Depolymerization of silicone polymers to obtain organopolysiloxanes

Abstract

The present invention generally relates to the reuse, reprocessing or recycling of silicone polymers. More precisely, the process of the present invention relates to a method for preparing organopolysiloxanes OR by a depolymerization reaction of at least one silicone S in the presence of an acid catalyst and at least one chain blocker Bc having at least one siloxane function. These organopolysiloxanes OR can subsequently be used in polymerization reactions or directly in various formulations.

Description

[0001] DESCRIPTION

[0002] TITLE: Depolymerization of silicone polymers into organopolysiloxanes

[0003] Technical field:

[0004] The present invention relates generally to the reuse, reprocessing or recycling of silicone polymers. More specifically, the method of the present invention relates to the depolymerization of silicone polymers to obtain lower molecular weight organopolysiloxanes OR which can subsequently be used in polymerization reactions or directly in various formulations.

[0005] Technological background:

[0006] A major societal and industrial challenge for the coming years is the ecological transition. Thus, from an economic perspective, the so-called "linear" economic model (take, make, use, throw away) must eventually be replaced by a so-called circular model.

[0007] A circular economy describes an economic system based on models that replace the concept of "end-of-life" products with the reduction, alternative reuse, recycling and recovery of these materials in the production / distribution and consumption processes, with the aim of achieving sustainable development for the benefit of current and future generations.

[0008] With the ever-increasing silicone market and the increasing number of applications for such materials, recycling used silicone products is a major challenge in the silicone industry. Silicone recycling could reduce gas emissions (CO, CO2) from the silicone industry by 75% and silicone waste by 65%.

[0009] Furthermore, cyclic silicones or organopolysiloxanes such as octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) are and will be subject to restrictions for their use. In addition to the fact that these cyclic compounds present environmental risks due to their non-biodegradability, they are also suspected of being endocrine disruptors and potentially carcinogenic.

[0010] In this sense, in 2018 European regulations limited the content of D4 and Ds to 0.1% by mass in rinse-off cosmetic products. This regulation will soon be adopted for other cosmetic products and also in other areas of silicone application.

[0011] Therefore, there is a need to provide methods for providing silicone products free from or at least having a low content of cyclic silicones.

[0012] In the prior art, the depolymerization of organopolysiloxanes has been described by implementing different processes. In 2002, the content of patent application JP2002348407A disclosed a process for chemically transforming a silicone product such as a silicone resin or a silicone mold into linear polysiloxane. This process, however, requires a significant amount of acid catalyst, 12%, and the product obtained is mixed with cyclic compounds, formed by a retroscission reaction. This reaction is commonly called "back-biting" in English.

[0013] More recently in 2020, patent application US20200377686 describes a process for recycling silicones (silicone oils, resins) by chemical transformation in order to obtain an α, ε-diacetoxypolydimethylsiloxane. However, this process requires heating the reaction medium and placing an excess of acetic anhydride.

[0014] In addition, the a.oj-diacetoxypolydimethylsiloxane is chemically modifiable further to obtain a polydimethylsiloxane having hydroxyl or acetoxyl terminal groups which can be used in adhesive compositions or in sealants.

[0015] In 2022, patent application US2022119617 describes a similar process. The obtained α,β-diacetoxypolydimethylsiloxane is re-engaged to obtain an α,β-di-isopropoxypolydimethylsiloxane or a polydimethylsiloxane-polyoxyalkylene block polymer.

[0016] There is therefore an interest in providing an alternative process for depolymerizing silicones into organopolysiloxanes that can be directly reused for subsequent formulations. In particular, there is an interest in providing a catalytic system that allows this depolymerization to be carried out at lower temperatures, to limit the amount of catalyst used, and to implement a robust, selective, and flexible process. There is also an interest in being able to reliably control the molecular weight of the products formed. This possibility increases the prospects for the use and applications of such polymers.

[0017] Summary of the invention:

[0018] An objective of the present application is therefore to propose a process for depolymerizing silicones which makes it possible to control the molecular mass of the final product while being able to vary the chemical nature of the terminal groups.

[0019] Another objective of the present application is to provide a catalytic system for implementing this process.

[0020] Another objective of this application is to propose a simple and non-hazardous catalytic system compatible with industrialization of the process. Another objective of this application is to propose a process that is satisfactory from an industrial point of view and that is part of a so-called environmentally friendly chemistry.

[0021] Another objective of the present application is to obtain at the end of this process an organopolysiloxane OR having a low cyclic organopolysiloxane content.

[0022] Still other objectives will appear upon reading the description of the invention which follows.

[0023] Surprisingly, the Applicant has developed a catalytic system which meets these expectations. Thus, the present invention relates to a process for the preparation of organopolysiloxanes OR, by a depolymerization reaction of at least one silicone S in the presence of an acid catalyst chosen from benzenesulfonic acid derivatives of formula (Via), alone or in mixtures: Formula (Via) let R1 and R2 represent a hydrogen atom and preferably let R1 and R3 represent a hydrogen atom and preferably or either R2 and R3 represent a hydrogen atom and preferably and at least one Bc chain blocker having at least one siloxane function.

[0024] In this case, the acid catalyst and the Bc chain blocker allow the molecular mass of the final product to be controlled during the depolymerization reaction while allowing the chemical nature of the terminal groups to be varied.

[0025] Detailed description of the invention:

[0026] Silicones, otherwise known as organopolysiloxanes, are polymeric materials comprising alternating silicon and oxygen atoms with various organic radicals bonded to the silicon.

[0027] In the context of the present invention, silicone or silicone product or silicone polymer or organopolysiloxane means polymers comprising a siloxane backbone (Si-O-Si) having silicon and oxygen atoms alternating with various organic radicals bonded to the silicon. These silicone polymers can be liquid or solid, depending on the molecular weight and the degree of crosslinking. The silicones S of the invention can be of any type, for example, they can be linear organopolysiloxanes O such as oils or gums, branched organopolysiloxanes O such as resins, crosslinked organopolysiloxanes such as gels or elastomers, or mixtures of such compounds.

[0028] The organopolysiloxane O may in particular be an oil, and preferably has a dynamic viscosity of between 10,000 and 600,000 mPa.s at 25°C, preferably between 30,000 and 600,000 mPa.s at 25°C.

[0029] All the viscosities discussed in this presentation correspond to a dynamic viscosity quantity at 25°C called “Newtonian”, i.e. the dynamic viscosity which is measured, in a manner known per se, with a Brookfield viscometer at a shear rate gradient sufficiently low so that the measured viscosity is independent of the rate gradient.

[0030] The term gum is classically used for organopolysiloxane compounds with viscosities classically greater than 600,000 mPa.s, which corresponds to a molecular weight greater than 300,000 g / mol.

[0031] These organopolysiloxanes O may comprise one or more functional units such as:

[0032] - OH ;

[0033] - H ;

[0034] - alkenyl in particular comprising from 2 to 6 carbon atoms, preferably vinyl;

[0035] - O-Alk with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl;

[0036] - (O-Alk) x with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x represents an integer between 2 and 200;-a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5) alkyl-CF3, the alkyl being linear or branched.

[0037] Preferably, the functional patterns are chosen from:

[0038] - OH ;

[0039] - H ;

[0040] - alkenyl in particular comprising from 2 to 6 carbon atoms, preferably vinyl;

[0041] - a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5) alkyl-CF3, the alkyl being linear or branched.

[0042] Preferably, the organopolysiloxanes O may comprise one or more functional units such as H, OH, alkenyl (preferably vinyl), aryl, cyclic amine, as defined above. The organopolysiloxanes O may be partially crosslinked. The organopolysiloxanes O may in particular be used organopolysiloxanes, having served for example as a heat transfer fluid, which should be recycled, the process of the invention thus making it possible to generate organopolysiloxanes OR which can then be directly used in industrial processes. In the case of the use of used organopolysiloxanes O, the organopolysiloxane may then contain other elements such as additives, pigments, etc. The inventors have shown that it is possible to carry out the depolymerization reaction and the formation of organopolysiloxanes OR under such conditions.

[0043] According to one embodiment of the invention, the organopolysiloxane O comprises:

[0044] - at least 500 units, preferably at least 700 siloxyl units of formula (I): RcSiO(4-c) / 2 (I) in which,

[0045] R, identical or different, represents:

[0046] -an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, or an aryl group comprising from 6 to 10 carbon atoms, preferably phenyl, and c = 0, 1, 2 or 3; and optionally one or more units of formula (II): in which,

[0047] R is as defined above;

[0048] R 1 , identical or different, represents:

[0049] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0050] -a hydroxyl group (OH),

[0051] -a group (O-Alk) with Alk representing an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5, -a group (O-Alk) x with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x represents an integer between 2 and 200,

[0052] -a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (Ci-Cs)alkyl-CF3, the alkyl being linear or branched, or -a hydrogen; d=1, 2 or 3, preferably d=1 or 2, more preferably d=1; e=0, 1 or 2; and the sum d+e=1, 2 or 3.

[0053] It is understood in the above formulas that if more than one R group is present or if more than one R group 1 are present, they can be the same or different from each other.

[0054] Preferably, in the above formulas R 1 , identical or different, represents:

[0055] - an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0056] - a hydroxyl group (OH),

[0057] - a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched, or

[0058] -a hydrogen.

[0059] In the present invention:

[0060] - a siloxyl unit “M” represents a siloxyl unit of formula Y3SiO 1 / 2 ,

[0061] - a siloxyl unit “D” represents a siloxyl unit of formula Y2SiC> 2 / 2 ,

[0062] - a siloxyl unit “T” represents a siloxyl unit of formula YSiO 3 / 2 ,

[0063] - a siloxyl unit “Q” represents a siloxyl unit of formula SiO 4 / 2 , the symbols Y being R or R 1 .

[0064] The organopolysiloxane O may optionally be linear or branched and in particular comprise T and Q units.

[0065] According to a preferred embodiment, the organopolysiloxane O is chosen from the compounds of formula (III): R 1 a R (3-a) SiO-(SiR2O) n1 -(SiR 1 RO)m1-SiR 1 aR(3-a) (III) in which:

[0066] R, identical or different, represents:

[0067] -an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, or

[0068] -an aryl group comprising from 6 to 10 carbon atoms, preferably phenyl; R 1 , identical or different, represents:

[0069] - an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0070] -a hydroxyl group (OH),

[0071] -a group (O-Alk) with Alk representing an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5, -a group (O-Alk) x with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x represents an integer between 2 and 200,

[0072] -a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched, or

[0073] -a hydrogen; a is an integer and represents 0, 1, 2 or 3, preferably 0, 1 or 2, more preferably 0 or 1;

[0074] -n1 represents an integer between 500 and 10,000, preferably between 1,000 and 5,000, preferably between 500 and 5,000, more preferably between 600 and 2,000;

[0075] -m1 represents an integer between 0 and 100, preferably between 0 and 50, more preferably between 0 and 30, preferably m=0.

[0076] Particularly preferably, the organopolysiloxane O is a compound of formula (III) in which R 1 , identical or different, represents:

[0077] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0078] -a hydroxyl group (OH),

[0079] -a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched, or

[0080] -a hydrogen.

[0081] Particularly preferably, the organopolysiloxane O is a compound of formula (III) in which, R 1 , identical or different, represents: -CH3, vinyl, H, (C1-C5)alkyl-CF3 or OH. Particularly preferably, the organopolysiloxane O is a compound of formula (III) in which,

[0082] R, identical or different, represents CH3 or phenyl, preferably CH3;

[0083] R 1 , identical or different, represents:

[0084] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0085] -a hydroxyl group (OH),

[0086] -a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted or not by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (Ci-C5)alkyl-CF3, the alkyl being linear or branched, or

[0087] -a hydrogen.

[0088] Particularly preferably, the organopolysiloxane O is a compound of formula (III) in which,

[0089] R, identical or different, represents CH3 or phenyl, preferably CH3, R 1 , identical or different, represents CH3, vinyl, H, (C1-C5) alkyl-CF3 or OH.

[0090] The S silicones of the invention may also be of the crosslinked silicone material type such as gels or elastomers. Crosslinked silicone materials are well known to those skilled in the art. These materials may in particular be obtained by polycondensation, radical polymerization, thermal polyaddition or irradiation under UV. Silicone products have a multitude of applications. For example, we can find them in food applications such as baking molds, medical applications and in the pharmaceutical sector such as in baby bottle teats, catheters, implants or tubes for medical applications. In technical industrial applications, silicone is often used as a material for seals or membranes. In the automotive sector, it is used for hoses, sheathing or insulation of cables and as a damping material.

[0091] Silicone elastomers are crosslinked silicone materials containing fillers, such as silica, to achieve good mechanical properties. By varying the silicone oils, fillers and additives, as well as the crosslinking method, silicone elastomers exhibit different properties and colors. Silicone elastomers can be divided into three main groups well known to those skilled in the art.

[0092] Hot-cured elastomers (HCR or high temperature vulcanization) are silicone elastomers made from silicone compositions with very high viscosity, including silicone gums and fillers. They are vulcanized at high temperatures, generally between 140°C and 200°C. Crosslinking is either radical, catalyzed by peroxides, or obtained by an addition reaction where platinum compounds are used as catalysts.

[0093] Liquid silicone rubber (LSR) is a silicone elastomer made from compositions containing viscous silicone oils and fillers. Crosslinking occurs through an addition reaction at temperatures similar to those of LSR, with crosslinking generally occurring much more rapidly.

[0094] The third group is that of silicones obtained by crosslinking at room temperature of silicone compositions from silicone oils and fillers crosslinking by polycondensation or polyaddition reactions. These elastomers are known in French as cold vulcanizable silicone elastomers (RTV). These compositions are available in one- and two-component systems.

[0095] In the process of the present application, silicone S also means silicone-based materials, for example materials comprising at least 0.1% by mass of silicone relative to the total mass of silicone-based material. Conventionally, these materials can be found in silicone-coated textiles (airbags or synthetic leather), silicone coatings (food paper).

[0096] The silicone-based material may comprise up to 100% by mass of silicone, preferably up to 99.9% by mass of silicone relative to the total mass of silicone-based material. These silicone-based materials may also comprise additives or fillers such as colorants, silica, calcium carbonate, calcium oxide, celite, quartz, titanium oxide, cerium hydroxide, magnesium oxide, mica, etc.

[0097] According to one embodiment, the silicone S comprises silica, calcium oxide, quartz, titanium oxide, magnesium oxide, mica and mixtures thereof.

[0098] In the context of the present invention, the term “number of moles of (Si-O)” means the number of moles of (Si-O) bonds in the silicone S. In the case where the starting silicone S is of unknown formula, in particular in the case of formulated commercial products, it is possible to estimate the number of moles of (Si-O) bonds. Indeed, for formulated silicone elastomers, those skilled in the art know that the amount of filler is between 20 and 40% by mass, thus, by estimating the amount of filler at an average of 30% by mass, we have 70% by mass of silicone, which makes it possible to calculate the number of moles of (Si-O) bonds, from the average molar mass of the repeating unit. In the context of the present application, the term chain blocker Bc has at least one siloxane function.

[0099] In the method of the invention, the chain blocker Bc is represented by the formula (IV): in which,

[0100] R 1 , identical or different, represents:

[0101] - a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 8 carbon atoms, optionally substituted by a heteroatom O, N, S or a halide,

[0102] -an alkenyl group comprising from 2 to 6 carbon atoms,

[0103] - a cycloalkyl group of 5 to 10 carbon atoms, optionally substituted by a heteroatom O, N, S or a halide, - a C6-C aryl group 18 , -a hydroxyl group, or -a hydrogen,

[0104] R 2 identical or different, represents:

[0105] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0106] -a hydroxyl group (OH),

[0107] -a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms, optionally substituted by at least one heteroatom O, N, S or a halide such as a fluorine atom, for example 1 to 10 fluorine atoms, for example (Ci-C5)alkyl-CF3, the alkyl being linear or branched; or -a hydrogen; and q is an integer between 1 and 50, preferably between 1 and 20, more preferably between 1 and 10.

[0108] In another embodiment, the Bc chain blocker is represented by formula (IV) wherein:

[0109] R 1 , identical or different, represents CH3 or phenyl, preferably CH3;

[0110] R 2 identical or different, represents:

[0111] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0112] -a hydroxyl group (OH),

[0113] -a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms, optionally substituted by at least one heteroatom O, N, S or a halide such as a fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched, -a C5-C cycloalkyl group 10 , optionally substituted, -a C6-C aryl group 10 , optionally substituted, or -a hydrogen; and q is an integer between 1 and 50, preferably between 1 and 20, more preferably between 1 and 10.

[0114] Particularly preferably, the Bc chain blocker of the invention is represented by formula (IV), in which: R 1 , identical, represents CH3, R 2 identical or different, represents:

[0115] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0116] -a hydroxyl group (OH),

[0117] - a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms,

[0118] -a C6-C aryl group 18 , optionally substituted, or

[0119] -a hydrogen. and q is an integer between 1 and 20, preferably between 1 and 10, more preferably between 1 and 5.

[0120] Other blockers having a siloxane function according to the invention are described in the work Chemistry and Technology of Silicones, published in 1968 by Académie Press, on page 264.

[0121] The Bc chain blocker may be in a solvent. This is particularly advantageous in order to solubilize it in the reaction medium. The solvent may in particular be a non-polar solvent such as an organic solvent of the alkane or aromatic hydrocarbon type. Preferably, the solvent is chosen from n-hexane, n-heptane, n-decane, n-dodecane, isododecane, EXXSOL D60, xylene, toluene and mixtures thereof.

[0122] The amount of Bc chain blocker used in the method of the invention is at least 10 -4 moles relative to the moles of bond (Si-O), in silicone S, preferably between 10 -3 and 5x10 -1 mol, preferably between 10 -3 and 10 -2 mol, even more preferably between 3x10 -3 and 6x10 -1 mol, for example 5x10 -3 mol relative to the moles of bond (Si-O) in silicone S.

[0123] These chain blockers allow the functionalization of the organopolysiloxane OR during the depolymerization reaction. Thus, it is possible to obtain organopolysiloxane OR having, for example, Si-vinyl or Si-H functions. In the process according to the invention, it is possible to use a mixture of different chain blockers. Thus, it is possible to obtain an organopolysiloxane OR which can have different functional groups at the end of the chain.

[0124] In an alternative embodiment, the method of the invention can be carried out without a Bc chain blocker.

[0125] The acid catalyst used as catalyst in the process of the present invention is chosen from the group comprising Bronsted acids having a pKa less than or equal to 2 such as trifluoromethanesulfonic acid, benzenesulfonic acid and its derivatives alone or in mixtures.

[0126] Preferably, the acid catalyst is chosen from benzene sulfonic acid and its derivatives of formula (Va), alone or in mixtures:

[0127] Formula (Va) let Ri and R2 represent a hydrogen atom and R3 = C n H 2n+1 where 1 ≤n≤20, or Ri and R3 represent a hydrogen atom and R2= C n H 2n+1 where 1 ≤n≤20, or either R2 and R3 represent a hydrogen atom and Ri = C n H 2n+1 where 1≤n≤20

[0128] In one embodiment, the acid catalyst is chosen from benzene sulfonic acid and its derivatives of formula (Vb), alone or in mixtures:

[0129] Formula (Vb) with R= H or C n H 2n+1 where 1≤n≤20.

[0130] More preferably, the acid catalyst is chosen from benzene sulfonic acid derivatives of formula (Via), alone or in mixtures: Formula (Vb) let Ri and R2 represent a hydrogen atom and R3 = Cn H 2n+1 where 5 <n<20, de préférence 10≤n≤20, soit Ri et R3représentent un atome d’hydrogène et R2= C n H 2n+1 where 5 <n<20, de préférence 10≤n≤20, ou soit R2et R3représentent un atome d’hydrogène et Ri = C n H 2n+1 where 5 <n<20, de préférence 10≤n≤20.

[0131] In one embodiment, the acid catalyst is chosen from benzene sulfonic acid derivatives of formula (VIb), alone or in mixtures:

[0132] Formula (Vlb) with R= C n H 2n+1 where 5 <n<20, de préférence 10≤n≤20.

[0133] Note that the alkyl groups mentioned in formulas (Va), (Vb), (Via) and (Vlb) can be primary, secondary or tertiary alkyl groups.

[0134] Even more preferably, the acid catalyst is HDBS also known as 4-dodecylbenzenesulfonic acid (CAS 121-65-3).

[0135] Alternatively, the acid catalyst is chosen from Bronsted acids having a pKa less than or equal to -2 such as perfluoroalkane acids, for example trifluoromethanesulfonic acid (triflic acid), pentafluoroethanesulfonic acid, heptafluoropropanesulfonic acid, or chlorinated derivatives, alone or in mixtures.

[0136] Depending on the nature of the acid catalyst, it is possible to solubilize it in a solvent. Preferably, the solvent is a non-polar solvent. The solvent may in particular be an organic solvent of the alkane or aromatic hydrocarbon type. Preferably, the solvent is identical to that chosen during the depolymerization reaction. Thus, the solvent may in particular be an organic solvent of the alkane or aromatic hydrocarbon type. The quantity of acid catalyst used in the process of the invention is between 0.001 and 3% by mass relative to the mass of silicone S, preferably between 0.05 and 1%, more preferably between 0.1 and 1%, for example 0.4% by mass relative to the mass of silicone S.

[0137] In one embodiment, the organopolysiloxane OR which can have at the end of the chain functional groups derived from the chain blocker such as vinyl functions, Si-H functions, Si-aryl functions for example.

[0138] Depending on the implementation of the process, they may be identical or different. The organopolysiloxane OR as defined above may optionally comprise T and Q units.

[0139] According to one embodiment of the invention, the organopolysiloxane OR comprises:

[0140] - at least 2 siloxyl units of formula (VII): in which,

[0141] R, identical or different, represents:

[0142] -an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl,

[0143] -an aryl group comprising from 6 to 10 carbon atoms, preferably phenyl, c = 1, 2 or 3;

[0144] R 1 , identical or different, represents:

[0145] - a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 8 carbon atoms, optionally substituted by a heteroatom O, N, S or a halide,

[0146] -an alkenyl group comprising from 2 to 6 carbon atoms,

[0147] - a cycloalkyl group of 5 to 10 carbon atoms, optionally substituted by a heteroatom O, N, S or a halide,

[0148] -a C6-C aryl group 18 ,

[0149] -a hydroxyl group, or

[0150] -a hydrogen

[0151] R 2 identical or different, represents:

[0152] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0153] -a hydroxyl group (OH),

[0154] -a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms, optionally substituted by at least one heteroatom O, N, S or a halide such as a fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched,

[0155] -a C5-C cycloalkyl group 10 , possibly substituted,

[0156] -a C6-C aryl group 18 optionally substituted, or -a hydrogen; q is an integer between 1 and 50, preferably between 1 and 20, more preferably between 1 and 10. and one or more units of formula (VIII), preferably from 10 to 1,500 units, preferably from 50 to 1,000 units and even more preferably from 100 to 500 units:

[0157] SiR 3 d R e O (4-d-e) / 2 (Formula VIII) in which,

[0158] R identical or different is as defined previously;

[0159] R 3 , identical or different is as previously defined by group R 1 ; and d= 0,1, 2, preferably d=0 or 1; e= 1, 2 or 3; and the sum d+e=1, 2 or 3.

[0160] Preferably, in the above formulas R 3 , identical or different, represents:

[0161] - an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl;

[0162] - a hydroxyl group (OH);

[0163] - a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched;

[0164] -a hydrogen.

[0165] According to one embodiment of the invention, the organopolysiloxane OR may be a compound of formula (IX): in which,

[0166] R, identical or different, represents:

[0167] -an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl,

[0168] -an aryl group comprising from 6 to 10 carbon atoms, preferably phenyl, R 1 , identical or different, represents:

[0169] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl, -a hydroxyl group (OH),

[0170] -a group (O-Alk) with Alk representing an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5, -a group (O-Alk) x with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x represents an integer between 2 and 200, or -a hydrogen;

[0171] R 2 identical or different, represents:

[0172] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0173] -a hydroxyl group (OH),

[0174] -a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms, optionally substituted by at least one heteroatom O, N, S or a halide such as a fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched, -a C5-C10 cycloalkyl group, optionally substituted, -a C6-C aryl group 18 optionally substituted, or -a hydrogen; q is an integer between 1 and 50, preferably between 1 and 20, more preferably between 1 and 10; n2represents an integer between 10 and 1,500, preferably between 10 and 1,000, preferably between 50 and 1,000, more preferably between 100 and 500; m2represents an integer between 0 and 100, preferably between 0 and 50, more preferably between 0 and 30, preferably m=0.

[0175] According to a preferred embodiment of the invention, the organopolysiloxane OR is a compound of formula (IX): in which,

[0176] R, identical or different, represents CH3 or phenyl, preferably CH3;

[0177] R 1 identical or different, represents:

[0178] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0179] -a hydroxyl group (OH),

[0180] -a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (Ci-C5)alkyl-CFs, the alkyl being linear or branched, or -a hydrogen;

[0181] R 2 identical or different, represents:

[0182] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0183] -a hydroxyl group (OH),

[0184] -a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms, optionally substituted by at least one heteroatom O, N, S or a halide such as a fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched, -a C5-C cycloalkyl group 10 , possibly substituted,

[0185] -a C6-C aryl group 18 , optionally substituted, or

[0186] -a hydrogen; q is an integer between 1 and 50, preferably between 1 and 20, more preferably between 1 and 10; n2 represents an integer between 10 and 1,500, preferably between 10 and 1,000, preferably between 50 and 1,000, more preferably between 100 and 500; m2 represents an integer between 0 and 100, preferably between 0 and 50, more preferably between 0 and 30, preferably m=0.

[0187] According to a particularly preferred embodiment of the invention, the organopolysiloxane OR of the invention is a compound of formula (IX) in which, R, identical or different, represents CH3 or phenyl, preferably CH3, R 1 , identical or different, represents CH3, vinyl, H, (C1-C5) alkyl-CF3 or OH;

[0188] R 2 identical or different, represents:

[0189] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0190] -a hydroxyl group (OH),

[0191] - a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms,

[0192] -a C6-C aryl group 18 , optionally substituted, or

[0193] -a hydrogen; q is an integer between 1 and 20, preferably between 1 and 10, more preferably between 1 and 5; n2 represents an integer between 10 and 1,500, preferably between 10 and 1,000, preferably between 50 and 1,000, more preferably between 100 and 500; m2 represents an integer between 0 and 100, preferably between 0 and 50, more preferably between 0 and 30, preferably m=0.

[0194] In one embodiment, the organopolysiloxane OR of the invention is a compound of formula (X) in which:

[0195] Formula (X)

[0196] R, identical or different, represents:

[0197] -an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl,

[0198] -an aryl group comprising from 6 to 10 carbon atoms, preferably phenyl, R 1 , identical or different, represents:

[0199] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0200] -a hydroxyl group (OH),

[0201] -a group (O-Alk) with Alk representing an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5, -a group (O-Alk) x with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x represents an integer between 2 and 200,

[0202] -a linear or branched alkyl group comprising from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, substituted by at least one fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched,

[0203] -a hydrogen, or

[0204] - a group -CH2CH2(R3SiO) n3 with R as defined above and n3 represents an integer between 0 and 1000, preferably between 0 and 500, more preferably between 0 and 200;

[0205] R 2 identical or different, represents:

[0206] -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl,

[0207] -a hydroxyl group (OH),

[0208] -a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms, optionally substituted by at least one heteroatom O, N, S or a halide such as a fluorine atom, for example 1 to 10 fluorine atoms, for example (C1-C5)alkyl-CF3, the alkyl being linear or branched, -a C5-C10 cycloalkyl group, optionally substituted, -a C6-C aryl group 18optionally substituted, or -a hydrogen; q is an integer between 1 and 50, preferably between 1 and 20, more preferably between 1 and 10; n2 represents an integer between 10 and 1,500, preferably between 10 and 1,000, preferably between 50 and 1,000, more preferably between 100 and 500; m2represents an integer between 0 and 100, preferably between 0 and 50, more preferably between 0 and 30, preferably m=0; n3represents a different or identical integer between 0 and 1,000, preferably between 0 and 500, more preferably between 0 and 200; a represents a different or identical integer equal to 0 or 1.

[0209] For the purposes of the present invention, the term “degree of polymerization” means the whole number representing the number of siloxyl repeating units.

[0210] According to one embodiment of the process of the invention, the organopolysiloxane OR thus obtained has a degree of polymerization at least divided by two compared to the degree of polymerization of the silicone S introduced, preferably at least divided by three, preferably at least divided by five compared to the degree of polymerization of the silicone S introduced.

[0211] According to one embodiment of the process of the invention, the organopolysiloxane OR thus obtained has a degree of polymerization at least divided by ten compared to the degree of polymerization of the silicone S introduced.

[0212] For the purposes of the present invention, the mass-average molecular mass and the number-average molecular mass, respectively denoted M w and M n of the different organopolysiloxanes OR can be determined by size exclusion chromatography (SEC) in the presence of polystyrene standards in a solvent such as toluene at 40°C.

[0213] According to one embodiment of the process of the invention, the organopolysiloxane OR thus obtained has a mass-average molecular mass M w at least divided by two compared to the mass average molecular mass of the silicone S introduced, preferably at least divided by three, preferably at least divided by five compared to the mass average molecular mass Mw of the silicone S introduced.

[0214] It is also conceivable that according to one embodiment of the process of the invention, the organopolysiloxane OR thus obtained has a mass-average molecular mass M w at least divided by ten relative to the mass average molecular mass of the silicone S introduced, or at least divided by fifteen relative to the mass average molecular mass Mw of the silicone S introduced. According to one embodiment of the process of the invention, the organopolysiloxane OR of the invention is characterized in that its mass average molecular mass Mw may be between 500 and 300,000 g / mol, preferably between 1,000 and 150,000 g / mol, preferentially between 1,000 and 100,000 g / mol, even more preferentially between 5,000 and 40,000 g / mol.

[0215] According to one embodiment of the process of the invention, the organopolysiloxane OR thus obtained has a number-average molecular mass M n at least divided by two compared to the number-average molecular mass of the silicone S introduced, preferably at least divided by three, preferably at least divided by five compared to the number-average molecular mass M n silicone S introduced.

[0216] It is also conceivable that according to one embodiment of the process of the invention, the organopolysiloxane OR thus obtained has a number-average molecular mass M nat least divided by ten compared to the mass-average molecular mass of the silicone S introduced, or at least divided by fifteen compared to the number-average molecular mass M n silicone S introduced.

[0217] According to one embodiment of the process of the invention, the organopolysiloxane OR of the invention is characterized in that its number-average molecular mass M n is between 500 and 300,000 g / mol, preferably between 1,000 and 150,000 g / mol, preferentially between 1,000 and 70,000 g / mol and even more preferentially between 2,500 and 30,000 g / mol.

[0218] According to one embodiment of the process of the invention, the organopolysiloxane OR of the invention is characterized in that its dynamic viscosity is between 100 and 100,000 mPa.s at 25°C, preferably between 1,000 and 80,000 mPa.s at 25°C, even more preferably between 10,000 and 70,000 mPa.s at 25°C.

[0219] In one embodiment, the organopolysiloxane of the invention OR has a quantity of (Si-OH) bond at the chain end of less than or equal to 15%, preferably less than or equal to 10%, preferentially less than or equal to 5% and even more preferentially less than or equal to 1% relative to the total quantity of silicon atoms at the chain end of the organopolysiloxane of the invention OR.

[0220] In the context of the present application, the mass percentage or the weight percentage of D4 of the products obtained according to the process of the present invention can be measured via the quantitative NMR spectra. 29Yes. Alternatively, the mass percentage or the weight percentage of D4 of the products obtained according to the process of the present invention could be measured via the chromatograms resulting from a size exclusion chromatography (SEC) analysis. For the purposes of the present invention, cyclic organopolysiloxanes are the compounds of formula (XI): in which n represents a natural number between 1 and 5.

[0221] Generally within the meaning of the present invention, cyclic organopolysiloxanes consist of compounds of formula (XI) where n is equal to 2 or 3 or 4.

[0222] In other words, octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (Ds), dodecamethylcyclohexasiloxane (De) or mixtures thereof.

[0223] In one embodiment, the method according to the invention is characterized in that the content of cyclic organopolysiloxanes is less than 5%, preferably less than or equal to 3%, preferably less than or equal to 2% and even more preferably less than or equal to 1.5% relative to the total mass of the organopolysiloxanes of the invention OR.

[0224] In one embodiment, the process according to the invention is characterized in that the octamethylcyclotetrasiloxane (D4) content is less than 5%, preferably less than or equal to 3%, preferably less than or equal to 2% and even more preferably less than or equal to 1.5% relative to the total mass of the organopolysiloxanes of the invention OR.

[0225] Preferably, the process of the invention is carried out in a solvent. The process of the invention is preferably carried out in a non-polar solvent. The solvent may in particular be an organic solvent of the alkane or aromatic hydrocarbon type.

[0226] Preferably, the solvent is chosen from n-hexane, n-heptane, n-decane, n-dodecane, isododecane, EXXSOL D60, xylene, toluene and mixtures thereof.

[0227] In one embodiment, the method of the invention is characterized in that the mass ratio, mass of silicone S relative to the mass of solvent used is between 0.01 and 15, preferably between 0.1 and 5, preferentially between 0.1 and 2.

[0228] In one embodiment, the method of the invention is characterized in that the depolymerization reaction takes place without solvent.

[0229] This embodiment is particularly advantageous because it makes it possible to avoid the use of solvent, its treatment or recycling once used while obtaining satisfactory results when carrying out the method of the present invention. Advantageously, and preferably, the reaction is carried out at a temperature between 0 and 100°C, preferably between 0 and 50°C, more preferably between 10 and 35°C, for example at room temperature.

[0230] According to the process of the invention, the duration of the reaction is between 2 and 72 hours, preferably between 5 and 24 hours, more preferably between 8 and 24 hours, for example 24 hours.

[0231] The person skilled in the art will know how to adapt these parameters according to the nature of the reactors and the species used.

[0232] The method according to the invention may further comprise a step of neutralizing the acid catalyst. This neutralization step makes it possible to prevent the occurrence of side reactions and deactivate the acid catalyst.

[0233] Advantageously, this neutralization step is carried out by the addition of a base to the reaction medium or by thermal degradation of the acid catalyst.

[0234] According to the process of the invention, the base is chosen from amines, alkali metal hydroxides, alkaline earth metal hydroxides, carbonates, hydrogen carbonates, and mixtures thereof.

[0235] Preferably, the base is selected from the group of tertiary amines or hydrogen carbonates.

[0236] Alternatively, the neutralization step is carried out by “thermal degradation”.

[0237] "Thermal degradation" means heating to a temperature above 120°C for a period of between 10 minutes and 3 hours. Those skilled in the art will be able to adapt the operating conditions to optimize this thermal degradation step. This step degrades the catalyst and stops the depolymerization reaction.

[0238] The process according to the invention may further comprise a filtration step in order to extract the neutralized catalyst and / or the excess base from the reaction medium. This step may also make it possible to extract any charges resulting from the depolymerized silicone S according to the process of the present invention. A person skilled in the art will be able to adapt the filtration method according to the size of the reactor and the species used in the process according to the invention.

[0239] According to a preferred embodiment of the invention, the method of the present invention comprises the following three steps:

[0240] 1) Implementation of the process for preparing organopolysiloxanes OR, by a depolymerization reaction of at least one silicone S in the presence of an acid catalyst and at least one chain blocker Bc having at least one siloxane function; 2) Neutralization of the acid catalyst mentioned in the previous step by adding a base to the reaction medium or by thermal degradation of the acid catalyst; and

[0241] 3) Filtration of the reaction medium obtained at the end of step 2.

[0242] The present application also relates to the use of the organopolysiloxanes OR obtained according to the process of the present invention as an ingredient which can be directly used in various silicone formulations useful in fields such as cosmetics, household cleaning products, automobiles, energy.

[0243] The OR organopolysiloxanes derived from silicone S as detailed previously in the present application, can be re-engaged in various formulations in order to prepare a new silicone S.

[0244] Thus, the present application also relates to the use of the organopolysiloxanes OR obtained by the process of the present invention for the preparation of silicone S, for example for the preparation of silicone oils, resins, gums, gels or elastomers.

[0245] The present application also relates to a process for preparing silicone, in particular silicone oils, resins or gums, comprising the following steps:

[0246] 1) Implementation of the process for preparing organopolysiloxanes OR according to the invention;

[0247] 2) Preparation of silicone S, in particular oils, resins, gums, or elastomers from the organopolysiloxanes OR obtained in step 1).

[0248] In one embodiment, the method for preparing silicone S is characterized in that step 2 is carried out by a polyaddition, polycondensation, cationic mechanism or radical mechanism reaction.

[0249] Step 2 may include manufacturing liquid silicone elastomers (LSR), hot vulcanizable silicone elastomers (HVS) or cold vulcanizable silicone elastomers (RTV).

[0250] According to another embodiment, step 2 may in particular consist of preparing silicones S useful in the field of cosmetics, health, household products, technical industrial formulations (seals, membranes, tubes), transport such as automobiles or aviation, or even in the energy field.

[0251] Examples:

[0252] Silicones used in the examples: In the following Me = Methyl;

[0253] Silicone S1: n= 943 M n = 70,000 g / mol

[0254] Silicone S2:

[0255] Mixture of three silicone oils where n= 81, (M n = 6000 g / mol), n = 943 (M n = 70 OOOg / mol) and n=1080 (M n = 80,000g / mol)

[0256] S3 Silicone:

[0257] S3 silicone is an RTV2 gel formulated by ELKEM. This silicone was obtained by polyaddition reaction.

[0258] Silicone S4:

[0259] A commercial silicone tube of unknown composition, cut into pieces.

[0260] Silicone S5:

[0261] S5 silicone is a PDMS gum, marketed by ELKEM under the name BLUESIL™ FB Silicone Gum.

[0262] The acid catalyst is HDBS also known as 4-dodecylbenzenesulfonic acid (CAS 121-65-3).

[0263] The solvent used in the examples is a non-polar solvent, preferably toluene or heptane.

[0264] Chain blockers implemented in the examples:

[0265] Bd chain blocker: divinyltetramethyldisiloxane (CAS 2627-95-4).

[0266] Bc2 chain blocker: hexamethyldisiloxane (CAS 107-46-0)

[0267] Bc3 chain blocker: tetramethyldisiloxane (CAS 3277-26-7)

[0268] Bc4 Chain Blocker:

[0269] With n= 13 (M n = 977 g / mol).

[0270] Example 1: General protocol of the process: In a 250mL flask, a silicone S and 120mL of toluene are introduced as well as variable quantities of acid catalyst and chain blocker Bc. The reaction medium is placed at room temperature under stirring for a period of 24 hours. A large excess of inorganic or amine base is then added to the reaction medium. A sample is taken and analyzed by NMR- 1 H and NMR- 29 If.

[0271] In the context of the examples described below, the percentage by mass of D4 relative to the total mass of the organopolysiloxane OR obtained according to the process of the present invention is measured by size exclusion chromatography (SEC) in the presence of polystyrene standards in a solvent such as toluene at 40°C.

[0272] Similarly, the number-average molecular mass denoted M nof the different organopolysiloxanes according to the present invention OR is determined by the same size exclusion chromatography (SEC) method.

[0273] The quantity QBc can be found in the various tables exemplified below. This quantity expresses the number of moles of Bc in relation to the moles of bond (Si-O) in the silicone S.

[0274] Example 2: Influence of the nature of silicone S on the process of the invention:

[0275] The protocol of Example 1 is implemented with a silicone S (30g, approximately 404mmol of bond (Si-O) in the silicone S for SI, S2, S3 and S5), HDBS (4400 ppm by mass, 0.132g) as an acid catalyst and Bd as a chain blocker Bc. The reaction medium is placed at room temperature under stirring for a period of 24 hours. The silicone S4 is a commercial silicone tube of unknown composition, cut into pieces. In the remainder of this example, we will consider that this tube is composed of both a significant amount of filler, 30%, and a quantity of silicone of 70%. Thus, for 30g of silicone tube, i.e. this test, we consider that we have 21g of silicone S. We then introduced 0.265g of chain blocker Bd and 0.0925g of HDBS into the reaction medium.

[0276] The nature of silicone S and the size QBc are mentioned in the table below. The results show that the process of the invention is versatile and can be used on all types of silicone including silicone blends and silicones comprising fillers.

[0277] Example 3: Influence of the nature of the Bc chain blocker on the process of the invention:

[0278] The protocol of Example 1 is implemented with silicone S1 (30g, 404 mmol of bond (Si-O) in silicone S1), HDBS (4400 ppm by mass, 0.132g) as acid catalyst and a chain blocker Bc. The reaction medium is placed at room temperature for a period of 24h.

[0279] The nature of the chain blocker and the size QBc are mentioned in the table below.

[0280] This test was repeated by substituting the S1 silicone with an RTV2 silicone gel (S3 silicone) manufactured by ELKEM. The other operating conditions remain unchanged from those mentioned above. Thus, it is implemented with the S3 silicone (30g, 404mmol of bond (Si-O) in the S3 silicone), HDBS (4400 ppm by mass, 0.132g) as an acid catalyst and a Bc chain blocker as indicated in the table below:

[0281] These tests demonstrate the versatility and robustness of the process according to the present invention. Indeed, the nature of the Bc chain blocker has a limited effect on the number-average molecular weight (Mn) of the organopolysiloxane OR obtained according to the process of the invention. This process can therefore be adapted with different S silicones and different Bc chain blockers. In the context of this example, the product obtained according to the process of the invention has a percentage of D4 less than or equal to 2% by mass relative to the total mass of the organopolysiloxane OR. Example 4: Influence of the quantity of Bc chain blocker on the process of the invention:

[0282] The protocol of Example 1 is implemented with silicone S1 (30g, 404mmol of bond (Si-O) in silicone S1), HDBS (4400 ppm by mass, 0.132g) as acid catalyst and Bd as chain blocker. The reaction medium is placed at room temperature for a period of 24h.

[0283] The mass of Bc and the quantity QBc are mentioned in the table below.

[0284] In the context of each test (tests 1 to 8) of this example the mass percentage in D4 is less than 2% by mass compared to the total mass of the OR product.

[0285] This test was repeated by substituting the S1 silicone with an RTV2 silicone gel (S3 silicone) formulated by ELKEM. The other operating conditions remain unchanged from those mentioned above. Thus, it is implemented with S3 silicone (30g, 404mmol of bond (Si-O) in S3 silicone), HDBS (4400 ppm by mass, 0.132g) as an acid catalyst and a Bc chain blocker.

[0286] The mass of Bc and the quantity QBc are mentioned in the table below.

[0287] These two tests demonstrate the control of the number-average molecular mass (M n) of the organopolysiloxane OR according to the process of the invention. The variation in the quantity of material of the chain blocker Bc influences the molecular mass of OR. It can be noted that the product obtained according to the process of the invention has a percentage of D4 less than or equal to 1.3% by mass relative to the total mass of the organopolysiloxane OR.

[0288] Example 5: Influence of the quantity of acid on the process of the invention:

[0289] The protocol of Example 1 is implemented with silicone S1 (30g, 404mmol of bond (Si-O) in silicone S1), HDBS (1100ppm to 17600ppm mass) as acid catalyst and a chain blocker Bc.

[0290] The quantity QBc and molar amount of HDBS are mentioned in the table below.

[0291] It can be noted that at a fixed quantity of chain blocker QBc, when the quantity of acid catalyst is increased, an increase in the percentage of D4 is also observed.

[0292] Thus, the quantity of acid catalyst used in the reaction has an impact on both the kinetics of the reaction, the average molecular masses obtained but also on the quantity of undesirable co-products such as D4.

[0293] Using the information disclosed in the present invention, a person skilled in the art will be able to adapt these parameters to obtain, using the method of the present invention, a polyorganosiloxane OR with the number-average molecular mass M n desired while controlling the cyclic content.

[0294] Example 6: Comparison according to the protocol of patent application JP2002348407A: 20 g of PDMS S4, 47 g of toluene and 2.4 g of HDBS solution were introduced into a 250 mL round flask equipped with a magnetic stirrer. After stirring for 1 hour at room temperature using a stirrer, the silicone tube was completely decomposed and dissolved. Then, a solution of 0.54 g of calcium hydroxide in 15 g of isopropanol was added for neutralization as well as 50 g of water. The resulting mixture was stirred for 10 minutes. After standing for 30 minutes, a sample of the organic phase obtained was taken, diluted to the appropriate concentration, filtered and analyzed by size exclusion chromatography. The number-average molecular mass (M n) of the organopolysiloxane of 11,000 g / mol and a quantity of undesirable co-products such as octamethyltetrasiloxane (D4) equal to 15% by mass relative to the total mass of the organopolysiloxane obtained.

[0295] Example 7: Influence of the nature of the acid catalyst:

[0296] The protocol of example 1 is implemented with silicone S1 (30g, 404mmol of bond (Si-O) in silicone S1), an acid catalyst (4400 ppm by mass) and a chain blocker Bc. The nature of the acid catalyst, the mass of catalyst used are mentioned in the table below.

[0297] It can be noted that tests 2 and 3 have satisfactory results within the meaning of the present invention. However, it can be noted that trifluoromethanesulfonic acid leads to 3% by mass of D4 relative to the total mass of the organopolysiloxane OR.

[0298] On the other hand, 4-dodecylbenzenesulfonic acid (CAS 121-65-3) shows a satisfactory implementation of the process of the present invention as has already been presented in the previous examples.

[0299] Example 8: Influence of reaction time on the process of the invention:

[0300] The protocol of Example 1 is implemented with silicone S1 (30g, 404mmol of bond (Si-O) in silicone S1), HDBS (4400ppm mass, 0.132g) as acid catalyst and a chain blocker Bc.

[0301] The quantity QBc and the reaction time are mentioned in the table below.

[0302] These tests demonstrate that the reaction time also allows the number-average molecular mass M to be controlled. n polyorganosiloxane OR obtained according to the process of the invention.

[0303] Example 9: Influence of temperature on the process of the invention:

[0304] The protocol of Example 1 is implemented with silicone S1 (30g, 404mmol of bond (Si-O) in silicone S1), HDBS (4400ppm mass, 0.132g) as acid catalyst and a chain blocker Bc.

[0305] The table below shows the temperature, the degree of polymerization of the OR product and the mass percentage in D4:

[0306] The temperature during the implementation of the method of the invention makes it possible to control the number-average molecular mass M n polyorganosiloxane OR obtained according to the process of the invention.

[0307] Example 10: Influence of the solvent content on the process of the invention:

[0308] The protocol of Example 1 is implemented with silicone S1 (30g, 404mmol of bond (Si-O) in silicone S1), HDBS (4400ppm mass, 0.132g) as acid catalyst and a chain blocker Bc and toluene as solvent.

[0309] In this example, five trials with different volumes of solvents were carried out.

[0310] This example aims to study a possible influence on the volume of solvent introduced into the process of the invention. The table below mentions the volume of solvent introduced in the different tests:

[0311] The amount of solvent introduced during the implementation of the process of the invention has a small influence on the variation of the number-average molecular mass M n of the polyorganosiloxane OR obtained according to the process of the invention. Furthermore, in this same example, the mass percentage of D4 in mass relative to the total mass of the product OR is less than or equal to 2% for each of the tests.

[0312] Example 11: Reuse of depolymerized S2 silicone in organopolysiloxane OR in a new RTV2 formula:

[0313] In this example, the ability to use the functional organopolysiloxane OR (obtained under the conditions of Test 1 of Example 2) to prepare an RTV2 gel was tested. Thus, the recycled product OR of Example 2, Test 1 comprising vinyl functions was used in combination with a crosslinker of the poly(methylhydrogensiloxane)-co-poly(dimethylsiloxane) type where [Si-H] / [Si-vinyl] = 2.25. In order to obtain this RTV2 gel, the hydrosylilation reaction was carried out in the presence of a Karstedt catalyst (275 ppm of a 2% Pt solution) and 1-ethynylcyclohexanol used as a moderator ([1- Ethynylcyclohexanol] / [Pt] = 14.6 ppm). Then, the reaction mixture was mixed, degassed and crosslinked for 4 h at 70°C.

[0314] [Fig 1] in the appendix illustrates a photograph of the RTV2 gel obtained under the conditions of this example. This RTV2 formulation was prepared twice under the same conditions and each of these tests has similar physical characteristics. Indeed, the RTV2 gel obtained during the first test has a swelling rate of 280% and an extractable fraction of 10% while the RTV2 gel obtained during the second test has a swelling rate of 285% and an extractable fraction of 10%.

[0315] Therefore, this example demonstrates that the OR organopolysiloxanes obtained according to the process of the invention can be reused in formulations to obtain RTV2 type silicone gels. In view of the information disclosed in the present invention and more particularly in this example, the person skilled in the art will know how to adapt the operating conditions to use the organopolysiloxanes obtained according to the process of the invention in other silicone formulations (EVC, RTV1, LSR).

Claims

CLAIMS 1. Method for preparing organopolysiloxanes OR, by a depolymerization reaction of at least one silicone S in the presence of: - an acid catalyst chosen from benzene sulfonic acid derivatives of formula (Via), alone or in mixtures: Formula (VIa) let R1 and R2 represent a hydrogen atom and R3 = C n H 2n+1 where 5≤n≤20, preferably 10≤n≤20 or R1 and R3 represent a hydrogen atom and R2= C n H 2n+1 where 5≤n≤20, preferably 10≤n≤20 or either R2 and R3 represent a hydrogen atom and Ri = C n H 2n+1 where 5≤n≤20, preferably 10≤n≤20 and at least one Bc chain blocker having at least one siloxane function.

2. Method according to claim 1, in which the acid catalyst is chosen from benzene sulfonic acid derivatives of formula (VIb), alone or in mixtures: Formula (VIb) with R= C n H 2n+1 where 5≤n≤20, preferably 10≤n≤20.

3. Method according to claim 1 or 2, in which the Bc chain blocker is chosen from the compounds of formula (IV): Formula (IV) in which, R 1 identical or different, represents: - a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 8 carbon atoms, optionally substituted by a heteroatom O, N, S or a halide, - an alkenyl group comprising from 2 to 6 carbon atoms, - a cycloalkyl group of 5 to 10 carbon atoms, optionally substituted by a heteroatom O, N, S or a halide, - a C6-C aryl group 18 , - a hydroxyl group, or - a hydrogen R 2 identical or different, represents: -an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl, -a hydroxyl group, -a linear or branched alkyl group comprising from 1 to 12 carbon atoms, preferably from 1 to 5 carbon atoms, optionally substituted by at least one heteroatom O, N, S or a halide such as a fluorine atom, for example 1 to 10 fluorine atoms, or -a hydrogen; and q is an integer between 1 and 50, preferably between 1 and 20, more preferably between 1 and 10.

4. Method according to claim 1 to 3, wherein the amount of Bc chain blocker used in the method of the invention is at least 10 -4 mol per mole of bond (Si-O) in silicone S, preferably between 10 -3 and 5x10 -1 mol, preferably between 10 -3 and 10 -2 mol, even more preferably between 3x10 -3 and 6x10 -1mol per mole of bond (Si-O) in silicone S.

5. Method according to any one of claims 1 to 4, in which the quantity of acid catalyst is between 0.001 and 1% by mass relative to the mass of silicone S, preferably between 0.05 and 1%, more preferably between 0.1 and 1% relative to the mass of silicone S.

6. Method according to any one of claims 1 to 5, in which the organopolysiloxane OR is characterized in that its number-average molecular mass, denoted M n , is between 500 and 300,000 g / mol, preferably between 1,000 and 150,000 g / mol, preferentially between 1,000 and 70,000 g / mol and even more preferentially between 2,500 and 30,000 g / mol.

7. Method according to any one of claims 1 to 6, in which the content of cyclic organopolysiloxanes is less than 5% by mass, preferably less than or equal to 3% by mass, preferentially less than or equal to 2% by mass and even more preferentially less than or equal to 1.5% by mass relative to the total mass of the organopolysiloxanes OR.

8. Method according to any one of claims 1 to 7, wherein the reaction is carried out at a temperature between 0 and 100°C, preferably between 0 and 50°C, more preferably between 10 and 35°.

9. Method according to any one of claims 1 to 8, wherein the reaction is carried out in the presence of an apolar solvent.

10. Method according to any one of claims 1 to 9, characterized in that the mass ratio, mass of silicone S relative to the mass of solvent used, is between 0.01 and 15, preferably between 0.1 and 5, preferentially between 0.1 and 2.

11. Method according to any one of claims 1 to 10, characterized in that it further comprises a step of neutralization of the acid catalyst carried out by the addition of a base to the reaction medium or by thermal degradation of the acid catalyst.

12. Method according to any one of claims 1 to 11, characterized in that it comprises the following steps: 1) Implementation of the process for preparing organopolysiloxanes OR, by a depolymerization reaction of at least one silicone S in the presence of an acid catalyst and at least one chain blocker Bc having at least one siloxane function; 2) Neutralization of the acid catalyst mentioned in the previous step by adding a base to the reaction medium or by thermal degradation of the acid catalyst; and 3) Filtration of the reaction medium obtained at the end of step 2.

13. Use of the organopolysiloxane OR obtained according to any one of the preceding claims as an ingredient in silicone formulations in the field of cosmetics, health, household products, technical industrial formulations, transport such as automobiles or aviation, or in the energy field.

14. Process for the preparation of silicone S, in particular oils, resins, gums or silicone elastomers, comprising the following steps: 1) Implementation of the process for preparing organopolysiloxanes OR according to any one of claims 1 to 12; 2) Preparation of silicone S from the organopolysiloxanes OR obtained in step 1).

15. Process for preparing silicone S according to claim 14, characterized in that step 2 is carried out by a polyaddition, polycondensation, cationic mechanism or radical mechanism reaction.

16. Use of silicone S obtained by the process according to claim 14 or 15 in the field of cosmetics, health, household products, technical industrial formulations, transport such as automobiles or aviation, or in the energy field.

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