A method for purifying acetoxy siloxane

Abstract

The present invention relates to a process for purifying acetoxy siloxanes. A process for purifying acidified, preferably superacidified, in particular triflic acidified, end equilibrated acetoxy siloxanes is described, wherein acidified, preferably superacidified, in particular triflic acidified, acetic anhydride and optionally acetic acid containing equilibrated, preferably end equilibrated, acetoxy siloxanes are contacted with a base, after which the precipitate is filtered off, and the resulting filtrate is optionally purified by distillation, the acetoxy siloxanes optionally being dissolved in an inert solvent.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for purifying acetoxy siloxanes, to the purified acetoxy siloxanes obtained in this way, and also to the use thereof as starting materials for the preparation of SiOC-bonded polyether siloxanes. BACKGROUND

[0002] Reference is made to EP 3467006 A1 and the as yet unpublished European patent applications with application reference numbers EP 18172882.5, EP 18172876.7 and EP 17204277.2, which relate to the preparation of SiOC-bonded polyether siloxanes, in which equilibrated acetoxy siloxanes of linear or branched structure type, acidified with triflic acid, are used as reactive intermediates, and also to the teaching of the as yet unpublished European patent application EP 18189073.2, which is applicable to a process for preparing triflic acid-acidified, terminally equilibrated siloxanes bearing acetoxy groups, in which cyclic siloxanes, in particular cyclic siloxanes comprising D4 and / or D5, and / or mixtures of D / T type cyclic branched siloxanes, are reacted with acetic anhydride, while using triflic acid as catalyst and adding acetic acid.

[0003] The as yet unpublished European patent applications with application reference numbers EP 17204277.2, EP 18189072.4 and EP 18189074.0 are applicable to processes for preparing acetoxy-modified siloxanes, in which, respectively, DT siloxane rings and simple siloxane rings comprising only D units are used as reactants.

[0004] EP 17204277.2 relates to a process for preparing SiOC-bonded polyether siloxanes, which are branched in the siloxane moiety starting from mixtures of D / T type cyclic branched siloxanes by the following steps: in a first step, D / T type cyclic branched siloxanes are reacted with acetic anhydride, optionally in mixture with simple siloxane rings, to form branched siloxanes bearing acetoxy groups under acid catalysis, and in a second step, the acetoxy-modified branched siloxanes are equilibrated with triflic acid, and in a third step, the triflic acid-acidified acetoxy siloxanes are reacted with polyether alcohols, optionally in the presence of a base and optionally in the presence of an inert solvent. The branched acetoxy siloxanes obtained here contain, in addition to the triflic acid used, about 0.10 mol of free acetic anhydride per mol of acetoxy function bonded to silicon.

[0005] The not yet published European patent applications with the application reference numbers EP 18189072.4 and EP 18189074.0, directed to SiOC-bonded organosilicon polyether structures which are not branched but linear, for this purpose indicate that an equilibrated a, w-diacetyloxy polydimethylsiloxane is produced by contacting the reactants with 0.1 to 0.3 mass-%, based on the total reaction mass, of trifluoromethanesulfonic acid, while the reactants are mixed thoroughly, and then heating to 140 to 160 °C for 4 to 8 hours, by means of the reaction of a siloxane ring body (D4 / D5) with acetic anhydride in the presence of trifluoromethanesulfonic acid. Here, the initially slightly turbid reaction mixture provides a clear, equilibrated trifluoromethanesulfonic acid-acidified a, w-diacetyloxy polydimethylsiloxane which, in addition to the trifluoromethanesulfonic acid used, also contains free acetic anhydride in an amount of 0.125 mol based on the chemically bonded acetic anhydride equivalents in the a, w-diacetyloxy polydimethylsiloxane.

[0006] The not yet published European application 18210035.4 describes (i) a reaction system for the preparation of siloxanes with acetoxy functionality comprising a) silane and / or siloxane with alkoxy groups and / or b) silane and / or siloxane with acetoxy groups, c) silane and / or siloxane with hydroxyl groups, d) optionally simple siloxane ring bodies and / or DT ring bodies, e) a reaction medium comprising acetic anhydride, perfluoroalkanesulfonic acid and preferably acetic acid, (ii) a process for the preparation of linear or branched acetoxy-functional siloxanes and their use in the preparation of polyethersiloxanes, all incorporated by reference into the disclosure of the present application.

[0007] According to the above identified applications, branched siloxanes with terminal acetoxy groups can be obtained, for example, by equilibrating (= pre-equilibrating) branched siloxanes with terminal alkoxy groups as the only reactants with a reaction medium (consisting of acetic anhydride, trifluoromethanesulfonic acid and acetic acid).

[0008] As an alternative, the not yet published European patent application 18210035.4 indicates in the scope of another preferred embodiment that it is also possible to charge all reactants and / or combinations thereof directly with the reaction medium from the outset, while mixing thoroughly, and then to react them by heating and removing volatile by-products, thereby directly producing branched siloxanes with terminal acetoxy groups.

[0009] According to the teachings of the European patent application 18210035.4, depending on the target structure of the siloxanes with terminal acetoxy groups, it can be advantageous to select the method with the sequence, i.e. to use pre-equilibration, or to use the agreed method (to charge all reactants and / or combinations of these reactants from the outset) can be advantageous.

[0010] In operational practice it is desirable to be able to quickly determine the content of active silicon-bonded groups by wet-chemical methods to have a reliable calculation basis for the stoichiometric calculation of the production batch independent from expensive and sometimes time-consuming device-based analyses such as for example 1 H, 13 C and 29 Si NMR spectroscopy). The presence of triflic acid and acetic anhydride in the reactive acetoxy siloxane precursors obtained according to EP 17204277.2 or EP 18189072.4, EP 18189074.0 and EP 18210035.4 or the presence of triflic acid, acetic anhydride and acetic acid in EP 18189073.2 makes the titration determination of the content of silicon-bonded acetoxy groups more difficult because this must always be carried out together with the titration of the acetic anhydride or together with the acetic anhydride and acetic acid present in the matrix. Thus, for the detection of the individual acetoxy species in complex material matrices two or more titrations are unavoidable.

[0011] A reliable calculation basis for the stoichiometric calculation of the production batch, in particular for the preparation of SiOC-bonded linear polydimethylsiloxane-polyalkylene block copolymers having repeating (AB) units, is especially important. Likewise, the unpublished European patent application of the applicant reference number EP 18189072.4 relating to a process for the preparation of these polydimethylsiloxane-polyalkylene block copolymers states that because the obtainable degree of polymerization is directly related to the ideal stoichiometry of the maintained reactants, the molar ratio of the a, w-diacetoxy siloxane to the polyether diol should preferably be chosen in the range of 0.90 to 1.10, preferably in the range of 0.95 to 1.05, particularly preferably in the range of 0.99 to 1.01.

[0012] A further aspect of EP 17204277.2 on the further processing of triflic acid- acidified branched acetoxy siloxane still containing acetic anhydride is as follows: the neutralization of the acid present in the reaction system at a later point in time, in particular after thermal removal of the formed acetic acid, the residual acetic anhydride and any solvent used, leads to partial esterification of the polyether alcohol present in the system with acetic acid. Experience shows that a longer action time of the triflic acid present in the system generally also results in a darker product.(Example 3, supra).

[0013] The distillative removal of the acetic acid results in a formulation consisting of SiOC-bonded, branched siloxane polyether as well as polyether alcohol and polyether alcohol blocked with acetyl groups at the end. This formulation with reduced hydroxyl functionality is of interest for specific applications but not for the possible range of applications. SUMMARY

[0014] Surprisingly, it has now been found that the content of the two superacids present in branched (cf. EP 17204277.2) and linear acetoxy siloxanes (cf. EP 18189072.4 and EP 18189074.0), in particular trifluoromethanesulfonic acid and acetic anhydride, or according to EP 18189073.2 trifluoromethanesulfonic acid, acetic anhydride and acetic acid, can be simply removed, thus obtaining purified acetoxy siloxanes, which reduces the task of titration determination and, in turn, the task of avoiding acetylated polyether alcohols.

[0015] Furthermore, it is now surprisingly found that the acetoxy siloxanes purified according to the present application can be easily freed from free simple siloxane ring bodies (containing D4 / D5 / D6) by distillation, preferably with the application of an auxiliary vacuum, without causing the formation of undesirable impurities, in particular without causing the so-called "backbiting reaction" to occur, which would otherwise again produce cyclic siloxanes. The possibility of removing ring bodies at the stage of reactive siloxanes (acetoxy siloxanes) found here according to the present application has great industrial significance, since the market's demand for VOC-free (volatile organic compounds), organically modified organosilicon additives is growing, but due to the fact that ring bodies removed by distillation at the stage of organically modified siloxanes always contain different proportions of entrained organics, so that these ring bodies can only be reused in a limited range when synthesizing siloxane parent molecules, thermal removal of siloxane ring bodies from the end product is difficult. In addition, thermal stress on polyether siloxanes of SiOC structure always harbors the risk of increased undesired product discoloration.

[0016] The dilemma arising from the requirements for product quality on the one hand and the requirement of being free of ring bodies on the other hand is extensively discussed in WO 2013 / 050149 A1, which aims at a solvent-assisted stripping process for removing cyclic organosilicon from organosilicon-based products, and in this context, in particular glyoxal acetal (such as tetraethoxy and tetramethoxyethane) is taught as a solvent for forming azeotropes for distillative removal of cyclic siloxanes from amino-functional siloxanes.

[0017] According to the present application, the acetoxy siloxanes obtained according to EP 17204277.2 or EP 18189072.4, EP 18189074.0 and 18210035.4 are preferably purified in the following way:

[0018] introducing ammonia into an acetoxy siloxane, which is acidified, preferably triflic acidified, contains acetic anhydride and optionally an acetic acid containing equilibrium, preferably a terminal equilibrium, optionally dissolved in an inert solvent, filtering off a precipitate, in particular an ammonium triflate, ammonium acetate and acetamide containing precipitate, and then optionally distilling the obtained filtrate to remove siloxane ring bodies (D4 / D5 / D6) and any inert solvent used,

[0019] or contacting an acetoxy siloxane, which is acidified, preferably triflic acidified, contains acetic anhydride and optionally an acetic acid containing equilibrium, preferably a terminal equilibrium, optionally dissolved in an inert solvent, with a solid base and / or a liquid base, preferably with an acetate, filtering off a precipitate, in particular a triflate precipitate, and then optionally distilling the obtained filtrate to remove acetic acid, acetic anhydride, siloxane ring bodies (D4 / D5 / D6) and any inert solvent used.

[0020] In this context, the present application provides a method for purifying an acidified, preferably superacidified, in particular triflic acidified, acetoxy siloxane containing acetic anhydride, wherein

[0021] (a) contacting an acidified, preferably superacidified, in particular triflic acidified, acetoxy siloxane containing acetic anhydride and optionally an acetic acid containing equilibrium, preferably a terminal equilibrium, optionally dissolved in an inert solvent, with a base,

[0022] (b) filtering off a precipitate, and

[0023] (c) optionally purifying the obtained filtrate by distillation.

[0024] The term "end equilibrated" refers to an equilibrium which has been established at a temperature of 23 °C and a pressure of 1013.25 hPa. The indicator for reaching the equilibrium can be the total cyclics content determined by gas chromatography and defined as the sum of the siloxane matrix D4, D5 and D6 content and determined after derivatization of the linear alpha, omega-diacetyloxy polydimethylsiloxane to the corresponding alpha, omega-diisopropoxy polydimethylsiloxane or after derivatization of the branched acetoxy siloxane to the corresponding branched isopropoxy siloxane. In this context, it is possible without difficulty to deviate from the conventional equilibrium ratio using acetic acid, for linear alpha, omega-diacetyloxy polydimethylsiloxane, by about 13 wt.-% of the total cyclics content and for branched acetoxy siloxane by about 8 wt.-% of the total cyclics content. When the equilibrium ratio of the total cyclics content is less than 13 wt.-%, preferably less than 12 wt.-%, for linear alpha, omega-diacetyloxy polydimethylsiloxane and less than 8 wt.-%, preferably less than 7 wt.-%, for branched acetoxy siloxane is not reached, it corresponds to the preferred embodiment. The derivatization to alpha, omega-diisopropoxy polydimethylsiloxane or branched isopropoxy siloxane is intentionally chosen here to prevent the thermally induced reverse cleavage reaction of the alpha, omega-diacetyloxy polydimethylsiloxane or branched acetoxy siloxane which can occur under the gas chromatography analysis conditions (for the reverse cleavage reaction see inter alia J. Pola et al., Collect. Czech. Chem. Commun. 1974, 39(5), 1169-1176 and W. Simmler, Houben-Weyl, Methods of Organic Chemistry, Vol. VI / 2, 4th Edition, O-Metal Derivates of Organic Hydroxy Compounds p. 162 ff.).

[0025] In a preferred embodiment of the present application, in step (a) the introduced base is ammonia and then the precipitate, in particular the precipitate comprising ammonium triflate, ammonium acetate and acetamide, is filtered off and then the resulting filtrate is optionally distilled to remove the siloxane cyclics (D4 / D5 / D6) and any inert solvent used, wherein the treatment of the siloxane with ammonia is preferably carried out in a temperature range of 0 °C to 50 °C, preferably 15 °C to 35 °C.

[0026] In another preferred embodiment of the invention, in step (a), the precipitate is contacted with a solid base and / or a liquid base, and then filtered off. This precipitate, in particular, always contains trifluoromethanesulfonate and acetate, and may also contain acetamide and a precipitate of any excess solid base used. The resulting filtrate is then optionally distilled to remove any remaining acetic acid, any remaining acetic anhydride and siloxane cyclic compounds (D4 / D5 / D6), and any inert solvent used. The solid base and / or liquid base to be used comprises bicarbonates and / or carbonates of alkali metals or alkaline earth metals, which may also be in the form of hydrates in this case, and / or organic amine bases, comprising primary and / or secondary and / or tertiary amines, particularly amines also containing hydroxyalkyl groups, such as diisopropanolamine and / or triisopropanolamine, or particularly preferably acetates. The treatment of the siloxane with the solid base and / or liquid base is preferably carried out in a temperature range of 0°C to 140°C, preferably in a temperature range of 20°C to 110°C.

[0027] Surprisingly, it has been found that the salt bodies separated after the introduction of ammonia, particularly the mixed ammonium trifluoromethanesulfonate / ammonium acetate / acetamide salt bodies (depending on the selected precipitation conditions), are obtained as crude salts, and generally also as well-crystallized spherical salts. This morphological aspect is of considerable importance for the industrial implementation of the present invention, as it greatly facilitates filtration separation from the liquid (low pressure drop within the filter cake) while minimizing the loss of acetoxysiloxanes observed due to adhesion to the salt bodies.

[0028] When using ammonia, the minimum amount of ammonia to be used is specifically proportional to the cumulative amount of acid present in the terminally balanced acetoxysiloxane, particularly acid containing trifluoromethanesulfonic acid and optionally acetic acid, as well as acetic anhydride. However, for practical considerations of ensuring complete precipitation, an excess of ammonia is advantageously selected based on the total amount of reactants; of course, the excess ratio of ammonia will not be too high in terms of economy and waste treatment. According to the invention, it is preferred to use an excess of 1 to 10 times the stoichiometric amount of ammonia, and particularly preferred to use an excess of 1 to 5 times the stoichiometric amount of ammonia.

[0029] It is preferable to avoid large amounts of excess ammonia, especially in combination with prolonged reaction times and temperatures, because the inventors, under such conditions... 29 The Si NMR spectrum showed degradation of very short siloxanes with acetoxy groups and an increase in the average siloxane chain length, which can be reliably demonstrated, for example, by the integration ratio of acetoxy end groups to D units.

[0030] For example, samples of terminally balanced, trifluoromethanesulfonic acid-acidified α,ω-diacetoxy polydimethylsiloxane treated with a relatively large amount of ammonia at 22°C (depending on contact time and reaction sequence) are used, for example... 29Si NMR spectra, the disappearance of silane acetoxy molecules can first be observed, for example, diacetoxydimethylsilane (N = 1 ), then the disappearance of a, co-diacetoxytetramethyldisiloxane (N = 2), then the degradation of a, co-diacetoxyhexamethyltrisiloxane (N = 3), then further still the degradation of higher oligomers.

[0031] According to the application, the purification of acetoxy siloxanes, which is envisaged in the following embodiment variants with the introduction of ammonia for acidification, preferably triflic acid acidification, with acetic anhydride and optionally with acetic acid, equilibrated, preferably end equilibrated, is preferred, wherein the ammonia is in the temperature range from 0 °C to 50 °C, preferably from 15 °C to 35 °C.

[0032] The acetoxy siloxanes obtained after filtration of the mixed salt are reactive siloxane intermediates, which can be stably stored in the absence of moisture and are immediately suitable, for example, for further processing into SiOC-bonded polyether siloxanes.

[0033] The linear or branched acetoxy siloxanes obtained according to the application according to the embodiment envisaging the introduction of ammonia and which are free of acid and acetic anhydride have improved storage stability compared to untreated starting materials and, in addition, the branched acetoxy siloxanes in particular show only a low tendency to gel when in contact with water. The last-mentioned aspect of the improved stability achieved according to the application can be tested very simply by experiment; by applying a small amount (for example about 1 ml) of untreated / inventively treated branched acetoxy siloxane to a black bakelite lid and then mixing this with a few millilitres of distilled water. Within a few minutes, the untreated branched acetoxy siloxane gels completely to form a white silicone network, whereas the branched acetoxy siloxane treated according to the application and used in the comparative experiment shows a significantly prolonged timeline for the onset of gelling (more than 24 hours).

[0034] In order to solve the previously mentioned VOC-free problem, however, as an alternative, the acetoxy siloxanes purified according to the application can also be subjected to further downstream distillation in order to reduce (as previously mentioned) the content of simple siloxane ring bodies (D4 / D5 / D6) and to remove any used inert solvents.

[0035] According to the application, the solvents which are considered to be inert for both embodiment variants (introduction of ammonia and use of liquid or solid bases) are preferably those which have no tendency to react with the components present in the acetoxy siloxane matrix, in particular alkanes, cycloalkanes, aromatic compounds and alkylaromatic compounds, here in particular toluene. With regard to the avoidable separation effects, however, the solvent-free purification of acetoxy siloxanes according to the application is particularly preferred.

[0036] In contrast to the original, in particular triflic acidified, acetoxy- containing siloxanes with acetic anhydride and optionally with acetic acid, the acetyl- oxy siloxanes purified according to the application have a greatly reduced vinegar taste.

[0037] The solid base and / or the liquid base used according to the application, preferably according to the further embodiment, is preferably a bicarbonate and / or a carbonate of an alkali metal or an alkaline earth metal, in this case also in the form of a hydrate, and / or an organic amine base comprising primary, secondary and tertiary amines, wherein in particular those having a hydroxyalkyl functional group, such as diisopropanolamine or triisopropanolamine or more preferably acetate.

[0038] According to the preferred embodiment of the application, the triflic acidified, equilibrated, preferably end equilibrated, acetoxy-bearing siloxane is treated with the solid base and / or the liquid base in the temperature range from 0°C to 140°C, preferably in the temperature range from 20°C to 110°C.

[0039] The ideal temperature when adding the solid base and / or the liquid base is naturally also influenced by the physicochemical properties of the solid base and / or the liquid base itself. In the case of the use of potassium acetate, which is particularly preferred according to the application, in order to ensure good solubility of the potassium acetate in the triflic acidified, equilibrated, preferably end equilibrated, acetoxy-bearing siloxane and thus to ensure effectiveness (Example 5), it is advisable to select an addition temperature of more than 90°C, preferably at 100°C, for the base. Here, a few exploratory experiments are sufficient to enable the person skilled in the art to determine the optimum addition temperature in each case.

[0040] According to the application, preferably according to the variant of the embodiment, it is envisaged to use a solid base and / or a liquid base, to contact an acetoxy-bearing siloxane with acetic anhydride and optionally with acetic acid, which is triflic acidified, equilibrated, preferably end equilibrated, optionally dissolved in an inert solvent.

[0041] According to the application, preferably according to the variant of the embodiment, the minimum amount of solid base and / or liquid base, preferably of acetate, used is proportional to the amount of acid, in particular triflic acid, present in the equilibrated, preferably end equilibrated, acetoxy-bearing siloxane. However, for practical considerations for the purpose of ensuring complete precipitation, an excess of solid base and / or liquid base, preferably of acetate, based on the acid equivalent, in particular triflic acid equivalent, is always selected. According to the application, a stoichiometric excess of 1 to 10 times, particularly preferably a stoichiometric excess of 1 to 5 times, of the solid base and / or the liquid base, preferably of the acetate, based on the acid equivalent, in particular triflic acid equivalent, is preferably used.

[0042] According to the application, the acetate used is preferably sodium, potassium, magnesium, aluminium acetate. Potassium acetate is particularly preferred.

[0043] After the introduction of the solid base and / or the liquid base, preferably the acetate, a triflate precipitate is formed, which can be removed by simple filtration. The acetoxy siloxane obtained after filtration is a reactive siloxane intermediate, which can be stored stably in the absence of moisture and can be used immediately, for example for further processing into SiOC-bonded polyether siloxanes, or can optionally be distilled to remove acetic acid, acetic anhydride, siloxane ring bodies (D4 / D5 / D6) and any inert solvent used.

[0044] All acetoxy siloxanes purified according to the application can be easily further processed by reaction with polyether alcohols or polyether diols, respectively, to give the corresponding linear or branched SiOC-bonded polyether siloxanes (Examples 4, 7 and 8). DETAILED DESCRIPTION

[0045] EXAMPLE

[0046] The following examples are merely intended to illustrate the application to those skilled in the art and do not constitute any limitation of the claimed method. In principle, the water content determination of the application is carried out by Karl Fischer method based on DIN 51777, DGF E-III 10 and DGF C-III 13a. In all examples, the 29 Si NMR spectra are used for reaction monitoring.

[0047] In the context of the present application, the Si NMR samples are analyzed in a Bruker Avance III spectrometer equipped with a 287430 sample head and a gap width of 10 mm at a measurement frequency of 79.49 MHz, the sample being dissolved in CDCI3at 22°C and referenced to the external tetramethylsilane (TMS) [delta (Si) = 0.0 ppm]. 29 29 Si) = 0.0 ppm].

[0048] The gas chromatograms are recorded on a GC instrument of the type GC 7890B from Agilent Technologies, equipped with a chromatographic column of the type HP-1 ; 30 m x 0.32 mm ID x 0.25 pm dF (Agilent Technologies No. 19091Z-413E) and hydrogen as carrier gas, with the following parameters:

[0049] Detector: FID; 310 °C

[0050] Injektor: split; 290 °C

[0051] Mode: constant flow, 2 ml / min

[0052] ​Temperature program: 60°C at 8°C / min - 150°C at 40°C / min - 300°C 10 min.

[0053] The indicator for reaching equilibrium is the total cyclic content determined by gas chromatography and defined as the sum of the siloxane matrix D4, D5 and D6 content and after derivatization of the a, w-acetoxy polydimethylsiloxane or branched acetoxy siloxane derivatization to the corresponding a, w-diisopropoxy polydimethylsiloxane or to the corresponding branched isopropoxy siloxane. To prevent the thermal induced reverse cleavage reaction of the acetoxy siloxane under the gas chromatography analysis conditions, the derivatization is intentionally chosen to give isopropoxy siloxane (for the reverse cleavage reaction see inter alia J. Pola et al., Collect. Czech. Chem. Commun. 1974, 39(5), 1169-1176 and W. Simmler, Houben-Weyl, Methods of Organic Chemistry, Vol. VI / 2, 4th Edition, O-Metal Derivates of Organic Hydroxy Compounds p. 162 ff.).

[0054] The water content of the polyether alcohol used was about 0.2 mass-% and could be used without further pre-drying. The water content of the toluene and alkylbenzene (C 10 -C 13 ) used was 0.03 mass-% and was likewise used without pre-drying.

[0055] The OH number of the polyether alcohol was determined according to DGF C-V 17a (53) or according to Ph. Eur. 2.5.3 Method A, wherein the hydroxyl groups of the sample to be analyzed are first acetylated with acetic anhydride in the presence of pyridine and then the released acetic acid is titrated as consumption of KOH in the differential titration range (blank sample, for illustration of the acetic anhydride excess) (mg / g polyether glycol).

[0056] Example 1 (non-inventive)

[0057] Preparation of the cyclic branched siloxane with a target D / T ratio of 6:1

[0058] In a 10 L four necked round bottom flask with a precision glass stirrer and reflux condenser on the top, 783 g (4.39 mol) methyltriethoxysilane and 978.7 g (2.64 mol) decamethylcyclopentasiloxane were heated to 60°C together with 2.98 g trifluoromethanesulfonic acid under stirring, the mixture was allowed to equilibrate for 4 hours. Then 237 g water and 59.3 g ethanol were added and the mixture was heated to reflux temperature for another 2 hours. 159.0 g water and 978.8 g (2.64 mol) decamethylcyclopentasiloxane (D5) were added and the reflux condenser was exchanged to a distillation bridge and the components which are volatile up to 90°C were distilled off over the next one hour. Then 3000 ml toluene were added to the reaction mixture and the water still present in the system was removed by distillation in a water separator until a bottom temperature of 100°C. The reaction mixture was allowed to cool to about 60°C, the acid was neutralized by adding 60.0 g solid sodium bicarbonate and then the mixture was stirred for another 30 minutes to achieve complete neutralization. After cooling to 25°C the salt was removed by means of a fluted filter.

[0059] The toluene used as solvent was distilled off at 70°C with an applied auxiliary vacuum of < 1 mbar. The distillation bottoms was a colorless, flowing liquid which 29 The Si NMR spectrum showed a D / T ratio of 6.18:1 (target 6.0:1). The ratio of D units and T units with Si-alkoxy and / or SiOH groups was 0.52 mol% based on the sum of Si units detected by spectroscopy. Gas chromatographic analysis of the liquid also showed a proportion of simple siloxane ring bodies in the form of D4, D5 and D6 of about 15% by weight. The GPC had a broad molar mass distribution which was characterized by Mw = 55258 g / mol; Mn: 1693 g / mol, Mw / Mn = 32.63.

[0060] Example 2 (non-inventive)

[0061] Acetoxy terminated branched siloxane prepared by adding 1.5% acetic acid

[0062] First 49.9 g (0.489 mol) acetic anhydride and 268.1 g of the DT ring body prepared in example 1 (according to the procedure described in example 1) were charged under stirring in a 1000 ml four necked flask with a precision glass stirrer on the top, an internal thermometer and a reflux condenser. Then 0.5 g of a 5% platinum catalyst solution in water was added and the mixture was heated to 60°C. The reaction mixture was allowed to equilibrate for 4 hours. Then 237 g water and 59.3 g ethanol were added and the mixture was heated to reflux temperature for another 2 hours. 159.0 g water and 978.8 g (2.64 mol) decamethylcyclopentasiloxane (D5) were added and the reflux condenser was exchanged to a distillation bridge and the components which are volatile up to 90°C were distilled off over the next one hour. Then 3000 ml toluene were added to the reaction mixture and the water still present in the system was removed by distillation in a water separator until a bottom temperature of 100°C. The reaction mixture was allowed to cool to about 60°C, the acid was neutralized by adding 60.0 g solid sodium bicarbonate and then the mixture was stirred for another 30 minutes to achieve complete neutralization. After cooling to 25°C the salt was removed by means of a fluted filter. 29The D / T ratio of the Si NMR spectrum = 6.18:1, M = 525.42 g / mol, the ratio of SiOH / SiOEt groups = 0.52 mol%) and 188.5 g of decamethylcyclopentasiloxane (D5), and the mixture was mixed with 1.03 g (0.56 ml) of trifluoromethanesulfonic acid (0.2 mass% based on the total mixture) and 7.6 g of acetic acid (1.5 mass% based on the mass of the reactants) and quickly heated to 150°C. The initially slightly turbid reaction mixture was left at this temperature for 6 hours under constant stirring.

[0063] After cooling of the mixture, a colorless, clear, mobile liquid was isolated, which 29 The Si NMR spectrum confirmed the presence of Si-acetoxy groups, the yield (based on the acetic anhydride used) was about 88.2% and the fraction of Si-alkoxy and SiOH groups, which was detectable spectroscopically, completely disappeared.

[0064] Conversion of the branched acetoxy siloxane into the corresponding branched isopropoxy siloxane for analytical characterization

[0065] Immediately after synthesis, 25.0 g of this trifluoromethanesulfonic acid acidified equilibrated branched acetoxy siloxane were mixed together with 5.8 g of molecular sieve dried isopropanol at 22°C under stirring in a 100 ml four-necked round bottom flask equipped with a precision glass stirrer on the top, an internal thermometer and a reflux condenser. Gaseous ammonia (NH3) was then introduced into the reaction mixture until basic reaction (moist universal test paper) and then the mixture was stirred for another 45 minutes at this temperature. The precipitated salt was removed using a slot filter. A colorless, clear liquid was isolated, which was accompanied by 29 The Si NMR spectrum confirmed the quantitative conversion of the branched acetoxy siloxane into the branched isopropoxy siloxane.

[0066] An aliquot of this branched isopropoxy siloxane was taken and analyzed by gas chromatography. The gas chromatogram showed the following contents (reported in mass percentages):

[0067]

[0068] The content of siloxane ring members (D4, D5 and D6) is here calculated only based on the siloxane fraction, taking into account the isopropanol excess.

[0069] Example 3 (invention)

[0070] Purification of the branched acetoxy siloxane obtained in example 2

[0071] First, 150 g of the triflic-acidified branched acetoxy-containing siloxane obtained in Example 2 was charged into a four-necked round-bottom flask with a precision glass stirrer on the top, a reflux condenser, an internal thermometer and a gas inlet tube at 23°C under stirring. Over the course of 30 minutes, about 3 L of gaseous ammonia (rotameter) was introduced. Only 5 minutes later, the stirred liquid phase became visibly turbid due to the onset of salt precipitation.

[0072] After the introduction of ammonia was completed, the precipitate in the liquid was removed using a filter press (Seitz K 300 filter disc). The salt cake on the filter disc consisted of coarse, light brown crystals. The separated filtrate was a clear, colorless liquid which was subjected to an oil pump vacuum of about 1 mbar on a rotary evaporator for about 5 minutes to remove any ammonia still dissolved therein.

[0073] 29 The Si NMR spectrum confirmed the structure of the branched acetoxy-containing siloxane obtained. In contrast to the untreated starting material, a considerable increase in hydrolytic stability was produced, which was indicated, for example, by the fact that the purified material at most had a very small tendency to gel upon contact with water. In a simple manual experiment, about 1 ml of the branched acetoxy siloxane purified according to the application can be brought into contact with a few drops of water on a black bakelite lid. The gelling (formation of a solid, white gel layer) of the unpurified material, which sets in within a few minutes, does not occur here.

[0074] Example 4 (invention)

[0075] The conversion of the purified branched acetoxy siloxane obtained in Example 3 to a polyether siloxane (flexible polyurethane foam stabilizer)

[0076] First, 169.4 g of a butanol-started polyether alcohol mixture having an average molar mass of 2200 g / mol (determination of the respective molar masses from the respective OH values) in 200 ml of toluene (propylene oxide proportion 47 mass-%, ethylene oxide proportion 53 mass-%) was charged into a four-necked flask with a precision glass stirrer on the top, an internal thermometer and a reflux condenser under stirring, and this mixture was mixed with 40 g of the purified branched acetoxy siloxane prepared in Example 3.

[0077] The reaction mixture was heated to 50°C over the course of 30 minutes under continued stirring. Then, over the course of a further 30 minutes, a neutralization- required amount of gaseous ammonia was first introduced into the reaction matrix. Over the course of a further 45 minutes, an additional mild ammonia stream was introduced, so that the reaction mixture clearly showed an alkaline reaction (moist test paper). The precipitated salt was removed from the toluene phase via a double-sieve filter.

[0078] Toluene was removed from the crude product by distillation on a rotary evaporator at a bottom temperature of 70°C and an applied auxiliary vacuum of 1 mbar. An almost colourless SiOC-bonded branched polyether siloxane preparation was isolated, the target structure of which was determined by 29 Si NMR spectroscopy.

[0079] Example 5 (invention)

[0080] Purification of the branched acetoxy siloxane obtained in example 2

[0081] First, 150 g of the triflic acidified branched acetoxy siloxane obtained in example 2 were charged in a four-necked round bottom flask with a precision glass stirrer in the 500 ml head, a reflux condenser, an internal thermometer and a gas inlet tube at 100°C under stirring. 0.3 g (0.004 mol) of solid potassium acetate were added. The mixture was stirred for another 30 minutes at 100°C and then allowed to cool to a temperature of about 35°C.

[0082] The precipitate in the liquid was then removed using a filter press (Seitz K 300 filter disc). The salt cake on the filter disc consisted of coarse, almost colourless crystals. The isolated filtrate was a colourless clear liquid.

[0083] 29 Si NMR spectroscopy confirmed the structure of the branched acetoxy siloxane obtained. In contrast to the untreated starting material, considerable hydrolytic stability was produced, which was indicated, for example, by the fact that the material after purification had only a small tendency to gelate on contact with water. In a simple manual experiment, about 1 ml of the branched acetoxy siloxane purified according to the application could be brought into contact with a few drops of water on a black bakelite lid. The gelation (formation of a solid white gel layer) of the unpurified material, which solidified a gel within a few minutes, did not occur here.

[0084] Distillation of the filtrate to remove acetic acid, acetic anhydride and siloxane ring bodies

[0085] A one-hour distillation was carried out on a rotary evaporator at 130°C with an applied auxiliary vacuum of about 1 mbar. The distillation residue was used further.

[0086] Conversion of the branched acetoxy siloxane into the corresponding branched isopropoxy siloxane for analytical characterisation

[0087] In a 100 ml four necked round bottom flask, equipped with a precision glass stirrer, an internal thermometer and a reflux condenser at the top, 25.0 g of branched acetoxy siloxane purified by distillation were mixed with 5.8 g of dry isopropyl alcohol with molecular sieves under stirring at 22°C. Then gaseous ammonia (NH3) was introduced into the reaction mixture until basic reaction (wet universal test paper) and then the mixture was stirred for further 45 minutes at this temperature. The precipitated salt was removed using a slot filter. A colorless clear liquid was isolated which was accompanied by 29 The Si NMR spectrum confirmed the quantitative conversion of branched acetoxy siloxane into branched isopropoxy siloxane.

[0088] An aliquot of this branched isopropoxy siloxane was taken and analyzed by gas chromatography. The gas chromatogram showed the following contents (reported as mass percentages):

[0089]

[0090] The content of siloxane ring members (D4, D5 and D6) was calculated here only based on the siloxane part in view of the isopropyl alcohol excess.

[0091] Example 6

[0092] Conversion of the distilled branched acetoxy siloxane obtained in Example 5 to a polyether siloxane (flexible polyurethane foam stabilizer)

[0093] First, a 500 ml four necked flask was charged with 169.4 g of a butanol started polyether alcohol mixture with an average molar mass of 2200 g / mol (individual molar masses determined from the respective OH values) in 200 ml of toluene with a ratio of propylene oxide of 47 mass-% and a ratio of ethylene oxide of 53 mass-% under stirring and the mixture was mixed with 40 g of the branched acetoxy siloxane distilled in Example 5.

[0094] The reaction mixture was heated to 50°C for 30 minutes under continuous stirring. Then, during a further 30 minutes, a neutralizing amount of gaseous ammonia was first introduced into the reaction matrix. During a further 45 minutes, an additional mild ammonia stream was introduced, so that the reaction mixture clearly showed a basic reaction (wet test paper).

[0095] The precipitated salt was removed from the toluene phase via a double slot filter. Toluene was removed from the crude product by distillation on a rotary evaporator at a bottom temperature of 70°C and an applied auxiliary vacuum of 1 mbar.

[0096] A nearly colorless, SiOC bonded branched polyether siloxane was isolated with a target structure by 29The Si NMR spectrum confirmed and the content of siloxane ring bodies (D4, D5 and D6) determined by gas chromatography was less than 0.08 mass %.

[0097] Example 7 (non-inventive)

[0098] The addition of 1.5% acetic acid to produce acetoxy terminated linear polydimethylsiloxane

[0099] Under stirring, a 1000 ml four necked flask with a precision glass stirrer on top, an internal thermometer and a reflux condenser was first charged with 77.3 g (0.757 mol) acetic anhydride, 732.8 g (1.98 mol) decamethylcyclopentasiloxane (D5) and 12.2 g acetic acid (1.5 wt% based on the total mass of the reactants), the mixture was mixed with 1.62 g (0.88 ml) trifluoromethanesulfonic acid (0.2 mass% based on the total mixture) and quickly heated to 150°C. The initially slightly hazy reaction mixture was left at this temperature for 6 hours under continuous stirring.

[0100] After cooling the mixture, a colorless clear flowing liquid was isolated which 29 The Si NMR spectrum confirmed the presence of Si-acetoxy groups, the yield was about 93% based on the acetic anhydride used, corresponding to an alpha, omega-diacetoxy polydimethylsiloxane with an average total chain length of about 14.

[0101] The conversion of the alpha, omega-diacetoxy polydimethylsiloxane into the corresponding alpha, omega-diisopropoxy polydimethylsiloxane for analytical characterization

[0102] Immediately after synthesis, 50.0 g of this trifluoromethanesulfonic acid acidified equilibrated alpha, omega-diacetoxy polydimethylsiloxane was mixed together with 11.3 g molecular sieve dried isopropanol in a 250 ml four necked round bottom flask with a precision glass stirrer on top, an internal thermometer and a reflux condenser under stirring at 22°C. Gaseous ammonia (NH3) was then introduced into the reaction mixture until basic reaction (moist universal test paper) and the mixture was then stirred for another 45 minutes at this temperature. The precipitated salt was removed using a slot filter. A colorless clear liquid was isolated which was accompanied by 29 The Si NMR spectrum confirmed the quantitative conversion of the alpha, omega-diacetoxy polydimethylsiloxane into the alpha, omega-diisopropoxy polydimethylsiloxane. An aliquot of this alpha, omega-diisopropoxy polydimethylsiloxane was taken and analyzed by gas chromatography. The gas chromatogram showed the following content (reported in mass percent):

[0103]

[0104] The content of siloxane ring bodies (D4, D5 and D6) is calculated here only on the basis of the siloxane portion, taking into account the excess of isopropanol.

[0105] Example 8 (invention)

[0106] Purification of the linear acetoxy siloxane obtained in example 7

[0107] First, 310.4 g of the triflic acid- acidified linear acetoxy siloxane obtained in example 5 were charged into a four-necked round-bottom flask with a precision glass stirrer on the 500 ml top, a reflux condenser, an internal thermometer and a gas inlet tube at 23 °C under stirring. Over the course of 30 minutes, approximately 3 L of gaseous ammonia (rotameter) were introduced. Only 5 minutes later, the stirred liquid phase became visibly turbid as a result of the onset of salt precipitation.

[0108] After the introduction of ammonia was complete, the precipitate in the liquid was removed using a filter press (Seitz K 300 filter disc). The salt cake on the filter disc consisted of coarse, light brown crystals. The separated filtrate was a colourless, clear liquid which was subjected to an oil pump vacuum of approximately 1 mbar on a rotary evaporator for approximately 5 minutes in order to remove any ammonia still dissolved therein.

[0109] 29 The Si NMR spectrum confirmed the structure of the linear, alpha, omega-acetoxy- bearing siloxane obtained.

[0110] Example 9 (invention)

[0111] The purified linear acetoxy siloxane obtained in example 8 was converted in toluene with ammonia as auxiliary base to give a block copolymer of the SiOC- bonded, linear polydimethylsiloxane-polyalkylene oxide ABA structure type.

[0112] First, 96.0 g of a polypropyleneoxy-bearing polyether alcohol with a butanol start- ing and an average molar mass of 1935 g / mol (determined from the respective OH value) were charged into a four-necked flask with a precision glass stirrer on the 500 ml top, an internal thermometer and a reflux condenser under stirring. Then, 30.0 g of the purified, acetoxy-terminated linear siloxane prepared in example 6 were added. After only 5 minutes of stirring at 23 °C, the reaction matrix was clear. Using an inlet tube, gaseous ammonia was introduced into the reaction matrix, which continued to be stirred in moderate flow over the course of 45 minutes until a spot test on moist universal test paper indicated the basic reaction clearly.

[0113] Within a further 45 minutes, a reduced ammonia stream was introduced and the reaction mixture was heated to 50°C. The gas introduction was terminated and the mixture was cooled to 23°C before the salts present in the mixture were removed from the liquid using a tank filter. The clear filtrate thus obtained was stripped of volatiles on a rotary evaporator at a bath temperature of 70°C and an applied auxiliary vacuum of <1 mbar.

[0114] A colourless, clear polydimethylsiloxane-polyalkylene oxide block copolymer of the ABA structure was isolated which had a number average molecular weight of 10,000 g / mol and a polydispersity of 1.05. 29 Si NMR spectra confirmed the target structure. The polyether siloxane was then mixed with 0.2% N-methylmorpholine for end-stabilisation.

Claims

1. A process for purifying triflic acid acidified equilibrated acetoxy siloxanes containing acetic anhydride, characterized in that (a) triflic acid acidified equilibrated acetoxy siloxanes containing acetic anhydride and optionally acetic acid, optionally dissolved in an inert solvent, are contacted with a base, (b) the precipitate is filtered off, and (c) the resulting filtrate is optionally purified by distillation, wherein the base introduced in step (a) is ammonia, or in step (a) is contacted with a solid base and / or a liquid base, wherein the solid base and / or the liquid base to be used is a bicarbonate and / or a carbonate of an alkali metal or an alkaline earth metal, in this case optionally also in the form of a hydrate, and / or an organic amine base, or an acetate, wherein the triflic acid acidified equilibrated acetoxy siloxane to be purified is a triflic acid acidified equilibrated linear alpha, omega-acetoxy siloxane to be purified or a triflic acid acidified equilibrated branched acetoxy siloxane to be purified, said triflic acid acidified equilibrated linear alpha, omega-acetoxy siloxane to be purified has a total cyclics content of less than 13 wt.%, defined as the sum of the content fractions of cyclic siloxanes comprising D4, D5 and D6, based on the siloxane matrix and determined by gas chromatography after derivatization to the corresponding linear alpha, omega-isopropoxy siloxane, said triflic acid acidified equilibrated branched acetoxy siloxane to be purified has a total cyclics content of less than 8 wt.%, defined as the sum of the content fractions of cyclic siloxanes comprising D4, D5 and D6, based on the siloxane matrix and determined by gas chromatography after derivatization to the corresponding branched isopropoxy siloxane.

2. The process according to claim 1, wherein the triflic acid acidified equilibrated acetoxy siloxane containing acetic anhydride is terminally equilibrated.

3. The process according to claim 1, wherein the triflic acid acidified equilibrated acetoxy siloxane containing acetic anhydride and optionally acetic acid is terminally equilibrated. The base introduced in step (a) is ammonia, then the precipitate is filtered off, then the resulting filtrate is optionally distilled to remove siloxane cyclics and any inert solvent used, wherein the treatment of the siloxane with ammonia is carried out in a temperature range from 0 °C to 50 °C, wherein based on the cumulative amount of acids present in the equilibrated acetoxy siloxane, and optionally acetic acid, and acetic anhydride, an excess of ammonia is used in a stoichiometric excess of 1 to 10 times. The precipitate comprises ammonium triflate, ammonium acetate and acetamide, the siloxane cyclics include D4, D5, D6.

6. The process according to claim 4, wherein the treatment of the siloxane with ammonia is carried out in a temperature range from 15 °C to 35 °C.

7. The process according to claim 4, wherein the equilibrated acetoxy siloxane is terminally equilibrated.

4. The method according to claim 1, characterized in that The acids present in the equilibrated acetoxy siloxane comprise triflic acid. ​ ​ ​ 5. The method according to claim 4, characterized in that, ​ ​ ​ 8. The method of claim 4, wherein, ​ 9. The process according to claim 4, wherein 1 to 5 stoichiometric excess of ammonia is used, based on the cumulative amount of acid present in the equilibrated acetyloxysiloxane, and optionally of acetic acid, and of acetic anhydride.

10. The method of claim 1, wherein, In step (a), the contact with the solid base and / or the liquid base is followed by filtration of the precipitate, and the resulting filtrate is optionally distilled, wherein the treatment of the siloxane with the solid base and / or the liquid base is carried out at a temperature in the range of 0 °C to 140 °C, wherein 1 to 10 stoichiometric excess of the solid base and / or the liquid base is used, based on the equivalent amount of acid to be neutralized.

11. The method according to claim 1, wherein, The organic amine base is a primary and / or secondary and / or tertiary amine, an amine bearing a hydroxyalkyl group.

12. The method according to claim 10, wherein, The precipitate comprises triflate.

13. The method according to claim 10, wherein, The resulting filtrate is optionally distilled in order to remove acetic acid, acetic anhydride, siloxane ring body and any inert solvent used.

14. The method according to claim 13, wherein, The siloxane ring body comprises D4, D5, D6.

15. The method according to claim 11, wherein, The amine bearing a hydroxyalkyl group is diisopropanolamine and / or triisopropanolamine.

16. The method according to claim 10, wherein, The treatment of the siloxane with the solid base and / or the liquid base is carried out at a temperature in the range of 20 °C to 110 °C.

17. The method according to claim 10, wherein, 1 to 10 stoichiometric excess of the solid base and / or the liquid base is used, based on the equivalent amount of triflate to be neutralized.

18. The method according to claim 17, wherein, 1 to 5 stoichiometric excess of the solid base and / or the liquid base is used, based on the equivalent amount of triflate to be neutralized.

19. The method according to claim 10, wherein, 1 to 5 stoichiometric excess of the solid base and / or the liquid base is used, based on the equivalent amount of acid to be neutralized.

20. The method according to any one of claims 1 to 19, characterized in that, The acetyloxysiloxane to be purified is prepared from a cyclic siloxane, and / or from a mixture of siloxanes bearing hydroxyl groups and / or from a mixture of cyclic branched siloxanes of the D / T type, using triflic acid as catalyst with acetic anhydride and the addition of acetic acid, or The linear or branched acetyloxysiloxane to be purified has been prepared in a reaction system comprising a) to e): a) silane and / or siloxane bearing an alkoxy group, and / or b) silane and / or siloxane bearing an acetoxy group, and / or c) silane and / or siloxane bearing a hydroxyl group, d) optionally simple siloxane ring body and / or DT ring body, e) reaction medium comprising acetic anhydride, perfluoroalkanesulfonic acid, acetic acid.

21. The method according to claim 20, wherein, The cyclic siloxane comprises D4 and / or D5.

22. The method according to claim 20, wherein, The perfluoroalkanesulfonic acid is triflic acid.

23. The method according to any one of claims 1 to 19, characterized in that, The amount of acetic acid contained in the acetyloxysiloxane to be purified is 0.4-3.5 wt.%, based on the acetyloxysiloxane to be purified.

24. The method of claim 23, wherein, The amount of acetic acid contained in the acetyloxysiloxane to be purified is 0.5-3 wt.%, based on the acetyloxysiloxane to be purified.

25. The method of claim 23, wherein, The amount of acetic acid contained in the acetyloxysiloxane to be purified is 0.8-1.8 wt.%, based on the acetyloxysiloxane to be purified.

26. The method of claim 23, wherein, The amount of acetic acid contained in the acetyloxysiloxane to be purified is 1.0-1.5 wt.%, based on the acetyloxysiloxane to be purified.

27. The method according to any one of claims 1 to 19, characterized in that, The acetyloxysiloxane to be purified is prepared from a mixture of cyclic branched siloxanes of the D / T type, wherein the mixture of D / T cyclic branched siloxanes consists only of siloxanes having D units and T units and they are present in the siloxane matrix, are able to pass through 29 a cumulative proportion of D units and T units having Si-alkoxy and / or SiOH groups determined by Si NMR spectroscopy of < 2 mol%, Alternatively, the acetoxy-bearing siloxane to be purified is prepared from a mixture of cyclic branched siloxanes having only D units and T units, and which is present in the siloxane matrix, able to be purified by 29 The cumulative proportion of D units and T units having Si-alkoxy and / or SiOH groups determined by Si NMR spectroscopy is greater than 2 mol% and less than 10 mol%.

28. The method of claim 27, wherein, The mixture of D / T type cyclic branched siloxanes consists only of siloxanes having D units and T units, and they are present in the siloxane matrix, are able to pass through 29 The cumulative proportion of D units and T units having Si-alkoxy and / or SiOH groups determined by Si NMR spectroscopy is less than 1 mol%.

29. The method of claim 28, wherein, The mixture comprises at least 5 wt.% of siloxane ring body.

30. The method of claim 29, wherein, The siloxane ring bodies are octamethylcyclotetrasiloxane D4, decamethylcyclopentasiloxane D5 and / or mixtures thereof.

31. The method of claim 1, wherein, The triflic acidified, equilibrated, linear, alpha, omega-acetoxy-bearing siloxane to be purified has a total ring body content of less than 12% by weight.

32. The method of claim 1, wherein, The triflic acidified, equilibrated, linear, alpha, omega-acetoxy-bearing siloxane to be purified is terminally equilibrated.

33. The method of claim 1, wherein, The triflic acidified, equilibrated, branched, acetoxy-bearing siloxane to be purified has a total ring body content of less than 7% by weight.

34. The method of claim 1, wherein, The triflic acidified, equilibrated, branched, acetoxy-bearing siloxane to be purified is terminally equilibrated.

35. The method according to any one of claims 1 to 19, characterized by, The acetoxy-bearing siloxane to be purified contains triflic acid in an amount of 0.1 to 1.0 mass %.

36. The method of claim 35, wherein, The acetoxy-bearing siloxane to be purified contains triflic acid in an amount of 0.1 to 0.3 mass %.

37. The method according to any one of claims 1 to 19, characterized by, The inert solvents used are alkanes, cycloalkanes, aromatics and alkylaromatics.

38. The method of claim 37, wherein, The inert solvents used are toluene.

39. The method according to any one of claims 1 to 19, characterized by, The process is carried out without solvent.

40. Linear siloxane with terminal balance of α,ω-acetoxy prepared by the method according to any one of claims 1 to 26, 32, characterized in that, They have a total ring body content of less than 13% by weight, defined as the sum of the content fractions of the cyclic siloxanes comprising D4, D5 and D6, based on the siloxane matrix and determined by gas chromatography after their derivatization to the corresponding linear alpha, omega-isopropoxy siloxanes.

41. End-balanced linear siloxane with α,ω-acetoxy groups according to claim 40, characterized in that, They have a total ring body content of less than 12% by weight.

42. A terminally balanced branched acetoxy-functional siloxane prepared by the method according to any one of claims 1 to 30 and 33 to 34, characterized in that, They have a total ring body content of less than 8% by weight, defined as the sum of the content fractions of the ring body siloxanes comprising D4, D5 and D6, based on the siloxane matrix and determined by gas chromatography after their derivatization to the corresponding branched isopropoxy siloxanes.

43. End-balanced branched acetoxy-containing siloxane according to claim 42, characterized in that, They have a total ring body content of less than 7% by weight.

44. Use of the purified, terminally equilibrated, acetoxy group-bearing siloxane according to any one of claims 40 to 43 as starting material for the preparation of SiOC-bonded polyether siloxanes for use in PU foam stabilizers, defoamers, demulsifiers, emulsifiers and in paint and levelling additives.

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