Stabilizers for polymer foams based on recycling of polydimethylsiloxane

Abstract

The present invention relates to polyether polydimethylsiloxanes that can be used as stabilizers for polymer foams, such as polyurethane foams. It has been found that polyether polydimethylsiloxanes can be manufactured based on compounds from recycling processes. Accordingly, there is provided a process for producing polyether polydimethylsiloxanes based on a recycled linear polydimethylsiloxane. The present invention also relates to a process and composition for preparing a polymeric foam making use of the polyether polydimethylsiloxane as well as articles produced thereof. The present invention is also directed to the use of a recycled-polydimethylsiloxane- containing composition and to the use of the polyether polydimethylsiloxanes as foam stabilizers.

Description

STABILIZERS FOR POLYMER FOAMS BASED ON RECYCLING OF POLYDIMETHYLSILOXANETECHNICAL FIELD

[0001] The present invention relates to polyether polydimethylsiloxanes that can be used as stabilizers for polymer foams, such as polyurethane foams. It has been found that polyether polydimethylsiloxanes can be manufactured based on compounds from recycling processes. Accordingly, there is provided a process for producing polyether polydimethylsiloxanes based on a recycled linear polydimethylsiloxane. The present invention also relates to a process and composition for preparing a polymeric foam making use of the polyether polydimethylsiloxane as well as articles produced thereof. The present invention is also directed to the use of a recycled- polydimethylsiloxane-containing composition and to the use of the polyether polydimethylsiloxanes as foam stabilizers.TECHNICAL BACKGROUND

[0002] Foam stabilizers are usually used to ensure the formation of a stable foam. These compounds ensure that the gas produced during the reaction does not escape from the reaction mixture and that the resulting foam remains stable until the reaction is complete to prevent the resulting foam from collapsing. Usually, the polymer foam is a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam.

[0003] Frequently utilized foam stabilizers are selected from polyether polydimethylsiloxanes. As starting materials for the manufacturing of polyether polydimethylsiloxanes linear polydimethylsiloxanes and cyclic polydimethylsiloxanes such as octamethylcyclotetrasiloxane can be utilized. Cyclic polydimethylsiloxanes with high purities are conventionally obtained from chlorosilanes of the Muller-Rochow process (herein abbreviated as MR or MR process) followed by hydrolysis. The Muller-Rochow process is the most common process for preparing organosilicon compounds on an industrial scale directly from natural silicon sources like sand. In the Muller- Rochow process alkyl chlorides react with elemental silicon in a fluidized bed reactor. Unfortunately, the Muller-Rochow process requires a waste amount of energy.

[0004] Accordingly, it is desired to reduce the carbon footprint of the production process and the thus produced polyether polydimethylsiloxane foam stabilizers and to provide alternative methods for their preparation.

[0005] On the other hand, the accumulation of huge amounts of plastic waste is one of the global challenges that the world is currently facing. Indeed, the serious environmental risks of landfills or the incineration of plastic waste are a growing global concern. Under these conditions, recycling of polymers like polydimethylsiloxane (herein also abbreviated as PDMS) is inevitable for the transition of the polymer industry to carbon neutrality. Polydimethylsiloxane is thereby widely used in industry, for example, in sealants, adhesives, lubricants, cooking utensils, and devices for medical applications, thermal insulation, and electrical insulation.

[0006] Different methods for the recycling of polydimethylsiloxane are known. For example, EP 0 009 202 A1 discloses that waste material comprising polyorganylsiloxane can be recycled by means of catalytic depolymerization. To this end, a composition of linear organo-polysiloxanes that consist of at least 50 mol-% dimethylsiloxane units and aqueous sulfuric acid as a catalyst that promotes the rearrangement of siloxane bonds is heated to obtain cyclic dimethylpolysiloxane-containing compositions.

[0007] Also, US 5,110,972 A is directed to the recycling of waste silicone by dissolving the silicone in a suitable solvent and converting it into cyclic siloxanes by applying a two-step acid / base catalyzed cracking process. The silicone waste thereby consists of liquids or elastomeric materials of high molecular weight formed by a silicone polymer typically carrying short alkyl groups, especially methyl groups. Cyclic siloxane-containing compositions are finally obtained in high yields by distillation.

[0008] CA 2 737 235 A1 discloses a process for the preparation of equilibration products of organosiloxanes, useful as polyurethane soft-foam stabilizers. Specifically, this document discloses a first step consisting of the production of a hydrogenpolysiloxane comprising reacting decamethylcyclo-pentasiloxane (D5), poly(methyl)hydrogen-siloxane and hexamethyldisiloxane (HMDS) using a predried ion exchange resin. The obtained polyhdrogendimethylsiloxane is then reacted with a polyether of the median formula CH2=CH-CH2O-(C2H4O)5-(C3H6O)2iCH3 with a platinum metal complex to form a block polysiloxane-polyoxyalkylene, which is used as a soft polyurethane foam stabilizer.

[0009] US 2006 / 0241270 A1 discloses a process for the preparation of equilibration products of organohydrogensiloxanes, In detail, this document discloses a first step in which a mixture of decaethylcyclopentasiloxane (D5), poly(methyl)hydrogensiloxane PTF1 and hexamethyldisiloxane HMDS is mixed with predried ion exchange resin, followed for equilibration, to give a hydrogensiloxane. In the next step, the hydrogensiloxane is further processed with a polyethers of varying average formulae to give a block polysiloxane-polyoxyalkylene.

[0010] Cyclic polydimethylsiloxanes can be polymerized in the presence of a polymerization catalyst to obtain a linear polydimethylsiloxane. As detailed above, linear or polydimethylsiloxanes can be utilized as a starting material in the production of polyether polydimethylsiloxanes. However, the prior art remains silent regarding the production of polyether polydimethylsiloxanes that are derived from linear -polydimethylsiloxanes from recycling processes because it is believed in the field that the siloxanes must have a high purity and that the siloxanes from recycling processes would not have the required purity to allow the production of suitable polyether polydimethylsiloxanes foam stabilizers.

[0011] However, the classification of at least some cyclic polydimethylsiloxanes as POP is a significant problem. POPs (persistent organic pollutants) are organic substances with certain properties that can harm humans and the environment. In detail, POPs are organic compounds that are characterized by the fact that they remain in the environment for a long time (persistence), accumulate through the food chain (bioaccumulation), may harm human health and the environment((eco-)toxicity), and have the ability to be transported over long distances in the environment. They are regulated not only at EU level by the POPs Regulation, but globally by the Stockholm Convention. The aim is clear: to prohibit or at least restrict the production, marketing and use of POPs. Of particular importance in the context are the cyclosiloxanes octamethylcyclotetrasiloxane (D4, CAS no.: 556-67-2), decamethylcyclopentasiloxane (D5, CAS no.: 541-02-6) and dodecamethylcyclo-hexasiloxane (D6, CAS no.: 540-97-6). Octamethylcyclotetrasiloxane meets the criteria of POP. The POP classification of D4 / 5 is a future problem.

[0012] Accordingly, there remains an object to provide polyether polydimethylsiloxanes with reduced carbon footprint that are based on products from recycling processes and from an environmental and health point of view.SUMMARY

[0013] It has been found that a process for producing polyether polydimethylsiloxanes may solve or alleviate the shortcomings of the prior art, whereby the process comprises: (a) submitting a recycled-polydimethylsiloxane-containing composition comprising a recycled linear polydimethylsiloxane to an equilibration reaction with at least one poly(methylhydrogen)siloxane in the presence of at least one equilibration catalyst to form a poly(methylhydrogen)- polydimethylsiloxane copolymer; and (b) submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in step (a) to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain a polyether polydimethylsiloxane, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof, wherein recycling of at least one linear polydimethylsiloxane or copolymer thereof comprises (c) submitting a polydimethylsiloxane-containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at least one cyclic polydimethylsiloxane in a depolymerization reaction mixture; (d) distilling the depolymerization reaction mixture to obtain a cyclic-polydimethylsiloxane-containing composition comprising at least one cyclic polydimethylsiloxane; (e) optionally submitting the cyclic-polydimethylsiloxane-containing composition to a fractional distillative purification; (f) submitting the cyclic-polydimethylsiloxane- containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane-containing composition; and (g) optionally purifying the recycled- polydimethylsiloxane-containing composition.

[0014] The present invention also relates to a composition for preparing a polymer foam comprising at least one monomer species and one or more polyether polydimethylsiloxanes obtained according to the process for producing polyether polydimethylsiloxanes disclosed herein, whereby the polymer foam is preferably a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam, more preferably a polyurethane foam.

[0015] The present invention is also directed to a method for preparing a polymer foam comprising reacting one or more monomer species in the presence of one or more polyether polydimethylsiloxanes obtained according to the process for producing polyether polydimethylsiloxanes disclosed herein to obtain a polymer foam.

[0016] The present invention also provides an article comprising the polymer foam obtained according to the method for preparing a polymer foam disclosed herein or as the reaction product of the composition for preparing a polymer foam disclosed herein.

[0017] The present invention further relates to the use of a recycled linear polydimethylsiloxane for producing a polyether polydimethylsiloxane.

[0018] The present invention furthermore relates to the use of at least one polyether polydimethylsiloxane obtained according to the process for producing polyether polydimethylsiloxanes disclosed herein as an additive in a method of producing a polymer foam or a composition for preparing a polymer foam, whereby the polymer foam is preferably a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam.

[0019] Advantageously, the process for producing polyether polydimethylsiloxanes as defined in appended claim 1 provides polyether polydimethylsiloxanes with properties suitable for their application as foam stabilizers. Concomitantly, the polyether polydimethylsiloxanes advantageously have a carbon footprint that is reduced compared to polyether polydimethylsiloxanes obtained from the conventional route based on the Muller-Rochow process. The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description.DETAILED DESCRIPTION

[0020] Any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of “1 to 10” is intended to include any and all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, all subranges beginning with a minimum value equal to or greater than 1 and ending with a maximum value up to 10, and all subranges in between, e.g., 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1 . Any endpoints of ranges and / or numbers within those ranges can be combined within the scope of the present disclosure.

[0021] A component that is described as being present “up to” or in "at most" a specified amount with no minimum amount stated is not necessarily be present in the respective composition. For example, the recycled-polydimethylsiloxane-containing composition comprising at most 40 ppm by weight water may be substantially free or even completely free of water.

[0022] All parts, amounts, concentrations etc. referred to herein are by weight, unless specified otherwise.

[0023] As used herein, the term “comprising” is understood to be open-ended and to not exclude the presence of additional undescribed or unrecited elements, materials, ingredients, or method steps etc. The terms “including”, “containing” and like terms are understood to be synonymous with“comprising”. As used herein, the term “consisting of’ is understood to exclude the presence of any unspecified element, ingredient, or method step etc. Although the disclosure has been described in terms of “comprising”, “consisting of’ or “consisting essentially of’ are also within the scope of the present disclosure. For example, while the disclosure has been described in terms of a recycled- polydimethylsiloxane-containing composition comprising a recycled linear polydimethylsiloxane, a recycled-polydimethylsiloxane-containing composition consisting essentially of and / or consisting of a recycled linear polydimethylsiloxane is also within the present scope. In this context, “consisting essentially of’ means that any additional composition components will not materially affect the relevant properties of the recycled-polydimethylsiloxane-containing composition in the process for producing polyether polydimethylsiloxanes.

[0024] As used herein, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0025] As used herein, the term “substantially free” means that the material being discussed is present in the composition, if at all, as an incidental impurity. In other words, the material does not affect the properties of the composition. Thus, the material may be present in an amount of less than 1 weight precent, or preferably less than 0.5 weight percent, or more preferably less than 0.1 weight percent. This means that, for example, the recycled-polydimethylsiloxane-containing composition contains less than 1 weight percent of chlorine-containing compounds or, in some cases, less than 0.05 weight percent of chlorine-containing compounds, wherein such weight percents are based on the total weight of the recycled-polydimethylsiloxane-containing composition. As used herein, the term “completely free” means that the material is not present in the composition at all. Thus, the recycled-polydimethylsiloxane-containing composition disclosed herein may contain no chlorine- containing compounds.

[0026] Further, the term “polymer” refers to oligomers, homopolymers (e.g., prepared from a single monomer species), copolymers (e.g., prepared form at least two monomer species such as three or more monomer species), and graft polymers.

[0027] As already mentioned, the present invention provides a process for producing polyether polydimethylsiloxanes comprising: (a) submitting a recycled-polydimethylsiloxane-containing composition comprising a recycled linear polydimethylsiloxane to an equilibration reaction with at least one poly(methylhydrogen)siloxane in the presence of at least one equilibration catalyst to form a poly(methylhydrogen)-polydimethylsiloxane copolymer; and (b) submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in step (a) to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain a polyether polydimethylsiloxane, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof, wherein recycling of at least one linear polydimethylsiloxane or copolymer thereof comprises (c) submitting a polydimethylsiloxane- containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at leastone cyclic polydimethylsiloxane in a depolymerization reaction mixture; (d) distilling the depolymerization reaction mixture to obtain a cyclic-polydimethylsiloxane-containing composition comprising at least one cyclic polydimethylsiloxane; (e) optionally submitting the cyclic- polydimethylsiloxane-containing composition to a fractional disti Native purification; (f) submitting the cyclic-polydimethylsiloxane-containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane-containing composition; and (g) optionally purifying the recycled polydimethylsiloxane-containing composition.

[0028] In silicone recycling, cyclic siloxanes are produced intermediary. As mentioned above, at least some cyclic siloxanes are classified as persistent organic pollutants, why their presence in the final products is to be avoided or even legally banned. A further problem is that aromatic and aliphatic contaminants are frequently found in recycled siloxanes. Said aromatic or aliphatics can be used as an auxiliary agent in the recycling process, e.g., as a solvent or to improve phase separation. Alternatively, they may come from the waste streams used in the recycling process, or they may be formed during the recycling process. For example, benzene can be formed during the thermal treatment of phenyl siloxanes. However, impurities such as alkanes or benzene cannot be separated from D4 / D5 by distillation. However, it was found that these impurities can be separated by distillation after the conversion of the contaminated cyclic siloxanes into higher molecular weight PDMS oils. Examples of the present application involve the use of a cyclic organosiloxane- containing composition derived from a recycling process. Said composition contained cyclic organosiloxanes D3 to D6, but also different alkanes and benzene as impurities. The impurities could not be removed completely from the compositions. However, when the cyclic organosiloxanes were first converted to polydimethylsiloxanes oils, it was possible to remove the said impurities. The advantage is that cycles from recycling processes with lower purity can be used. The impurities contained can be separated at the level of the PDMS oils. A further advantage is that PDMS oils as raw materials are toxicologically less harmful than cyclic siloxanes and can be transported or stored better. POP classification of D4 / 5 as a future problem.

[0029] As understood herein, a polydimethylsiloxane is a polymer with siloxane units (repeating unit), i.e., Oi / 2-Si-Oi / 2 units, and methyl substituents (herein abbreviated as "Me") at the silicon atoms. Thereby, individual siloxane units are interconnected at the oxygen atoms. The Oi / 2-SiMe2- O1 / 2 unit is conventionally and herein also denoted as D unit. A polydimethylsiloxane copolymer refers herein to a polymer that comprises beside the Oi / 2-SiMe2-Oi / 2 repeating unit (D unit) a further repeating unit that is different from Oi / 2-SiMe2-Oi / 2. The polydimethylsiloxanes or copolymers thereof may comprise branching units conventionally and herein denoted as T units and Q units. Thereby, a T unit refers to a MeiSiO3 / 2 unit and a Q unit refers to a SiO4 / 2 unit. Further, an M unit refers herein to a MesSiOie unit, thus forming a chain end. A branched polydimethylsiloxane refers to a polydimethylsiloxane comprising T and / or Q units. A branched polydimethylsiloxane copolymer refers to a copolymer that comprises T and / or Q units and / or further branching units in the polymer chain that are not a T unit or Q unit.

[0030] A recycled linear polydimethylsiloxane as understood herein refers to a linear polydimethylsiloxane that is obtained from recycling of a waste material. As waste material, for example, used, wide-spec, expired, surplus materials, or any mixtures or combinations thereof can be utilized. In a preferred practice of the present invention, the recycled linear -polydimethylsiloxane is obtained from recycling of at least one linear -polydimethylsiloxane or copolymer thereof as detailed further hereinbelow.

[0031] The recycled-polydimethylsiloxane-containing composition of the present invention can have a total content of the recycled linear -polydimethylsiloxane of more than 90% by weight, preferably more than 95% by weight, or even more preferably by 98% by weight, based on the total weight of the recycled-polydimethylsiloxane-containing composition.

[0032] The recycled-polydimethylsiloxane-containing composition may be characterized by also its molar content of M, T, and Q units based on the total mols of M, D, T, and Q units in the recycled- polydimethylsiloxane-containing composition. In a preferred practice of the present invention, the recycled-polydimethylsiloxane-containing composition comprises at most 7.5 mol %, or preferably at most 4 mol %, or more preferably at most 2.5 mol % M units, based on the total mols of M, D, T, and Q units in the recycled-polydimethylsiloxane-containing composition. The recycled- polydimethylsiloxane-containing composition may comprise at least 0.15 mol %, or preferably at least 0.25 mol %, or more preferably at least 1 .5 mol % M units, based on the total mols of M, D, T, and Q units in the recycled-polydimethylsiloxane-containing composition. The sum of T and Q units of the recycled-polydimethylsiloxane-containing composition can be at most 0.75 mol %, or preferably at most 0.5 mol %, or more preferably at most 0.25 mol %, based on the total mols of M, D, T, and Q units in the recycled-polydimethylsiloxane-containing composition. In29Si NMR spectroscopy M units result in signals in the range of 6 - 9 ppm, D units of -16 to -24 ppm, T units of -40 to -80 ppm, and Q units of -95 to -140 ppm.The proportion of, e.g., M units is determined by setting the sum of the signal intensities of the signals from 6 - 9 ppm in relation to the sum of the signal intensities of all signals of the M, D, T, and Q units. Suitable parameters for recording the29Si- NMR can be found in the following literature: M. Cypryk, K. Kazmierski, W. Fortuniak, and J. Chojnowski, Macromolecules 2000, 33, 5, 1536-1545.

[0033] The recycled-polydimethylsiloxane-containing composition can further be described by the content of components not being recycled linear polydimethylsiloxane such as water, cyclic siloxanes, and siloxanes comprising hydroxyl or vinyl groups.

[0034] In a preferred practice of the present invention, the recycled-polydimethylsiloxane- containing composition comprises at most 0.05% by weight, or preferably at most 100 ppm by weight, or more preferably at most 40 ppm by weight, or most preferably at most 10 ppm, based on the total weight of the recycled-polydimethylsiloxane-containing composition, water as measured according to DIN 51777:2020-04. Even more preferably the recycled-polydimethylsiloxane- containing composition is substantially free or completely free of water. The recycled- polydimethylsiloxane-containing composition can comprise at most 0.2 mol %, or preferably at most 0.1 mol %, or more preferably at most 0.05 mol %, based on the total mols of silicon atoms in therecycled-polydimethylsiloxane-containing composition, hydroxyl-substituted silicon atoms as preferably determined based on29Si-NMR spectroscopy. To this end, the peak area in the29Si-NMR spectrum is calculated for the signals corresponding to hydroxyl-substituted silicon atoms. Also, the sum of the peak areas for all silicon atom signals without the standard is determined and set into the ratio with the peak area of the hydroxyl-substituted silicon atoms to obtain the molar content of hydroxyl-substituted silicon atoms. A measuring frequency of the NMR measurement of at least 400 MHz is advantageous. Even more preferably the recycled-polydimethylsiloxane-containing composition is substantially free or completely free of hydroxyl-substituted silicon atoms. Water and hydroxyl-substituted siloxanes may lead to hydrolysis of the SiH functionalities in the equilibration reaction step and therefore finally to polyether polydimethylsiloxane with altered structures and thus potentially deteriorated application properties in polymer foams. Water may also lead to solubilization of the equilibration catalyst thereby potentially slowing down or even completely terminating the equilibration reaction such that no sufficient statistical distribution of the SiH units in the resulting poly(methylhydrogen)-polydimethylsiloxane copolymers may be achieved.

[0035] The recycled-polydimethylsiloxane-containing composition can comprise at most 20% by weight, or preferably at most 15% by weight, based on the total weight of the recycled- polydimethylsiloxane-containing composition, cyclic siloxanes as preferably measured gas chromatography, e.g., according to the method described below. Even more preferably the recycled- polydimethylsiloxane-containing composition is substantially free or completely free of cyclic siloxanes. Such cyclic siloxanes can have 2 to 8 repeating units such as hexamethylcyclotrisiloxane (denoted conventionally and herein as D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), tetradecamethylcycloheptasiloxane (D7), and hexadecamethylcyclooctasiloxane (D8).

[0036] The content of cyclic polydimethylsiloxanes (such as D3, D4, D5, D6, D7 and D8) in the recycled-polydimethylsiloxane-containing composition can be determined as follows. The substances are separated according to the boiling point and detected by means of a thermal conductivity detector (TCD). An aliquot of the sample to be examined is analyzed by GC without further dilution. This is carried out in a gas chromatograph equipped with a split / splitless injector, a capillary column and a thermal conductivity detector under the following conditions: Injector: 290 °C, split 40 mL; Injection volume: 1 pL; Column: 5 m *0.32 mm HP5 1 pm; Carrier gas: Hydrogen, const, flow 2 mL / min; Temperature program: 1 minute at 80 °C, then 80 °C - 300 °C at 30 °C / min, then conditioning for 10 minutes at 300 °C; Detector: TCD at 320 °C; Make Up Gas flow: 8 mL / min; Reference gas flow: 22 mL / min. The cyclic siloxanes are separated according to their boiling point. The mass fraction of the individual substances is determined as a percentage of the peak areas determined for the respective substance compared to the total area of all detected substances (area- % method).

[0037] The recycled-polydimethylsiloxane-containing composition can comprise at most 0.5 mol %, or preferably at most 0.2 mol %, or more preferably at most 0.1 mol %, based on the total mols silicon atoms in the recycled-polydimethylsiloxane-containing composition, vinyl-substituted siliconatoms as preferably determined based on29Si-NMR spectroscopy. To this end, the peak area in the29Si-NMR spectrum is calculated for the signal corresponding to vinyl-substituted silicon atoms. Also, the sum of the peak areas for all silicon atom signals without the standard is determined and set into the ratio with the peak area of the vinyl-substituted silicon atoms to obtain the molar content of vinyl- substituted silicon atoms. A measuring frequency of the NMR measurement of at least 400 MHz is advantageous. Even more preferably the recycled-polydimethylsiloxane-containing composition is substantially free or completely free of vinyl-substituted silicon atoms. Vinyl-substituted siloxanes provide cross-linking sites of the polymer chains in the subsequent hydrosilylation reaction and therefore potentially lead to an unfavorably increased viscosity of the resulting polyether polydimethylsiloxane.

[0038] The recycled-polydimethylsiloxane-containing composition can comprise the recycled linear polydimethylsiloxane and additionally at least one further polydimethylsiloxane not being recycled. The at least one further polydimethylsiloxane not being recycled may be added to the recycled- polydimethylsiloxane-containing composition before being submitted to the equilibration reaction. For example, the recycled-polydimethylsiloxane-containing composition may comprise a nonrecycled cyclic polydimethylsiloxane such as octamethylcyclotetrasiloxane. Such non-recycled cyclic polydimethylsiloxanes like octamethylcyclotetrasiloxane may be derived, for example, from chlorosilanes of the conventionally applied Muller-Rochow process. Preferably, however, the recycled-polydimethylsiloxane-containing composition is substantially free or completely free of nonrecycled further polydimethylsiloxanes obtained, for example, based on methylchlorosilanes from the Muller-Rochow process. The recycled-polydimethylsiloxane-containing composition of the present invention can therefore have a content of chlorine-containing compounds that is below the respective content of polydimethylsiloxane-containing compositions with polydimethylsiloxanes derived from methylchlorosilanes. Chlorine-containing compounds as understood herein include inorganic compounds such as chlorine-containing salts like NaCI as well as organic compounds such as chlorosilanes. The recycled-polydimethylsiloxane-containing composition may comprise less than 100 ppm chlorine-containing compounds, preferably less than 50 ppm chlorine-containing compounds, more preferably less than 25 ppm chlorine-containing compounds, and most preferably less than 10 ppm chlorine-containing compounds, based on the total weight of the recycled- polydimethylsiloxane-containing composition. Preferably, the recycled-polydimethylsiloxane- containing composition is substantially free of chlorine-containing compounds or is most preferably completely free of chlorine-containing compounds.

[0039] By utilizing a recycled linear polydimethylsiloxane, the carbon footprint of the recycled- polydimethylsiloxane-containing composition utilized in the practice of the present invention can be reduced compared to the use of non-recycled polydimethylsiloxanes which are, e.g., directly obtained, for example, from products of the Muller-Rochow process and which are conventionally utilized in the preparation of polyether polydimethylsiloxanes. Accordingly, the recycled linear polydimethylsiloxane can have a carbon footprint of less than 4 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane or preferably of less than 2 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane as determined according to DIN EN ISO standard 14067:2018.

[0040] As already mentioned, the recycled linear polydimethylsiloxane is obtained in a preferred practice of the present invention from recycling of at least one linear polydimethylsiloxane or copolymer.

[0041] Advantageously, the at least one linear polydimethylsiloxane or copolymer thereof submitted to the recycling process comprises at least 50% by weight, or preferably at least 90% by weight, or more preferably at least 99% by weight dimethylsiloxane units (D units), based on the total weight of the at least one linear polydimethylsiloxane or copolymer thereof. Preferably, the at least one linear polydimethylsiloxane or copolymer thereof comprises a ratio of M units to D units of at least 1 :500, or preferably at least 1 :750, or more preferably at least 1 :1000 as preferably determined by29Si-NMR spectroscopy. In a preferred practice of the present invention, the at least one linear polydimethylsiloxane is not a copolymer thus comprising only a dimethylsiloxane (D) repeating unit and M units. In a preferred practice of the present invention, the at least one polydimethylsiloxane or copolymer thereof is a linear polydimethylsiloxane. In an even more preferred practice of the present invention, the at least one linear polydimethylsiloxane or copolymer thereof is a linear polydimethylsiloxane homopolymer.

[0042] The at least one linear polydimethylsiloxane or copolymer thereof can, for example, correspond to or is derived from a waste polydimethylsiloxane polymer or copolymer material, a wide-spec polydimethylsiloxane polymer or copolymer material, a used polydimethylsiloxane polymer or copolymer material, an expired polydimethylsiloxane polymer or copolymer material, a surplus polydimethylsiloxane polymer or copolymer material, or any mixtures or combinations thereof.

[0043] The at least one linear polydimethylsiloxane or copolymer thereof can correspond to different polydimethylsiloxane polymer or copolymer products. For example, the at least one linear polydimethylsiloxane or copolymer thereof can be a polydimethylsiloxane material from a lubricant or a heat transfer oil. The polydimethylsiloxane polymer or copolymer can be a polydimethylsiloxane oil, a polydimethylsiloxane rubber, a polydimethylsiloxanes elastomer, or any mixtures thereof. The polydimethylsiloxane oil refers to the state of aggregation at 25°C and standard pressure (i.e., 1 atm). For example, the at least one linear polydimethylsiloxane or copolymer thereof can be a mixture of a polydimethylsiloxane oil and a polydimethylsiloxane elastomer or rubber. The linear polydimethylsiloxanes or copolymers thereof can, of course, also be a mixture of two or more different polydimethylsiloxane oils respectively polydimethylsiloxane elastomers or rubbers. Preferred are polydimethylsiloxanes oils. The polydimethylsiloxane oil preferably has a viscosity at 20°C of at least 1000 mPa s as preferably measured according to DIN 53019-1 :2008-09. If the viscosity is below 1000 mPa s, the polydimethylsiloxane oil has an unfavorably high fraction of M units which act as chain stoppers in the equilibration reaction. Advantageously, polydimethylsiloxane elastomers or rubbers are shredded before further processing.

[0044] Typically, the at least one linear polydimethylsiloxane or copolymer thereof is contained in a polydimethylsiloxane-containing composition that is utilized for producing the recycled linear polydimethylsiloxane.

[0045] The polydimethylsiloxane-containing composition can be characterized by the weight fraction of the at least linear polydimethylsiloxane or copolymer thereof. Thus, the polydimethylsiloxane-containing composition preferably comprises at least 50% by weight, or preferably at least 70% by weight, or more preferably at least 90% percent by weight, based on the total weight of the polydimethylsiloxane-containing composition, of the at least one linear polydimethylsiloxane or copolymer thereof. The polydimethylsiloxane-containing composition may also essentially consist of or consist of at least one linear polydimethylsiloxane or copolymer thereof.

[0046] The polydimethylsiloxane-containing composition can furthermore be characterized by its silicon content. Preferably, the polydimethylsiloxane-containing composition has a silicon content of from 19% to 38% by weight, or preferably from 26% to 38% by weight, or more preferably from 34% to 38% by weight, based on the total weight of the polydimethylsiloxane-containing composition. The silicon content is preferably determined according to the methods described in “Determination of Silicon in Organosilicon Compounds”, J. A. McHard, P. C. Servais, and H. A. Clark, Analytical Chemistry, 1948, 20 (4), 325-328.

[0047] Linear polydimethylsiloxane polymer or copolymer products often comprise additives such as fillers, colorants, waxes, cross-linking catalysts, or catalyst residues. Such additives may thus be present in the polydimethylsiloxane-containing composition and can influence the process steps for yielding the recycled-polydimethylsiloxane-containing composition and subsequent reaction steps if not completely eliminated from the recycled-polydimethylsiloxane-containing composition. The polydimethylsiloxane-containing composition can be characterized by its content of fillers. Accordingly, the polydimethylsiloxane-containing composition preferably comprises less than 50% by weight, or preferably less than 25% by weight, or more preferably less than 5% by weight, based on the total weight of the polydimethylsiloxane-containing composition, fillers. The polydimethylsiloxane-containing composition can also be substantially free or even completely free of fillers.

[0048] The polydimethylsiloxane-containing composition can also be characterized by its content of colorants, which may be contained in linear polydimethylsiloxane polymer or copolymer products. Accordingly, the polydimethylsiloxane-containing composition preferably comprises less than 5% by weight, or preferably less than 3% by weight, or more preferably less than 1 % by weight, based on the total weight of the polydimethylsiloxane-containing composition, colorants. The polydimethylsiloxane-containing composition can also be substantially free or even completely free of colorants.

[0049] The polydimethylsiloxane-containing composition can also be characterized by its content of polymers that are not polydimethylsiloxanes or copolymers thereof. In a typical practice of the present invention, the polydimethylsiloxane-containing composition is substantially free or even completely free of polyamides. The polydimethylsiloxane-containing composition may comprise at most 5 % by weight polypropylene and / or polyethylene, based on the total weight of the polydimethylsiloxane-containing composition. In a preferred practice of the present invention, thepolydimethylsiloxane-containing composition is substantially free or completely free of polypropylene and / or polyethylene.

[0050] The polydimethylsiloxane-containing composition may comprise a total amount of polymers other than polydimethylsiloxanes or copolymers thereof of at most 10 % by weight, or preferably at most 5 % by weight, or more preferably at most 2 % by weight, based on the total weight of the polydimethylsiloxane-containing composition.

[0051] The polydimethylsiloxane-containing composition may comprise further components added intentionally or unintentionally to the composition. The polydimethylsiloxane-containing composition may, for example, comprise one or more solvents, which may aid in dissolving the at least one linear polydimethylsiloxane or copolymer thereof. Suitable solvents include, for example, organic solvents, such as cyclopentane, hexane, dimethylbenzene, toluene, xylene, ether, chloroform, and tetra hydrofuran. However, the polydimethylsiloxane-containing composition may also be substantially or completely free of solvents.

[0052] As already mentioned, the recycled linear polydimethylsiloxane is obtained in a preferred practice of the present invention from recycling of at least one linear polydimethylsiloxane or copolymer. According to a particularly preferred practice of the present invention, recycling of at least one linear polydimethylsiloxane or copolymer thereof may comprise (c) submitting a polydimethylsiloxane-containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at least one cyclic polydimethylsiloxane in a depolymerization reaction mixture; (d) distilling the depolymerization reaction mixture to obtain a cyclic-polydimethylsiloxane-containing composition comprising at least one cyclic polydimethylsiloxane; (e) optionally submitting the cyclic- polydimethylsiloxane-containing composition to a fractional disti Native purification; (f) submitting the cyclic-polydimethylsiloxane-containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane-containing composition; and (g) optionally purifying the recycled-polydimethylsiloxane-containing composition. Distilling in step (d) may be carried out at least partially during the catalytic depolymerization. Purifying the recycled-polydimethylsiloxane-containing composition in step (g) is intended to reduce the amounts of unwanted compounds in the recycled-polydimethylsiloxane-containing composition that may, e.g., interfere with the subsequent equilibration and / or hydrosilylation reaction or which should not be present in the obtained polyether polydimethylsiloxane material. For example, cyclic siloxanes can be removed from the recycled-polydimethylsiloxane-containing composition by means of, e.g., distillation.

[0053] Exemplary reactions for the catalytic depolymerization are revealed in US 5,110,972 A under items D. and E. Furthermore, reaction conditions for the catalytic depolymerization are disclosed in Degradation of silicone-based materials as a driving force for recyclability, Buddhima Rupasinghe and Joseph C Furgal, Polym Int 2022; 71 : 521-531 , and Full Circle Recycling of Polysiloxanes via Room-Temperature Fluoride-Catalyzed Depolymerization to RepolymerizableCyclics, Buddhima Rupasinghe and Joseph C Furgal, ACS Appl. Polym. Mater. 2021 , 3, 1828-1839. The D3, D4, D5, D6, D7 and D8 content can be adjusted by the type of catalytic depolymerization such as the catalyst, temperature, solvent, water content etc. It is particularly, desired to adjust or control the content of linear siloxanes, water, M-units, T-units, Q-units, Si-hydroxyls and Si-vinyls of the recycled-polydimethylsiloxane-containing composition before subjecting the recycled- polydimethylsiloxane-containing composition to the equilibration reaction. Accordingly, the content of linear siloxanes, water, M-units, T-units, Q-units, Si-hydroxyls and Si-vinyls of the recycled- polydimethylsiloxane-containing composition is chosen as described above. The cyclic- polydimethylsiloxane-containing composition may in particular be purified by distillative purification, such as fractional distillative purification before subjecting the recycled-polydimethylsiloxane- containing composition to the equilibration reaction.

[0054] The catalytic depolymerization is preferably carried out at a temperature of between 40°C and 200°C, or preferably between 50°C and 190°C, or more preferably between 80°C and 180°C.

[0055] The catalytic depolymerization can advantageously be carried out at standard pressure (i.e., 1013 hPa), reduced pressure (<1013 hPa), or else, in order to achieve high heat treatment temperatures up to 200°C, in pressure-rated apparatuses under elevated pressure (>1013 hPa). Preferably, the catalytic depolymerization according to the invention is conducted at a pressure of 1013±10 hPa. Advantageously, the catalytic depolymerization is carried out in a reactor that is resistant to corrosion, temperatures of at least 250°C, and optionally pressures above standard pressure.

[0056] The depolymerization reaction is advantageously carried out in the presence of at least one depolymerization catalyst. The at least one depolymerization catalyst is preferably selected from Bransted acids or Bransted bases. Preferred Bransted acids are selected from the group consisting of trifluoromethanesulfonic acid, sulfuric acid, hydrochloric acid, and combinations thereof. Preferred Bransted bases are selected from the group consisting of alkali metal hydroxides, tetraalkylammonium hydroxides, tetraalkylphosphonium hydroxides, phosphazenes, guanidines, and combinations thereof.

[0057] The catalytic depolymerization can also be carried out in a two-step process combining a treatment with an acidic depolymerization catalyst, such as the ones mentioned hereinbefore, followed by treatment with a basic depolymerization catalyst, such as the ones mentioned hereinbefore.

[0058] Further components such as solvents can be added to the depolymerization reaction mixture, if needed.

[0059] The depolymerization reaction is typically carried out for 1.5 to 6 hours. Thereby, it is preferred that the depolymerization reaction mixture is stirred in order to ensure that the substances are thoroughly mixed.

[0060] The catalytic depolymerization step can be carried out batchwise, or as semi-continuous process, or as continuous process.

[0061] As detailed above, the cyclic-polydimethylsiloxane-containing composition comprising the at least one cyclic polydimethylsiloxane is typically submitted to a polymerization reaction in the presence of a polymerization catalyst to obtain the recycled linear polydimethylsiloxane. The polymerization reaction of the at least one cyclic polydimethylsiloxane can be carried out according to any method known in the art in this respect such as for example described in Chojnowski, H. Ring-Opening Polymerization of Cyclosiloxanes, in Silicon Compounds: Silanes and Silicones 4000A, Ed. B Arkles, G- Larson, Geles Inc. 2008, Morrisville, PA, 389 - 405. The conditions during the polymerization are advantageously chosen such that a recycled linear polydimethylsiloxane is obtained having a desired viscosity and desired end groups. The polymerization reaction can be carried out as an anionic polymerization or a cationic polymerization. Suitable polymerization catalysts for an anionic polymerization include, for example, strong inorganic or organic bases. Suitable polymerization catalysts for a cationic polymerization include strong protic acids such as H2SO4, CF3SO3H, HCIO4, CH3SO3H, and CF3SO3H. A chain blocker such as a disiloxane or a short chain oligosiloxane introducing end groups can be utilized to control the molecular weight of the recycled linear polydimethylsiloxane and its end groups.

[0062] In a preferred practice of the present invention the recycled linear polydimethylsiloxane has a viscosity at 25°C of 25 to 2500 mPa s, or preferably 50 to 2000 mPa s, or more preferably 100 to 1500 mPa s, as measured according to DIN 53019-1 :2008-09.

[0063] The recycled-polydimethylsiloxane-containing composition is submitted in the process of the present invention to an equilibration reaction with at least one poly(methylhydrogen)siloxane and in the presence of at least one equilibration catalyst to form a poly(methylhydrogen)- polydimethylsiloxane copolymer in an equilibration reaction mixture. As utilized herein, an equilibration reaction refers to the reorganization of the recycled linear polydimethylsiloxane with a poly(methylhydrogen)siloxane in the presence of at least one equilibration catalyst resulting in the formation of a poly(methylhydrogen)-polydimethylsiloxane copolymer in an equilibration reaction mixture. The poly(methylhydrogen)-polydimethylsiloxane copolymer typically has the general molecular structure according to Formula 1 , whereby the units m and n are preferably statistically distributed in the structure:(Formula 1), wherein R is independently selected from methyl and hydrogen. Preferably R is methyl.

[0064] Typically, one or more chain length modifiers are also added to the equilibration reaction mixture for controlling the chain length of the resulting poly(methylhydrogen)-polydimethylsiloxane copolymer. Thereby, the amount of the one or more chain length modifiers added to the equilibration reaction mixture may be adjusted based on the amount of M units contained in the recycled- polydimethylsiloxane-containing composition. One typical chain length modifier ishexamethyldisiloxane, which introduces only M units. Alternatively, or additionally, 1 , 1 ,3,3- tetramethyldisiloxane may be added to the equilibration reaction mixture, which introduces hydrogen containing end units (HSiMe2-, so-called M’ units). Also, HSiMe2-endfunctional polydimethylsiloxane oils, which have the general formula HSiMe2-O-(-SiMe2-O-)q-SiMe2H, may be added, which introduce D units and M’ units. Such oils may have of the CAS number 70900-21-9. Preferably the HSiMe2-endfunctional polydimethylsiloxane oil has about 5 to 10 dimethylsiloxane units (D units); i.e., q = 5 to 10.

[0065] The chain length and thus the viscosity of the resulting poly(methylhydrogen)- polydimethylsiloxane copolymer inter alia depends on the amount of endgroups in the equilibration reaction mixture, which are in particular M units. The amount of chain length modifier added to the equilibration reaction mixture may thus be chosen based on the amount of endgroups already contained in the recycled-polydimethylsiloxane-containing composition. Accordingly, the process for producing polyether polydimethylsiloxanes according to the present invention can further comprise measuring the content of endgroups such as M units in the recycled-polydimethylsiloxane-containing composition and adding based on the measured content an amount of the at least one chain length modifier such as the one mentioned hereinbefore to achieve a desired viscosity of the poly(methylhydrogen)-polydimethylsiloxane copolymer.

[0066] The poly(methylhydrogen)siloxane may have the molecular structure according to Formula 2:(Formula 2)

[0067] The poly(methylhydrogen)siloxane may have a SiH content of from 4.5 to 16.7 mol / kg or preferably from 10 to 16.5 mol / kg, based on the weight of the poly(methylhydrogen)siloxane. One particularly suitable poly(methylhydrogen)siloxane has a SiH content of about 16 mol / kg and a molar mass Mnof about 2500 g / mol.

[0068] As already mentioned, the equilibration reaction is carried out in the presence of at least one equilibration catalyst. Typically, the at least one equilibration catalyst is selected from acidic equilibration catalysts. Suitable acidic equilibration catalysts are strong protic acids such as sulfuric acid, trifluoromethanesulfonic acid, methanesulfonic acid, and perchloric acid, protic and Lewis acids such as HCI+FeCh and HCI+SbCh, acid-activated minerals such as bleaching earths like bentonites, montmorillonites, and Fuller’s earth, and cation exchange resins such as sulfonic acid, macro-crosslinked cation exchange resins, as well as mixtures thereof.

[0069] The amount of the at least one equilibration catalyst is preferably from 0.02 to 10% by weight, or more preferably from 0.05 to 8% by weight, based on the total weight of the equilibration reaction mixture. The amount of the at least one equilibration catalyst in the equilibration reactionmixture may be adjusted based on the amount of water and hydroxyl-substituted silicon atoms in the recycled-polydimethylsiloxane-containing composition.

[0070] The equilibration reaction can be carried out at a temperature of between 10°C and 110°C, or preferably between 25°C and 100°C. The equilibration reaction can be carried out at reduced pressure (<1013 hPa), standard pressure (1013 hPa), or superatmospheric pressure (>1013 hPa). Preferably, the equilibration reaction is carried out at a pressure of 950 hPa to 1100 hPa, or more preferably at 1013 hPa.

[0071]

[0064] The equilibration reaction can be carried out in 20 minutes to 20 hours, or preferably of 30 minutes to 14 hours. However, it is desired that the equilibration reaction is carried out in 20 minutes to 7 hours, or preferably of 30 minutes to 5 hours. Thereby, the equilibration reaction time should be chosen such that the molecular weight distribution, the distribution of SiH functionalities, and the molecular structure of the poly(methylhydrogen)-polydimethylsiloxane copolymer have reached the equilibrium state. If the equilibrium state has not been reached, the subsequent hydrosilylation reaction making use of the poly(methylhydrogen)-polydimethylsiloxane copolymer may lead to a greatly turbid polyether polydimethylsiloxane solution, which, when used as foam stabilizer in, for example, polyurethane soft foam systems, often lead to great foam decay up to foam collapse.

[0072] If desired, the equilibration reaction can be carried out in the presence of one or more solvents. Suitable solvents are all those solvents which, in the equilibration reaction, are inert to the equilibration catalysts, starting materials and products. Particularly preferably, however, the equilibration reaction is carried out in the absence of a solvent.

[0073] The equilibration step can be carried out batchwise, semi-continuously, or continuously.

[0074] It can be advantageous to separate off a subquantity having a desired boiling range from the equilibration reaction mixture. The remaining residue of the equilibration reaction mixture which does not have the desired boiling range can be fed again into the equilibration reaction, to be used again, for example, as starting material. Particularly preferably, in particular when the process is carried out continuously, a subquantity having a desired boiling range is separated off from the equilibration reaction mixture and the remainder which does not have the desired boiling range is fed again into the equilibration reaction mixture. This separation can proceed, for example, by a simple thermal separation (such as, for example, by simple distillation or by similar measures). The fraction having the unwanted boiling range can, for example, be recirculated into the feed of the recycled-polydimethylsiloxane-containing composition, when the equilibration reaction step is carried out as a continuous process.

[0075] If necessary, and especially if the equilibration step is carried out as a batch process, cyclic polydimethylsiloxanes as toxicologically critical components and other volatiles are removed from the equilibration reaction mixture by applying heat and vacuum after the equilibration state has been achieved. The remainder of the equilibration reaction mixture can further be filtered to remove, for example, solid-phase equilibration catalysts, if present. The thus obtained poly(methylhydrogen)-polydimethylsiloxane copolymer can be submitted to the hydrosilylation reaction step without any further purification.

[0076] The poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in the equilibration reaction step can be characterized by its density, viscosity, and SiH value. The poly(methylhydrogen)-polydimethylsiloxane copolymer can have a density at 25°C of from 0.95 to 0.98 g / mL, or preferably from 0.96 to 0.98 g / mL, or more preferably from 0.97 to 0.98 g / mL as preferably determined according to DIN 51757:2011-01. The poly(methylhydrogen)- polydimethylsiloxane copolymer can have a viscosity at 25°C of from 2 to 2000 mPa s, or preferably from 3 to 1000 mPa s, or more preferably from 10 to 500 mPa s as preferably determined according to DIN 53019-1 :2008-09. The poly(methylhydrogen)-polydimethylsiloxane copolymer can have an SiH value corresponding to the content of SiH functionalities of from 0.2 to 10 mol / kg, or preferably from 0.4 to 8 mol / kg, or more preferably from 0.6 to 6 mol / kg as preferably measured with gas volumetry. To this end, a weighed sample of the poly(methylhydrogen)-polydimethylsiloxane copolymer is decomposed by means of a sodium butylate solution to form hydrogen gas. The amount of hydrogen gas is measured and the SiH value is determined using the definition of the SiH value: n(H2) [mol] / m(sample) [kg].

[0077] The poly(methylhydrogen)-polydimethylsiloxane copolymer can have (A) a density at 25°C of from 0.94 to 0.99 g / mL, preferably from 0.95 to 0.98 g / mL, or more preferably from 0.96 to 0.98 g / mL determined according to DIN 51757:201 1-01 ; a viscosity at 25°C of from 50 to 70 mPa s, preferably from 52 to 64 mPa s, more preferably from 53 to 63 mPa s determined according to DIN 53019-1 :2008-09; and an SiH value of from 1.1 to 1 .60 mol / kg, preferably from 1 .0 to 1 .50 mol / kg, more preferably from 1 .2 to 1 .45 mol / kg measured with gas volumetry; or (B) a density at 25°C of from 0.95 to 1 .00 g / mL, preferably from 0.96 to 0.99 g / mL, or more preferably from 0.965 to 0.972 g / mL determined according to DIN 51757:201 1-01 ; a viscosity at 25°C of from 60 to 85 mPa s, preferably from 64 to 84 mPa s, more preferably from 67 to 85 mPa s determined according to DIN 53019-1 :2008-09; and an SiH value of from 1 .40 to 1 .80 mol / kg, preferably from 1 .50 to 1 .70 mol / kg, more preferably from 1 .57 to 1 .67 mol / kg measured with gas volumetry.

[0078] According to the process of the present invention, the poly(methylhydrogen)- polydimethylsiloxane copolymer is submitted to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain a polyether polydimethylsiloxane.

[0079] The hydrosilylation reaction is described, for example, in EP 1 520 870 A1 . In this reaction, the SiH functional groups react with the carbon-carbon double bond of the polyether to form Si-C bonds and thus link the polyether to the polydimethylsiloxane copolymer. The obtained polyether polydimethylsiloxane thus comprises dimethylsiloxane units as well as siloxane units in which the silicon atom is substituted with a methyl group and with a polyether derived from the at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds. In case the at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds comprises more than one carbon double bond reactive to Si-H bonds, the polyether moiety may belinked to two or more siloxane moieties. Preferably, however, the at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds comprises only one carbon-carbon double bond reactive to Si-H bonds.

[0080] As the at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds all the respective compounds known in the art can be utilized. Examples of suitable polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds include:CH2=CH-CH2-O-(CH2-CH2O-)x-(CH2-CH(R’)O-)y-R” CH2=CH-O-(CH2-CH2O-)x-(CH2-CH(R’)O-)y-R” in which x = O to 100; y = O to 100;R’ are same or different groups from the selection: substituted alkyl group having 1 to 4 carbon atoms or phenyl;R” is a hydrogen radical or an alkyl group having 1 to 4 carbon atoms; the group -C(O)-R”’ in which R’” = alkyl radical; the group -CH2-O-R’; an alkylaryl group, such as the benzyl group; the group -C(O)NH-R’.

[0081] The at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds is preferably selected from the group consisting of polyethers with the CAS numbers 27274-31-3, 9042-19-7, 9041-33-2, 27252-80-8, 62744-60-9, 52232-27-6, 27252-87-5, 132935-51- 4, and 56090-69-8.

[0082] In addition to the at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, at least one compound which is not a polyether and which comprises at least one carbon-carbon double bond reactive to Si-H bonds may also be present in the hydrosilylation reaction mixture and may take part in the hydrosilylation reaction. Such compounds are, however, preferably present only in small amounts, if present at all, such as in at most 10 mol %, or preferably at most 5 mol %, based on the total mols of the at least one polyether comprising at least one carboncarbon double bond reactive to Si-H bonds and the at least one compound which is not a polyether and which comprises at least one carbon-carbon double bond reactive to Si-H bonds.

[0083] Suitable hydrosilylation catalysts comprise noble metals such as Pt(O) or rhodium. A suitable Pt(O) catalyst is, for example, disclosed in EP 1 520 870 A1 .

[0084] The hydrosilylation reaction may be carried out in the presence of one or more solvents, if necessary, which can be separated from the obtained polyether polydimethylsiloxane by means of, e.g., distillation.

[0085] The hydrosilylation reaction can be carried out at a temperature of between 20°C and 140°C, or preferably between 40°C and 130°C, and more preferably between 60°C and 110°C.

[0086] According to the invention, the process is preferably carried out at standard pressure (1013 hPa), but pressure ranges deviating from this are also possible, if desired.

[0087] The polyether polydimethylsiloxane can be characterized by its viscosity. Thus, the polyether polydimethylsiloxane can have a viscosity at 25°C of from 100 mPa s to 12000 mPa s or preferably from 200 to 8000 mPa s as preferably determined according to DIN 53019-1 :2008-09, DIN 53019-2:2008-09, DIN 53019-3:2008-09 and DIN 53019-4:2008-09.

[0088] The polyether polydimethylsiloxane can have (A) a density at 25°C of from 1 .030 to 1 .060 g / mL, preferably from 1 .032 to 1 .057 g / mL, or more preferably from 1 .035 to 1 .055 g / mL determined according to DIN 51757:2011-01 ; and a viscosity at 25°C of from 700 to 1300 mPa s, preferably from 750 to 1250 mPa s, more preferably from 800 to 1200 mPa s determined according to DIN 53019-1 :2008-09; or (B) a density at 25°C of from 1.010 to 1.050 g / mL, preferably from 1.015 to 1 .045 g / mL, or more preferably from 1 .020 to 1 .040 g / mL determined according to DIN 51757:2011 - 01 ; and a viscosity at 25°C of from 500 to 1000 mPa s, preferably from 530 to 900 mPa s, more preferably from 550 to 850 mPa s determined according to DIN 53019-1 :2008-09.

[0089] The present invention also provides a composition for preparing a polymer foam comprising at least one monomer species and one or more polyether polydimethylsiloxanes obtained according to the process disclosed hereinbefore. The composition for preparing a polymer foam may comprise in addition to the polyether polydimethylsiloxane obtained according to the process disclosed herein at least one further polyether polydimethylsiloxane that is not obtained by the herein disclosed process and that may not be based on recycled products, but, e.g., on cyclic polydimethylsiloxanes from the Muller-Rochow process. In a preferred practice of the present invention the polymer foam is a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam. A polyurethane foam is particularly preferred. The polyurethane foam can in particular be a flexible polyurethane foam, a rigid polyurethane foam, a semi rigid polyurethane foam, a moulded polyurethane foam, a high resilience polyurethane foam, a viscoelastic foam, a hypersoft polyurethane foam, or an integral foam.

[0090] A composition for preparing a polyurethane foam typically comprises at least one isocyanate-reactive compound having in average at least two groups per molecule being reactive to isocyanate groups; at least one polyisocyanate having in average at least two isocyanate groups per molecule; at least one blowing agent; at least one catalyst; at least one polyether polydimethylsiloxane as obtained according to the process disclosed herein and optionally one or more additives selected from the group comprising dyes, pigments, fillers, antistatic additives, crosslinkers, chain extenders, cell openers, nucleating agents, thickeners, fragrances, cell expanders, plasticizers, hardening promoters, additives for preventing cold flow, aldehyde scavengers, additives for increasing resistance of polyurethane foams towards hydrolysis, compatibilizers (emulsifiers), adhesion promoters, and hydrophobization additives.

[0091] The present invention also relates to a method for preparing a polymer foam, such as the ones mentioned hereinbefore, comprising reacting one or more monomer species in the presence of one or more polyether polydimethylsiloxanes obtained according to the process disclosed herein to obtain a polymer foam. Additionally, at least one further polyether polydimethylsiloxane that is notobtained by the herein disclosed process and that may not be based on recycled products but, e.g., on cyclic polydimethylsiloxanes from the Muller-Rochow process may also be present.

[0092] A method for preparing a polyurethane foam may comprise providing a composition comprising at least one isocyanate-reactive compound having in average at least two groups being reactive to isocyanate groups, one or more polyether polydimethylsiloxanes obtained according to the process disclosed herein, at least one blowing agent, at least one catalyst, and optionally one or more further additives; contacting the composition with a polyisocyanate having in average at least two isocyanate groups per molecule or a mixture of polyisocyanates; and curing the composition under the formation of a polyurethane foam.

[0093] The present invention also relates to an article comprising the polymer foam obtained according to the method for preparing a polymer foam disclosed hereinbefore or as the reaction product of the composition for preparing a polymer foam disclosed hereinbefore. Articles comprising a polyurethane foam as the polymer foam of the present invention may be a refrigerator insulation, an insulation panel, a sandwich element, a pipe insulation, a spray foam, a 1- or 1 .5-component can foam, an imitation wood, a modelling foam, a packaging foam, a mattress, a furniture cushioning, an automotive seat cushioning, a seat cushioning in a plane or a train, a headrest, an armrest, an instrument panel, an automotive interior trim, an automotive headlining, a sound absorption material, a steering wheel, a shoe sole, a carpet backing foam, a filter foam, a sealing foam, a sealant, an adhesive, a coating, or for use in manufacturing corresponding products.

[0094] The present invention furthermore relates to the use of a recycled linear polydimethylsiloxane for producing a polyether polydimethylsiloxane, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof, wherein recycling of at least one linear polydimethylsiloxane or copolymer thereof comprises (c) submitting a polydimethylsiloxane-containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at least one cyclic polydimethylsiloxane in a depolymerization reaction mixture; (d) distilling the depolymerization reaction mixture to obtain a cyclic-polydimethylsiloxane-containing composition comprising at least one cyclic polydimethylsiloxane; (e) optionally submitting the cyclic-polydimethylsiloxane-containing composition to a fractional distillative purification; (f) submitting the cyclic-polydimethylsiloxane- containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane-containing composition; and (g) optionally purifying the recycled- polydimethylsiloxane-containing composition. The recycled linear polydimethylsiloxane can in particular have a carbon footprint of less than 4 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane or preferably of less than 2 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane as determined according to DIN EN ISO standard 14067:2018.

[0095] The present invention is also directed to the use of a recycled-polydimethylsiloxane- containing composition comprising a recycled linear polydimethylsiloxane in an equilibration reactionfor obtaining a poly(methylhydrogen)-polydimethylsiloxane copolymer in a process for producing a polyether polydimethylsiloxane. A recycled linear polydimethylsiloxane is preferably obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof. Recycling of at least one linear polydimethylsiloxane or copolymerthereof is preferably carried out as described hereinabove. The use may further comprise submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in the equilibration reaction to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain the polyether polydimethylsiloxane. The components and reaction conditions are thereby preferably selected as described hereinbefore.

[0096] Further, the present invention also relates to the use of at least one polyether polydimethylsiloxane obtained according to the process disclosed herein as an additive in a method of producing a polymer foam or a composition for preparing a polymer foam, whereby the polymer foam is preferably a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam. A polyurethane foam is particularly preferred.

[0097] The invention is further described according to the following aspects:1 . A process for producing polyether polydimethylsiloxanes comprising:(a) submitting a recycled-polydimethylsiloxane-containing composition comprising a recycled linear polydimethylsiloxane to an equilibration reaction with at least one poly(methylhydrogen)siloxane in the presence of at least one equilibration catalyst to form a poly(methylhydrogen)-polydimethylsiloxane copolymer; and(b) submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in step (a) to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain a polyether polydimethylsiloxane.2. A process for producing polyether polydimethylsiloxanes comprising:(c) submitting a polydimethylsiloxane-containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at least one cyclic polydimethylsiloxane in a depolymerization reaction mixture;(d) distilling the depolymerization reaction mixture to obtain a cyclic-polydimethylsiloxane- containing composition comprising at least one cyclic polydimethylsiloxane;(e) optionally submitting the cyclic-polydimethylsiloxane-containing composition to a fractional distillative purification;(f) submitting the cyclic-polydimethylsiloxane-containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane- containing composition;(g) optionally purifying the recycled-polydimethylsiloxane-containing composition;(a) submitting the recycled-polydimethylsiloxane-containing composition comprising the recycled linear polydimethylsiloxane to an equilibration reaction with at least one poly(methylhydrogen)siloxane in the presence of at least one equilibration catalyst to form a poly(methylhydrogen)-polydimethylsiloxane copolymer; and(b) submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in step (a) to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain a polyether polydimethylsiloxane.The process according to any one of aspects 1 and 2, wherein the recycled linear polydimethylsiloxane has a viscosity at 25°C of 25 to 2500 mPa s, preferably 50 to 2000 mPa s, more preferably 100 to 1500 mPa s, most preferably 150 to 1000 mPa s, as measured according to DIN 53019-1 :2008-09, DIN 53019-2:2008-09, DIN 53019-3:2008-09 and DIN 53019-4:2008-09.4. The process according to any one of the preceding aspects, wherein the recycled- polydimethylsiloxane-containing composition comprises at most 7.5 mol % of M units, or preferably at most 4 mol % of M units, or more preferably at most 2.5 mol % of M units, based on the total mols of M, D, T, and Q units of the recycled-polydimethylsiloxane-containing composition.5. The process according to any one of the preceding aspects, wherein the sum of T and Q units of the recycled-polydimethylsiloxane-containing composition is at most 0.75 mol %, or preferably at most 0.5 mol %, or more preferably at most 0.25 mol %, based on the total mols of M, D, T, and Q units of the recycled-polydimethylsiloxane-containing composition.6. The process according to any one of the preceding aspects, wherein the recycled- polydimethylsiloxane-containing composition is substantially free of chlorine-containing compounds, or is most preferably completely free of chlorine-containing compounds and / or wherein the recycled- polydimethylsiloxane-containing composition comprises less than 100 ppm chlorine-containing compounds, preferably less than 50 ppm chlorine-containing compounds, more preferably less than 25 ppm chlorine-containing compounds, and most preferably less than 10 ppm chlorine-containing compounds, based on the total weight of the recycled-polydimethylsiloxane-containing composition.7. The process according to any one of the preceding aspects, wherein the recycled- polydimethylsiloxane-containing composition has a total content of the recycled linear polydimethylsiloxane of more than 90% by weight, preferably more than 95% by weight, or even more preferably by 98% by weight, based on the total weight of the recycled-polydimethylsiloxane- containing composition.8. The process according to any one of the preceding aspects, wherein the recycled- polydimethylsiloxane-containing composition comprises at most 0.05% by weight, preferably at most 100 ppm, more preferably at most 40 ppm by weight, most preferably at most 10 ppm water as measured according to DIN 51777:2020-04, based on the total weight of the recycled- polydimethylsiloxane-containing composition.9. The process according to any one of the preceding aspects, wherein the recycled- polydimethylsiloxane-containing composition comprises at most 0.5 mol %, preferably at most 0.2 mol %, more preferably at most 0.1 mol % vinyl-substituted silicon atoms as determined based on29Si-NMR spectroscopy, based on the total mols of silicon atoms in the recycled- polydimethylsiloxane-containing composition.10. The process according to any one of the preceding aspects, wherein the recycled- polydimethylsiloxane-containing composition comprises at most 0.2 mol %, preferably at most 0.1 mol %, more preferably at most 0.05 mol % hydroxyl-substituted silicon atoms as determined based on29Si-NMR spectroscopy, based on the total mols of silicon atoms in the recycled- polydimethylsiloxane-containing composition.11. The process according to any one of the preceding aspects, wherein the recycled linear polydimethylsiloxane has a carbon footprint of less than 4 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane or preferably of less than 2 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane as determined according to DIN EN ISO standard 14067:2018.12. The process according to any one of the preceding aspects, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof.13. The process according to any of aspects 2 and 12, wherein the at least one linear polydimethylsiloxane or copolymer thereof comprises at least 50% by weight, preferably at least 90% by weight, more preferably at least 99% by weight dimethylsiloxane units, based on the total weight of the at least one linear polydimethylsiloxane or copolymer thereof.14. The process according to any one of aspects 2, 12 and 13, wherein the at least one linear polydimethylsiloxane or copolymer thereof is a linear polydimethylsiloxane homopolymer.15. The process according to any one of aspects 2 and 12 to 14, wherein the at least one linear polydimethylsiloxane or copolymer thereof corresponds to or is derived from a waste polydimethylsiloxane polymer or copolymer material, a wide-spec polydimethylsiloxane polymer or copolymer material, a used polydimethylsiloxane polymer or copolymer material, an expired polydimethylsiloxane polymer or copolymer material, a surplus polydimethylsiloxane polymer or copolymer material, or any mixtures or combinations thereof.16. The process according to any one of aspects 2 and 12 to 15, wherein the at least one linear polydimethylsiloxane or copolymer thereof is contained in a polydimethylsiloxane-containing composition.17. The process according to any one of aspects 2 and 16, wherein the polydimethylsiloxane- containing composition comprises at least 50% by weight, or preferably at least 70% by weight, or more preferably at least 90% percent by weight of the at least one linear polydimethylsiloxane or copolymer thereof, based on the total weight of the polydimethylsiloxane-containing composition.18. The process according to any one of aspects 2, 16 and 17, wherein the polydimethylsiloxane-containing composition has a silicon content of from 19% to 38% by weight, preferably from 26% to 38% by weight, more preferably from 34% to 38% weight, based on the total weight of the polydimethylsiloxane-containing composition.19. The process according to any one of aspects 2 and 16 to 18, wherein the polydimethylsiloxane-containing composition comprises less than 50% by weight, preferably lessthan 25% by weight, more preferably less than 5% by weight fillers, based on the total weight of the polydimethylsiloxane-containing composition.20. The process according to any one of aspects 2 and 12 to 19, wherein the at least one linear polydimethylsiloxane or copolymer thereof has a ratio of M units to D units of at least 1 :500, or preferably at least 1 :750, or more preferably at least 1 :1000.21. The process according to any one of aspects 2 and 12 to 20, wherein the at least one linear polydimethylsiloxane or copolymer thereof is a polydimethylsiloxane oil, a polydimethylsiloxane elastomer, a polydimethylsiloxane rubber, or a mixture thereof, whereby the polydimethylsiloxane oil preferably has a viscosity at 25°C of at least 1000 mPa s as measured according to DIN 53019- 1 :2008-09.22. The process according to any one of aspects 2 and 12 to 21 , wherein the at least one linear polydimethylsiloxane or copolymer thereof is a polydimethylsiloxane oil and the polydimethylsiloxane oil preferably has a viscosity at 25°C of at least 1000 mPa s as measured according to DIN 53019-1 :2008-09.23. The process according to any one of the preceding aspects, wherein at least one further polydimethylsiloxane not being recycled is added to the recycled-polydimethylsiloxane-containing composition before being submitted to the equilibration reaction.24. The process according to any one of the preceding aspects, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof, wherein recycling of at least one linear polydimethylsiloxane or copolymer thereof comprises(c) submitting a polydimethylsiloxane-containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at least one cyclic polydimethylsiloxane in a depolymerization reaction mixture;(d) distilling the depolymerization reaction mixture to obtain a cyclic-polydimethylsiloxane- containing composition comprising at least one cyclic polydimethylsiloxane;(e) optionally submitting the cyclic-polydimethylsiloxane-containing composition to a fractional distillative purification;(f) submitting the cyclic-polydimethylsiloxane-containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane- containing composition; and(g) optionally purifying the recycled-polydimethylsiloxane-containing composition.25. The process according to aspect 27, wherein the catalytic depolymerization is carried out at a temperature of between 40°C and 200°C or preferably between 50°C and 190°C, or more preferably between 80°C and 180°C.26. The process according to any one of aspects 2, 27, and 28, wherein the at least one depolymerization catalyst is selected from Bransted acids or Bransted bases, whereby the Bransted acids are preferably selected from the group consisting of trifluoromethanesulfonic acid, sulfuricacid, hydrochloric acid, and combinations thereof; and the Bransted bases are preferably selected from the group consisting of alkali metal hydroxides, tetraalkylammonium hydroxides, tetraalkylphosphonium hydroxides, phosphazenes, guanidines, and combinations thereof.27. The process according any one of aspects 2 to 26, wherein the catalytic depolymerization is carried out in a reactor that is resistant to corrosion and temperatures of at least 250°C.28. The process according any one of aspects 2 to 27, wherein distilling the depolymerization reaction mixture is at least partially carried out during the catalytic depolymerization.29. The process according to any one of the preceding aspects, wherein the equilibration reaction is carried out in the presence of at least one chain length modifier, whereby the at least one chain length modifier is preferably selected from the group comprising hexamethyldisiloxane, 1 ,1 ,3,3-tetramethyldisiloxane, a HSiMe2-endfunctional polydimethylsiloxane oil, and mixtures thereof.30. The process according to aspect 29, wherein the process further comprises measuring the content of endgroups such as M units in the recycled-polydimethylsiloxane-containing composition and adding based on the measured content an amount of the at least one chain length modifier to achieve a desired viscosity of the poly(methylhydrogen)-polydimethylsiloxane copolymer.31. The process according to any one of the preceding aspects, wherein the at least one equilibration catalyst is selected from acidic equilibration catalysts, whereby the acidic equilibration catalysts are preferably selected from the group consisting of strong protic acids such as sulfuric acid, trifluoromethanesulfonic acid, methanesulfonic acid, and perchloric acid, protic and Lewis acids such as HCI+FeCh and HCI+SbCk, acid-activated minerals such as bleaching earths, and cation exchange resins such as sulfonic acid, macro-crosslinked cation exchange resins, and combinations thereof.32. The process according to aspect 29, wherein the amount of the at least one chain length modifier is adjusted based on the content of endgroups such as M units in the recycled- polydimethylsiloxane-containing composition.33. The process according to any one of the preceding aspects, wherein the equilibration reaction is carried out at a temperature of between 10°C and 110°C, or preferably between 25°C and 100°C.34. The process according to any one of the preceding aspects, wherein the poly(methylhydrogen)-polydimethylsiloxane copolymer has a density at 25°C of from 0.95 to 0.98 g / mL, or preferably from 0.96 to 0.98 g / mL, or more preferably from 0.97 to 0.98 g / mL determined according to DIN 51757:2011-01.35. The process according to any one of the preceding aspects, wherein the poly(methylhydrogen)-polydimethylsiloxane copolymer has a viscosity at 25°C of from 2 to 2000 mPa s, or preferably from 3 to 1000 mPa s, or more preferably from 10 to 500 mPa s determined according to DIN 53019-1 :2008-09.36. The process according to any one of the preceding aspects, wherein the poly(methylhydrogen)-polydimethylsiloxane copolymer has an SiH value of from 0.2 to 10 mol / kg,or preferably from 0.4 to 8 mol / kg, or more preferably from 0.6 to 6 mol / kg measured with gas volumetry.37. The process according to any one of the preceding aspects, wherein the poly(methylhydrogen)-polydimethylsiloxane copolymer has(A) a density at 25°C of from 0.94 to 0.99 g / mL, preferably from 0.95 to 0.98 g / mL, or more preferably from 0.96 to 0.98 g / mL determined according to DIN 51757:2011-01 ; a viscosity at 25°C of from 50 to 70 mPa s, preferably from 52 to 64 mPa s, more preferably from 53 to 63 mPa s determined according to DIN 53019-1 :2008-09; and an SiH value of from 1.1 to 1.60 mol / kg, preferably from 1.0 to 1.50 mol / kg, more preferably from 1.2 to 1.45 mol / kg measured with gas volumetry; or(B) a density at 25°C of from 0.95 to 1 .00 g / mL, preferably from 0.96 to 0.99 g / mL, or more preferably from 0.965 to 0.972 g / mL determined according to DIN 51757:2011-01 ; a viscosity at 25°C of from 60 to 85 mPa s, preferably from 64 to 84 mPa s, more preferably from 67 to 85 mPa s determined according to DIN 53019-1 :2008-09; and an SiH value of from 1.40 to 1.80 mol / kg, preferably from 1.50 to 1.70 mol / kg, more preferably from 1.57 to 1.67 mol / kg measured with gas volumetry.38. The process according to any one of the preceding aspects, wherein the poly(methylhydrogen)-polydimethylsiloxane copolymer is separated from cyclic polydimethylsiloxanes and other volatiles by applying heat and vacuum to the equilibration reaction mixture obtained in step (a) before submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer to the hydrosilylation reaction.39. The process according to any one of the preceding aspects, wherein the hydrosilylation reaction is carried out at a temperature of between 20°C and 140°C, or preferably between 40°C and 130°C, or more preferably between 60°C and 110°C.40. The process according to any one of the preceding aspects, wherein the at least one hydrosilylation catalyst is a noble metal catalyst, preferably Pt(O) or rhodium.41. The process according to any one of the preceding aspects, wherein the polyether polydimethylsiloxane has a viscosity at 25°C of from 100 mPa s to 12000 mPa s or preferably from 200 to 8000 mPa s as determined according to DIN 53019-1 :2008-09.42. The process according to any one of the preceding aspects, wherein the polyether polydimethylsiloxane has(A) a density at 25°C of from 1 .030 to 1 .060 g / mL, preferably from 1 .032 to 1 .057 g / mL, or more preferably from 1.035 to 1.055 g / mL determined according to DIN 51757:2011-01 ; and a viscosity at 25°C of from 700 to 1300 mPa s, preferably from 750 to 1250 mPa s, more preferably from 800 to 1200 mPa s determined according to DIN 53019-1 :2008-09; or(B) a density at 25°C of from 1 .010 to 1 .050 g / mL, preferably from 1 .015 to 1 .045 g / mL, or more preferably from 1.020 to 1.040 g / mL determined according to DIN 51757:2011-01 ; and a viscosity at 25°C of from 500 to 1000 mPa s, preferably from 530 to 900 mPa s, more preferably from 550 to 850 mPa s determined according to DIN 53019-1 :2008-09.43. A composition for preparing a polymer foam comprising at least one monomer species and one or more polyether polydimethylsiloxanes obtained according to the process of any one of aspects 1 to 42, whereby the polymer foam is preferably a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam, more preferably a polyurethane foam.44. A method for preparing a polymer foam comprising reacting one or more monomer species in the presence of one or more polyether polydimethylsiloxanes obtained according to the process of any one of aspects 1 to 42 to obtain a polymer foam.45. An article comprising the polymer foam obtained according to the method according to aspect 44 or as the reaction product of the composition of aspect 43.46. Use of a recycled-polydimethylsiloxane-containing composition comprising a recycled linear polydimethylsiloxane in an equilibration reaction for obtaining a poly(methylhydrogen)- polydimethylsiloxane copolymer in a process for producing a polyether polydimethylsiloxane.47. The use according to aspect 46, wherein the recycled linear -polydimethylsiloxane is obtained from recycling of at least one linear -polydimethylsiloxane or copolymer thereof.48. The use according to any one of aspects 46 and 47, wherein the recycled- polydimethylsiloxane-containing composition is as defined in any one of aspects 4 to 11 .49. The use according to any of aspects 46 to 48, wherein the recycled linear polydimethylsiloxane is as defined in any one of aspects 3, 11 , and 12 to 22.50. The use according to any one of aspects 47 to 50, wherein the poly(methylhydrogen)- polydimethylsiloxane copolymer is as defined in any one of aspects 35 to 38.51. The use according to any one of aspects 46 to 50, wherein the polyether polydimethylsiloxane is as defined in any one of aspects 41 or 42.52. The use according to any one of aspects 46 to 51 , wherein the equilibration reaction is carried out as defined in any one of aspects 29 to 33.53. The use according to any one of aspects 46 to 52, further comprising submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in the equilibration reaction to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain the polyether polydimethylsiloxane.54. The use according to aspects 53, wherein the hydrosilylation reaction is carried out as defined in any one of aspects 39 and 40.55. Use of at least one polyether polydimethylsiloxane obtained according to the process of any one of aspects 1 to 42 as an additive in a method of producing a polymer foam or a composition for preparing a polymer foam, whereby the polymer foam is preferably a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam, more preferably a polyurethane foam.56. Use of a recycled linear polydimethylsiloxane for producing a polyether polydimethylsiloxane.57. The use of aspect 56, wherein the recycled linear polydimethylsiloxane has a carbon footprint of less than 4 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane orpreferably of less than 2 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane as determined according to DIN EN ISO standard 14067:2018.Examples:Starting material:In the Examples 1 the cyclic organosiloxane-containing composition A was used, which was obtained from recycling and contained 0.9 wt.-% D3, 67.7 wt.-% D4, 23.0 wt.-% D5, and 3.4 wt.-% D6, but also different alkanes and 130 ppm benzene as impurities. Said cyclic organosiloxane- containing composition A was converted into the recycled linear polydimethylsiloxane.Said recycled linear polydimethylsiloxane was used in the equilibration reaction of Example 2b according to the invention to give a SiH-functional siloxane, which was further processed in the hydrosilylation reaction of Example 3b according to the invention to give the polyether polydimethylsiloxane.Example 2a not according to the invention used the cyclic organosilixane-containing composition A as it was and gave the SiH-functional siloxane, which was further processed in the hydrosilylation reaction of Example 3a not according to the invention to give the polyether polydimethylsiloxane.The content of the individual cyclic organosiloxanes in composition A and in the products of the Examples was determined using the GC-method “cyclics” below. The content of benzene was determined using the method DIN 51405:2004-01.GC-Method “Cyclics”:The mass fraction of the cyclic siloxanes was determined by a GC method in which the substances were first separated according to the boiling point and then detected by means of a thermal conductivity detector. An aliquot of the sample to be examined was analyzed by GC without further dilution. This was carried out in a gas chromatograph equipped with a split / splitless injector, a capillary column, and a thermal conductivity detector under the following conditions: Injector: 290 °C, split 40 ml Injection volume: 1 plColumn: 5 m *0.32 mm HP5 1 mCarrier gas: Hydrogen, const, flow 2 mL / minTemperature program: 1 minute at 80 °C, then 80 °C - 300 °C at 30 °C / min, then conditioning for 10 minutes at 300 °C. Detector: TCD at 320 °CMake Up Gas 8 mL / minReference gas 22 mL / minThe SiH value was determined by gas volumetry. To this end, a weighed sample of the poly(methylhydrogen)-polydimethylsiloxane copolymer was decomposed by means of a sodium butylate solution to form hydrogen gas. The amount of hydrogen gas was measured and the SiH value was determined using the definition of the SiH value: n(H2) [mol] / m(sample) [kg].Example 1 (according to the invention): Conversion of recycled cyclic organosiloxane-containing composition A into recycled linear polydimethylsiloxane with the structure Me3SiO[SiMe2O]98SiMe3In a 500 ml four-neck flask equipped with stirrer, thermometer, gas inlet and reflux condenser, a mixture consisting of 293.4 g of the cyclic organosiloxane-containing composition A and 6.6 g of hexamethyldisiloxane (CAS: 107-46-0) was blended and 0.30 g trifluoromethanesulfonic acid (CAS: 1493-13-6 Purity > 99 % ) was added. The mixture was stirred for 6 hours at 35 ° C. Thereafter, 3.0 g NaHCOs was added, and the mixture was stirred for another 2 h. The mixture was filtered. The product was the filtrate. The product was then freed from volatile components on a rotary evaporator for 2 h at 130 °C and a reduced pressure of < 1 mbar. The product had a viscosity of 141 mPa s and a benzene content of 5 ppm.Example 2a (not according to the invention): Equilibration reaction with cyclic organosiloxane- containing composition A into an SiH-functional siloxane with the structure Me3SiO[SiMe2O]5i[SiMeHO]7SiMe3In a 500 ml four-neck flask equipped with stirrer, thermometer, gas inlet and reflux condenser, a mixture consisting of 216.6 g of the cyclic organosiloxane-containing composition A, 26.3 g of poly(methyl)hydrogen siloxane (CAS: 63148-57-2, SiH-content: 15.25 mol / kg) and 7.1 g of hexamethyldisiloxane (CAS: 107-46-0) was blended and 0.25 g trifluoromethanesulfonic acid (CAS: 1493-13-6 Purity > 99 % ) was added. The mixture was stirred for 6 hours at 35 ° C. Thereafter, 2.5 g NaHCOs was added, and the mixture was stirred for another 2 h. The mixture was filtered. The product was the filtrate (Equilibration reaction mixture 2a).Example 2b (according to the invention): Equilibration reaction with recycled linear polydimethylsiloxane into an SiH-functional siloxane with the structure Me3SiO[SiMe2O]5i[SiMeHO]7SiMe3In a 500 ml four-neck flask equipped with stirrer, thermometer, gas inlet and reflux condenser, a mixture consisting of 221.4 g of the recycled linear polydimethylsiloxane from example 1 , 26.3 g of poly(methyl)hydrogen siloxane (CAS: 63148-57-2, SiH-content: 15.25 mol / kg) and 2.3 g of hexamethyldisiloxane (CAS: 107-46-0) was blended and 0.25 g trifluoromethanesulfonic acid (CAS:1493-13-6 Purity > 99 % ) was added. The mixture was stirred for 6 hours at 35 ° C. Thereafter, 2.5 g NaHCOs was added, and the mixture was stirred for another 2 h. The mixture was filtered. The product was the filtrate (Equilibration reaction mixture 2b).Table 1 summarizes the results from the equilibration reaction using the cyclic organosiloxane- containing composition and the recycled linear polydimethylsiloxane.Table 1 : Results of the equilibration reactions (1the SiH value was determined using gas volumetry, as described above,2viscosity was determined according to DIN 53019-1 :2008-09, and3the content of benzene was determined according to DIN 51405:2004-01).Example 3a (not according to the invention): Hydrosilylation reactionIn a 250 ml four-neck flask equipped with stirrer, thermometer, gas inlet and reflux condenser, a mixture consisting of 70 g of a polyether having the average formula: CH2=CHCH2O- (CH2CH20)IO(CH2CH(CH3)0)20H and 55 g of poly(organylhydrogen)-polyorganosiloxane from example 2a was blended. The mixture was stirring and heated to 90 °C. 5 ppm Pt in form of a platinum(0)-1 ,3-divinyl-1 ,1 ,3,3-tetramethyldisiloxane complex solution (CAS: 68478-92-2) was added. An exothermic reaction took place. By cooling, the reaction was kept below 100 °C. The reaction mixture was then stirred for 2 h at 90 ° C. A clear, homogeneous product was obtained.The product was then freed from volatile components on a rotary evaporator for 2 h at 130 °C and a reduced pressure of < 1 mbar. The product had a benzene content of 11 ppm.Example 3b (according to the invention): Hydrosilylation reactionIn a 250 ml four-neck flask equipped with stirrer, thermometer, gas inlet and reflux condenser, a mixture consisting of 70 g of a polyether having the average formula: CH2=CHCH2O- (CH2CH20)IO(CH2CH(CH3)0)20H and 55 g of poly(organylhydrogen)-polyorganosiloxane from example 2b was blended. The mixture was stirring and heated to 90 °C. 5 ppm Pt in form of a Platinum(0)-1 ,3-divinyl-1 ,1 ,3,3-tetramethyldisiloxane complex solution (CAS: 68478-92-2) was added. An exothermic reaction took place. By cooling, the reaction was kept below 100 °C. Thereaction mixture was then stirred for 2 h at 90 ° C. A clear, homogeneous product was obtained. The product was then freed from volatile components on a rotary evaporator for 2 h at 130 °C and a reduced pressure of < 1 mbar. The product had a benzene content of 1 ppm.Table 2: Analytical data of the examples (1the SiH value was determined using gas volumetry, as described above,2viscosity was determined according to DIN 53019-1 :2008-09, and3the content of benzene was determined according to DIN 51405:2004-01).The examples show that it is advantageous to first convert the cyclic organosiloxane-containing composition to a linear polydimethylsiloxane and then distill them at this stage and only then convert them to SiH functional siloxane or to the polyether siloxane. In this way, volatile contaminants, such as aromatic or aliphatic hydrocarbons, can be removed more easily. This is probably because the viscosity of linear polydimethylsiloxane is lower than the viscosity of polyether siloxanes. In addition, siloxane oil has a less critical toxicological classification, as it contains fewer toxicologically questionable cycles. This makes it easier to transport and store.

Claims

Patent claims1 . A process for producing polyether polydimethylsiloxanes comprising:(a) submitting a recycled-polydimethylsiloxane-containing composition comprising a recycled linear-polydimethylsiloxane to an equilibration reaction with at least one poly(methylhydrogen)siloxane in the presence of at least one equilibration catalyst to form a poly(methylhydrogen)-polydimethylsiloxane copolymer; and(b) submitting the poly(methylhydrogen)-polydimethylsiloxane copolymer obtained in step (a) to a hydrosilylation reaction with at least one polyether comprising at least one carbon-carbon double bond reactive to Si-H bonds, preferably in the presence of at least one hydrosilylation catalyst, to obtain a polyether polydimethylsiloxane, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof, wherein recycling of at least one linear polydimethylsiloxane or copolymer thereof comprises(c) submitting a polydimethylsiloxane-containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at least one cyclic polydimethylsiloxane in a depolymerization reaction mixture;(d) distilling the depolymerization reaction mixture to obtain a cyclic- polydimethylsiloxane-containing composition comprising at least one cyclic polydimethylsiloxane;(e) optionally submitting the cyclic-polydimethylsiloxane-containing composition to a fractional distillative purification;(f) submitting the cyclic-polydimethylsiloxane-containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane-containing composition; and(g) optionally purifying the recycled-polydimethylsiloxane-containing composition.

2. The process according to claim 1 , wherein the recycled linear polydimethylsiloxane has a viscosity at 25°C of 25 to 2500 mPa s, preferably 50 to 2000 mPa s, more preferably 100 to 1500 mPa s, most preferably 150 to 1000 mPa s, as measured according to DIN 53019- 1 :2008-09 .

3. The process according to any one of claims 1 and 2, wherein the recycled-polydimethylsiloxane-containing composition comprises at most 7.50 mol % of M units, or preferably at most 4 mol % of M units, or more preferably at most 2.50 mol % of M units, ...at most 1 % based on the total mols of M, D, T, and Q units of the recycled-polydimethylsiloxane-containing composition,the sum of T and Q units of the recycled-polydimethylsiloxane-containing composition is at most 0.75 mol %, or preferably at most 0.5 mol %, or more preferably at most 0.25 mol %, based on the total mols of M, D, T, and Q units of the recycled-polydimethylsiloxane-containing composition.

4. The process according to any one of the preceding claims, wherein the recycled- polydimethylsiloxane-containing composition comprises at most 0.05% by weight, preferably at most 100 ppm, more preferably at most 40 ppm by weight, most preferably at most 10 ppm water as measured according to DIN 51777:2020-04, based on the total weight of the recycled-polydimethylsiloxane- containing composition; and / or at most 0.5 mol %, preferably at most 0.2 mol %, more preferably at most 0.1 mol % vinyl-substituted silicon atoms as determined based on29Si-NMR spectroscopy, based on the total mols of silicon atoms in the recycled-polydimethylsiloxane- containing composition; and / or at most 0.2 mol %, preferably at most 0.1 mol %, more preferably at most 0.05 mol % hydroxyl-substituted silicon atoms as determined based on29Si-NMR spectroscopy, based on the total mols of silicon atoms in the recycled- polydimethylsiloxane-containing composition.

5. The process according to any one of the preceding claims, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof.

6. The process according to claim 5, wherein the at least one linear polydimethylsiloxane or copolymer thereof corresponds to or is derived from a waste polydimethylsiloxane polymer or copolymer material, a wide-spec polydimethylsiloxane polymer or copolymer material, a used polydimethylsiloxane polymer or copolymer material, an expired polydimethylsiloxane polymer or copolymer material, a surplus polydimethylsiloxane polymer or copolymer material, or any mixtures or combinations thereof.

7. The process according to any one of claims 5 and 6, wherein the at least one linear polydimethylsiloxane or copolymer thereof is contained in a polydimethylsiloxane-containing composition and wherein the polydimethylsiloxane-containing composition comprises at least 50% by weight, or preferably at least 70% by weight, or more preferably at least 90% percent by weight of the at least one linear polydimethylsiloxane or copolymer thereof, based on the total weight of the polydimethylsiloxane-containing composition; and / or has a silicon content of from 19% to 38% by weight, preferably from 26% to 38% by weight, more preferably from 34% to 38% weight, based on the total weight ofthe polydimethylsiloxane-containing composition; and / or comprises less than 50% by weight, preferably less than 25% by weight, more preferably less than 5% by weight fillers, based on the total weight of the polydimethylsiloxane-containing composition.

8. The process according to any one of the preceding claims, wherein the poly(methylhydrogen)-polydimethylsiloxane copolymer has a density at 25°C of from 0.95 to 0.98 g / mL, or preferably from 0.96 to 0.98 g / mL, or more preferably from 0.97 to 0.98 g / mL determined according to DIN 51757:2011-01 ; a viscosity at 25°C of from 2 to 2000 mPa s, or preferably from 3 to 1000 mPa s, or more preferably from 10 to 500 mPa s determined according to DIN 53019-1 :2008- 09; and / or an SiH value of from 0.2 to 10 mol / kg, or preferably from 0.4 to 8 mol / kg, or more preferably from 0.6 to 6 mol / kg measured with gas volumetry.

9. A composition for preparing a polymer foam comprising at least one monomer species and one or more polyether polydimethylsiloxanes obtained by the process according to any one of claims 1 to 8, wherein the polymer foam is preferably a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam, more preferably a polyurethane foam.

10. A method for preparing a polymer foam comprising reacting one or more monomer species in the presence of one or more polyether polydimethylsiloxanes obtained by the process according to any one of claims 1 to 8 to obtain a polymer foam.

11. An article comprising the polymer foam obtained by the method according to claim 10 or as the reaction product of the composition of claim 9.

12. Use of a recycled linear polydimethylsiloxane for producing a polyether polydimethylsiloxane, wherein the recycled linear polydimethylsiloxane is obtained from recycling of at least one linear polydimethylsiloxane or copolymer thereof, wherein recycling of at least one linear polydimethylsiloxane or copolymer thereof comprises(c) submitting a polydimethylsiloxane-containing composition comprising at least one linear polydimethylsiloxane or copolymer thereof to catalytic depolymerization in the presence of at least one depolymerization catalyst to form at least one cyclic polydimethylsiloxane in a depolymerization reaction mixture;(d) distilling the depolymerization reaction mixture to obtain a cyclic- polydimethylsiloxane-containing composition comprising at least one cyclic polydimethylsiloxane;(e) optionally submitting the cyclic-polydimethylsiloxane-containing composition to a fractional distillative purification;(f) submitting the cyclic-polydimethylsiloxane-containing composition comprising the at least one cyclic polydimethylsiloxane to a polymerization reaction in the presence of a polymerization catalyst to obtain a recycled linear polydimethylsiloxane in a recycled-polydimethylsiloxane-containing composition; and(g) optionally purifying the recycled-polydimethylsiloxane-containing composition.

13. The use of claim 12, wherein the recycled linear polydimethylsiloxane has a carbon footprint of less than 4 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane or preferably of less than 2 kg CO2 equivalents / kg of the recycled linear polydimethylsiloxane as determined according to DIN EN ISO standard 14067:2018.

14. Use of at least one polyether polydimethylsiloxane obtained by the process according to any one of claims 1 to 8 as an additive in a method of producing a polymer foam or a composition for preparing a polymer foam, whereby the polymer foam is preferably a polyurethane foam, a phenol resin foam, or a polyvinylchloride foam, more preferably a polyurethane foam.

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