Silicone composition for low-temperature applications

Abstract

To provide a silicone material and a method for producing the same, the material being capable of withstanding temperatures well below -100°C and having a tensile yield strength greater than 3 MPa and an elongation at break exceeding 300%, which are required in many space applications such as space exploration missions.SOLUTION: The invention relates to poly(dimethyl-co-diethyl)siloxane of formula (IIIa), poly(methylhydro-co-diethyl)siloxane, a composition for producing silicone rubber comprising the polymers, a silicone rubber obtainable by curing the composition, and use of the silicone rubber in the aerospace industry.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to reinforced silicone rubber and silicone oil compositions that can withstand the extremely low temperatures required for aerospace applications. [Background technology]

[0002] Silicones are organosilicon polymers with a siloxane structure, characterized by silicon atoms bonded to alkyl groups such as ethyl or methyl groups, trifluoromethyl groups, aryl groups, or other functional groups. Silicone rubber compositions derived from poly(dimethylsiloxane), commonly known as PDMS, are known to withstand temperatures down to -60°C. However, many space applications, such as space exploration missions, require silicone materials that can withstand temperatures well below -100°C and have a tensile yield strength (>3 MPa) and elongation at break of over 300%.

[0003] Poly(diethylsiloxane) (PDIES) is the only polymeric material with a glass transition temperature of -142°C. However, pure PDIES exhibits several crystallization / melting transitions between -142°C and 0°C, making it unsuitable for such applications. Silicone crystallization is usually accompanied by its hardening, embrittlement, and loss of elasticity. This can degrade or even fatally impair the mechanical properties of objects for automotive applications, such as space rovers. It is known from the prior art that the addition of small amounts of phenyl, biphenyl, or diethyl groups (less than 10 mol%) to poly(dimethylsiloxane) prevents cold crystallization of dimethylpolysiloxane copolymers. In fact, the majority of currently commercially available silicones for space applications (e.g., from Momentive, Elkem, Nusil, Dow Corning, and IOTA) belong to the poly(biphenyl-co-dimethylsiloxane) or poly(methylphenyl-co-dimethylsiloxane) families. Interestingly, when the biphenyl or methylphenyl content in such copolymers exceeds 10 mol%, the glass transition shifts to higher temperatures, limiting their use at cryogenic temperatures (down to -150 °C). For example, RTV 560, RTV 566, and RTV 567 (methyl-phenyl silicones) sold by Momentive have a glass transition temperature, Tg, of -115 °C, making these materials unsuitable for missions to the lunar south pole. It is important to note that cold crystallization of RTV 566 under 25% strain and prolonged exposure (60 h) at -80 °C increased the modulus from 5 MPa to 240 MPa, which is likely the main cause of mechanical failure and telescope misalignment.

[0004] Currently, there are no commercially available silicones that have a relatively high tensile strength (i.e., greater than 4 MPa), an elongation at break greater than 100%, and low-temperature resistance below -120°C. The only commercially available silicone is sold by Gelest (EDV-2022), which contains 18-22 mol% poly(diethyl)- and 78-82 mol% poly(dimethylsiloxane), and has a Tg of -131°C. However, this material is unsuitable for aerospace applications because it has a relatively low molecular weight (10,000-12,000 g / mol) and may contain cyclic siloxane oligomers that make the material brittle.

[0005] The classical method of silicone synthesis relies on the hydrolysis of dimethyldichlorosilane, resulting in the disilanol H[O-Si(CH3)2] n This produces -OH, hydrochloric acid, and varying amounts of cyclic siloxanes. The hydrochloric acid then acts as a catalyst to condense the disilanols into polydimethylsiloxanes. From there, the silanol-terminated silicones can be polymerized in a variety of ways depending on the desired properties of the final product.

[0006] U.S. Patent No. 4,960,850 describes polycondensation of silanol-terminated polydiorganosiloxane oligomers in the presence of a catalytically effective amount of trifluoromethylsulfonic acid in a sealed reaction zone at a temperature of 20°C to 160°C while continuously removing polycondensation water using a vacuum, and terminating the polycondensation reaction by adding a catalyst-neutralizing amount of cyclopolydiorganosilazane or polydiorganosilazane having diorganoaminosilyl terminal groups to the reaction liquid. However, trifluoromethylsulfonic acid has a boiling point of 162°C, and can be distilled under high vacuum while removing water.

[0007] Controlled molecular weight silicones are obtained by ring-opening polymerization (ROP) of cyclic siloxanes. This is a highly controlled process and is the primary method used in industry. While this process is relatively straightforward for the polymerization of a single cyclosiloxane, it becomes difficult to control when attempting to prepare 1:1 poly(dimethyl-co-diethyl)siloxane by copolymerizing two cyclosiloxanes, such as decamethylcyclosiloxane (D5Me10) and hexaethylcyclosiloxane (D3Et6). The latter is due to the different strains of the monomer molecules in D3Et6 and D5Me10, resulting in different ring-opening rates. Ring-opening requires relatively high reaction temperatures (95–160°C), appropriate anionic initiators, end-capping agents, additives, and pressure-treating reactors. Silicones typically undergo some degree of back-biting, resulting in the production of varying (or fluctuating) amounts of cyclic siloxanes that can be difficult to remove from high-viscosity silicones. Additionally, hexaethylcyclosiloxane is known to preferentially polymerize with itself to form brittle regions in the crosslinked rubber, thereby reducing the mechanical properties of the resulting material.

[0008] Another method for synthesizing polysiloxanes from monomeric silane precursors relies on the polycondensation of silane monomers or oligomers in the presence of a perfluoroarylborane catalyst such as B(C6F5)3 (Michael A. Brooks, J.B. Grande, F. Ganachaud, "New Synthetic Strategies for Structured Silicones Using B(C6F5)3." Adv. Polym. Sci. 2011, 235, 161-183). One advantage of this method, known as the Piers-Rubinsztajn reaction, compared with ROP (which relies on cyclic monomers), is that it can be performed at room temperature and produces far less cyclic product than high-temperature ROP synthesis. However, the main drawback of this method stems from the fact that, while it can be used to synthesize small amounts of silicones (mmol amounts), it is rarely applicable to the synthesis of kg quantities of dimethyl-co-diethyl (1:1) polysiloxane. This is because such reactions are highly exothermic and generate large amounts of gaseous products (typically over 100 liters of H2, CH4, or CH3-CH3 per kg of silicone). Attempting to scale up this reaction clearly poses a serious explosion hazard. Another drawback of using the Piers-Rubinsztajn reaction is the fact that the borane catalyst must be dissolved in a solvent like toluene (heptane causes catalyst precipitation) because water causes catalyst degradation. While viscosity monitoring in solventless silicone synthesis is very simple, since the polymer viscosity can be checked visually or by viscometer at any time, in organic solvents like toluene, it can be difficult to monitor the progress of the reaction. Furthermore, depending on the structure of the silane precursor (i.e., -OH, -OCH3, or -OCH2CH3), the reaction temperature may need to be increased to polymerize the monomer. For example, the reaction of the -OCH3 group of dimethoxydimethylsilane with diethylsilane occurs at 22-23 °C, whereas the conversion of -OCH2CH3 to ethane in the presence of B(C6F5)3 requires 70 °C.

[0009] It is known from the prior art that the rate of hydrolysis of a silane depends on its electronic structure, the solvent used, the presence or absence of a catalyst, and the reaction temperature. For example, the hydrolysis of dichlorodimethylsilane in water occurs even at temperatures close to zero, while diethoxydimethylsilane is stable at 25°C and its hydrolysis requires temperatures above 50°C and ultimately the presence of a suitable acid or base catalyst. Summary of the Invention

[0010] Applicants have discovered that hydrolysis of diethyl, dimethyl, or ethylmethylchlorosilanes at low temperatures (1-7°C) reproducibly produces silanol-terminated poly(dimethyl-co-diethyl)siloxanes or polymethylethylsiloxanes with average molecular weights (Mw) of ∼1000 (viscosities of 33-36 mPa·s). In the presence of an appropriate Lewis acid catalyst, these siloxanes can be easily polymerized to high molecular weight PDIES or PEMS (Mw ∼50,000-100,000) with very low glass transition temperatures and no crystallization / melting transition at low temperatures. This method does not require high reaction temperatures (above 100°C) and produces a relatively rapid viscosity increase (within minutes) while minimizing (ppm) the production of cyclic silicone by-products. The inventive method of PDIES / PEMS synthesis solves the problem of the formation of large amounts of gaseous products (H, methane or ethane) as experienced in the Piers-Rubinsztajn reaction, thus reducing the high exothermicity and explosion hazards mentioned above.

[0011] Another issue that needs to be resolved is the compatibility of crosslinkers with vinyl-terminated PDIES. Generally, phenyl-containing crosslinkers are required for crosslinking phenylsilicones because phase separation and increased foaming occur when using classic methylhydrogenpolysiloxane (PHMS) or dimethyl-co-methylhydrogenpolysiloxane crosslinkers. The applicant has noticed a similar phenomenon with dimethyl-co-diethylpolysiloxane. Extensive foaming was observed when a vacuum was applied to a PDIES / PHMS mixture in the absence or presence of silica. To address this crosslinker / diethylsilicone incompatibility issue, the applicant has synthesized a new type of methylhydrogen-co-diethylsiloxane crosslinker that exhibits excellent compatibility with PDIES.

[0012] The present invention therefore relates to a method for preparing polysiloxanes containing methyl and ethyl groups, said method comprising: Step a) hydrolysis reaction of silanol precursor; Step b) Chain extension of the silanol-terminated siloxane oligomers obtained in step a) by Lewis acid-induced polycondensation by adding a triflate salt catalyst, in particular In(III) triflate, followed by a perfluoroborane catalyst, in particular tris(pentafluorophenyl)borane. Includes:

[0013] Advantageously, the polysiloxane containing methyl and ethyl groups is selected from the group consisting of: poly(dimethyl-co-diethyl)siloxanes or poly(methylhydro-co-diethyl)siloxanes of formula (I): [ka] A represents a methyl group or a hydrogen atom; m and n represent the mole percentages of the repeating motifs -O-Si(Me)(A) and -O-Si(Et), respectively; m=0.5 to 0.8, n=0.2 to 0.5, and m+n=1; p represents the number of both repeating motifs to obtain a weight average molecular weight in the range of 20,000 g / mol to 150,000 g / mol when A represents a methyl group, or in the range of 300 g / mol to 3,500 g / mol when A represents a hydrogen atom. and, poly(ethylmethylsiloxane) of formula (II): [ka] q represents the number of repeat motifs.

[0014] More preferably, the silanol precursor in step a) is selected from among (R1)2 ethylmethylsilane, a mixture of (R1)2 dimethylsilane and (R1)2 diethylsilane, and a mixture of (R1)2 methylsilane and (R1)2 diethylsilane, wherein R1 represents a chlorine atom, a (C1-C6) alkoxy group (preferably a methoxy group or an ethoxy group), an acetoxy group, or an oxime group, preferably R1 represents a chlorine atom, a methoxy group, or an ethoxy group, more preferably R1 represents a chlorine atom.

[0015] In the formulas of the present invention, Me is a methyl group and Et is an ethyl group.

[0016] In the present invention, the terms "included between x and y", "within the range of x to y", "= x to y", and "x to y" are intended to mean that the limits of the range, x and y, are included.

[0017] In the present invention, the term "(C1-C6)alkoxy group" is intended to mean any linear or branched saturated alkoxy group having from 1 to 6 carbon atoms, in particular the OCH3 (methoxy) group and the OCH2CH3 (ethoxy) group.

[0018] The process of the present invention is therefore for producing polysiloxanes containing methyl and ethyl groups, preferably poly(dimethyl-co-diethyl)siloxanes or poly(methylhydro-co-diethyl)siloxanes of formula (I): [ka] Here, A represents a methyl group or a hydrogen atom. m and n represent the mole percentages of the repeating motifs -O-Si(Me)(A) and -O-Si(Et), respectively; m=0.5 to 0.8, n=0.2 to 0.5, and m+n=1; p represents the number of both repeating motifs to obtain a weight average molecular weight ranging from 20,000 g / mol to 150,000 g / mol when A represents a methyl group, and represents the number of both repeating motifs to obtain a weight average molecular weight ranging from 300 g / mol to 3,500 g / mol when A represents a hydrogen atom. The weight average molecular weight of a polymer can be measured using viscometry (in accordance with ASTM E3116-18 standard of January 25, 2018), 1H NMR, and FTIR.

[0019] Advantageously, m=0.5 to 0.7, n=0.3 to 0.5, and m+m=1, more advantageously, m=0.5 to 0.6, n=0.4 to 0.5, and m+m=1, and even more advantageously, m=n=0.5.

[0020] Specifically, the poly(dimethyl-co-diethyl)siloxane of the present invention has the following formula Ia: [ka] where m, n, and p are as defined above.

[0021] The poly(dimethyl-co-diethyl)siloxanes of formula Ia according to the invention advantageously have a weight-average molecular weight, in particular using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018, in the range of 20,000 g / mol to 150,000 g / mol, more advantageously between 30,000 g / mol and 100,000 g / mol, even more advantageously between 40,000 g / mol and 80,000 g / mol, in particular between 45,000 g / mol and 60,000 g / mol.

[0022] Specifically, the poly(methylhydro-co-diethyl)siloxane of the present invention has the following formula Ib: [ka] where m, n, and p are as defined above.

[0023] The poly(methylhydro-co-diethyl)siloxanes of formula Ib according to the invention advantageously have a weight-average molecular weight, in particular using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018, in the range of 300 g / mol to 3500 g / mol, more advantageously between 500 g / mol and 3000 g / mol, and even more advantageously between 1000 g / mol and 2000 g / mol.

[0024] The process of the present invention is also advantageously for producing poly(ethylmethylsiloxane) of formula (II): [ka] Here, q represents the number of repeat motifs.

[0025] Advantageously, the poly(ethylmethylsiloxane) according to the invention has a weight-average molecular weight ranging from 1,000 g / mol to 2,000,000 g / mol, in particular using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018.

[0026] Step a) in the method of the present invention consists of a hydrolysis reaction of a silanol precursor.

[0027] Advantageously, the silanol precursor is selected from among (R1)2 ethylmethylsilane, a mixture of (R1)2 dimethylsilane and (R1)2 diethylsilane, and a mixture of (R1)2 methylsilane and (R1)2 diethylsilane, wherein R1 represents a chlorine atom, a (C1-C6)alkoxy (advantageously a methoxy or ethoxy group), an acetoxy group, or an oxime group, advantageously R1 represents a chlorine atom, a methoxy group, or an ethoxy group, more advantageously R1 represents a chlorine atom.

[0028] Thus, preferably, the silanol precursors are chlorinated or ethoxylated silanol precursors, in particular chlorinated silanol precursors, more preferably selected from dichloroethylmethylsilane, diethoxyethylmethylsilane, a mixture of dichlorodimethylsilane and dichlorodiethylsilane, a mixture of dichloromethylsilane and dichlorodiethylsilane, a mixture of diethoxydimethylsilane and diethoxydiethylsilane, and a mixture of diethoxymethylsilane and diethoxydiethylsilane, and more preferably selected from dichloroethylmethylsilane, a mixture of dichlorodimethylsilane and dichlorodiethylsilane, and a mixture of dichloromethylsilane and dichlorodiethylsilane.

[0029] The product obtained after step a) is an oligomer of siloxanes containing methyl and ethyl groups, in particular (dimethyl-co-diethyl)siloxanes or (methylhydro-co-diethyl)siloxanes or ethylmethylsiloxanes, which advantageously have a weight-average molecular weight of between 500 and 3000 g / mol, in particular using a viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018, and more advantageously a weight-average molecular weight of 1000 to 3000 g / mol when A is methyl.

[0030] Possible reaction schemes for step a) (schemes 1 and 2) are as follows: [ka] [ka] wherein A, m, and n are as defined above, and R1 represents a chlorine atom, a C1-C6 alkoxy group (specifically a methoxy group or an ethoxy group), an acetoxy group, or an oxime group; preferably, R1 represents a chlorine atom, a methoxy group, or an ethoxy group; more preferably, R1 represents a chlorine atom.

[0031] In an advantageous embodiment, step a) is carried out at a temperature between 0°C and 40°C, more advantageously at a temperature between 5°C and 35°C.

[0032] In an advantageous embodiment, the reaction is first carried out at a temperature of 0 to 7°C, advantageously 5 to 7°C, and then the temperature is increased to a range of 30 to 40°C, advantageously 30 to 35°C.

[0033] More preferably, the reaction is carried out with stirring, and even more preferably by adding the silanol precursor to water, particularly dropwise, more preferably at a rate of 1 drop / second to 5 drops / second, particularly at a rate of 3 drops / second.

[0034] In an advantageous embodiment, step a) lasts from 1 to 2 hours.

[0035] In an advantageous embodiment, the molar concentration of water (w) is higher than the molar concentrations of both silanol precursors (a+b): w>a+b

[0036] In a further embodiment, the oligomers obtained in step a) are separated from the aqueous phase comprising HR1, in particular HCl, obtained after carrying out step a), advantageously by heptane extraction, before being used in step b) of the process according to the invention.

[0037] Step b) of the process of the present invention consists in extending the chains of the silanol-terminated siloxane oligomers obtained in step a), preferably poly(dimethyl-co-diethyl)siloxane oligomers or poly(methylhydro-co-diethyl)siloxane oligomers or ethylmethylsiloxa oligomers, by Lewis acid-induced polycondensation by adding a triflate salt catalyst followed by a perfluoroborane catalyst. Advantageously, the polymer obtained after step b) is a polymer of formula I or II as detailed above.

[0038] Advantageously, the triflate salt catalyst is selected from In(III) triflate, Bi(III) triflate, Al(III) triflate, and mixtures thereof, and more advantageously, the triflate salt catalyst is In(III) triflate.

[0039] Advantageously, the perfluoroborane catalyst is tris(pentafluorophenyl)borane.

[0040] The reaction schemes (schemes 3 and 4) of step b) using In(III) triflate and perfluoroborane catalyst are as follows: [ka] where A, m, n, and p are as defined above. [ka] where q is as defined above.

[0041] The polymer of formula (I) is an alternating copolymer.

[0042] The polymer of formula (II) is a homopolymer.

[0043] Advantageously, step (b) is carried out at room temperature (20-25°C).

[0044] In an advantageous embodiment: First, a triflate salt catalyst, in particular In(III) triflate, is added with stirring (step b1), and then the reaction is left to proceed without stirring, advantageously for at least 1 to 12 hours. A perfluoroborane catalyst, in particular tris(pentafluorophenyl)borane, is then added with stirring (step b2), and the reaction is then left to proceed without stirring, advantageously for at least 1 to 12 hours.

[0045] Advantageously, step (b) is carried out in bulk without the use of a solvent.

[0046] In an advantageous embodiment, the triflate salt catalyst, specifically In(III) triflate, is present in an amount of 0.1 mg to 1 mg per gram of oligomer.

[0047] In another advantageous embodiment, the perfluoroborane catalyst, specifically tris(pentafluorophenyl)borane, is present in an amount of 0.1 mg to 1 mg per gram of oligomer.

[0048] In a particular embodiment, step b) is carried out under an inert atmosphere, advantageously under nitrogen.

[0049] The process of the invention may further comprise a step c1) of adding vinyl end groups by reaction of the polymer obtained in step b) with vinyldimethylmethoxysilane or vinyl-1,1,3,3-tetramethyldisiloxane in the presence of a Lewis acid catalyst such as In(III) triflate without a solvent or B(CF) in toluene as solvent or without a solvent, at a temperature between 20 and 60°C, advantageously step c1) provides a polymer having formula (III): [ka] A, m, n, and p are as defined in Formula I; R2=-Si(CH3)2CH=CH2: or a polymer having formula (IV): [ka] q is as defined in Formula II, and R2 = -Si(CH3)2CH=CH2: This is to obtain

[0050] The polymer of formula (III) is an alternating copolymer.

[0051] The polymer of formula (IV) is a homopolymer.

[0052] Thus, the polymer obtained in step c1) Poly(dimethyl-co-diethyl)siloxane having the formula (IIIa): [ka] R2, m, n, and p are as defined in Formula III. Or, Poly(methylhydro-co-diethyl)siloxane having the formula (IIIb): [ka] R2, m, n, and p are as defined in Formula III. It could be.

[0053] The polymers of formula (IIIa) and formula (IIIb) are alternating copolymers.

[0054] Advantageously, the poly(dimethyl-co-diethyl)siloxane of formula (IIIa) has a glass transition temperature (Tg) measured by DSC in accordance with ASTM E1356 standard of May 15, 2014, in the range of −130° C. to −142° C., in particular in the range of −135° C. to −141° C., more particularly −139° C.

[0055] The polysiloxanes of formula (IIIa) more advantageously have a weight-average molecular weight, in particular using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018, in the range of 20,000 g / mol to 150,000 g / mol, even more advantageously between 30,000 g / mol and 100,000 g / mol, even more advantageously between 40,000 g / mol and 80,000 g / mol, in particular between 45,000 g / mol and 50,000 g / mol.

[0056] Advantageously, the poly(methylhydro-co-diethyl)siloxane of formula (IIIb) has a glass transition temperature (Tg) measured by DSC according to ASTM E1356 standard of May 15, 2014, in the range of −130° C. to −146° C.

[0057] The polysiloxane of formula (IIIb) more advantageously has a weight-average molecular weight, in particular using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018, in the range of 300 g / mol to 3500 g / mol, more advantageously between 500 g / mol and 3000 g / mol, and even more advantageously between 1000 g / mol and 2000 g / mol.

[0058] Advantageously, the poly(ethylmethylsiloxane) siloxane of formula (IV) has a glass transition temperature (Tg) measured by DSC according to ASTM E1356 standard of May 15, 2014, in the range of -130°C to -142°C.

[0059] The polysiloxane of formula (IV) more advantageously has a weight-average molecular weight in the range of 20,000 g / mol to 200,000 g / mol, advantageously in the range of 20,000 g / mol to 150,000 g / mol, in particular using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018.

[0060] The reaction schemes of step c1) (schemes 5 and 6) are as follows: [ka] where R2, A, m, n and p are as defined above. [ka] where R2 and q are as defined above.

[0061] In certain embodiments, the Lewis acid catalyst is a triflate salt, advantageously selected from among In(III) triflate, Bi(III) triflate, Al(III) triflate, and mixtures thereof, more advantageously In(III) triflate, and step c1) is carried out without a solvent, more advantageously at a temperature between 50° C. and 70° C., and even more advantageously the catalyst is present in an amount of 0.1 mg to 2 mg per gram of polymer.

[0062] In another particular embodiment, the Lewis acid catalyst is a perfluoroborane catalyst such as B(C6F5)3 and step c1) is carried out without a solvent or with toluene as solvent, more preferably at room temperature (20-25°C), and even more preferably the catalyst is present in an amount of 0.1 mg to 1 mg per gram of polymer.

[0063] In a more particular embodiment, the Lewis acid catalyst is a mixture of a triflate salt and perfluoroborane, advantageously a mixture of In(III) triflate and B(C6F5)3, step c1) is carried out without the use of a solvent, more advantageously at room temperature (20-25°C), and even more advantageously the catalyst is present in an amount of 0.1 mg to 1 mg per gram of polymer.

[0064] In a more particular embodiment, when step c1) is carried out, the catalyst used in step b) is not removed and perfluoroborane, in particular B(CF) is further added. Advantageously, step c1) is carried out without the use of a solvent and more advantageously at room temperature.

[0065] The process of the invention may comprise a step c2) of adding trialkylsilyl end groups by reaction of the polymer obtained in step b) with a trialkylsilane, in particular trimethylsilane or triethylsilane, more particularly triethylsilane, in the presence of a Lewis acid catalyst such as B(CF) in toluene as solvent, which step c2) advantageously gives a polymer having formula (V): [ka] A, m, n, and p are as defined in Formula I; Each R3 is independently a saturated, linear, or branched C1-C6 alkyl group, preferably an ethyl group: or a polymer having formula (VI): [ka] q is as defined in Formula II; Each R3 is independently a saturated, straight-chain, or branched C1-C6 alkyl group: This is to obtain

[0066] In the present invention, the term "(C1-C6) alkyl group" is intended to mean any linear or branched saturated alkyl group having from 1 to 6 carbon atoms, in particular the CH3 (methyl) group and the CH2CH3 (ethyl) group.

[0067] The polymer of formula (V) is a silicone oil and is an alternating copolymer. The polymer of formula (VI) is a silicone oil and is a homopolymer.

[0068] Advantageously, the poly(dimethyl-co-diethyl)siloxane of formula (IVa) has a glass transition temperature (Tg) measured by DSC in accordance with ASTM E1356 standard of May 15, 2014, in the range of −130° C. to −145° C., in particular in the range of −135° C. to −142° C., more particularly −136° C.

[0069] More preferably, the siloxane has a weight average molecular weight in the range of 40,000 g / mol to 65,000 g / mol, and even more preferably between 45,000 g / mol and 55,000 g / mol, using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018.

[0070] Advantageously, the poly(ethylmethyl)siloxane of formula (VI) has a glass transition temperature (Tg) in the range of −130° C. to −142° C., measured by DSC according to ASTM E1356 standard of May 15, 2014.

[0071] More advantageously, the siloxane has a weight average molecular weight in the range of 20,000 g / mol to 150,000 g / mol, measured by viscosity measurement according to standard ASTM E3116-18 of January 25, 2018.

[0072] The reaction schemes (schemes 7 and 8) of step c2) are as follows: [ka] where R3, A, m, n and p are as defined above. [ka] where R3 and q are as defined above.

[0073] In another particular embodiment, the Lewis acid catalyst is a perfluoroborane catalyst such as B(C6F5)3 and step c2) is carried out without a solvent or with toluene as solvent, more advantageously at room temperature (20-25°C), and even more advantageously the catalyst is present in an amount of 0.1 mg to 1 mg per gram of polymer.

[0074] In another particular embodiment, the process of the invention further comprises, after step c1) or c), a step d) of removing the catalyst used in steps b) and c1) or in step c), advantageously using aluminium oxide.

[0075] Advantageously, the process of the invention is for producing 50 / 50 poly(dimethyl-co-diethyl)siloxane or 50 / 50 poly(methylhydro-co-diethyl)siloxane.

[0076] The present invention also relates to poly(dimethyl-co-diethyl)siloxanes of formula (IIIa) as defined above, which siloxanes are advantageously obtainable by the process of the invention and which more advantageously have: a weight-average molecular weight, using the viscosity measurement method according to standard ASTM E3116-18 of 25 January 2018, in the range of 20,000 g / mol to 150,000 g / mol, more preferably between 30,000 g / mol and 100,000 g / mol, even more preferably between 40,000 g / mol and 80,000 g / mol, in particular between 45,000 g / mol and 50,000 g / mol; and / or a glass transition temperature measured by DSC in accordance with ASTM E1356 standard of May 15, 2014, in the range of -130°C to -142°C, specifically in the range of -135°C to -141°C, more specifically -139°C;

[0077] The polymer of formula (IIIa) is an alternating copolymer.

[0078] The present invention also relates to poly(methylhydro-co-diethyl)siloxanes of formula (IIIb) as defined above, which are advantageously obtainable by the process of the invention and which more advantageously have: a weight-average molecular weight, using the viscosity measurement method according to standard ASTM E3116-18 of January 25, 2018, in the range of 300 g / mol to 3500 g / mol, more preferably between 500 g / mol and 3000 g / mol, even more preferably between 1000 g / mol and 2000 g / mol; and / or - A glass transition temperature measured by DSC in accordance with ASTM E1356 standard of May 15, 2014, is in the range of -130°C to -146°C.

[0079] The polymer of formula (IIIb) is an alternating copolymer.

[0080] The present invention also relates to poly(dimethyl-co-diethyl)siloxanes of formula (V) as defined above, which siloxanes are advantageously obtainable by the process of the invention and which more advantageously have: - a weight-average molecular weight, using the viscosity measurement method according to standard ASTM E3116-18 of 25 January 2018, in the range of 500 g / mol to 150 000 g / mol, advantageously between 1 000 g / mol and 3 000 g / mol; and / or a glass transition temperature measured by DSC in accordance with ASTM E1356 standard of May 15, 2014, in the range of -130°C to -145°C, specifically in the range of -135°C to -142°C, more specifically -139°C;

[0081] The polymer of formula (V) is an alternating copolymer.

[0082] The polymer of formula (V) is a silicone oil.

[0083] The present invention also relates to a composition for making silicone rubber, the composition comprising: (A) 60 to 94% by weight of vinyl-terminated poly(dimethyl-co-diethyl)siloxane of formula (IIIa) according to the invention; - (B) a reinforcing filler, advantageously 5 to 35% by weight of pyrogenic silica; (C) 1 to 5% by weight of a crosslinker having a Tg<-130°C, advantageously having formula (IIIb) according to the invention; (D) a suitable amount of a curing catalyst, advantageously a Pt(0) catalyst such as platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane dissolved in methylvinylcyclosiloxane, and (E) optionally a Pt inhibitor such as 1-ethynyl-1-cyclohexanol

[0084] In this specification, the term "silicone rubber" is understood to mean a substance capable of maintaining elasticity in the temperature range of 200 to -140°C.

[0085] The respective amounts of compound (A) (vinyl-terminated poly(dimethyl-co-diethyl)siloxane of formula (IIIa)) and compound (C) (crosslinker) in the compositions of the present invention are determined by the ratio of the number of (R'HSiO2 / 2) units to the number of alkenyl groups, and are adjusted taking into account the relative proportion of alkenyl moieties in compound (A) and the relative proportion of (R'HSiO2 / 2) units in compound (C).

[0086] An essential feature of the silicone rubber composition of the present invention is the ratio of the number of units (R'HSiO2 / 2) in compound (C) introduced into the silicone base composition to the number of diethyl groups in compound (A) introduced into the rubber composition. According to the present invention, this ratio of the number of units (R'HSiO2 / 2) to the number of alkenyl groups is greater than 3. If this ratio value is 3 or less, the composition will have insufficient mechanical and adhesive properties for use as a self-adhesive PDIES silicone on metal surfaces such as stainless steel or titanium.

[0087] Advantageously, this ratio is greater than 4 and less than 25.

[0088] The curing catalyst is a hydrosilylation catalyst, specifically a platinum (Pt(0)) catalyst, more specifically complexed with a divinyltetraalkylsiloxane ligand, preferably 1,3-divinyltetramethylsiloxane, such as platinum (0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane dissolved in methylvinylcyclosiloxane. Such catalysts are described, for example, in WO 0142258 A1. Karstedt's catalyst is most particularly suitable. As in conventional hydrosilylation reactions, the amount of catalyst in the composition is catalytic. By catalytic amount, we mean less than 1 molar equivalent of platinum relative to the amount of olefinic double bond unsaturation present in the composition. Generally, it is sufficient to incorporate less than 1000 ppm, preferably more than 30 ppm, of platinum based on the total mass of compound (A) and compound (C).

[0089] Reaction design of compound (C) (R'HSiO 2 / 2 The hydrosilylation of the alkenyl groups of compound (A) and compound (B) causes crosslinking of the organopolysiloxane, producing a crosslinked silicone rubber composition. Crosslinking is typically initiated by subjecting the silicone rubber composition to a temperature sufficient to cause the hydrosilylation reaction. Crosslinking is typically carried out at temperatures between 15°C and 200°C, e.g., between 20°C and 150°C, and more preferably between 50°C and 150°C.

[0090] In known methods, crosslinkable silicone compositions generally contain an inhibitor. Inhibitors are generally used to control the temperature and time of the hydrosilylation crosslinking reaction, thereby further controlling the crosslinking reaction, particularly its initiation and rate. When a crosslinking inhibitor is used, the amount of inhibitor used is preferably 1 to 50,000 ppm, more preferably 20 to 2000 ppm, and particularly 100 to 1000 ppm, based on the total mass of compound (A) and compound (C). Examples of inhibitors include acetylene alcohols such as 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol, 3-methyl-1-dodecyn-3-ol, and 2-phenyl-3-butyn-2-ol. Preferably, the silicone rubber composition of the present invention contains an inhibitor.

[0091] The silicone rubber composition of the present invention also has the essential feature of containing a reinforcing filler, advantageously hydrophobic silica, specifically pyrogenic silica. In a known manner, the hydrophobic silica is silica whose surface is partially coated with organic groups such as alkyl groups. The silica may be any reinforcing silica known to those skilled in the art, specifically any precipitated silica or pyrogenic silica. Preferably, the silica is 450 ml 2 / g, preferably 80 to 400m 2 / g, particularly preferably 100 to 300m 2 / g, advantageously 150 to 250 m 2 / g。 It is also possible to use a mixture of silicas, such as Aerosil R 8200, Aerosil R 812 S, Aerosil E 9200 from Evonik or Cab-O-Sil TS 530 from Cabot.

[0092] It is well known that silica surface modification can be used to make silica hydrophobic.The surface modification of silica can be achieved by reacting silica with a compound having a hydrophobic group such as a trialkylsilyl group, specifically a trimethylsilyl group, in a known manner.Particularly suitable is silica surface-modified with a trimethylsilyl group.For example, silica modified with hexamethyldisilazane can be mentioned.

[0093] The content of hydrophobic silica can be adjusted by those skilled in the art depending on the specific surface area and the application of the silicone rubber composition. Preferably, the content of hydrophobic silica in the silicone rubber composition is 5% or more and 35% or less of the total weight of silica, compound (A), and compound (C). If the content of hydrophobic silica is less than 5% of the total weight of silica, compound (A), and compound (C), the reinforcing properties of the composition may be insufficient for certain applications. If the content of hydrophobic silica exceeds 35% of the total weight of silica, compound (A), and compound (C), it may become impossible to compound the silicone rubber (such as the solid paste obtained when using Wacker silica HDK H2000 or when using more than 20% by weight of Cab-O-Sil TS 530, Aerosil R 8200, or Aerosil E 9200).

[0094] The silicone rubber composition of the present invention can be prepared by blending the hydrophobic silica with compound (A), then adding compound (C) while mixing, and finally adding the catalyst. If an inhibitor is used, it is usually added to the mixture of hydrophobic silica and compound (A) before blending compound (C).

[0095] The present invention also relates to silicone rubbers obtainable by curing the compositions according to the invention, which, as described above, have a glass transition temperature in the range of −130° C. to −142° C., advantageously in the range of −135° C. to −140° C., in particular −138° C., measured by DSC in accordance with ASTM E1356 standard of May 15, 2014, and / or do not have a crystallization / melting transition in the range of −140° C. to +250° C., measured by DSC in accordance with ASTM E1356 standard of May 15, 2014.

[0096] More advantageously, the silicone rubber according to the invention has an elongation at break (measured on an INSTRON 34™-10, France, using the AFNOR NF T 46002 standard, H2, September 1988) of at least 100%, in particular at least 200%, more particularly at least 300%, for example 348%.

[0097] Furthermore, the silicone rubber according to the invention preferably has a modulus of elasticity measured by French INSTRON 34TM-10 according to the AFNOR NF T 46002 standard of September 1988 of >1 MPa, preferably >3 MPa.

[0098] More preferably, the silicone rubber according to the invention has a Shore A durometer hardness measured in accordance with the ASTM D2240 standard of July 23, 2021, in the range of 35 to 40.

[0099] The present invention also relates to the use of the silicone rubber or poly(dimethyl-co-diethyl)siloxane of formula (V) according to the present invention in the aerospace industry, in particular in space probes. More specifically, the present invention also relates to the use of the poly(dimethyl-co-diethyl)siloxane of formula (V) according to the present invention as a silicone oil for electric motors at low temperatures, in particular below -100°C.

[0100] The invention finally relates to the use of poly(methylhydro-co-diethyl)siloxanes having formula (IIIb) according to the invention as crosslinkers for preparing silicone rubbers.

[0101] The aforementioned and other features of the invention will be better understood on reading the following description of some exemplary embodiments of the invention, given by way of illustration and without limitation. [Example]

[0102] Example 1: Synthesis of poly(diethyl-co-dimethyl)siloxane (50 / 50) (PDIES-50 / 50) <Process 1 (Process a)> First, 1 kg of dichlorodiethylsilane (SID3402.0-1KG, Gelest, USA) was distilled at 40-50°C and a vacuum of 20 mbar into a 2 L flask cooled to -79°C using dry ice. The obtained silane was a transparent liquid.

[0103] The synthesis of poly(diethyl-co-dimethyl)siloxane (50 / 50) was carried out without prior oxygen removal from water. An 8 L glass cylinder was placed in an ice bath (polypropylene box) and cooled to 0–5°C. The reactor was equipped with a bubbler to monitor final gas evolution. Deionized water (3.7 L) was added to the glass reactor, cooled to 5°C in an ice bath. The agitation was set to 200 rpm. Next, 306 g of diethyldichlorosilane and 251.37 g of dichlorodimethylsilane (ThermoScientific, lot A0439125) were added to a glass column equipped with a Teflon valve (the glass was dried under vacuum at 100°C and maintained under a slight N2 flow). The silanes were mixed using a Teflon bar and added dropwise to the 3.7 L of water at a rate of approximately 3 drops per second. The temperature of the reaction mixture was maintained at 5–7°C. Silane hydrolysis was carried out at 300 rpm for 2 hours.

[0104] The reactor was then placed in a polypropylene water bath heated to 40°C, and the reaction mixture was allowed to reach a temperature of 30-35°C. The silanol was stirred at 300 rpm for an additional 2 hours. Then, 1.5 L of heptane was added to separate the silanol from the aqueous phase, and an HCl (aq) solution was pumped below the silanol oligomer layer using a silicone tube (slight vacuum). The silanol oligomer was extracted with 1 L of heptane, and the reactor and separatory funnel (500 ml) were washed with an additional 1.5 L of heptane. The silanol oligomer was dried by adding 25 g of MgSO4 and stirring at 200 rpm. The wet MgSO4 was filtered, and the silanol oligomer was stored overnight in 2 L of heptane under nitrogen. The organic solvent was removed under vacuum using a rotary evaporator at 90°C. The yield was 85% (313.2 g of silanol oligomer (theoretical value: 369.4 g). Viscosity according to ASTM E3116-18 standard dated January 25, 2018: 35 mPa s (Viscosimeter Model: VSC-N4 (Bioevopeak, China) Measurement range: 20 to 2,000,000 mPa s).

[0105] The silanol was placed in a 2 L glass flask and heated (air, no vacuum) to 145°C for 120 minutes. After 2 hours at 145°C, it was cooled to 25°C (thermostat) and the viscosity was measured. The viscosity was 38 mPa.s. The silanol was purged with nitrogen, sealed in a 1 L container with a silicone septum, and stored at -20°C (to prevent further condensation with water).

[0106] <Process 2 (Process b)> 298 g of the silanol oligomer obtained in step 1 was heated to 145°C for 15 minutes and, while hot, subjected to vacuum (<2 mbar) for 30 minutes until no more bubbles were observed. The silanol oligomer was then poured hot into a dry 1 L flask equipped with a silicon septum, a magnetic stirrer, and nitrogen flow. Subsequently, 35 mg of indium(III) triflate per 100 g of silanol oligomer was added under nitrogen flow. The catalyst was dispersed in the silanol oligomer by stirring at 500 rpm. The reaction was then allowed to proceed overnight (17 hours) in a sealed vessel without stirring. An increase in viscosity was observed. The next day, 57 mg of tris(pentafluorophenyl)borane catalyst (Sigma-Aldrich, #442593) was added under nitrogen, mixed at 500 rpm for 5 minutes, and the reaction was allowed to proceed for an additional 24 hours.

[0107] <Process 3 (Process c)> 35 mg of tris(pentafluorophenyl)borane catalyst (Sigma-Aldrich, #442593) was added to the reaction mixture, followed by 1.5 ml of vinyldimethylmethoxysilane (AB106075, ABCR, Germany). The reaction mixture was stirred for 5 minutes and then allowed to continue for an additional 5 hours without stirring. Finally, the reaction mixture was transferred to a rotary evaporator, and excess vinyldimethylmethoxysilane and other volatiles were removed at 95°C and a vacuum of 30 mbar.

[0108] <Step 4. Catalyst removal (step d)> The siloxane polymer obtained in step 3 was cooled to room temperature, and 150 g of neutral aluminum oxide (#199974, Sigma Aldrich) was added along with 600 ml of heptane. The suspension was stirred at 300 rpm for 20 minutes. The solids were then removed by filtration through a ceramic filter with a porosity of 2, then a porosity of 4, and finally a 0.45 μm PTFE filter. The solvent was removed using a rotary evaporator by heating to 95°C and reducing the vacuum to 30 mbar. Finally, the siloxane polymer was heated at 150°C for 1 hour under a vacuum of <1 mbar (vacuum oven). No significant mass loss was measured by DSC between -80 and 200°C.

[0109] Viscosity according to ASTM E3116-18 standard of January 25, 2018: 4012 mPa.s, Mw=45000 g / mol (Viscosimeter Model: VSC-N4 (Bioevopeak, China) Measurement range: 20~2,000,000 mPa.s).

[0110] DSC of this material according to ASTM E1356 standard of May 15, 2014 showed Tg = -139 °C (2 °C / min, N2) (Model: DSC 3, Mettler Toledo, Switzerland).

[0111] The polydispersity index (PD) measured by GPC was 1.63.

[0112] The GPC conditions are as follows: GPC (gel permeation chromatography): Agilent 1260 Infinity connected to a 390-MDS detector (Agilent, USA) Refractive index detector: 1260 Infinity RID (Agilent, USA) The heating unit is a Mistral column oven (Spark, Netherlands). Column set consists of: 1x Precolumn PSS SDV (PSS / Agilent) 2 columns: PSS Linear XL for SDV analysis (PSS / Agilent) The polymer samples were dissolved in 1 mL of toluene before injection. Toluene, HPLC Plus, for HPLC (#650579-1L, Merck) Experimental conditions: - Eluent: toluene - Flow rate: 1mL / min - Temperature: 35℃

[0113] Calibration was a conventional calibration of polystyrene narrow band standards from 682 to 130,000 g / mol.

[0114] The software used for Mw calculation was Cirrus GPC Software (Agilent, USA).

[0115] Example 2: Silicone compounding example for producing silicone rubber 50g siloxane polymer with a molecular weight of 45500g / mol (synthesized in steps 1 to 4 above) 15g SiO2 (HDK H2000, Wacker Germany) 7g 1-ethynyl-1-cyclohexanol, 99% (E51406, Sigma-Aldrich) (Pt inhibitor) 140 mg Pt catalyst* (Platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane complex solution (Sigma Aldrich, #479543) 1.35g HMS-H271 crosslinker (Gelest, USA) (25-30% methylhydro)-dimethylsiloxane copolymer, hydride terminated, 24-60cSt)

[0116] The components were mixed using a mixer at 2000 rpm and cured at 150°C / 1 hour or at room temperature for 24 hours.

[0117] The elastic cross-linked silicone rubber (30 wt% SiO2) had a Tg of -138°C and showed no crystallization or melting between -150°C and +250°C as measured by a DSC (Model: DSC 3, Mettler Toledo, Switzerland) in accordance with ASTM E1356 standard dated May 15, 2014. Shore A hardness: 35-40 (measured using an HBA100-0 (Kern, Switzerland) in accordance with ASTM D2240-15 standard dated July 23, 2021). Elongation at break: 348% (measured using an INSTRON 34TM-10, France, in accordance with AFNOR NF T 46002 standard dated September 1988, H2).

[0118] Example 3: Triethylsilyl-terminated poly(dimethyl-co-diethyl)siloxane (50 / 50) silicone oil Step (a): Hydrolysis A 1 L flask equipped with four inlets, a condenser, a side arm, a vent outlet, and a magnetic stirrer was filled with 370 ml of deionized water. The apparatus was then cooled to 5°C, and 30.0 g of dichlorodiethylsilane (Gelest, SID3402.0, Gelest) and 24.6 g of dichlorodimethylsilane (ThermoScientific, #113312500), both cooled to 5°C and mixed, were added dropwise over 1 hour (at a rate of 3 drops per second). The reaction mixture was stirred at 600 rpm. The reaction temperature was then increased to 30°C and stirred for an additional hour. 500 ml of heptane was added, and the silicone was separated from the aqueous phase in a separatory funnel. The organic phase was washed with deionized water until the pH was neutral.

[0119] The reaction product in heptane was transferred to a 1 L flask, and the remaining water was dried over 50 g of anhydrous MgSO4. The product was filtered using a P4 porosity ceramic filter and a 0.45 μm PTFE microfilter. The heptane and volatiles were removed using a rotary evaporator at 90°C / vacuum up to 18 mbar. Further vacuum at room temperature to 1 mbar revealed no volatiles.

[0120] Step (b): Chain extension The product was transferred to a dry 100 ml round-bottom flask equipped with a magnetic stirrer under nitrogen flow. Next, 14 mg of In(III) triflate was added and stirred for 30 minutes. This was followed by the addition of 14 mg of tris(pentafluorophenyl)borane catalyst (Sigma-Aldrich, #442593) dissolved in 2 ml of anhydrous toluene (Sigma-Aldrich, #244511). The reaction was stirred for an additional 30 minutes.

[0121] Process (c2): Finally, 5 ml of triethylsilane (Sigma 230197-25G) and 6.5 mg of tris(pentafluorophenyl)borane were dissolved in 1 ml of toluene. The solution was stirred for 30 minutes until bubbling ceased. The catalyst was adsorbed onto 25 g of neutral Al2O3 with constant stirring at 400 rpm. After stirring the reaction for 10 minutes, 200 ml of heptane was added, and the suspension was filtered through ceramic P2 and P4 filters, followed by a 0.45 μm PTFE microfilter. The solvent was evaporated at 90 °C / 20 mbar vacuum, followed by a vacuum of <1 mbar at room temperature. The product was characterized by FTIR and Raman spectroscopy. The glass transition, Tg = -140 °C, was measured by DSC at a rate of 2 °C / min under nitrogen flow.

[0122] Example 4: Triethylsilyl-terminated poly(methylhydro-co-diethyl)siloxane (50 / 50) silicone oil (crosslinker) Step a): Hydrolysis A 1 L flask equipped with four inlets, a condenser, a side arm, a vent outlet, and a magnetic stirrer was purged with a slight nitrogen flow at 25° C. Next, 22 g of diethyldiethoxysilane (Gelest, SID3404) and 16.8 g of methyldiethoxysilane (Sigma-Aldrich, #66612) were added with constant stirring at 400 rpm.

[0123] Steps b) and c1) Finally, 7.5 mg of In(III) triflate catalyst was added directly to the monomer mixture using a Pasteur pipette, followed by the addition of 11 ml of deionized water (3 x 3 ml + 2 ml) at 10 min intervals via pipette while stirring at 400 rpm at 29 °C. After 1 h of stirring, the reaction mixture was transferred to a 250 ml flask, and 25 g of anhydrous MgSO was added to dry the water. The product was dissolved in 100 ml of heptane, filtered using a 0.45 μm PTFE filter, and the volatiles / solvent were removed using a rotary evaporator at 80 °C and a vacuum of 35 mbar. Further reduction to a vacuum of 1 mbar at room temperature revealed no volatiles.

[0124] To the reaction product from the previous step, 7 mg of tris(pentafluorophenyl)borane catalyst (Sigma-Aldrich, #442593) dissolved in 1 ml of anhydrous toluene (Sigma-Aldrich, #244511) and 5 ml of triethylsilane (Sigma-Aldrich, #230197-25G) was added under N2 flow and constant stirring at 400 rpm. The solution was stirred for 30 min until bubbling ceased. The borane catalyst was adsorbed onto 25 g of neutral Al2O3. After stirring (magnetic Teflon stir bar) for 10 min, 100 ml of heptane was added, and the suspension was filtered through ceramic P2 and P4 filters, followed by a 0.45 μm PTFE microfilter. The solvent was evaporated at 90 °C / 20 mbar vacuum, and then at room temperature under a vacuum of <1 mbar. The product (a clear liquid) was characterized by FTIR and Raman spectroscopy. The glass transition Tg = -144.7°C was measured by DSC at a rate of 2°C / min under nitrogen flow.

[0125] Example 5: Synthesis of poly(ethyl-co-methylsiloxane)-PEMS Step a (hydrolysis) Ethylmethyldichlorosilane (#AB111135, ABCR Germany) was used as received (purity 97%) and appeared as a clear pink liquid.

[0126] This synthesis was carried out in an air atmosphere. A 20 L glass reactor was cooled to 5 °C. A 1 L side arm, equipped with a bubbler, was used for the dropwise addition of the silanes and maintained under a slight nitrogen flow during the silane addition. Deionized water (1.4 L) was cooled and maintained at 4-6 °C during the chlorosilane addition. The stirring was set to 200 rpm. First, 213.0 g (instead of 210 g) of ethylmethyldichlorosilane was added dropwise (3 drops per second) to 1.4 L of water. The temperature of the reaction mixture was then gradually increased to 30 °C and stirred at 200 rpm for 2 hours and 30 minutes. A transparent silanol layer formed on the water surface.

[0127] The silanol was extracted with 1.25 L of heptane and dried with 250 g of MgSO4. The heptane was removed using a rotary evaporator at 90-95 °C, followed by further vacuum at room temperature to 1 mbar. The resulting silanol had a viscosity of 31.7 mPa.s. The silanol in the 1 L round-bottom flask was then placed in an oven at 145 °C for 20 minutes. The silanol was allowed to cool to room temperature. Subsequently, 100 mg of indium(III) triflate was added with constant stirring at 200 rpm. The silanol was then polymerized over the weekend. 115.0 g of silicone (theoretical value: 131.83 g) was obtained, representing a yield of 87%.

[0128] Step b (chain extension) 50 g of the PEMS silanol obtained in step a) was mixed with 50 mg of In(III) triflate (#422151, Sigma-Aldrich) and stirred at 200 rpm for 5 minutes, then polymerized over the weekend (without stirring). Water and volatiles were then removed from the silicone using a rotary evaporator at 95°C under a vacuum of 30 mbar. The silanol was then mixed with 125 g of anhydrous MgSO4 and dissolved in 400 ml of heptane. The solid was filtered through a P4 ceramic filter, and the heptane was distilled off at 95°C. The silanol was heated at 145°C for 10 minutes under a vacuum of 1 mbar. The silanol was then cooled to room temperature, and 25 mg of tris(pentafluorophenyl)borane was added, followed by 2 ml of toluene. The mixture was mixed for 2 minutes and placed in a 1 L flask sealed with a silicon septum under a N2 atmosphere (without stirring). The silanol was left to polymerize overnight.

[0129] Process c1 The silanol obtained in step b was heated to 95°C under a vacuum of 25 mbar to remove water and volatiles. Next, 0.33 g of vinyl-1,1,3,3-tetramethyldisiloxane 98% (SIV9097.5, Gelest, USA) and 25 mg of tris(pentafluorophenyl)borane 95% (#442593, Sigma-Aldrich) were added, followed by 2 ml of toluene. The silicone was mixed at 200 rpm for 5 minutes and allowed to react at 25°C for 2 hours. Finally, a vacuum line was connected, and the volatiles were removed at 95°C under a vacuum of 30 mbar. The silicone was diluted with 200 ml of hexane and mixed with 25 g of Al2O3 (neutral alumina), and the suspension was stirred for 10 minutes. The catalyst adsorbed on the alumina was removed by filtration through a ceramic P4 filter and then through a 0.45 μm PTFE microfilter. The solvent was removed using a rotary evaporator at 95°C and the polymer was transferred to a dry 250 ml glass flask and subjected to 150°C and then 170°C (20 min each) under a vacuum of 1 mbar. The viscosity was 5500 mPa.s.

[0130] The resulting material was analyzed by DSC at 2°C / min under N2, yielding a Tg of -141°C. FTIR and Raman analyses indicated the absence of cyclic products. The FTIR and Raman spectra of the product were consistent with the PEMS spectrum calculated using B3LYP / 6-311G (d,p) level (Gaussian 16).

[0131] Viscosity according to ASTM E3116-18 standard of January 25, 2018: 25 mPa.s, Mw=2000 g / mol (Viscosimeter Model: VSC-N4 (Bioevopeak, China) - measurement range: 20~2,000,000 mPa.s).

[0132] The polydispersity index (PD) measured by GPC was 2.41. The GPC conditions were the same as in Example 1.

[0133] Crosslinking: 5 g of PEMS silicone (step c1), 1.5 g of SiO2 (HDK H2000), 14 mg of Pt(0) tetravinylcyclotetrasiloxane (Sigma Aldrich, #479543), 135 mg of HMS H271 (Gelest, USA) at 35 °C / overnight, then at 150 °C for 20 min.

[0134] The elastic cross-linked silicone rubber had a Tg of -139°C, and neither crystallization nor melting occurred between -139 and +250°C.

[0135] No crystallization of silicone was observed from +25 to -130°C at 2°C / min under N2 atmosphere.

Claims

1. A polysiloxane containing methyl and ethyl groups and having the following formula (III): 【Chemical 1】 R 2 = -Si(CH 3 ) 2 CH=CH 2 and A represents a methyl group or a hydrogen atom; m and n are the repeating motifs -O-Si(Me)(A) and -O-Si(Et), respectively. 2 represents the mole percentage of m=0.5 to 0.8, n=0.2 to 0.5, and m+n=1; p represents the number of both repeating motifs to obtain a weight average molecular weight in the range of 20,000 g / mol to 150,000 g / mol when A represents a methyl group, or in the range of 300 g / mol to 3,500 g / mol when A represents a hydrogen atom; Polysiloxane.

2. Poly(dimethyl-co-diethyl)siloxane, having the following formula (IIIa): 【Chemistry 2】 R 2 , m, n, and p are as defined in Formula III; - has a weight average molecular weight in the range of 20,000 g / mol to 150,000 g / mol, and - has a glass transition temperature in the range of -130°C to -142°C, The polysiloxane of claim 1.

3. Poly(methylhydro-co-diethyl)siloxane, having the following formula (IIIb): 【Chemistry 3】 R 2 , m, n, and p are as defined in Formula III; - has a weight average molecular weight in the range of 300 g / mol to 3500 g / mol, and - has a glass transition temperature in the range of -130°C to -146°C, The polysiloxane of claim 1.

4. (A) 60 to 94% by weight of vinyl-terminated poly(dimethyl-co-diethyl)siloxane of formula (IIIa) according to claim 2; (B): reinforcing filler, preferably 5 to 35% by weight of pyrogenic silica; (C): 1 to 5% by weight of a crosslinker having a Tg of <-130°C; (D): a suitable amount of a curing catalyst, preferably a Pt(0) catalyst such as platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane dissolved in methylvinylcyclosiloxane, and (E): optionally an inhibitor such as 1-ethynyl-1-cyclohexanol; Including, A composition for producing silicone rubber.

5. (A) 60 to 94% by weight of vinyl-terminated poly(dimethyl-co-diethyl)siloxane of formula (IIIa) according to claim 2; (B): reinforcing filler, preferably 5 to 35% by weight of pyrogenic silica; (C): 1 to 5% by weight of a crosslinker having Tg<-130°C and formula (IIIb); (D): a suitable amount of a curing catalyst, preferably a Pt(0) catalyst such as platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane dissolved in methylvinylcyclosiloxane, and (E): optionally an inhibitor such as 1-ethynyl-1-cyclohexanol; Including, A composition for producing silicone rubber.

6. obtainable by curing a composition according to claim 4 or 5, and having a glass transition temperature in the range of -130°C to -142°C, no crystallization / melting transition in the range of -140°C to +250°C, and an elongation at break of greater than 100%; Silicone rubber.

7. Use of the silicone rubber according to claim 6 in the aerospace industry, in particular in space probes.

8. 4. Use of poly(methylhydro-co-diethyl)siloxane having formula (IIIb) according to claim 3 as a crosslinking agent for the production of silicone rubber.

9. 4. A method for producing the polysiloxane of formula (III) containing methyl and ethyl groups according to any one of claims 1 to 3, comprising: Step a) Hydrolysis reaction of silanol precursor; Step b) chain-extending the silanol-terminated siloxane oligomers obtained in step a) by Lewis acid-induced polycondensation by adding a triflate salt catalyst, in particular In(III) triflate, followed by a perfluoroborane catalyst, in particular tris(pentafluorophenyl)borane; Step c1) In(III) triflate without solvent or B(C) in toluene as solvent or without solvent 6 F 5 ) 3 , or In(III) triflate and B(C 6 F 5 ) 3 adding vinyl end groups by reaction of the polymer obtained in step b) with vinyldimethylmethoxysilane or vinyl-1,1,3,3-tetramethyldisiloxane in the presence of a Lewis acid catalyst such as a mixture of Including, A method for producing polysiloxane.

10. The silanol precursor of step a) is (R1) 2 Ethylmethylsilane and (R1) 2 Dimethylsilane and (R1) 2 a mixture of diethylsilane and (R1) 2 Methylsilane and (R1) 2 and a mixture of diethylsilane, wherein R1 is a chlorine atom, (C 1 -C 6 ) an alkoxy group, an acetoxy group or an oxime group, and preferably R1 represents a chlorine atom, a methoxy group or an ethoxy group; 10. The method of claim 9.

11. the In(III) triflate catalyst is present in an amount of 0.1 mg to 1 mg per gram of oligomer; 11. The method according to claim 9 or 10.

12. Step b) is carried out at room temperature.

12. The method according to any one of claims 9 to 11.

13. step b) is carried out in bulk without the use of a solvent, 13. The method according to any one of claims 9 to 12.

14. A space rover comprising the silicone rubber of claim 6.

Images