Silicone composition for low temperature applications

Abstract

FIELD: aerospace.SUBSTANCE: polysiloxane containing methyl and ethyl groups is proposed, having the following formula (III), where R2 is -Si(CH3)2CH=CH2; A is a methyl group or a hydrogen atom; m and n are the molar% of the repeating motif -O-Si(Me)(A) and -O-Si(Et2), respectively, wherein m is 0.5-0.8, n is 0.2-0.5 and the sum of m+n is 1; p is the number of both repeating motifs to obtain a weight average molecular weight in the range from 20,000 to 150,000 g / mol when A is a methyl group and in the range from 300 to 3500 g / mol when A is a hydrogen atom. A method for producing said polysiloxane, composition for producing silicone rubber using said polysiloxanes (variants) and silicone rubber obtained by curing said compositions is also proposed.EFFECT: silicone rubbers and oils obtained on the basis of the proposed polysiloxane are capable of withstanding very low temperatures and are applicable in the aerospace industry.14 cl, 5 ex

Description

[0001] The field of the present invention is compositions for producing reinforced silicone rubber and for producing silicone oil capable of withstanding the very low temperatures required for use in the aerospace industry.

[0002] Silicones are organosilicon polymers with a siloxane structure characterized by the presence of silicon atoms linked to alkyl groups such as ethyl or methyl, trifluoromethyl, aryl, and other functional groups. Silicone rubber compounds derived from poly(dimethylsiloxane), commonly known as PDMS, are known to be stable at temperatures as low as -60°C. However, many astronautics applications, such as space exploration operations, require silicone materials that can withstand temperatures well below -100°C, as well as possess a tensile strength at yield (above 3 MPa) and an elongation at break greater than 300%.

[0003] Poly(diethylsiloxane), PDIES, is the only polymer material with a glass transition temperature of -142°C. However, pure PDIES exhibits several crystallization / melting transitions in the range from -142°C to 0°C and is therefore not suitable for such applications. Crystallization of silicon-containing materials is usually accompanied by their hardening, embrittlement, and loss of elasticity. This can lead to deterioration or even catastrophic loss of the mechanical properties of objects intended for automotive applications, such as 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-induced crystallization of the dimethylpolysiloxane-based copolymer.Indeed, the vast majority of commercially available space-grade silicones sold today (by Momentive, Elkem, Nusil, Dow Corning, IOTA Corporation Ltd., and others) belong to the family of biphenyl- and dimethylsiloxane copolymers or methylphenyl- and dimethylsiloxane copolymers. Interestingly, increasing the content of biphenyl or methylphenyl groups in such copolymers above 10 mol% shifts the glass transition temperature to higher temperatures and therefore limits their use at very low temperatures (down to -150°C). For example, RTV 560, RTV 566, and RTV 567 (methylphenylsilicones) sold by Momentive have a glass transition temperature, Tg, of -115°C, making such materials unsuitable for space flight to the South Pole of the Moon.It is important to note that cold crystallization of RTV 566 under 25% strain and long waiting periods (60 hours) at -80°C resulted in an increase in its elastic modulus from 5 MPa to 240 MPa, which was likely the main cause of its mechanical failure and misalignment in the telescope.

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

[0005] The classical route to silicone synthesis is based on the hydrolysis of dimethyldichlorosilane, which results in the formation of disilanols H[O-Si(CH3)2] n -OH, hydrochloric acid, and cyclic siloxanes in varying quantities. Hydrochloric acid then acts as a catalyst for disilanol, causing it to condense to form polydimethylsiloxane. The silanol-terminated silicone is then polymerized using various methods depending on the desired properties of the final product.

[0006] US4960850A describes a polycondensation reaction of a polydiorganosiloxane oligomer having silanol end groups in a closed reaction zone in the presence of a catalytically effective amount of trifluoromethylsulfonic acid at a temperature of from 20° to 160°C, with continuous removal of polycondensation water using a vacuum, and completion of the polycondensation reaction by adding a catalyst-neutralizing amount of cyclopolydiorganosilazane or polydiorganosilazane having diorganoaminosilyl end groups to the reaction medium. However, trifluoromethylsulfonic acid has a boiling point of 162°C and can be distilled off by removing water under a high vacuum.

[0007] Silicones with desired molecular weights can be prepared in a strictly controlled manner by ring-opening polymerization (ROP) of cyclic siloxanes, which is also the main industrial route. The above method is relatively simple for the polymerization of a single cyclosiloxane; however, control becomes difficult when attempting to copolymerize two cyclosiloxanes, for example, decamethylcyclosiloxane (D5Me10) with hexaethylcyclosiloxane (D3Et6), to obtain copolymers of (dimethyl- and diethyl)siloxanes in a 1:1 ratio. The latter is due to the different tension in the monomer molecules and the different ring-opening kinetics for D3Et6 compared to D5Me10. Ring opening requires reactions at relatively high temperatures of 95-160°C, the use of a suitable anionic polymerization initiator, end-protecting agents, auxiliary substances, a pressure-controlled reactor, and much more.Silicone typically undergoes some degree of backbiting, resulting in varying amounts (or quantities) of cyclic siloxanes, which can be difficult to remove from high-viscosity silicones. Furthermore, hexaethylcyclosiloxane is known to preferentially polymerize on its own, forming unstable domains in the cross-linked rubber that are responsible for the poor mechanical properties of the resulting material.

[0008] Another route to synthesize polysiloxanes from monomeric silane precursors is based on the polycondensation reaction of silane monomers or oligomers in the presence of perfluoroarylborane-based catalysts 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 route, known as the Piers-Rubinsztajn reaction, over ROP (based on the use of cyclic monomers), is that it can be performed at room temperature and produces far fewer cyclic products than the high-temperature synthesis using ROP. However, the main disadvantage of this method is that it can be used to synthesize small quantities of silicones (mmol quantities), but is unlikely to be suitable for the synthesis of kilogram quantities of dimethyl- and diethyl- (1:1) siloxane copolymer.This is due to the fact that such reactions are extremely exothermic and result in the formation of enormous quantities of gaseous products (typically over 100 liters of H2, CH4, or CH3-CH3 per kg of silicone). Clearly, this would be associated with a serious explosion hazard when attempting to scale up the reaction. Furthermore, another drawback of using the Pierre-Rubinstein reaction is that the borane-based catalyst must be dissolved in a solvent such as toluene (heptane causes it to precipitate), since water causes catalyst decomposition. Although the viscosity situation in the case of solvent-free silicone synthesis is quite straightforward, since the polymer viscosity can be checked visually or using a viscometer at any given time, monitoring the progress of the reaction in organic solvents such as toluene can be difficult to achieve. Furthermore, depending on the structure of the starting silane (i.e.,(depending on the presence of -OH, -OCH3, or -OCH2CH3 groups), the reaction temperature for monomer polymerization must be increased. For example, the reaction of the -OCH3 group of dimethoxydimethylsilane with diethylsilane occurs at 22-23°C, while the conversion of -OCH2CH3 into ethane in the presence of B(C6F5)3 requires a temperature of 70°C.

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

[0010] The applicants have discovered that a method for hydrolyzing diethyl / dimethyl / ethylmethyl-chlorosilane at low temperatures (1-7°C) results in the reproducible production of a silanol-terminated copolymer of (dimethyl- and diethyl)siloxanes or polymethylethylsiloxane of medium molecular weight, Mw, of approximately 1000 (with a viscosity of 33-36 mPa⋅s), which can be suitably polymerized in the presence of a suitable Lewis acid catalyst to form high molecular weight PDIES or poly(ethylmethylsiloxane) (PEMS) (Mw 50,000-100,000) having a very low glass transition temperature and not exhibiting any crystallization / melting transitions at low temperature. This method results in a relatively rapid (within minutes) increase in viscosity without the need for high reaction temperatures (above 100°C) and the formation of a minimal amount of by-products in the form of cyclic silicones (expressed quantitatively in ppm). -1). This method of synthesizing PDIES / PEMS according to the invention solves the problem of the formation of large volumes of gaseous products (H2, methane or ethane), which is observed in the Pierre-Rubinstein reaction, thereby reducing the likelihood of high exothermicity and preventing the risk of explosion, as discussed above.

[0011] However, another issue that needs to be addressed is the compatibility of crosslinkers with vinyl-terminated PDIES. In general, phenyl-containing crosslinkers are required for crosslinking phenyl silicones due to the occurrence of phase separation and increased foaming when using classical crosslinkers, poly(methylhydrogensiloxanes) (PHMS) or copolymers of dimethyl- and methylhydrogensiloxanes. The applicants noted a similar phenomenon with copolymers of dimethyl- and diethylsiloxanes. Excessive foaming was observed when vacuum was applied to the PDIES / PHMS blend either in the absence or presence of silica. To address these issues related to the incompatibility of the crosslinker with diethyl silicone, the applicants synthesized a new type of crosslinker, a copolymer of methylhydrogen- and diethylsiloxanes, characterized by excellent compatibility with PDIES.

[0012] Thus, the present invention relates to a method for producing a polysiloxane containing methyl and ethyl groups, said method comprising the step of

[0013] a) hydrolysis reactions of silanol precursors;

[0014] b) chain extension of the siloxane oligomers with silanol end groups obtained in step a) by performing Lewis acid-induced polycondensation by adding a triflate salt-based catalyst, in particular In(III) triflate, followed by adding a perfluoroborane-based catalyst, in particular tris(pentafluorophenyl)borane.

[0015] Preferably, the polysiloxane containing methyl and ethyl groups is selected from the group consisting of:

[0016] - copolymer of dimethyl- and diethyl-siloxanes or copolymer of methylhydro- and diethyl-siloxanes of the following formula (I):

[0017]

[0018] where A represents a methyl group or a hydrogen atom; the type represents the molar % of the repeating motif -O-Si(Me)(A) and -O-Si(Et2), respectively, wherein

[0019] m is 0.5-0.8; n is 0.2-0.5; and the sum of m+n is 1;

[0020] 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 is a methyl group, and in the range of 300 g / mol to 3,500 g / mol when A is a hydrogen atom,

[0021] and

[0022] - poly(ethylmethylsiloxane) of the following formula (II):

[0023]

[0024] where q represents the number of repeating motifs.

[0025] More preferably, the silanol precursors of step a) are selected from (R1)2ethylmethylsilane, a mixture of (R1)2dimethylsilane and (R1)2diethylsilane, a mixture of (R1)2methylsilane and (R1)2diethylsilane, wherein R1 is a chlorine atom, a (C1-C6)alkoxy group (preferably a methoxy group or an ethoxy group), and a cetoxy group or an oxime group, preferably R1 is a chlorine atom, a methoxy group or an ethoxy group, more preferably R1 is a chlorine atom.

[0026] In the formulas of the present invention, Me represents a methyl group, and Et represents an ethyl group.

[0027] According to the present invention, the terms "contained in the range from x to y", "in the range x-y", "=x-y", "from x to y" are meant to mean that the limits of the range, namely, the values ​​x and y, are included.

[0028] According to the present invention, the term "(C1-C6)alkoxy group" is understood to mean any linear or branched saturated alkoxy group having 1 to 6 carbon atoms, in particular, the OCH3(methoxy) group and OCH2CH3(ethoxy).

[0029] Thus, the method of the present invention is intended for producing a polysiloxane containing methyl and ethyl groups, preferably a copolymer of (dimethyl- and diethyl)siloxanes or a copolymer of (methylhydro- and diethyl)siloxanes of the following formula (I):

[0030]

[0031] where A represents a methyl group or a hydrogen atom; the type represents the molar % of the repeating motif -O-Si(Me)(A) and -O-Si(Et2), respectively, while

[0032] m is 0.5-0.8; n is 0.2-0.5; and the sum of m+n is 1;

[0033] p represents the number of both repeating motifs, resulting in a weight-average molecular weight in the range of 20,000 g / mol to 150,000 g / mol when A is a methyl group, and in the range of 300 g / mol to 3,500 g / mol when A is a hydrogen atom. Viscosity measurement can be used to measure the weight-average molecular weight of the polymer (according to the American Society for Testing and Materials (ASTM) standard E3116-18 dated January 25, 2018). 1 H NMR (nuclear magnetic resonance) and FTIR (Fourier transform infrared spectroscopy).

[0034] Preferably, m is 0.5-0.7 and n is 0.3-0.5, wherein the sum of m+n is 1, more preferably, m is 0.5-0.6 and n is 0.4-0.5, wherein the sum of m+n is 1, even more preferably, both are 0.5.

[0035] In particular, the copolymer of (dimethyl- and diethyl)siloxanes according to the invention has the following formula Ia:

[0036]

[0037] where m, n and p are as defined above.

[0038] Preferably, the copolymer of (dimethyl- and diethyl)siloxanes of formula Ia according to the invention has a weight average molecular weight, in particular obtained using the viscometry method for measurement according to the ASTM E3116-18 standard of January 25, 2018, in the range of from 20,000 g / mol to 150,000 g / mol, more preferably from 30,000 g / mol to 100,000 g / mol, even more preferably from 40,000 g / mol to 80,000 g / mol, in particular from 45,000 g / mol to 60,000 g / mol.

[0039] In particular, the copolymer of (methylhydro- and diethyl)siloxanes according to the invention has the following formula Ib:

[0040]

[0041] where m, n and p are as defined above.

[0042] Preferably, the copolymer of (methylhydro- and diethyl)siloxanes of formula Ib according to the invention has a weight average molecular weight, in particular obtained using the viscometry method for measurement according to the ASTM E3116-18 standard of January 25, 2018, in the range of from 300 g / mol to 3500 g / mol, more preferably from 500 g / mol to 3000 g / mol, even more preferably from 1000 g / mol to 2000 g / mol.

[0043] Furthermore, the method of the present invention is preferably for producing poly(ethylmethylsiloxane) of the following formula (II):

[0044]

[0045] where q represents the number of repeating motifs.

[0046] Preferably, the poly(ethyl methyl silyl) of the invention has a weight average molecular weight, in particular obtained using the viscometry method for measurement according to the ASTM E3116-18 standard of January 25, 2018, in the range of 1000 g / mol to 2,000,000 g / mol.

[0047] Step a) of the method of the present invention comprises a hydrolysis reaction of silanol precursors.

[0048] It is preferable that the silanol precursors are selected from (R1)2ethylmethylsilane, a mixture of (R1)2dimethylsilane and (R1)2diethylsilane, and a mixture of (R1)2methylsilane and (R1)diethylsilane, wherein R1 is 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 is a chlorine atom, a methoxy group, or an ethoxy group, more preferably R1 is a group containing a chlorine atom.

[0049] Thus, it is preferable that the silanol precursors are chlorinated or ethoxylated silanol precursors, in particular chlorinated silanol precursors. More preferably, they are 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, more preferably, from dichloroethylmethylsilane, a mixture of dichlorodimethylsilane and dichlorodiethylsilane, and a mixture of dichloromethylsilane and dichlorodiethylsilane.

[0050] The products obtained after step a) are oligomers of siloxane containing methyl and ethyl groups, in particular oligomers of (dimethyl- and diethyl)siloxanes, or (methylhydro- and diethyl)siloxanes, or ethylmethylsiloxane. Preferably, these oligomers have weight average molecular weight values, in particular obtained using the viscometry method for measurement according to ASTM E3116-18 of January 25, 2018, in the range of 500 and 3000 g / mol, more preferably 1000-3000 g / mol, when A is methyl.

[0051] Possible reaction schemes (Schemes 1 and 2) for step a) are shown below:

[0052]

[0053] wherein A, m and n are as defined above, and R1 is a chlorine atom, a C1-C6 alkoxy group (particularly a methoxy group or an ethoxy group), an acetoxy group or an oxime group, preferably R1 is a chlorine atom, a methoxy group or an ethoxy group, more preferably R1 is a chlorine atom.

[0054] In a preferred embodiment, step a) is carried out at a temperature of from 0°C to 40°C, more preferably from 5°C to 35°C.

[0055] Preferably, the reaction is first carried out at a temperature of 0°C to 7°C, preferably 5°C to 7°C, after which the temperature is increased to a range of 30-40°C, preferably 30-35°C.

[0056] More preferably, the reaction is carried out with stirring, even more preferably by adding silanol precursors in water, in particular dropwise, more preferably at a rate of 1 to 5 drops per second, in particular 3 drops per second.

[0057] In a preferred embodiment, step a) lasts from 1 to 2 hours.

[0058] In a preferred embodiment, the molar concentration of water (w) is higher than that of both silanol precursors (a+b): w is higher than a+b.

[0059] In another embodiment, the oligomers obtained in step a) are separated from the aqueous phase containing HR1, in particular HCl, obtained after step a), and then used in step b) of the method according to the invention, preferably by using extraction from heptane.

[0060] Step b) of the process of the present invention consists in chain extending the siloxane oligomers with silanol end groups obtained in step a), preferably oligomers which are copolymers of (dimethyl- and diethyl)siloxanes or oligomers which are copolymers of (methylhydro- and diethyl)siloxanes or oligomers of ethylmethylsiloxane, by carrying out Lewis acid-induced polycondensation by adding a triflate salt catalyst, followed by adding a perfluoroborane catalyst. Preferably, the polymer obtained after step b) is thus a polymer of formula I or II, which is described in detail above.

[0061] Preferably, the triflate salt catalyst is selected from In(III) triflate, Bi(III) triflate, Al(III) triflate and a mixture thereof, more preferably, it is In(III) triflate.

[0062] Preferably, the perfluoroborane-based catalyst is tris(pentafluorophenyl)borane.

[0063] The reaction schemes (Schemes 3 and 4) for step b) using In(III) triflate and tris(pentafluorophenyl)borane catalysts are shown below:

[0064]

[0065] where A, m, n and p are as defined above;

[0066]

[0067] where q is as defined above.

[0068] The polymer of formula (I) is an alternating copolymer. The polymer of formula (II) is a homopolymer. Preferably, step (b) is carried out at room temperature (20-25°C).

[0069] In a preferred embodiment:

[0070] - first, a triflate salt catalyst, in particular In(III) triflate, is added with stirring (step b1), then the reaction mixture is left to react without any stirring, preferably for at least 1-12 hours;

[0071] - Next, a perfluoroborane-based catalyst, in particular tris(pentafluorophenyl)borane (step b2), is added with stirring, then the reaction mixture is left to react without any stirring, preferably for at least 1-12 hours.

[0072] Preferably, step (b) is carried out in bulk, without any solvent.

[0073] In a preferred embodiment, the triflate salt catalyst, in particular In(III) triflate, is present in an amount of 0.1 mg to 1 mg per gram of oligomers.

[0074] In another preferred embodiment, the perfluoroborane-based catalyst, in particular tris(pentafluorophenyl)borane, is present in an amount of from 0.1 mg to 1 mg per gram of oligomers.

[0075] In a particular embodiment, step b) is carried out in an inert gas atmosphere, preferably in a nitrogen atmosphere.

[0076] The method of the present invention may comprise a step of c1) adding a vinyl end group by reacting the polymer obtained in step b) with vinyl dimethyl methoxysilane or vinyl 1,1,3,3-tetramethyldisiloxane in the presence of a Lewis acid catalyst such as In(III) triflate without any solvent or B(C6F5)3 in toluene as a solvent or without any solvent, at temperatures of 20 to 60°C, preferably to obtain a polymer having the following formula (III):

[0077]

[0078] where A, m, n and p are as defined in formula I, and R2 is -Si(CH3)2CH=CH2;

[0079] - or a polymer having the following formula (IV):

[0080]

[0081] where q is as defined in Formula II, and R2 is -Si(CH3)2CH=CH2.

[0082] The polymer of formula (III) is an alternating copolymer.

[0083] The polymer of formula (IV) is a homopolymer.

[0084] Thus, the polymer obtained in step c1) may be a copolymer of (dimethyl- and diethyl)siloxanes having the following formula (IIIa):

[0085]

[0086] where R2, m, n and p are as defined in formula III, or

[0087] copolymer of (methylhydro- and diethyl)siloxanes having the following formula (IIIb):

[0088]

[0089] where R2, m, n and p are as defined in Formula III.

[0090] Polymers of formula (IIIa) and (IIIb) are alternating copolymers.

[0091] Preferably, the (dimethyl and diethyl)siloxane copolymer of formula (IIIa) has a glass transition temperature (Tg), measured using differential scanning calorimetry (DSC) according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -142°C, in particular in the range of -135°C to -141°C, more specifically -139°C.

[0092] More preferably, it has a weight average molecular weight, measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of from 20,000 g / mol to 150,000 g / mol, still more preferably from 30,000 g / mol to 100,000 g / mol, even more preferably from 40,000 g / mol to 80,000 g / mol, in particular from 45,000 g / mol to 50,000 g / mol.

[0093] Preferably, the (methylhydro and diethyl)siloxane copolymer of formula (IIIb) has a glass transition temperature, measured using DSC according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -146°C.

[0094] More preferably, it has a weight average molecular weight, measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of 300 g / mol to 3500 g / mol, more preferably 500 g / mol to 3000 g / mol, even more preferably 1000 g / mol to 2000 g / mol.

[0095] Preferably, the poly(ethylmethylsiloxane)siloxane of the formula (IV) has a glass transition temperature, measured using DSC according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -142°C.

[0096] More preferably, it has a weight average molecular weight, measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of 20,000 g / mol to 200,000 g / mol, preferably 20,000 g / mol to 150,000 g / mol.

[0097] The reaction schemes (Schemes 5 and 6) for step c1) are shown below:

[0098]

[0099]

[0100] where R2, A, m, n and p are as defined above;

[0101]

[0102] where R2 and q are as defined above.

[0103] In a particular embodiment, the Lewis acid catalyst is a triflate salt, preferably selected from In(III) triflate, Bi(III) triflate, Al(III) triflate and a mixture thereof, more preferably it is In(III) triflate, and step c1) is carried out without any solvent, more preferably at a temperature of between 50°C and 70°C, even more preferably the catalyst is present in an amount of between 0.1 mg and 2 mg per gram of polymer.

[0104] In another particular embodiment, the Lewis acid catalyst is a perfluoroborane such as B(C6F5)3, and step c1) is carried out without any solvent or using toluene as a solvent, more preferably at room temperature (20-25°C), even more preferably the catalyst is present in an amount of 0.1-1 mg per gram of polymer.

[0105] In another particular embodiment, the Lewis acid catalyst is a mixture of a triflate salt and a perfluoroborane, preferably a mixture of In(III) triflate and B(C6F5)3, and step c1) is carried out without any solvent, more preferably at room temperature (20-25°C), even more preferably the catalyst is present in an amount of 0.1-1 mg per gram of polymer.

[0106] In another particular embodiment, the catalyst used in step b) is not removed during step c1) and an additional amount of perfluoroborane, in particular B(C6F5)3, is added. Preferably, step c1) is carried out without any solvent, more preferably at room temperature.

[0107] The method of the present invention may comprise the step of c2) adding a trialkylsilyl end group by reacting the polymer obtained in step b) with a trialkylsilane, in particular trimethylsilane or triethylsilane, more in particular triethylsilane, in the presence of a Lewis acid catalyst such as B(C6F5)3, in toluene as a solvent, preferably to obtain a polymer having the following formula (V):

[0108]

[0109] where A, m, n and p are as defined in formula I,

[0110] and each of R3 is independently a saturated linear or branched C1-C6 alkyl group, preferably an ethyl group, or

[0111] - polymer having the following formula (VI):

[0112]

[0113] where q is as defined in formula II,

[0114] and each of R3 represents, independently of each other, a saturated linear or branched C1-C6 alkyl group.

[0115] According to the present invention, the term "(C1-C6)alkyl group" is understood to mean any linear or branched saturated alkyl group having 1 to 6 carbon atoms, in particular, a CH3(methyl) group and a CH2CH3(ethyl) group.

[0116] 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.

[0117] Preferably, the (dimethyl- and diethyl)siloxane copolymer of formula (IVa) has a glass transition temperature (Tg), measured using DSC according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -145°C, in particular in the range of -135°C to -142°C, more specifically -136°C.

[0118] More preferably, it has a weight average molecular weight, measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of 40,000 g / mol to 65,000 g / mol, even more preferably 45,000 g / mol to 55,000 g / mol.

[0119] Preferably, the poly(ethylmethylsiloxane) of the formula (VI) has a glass transition temperature (Tg), measured using DSC according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -142°C.

[0120] More preferably, it has a weight average molecular weight, measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of 20,000 g / mol to 150,000 g / mol.

[0121] The reaction schemes (Schemes 7 and 8) for step c2) are shown below:

[0122]

[0123]

[0124] where R3, A, m, n and p are as defined above;

[0125]

[0126] where R3 and q are as defined above.

[0127] In another particular embodiment, the Lewis acid catalyst is a perfluoroborane such as B(C6F5)3, and step c2) is carried out without any solvent or using toluene as a solvent, more preferably at room temperature (20-25°C), even more preferably the catalyst is present in an amount of 0.1-1 mg per gram of polymer.

[0128] In another particular embodiment, the method of the invention comprises, after step c1) or c2), an additional step d) of removing the catalyst used in step b) and in step c1) or c2), preferably by using aluminum oxide.

[0129] Preferably, the method of the invention is for producing a 50 / 50 copolymer of (dimethyl- and diethyl)siloxanes or a 50 / 50 copolymer of (methylhydro- and diethyl)siloxanes.

[0130] The present invention also relates to a copolymer of (dimethyl- and diethyl)siloxanes of formula (IIIa) described above, preferably obtained by the process of the present invention, more preferably having:

[0131] - weight average molecular weight measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of 20,000 g / mol to 150,000 g / mol, more preferably 30,000 g / mol to 100,000 g / mol, even more preferably 40,000 g / mol to 80,000 g / mol, in particular 45,000 g / mol to 50,000 g / mol, and / or

[0132] - glass transition temperature measured using DSC according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -142°C, in particular, in the range of -135°C to -141°C, more specifically -139°C.

[0133] The polymer of formula (IIIa) is an alternating copolymer.

[0134] The present invention also relates to a copolymer of (methylhydro- and diethyl)siloxanes of formula (IIIb) described above, preferably obtained by the process of the present invention, more preferably having:

[0135] - weight average molecular weight measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of 300 g / mol to 3500 g / mol, more preferably 500 g / mol to 3000 g / mol, even more preferably 1000 g / mol to 2000 g / mol, and / or

[0136] - glass transition temperature measured using DSC according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -146°C.

[0137] The polymer of formula (IIIb) is an alternating copolymer.

[0138] The present invention also relates to a copolymer of (dimethyl- and diethyl)siloxanes of formula (V) described above, preferably obtained by the process of the present invention, more preferably having:

[0139] - weight average molecular weight measured using viscometry according to ASTM E3116-18 dated January 25, 2018, in the range of 500 g / mol to 150,000 g / mol, preferably in the range of 1,000 g / mol to 3,000 g / mol, and / or

[0140] - glass transition temperature measured using DSC according to ASTM E1356 dated May 15, 2014, in the range of -130°C to -145°C, in particular in the range of -135°C to -142°C, more specifically -139°C.

[0141] The polymer of formula (V) is an alternating copolymer.

[0142] The polymer of formula (V) is silicone oil.

[0143] The present invention also relates to a composition for producing silicone rubber, comprising:

[0144] - (A) 60-94 wt.% of the vinyl-terminated copolymers (dimethyl and diethyl) siloxanes of formula (IIIa) according to the present invention;

[0145] - (B) 5-35% by weight of reinforcing filler(s), preferably pyrogenic silicon dioxide;

[0146] - (C) 1-5 wt.% of crosslinking agents having a Tg below -130°C; preferably having formula (IIIb) according to the present invention;

[0147] - (D) a suitable amount of a curing catalyst, preferably a Pt(0)-based catalyst such as a platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane complex, dissolved in methylvinylcyclosiloxanes, and

[0148] - (E) possibly a Pt inhibitor such as 1-ethynyl-1-cyclohexanol.

[0149] In this application, the term "silicone rubber" is understood to mean a substance having the ability to maintain elasticity in the temperature range of 200 to -140°C.

[0150] The corresponding amounts of compound (A) (vinyl-terminated copolymers of (dimethyl- and diethyl)siloxanes of formula (IIIa)) and compound (C) (crosslinking agents) in the composition according to the invention are determined by the ratio between the number of (R'HSiO 2 / 2) units and the number of alkenyl groups and are adjusted accordingly taking into account the relative proportion of alkenyl groups in compound (A) and the relative proportion of (R'HSiO 2 / 2) units in compound (C).

[0151] An essential feature of the composition for producing silicone rubber according to the invention is the ratio between the number of units (R'HSiO 2 / 2) in the compound (C) introduced into the basic silicone composition and the number of diethyl groups in the compound (A) introduced into the composition for producing rubber. According to the present invention, this ratio between the number of units (R'HSiO 2 / 2) and the number of alkenyl groups exceeds 3. With a value less than or equal to 3, a composition is obtained whose mechanical and adhesive properties are insufficient for use as a PDIES silicone capable of self-adhesion on metal surfaces such as stainless steel or titanium.

[0152] It is preferable that this ratio be greater than 4 and less than 25.

[0153] The curing catalyst is a hydrosilylation catalyst, in particular a platinum Pt(0) catalyst, more particularly in the form of a complex with divinyltetraalkylsiloxane ligands, preferably 1,3-divinyltetramethylsiloxane, such as a platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane complex dissolved in methylvinylcyclosiloxanes. Such catalysts are described, for example, in WO 0142258 A1. The most suitable is the Karstedt catalyst. As in any conventional hydrosilylation reaction, the amount of catalyst in the composition is catalytic. By catalytic amount is meant less than one molar equivalent of platinum relative to the amount of unsaturated double bonds of the olefin type present in the composition. In general, it is sufficient to introduce less than 1000 ppm -1 and preferably more than 30 million -1 platinum based on the total mass of compound (A) and compound (C).

[0154] The purpose of this reaction is hydrosilylation involving the (R'HSiO2 / 2) groups of compound (C) and the alkenyl groups of compound (A), which leads to cross-linking of the organopolysiloxanes and allows the production of a cross-linked silicone rubber composition. Cross-linking is typically initiated by raising the temperature of the silicone rubber composition to a temperature sufficient for the hydrosilylation reaction to occur. This is typically carried out at a temperature of 15°C to 200°C, for example, from 20°C to 150°C, or even better, from 50°C to 150°C.

[0155] As is known, cross-linkable silicone compositions typically contain an inhibitor. Inhibitors are typically used to regulate the temperature and duration of cross-linking in the hydrosilylation reaction and thus further control the cross-linking reaction, especially its onset and rate. If a cross-linking inhibitor is used, the amount of the inhibitor used is preferably from 1 to 50,000 ppm. -1 , more preferably from 20 to 2000 million -1 and, in particular, from 100 to 1000 million -1 , relative to the total weight of compound (A) and compound (C). 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, 2-phenyl-3-butyn-2-ol are used as inhibitors. Preferably, the composition for producing silicone rubber according to the invention contains an inhibitor.

[0156] Furthermore, an essential property of the composition for producing silicone rubber according to the invention is the content therein of a reinforcing filler, preferably hydrophobic silica, in particular fumed silica. As is known, hydrophobic silica is silica, part of the surface of which is covered with organic groups, such as alkyl groups. The silica can be a reinforcing silica known to those skilled in the art, in particular any precipitated or fumed silica. Preferably, the silica has a specific surface area according to the Brunauer-Emmett-Teller (BET) method of less than 450 m 2 / g, preferably within a range varying from 80 to 400 m 2 / g, in particular from 100 to 300 m 2 / g, preferably from 150 to 250 m 2 / g. It is also possible to use a mixture of several silicon dioxides, for example, Aerosil R 8200, Aerosil R 812 S, Aerosil E 9200 from Evonik or Cab-O-Sil TS 530 from Cabot.

[0157] It is well known that silicon dioxide is surface modified to impart hydrophobicity. Surface modification of silicon dioxide can be accomplished in a known manner by reacting silicon dioxide with compounds bearing hydrophobic groups, such as trialkylsilyl groups, particularly trimethylsilyl groups. Particularly suitable is silicon dioxide whose surface is modified with trimethylsilyl groups. Examples include compounds obtained by modification with hexamethyldisilazane.

[0158] The content level of hydrophobic silica is adjusted by a person skilled in the art depending on its specific surface area and the intended use of the composition for producing silicone rubber. It is preferable that the content level of hydrophobic silica in the composition for producing silicone rubber is greater than or equal to 5% of the total weight of compound (A) and compound (C) and less than or equal to 35% of the total weight of compound (A) and compound (C). If the silicon dioxide content is less than 5% of the total weight of compound (A) and compound (C), the reinforcing properties of the composition may be insufficient for some applications.If the silicon dioxide content is higher than 35% of the total mass of compound (A) and compound (C), the preparation of a composition for obtaining silicone rubber may not be possible (in the case of using HDK H2000, Wacker silicon dioxide, or using Cab-O-Sil TS 530, Aerosil R 8200 or Aerosil E 9200 in an amount higher than 20% by mass, a solid paste was obtained).

[0159] The silicone rubber composition according to the invention can be prepared by adding hydrophobic silica to compound (A), then adding compound (C) with stirring, and finally adding a catalyst. If an inhibitor is used, it is typically added to a mixture of hydrophobic silica and compound (A), followed by the addition of compound (C).

[0160] The present invention also relates to a silicone rubber obtained by curing the composition of the present invention and as described above, and having a glass transition temperature, measured using DSC according to ASTM standard E1356 of May 15, 2014, in the range of from -130°C to -142°C, preferably in the range of from -135°C to -140°C, in particular -138°C, and / or not showing any crystallization / melting transition, measured using DSC according to ASTM standard E1356 of May 15, 2014, in the range of -140°C to +250°C.

[0161] More preferably, the silicone rubber of the invention is characterized by an elongation at break (measured on a 34TM-10 testing machine from INSTRON, France, using the NF T 46002 standard of the French Association for Standardization (AFNOR; from French: Association Francaise de NORmalization) of September 1988, H2) greater than 100%, in particular greater than 200%, more particularly greater than 300% and, for example, 348%.

[0162] Even more preferably, the silicone rubber of the invention has an elastic modulus of greater than 1 MPa, preferably greater than 3 MPa, measured on a 34TM-10 testing machine from INSTRON, France, according to the AFNOR standard NF T 46002 of September 1988.

[0163] Even more preferably, the silicone rubber of the invention has a Shore A hardness in the range of 35-40 as measured by a durometer in accordance with ASTM D 2240 of July 23, 2021.

[0164] The present invention also relates to the use of silicone rubber or the (dimethyl- and diethyl)siloxane copolymer of formula (V) according to the present invention in the aerospace industry, in particular in planetary rovers. More specifically, the present invention also relates to the use of the (dimethyl- and diethyl)siloxane copolymer of formula (V) according to the present invention as a silicone oil for electric motors at low temperatures, in particular below -100°C.

[0165] Finally, the present invention relates to the use of a copolymer of (methylhydro- and diethyl)siloxanes having the following formula (IIIb) according to the present invention as a crosslinking agent for producing silicone rubber.

[0166] The above mentioned characteristics of the present invention, as well as other features, will be better understood upon reading the following description of several typical embodiments of the invention, given by way of illustration and without limitation.

[0167] Example 1. Synthesis of a copolymer of 50 / 50 (diethyl- and dimethyl)siloxanes (PDIES-50 / 50)

[0168] STAGE 1 (stage a)

[0169] First, 1 kg of dichlorodiethylsilane (SID3402.0-1 KG, Gelest, USA) was distilled at 40-50°C / 20 mbar (2 kPa) vacuum into a 2 L flask cooled to -79°C using dry ice. The resulting silane was a transparent liquid.

[0170] The synthesis of a 50 / 50 (diethyl- and dimethyl)siloxane copolymer was carried out without preliminary deoxygenation of water. A cylindrical 8-liter glass reactor was placed in an ice bath (polypropylene chamber) and cooled to 0-5°C. The reactor was equipped with a bubbler to detect possible gas evolution. Deionized water (3.7 L) was added to the glass reactor, which was cooled in an ice bath to 5°C. Stirring was set at 200 rpm. Then, 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 glassware was dried at 100°C under vacuum and maintained under a weak flow of N2). The silanes were mixed using a Teflon-lined rod and added dropwise into 3.7 L of water at a rate of approximately three drops per second. The reaction medium temperature was maintained in the range of 5-7°C. Hydrolysis of the silanes was carried out for two hours at 300 rpm.

[0171] After this, the reactor was placed in a polypropylene water bath heated to 40°C so that the reaction medium temperature was 30-35°C. The silanols were stirred at 300 rpm for another 2 hours. Then, 1.5 L of heptane was added, the silanol-containing phase was separated from the aqueous phase, and an HCl (aq) solution was pumped under the silanol oligomer layer using silicone supply hoses (under weak vacuum conditions). Silanol oligomers were extracted using 1 L of heptane, and another 1.5 L of heptane was used to rinse the reactor and separatory funnel (500 mL funnel). 25 g of MgSO4 was added and stirred at 200 rpm to dehydrate the silanol oligomers. The wet MgSO4 was filtered off, and the silanol oligomers were stored overnight in 2 L of heptane under a nitrogen atmosphere. The organic solvent was removed under vacuum at 90°C using a rotary evaporator. This yielded 313.2 g of silanol oligomer (the theoretical value was 369.4 g), representing a yield of 85%.Viscosity according to ASTM E3116-18 dated January 25, 2018: 35 mPa s (viscometer model: VSC-N4 (Bioevopeak, China); measurement range: 20-2,000,000 mPa⋅s).

[0172] Silanols were placed in a 2-liter glass flask for 120 minutes at 145°C (in air, without vacuum). Viscosity was measured after 2 hours at 145°C after cooling to 25°C (in a thermostat). Viscosity: 38 mPa⋅s. The silanol was purged with nitrogen, sealed with a silicone membrane in a 1-liter container, and stored at -20°C (to prevent further water condensation).

[0173] STAGE 2 (stage b)

[0174] 298 g of the silanol oligomers obtained in step 1 were heated at 145°C for 15 minutes and, while heated, were subjected to a vacuum (vacuum below 2 mbar (200 Pa)) for 30 minutes until bubble formation was observed. The heated silanol oligomers were then poured into a dry 1 L flask equipped with a silicone septum and a magnetic stirrer, and nitrogen was passed through it. Afterwards, 35 mg of indium(III) triflate was added under a stream of nitrogen per 100 g of silanol oligomer. The catalyst was dispersed in the silanol oligomer by stirring at 500 rpm. The reaction mixture was then left to react overnight (17 hours) without stirring in a tightly sealed container. An increase in viscosity was observed. The next day, 57 mg of tris(pentafluorophenyl)borane (Sigma-Aidrich, No. 442593) was added as a catalyst under nitrogen atmosphere, stirred for 5 min at 500 rpm, and left to react for another 24 h.

[0175] STAGE 3 (stage c)

[0176] 35 mg of tris(pentafluorophenyl)borane (Sigma-Aid rich, No. 442593) was added to the reaction medium as a catalyst, followed by 1.5 ml of vinyl dimethyl methoxysilane (AB106075, ABCR, Germany). The reaction medium was stirred for 5 minutes, then the reaction was continued for another 5 hours without stirring. Finally, the reaction product was transferred to a rotary evaporator, and excess vinyl dimethyl methoxysilane and other volatiles were distilled off under conditions of 95°C / 30 mbar (3 kPa).

[0177] STAGE 4: Catalyst removal (Stage d)

[0178] The siloxane polymer obtained in step 3 was cooled to room temperature and 150 g of neutral alumina (No. 199974, Sigma Aldrich) was added along with 600 ml of heptane. The suspension was stirred at 300 rpm for 20 minutes. Then, the solids were removed by filtration on a ceramic filter with a porosity of 2, then with a porosity of 4, and finally on a polytetrafluoroethylene (PTFE) filter with a pore size of 0.45 μm. The solvent was distilled off using a rotary evaporator with heating to 95 °C, under vacuum up to 30 mbar (3 kPa). Finally, the siloxane polymer was heated at 150 °C and under vacuum below 1 mbar (100 Pa) for one hour (in a vacuum drying oven). No significant mass loss was observed in the temperature range from -80 to 200°C as measured using DSC.

[0179] Viscosity according to ASTM E3116-18 dated January 25, 2018: 4012 mPa⋅s; Mw 45000 g / mol (viscometer model: VSC-N4 (Bioevopeak, China); measurement range: 20-2000000 mPa⋅s).

[0180] According to DSC data in accordance with ASTM E1356 dated May 15, 2014, the Tg of this substance is -139°C (2°C / min; N2) (Model: DSC 3, Mettler Toledo, Switzerland).

[0181] The polydispersity index (PD) determined using GPC was 1.63.

[0182] The GPC terms are as follows.

[0183] GPC (Gel Permeation Chromatography): Agilent 1260 Infinity system connected to 390-MDS detector (Agilent, USA).

[0184] Refractometric detector: Refractometric detector (RID) 1260 Infinity (Agilent, USA).

[0185] A Mistral column thermostat (Spark, Netherlands) was used as a heating device.

[0186] The speakers included in the set are listed below:

[0187] 1 styrene-divinylbenzene copolymer (SDV) pre-column from PSS (Polymer Standards Service) (PSS / Agilent);

[0188] 2 analytical columns PSS SDV LINEAR XL (PSS / Agilent).

[0189] Before administration, polymer samples were dissolved in 1 ml of toluene.

[0190] Toluene, H PLC Plus, for high-performance liquid chromatography (HPLC; No. 650579-1L, Merck).

[0191] Experimental conditions:

[0192] - eluent: toluene;

[0193] - flow rate: 1 ml / min;

[0194] - temperature: 35°C.

[0195] Traditional calibration using polystyrene standards in the range of Mw 682-130000 g / mol with a narrow distribution is used for calibration.

[0196] The software used to calculate Mw was Cirrus GPC software (Agilent, USA).

[0197] Example 2. Silicone composition for producing a silicone rubber sample

[0198] 50 g of siloxane polymer with Mw 45500 g / mol (synthesized in the above steps 1-4);

[0199] 15 g SiO2 (HDK H2000, Wacker, Germany);

[0200] 7 mg 1-ethynyl-1-cyclohexanol, 99% (E51406, Sigma-Aid rich) (Pt inhibitor);

[0201] 140 mg Pt* based catalyst (platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane complex solution, Sigma Aldrich, No. 479543);

[0202] 1.35 g of crosslinking agent HMS-H271 (Gelest, USA; copolymer (25-30% methylhydro)- and dimethyl-siloxanes, with hydride end groups; 24-60 centistokes (cSt)).

[0203] The ingredients were mixed in a mixer at 2000 rpm and cured under conditions of 150°C / 1 hour or at room temperature for 24 hours.

[0204] An elastic crosslinked silicone rubber (30 wt% SiO2) having a Tg of -138°C and no crystallization or melting properties in the range of -150 to +250°C was obtained as measured using DSC according to ASTM E1356 on May 15, 2014 (model: DSC 3, Mettler Toledo, Switzerland). Shore A hardness: 35-40 (measured using HBA100-0 (Kern, Switzerland; according to ASTM D2240-15(2021) dated July 23, 2021). Elongation at break: 348% (measured on a 34TM-10 testing machine from INSTRON, France, using the AFNOR standard NF T 46002 dated September 1988, H2).

[0205] Example 3. Silicone oil based on a copolymer of (dimethyl and diethyl) siloxanes (50 / 50) with terminal triethylsilyl groups

[0206] Stage (a): hydrolysis

[0207] A 1 L flask with four inlets, a condenser, a side inlet, a gas outlet, and a magnetic stirrer bar 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, USA) and 24.6 g of dichlorodimethylsilane (ThermoScientific, No. 113312500), both cooled to 5 °C and as a mixture, were added dropwise (at a rate of 3 drops per second) over 1 hour. The reaction mixture was stirred at 600 rpm. Afterwards, the reaction mixture was raised to 30 °C and stirred for another hour. 500 ml of heptane were added, and the silica-containing phase was separated from the aqueous phase in a separatory funnel. The organic phase was washed with deionized water until neutral pH.

[0208] The reaction product in heptane was transferred to a 1 L flask, and the remaining water was removed using 50 g of anhydrous MgSO4. The product was filtered using a ceramic filter with a porosity of P4 and a PTFE microfilter with a pore size of 0.45 μm. Heptane and volatiles were removed using a rotary evaporator at 90°C / vacuum down to 18 mbar (1.8 kPa). Applying an additional vacuum to 1 mbar (100 Pa) at room temperature (RT) did not reveal the presence of any volatiles.

[0209] Stage (b): chain extension

[0210] The product was transferred under a stream of N2 into a dry 100 mL round-bottomed flask equipped with a magnetic stirrer bar. Then 14 mg of In(III) triflate was added and stirred for 30 minutes. After this, 14 mg of tris(pentafluorophenyl)borane (Sigma-Aldrich, No. 442593) dissolved in 2 mL of anhydrous toluene (Sigma Aldrich, No. 244511) was added as a catalyst. The reaction mixture was stirred for another 30 minutes.

[0211] Stage (c2)

[0212] 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 min until bubbling ceased. The catalysts were adsorbed on 25 g of neutral Al2O3 with constant stirring at 400 rpm. The reaction medium was stirred for 10 minutes, then 200 ml of heptane were added and the suspension was filtered using P2 and P4 ceramic filters, then a PTFE microfilter with a pore size of 0.45 μm. The solvent was distilled off under conditions of 90°C / 20 mbar (2 kPa), then in a vacuum below 1 mbar (100 Pa) at room temperature. The identity of the product was confirmed using FTIR and Raman spectroscopy. The glass transition temperature, Tg, equal to -140°C, was measured by DSC at a rate of 2°C / min in a nitrogen flow.

[0213] Example 4. Silicone oil based on a copolymer of (methylhydro- and diethyl)siloxanes (50 / 50) with terminal triethylsilyl groups (crosslinking agent)

[0214] Stage a): hydrolysis

[0215] A 1L flask with four inlet ports, a condenser, a side inlet, a gas outlet port, and a magnetic stirrer bar was purged with a weak stream of nitrogen at 25°C. Then, 22g of diethyldiethoxysilane (Gelest, SID3404) was added, followed by 16.8g of methyldiethoxysilane (Sigma-Aldrich, No. 66612) with constant stirring at 400 rpm.

[0216] Stages b) and c1)

[0217] Finally, 7.5 mg of In(III) triflate as a catalyst was added directly to the monomer mixture using a Pasteur pipette, then 11 mL of deionized water was added using a pipette at 10-minute intervals (3×3 mL + 2 mL) at 400 rpm and 29°C. After stirring for 1 hour, the reaction product was transferred to a 250 mL flask, and water was removed by adding 25 g of anhydrous MgSO4. The product was dissolved in 100 mL of heptane and filtered using a PTFE filter with a pore size of 0.45 μm, and the volatiles / solvent were removed using a rotary evaporator under the condition of 80°C / vacuum up to 35 mbar (3.5 kPa). The use of additional vacuum up to 1 mbar (100 Pa) during CT did not reveal the presence of any volatile substances.

[0218] 7 mg of tris(pentafluorophenyl)borane catalyst (Sigma-Aldrich, No. 442593) dissolved in 1 ml of anhydrous toluene (Sigma Aldrich, No. 244511) and 5 ml of triethylsilane (Sigma, 230197-25G) were added to the reaction product obtained in the previous step under N2 flow with constant stirring at 400 rpm. The solution was stirred for 30 min until bubbling ceased. The borane catalyst was adsorbed on 25 g of neutral Al2O3. The reaction mixture was stirred for 10 minutes (using a Teflon-coated magnetic stirrer rod), then 100 ml of heptane was added, and the suspension was filtered using P2 and P4 ceramic filters, followed by a 0.45 μm PTFE microfilter. The solvent was distilled off at 90°C / 20 mbar (2 kPa), then under vacuum below 1 mbar (100 Pa) at room temperature. The identity of the product (a clear, colorless liquid) was confirmed using FTIR and Raman spectroscopy.The glass transition temperature, Tg, equal to -144.7°C, was measured by DSC at a rate of 2°C / min in a nitrogen flow.

[0219] Example 5. Synthesis of poly(ethylmethylsiloxane) - PEMS

[0220] STAGE a (hydrolysis)

[0221] Ethylmethyldichlorosilane (No. AB111135, ABCR, Germany) was used as received (97% purity). It appeared as a clear pink liquid.

[0222] This synthesis was carried out in air. A 20 L glass reactor was cooled to 5°C. The 1 L side arm, used for dropwise addition of silane, was equipped with a bubbler and was under a weak nitrogen flow during the silane addition. Deionized water (1.4 L) was cooled and maintained at 4-6°C during the addition of chlorosilane. Stirring was set at 200 rpm. First, 213.0 g (instead of 210 g) of ethylmethyldichlorosilane were added dropwise (3 drops per second) into 1.4 L of water. Then, the reaction medium temperature was gradually raised to 30°C and stirred at 200 rpm for 2 h 30 min. A transparent silanol-containing layer formed on the surface of the water.

[0223] Silanol was extracted with 1.25 L of heptane and dried using 250 g of MgSO4. Heptane was distilled off using a rotary evaporator at 90-95 °C, then under vacuum at 1 mbar (100 Pa) at room temperature. The viscosity of the obtained silanol was 31.7 mPa⋅s. Then, silanol in a 1 L round-bottomed flask was placed in a drying oven at 145 °C for 20 min. The silanol was cooled to RT. After this, 100 mg of indium(III) triflate was added with constant stirring at 200 rpm. Then, silanol was left to polymerize over the weekend. 115.0 g of silicone were obtained (theoretical 131.83 g), the yield is 87%.

[0224] STAGE b (chain extension)

[0225] 50 g of PEMS silanol obtained in step a) was mixed with 50 mg of In(III) triflate (No. 422151, Sigma-Aldrich), stirred for 5 min at 200 rpm and left to polymerize over the weekend (without stirring). Afterwards, water and volatiles were removed from the silicone using a rotary evaporator at 95 °C under a vacuum of 30 mbar (3 kPa). Then, the silanol was mixed with 125 g of anhydrous MgSO4 and dissolved in 400 ml of heptane. The solids were filtered off using a P4 ceramic filter, and the heptane was distilled off at 95 °C. The silanol was heated at 145 °C for 10 min under a vacuum of 1 mbar (100 Pa). 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 stirred for 2 minutes and then stored in a 1-liter flask sealed with a silicone septum under an N2 atmosphere (without stirring). The silanol was left to polymerize overnight.

[0226] STAGE c1

[0227] The silanol obtained in step b was heated to 95°C under a vacuum of 25 mbar (2.5 kPa) to remove water and volatiles. Then, 0.33 g of vinyl-1,1,3,3-tetramethyldisiloxane, 98% (SIV9097.5, Gelest, USA) and 25 mg of tris(pentafluorophenyl)borane, 95% (No. 442593, Sigma Aldrich) were added, followed by 2 ml of toluene. The silicone was stirred for 5 min at 200 rpm and left to react for 2 h at 25°C. Finally, the vacuum line was connected and the volatiles were distilled off at 95°C under a vacuum of 30 mbar (3 kPa). The silicone was diluted in 200 ml of hexane, 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 using a P4 ceramic filter, then a PTFE microfilter with a pore size of 0.45 μm.The solvent was removed at 95°C using a rotary evaporator. The polymer was transferred to a dry 250-ml glass flask and placed under a 1 mbar (100 Pa) vacuum at 150°C and then at 170°C (for 20 minutes each time). The viscosity was 5500 mPa⋅s.

[0228] The obtained compound was subjected to DSC. The measured Tg value was -141°C at a rate of 2°C / min under an N2 atmosphere. FTIR and Raman spectroscopy measurements revealed the absence of cyclic products. The FTIR and Raman data for the product were consistent with the calculated spectra for PEMS at the B3LYP / 6-311G (d,p) level of theory (Gaussian16 program).

[0229] Viscosity according to ASTM E3116-18 dated January 25, 2018: 25 mPa⋅s, Mw 2000 g / mol (viscometer model: VSC-N4 (Bioevopeak, China); measurement range: 20-2000000 mPa⋅s).

[0230] The polydispersity index (PD) determined using GPC was 2.41. The GPC conditions were the same as Example 1.

[0231] Cross-linking: 5g PEMS silicone (STAGE c1), 1.5g SiO2(HDK H2000), 14mg Pt(0) in tetravinylcyclotetrasiloxane (No. 479543, Sigma Aldrich), 135mg HMS-H271 (Gelest, USA) at 35°C overnight, then 20 minutes at 150°C.

[0232] An elastic cross-linked silicone rubber with a Tg of -139°C was obtained, which did not show crystallization or melting properties in the range from -139 to +250°C.

[0233] No crystallization of silicone was observed at a rate of 2°C / min in N2 atmosphere in the range of +25 to -130°C.

Claims

1. Polysiloxane containing methyl and ethyl groups of the following formula (III): where R2 is -Si(CH3)2CH=CH2; A represents a methyl group or a hydrogen atom; m and n represent the molar % of the repeating motif -O-Si(Me)(A) and -O-Si(Et2), respectively, where m is equal to 0.5-0.8, n is equal to 0.2-0.5 and the sum of m+n is equal to 1; p is the number of both repeating motifs to give a weight average molecular weight in the range of 20,000 to 150,000 g / mol when A is a methyl group and in the range of 300 to 3,500 g / mol when A is a hydrogen atom.

2. Polysiloxane according to claim 1, which is a copolymer of (dimethyl- and diethyl)siloxanes, having - the following formula (IIIa): where R2, m, n and p are as defined in formula (III); - a weight average molecular weight in the range from 20,000 to 150,000 g / mol; and - glass transition temperature in the range from -130 to -142°C.

3. Polysiloxane according to claim 1, which is a copolymer of (methylhydro- and diethyl)siloxanes having - the following formula (IIIb): where R2, m, n and p are as defined in formula (III); - a weight average molecular weight in the range from 300 to 3500 g / mol; and - glass transition temperature in the range from -130 to -146°C.

4. A composition for producing silicone rubber, comprising: (A) 60-94 wt.% of copolymers of (dimethyl- and diethyl)siloxanes of formula (IIIa) having vinyl end groups according to claim 2; (B) 5-35% by weight of reinforcing filler(s), preferably fumed silicon dioxide; (C) 1-5 wt.% crosslinking agents having a glass transition temperature Tg below -130°C; (D) a suitable amount of a Pt(0) based curing catalyst; and (E) possibly an inhibitor such as 1-ethynyl-1-cyclohexanol, characterized in that the suitable amount is from 30 parts per million (ppm) to 1000 ppm of platinum based on the total weight of the compound (A) and the compound (C).

5. A composition for producing silicone rubber, comprising: (A) 60-94 wt.% of copolymers of (dimethyl- and diethyl)siloxanes of formula (IIIa) having vinyl end groups according to claim 2; (B) 5-35% by weight of reinforcing filler(s), preferably fumed silicon dioxide; (C) 1-5 wt.% of crosslinking agents having a glass transition temperature Tg below -130°C, having formula (IIIb) according to claim 3; (D) a suitable amount of a Pt(0) based curing catalyst; and (E) possibly an inhibitor such as 1-ethynyl-1-cyclohexanol, characterized in that the suitable amount is from 30 parts per million (ppm) to 1000 ppm of platinum based on the total weight of the compound (A) and the compound (C).

6. The composition according to any one of claims 4 or 5, characterized in that the curing catalyst is platinum(0)-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane dissolved in methylvinylcyclosiloxanes.

7. Silicone rubber obtained by curing the composition according to any one of claims 4 to 6 and having a glass transition temperature in the range from -130 to -142°C, not exhibiting any crystallization / melting transitions in the range from -140 to +250°C and having an elongation at break greater than 100%.

8. Use of a copolymer of (methylhydro- and diethyl)siloxanes having the formula (IIIb), according to claim 3, as a crosslinking agent for producing silicone rubber.

9. A method for producing a polysiloxane containing methyl and ethyl groups of formula (III) according to any one of paragraphs 1-3, wherein said method includes the steps of: a) a hydrolysis reaction of silanol precursors is carried out; b) chain-extending the siloxane oligomers with silanol end groups obtained in step a) by performing Lewis acid-induced polycondensation by adding a triflate salt catalyst, in particular In(III) triflate, followed by adding tris(pentafluorophenyl)borane; c1) adding a vinyl end group by reacting the polymer obtained in step b) with vinyl dimethyl methoxysilane or vinyl 1,1,3,3-tetramethyldisiloxane in the presence of In(III) triflate without any solvent, or B(C6F5)3 in toluene as a solvent or without any solvent, or a mixture of In(III) triflate and B(C6F5)3, at temperatures from 20 to 70°C.

10. The method according to claim 9, characterized in that the silanol precursors of step a) are selected from (R1)2ethylmethylsilane, a mixture of (R1)2dimethylsilane and (R1)2diethylsilane and a mixture of (R1)2methylsilane and (R1)2diethylsilane, where R1 is a chlorine atom, a (C1-C6)alkoxy group, an acetoxy group or an oxime group, preferably R1 is a chlorine atom, a methoxy group or an ethoxy group.

11. The method according to any one of paragraphs 9, 10, characterized in that the In(III) triflate catalyst is present in an amount of 0.1 to 1 mg per one gram of oligomers.

12. The method according to any one of paragraphs 9-11, characterized in that step b) is carried out at room temperature.

13. The method according to any one of paragraphs 9-12, characterized in that step b) is carried out in bulk, without any solvent.

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