] It is further preferred that in step (i) at least one catalyst (D) is used, preferably selected from the group consisting of Lewis acids and Bronsted acids, and in particular selected from the group consisting of octylphosphonic acid, phosphoric acid, bismuth neodecanoate, and zinc neodecanoate.

[0068] It is also preferred that step (i) is carried out at a temperature of 60 °C to 170 °C, preferably of 100 °C to 150 °C, particularly of 120 °C to 140 °C.

[0069] It is also preferred that step (i) be carried out at atmospheric pressure (1013.25 hPa) ± 500 hPa, preferably ± 200 hPa, and particularly ± 100 hPa. Higher pressures can be beneficial for the reaction, however, as the temperature can also be increased in this case; on the other hand, this makes the manufacturing process more complex.

[0070] It is also preferred that step (i) is carried out over a period of 4 h to 16 h, preferably from 5 h to 14 h, in particular from 6 h to 10 h.

[0071] Immediately or indirectly after step (i), i.e. after the reaction of at least part of at least one silanol group-bearing organosiloxane (B) with at least one SiRs group carrier (C), in which part of the silanol groups is converted into SiOSiRs groups, step (ii) takes place, i.e. the condensation of a part of the silanol groups not reacted in step (i) with elimination of water.

[0072] It is preferred that at least one condensation catalyst (E) is used in step (ii). It is particularly preferred that the condensation catalyst (E) is selected from lithium compounds that achieve a pH value >7 in water.

[0073] The condensation catalyst (E) is preferably selected from compounds of the formula LiaAb, where A is a basic anion in water, and the indices a and b are integers > 1, provided that LiaAb is electroneutral. Preferably, the anion A is selected from the group consisting of hydroxide, amide, Ci- to Cia-alkoxide, silicate, and silanolate.

[0074] It is particularly preferred that the condensation catalyst (E) is selected from the group consisting of LiOH, lithium silanolate and lithium butoxide.

[0075] In a preferred embodiment of the process, in step (ii) at least one additional cocatalyst (F) is used alongside the at least one condensation catalyst (E). It is preferred that the cocatalyst (F) is a bidentate chelating ligand containing units of the formula NXN, where X is a divalent linear, cyclic, and / or aromatic Ci to Cso hydrocarbon residue. Corresponding catalyst systems comprising a condensation catalyst (E) and a cocatalyst (F) are described, for example, in EP1020486A1.

[0076] In an alternative preferred embodiment of the process, no bidentate chelating ligand containing units of formula NXN, where X is a divalent linear, cyclic and / or aromatic Ci to Cso hydrocarbon residue, is used as a cocatalyst (F) in step (ii). It is particularly preferred that no cocatalyst (F) is used at all in step (ii).

[0077] It is preferred that step (ii) is carried out at a temperature of 80 °C to 200 °C, preferably from 100 °C to 190 °C, particularly from 150 °C to 180 °C.

[0078] It is further preferred that step (ii) is carried out at a pressure of at most 50 mbar, preferably from 0 to 10 mbar, in particular from 0 to 5 mbar.

[0079] It is also preferred that step (ii) is carried out over a period of 2 h to 16 h, preferably from 4 h to 14 h, in particular from 6 to 10 h.

[0080] As described in the introduction, the process according to the invention serves to produce organosiloxanes (A) bearing SiRs groups.

[0081] A further object of the invention is therefore an organosiloxane (A) containing SiRs groups, obtainable by the process according to the invention. It is preferred that the organosiloxane (A) containing SiRs groups has a viscosity of 40 to 1,000,000 mPa s, preferably of 50 to 750,000 mPa s, and particularly of 80 to 500,000 mPa s. The viscosity is preferably determined in accordance with the standard DIN 53019-1 (publication date September 2008).

[0082] The SiRs-group-bearing organosiloxane (A) is usually subject to a molecular weight distribution.

[0083] It is preferred that the SiRs-group-bearing organosiloxane (A) has, on average, 20 to 10,000, preferably 30 to 5,000, and particularly 40 to 3,000 silicon atoms, neglecting the SiRs groups. This average value is the quotient of the number of silicon atoms of all molecules considered, neglecting the SiRs groups, divided by the total number of molecules considered.

[0084] It is also preferred that the SiRs-group-bearing organosiloxane (A) has a number-average molecular weight M n from 1,500 to 2,250,000 g / mol, preferably from 2,250 to 1,125,000 g / mol, in particular from 3,000 to 675,000 g / mol.

[0085] It is also preferred that the SiRs group-bearing organosiloxane (A) has a weight-average molecular weight Mw of 1,800 to 4,500,000 g / mol, preferably of 2,700 to 2,250,000 g / mol, and in particular of 3,600 to 1,350,000 g / mol.

[0086] It is still preferred that the SiRs-group-bearing organosiloxane (A) has a polydispersity M w / M n from 1.2 to 6.0, preferably from 1.4 to 5.0, in particular from 1.6 to 3.0.

[0087] The number-average molecular weight M n , the weight-mean molecular weight Mw and the polydispersity M w / M n are preferably determined in accordance with the standard DIN EN ISO 13885-1 (issue date November 2021), with the difference that toluene is used as the eluent instead of tetrahydrofuran (THF).

[0088] The SiRs-group-containing organosiloxane (A) can be linear or branched with respect to the silox fraction. Preferably, the SiRs-group-containing organosiloxane (A) is a linear organosiloxane with respect to the silox fraction.

[0089] It is preferred that the SiRs-group-bearing organosiloxane (A) is selected from the group consisting of α,co-dialkenyl-polydiorganylsiloxanes and α,co-dialkyl-polydiorganylsiloxanes, preferably from the group consisting of α,co-dialkenyl-polydimethylsiloxanes and α,co-dialkyl-polydimethylsiloxanes, and in particular from the group consisting of α,co-divinyl-polydimethylosiloxanes and α,co-dimethyl-polydimethylsiloxanes. The SiRs-group-bearing organosiloxane (A) is particularly preferred to be α,co-divinyl-polydimethylosiloxane.

[0090] It is still preferred that the SiRs-group-bearing organosiloxane (A) is selected from compounds of formula (II) Formula (II); where:

[0091] R is selected independently from the group consisting of monovalent, substituted and unsubstituted hydrocarbon residues with 1 to 18 carbon atoms, preferably selected independently from the group consisting of alkyl residues with 1 to 6 carbon atoms and alkenyl residues with 2 to 6 carbon atoms, in particular selected independently from the group consisting of methyl and vinyl;

[0092] R' is each independently selected from the group consisting of monovalent, substituted and unsubstituted hydrocarbon residues with 1 to 18 carbon atoms, preferably each independently selected from the group consisting of methyl, ethyl, propyl and phenyl, in particular methyl; n is a number from 20 to 10,000, preferably from 30 to 5,000, in particular from 40 to 3,000.

[0093] The number n is preferably to be understood as the mean value (number mean) and then represents the quotient of the number of all SiR'2 groups divided by the number of all polymer molecules in the SiRs-containing organosiloxane (A) of formula (II), i.e., in short, the average number of SiR'2 groups per polymer molecule of the SiRs-containing organosiloxane (A) of formula (II), whereby, of course, the SiRs groups are not counted. The number n is therefore equivalent to the quotient of the number of all D units (D = [R'2SiO2 / 2]) divided by the number of all polymer molecules in the SiRs-containing organosiloxane (A) of formula (II), i.e., in short, the average number of D units per polymer molecule of the SiRs-containing organosiloxane (A) of formula (II). The mean number of silicon atoms per polymer molecule of the obtained SiRs group-bearing organosiloxane (A) of formula (II) is therefore n+2.

[0094] Preferably, a silanol-containing organosiloxane (B) of formula (I) is used for the preparation of the SiRs-containing organosiloxane (A) (see above). It is correspondingly preferred that the SiRs-containing organosiloxane (A) is selected from compounds of formula (III). Formula (III); where:

[0095] R is selected independently from the group consisting of monovalent, substituted and unsubstituted hydrocarbon residues with 1 to 18 carbon atoms, preferably selected independently from the group consisting of alkyl residues with 1 to 6 carbon atoms and alkenyl residues with 2 to 6 carbon atoms, in particular selected independently from the group consisting of methyl and vinyl.

[0096] R' is each independently selected from the group consisting of monovalent, substituted and unsubstituted hydrocarbon residues with 1 to 18 carbon atoms, preferably each independently selected from the group consisting of methyl, ethyl, propyl and phenyl, in particular methyl; n = m*q; m is a number from 5 to 600, preferably from 10 to 400, in particular from 20 to 300; q is a number > 2, preferably from 3 to 20, in particular from 4 to 10.

[0097] The number m is defined as in formula (I). It preferably corresponds to the quotient of the number of all SiR'2 groups divided by the number of all polymer molecules of the silanol-containing organosiloxane (B) of formula (I) used. The number q indicates the average number of silanol-containing organosiloxanes (B) that were reacted to produce one polymer molecule of the SiRs-containing organosiloxane (A). The average number of silicon atoms per polymer molecule of the resulting SiRs-containing organosiloxane (A) of formula (III) is therefore n+2.

[0098] The process according to the invention enables the construction of SiRs-group-bearing organosiloxanes (A) with a low content of cyclosiloxanes.

[0099] It is therefore preferred that the sum of the D4, D5, and De mass fractions, based on the mass of the SiRs-group-bearing organosiloxane (A), is < 2500 ppm, preferably < 1500 ppm, and particularly < 900 ppm. It is even more preferred that the mass fraction of all cyclosiloxanes, based on the mass of the SiRs-group-bearing organosiloxane (A), is < 2500 ppm, preferably < 1500 ppm, and particularly < 900 ppm.

[0100] It is particularly advantageous that the SiRs-group-bearing organosiloxane (A) is essentially free of cyclosiloxanes.

[0101] As mentioned at the outset, a disadvantage of the process described in JPH06329804A is that C3F7OCF(CF3)CF2OCF(CF3)COOH (perfluoro- 2,5-dimethyl-3,6-dioxananoic acid; 2,3,3,3-tetrafluoro-2-(1 ,1 , 2,3,3, 3-hexafluoro-2-

[0102] (perfluoropropoxy)propoxy)propanoic acid; CAS: 13252-14-7), while the use of per- and polyfluoroalkyl substances (PFAS), so-called "perpetual chemicals," should be avoided as much as possible. In contrast, the process according to the invention eliminates the need for PFAS.

[0103] It is therefore preferred that the mass fraction of fluorine relative to the mass of the SiRs group-bearing organosiloxane (A) is less than 30 ppb, preferably less than 20 ppb, in particular less than 10 ppb.

[0104] It is therefore particularly preferred that the SiRs-group-bearing organosiloxane (A) is essentially free of fluorine.

[0105] Description of the image

[0106] FIG. 1 : Schematic representation of the process according to the invention using the example of the synthesis of a higher molecular weight α,co-divinyl-polydimethylsiloxane as an organosiloxane bearing SiRs groups (A) starting from a low molecular weight α,co-dihydroxy-polydimethylsiloxane as an organosiloxane bearing silanol groups (B) with divinyltetramethyldisilazane as a SiRs group carrier (C).

[0107] Examples:

[0108] The following examples serve solely to illustrate this invention to the person skilled in the art and do not constitute any limitation of the claimed subject matter.

[0109] General methods:

[0110] Gel Permeation Chromatography (GPC):

[0111] The number-average molecular weight M n , the weight-mean molecular weight Mw and the polydispersity M w / M nwere determined using GPC, in accordance with the standard DIN EN ISO 13885-1 (issue date November 2021), with the difference that toluene is used as the eluent instead of tetrahydrofuran (THF).

[0112] Determination of viscosity:

[0113] The viscosity was determined according to the standard DIN 53019-1 (issue date September 2008).

[0114] Nuclear magnetic resonance spectroscopy (NMR spectroscopy):

[0115] The characterization of the organosiloxanes, particularly with the aim of determining the vinyl content, was carried out using the 1 Dog 29 Si-NMR spectroscopy. These methods, especially considering the multiplicity of couplings, are familiar to those skilled in the art.

[0116] Gas chromatography:

[0117] Determination of the cyclosiloxane content for siloxanes:

[0118] The method for determining cyclosiloxane contents in siloxanes by gas chromatography (GC) was based on the method described in the publication “Quantification of residual amounts of cyclic volatile methyl siloxanes in silicone fluids” by Silicones Europe, Rue Belliard 40, 1040 Brussels, Belgium, using a doubled sample weight to improve the detection limit.

[0119] Link to the method: https: / / www.silicones.eu / wp-content / uploads / 2019 / 01 / Quantification-of-residual-amounts-of-

[0120] Volatile-Siloxanes-in-silicone-products final-1 .pdf

[0121] Unless otherwise stated, all values ​​in ppm are to be understood as mass fractions. Synthesis examples:

[0122] Example 1 (not according to the invention) - Preparation of a higher molecular weight α,co-dihydroxy-polydime ethylsiloxane:

[0123] Following example 1 from JPH06329804A, a higher molecular weight α,co-dihydroxy-polydimethylsiloxane was prepared from a lower molecular weight α,co-dihydroxy-polydimethylsiloxane as follows:

[0124] 92.45 g of an α,co-dihydroxy-polydimethylsiloxane with a viscosity of 720 mm² 2 / s (= 720 cSt, corresponding to approx. 720 mPa s) were mixed with 0.09 g of perfluoro-2,5-dimethyl-3,6-dioxananoic acid (2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(perfluoropropoxy)propoxy)propanoic acid; CAS: 13252-14-7) and heated to 100 °C for 0.5 h. The cyclosiloxane content of the α,co-dihydroxy-polydimethylsiloxane used, determined by GC, was: D4 = 700 ppm, D5 = 500 ppm, and De = 600 ppm. Samples were taken from the resulting intermediate and further analyzed. The intermediate then exhibited a viscosity of 4,981 mPa s. As described in Example 1 from JPH06329804A, a low molecular weight α,co-dihydroxy-polydimethylsiloxane can apparently be polymerized to a higher molecular weight α,co-dihydroxy-polydimethylsiloxane using perfluoro-2,5-dimethyl-3,6-dioxananoic acid as a catalyst. However, this also leads to the formation of cyclosiloxanes.The cyclosiloxane content of the intermediate, determined by GC immediately after its preparation, was: D4 = 700 ppm, D5 = 700 ppm, and De = 600 ppm. This is a significantly higher cyclosiloxane content (D4-D6 = 2000 ppm) than described in Example 1 from JPH06329804A (D3-D20 = 950 ppm). However, no significant increase in the cyclosiloxane content was observed compared to the α,co-dihydroxy-polydimethylsiloxane used. Nevertheless, the intermediate showed an increase in cyclosiloxane content when stored at 45°C (see Table 1). This demonstrates that perfluoro-2,5-dimethyl-3,6-dioxananoic acid does indeed lead to the formation of cyclosiloxanes, albeit only over time, and then even at room temperature. After a further 0.5 h reaction time at 100 °C, the resulting final product could not be stirred further because the viscosity exceeded 1,000 Pas (1,000,000 mPa s).The final product could therefore not be further reacted with a SiRs group transferor. In the following Example 2, therefore, an α,co-dihydroxy-polydimethylsiloxane with a viscosity of 720 mmHg was not used. 2 / s was assumed, but rather an α,co-dihydroxy-polydimethylsiloxane with a viscosity of only 70 mPa s. Table 1: Content of cyclosiloxanes in the intermediate during storage

[0125] Example 2a (not according to the invention) - Preparation of a higher molecular weight α,co-dihydroxy-polydimethylsiloxane:

[0126] Following Example 1 from JPH06329804A, a higher molecular weight α,co-dihydroxy-polydimethylsiloxane was synthesized from a lower molecular weight α,co-dihydroxy-polydimethylsiloxane. However, unlike Example 1 from JPH06329804A, an α,co-dihydroxy-polydiorganylsiloxane with a viscosity of 720 mmol / L was not produced. 2 / s (= 720 cSt, corresponds to approx. 720 mPa s) but an a,co-dihydroxy-polydimethylsiloxane with a much lower viscosity of only 70 mPa s is reacted as follows:

[0127] 400 g of an α,co-dihydroxy-polydimethylsiloxane with a viscosity of 70 mPa s were heated to 100 °C together with 0.3 g (1.8 mmol) of perfluoro-2,5-dimethyl-3,6-dioxananoic acid (2,3,3,3-tetrafluoro-2-(1,1,2,3,3,3-hexafluoro-2-(perfluoropropoxy)propoxy)propanoic acid; CAS: 13252-14-7). The cyclosiloxane content of the α,co-dihydroxy-polydimethylsiloxane used, determined by GC, was: Ü4 = 600 ppm, D5 <50 ppm, and De = 200 ppm. After stirring the mixture for 1 h at 100 °C, the viscosity was 1.020 mPa s. As described in Example 1 from JPH06329804A, a low molecular weight α,co-dihydroxy-polydimethylsiloxane is thus apparently polymerized to a higher molecular weight α,co-dihydroxy-polydimethylsiloxane using perfluoro-2,5-dimethyl-3,6-dioxananoic acid as a catalyst. However, it should be noted that the viscosity of the resulting higher molecular weight α,co-dihydroxy-polydimethylsiloxane is 1.0.20 mPa s is still very low and thus corresponds more closely to the starting material and not the product from Example 1 from JPH06329804A. The cyclosiloxane content determined by GC immediately after preparation was: D4 = 300 ppm, D5 = 200 ppm, and De = 200 ppm. Thus, a similar cyclosiloxane content was found (D4-D6 = 700 ppm) as in Example 1 from JPH06329804A (D3-D20 = 950 ppm). Example 2b (not according to the invention) - Preparation of a higher molecular weight α,co-divinylpolydime ethylsiloxane:

[0128] Following example 3 from JPH06329804A, a higher molecular weight α,co-divinyl polydimethylsiloxane was prepared from a higher molecular weight α,co-dihydroxy polydimethylsiloxane as follows:

[0129] 200 g (approx. 8 mmol) of the higher molecular weight α,co-dihydroxy-polydimethylsiloxane prepared in Example 2a were mixed with 6.56 g (35 mmol) of divinyltetramethyldisilazane and stirred for 2 hours at room temperature. The initial weights were chosen to correspond to the molar ratio according to Example 3 from JPH06329804A. The mixture was then heated to 150 °C with the addition of nitrogen gas and stirred for another hour. Samples were taken from the resulting intermediate and further investigated. The intermediate was treated by 1 H-NMR, 29 Si-NMR and GC were analyzed. The GC analysis showed a slight reduction in the cyclosiloxane content after aeration with N2 to D4 < 200 ppm, D5 < 200 ppm, and De < 200 ppm. The signals for vinyl groups were in the 1 Dog 29Si NMR spectra of the product were found. The viscosity had increased to 1.984 mPa s. After aeration with nitrogen, the intermediate was heated to 80 °C and held at 0.025 mbar for 3 hours. The NMR analysis of the obtained material showed a decrease in the signals for vinyl groups in the 1 Dog 29Si NMR spectra and a viscosity increase to 4,776 mPa s were observed. GC analysis revealed cyclosiloxane content of D4 < 200 ppm, D5 < 200 ppm, and De < 200 ppm. The reaction at room temperature apparently does not increase the cyclic siloxane content; in fact, it is reduced by 100 ppm (D4) by aeration with N2. However, it should be noted that the viscosity of the resulting higher molecular weight α,co-dihydroxy-polydimethylsiloxane is still very low at 4,776 mPa s and thus does not correspond to the product from Example 1 in JPH06329804A. The viscosity increase indicates that the vinyl functionalization with divinyltetramethyldisilazane was evidently incomplete. Complete functionalization should not lead to a viscosity increase, as condensation would then be impossible. Furthermore, the vinyl groups apparently did not react, as they can be removed by applying a vacuum.This suggests that unreacted divinyltetramethyldisilazane is present.

[0130] Example 3 (not according to the invention) - Preparation of a higher molecular weight α,cD-divinyl polydime ethylsiloxane:

[0131] 500 g (13.9 mmol) of a commercially available higher molecular weight α,co-dihydroxy polydimethylsiloxane (polymer OH 5 from Evonik; 5,000 mPa s; approx. 350 silicon atoms; approx. 36,000 g / mol (M n The mixture was combined with 10.4 g (56 mmol) of divinyltetramethyldisilazane and stirred at room temperature for 2 hours. The mixture was then heated to 150 °C with the addition of nitrogen gas and stirred for another hour. Samples were taken from the resulting intermediate and analyzed using 1 Dog 29 Si-NMR analyzed. The signals for vinyl groups were found in the 1 Dog 29Si NMR spectra were found. After aeration with nitrogen, the intermediate was heated to 80 °C and held at 0.025 mbar for 3 hours. The NMR analysis of the obtained product showed no signals for vinyl groups in the 1 Dog 29 Si NMR spectra show that direct functionalization of a commercially available α,co-dihydroxy-polydimethylsiloxane with a similar viscosity to that used in Example 2b is therefore unsuccessful, and no vinyl functionalization occurs. Aeration with nitrogen at 150 °C led to an increase in viscosity, indicating a still reactive reaction mixture. After further distillation under vacuum, the viscosity increased further, resulting in a fivefold increase overall. Simple aeration with nitrogen is therefore insufficient.

[0132] Examples 4 to 9 (according to the invention) - Production of higher molecular weight α,cD-divinyl-polydim ethylsiloxanes and α,co-dim ethyl-polydim ethylsiloxanes:

[0133] General synthesis procedure:

[0134] An α,co-dihydroxy-polydimethylsiloxane (PDMS) with a viscosity of 70 mPa·s was mixed with hexamethyldisilazane (HMDS) or divinyltetramethyldisilazane (DVSN) and octylphosphonic acid and heated at 130 °C for 8 hours. The resulting intermediate was mixed with lithium hydroxide monohydrate and heated at 170 °C and a pressure of -0.04 mbar for 8 hours. Acetic acid was then added, and the product was analyzed. The sample weights and analyzed product properties are shown in Table 2.

[0135] Table 2: Examples according to the invention - weighings and product properties

[0136] Discussion of the results: In contrast to the examples from JPH06329804A, the process according to the invention can produce α,co-divinyl-polydimethylsiloxanes and α,co-dimethyl-polydimethylsiloxanes with a low cyclosiloxane content. Unlike the examples from JPH06329804A, the cyclosiloxane content remains stable at a low level even during storage. The values ​​for Example 5 are summarized in Table 3. Furthermore, the use of a perfluorinated acid, and thus PFAS, can be avoided. High storage stability is also achieved. Unlike the examples from JPH06329804A, there is no further increase in viscosity during storage. This suggests that a largely complete conversion of the silanol groups to SiOSiRs groups has occurred. Compared to EP1020486A1, the use of a cocatalyst is not required.

[0137] Table 3: Example 5 - Cycle content during storage

Claims

Patent claims 1. A process for the preparation of SiRs-group-bearing organosiloxanes (A), wherein the residues R are each independently selected from organic residues, comprising the steps: (i) Reaction of at least part of at least one silanol group-bearing organosiloxane (B) with at least one SiRs group carrier (C) such that some of the silanol groups are converted into SiOSiRs groups; (ii) Condensation of a portion of the silanol groups not converted in step (i) with elimination of water.

2. Method according to claim 1, characterized in that the silanol group-bearing organosiloxane (B) has a viscosity of 10 to 10,000 mPa s, preferably of 20 to 2,000 mPa s, in particular of 50 to 500 mPa s.

3. Method according to claim 1 or 2, characterized in that the silanol group-bearing organosiloxane (B) is selected from α,co-dihydroxy-polydiorganylsiloxanes, preferably from α,co-dihydroxy-polydimethylsiloxanes.

4. Method according to one of claims 1 to 3, characterized in that the residues R are each independently selected from the group consisting of substituted and unsubstituted hydrocarbon residues, preferably unsubstituted hydrocarbon residues.

5. Method according to any one of claims 1 to 4, characterized in that the residues R are each independently selected from the group consisting of methyl and vinyl.

6. Method according to any one of claims 1 to 5, characterized in that the SiRs- The group carrier (C) is selected from the group consisting of 1,3-Diviny 1-1,1,3,3-tetramethyl-disiloxane, 1,3-Diviny 1-1,1,3,3-tetramethyl-disiloxane, Dimethyl(dimethylamino)vinylsilane, methoxy(dimethyl)vinylsilane, Bis(dimethylamino)methylvinylsilane, chloro(dimethyl)vinylsilane, 1,3- Bis(trimethylsilyl)urea, chloro(trimethyl)silane, (dimethylamino)trimethylsilane, N-(trimethylsilyl)diethylamine, (diethylamino)trimethylsilane, methoxytrimethylsilane; Hexamethyldisilazane, hexamethyldisiloxane, 1-(trimethylsilyl)imidazole, N,N-bis-(trimethylsilyl)methylamine, N,O-bis(trimethylsilyl)acetamide.

7. Method according to any one of claims 1 to 6, characterized in that in step (i) the molar ratio of the silanol groups of the totality of all substances used The ratio of silanol group-bearing organosiloxanes (B) to the SiRs groups of the totality of all SiRs group carriers (C) used is from 0.5:1 to 110:1, preferably from 0.6:1 to 100:1, in particular from 0.7:1 to 90:

1.

8. A method according to any one of claims 1 to 7, characterized in that at least one catalyst (D) is used in step (i), preferably selected from the group consisting of Lewis acids and Bransted acids, and in particular selected from the group consisting of octylphosphonic acid, phosphoric acid, bismuth neodecanoate, and zinc neodecanoate.

9. Method according to any one of claims 1 to 8, characterized in that at least one condensation catalyst (E) is used in step (ii).

10. Method according to any one of claims 1 to 9, characterized in that the condensation catalyst (E) is selected from lithium compounds which achieve a pH value >7 in water.

11. Method according to any one of claims 1 to 10, characterized in that the condensation catalyst (E) is selected from the group consisting of LiOH, lithium silanolate and lithium butoxide.

12. SiRs group-bearing organosiloxane (A), obtainable by a method according to any one of claims 1 to 10.

13. Organosiloxane (A) bearing SiRs groups according to claim 12, characterized in that it has a viscosity of 40 to 1,000,000 mPa s, preferably of 50 to 750,000 mPa s, in particular of 80 to 500,000 mPa s.

14. SiRs-group-bearing organosiloxane (A) according to claim 12 or 13, characterized in that it is selected from the group consisting of α,co-dialkenyl-polydiorganylsiloxanes and α,co-dialkyl-polydiorganylsiloxanes, preferably from the group consisting of α,co-dialkenyl-polydimethylsiloxanes and α,co-dialkyl-polydimethylsiloxanes, in particular from the group consisting of α,co-divinyl-polydimethylosiloxanes and α,co-dimethyl-polydimethylsiloxanes.

15. SiRs group-bearing organosiloxane (A) according to one of claims 12 to 14, characterized in that the sum of the D4, Ds and De mass fractions based on the mass of the SiRs group-bearing organosiloxane (A) is < 2500 ppm, preferably < 1500 ppm, in particular < 900 ppm.

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