Process for the removal of cyclic siloxanes from compositions comprising polyalkylsiloxanes

Abstract

The present invention relates to a process for removing cyclic siloxanes from compositions comprising at least one polyalkylsiloxane and at least one cyclic siloxane by distillation, wherein the distillation takes place in the presence of at least one auxiliary substance selected from the group consisting of glycols, cyclic carbonates, sulfones and / or sulfoxides, and / or a mixture of any of these.

Description

[0001] Process for the removal of cyclic siloxanes from compositions comprising polyalkylsiloxanes

[0002] The present invention is in the field of siloxanes, more particularly in the field of polyalkylsiloxanes. In particular, the present invention relates to a process for removal of cyclic siloxanes from compositions comprising polyalkylsiloxanes.

[0003] Polyalkylsiloxanes are known polymers with outstanding substance properties and are used in many everyday products. They are molecules, especially macromolecules, whose basic structure consists of alternating silicon and oxygen atoms. Polyalkylsiloxanes can be linear or branched.

[0004] Formula 1 illustrates a linear polyalkylsiloxane:

[0005] Formula 1 : Linear polyalkylsiloxane

[0006] R in formula 1 are, each independently of one another, identical or different alkyl radicals, R preferably being a methyl group. R1in formula 1 are, each independently of one another, identical or different residues selected from the group consisting of R and R2, where R2is a different organic radical, i.e. not an alkyl radical. The parameter n is preferably between 10 and 2000 for formula 1 and the parameter m is preferably between 0 and 50 for formula 1 .

[0007] However, the siloxane scaffold can also be branched if it contains so-called T or Q units ([RSiOac] or [SiO.4 / 2]). The established M, D, T and Q nomenclature refers to the functionality of the siloxane units. T units accordingly are trifunctional siloxane units and Q units are tetrafunctional siloxane units. For the M, D, T and Q nomenclature see, e.g., W. Noll, Chemie und Technologie der Silicone, Verlag Chemie GmbH, Weinheim (1960), pages 2 ff.

[0008] Formula 2 shows, illustratively, a general formula for a branched polyalkylsiloxane:

[0009] [R1R2SiOi / 2]a[R2SiO2 / 2]b[R2RSiO2 / 2]c[RSiO3 / 2]d[SiO4 / 2]e

[0010] Formula 2: Branched polyalkylsiloxane

[0011] For formula 2: a = 2 to 12, b = 10 to 2000, c = 0 to 50, d = 0 to 10 and e = 0 to 5, with d+e > 1 . R in formula 2 are, each independently of one another, an alkyl- or an aryl residue, R preferably being a methyl group. R1in formula 2 is a hydroxyl group, hydrogen, or a vinyl residue. R2is a hydrogen or a vinyl residue. The polyalkylsiloxanes represented by Formulae 1 and 2 can be used as component of curable compositions. They are preferably used in cold and hot vulcanized silicone preparations.

[0012] In addition to linear and branched polyalkylsiloxanes, technical polyalkylsiloxanes often also contain cyclic siloxanes, also known as cyclosiloxanes. Cyclic siloxanes are annular siloxane compounds in which silicon and oxygen are bonded alternately.

[0013] Of particular importance within the scope of this invention are the cyclosiloxanes octamethylcyclotetrasiloxane (D4, CAS No.: 556-67-2), decamethylcyclopentasiloxane (D5, CAS No.: 541-02-6) and dodecamethylcyclohexasiloxane (D6, CAS No.: 540-97-6). Octamethylcyclotetrasiloxane meets the criteria for the identification of persistent, bioaccumulative and toxic substances and also very persistent and very bioaccumulative substances. Furthermore, the use of decamethylcyclopentasiloxane is also controversial for environmental reasons. The European Chemicals Agency classifies this substance as persistent and bioaccumulative. Hence, as of 31 January 2020, rinsable cosmetic products with a concentration of decamethylcyclopentasiloxane of 0.1 per cent by weight or higher may not be marketed in the EU.

[0014] The group of cyclic siloxanes comprises process according to any of claims 1 to 8, wherein the at least one cyclic siloxane comprises hexamethylcyclotrisiloxan (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptsiloxane (D7), hexadecamethylcyclooctasiloxane (D8), and / or a mixture of any of these.

[0015] Owing to the potential danger of D3 to D8, and the toxicological classification of D4 to D6, there is a desire to provide polyorganosiloxanes which contain as little as possible of any cyclic siloxanes D3 to D8, preferably D4, D5 and D6, or are free from them.

[0016] Cyclic siloxanes are often present in polyalkylsiloxanes, because the latter are produced, for example, by so-called equilibration. In the article by J. B. Carmichael, R. Winger, Journal of Polymer Science: Part A, Vol. 3, pp. 971-984 (1965) it is described that after the production of polyalkylsiloxanes by equilibration, different types of cyclic siloxanes are always found. These are present in addition to the linear polymer chains, and an equilibrium concentration is established during equilibration. The article states that typical D4 concentration for unmodified siloxanes is about 5% by weight. The content of cyclic siloxanes may vary greatly depending on the type of modified or unmodified polyalkylsiloxane. In addition, the type of production can also affect the content of cyclosiloxanes. For example, the content of cyclic siloxanes can range from 0.5% by weight to 12% by weight, when no measures are taken for their removal. In addition to D4, D5, and D6, higher molecular cyclic siloxanes are undesirable components in various applications, which therefore should be removed in possible.

[0017] Both the development of novel catalyst systems that suppress cycle formation and the physical removal of cyclic components have therefore been the focus of academic and industrial research for several decades. To date, however, neither the adaptation of the catalyst system nor physical methods have opened up easy access to low cycle contents.

[0018] For example, the article “Ring-opening polymerization of cyclic oligosiloxanes without producing cyclic oligomers” (Shi et al., Science 381 , 1011 , 2023) deals with the long-standing problem associated with silicone synthesis that backbiting reactions at the polymer chain ends result in a contamination of the polymer products with 10 to 15% cyclic oligosiloxanes. Said backbiting reactions are in competition with chain propagation through ring-opening polymerization (ROP) of cyclic monomers. According to the authors, alcohol coordination to the anionic chain ends prevents the backbiting process and that a well- designed phosphonium cation acts as a self-quenching system in response to loss of coordinating alcohols to stop the reaction before the backbiting process begins. However, the products have a D4 content of 0.4%, which is still much too high.

[0019] US 2014 / 155644 A1 discloses a process for the separation of cyclic siloxanes from short chain hydroxylterminated siloxanes by contact with steam at a pressure of at least 650 hPa absolute. This process gives products with D4 contents of ca. 2,000 ppm, which however is too high.

[0020] WO 2020 / 040886 A1 discloses a method for making long chain hydroxyl terminated polydiorganosiloxanes with low cyclics content via condensation polymerization employing a selective catalyst. The catalyst includes a salt - anion complex and a free acid. This process gives products with D4 contents of 1 ,000 ppm. From today's perspective, however, this cyclic siloxane content is too high.

[0021] Accordingly, there was still a need for a process which provides polyalkylsiloxanes with the desired low content of cyclic siloxanes, preferably with a total content of D3 to D8, preferably of D4, D5 and D6, of less than < 0.1 wt.-%, based on the total weight of a composition comprising at least one polyalkylsiloxane and at least one cyclic siloxane.

[0022] In order to obtain polyalkylsiloxanes with low cycle contents, the cyclosiloxanes are usually removed by distillation after the polyalkylsiloxane has been prepared. Depending on the viscosity of the polyalkylsiloxanes, however, distillation requires long residence times in the vessel, very low pressures, and high temperatures. This leads to a strong thermal load on the compounds, which can have a negative effect on the quality, e.g. the color, of the products. Special equipment such as thin-film evaporators can reduce thermal stress but requires significant equipment and additional process steps. This complicates the cost-effective and thus competitive production of products containing poylalkylsiloxanes.

[0023] In addition to the need explained above, there was also still a need for a simple, energy- and cost-efficient method for the removal of cyclic siloxanes from polyalkylsiloxane-containing compositions.

[0024] It was found that it is possible to remove cyclic siloxanes from polyalkylsiloxanes by distillation with the use of at least one auxiliary substance, as further described hereinbelow, under particularly mild conditions. In this way, the distillation times can also be significantly reduced.

[0025] One object of the present invention is therefore a process for removing cyclic siloxanes from compositions comprising at least one polyalkylsiloxane and at least one cyclic siloxane by distillation, wherein the distillation takes place in the presence of at least one auxiliary substance selected from the group consisting of glycols, sulfones and / or sulfoxides, cyclic carbonates, and / or a mixture of any of these.

[0026] The process according to the present invention allows for a complete or at least partial removal of the at least one cyclic siloxane from the compositions comprising at least one polyalkylsiloxane and at least one cyclic siloxane.

[0027] In an embodiment of the process according to the present invention the at least one cyclic siloxane is therefore completely removed or at least partially removed from the composition.

[0028] The process according to the present invention also allows for a simple and energy- as well as costefficient removal of cyclic siloxanes from polyalkylsiloxanes. For example, the distillation is carried out at a relative low temperature in the range of only 60 °C to 170 °C. The low temperatures applied according to the present invention also have the benefit to reduce negative impacts on the product quality, e.g., regarding color. Typically, the higher the temperature and thus the thermal load, the more likely decomposition products are formed in the distillation. By comparison, the process according to the present invention is performed at relatively low temperatures. This also reduces any potentially negative impacts on the product quality significantly.

[0029] In principle, the process according to the present invention is no subject to any limitation regarding a specific polyalkylsiloxane. Nevertheless, it is preferred in the context of the present invention that the at least one polyalkylsiloxane is selected from the group consisting of silanol, SiH, and vinyl modified poyldimethylsiloxanes, which in each case independently of one another can be linear or branched. It is also preferably possible to use any mixtures of linear and branched, silanol, SiH, and vinyl modified poyldimethylsiloxanes.

[0030] In an embodiment of the process according to the present invention the polyalkylsiloxane is one or more selected from the group consisting of linear and / or branched silanol, SiH, and vinyl modified polydimethylsiloxanes, and / or a mixture of any of these.

[0031] In yet another embodiment of the process according to the present invention the at least one polyalkylsiloxane has a number average molar mass of more than 2000 g / mol determined by gel permeation chromatography.

[0032] The determination of the number average molar mass by gel permeation chromatography is preferably carried out according to the DIN 55672-1 :2016-03 method. Preferred polyalkylsiloxanes are described below by formulae 3 to 6.

[0033] The following formula 3 shows particularly preferred linear, unmodified polyalkylsiloxanes:

[0034] Formula 3: Linear, unmodified polyalkylsiloxanes

[0035] R in formula 3 are, each independently of one another, identical or different radicals selected from the group consisting of alkyl and aryl groups having 1 to 6 carbon atoms, preferably identical or different radicals selected from the group consisting of methyl, ethyl, and phenyl, in particular methyl. R1in formula 3 is an OH group, hydrogen, or a vinyl radical. The following also applies to formula 3: n = 100 to 2000, preferably n = 300 to 2000, in particular n = 500 to 2000.

[0036] Particularly preferably, the unmodified polyalkylsiloxanes, in particular the linear polyalkylsiloxanes according to formula 3, have a number-average molar mass of more than 3000 g / mol.

[0037] The following formula 4 shows particularly preferred linear polyalkylsiloxanes with reactive groups in the side chain:

[0038] Formula 4: Linear polyalkylsiloxanes with reactive groups in the side chain

[0039] R in formula 4 are, each independently of one another, identical or different radicals selected from the group consisting of alkyl and aryl groups having 1 to 24 carbon atoms, preferably identical or different radicals selected from the group consisting of methyl, ethyl and phenyl, in particular methyl.

[0040] R1in formula 4 are, each independently of one another, identical or different radicals selected from the group consisting of OH group, R and R2.

[0041] R2in formula 4 is hydrogen or a vinyl radical. The following also applies to formula 4: x = 10 to 2000, preferably x = 30 to 1800, in particular x = 35 to

[0042] 1500 and y = 0 to 30, preferably y = 0 to 25, in particular y = 1 to 20, with x+y > 20, preferably x+y > 30.

[0043] When all R1radicals are R, then y > 1 .

[0044] Particularly preferably, the linear polyalkylsiloxanes with reactive groups in the side chain according to formula 4, have a number-average molar mass of more than 2000 g / mol.

[0045] The following formula 5 shows particularly preferred branched polyalkylsiloxanes:

[0046] [R1R2SiOi / 2]a[R2SiO2 / 2]b[R2RSiO2 / 2]c[RSiO3 / 2]d[SiO4 / 2]e

[0047] Formula 5: Branched polyalkylsiloxanes

[0048] R in formula 5 are, each independently of one another, identical or different radicals selected from the group consisting of alkyl and aryl groups having 1 to 24 carbon atoms, preferably identical or different radicals selected from the group consisting of methyl, ethyl and phenyl, in particular methyl.

[0049] R1in formula 5 are, each independently of one another, identical or different radicals selected from the group consisting of OH group, R and R2.

[0050] R2in formula 5 is hydrogen or a vinyl radical.

[0051] The following also applies to formula 4: x = 10 to 2000, preferably x = 30 to 1800, in particular x = 35 to 1500 and y = 0 to 30, preferably y = 0 to 25, in particular y = 1 to 20, with x+y > 20, preferably x+y > 30.

[0052] The following also applies to formula 5: a = 2 to 20, preferably 2 to 15, especially preferably 2 to 10, b = 10 to 2000, preferably 20 to 1800, especially preferably 30 to 1500, c = 0 to 50, preferably 1 to 40, especially preferably 2 to 35, d = 0 to 20, preferably 0 to 10, especially preferably 2 to 6, e = 0 to 20, preferably 0 to 10, especially preferably 0 to 6, d + e > 0, preferably d + e > 1 .

[0053] Particularly preferably, the branched polyalkylsiloxanes according to formula 5, have a number-average molar mass of more than 2000 g / mol.

[0054] According to the present invention the distillation is carried out in the presence of at least auxiliar substance selected from the group consisting of glycols, cyclic carbonates, sulfones and / or sulfoxides, and / or a mixture of any of these. The distillation in the process according to the present invention can be carried out in any way known to the person skilled in the art. The usual distillation processes and principles can be employed, including for example more complicated processes such as short-path distillation or thin-film evaporators.

[0055] The process according to the present invention is also not subject to any limitation regarding a specific time point at which the at least one auxiliary substance is added to the composition - provided that the distillation has not been finished yet. For example, said at least one auxiliary substance can be added before the distillation, during the distillation or before and during the distillation. In the latter case, said at least one auxiliary substance can be added in portions.

[0056] In a further embodiment the at least one auxiliary substance is added to the composition before and / or during the distillation, where appropriate in portions.

[0057] Glycols which can be used preferably for the purposes of the present invention are in particular those dialcohols (divalent alcohols), which are derived from ethylene glycol, so-called 1 ,2-diols or vicinal diols. Preferred example thereof are ethylene glycol and / or propylene glycol. Examples of further glycols, which can also be used preferably for the purposes of the present invention are a,w-diols which are formed by condensation of ethylene glycol and / or propylene glycol, such as diethylene glycol, dipropylene glycol, triethylene glycol and / or tripropylene glycol. The glycols for the purposes of the present invention preferably have a molar mass of less than 200 g / mol.

[0058] In another embodiment of the process according to the present invention the distillation is carried out in the presence of at least one glycol, wherein said at least one glycol is selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and / or a mixture of any of these. Preferably, the glycol is propylene glycol, and / or ethylene glycol.

[0059] The term cyclic carbonates is used as known to the person skilled in the art and denotes cyclic carbonate esters of an alkylene glycol and carbonic acid. Preferred cyclic carbonates are 5-membered cyclic carbonates, such as ethylene carbonate, propylene carbonate (pure isomers, or its racemic mixture), glycerine carbonate, or any mixture of these.

[0060] In another embodiment of the process according to the present invention the distillation is carried out in the presence of at least one cyclic carbonate, wherein said at least one cyclic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate (pure isomers, or its racemic mixture), and / or mixture of any of these.

[0061] Sulfones and sulfoxides which can be used preferably for the purposes of the present invention are in particular those sulfur containing compounds which, independently of one another, have linear alkyl radicals with 1 to 6 carbon atoms, preferably methyl and ethyl, wherein the said alkyl radicals may be part of a ring forming a cyclic sulfur compound, for example, a sulfolane. A preferred sulfone is sulfolane and a preferred sulfoxide is dimethyl sulfoxide.

[0062] In a further embodiment of the process according to the present invention the distillation is carried out in the presence of at least one sulfone and / or sulfoxide, wherein said at least one sulfone and / or sulfoxide is selected from the group consisting of sulfolane, dimethyl sulfoxide, or a mixture of any of these.

[0063] In principle, the process according to the present invention is not subject to any limitations regarding specific conditions, in particular with respect to temperature and / or pressure, under which the distillation is carried out. Rather, the temperature and / or pressure depend on the boiling point of the chosen auxiliary substance, the boiling point of the composition comprising at least one polyalkylsiloxane and at least one cyclic siloxane, and / or the boiling point of the mixture of said composition with the auxiliary substance in question.

[0064] For the purposes of the present invention, it was found that the distillation is preferably carried out at a (reduced) pressure in the range of 0 mbar to 100 mbar and a temperature in the range of 60 °C to 170 °C.

[0065] For the distillative separation of the cyclic siloxanes, the composition is preferably heated to temperatures between 40 °C and 170 °C, preferably between 60 °C and 170 °C and in particular preferably between 80 °C and 170 °C and the pressure is preferably reduced to the range of 0 mbar to 100 mbar, preferably 2 mbar to 50 mbar. The distillate containing cyclic siloxanes and preferably the auxiliary substance is then taken off, e.g., withdrawn from the head of the distillation apparatus.

[0066] In another embodiment the distillation is carried out a pressure in the range of 0 mbar to 100 mbar and a temperature in the range of 60 °C to 170 °C, preferably at a pressure of 2 mbar to 50 mbar and a temperature of 80 °C to 170 °C.

[0067] The invention facilitates the purification of modified and / or unmodified polyalkylosiloxanes which are contaminated with cyclic siloxanes. Of particular importance within the scope of this invention are the cyclosiloxanes octamethylcyclotetrasiloxane (D4, CAS No.: 556-67-2), decamethylcyclopentasiloxane (D5, CAS No.: 541-02-6) and dodecamethylcyclohexasiloxane (D6, CAS No.: 540-97-6).

[0068] Octamethylcyclotetrasiloxane meets the criteria for the identification of persistent, bioaccumulative and toxic substances and also very persistent and very bioaccumulative substances. Furthermore, the use of decamethylcyclopentasiloxane is also controversial for environmental reasons. The European Chemicals Agency classifies the substance as persistent and bioaccumulative. Hence, as of 31 January 2020, rinsable cosmetic products with a concentration of decamethylcyclopentasiloxane of 0.1 per cent by weight or higher may not be marketed in the EU.

[0069] In a further embodiment of the process according to the present invention the at least one cyclic siloxane comprises hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptasiloxan (D7), hexadecamethylcyclooctasiloxan (D8), and / or a mixture of any of these.

[0070] In order to remove the cyclic siloxanes, in particular, D4, D5 and / or D6, from the polyalkylsiloxane particularly effectively and to achieve the desired low cyclosiloxane contents particularly effectively, the at least one auxiliary substance is preferably used in such a way that the ratio of the mass fractions w (% by weight) of the at least one auxiliary substance to the sum w (% by weight) of D3 to D8, preferably D4, D5 and D6, is from 0.5:1 to 10:1 , more preferably from 0.7: 1 to 4:1 , particularly preferably from 0.8:1 to 3:1. Mass fraction w for the purposes of this invention indicates the relative proportion of the mass to the total mass of the substance mixture under consideration. In the case that two or more auxiliary substances are used, the sum of all mass fractions w (% by weight) of the auxiliary substances is set in relation to the sum w (% by weight) of D3 to D8, preferably D4, D5 and / or D6. In the case that exactly one auxiliary substance is used, the mass fraction w (% by weight) of the auxiliary substance is set exactly in relation to the sum w (% by weight) of D3 to D8, preferably D4, D5 and / or D6. In other words, the mass of the auxiliary substance used in total is taken into account.

[0071] In another embodiment the ratio of the mass fraction wAof the total employed auxiliary substance to the mass fraction wcof the sum of the cyclic siloxanes D3 to D8, preferably D4, D5 and D6, contained in the composition ranges from 0.5:1 to 8:1 , preferably from 0.7:1 to 4:1 , in particular from 0.8:1 to 3:1 .

[0072] In a further embodiment before the distillation the composition has a content of cyclic siloxanes, expressed as the sum of D3 to D8, preferably D4, D5 and D6, in the range of 0.025 wt.-% to 15 wt.-%, preferably 0.05 wt.-% to 14 wt.-%, based on the mass of the total composition before the distillation.

[0073] In yet another embodiment, before the distillation, the composition comprises at least one polyalkylsiloxane in a total amount of 74 wt.-% to 99.5 wt.-%, preferably 90 wt.-% to 99 wt.-%, at least one cyclic siloxane D3 to D8, preferably, preferably D4, D5 and / or D6, in a total amount of 0.025 wt.-% to 15 wt.-%, preferably 0.05 wt.-% to 14 wt.-%, in particular 0.1 wt.-% to 13 wt.-%, at least one auxiliary substance selected from the group consisting of glycols, cyclic carbonates, sulfones and / or sulfoxides, or a mixture of any of mixtures in a total amount of 0.025 wt.-% to 15 wt.- %, preferably 0.15 wt.-% to 14 wt.-%, and optional further components, such as reaction by-products, reactant surpluses or additional solvents, for example, in a total amount of less than 30 wt.-%, preferably < 20 wt.-%, especially < 10 wt.-%, in particular < 5 wt.-%, based on the total weight of the composition. Deviations from the values specifically mentioned herein, such as the end points of ranges, and the upper and / or lower end point of an open-ended range, are still comprised by the scope of the present invention, provided that those values deviating from the values specifically mentioned herein still provide for the benefits of the present invention.

[0074] The use of the said at least one auxiliary substance selected from the group consisting of glycols, cyclic carbonates, sulfones and / or sulfoxides and mixtures of any of these also leads to shorten the distillation times. This has the benefit that the thermal load on the composition comprising at least one polyalkylsiloxane and at least one cyclic siloxane in the distillation, in particular the thermal load on the at least one polyalkylsiloxane is significantly lower than in the processes of the prior art. This has the further benefit that there is significantly less deterioration of the components in the composition, in particular of the at least one polyalkylsiloxane, i.e., less by-products or decomposition products are formed, and thus a higher product quality is achieved.

[0075] This makes the polyalkylsiloxanes obtained by the process according to the present invention rather attractive for a variety of different applications, in particular as component in curable compositions.

[0076] A further object of the present invention is a polyalkylsiloxane, characterized in that it is obtained by the process according to the present invention.

[0077] Another object of the present invention is therefore the use of the at least one polyalkylsiloxane obtained by the process according to the present invention or of a polyalkylsiloxane according to the present invention as a component in curable compositions. The invention therefore also relates to a process for providing a curable composition comprising the steps a) removing cyclic siloxanes from compositions comprising at least one polyalkylsiloxane and at least one cyclic siloxane in a process according the invention, and b) using the purified polyalkylsiloxane obtained in step a) as a component in a curable composition.

[0078] Preferably, said curable composition is a cold or hot vulcanized silicone preparation.

[0079] Examples:

[0080] 1. Chemicals used:

[0081] Propylenglycol (> 99.5%) and diethy lenglyol were purchased from Carl-Roth. Ethylenglycol (> 99.5%) was purchased from TCI Deutschland GmbH.

[0082] 2. Determination of the number-average molar mass Mn by means of GPC measurement: GPC measurements were carried out under the following measurements conditions to determine the polydispersity and the number average molar mass:

[0083] Colum combination: SDV 1000 / 10000 A (length 65 cm), temperature: 30 °C, mobile phase: THF, flow rate: 1 mL / min, sample concentration: 10 g / L, detection: Rl detector.

[0084] Evaluation of the polyethers was carried out against polystyrene standard (162-2520000 g / mol).

[0085] 3. Determination of the cyclosiloxan contents for unmodified siloxanes and SiH-siloxanes:

[0086] The method of determination of cyclosiloxane contents in unmodified siloxanes and in SiH siloxanes by gas chromatography (GC) was based on the method described in detail below:

[0087] 3.1 Internal standard solution

[0088] An appropriate volume of internal standard solution in acetone is prepared for use in preparing stock standards, working standards, and for conducting sample extractions.

[0089] 3.1.1 Stock solution

[0090] The stock solution is prepared by dissolving 0.5 g of dodecane in acetone to a total dilute volume of 50 mL (10 mg / mL solution).

[0091] 3.1.2 Working solution

[0092] The working solution is prepared by diluting 10 mL of the 10 mg / mL solution per liter final volume of acetone to a final internal standard solution concentration of 0.1 mg / mL.

[0093] 3.2 Sample preparation

[0094] A sample is prepared by weighing 0.5 g of the sample material (recorded to the nearest 0.1 mg) into a 20 mL glass vial, followed by the addition of 10 mL of internal standard working solution (0.1 mg / mL). The vial is quickly capped securely, and extraction is done overnight (or a minimum of 12 hours) using gentle agitation. Multi-phase solutions may require time to separate or settle; however, the process may be accelerated, if necessary, by use of centrifugation. The sample extracts are placed in appropriate size autosampler vials for analysis. For samples with a cyclic content of less than 250 ppm for the individual cyclic component, the amount of sample material was doubled to 1 .0 g in order to improve the detection limit.

[0095] Note: shorter extraction times may be used for some matrices, however this would need to be validated by the testing laboratory for each matrix.

[0096] 3.3 GC analysis

[0097] 3.3.1 Recommended conditions

[0098] Injector temperature: 250 °C

[0099] Split: 50:1

[0100] Injection volume: 1 pL

[0101] Carrier gas: Helium, 1 .5 mL / min constant flow

[0102] Column: DB-5 30 m x 0.25 mm x 0.1 pm film (or equivalent column)

[0103] Oven: 50 °C (5 min) to 200 °C at 15 °C / min,

[0104] Then to 315 °C for 20 min to elute higher boiling point species,

[0105] Detector: Flame Ionization (FID) at 325 °C (or 15 °C higher than the highest column temperature achieved during the analysis)

[0106] 3.4 Calibration

[0107] 3.4.1 Stock solution of cyclic siloxane

[0108] 3.4.1.1 Stock solution A

[0109] The stock solution A is prepared by weighing approximately 50 mg of the cyclic siloxane to the nearest 0.1 mg into a 10 mL volumetric flask. The flask is filled up to the mark with the internal working solution.

[0110] 3.4.1.2 Stock solution B

[0111] The stock solution B is prepared by diluting 5 mL of stock standard solution A to a final volume of 50 mL with internal standard working solution.

[0112] 3.4.2 Gas Chromatography Standards The analytical standards in additional internal standard working solution are prepared according to Table 2, transferred to appropriate size well-sealed glass vials or bottles, and stored in a cool location prior to use.

[0113] Table 1 : Analytical standard preparation

[0114] Note: Mix each solution well prior to removing aliquots for instrument calibration. Place standard solutions in appropriate size autosampler vials for analysis.

[0115] Standard curves should be quite linear over this range of concentrations (up to 0.5 mg / mL concentration) when following the parameters described in this method.

[0116] 3.5 Calculation

[0117] This method uses internal standard calibration, and based on their corresponding peak areas, linear calibration functions of the form: are established individually for each cyclic siloxane. By applying these calibration functions, the individual concentrations of each analyte are calculated and reported as % by weight.

[0118] 4. Example 1 :

[0119] A mixture of 508 g (ca. 5 mmol) of an a,w-hydroxy terminated siloxane having a chain length of ca. 1 ,300 MezSiO units and 12.5 g (0.1 mmol) diethylene glycol was heated to 160 °C under reduced pressure (ca.

[0120] 2 mbar). After the mixture had been distilled for 15 minutes at 160 °C and under a pressure of ca. 2 mbar, the first sample was taken, and 12.5 g (0.1 mmol) diethylene glycol was added to the mixture.

[0121] Subsequently, the distillation was continued under the above conditions for 2.75 hours, and a second sample was taken. The samples thus obtained were subjected to gas chromatographic analysis, and the contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 1 .

[0122] Table 1 : Results of the gas chromatographic analysis of Example 1 .

[0123] 5. Example 2:

[0124] A mixture of 521 g (ca. 5 mmol) of an a, w-hydroxy terminated siloxane having a chain length of ca. 1 ,300 Me2SiO units and 12.5 g (0.2 mmol) ethylene glycol was heated to 160 °C under reduced pressure (ca. 2 mbar). After the mixture had been distilled for 15 minutes at 160 °C and under a pressure of ca. 2 mbar, the first sample was taken, and 12.5 g (0.1 mmol) diethylene glycol was added to the mixture. Subsequenlty, the distillation was continued under the above conditions for 2.75 hours, and a second sample was taken. The samples thus obtained were subjected to gas chromatographic analysis, and the contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 2.

[0125] Table 2: Results of the gas chromatographic analysis of Example 2.

[0126] 6. Example 3:

[0127] A mixture of 512 g (ca. 10 mmol) of an a,w-hydroxy terminated siloxane having a chain length of ca. 670 Me2SiO units and 25.1 g (0.4 mmol) ethylene glycol was heated to 160 °C under reduced pressure (ca. 2 mbar). After the mixture had been distilled for 2 hours at 160 °C and under a pressure of ca. 2 mbar, a sample was taken. The sample thus obtained was subjected to gas chromatographic analysis, and the contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 3.

[0128] Table 3: Results of the gas chromatographic analysis of Example 3.

[0129] 7. Example 4:

[0130] A mixture of 498 g (ca. 80 mmol) of an a,w-hydroxy terminated siloxane having a chain length of ca. 80 Me2SiO units and 24.8 g (0.3 mmol) propylene glycol was heated to 100 °C under reduced pressure (ca.

[0131] 2 mbar). After the mixture had been distilled for 2 hours at 100 °C and under a pressure of ca. 2 mbar, a sample was taken. The sample thus obtained was subjected to gas chromatographic analysis, and the contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 4.

[0132] Table 4: Results of the gas chromatographic analysis of Example 4.

[0133] 8. Example 5:

[0134] A mixture of 498 g (ca. 11 mmol) of an a,w-hydroxy terminated siloxane having a chain length of ca. 330 Me2SiO units and 24.3 g (0.2 mmol) diethylene glycol was heated to 160 °C under reduced pressure (ca. 2 mbar). After the mixture had been distilled for 2 hours at 160 °C and under a pressure of ca. 2 mbar, a sample was taken. The sample thus obtained was subjected to gas chromatographic analysis, and the contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 5.

[0135] Table 5: Results of the gas chromatographic analysis of Example 5.

[0136] 9. Example 6:

[0137] A mixture of 500 g (ca. 200 mmol) of an a,w-hydroxy terminated siloxane having a chain length of ca. 30 Me2SiO units and 0.01 g (0.3 mmol) sodium hydroxide was heated to 130 °C under reduced pressure (< 100 mbar), whereby water is constantly extracted from the reaction mixture. After a reaction time of 4 hours, 0.1 g (2 mmol) acetic acid was added at a temperature of less than 100 °C, and the mixture thus obtained was stirred for 2 hours at that temperature. Subsequently, 25 g (0.4 mmol) ethylene glycol was added, followed by heating to 130 °C under reduced pressure (ca. 2 mbar). After the mixture had been distilled for 3 hours at 130 °C and under a pressure of ca. 2 mbar, a sample was taken. The sample thus obtained was subject to a gas chromatographic analysis, and the contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 6.

[0138] Table 6: Results of the gas chromatographic analysis of Example 6.

[0139] 10. Example 7:

[0140] A mixture of 550 g (ca. 1.86 mmol) octamethyltetrasiloxane, 2.25 g (ca. 12 mmol) divinyltetramethylsiloxan, and 0.04 g (0.7 mmol) sodium hydroxide was heated under stirring to 150 °C for 6 hours. Subsequently, water was removed from the reaction mixture at 150 °C for 12 hours. Next, 0.1 g (2 mmol) acetic acid was added at a temperature of less than 100 °C, and the mixture thus obtained was stirred for 2 hours at that temperature. Subsequently, 25 g (0.4 mmol) ethylene glycol was added, and a first reference sample was taken and analyzed using gas chromatography. Subsequently, the mixture was heated to 160 °C under reduced pressure (ca. 2 mbar). After the mixture had been distilled for 3 hours at 160 °C and under a pressure of ca. 2 mbar, a second sample was taken and analyzed using gas chromatography. The contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 7.

[0141] Table 7: Results of the gas chromatographic analysis of Example 7.

[0142] 11. Example s:

[0143] A mixture of 513 g (ca. 11 mmol) of an a,w-hydroxy terminated siloxane having a chain length of ca. 330 Me2SiO units and 25.1 g (0.33 mmol) dimethylsulfoxide was heated to 130 °C under reduced pressure (ca. 2 mbar). After the mixture had been distilled for 2 hours at 160 °C and under a pressure of ca. 2 mbar, a sample was taken. The sample thus obtained was subject to a gas chromatographic analysis, and the contents of the remaining cyclic siloxanes were determined. The results are summarized in Table 8.

[0144] Table 8: Results of the gas chromatographic analysis of Example 8.

Claims

Patent claims1 . A process for removing cyclic siloxanes from compositions comprising at least one polyalkylsiloxane and at least one cyclic siloxane by distillation, wherein the distillation takes place in the presence of at least one auxiliary substance selected from the group consisting of glycols, sulfones and / or sulfoxides, cyclic carbonates, and a mixture of any of these.

2. The process according to claim 1 , wherein the polyalkylsiloxane is one or more selected from the group consisting of linear and / or branched silanol, SiH, and vinyl modified polydimethylsiloxanes, and / or a mixture of any of these.

3. The process according to claim 1 or 2, wherein the at least one polyalkylsiloxane has a number average molar mass of more than 2000 g / mol, determined by gel permeation chromatography.

4. The process according to any of claims 1 to 3, wherein the at least one auxiliary substance is added to the composition before and / or during the distillation, where appropriate in portions.

5. The process according to any of claims 1 to 4, wherein the distillation is carried out in the presence of at least one glycol, wherein said at least one glycol is selected from the group consisting of ethylene glycol, propylene glycol, dipropylene glycol, diethylene glycol, and / or a mixture of any of these.

6. The process according to any of claims 1 to 5, wherein the distillation is carried out in the presence of at least one cyclic carbonate, wherein said at least one cyclic carbonate is selected from the group consisting of ethylene carbonate, propylene carbonate, and / or a mixture of any of these.

7. The process according to any of claims 1 to 6, wherein the distillation is carried out in the presence of at least one sulfone and / or sulfoxide, wherein said at least one sulfone and / or sulfoxide is selected from the group consisting of sulfolane, dimethylsulfoxide, and / or mixture of any of these.

8. The process according to any of claims 1 to 7, wherein the distillation is carried out at a pressure of 0 mbar to 100 mbar and a temperature in the range of 60 °C to 170 °C, preferably at a pressure of 2 mbar to 50 mbar and a temperature in the range of 80 °C to 170 °C.

9. The process according to any of claims 1 to 8, wherein the at least one cyclic siloxane comprises hexamethylcyclotrisiloxan (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptsiloxane (D7), hexadecamethylcyclooctasiloxane (D8), and / or a mixture of any of these.

10. The process according to any of claims 1 to 9, wherein the ratio of the mass fraction wAof the total employed auxiliary substance to the mass fraction wcof the sum of the cyclic siloxanes D3 to D8, preferably D4, D5 and D6, contained in the composition ranges from 0.5:1 to 8:1 , preferably from 0.7:1 to 4:1 , in particular from 0.8:1 to 3:1.11 . The process according to any of claims 1 to 10, wherein before the distillation the composition has a content of cyclic siloxanes, expressed as the sum of D3 to D8, preferably D4, D5 and D6, in the range of 0.025 wt.-% to 15 wt.-%, preferably 0.05 wt.-% to 14 wt.-%, based on the mass of the total composition before the distillation.

12. The process according to any of claims 1 to 11 , wherein before the distillation the composition comprises at least one polyalkylsiloxane in a total amount of 74 wt.-% to 99.5 wt.-%, preferably 90 wt.-% to 99 wt.-%, at least one cyclic siloxane D3 to D8, preferably, preferably D4, D5 and / or D6, in a total amount of 0.025 wt.-% to 15 wt.-%, preferably 0.05 wt.-% to 14 wt.-%, in particular 0.1 wt.-% to 13 wt.-%, at least one auxiliary substance selected from the group consisting of glycols, cyclic carbonates, sulfones and / or sulfoxides, or a mixture of any of mixtures in a total amount of 0.025 wt.-% to 15 wt.-%, preferably 0.15 wt.-% to 14 wt.-%, and optional further components, such as reaction by-products, reactant surpluses or additional solvents, for example, in a total amount of less than 30 wt.-%, preferably < 20 wt.-%, especially < 10 wt.-%, in particular < 5 wt.-%, wherein the sum of all components gives 100 wt.-%.

13. Polyalkylsiloxane, characterized in that it is obtained by the process according to any of claims 1 to 12.

14. Process for providing a curable composition comprising the steps a) removing cyclic siloxanes from compositions comprising at least one polyalkylsiloxane and at least one cyclic siloxane in a process according to any of the claims 1 to 12, andb) using the purified polyalkylsiloxane obtained in step a) as a component in a curable composition.

15. Process according to claim 14, wherein the curable compositions is a cold or hot vulcanized silicone preparation.

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