LINEAR ACETOXY-BEARING SILOXANES AND DERIVATIVES

Description

[0001] The invention lies in the field of silicone chemistry. It relates to a process for the production of linear acetoxy group-bearing siloxanes and the superacidic (end) equilibrated linear α,ω-acetoxy group-bearing siloxanes produced according to the process.

[0002] Routes to acetoxy-functional siloxanes have already been described in the literature. For example, the non-equilibrating opening of simple, unbranched siloxane cycles with acetic anhydride to short-chain, chain-terminal acetoxy group-bearing siloxanes in the presence of catalysts is known.

[0003] Borisov and Sviridova describe the opening of cyclic dimethylsiloxanes with acetic anhydride in the presence of catalytic amounts of iron(III) chloride to give short-chain α,ω-acetoxysiloxanes (SN Borisov, NGSviridova, J. Organomet. Chem. 11 (1968), 27-33). Lewis et al., in US 4,066,680, devotes attention to the preparation of short-chain α,ω-siloxanediols, whereby he reacts octamethylcyclotetrasiloxane with acetic anhydride on acid-treated bleaching earths and hydrolyzes the mixtures of short-chain α,ω-acetoxysiloxanes thus obtained in alkaline water.

[0004] US 3,346,610 also discloses a route to short-chain siloxanes bearing acetoxy groups, based on the metal halide-induced acetoxy modification of strained cyclic siloxanes by reacting them with acetoxy-containing silicon compounds. A variety of Friedel-Crafts active metal halides act as catalysts, with zinc chloride being the preferred choice. A specific objective of US 3,3466,10 is the acetoxy modification of strained diorganosiloxane cycles while deliberately avoiding equilibration processes.

[0005] The state of the art thus refers to works that involve the opening of cyclic siloxanes - sometimes strained cyclosiloxanes - with reactants containing acyloxy groups, and whose objective is to obtain defined linear short-chain siloxane species and the siloxane species that can still be separated by fractional distillation.

[0006] However, the molecular weight-defined, chain-pure acetoxy-modified siloxane compounds synthesized in this way are not suitable for the production of organomodified siloxanes, especially polyethersiloxanes, which are used in demanding technical applications such as PU foam stabilization or fuel defoaming, etc. Active ingredients that effectively address such an application area are always characterized by a broad oligomer distribution encompassing high, medium, and low molecular weights, since the oligomers they contain, depending on their molecular weight and thus their diffusion behavior, very often perform differentiated surfactant functions in different time windows of the respective process.

[0007] Acyloxy-organopolysiloxanes, and in particular organosiloxanes with terminal acyloxy groups, are also known as starting materials for subsequent reactions. For example, the acyloxy groups on a diorganosiloxane can be hydrolyzed, after which the hydrolysate can be dehydrated and the dehydrated hydrolysate polymerized to form free-flowing diorganopolysiloxane. These free-flowing polysiloxanes are suitable as starting materials for the production of viscous oils and rubbers, which can be cured to form silicone elastomers.

[0008] Organosiloxanes with terminal acyloxy groups can be obtained, for example, by reacting an alkylsiloxane with an organic acid and / or its anhydride in the presence of sulfuric acid as a catalyst. Such a process is described in US Patent 2,910,496 (Bailey et al.). Although this process can, in principle, also yield organosiloxanes with terminal acyloxy groups, it has the disadvantage that the reaction product consists of a mixture of acyloxy-containing siloxanes and acyloxy-bearing silanes of varying composition. Specifically, the patent application states that alkylsiloxane copolymers composed of M, D, and T units are cleaved by this process into trimethylacyloxysilane, diacyloxydimethylsiloxane, and methyltriacyloxysilane.Thus, when Bailey reacts octamethylcyclotetrasiloxane with acetic anhydride and acetic acid, after neutralizing the sulfuric acid used as a catalyst, separating the salts, and removing water, residual acetic acid, and acetic anhydride, he obtains a complex mixture and by no means an equilibrate, which he then subjects to fractional distillation (see example, ibid.). The chemical identity of the fractions II and IV obtained in this way remains unclear, making it difficult to obtain defined products or to separate them from the mixture in high yields.

[0009] Referring to Bailey et al. (US 2,910,496), DE-OS 1545110 (A1) (Omietanski et al.) describes a process in which an acyloxy group of an acyloxysiloxane reacts with the hydroxyl group of a polyoxyalkylene hydroxypolymer to form a siloxane-oxyalkylene block copolymer and a carboxylic acid, with the carboxylic acid being removed from the reaction mixture. The solvent- and catalyst-free reactions described therein require, in some cases, considerable reaction times (up to 11.5 hours (Example 1)), very high, product-loading reaction temperatures (150 to 160°C (Example 1)), and the application of an auxiliary vacuum or stripping of the reaction matrix with dry nitrogen for the entire reaction duration. Despite the harsh reaction conditions, complete conversion at the product stage is not always achieved (Example 9, ibid.).

[0010] From a production engineering perspective, the combination of high conversion temperatures and long reaction times, as well as the unpredictable product quality, are particularly detrimental to the process described by Omietanski et al.

[0011] The teaching of application EP 3611217 A1 discloses that trifluoromethanesulfonic acid equilibrated α,ω-diacetoxysiloxanes can be produced by reacting siloxane cycles (D 4 and / or D 5 ) with acetic anhydride in the presence of trifluoromethanesulfonic acid and that these diacetoxysiloxanes react rapidly and completely with polyether(mono)ols at moderate temperatures to form SiOC-linked polyethersiloxanes of structure type ABA.

[0012] CA1125780 A discloses a process for the preparation of α,ω-siloxanediols from α,ω-diacetoxysiloxanes as an intermediate. The α,ω-diacetoxysiloxanes are prepared by reacting siloxanediols with acetic anhydride and acetic acid in the presence of acidic bleaching earth under reflux.

[0013] The inventors have now surprisingly found that it is also possible to obtain superacidic (preferably trifluoromethanesulfonic acids), end-equilibrated α,ω-diacetoxysiloxanes, in particular those described in EP 3611217 A1 and EP 3611216 A1, by reacting linear hydroxy group-bearing siloxanes with acetic anhydride, superacid (preferably perfluoroalkanesulfonic acid, especially trifluoromethanesulfonic acid) and acetic acid.

[0014] The present invention thus relates to a process for the production of superacidic, preferably trifluoromethanesulfonic, (end)equilibrated linear α,ω-acetoxy group-bearing siloxanes, wherein one (i) linear α,ω-hydroxy group-bearing siloxanes, (ii) using a superacid, preferably perfluoroalkanesulfonic acid, particularly preferably trifluoromethanesulfonic acid as a catalyst (iii) with acetic anhydride and with the addition of acetic acid implemented.

[0015] The superacidic, end-equilibrated linear α,ω-diacetoxysiloxanes resulting from the invention, produced according to the inventive process, exhibit such high reactivity that they can be further processed, for example, with polyetherols, polyetherdiols and / or monools to form the sophisticated linear SiOC-linked polyethersiloxane structures.

[0016] The resulting superacidic, end-equilibrated linear α,ω-diacetoxysiloxanes can be used to prepare linear SiOC-linked polyethersiloxanes.

[0017] Superacidic (preferably trifluoromethanesulfonic acid) end-equilibrated linear α,ω-diacetoxypolydimethylsiloxanes are obtainable according to the invention by reacting hydroxy group-bearing siloxanes using superacidic acid (preferably perfluoroalkanesulfonic acid, in particular trifluoromethanesulfonic acid) as a catalyst with acetic anhydride and with the addition of acetic acid.

[0018] The superacid (preferably trifluoromethanesulfonic acid) is preferably used in amounts of 0.1 to 1.0 wt%, more preferably 0.1 to 0.3 wt%, based on the reaction matrix comprising acetic anhydride and hydroxy-group-bearing siloxanes. The reaction is preferably carried out in the temperature range of 140 to 160°C and preferably over a period of 4 to 8 hours.

[0019] Preferably, the linear α,ω-hydroxy group-bearing siloxanes according to the invention satisfy at least formula (I) with R 1< equal to alkyl group and / or aromatic group comprising 1 to 10 C atoms, preferably a methyl group and with 1 ≤ n ≤ 19,000, preferably n between 3 and 200, particularly preferably n between 20 and 100.

[0020] According to the invention, the term "superacid" refers to Brønsted acids, that is, proton-donating compounds. Thus, both homogeneous and heterogeneous, liquid and solid acidic systems, and especially polymeric and / or supported acidic systems, can be considered superacids. Heteropolyacids are also included. Polyoxometalates, together with acidic hydrogen ions, form heteropolyacids, which can be used as acids according to the invention. According to the invention, these acids function as catalysts.

[0021] The catalyst superacid, preferably perfluoroalkanesulfonic acid, especially trifluoromethanesulfonic acid, is used according to a preferred embodiment of the invention in amounts of 0.1 to 1.0 wt. percent, preferably 0.1 to 0.3 wt. percent, based on the reaction matrix comprising the acetic anhydride and hydroxy group-bearing siloxanes.

[0022] According to a preferred embodiment of the invention, acetic acid is added in amounts of 0.4 to 3.5 wt%, preferably 0.5 to 3 wt%, preferably 0.8 to 1.8 wt%, and particularly preferably in amounts of 1.0 to 1.5 wt% based on the reaction matrix comprising acetic anhydride and hydroxy group-bearing siloxanes.

[0023] According to a preferred embodiment of the invention, the amount of acetic anhydride to be used is to be dimensioned at least such that all Si-bound hydroxy groups of the α,ω-hydroxy group-bearing siloxane used are replaced by acetoxy groups and at the same time the released water equivalent is bound by reaction with further acetic anhydride in the form of two equivalents of acetic acid.

[0024] According to a particularly preferred embodiment, the reaction takes place in a reactor whose volume is at least 1 liter, preferably at least 5 liters, in particular at least 10 liters, and preferably a maximum of 500,000 liters.

[0025] The term "reactor" is familiar to those skilled in the art. A reactor is defined as a confined space, such as a stirred vessel or a pipe, in which chemical reactions can be carried out in a controlled manner. As those skilled in the art know, these can be open or closed vessels in which the reactants are converted into the desired products or intermediates. The volume of reactors is specified by the manufacturer or can be determined by measuring the volume.

[0026] In addition to the linear α,ω-hydroxy group-bearing siloxanes which are mandatory according to the invention, optionally hydroxy group-bearing silanes, such as dimethylsilanediol, and / or simple siloxane cycles, in particular comprising D 4 and / or D 5, can also be used and can be part of the reaction matrix.

[0027] The superacidic, preferably trifluoromethanesulfonic, (end)equilibrated linear α,ω-acetoxy group-bearing siloxanes have, in a preferred embodiment of the invention, at least 3, preferably 5 to 50, preferably 7 to 25, particularly preferably 10 to 20 organosiloxane units.

[0028] According to the invention, trifluoromethanesulfonic acid end-equilibrated linear α,ω-diacetoxypolydimethylsiloxanes are particularly preferred.

[0029] The term "end-equilibrated" means that the equilibrium equilibration has been reached, which is established at a temperature of 23°C and a pressure of 1013.25 hPa. The total cycle content, determined by gas chromatography, can be used as an indicator of reaching equilibrium. This is defined as the sum of the D4, D5, and D6 contents relative to the siloxane matrix and determined after the derivatization of the α,ω-diacetoxypolydimethylsiloxanes to the corresponding α,ω-diisopropoxypolydimethylsiloxanes. The use of acetic acid according to the invention allows for the straightforward reduction of the otherwise typical equilibrium fractions of approximately 13% by weight of the total cycle content for the linear α,ω-diacetoxypolydimethylsiloxanes.Accordingly, a preferred embodiment is achieved if the equilibrium fractions of the total cycle content are less than 13, preferably less than 12, wt% for the linear α,ω-diacetoxypolydimethylsiloxanes. The derivatization to the α,ω-diisopropoxypolydimethylsiloxanes is deliberately chosen here to prevent a thermally induced back-cleavage reaction of the α,ω-diacetoxypolydimethylsiloxanes that may occur under the conditions of gas chromatographic analysis (for the back-cleavage reaction, see, among others, J. Pola et al., Collect. Czech. Chem. Commun. 1974, 39(5), 1169-1176 and also W. Simmler, Houben-Weyl, Methods of Organic Chemistry, Vol. VI / 2, 4th Edition, O-Metal Derivates of Organic Hydroxy Compounds, p. 162 ff.).

[0030] As shown, the process according to the invention provides elegant access to superacidic, preferably trifluoromethanesulfonic, end-equilibrated linear α,ω-acetoxy group-bearing siloxanes. A further object of the present invention is therefore superacidic, preferably trifluoromethanesulfonic, end-equilibrated linear α,ω-acetoxy group-bearing siloxanes, prepared according to a process as described above, which are characterized in that they have total cycle contents, 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 α,ω-isopropoxysiloxanes, of less than 13, preferably less than 12, wt%.According to a preferred embodiment, the superacidic, preferably trifluoromethanesulfonic, (end)equilibrated linear α,ω-acetoxy group-bearing siloxanes have at least 3, preferably 5 to 50, preferably 7 to 25, particularly preferably 10 to 20 organosiloxane units.

[0031] The end-equilibrated superacidic, preferably trifluoromethanesulfonic, linear acetoxy group-bearing siloxanes obtainable according to the invention can be used as starting materials for the production of SiOC-linked linear polyether siloxanes.

[0032] The end-equilibrated superacidic, preferably trifluoromethanesulfonic, linear acetoxy group-bearing siloxanes are used as starting materials for the production of linear SiOC-linked polyethersiloxanes, in particular for their subsequent use in PU foam stabilizers, defoamers, dismulsifiers, emulsifiers, and paint and leveling additives; as well as for their use as deaerators; as foam stabilizers, in particular as polyurethane foam stabilizers; as wetting agents; as water repellents; as leveling agents; for the production of polymer dispersions; for the production of adhesives or sealants; for the surface treatment of fibers, particles, or sheet structures, in particular for the finishing or impregnation of textiles, for the production of paper towels, and in the coating of fillers.For the manufacture of cleaning and care formulations for household or industrial applications, in particular for the manufacture of fabric softeners; for the manufacture of cosmetic, pharmaceutical and dermatological compositions, in particular cosmetic cleaning and care formulations, hair treatment products and hair after-treatment products; for the cleaning and care of hard surfaces; as a process aid in the extrusion of thermoplastics; for the manufacture of thermoplastic molded parts and / or as an adjuvant in plant protection; for the manufacture of building material compositions; for the manufacture of silicone-containing coatings, in particular silicone release coatings.

[0033] Furthermore, the desired SiOC-linked linear polyethersiloxanes are obtained by reacting the end-equilibrated linear α,ω-acetoxy group-bearing siloxanes with polyetherols, polyetherdiols and / or monools, wherein the reaction takes place in the presence of at least one base, in particular in the presence of carbonate salts, ammonia or an organic amine, and wherein the reaction is preferably carried out in the temperature range of 40 to 180°C, preferably between 50 and 160°C, particularly preferably between 80 and 150°C.

[0034] Preferably, the exchange of the siloxane-bound acetoxy groups can be carried out by reaction with polyetherols, polyetherdiols and / or monools using an inert solvent, preferably using an inert solvent that forms an azeotrope with the acetic acid produced and optionally already present, wherein the inert solvent is advantageously an aromatic, preferably alkyl-aromatic solvent, and most preferably selected from toluene, xylene and esters selected from methoxypropyl acetate, ethyl acetate or butyl acetate.

[0035] The reaction can take place in a reactor whose volume is at least 1 liter, preferably at least 5 liters, in particular at least 10 liters, and preferably a maximum of 500,000 liters.

[0036] Preferably, the exchange of the siloxane-bound acetoxy groups can be carried out solvent-free by reaction with polyetherols, polyetherdiols, and / or monools, i.e., without the addition of auxiliary solvents that are inert in the reaction. All compounds with alcoholic OH groups (polyetherols, polyetherdiols, and / or monools) are, however, reactants.

[0037] Polyetherols can be those of formula (II) A[-O-(CH 2 -CHR'-O-) m -(CH 2 -CH 2 -O-) n --(CH 2 -CH(CH 3 )-O-)oZ] a (II) with A is either hydrogen or a saturated or unsaturated organic residue having at least one carbon atom, preferably an organic residue having at least one carbon atom from an organic starting compound for preparing the compound, particularly preferably a methyl, ethyl, propyl, isopropyl, butyl, isobutyl, vinyl, or allyl group, R' is independently a saturated alkyl group with 2-18 carbon atoms or an aromatic residue, respectively preferably an ethyl group or a phenyl residue, Zhydrogen is equal to 0 to 50, preferably 0 to 30, particularly preferably 0 to 20, m is equal to 0 to 250, preferably 3 to 220, particularly preferably 5 to 200, o is equal to 0 to 250, preferably 3 to 220, particularly preferably 5 to 200, a is equal to 1 to 8, preferably greater than 1 to 6, especially preferably 1, 2, 3 or 4, with the proviso that the sum of m, n and o is equal to or greater than 1 and with the proviso that at least A or Z represent hydrogen.

[0038] The monools can be selected from ethanol, propanol, isopropanol, butanol, isobutanol and polyetherol according to formula (II), where A is not hydrogen.

[0039] One can use at least 1 mol of polyether-bound OH functionality per mol of acetoxy group of the siloxane, preferably 1 to 2 mol of polyether-bound OH functionality, preferably 1.1 to 1.6 mol of polyether-bound OH functionality, particularly preferably 1.2 to 1.4 mol of polyether-bound OH functionality per mol of acetoxy group of the siloxane.

[0040] The reaction of linear α,ω-diacetoxypolydimethylsiloxanes with polyetherols, polyetherdiols and / or monools is carried out in a solvent that is inert under reaction conditions, wherein preferred solvents are toluene and / or the pure xylenes or xylenes present as a mixture of isomers, and wherein these solvents are preferably used in total amounts of 5 to 35 wt.%, preferably 10 to 35 wt.%, based on the mass of the reaction matrix, and wherein the total water content of the solvents is ≤ 50 wt. ppm, preferably ≤ 25 wt. ppm, particularly preferably ≤ 10 wt. ppm, wherein the determination of the water content is carried out by titration according to Karl Fischer.

[0041] The reaction of the linear α,ω-diacetoxypolydimethylsiloxanes with polyetherols, polyetherdiols and / or monools is carried out in the temperature range of 40 to 180°C, preferably between 50 and 160°C, particularly preferably between 80 and 150°C.

[0042] The reaction of linear α,ω-diacetoxypolydimethylsiloxanes is carried out with polyetherols, polyetherdiols and / or monools at reduced pressure and / or by passing through an inert gas.

[0043] The superacidic (preferably trifluoromethanesulfonic acids) end-equilibrated linear α,ω-diacetoxy-polydimethylsiloxanes can be reacted with polyetherols, polyetherdiols, and / or monools by adding a solid, liquid, or gaseous base, optionally using an inert solvent. Suitable simple bases include, for example, alkali or alkaline earth carbonates and / or hydrogen carbonates and / or gaseous ammonia and / or amines. Taking into account the known tendency of acetoxysiloxanes to condense, bases that do not introduce water into the reaction system due to their chemical composition are particularly preferred. Thus, anhydrous carbonates are preferable to hydrogen carbonates, and bases free of hydration are preferable to those containing water of hydration.

[0044] Taking into account the low solubility of the alkali or alkaline earth carbonates and / or hydrogen carbonates in the reaction system, higher excesses of these are selected, preferably corresponding to at least 2000 times the stoichiometric equivalent of the superacid (preferably trifluoromethanesulfonic acid) contained in the α,ω-diacetoxypolydimethylsiloxane.

[0045] The use of gaseous ammonia as a base is particularly preferred, so that the acetic acid released during the reaction is bound as ammonium acetate.

[0046] The amount of solid, liquid, or gaseous base introduced into the reaction system is measured to neutralize the superacid present in the system (preferably trifluoromethanesulfonic acid), precipitate the acetate groups bound to the siloxane, and precipitate any remaining acetic anhydride and, optionally, free acetic acid. The reaction is preferably carried out at temperatures between 20 and 120°C, more preferably between 20 and 70°C, for a duration of 1 to 10 hours, preferably at least 1 to 3 hours.

[0047] The superacidic (preferably trifluoromethanesulfonic acid) end-equilibrated linear α,ω-diacetoxy-polydimethylsiloxane can be reacted with polyetherols, polyetherdiols, and / or monools at temperatures below 25°C with stirring, followed by the introduction of ammonia. This embodiment, carried out with a high ammonia input, binds the acetic acid released during the reaction as ammonium acetate, in addition to the superacidic acid (preferably trifluoromethanesulfonic acid), acetic anhydride, and optionally free acetic acid present in the reaction system. The reaction is preferably carried out at temperatures between 20 and 70°C for a duration of preferably 1 to 3 hours.

[0048] If the superacidic (preferably trifluoromethanesulfonic acids), (end)equilibrated linear α,ω-diacetoxypolydimethylsiloxanes produced according to the invention are reacted with polyether diols (formula (II) with A = hydrogen) by adding a solid, liquid or gaseous base, preferably using a suitable solvent, linear A(BA)n-polyethersiloxane structures are obtained, which are of particular importance as polyurethane foam stabilizers for viscoelastic PU foams and for the so-called PU impact foam (for example, for carpet backing).

[0049] The quality of the superacidic (preferably trifluoromethanesulfonic acid) linear α,ω-diacetoxypolydimethylsiloxane used is crucial for achieving a high-molecular-weight SiOC-linked A(BA)n polyethersiloxane structure. As the inventors surprisingly discovered during a comprehensive investigation, ensuring a perfect equilibration result in the α,ω-diacetoxypolydimethylsiloxane (i.e., end-equilibrated) is essential for constructing high-molecular-weight SiOC-linked A(BA)n polyethersiloxane structures.

[0050] Unforeseeably for the expert, structures are obtained in this way which, as stabilizers in the production of polyurethane foams (PU foams), especially flexible PU foams, exhibit dramatically improved properties.

[0051] Also of interest is a method for the preparation of SiOC-linked, linear polydimethylsiloxane-polyoxyalkylene block copolymers with repeating (AB) units by reacting polyether diols with superacidic (preferably trifluoromethanesulfonic) end-equilibrated linear α,ω-diacetoxypolydimethylsiloxanes, wherein the reaction is carried out by adding a solid, liquid or gaseous base and optionally using inert solvents.

[0052] Equilibrated linear α,ω-diacetoxypolydimethylsiloxanes of this quality, i.e., end-equilibrated α,ω-diacetoxypolydimethylsiloxanes, can be very advantageously prepared, even after a very short reaction time, by reacting hydroxy-bearing siloxanes with acetic anhydride in the presence of a superacid (preferably trifluoromethanesulfonic acid) and acetic acid. Acetic acid is preferably added in amounts of 0.4 to 3.5 wt%, more preferably 0.5 to 3 wt%, further preferably 0.8 to 1.8 wt%, and particularly preferably 1.0 to 1.5 wt% based on the reaction matrix comprising acetic anhydride and hydroxy-bearing siloxanes.

[0053] The provision of trifluoromethanesulfonic acids, end-equilibrated linear α,ω-diacetoxypolydimethylsiloxanes that can be used according to the invention is described by way of example in Example 1 of the present invention.

[0054] A reaction monitoring method has proven effective according to the invention, in which samples are taken from the reaction matrix over the course of the reaction and then analyzed, for example, using 29Si NMR and / or 13C NMR spectroscopy. The decrease in the integral of the signal levels characteristic of the presence of acetoxydimethylsiloxy groups -OSi(CH3)2OCOCH3 corresponds to the intended SiOC coupling to form the desired polyethersiloxane copolymer and is a reliable indicator of the achieved reaction conversion.

[0055] The linear silicon polyether copolymers produced according to the invention are suitable alone and / or in mixture with other components for the production of preparations for defoamers, deaerators, foam stabilizers, wetting agents, paint and leveling additives or as dismulsifiers.

[0056] Furthermore, the linear silicone polyether copolymers produced according to the invention are suitable for the production of diesel defoamers, hydrophobing agents, polymer dispersions, adhesives or sealants, paper towels; cleaning and care formulations for household or industrial applications, in particular for the production of fabric softeners, cosmetic, pharmaceutical and dermatological compositions, in particular cosmetic cleaning and care formulations, hair treatment products and hair after-treatment products; building material compositions, thermoplastic molded bodies.

[0057] The use of the preparation according to the invention as a process aid in the extrusion of thermoplastics, as an adjuvant in plant protection, as an additive for cleaning and maintaining hard surfaces, for surface treatment of fibers, particles or sheet structures, in particular for finishing or impregnating textiles, or in the coating of fillers is also conceivable, as is the use for the production of silicone-containing coatings, in particular silicone release coatings. Examples:

[0058] The following examples serve solely to illustrate this invention to those skilled in the art and do not constitute any limitation of the claimed subject matter. The determination of water content is generally carried out using the Karl Fischer method in accordance with DIN 51777, DGF E-III 10 and DGF C-III 13a. 29<Si NMR spectroscopy was used in all examples for reaction monitoring.

[0059] Within the scope of this invention, the 29< Si NMR samples are measured at a measurement frequency of 79.49 MHz in a Bruker Avance III spectrometer equipped with a 287430 probe head with a 10 mm slit width, dissolved in CDCl3 at 22°C and against tetramethylsilane (TMS) as an external standard [δ( 29< Si) ​​= 0.0 ppm].

[0060] The GPCs (gel permeation chromatography) are recorded using THF as the mobile phase on a column combination SDV 1000 / 10000A, length 65 cm, ID 0.80 at a temperature of 30°C on a SECcurity 2< GPC System 1260 (PSS Polymer Standards Service GmbH).

[0061] The gas chromatograms are recorded on an Agilent Technologies GC 7890B instrument equipped with an HP-1 column; 30m x 0.32mm ID x 0.25µm dF (Agilent Technologies No. 19091Z-413E) and hydrogen as the carrier gas with the following parameters: Detector: FID; 310°C Injector: Split; 290°C Mode: constant flow 2 mL / min Temperature program: 60°C with 8°C / min -150°C with 40°C / min - 300°C 10 min.

[0062] As an indicator of reaching equilibrium, the total cycle content determined by gas chromatography is defined as the sum of the D4, D5, and D6 contents based on the siloxane matrix and determined after derivatization of the α,ω-diacetoxypolydimethylsiloxanes to the corresponding α,ω-diisopropoxypolydimethylsiloxanes. The derivatization to the α,ω-diisopropoxypolydimethylsiloxanes is deliberately chosen here to prevent a thermally induced back-cleavage reaction of the α,ω-diacetoxy-polydimethylsiloxanes that might occur under the conditions of gas chromatographic analysis (for the back-cleavage reaction, see, among others, J. Pola et al., Collect. Czech. Chem. Commun. 1974, 39(5), 1169-1176 and also W. Simmler, Houben-Weyl, Methods of Organic Chemistry, Vol. VI / 2, 4th Edition, O-Metal Derivates of Organic Hydroxy Compounds, p. 162 ff.). Example 1 (according to the invention)

[0063] Preparation of an acetoxy-terminated, linear polydimethylsiloxane with 3.0% acetic acid addition

[0064] In a 1000 mL four-necked flask equipped with a KPG stirrer, internal thermometer, and attached reflux condenser, 77.3 g (0.757 mol) of acetic anhydride are stirred together with 732.8 g (0.267 mol) of an α,ω-dihydroxypolydimethylsiloxane (M: 2742 g / mol) and 24.3 g of acetic acid (3.0 wt% based on the total mass of reactants). 1.62 g (0.88 mL) of trifluoromethanesulfonic acid (0.2 wt% based on the total mass of reactants) are added and the mixture is rapidly heated to 150°C. The initially slightly cloudy reaction mixture is then incubated at this temperature for 4 hours with continued stirring.

[0065] After cooling the mixture, a colorless, clear, and highly mobile liquid is isolated, whose 29< Si NMR spectrum confirms the presence of Si acetoxy groups in a yield of approximately 93% based on the acetic anhydride used, corresponding to an α,ω-diacetoxypolydimethylsiloxane with a mean total chain length of approximately 14.

[0066] Conversion of the linear α,ω-diacetoxypolydimethylsiloxane into the corresponding α,ω-diisopropoxy-polydimethylsiloxane for analytical characterization.

[0067] Immediately after synthesis, 50.0 g of this trifluoromethanesulfonic acid, equilibrated α,ω-diacetoxypolydimethylsiloxane, are mixed in a 250 mL four-necked round-bottom flask equipped with a KPG stirrer, internal thermometer, and attached reflux condenser, together with 11.3 g of isopropanol dried over a molecular sieve, while stirring at 22°C. The reaction mixture is then subjected to the alkaline reaction (moist universal indicator paper) by introducing gaseous ammonia (NH₃) and then stirred for another 45 minutes at this temperature. The precipitated salts are separated using a fluted filter.

[0068] A colorless, clear liquid is isolated, the accompanying 29< Si-NMR spectrum of which confirms the quantitative conversion of α,ω-diacetoxypolydimethylsiloxane into α,ω-diisopropoxypolydimethylsiloxane.

[0069] An aliquot of this α,ω-diisopropoxypolydimethylsiloxane is taken and analyzed by gas chromatography. The gas chromatogram shows the following concentrations (in weight percent): D 4 D 5 D 6 Total (D 4 - D 6 ) Isopropanol content 4,12 % 2,61 % 0,84 % 7,57 % 4,58 %

[0070] Taking into account the excess of isopropanol, the contents of siloxane cycles (D 4 , D 5 and D 6 ) are calculated based solely on the siloxane content.

Claims

1. Process for producing superacid-acidified, in particular trifluoromethanesulfonic acid-acidified, (end-)equilibrated linear α,ω-acetoxy-bearing siloxanes, characterized in that (i) linear α,ω-hydroxy-bearing siloxanes, (ii) using superacid, particularly preferably perfluoroalkanesulfonic acid, especially preferably trifluoromethanesulfonic acid, as catalyst, (iii) are reacted with acetic anhydride and with addition of acetic acid.

2. Process according to Claim 1, characterized in that the acid employed in addition to the acetic acid is a superacid having a pKa of less than -3.0, preferably fluorinated and / or perfluorinated sulfonic acid, fluorosulfonic acid HSO3F, fluoroantimonic acid HSbF6 and / or perfluorobutanesulfonic acid C4F9SO3H and very particularly preferably trifluoromethanesulfonic acid CF3SO3H.

3. Process according to Claim 1 or 2, characterized in that the linear α,ω-hydroxy-bearing siloxanes satisfy formula (I): where R1 is independently at each occurrence an alkyl radical and / or aromatic radical comprising 1 to 10 carbon atoms, preferably a methyl radical, and where 1 ≤ n ≤ 19 000, preferably n is between 3 and 200, particularly preferably n is between 20 and 100.

4. Process according to at least one of Claims 1 to 3, characterized in that the acetic acid is added in amounts of 0.4 to 3.5 per cent by weight, by preference 0.5 to 3 per cent by weight, preferably 0.8 to 1.8 per cent by weight, particularly preferably in amounts of 1.0 to 1.5 per cent by weight, based on the reaction matrix comprising acetic anhydride and hydroxy-bearing siloxanes, and in that in addition to the acetic acid further superacid, particularly preferably perfluoroalkanesulfonic acid and in particular trifluoromethanesulfonic acid, is employed in amounts of 0.1 to 1.0 per cent by weight, preferably 0.1 to 0.3 per cent by weight, based on the reaction matrix comprising acetic anhydride and hydroxy-bearing siloxanes.

5. Process according to at least one of Claims 1 to 4, characterized in that the acetic anhydride amount to be employed has to be at least sufficient to ensure that all Si-bonded hydroxy groups of the employed α,ω-hydroxy-bearing siloxane are replaced by acetoxy groups while at the same time the liberated water equivalent is bound in the form of two equivalents of acetic acid by reaction with further acetic anhydride.

6. Process according to at least one of Claims 1 to 5, characterized in that the reaction is carried out in a reactor having a volume of at least 1 litre, preferably at least 5 litres, in particular at least 10 litres and preferably not more than 500 000 litres.

7. Process according to at least one of Claims 1 to 6, characterized in that the superacid-acidified, in particular trifluoromethanesulfonic acid-acidified, (end-)equilibrated linear α,ω-acetoxy-bearing siloxanes have at least 3, preferably 5 to 50, preferably 7 to 25, particularly preferably 10 to 20, organosiloxane units.

8. Superacid-acidified, in particular trifluoromethanesulfonic acid-acidified, (end-)equilibrated linear α,ω-acetoxy-bearing siloxanes produced by a process according to any of Claims 1 to 7, characterized in that they have total cycles contents 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 afford the corresponding linear α,ω-isopropoxysiloxanes of less than 13, preferably less than 12, per cent by weight, and wherein it is preferably the case that the superacid-acidified, in particular trifluoromethanesulfonic acid-acidified, (end-)equilibrated linear α,ω-acetoxy-bearing siloxanes have at least 3, preferably 5 to 50, preferably 7 to 25, particularly preferably 10 to 20, organosiloxane units.