SE427671B - Process for the preparation of a thermally stable methylpolysiloxane additive - Google Patents

Abstract

Terminally blocked methyl polysiloxane liquids such as trimethylsiloxane-end-blocked polydimethyl siloxanes can be made more resistant to the thermally induced siloxane rearrangement by incorporating in them titanium, zirconium or hafnium compounds. These compounds can be incorporated by admixing the organosiloxy derivative of titanium, zirconium or hafnium to the said liquid, or by admixing certain organic compounds of titanium, zirconium or hafnium to the liquid, and heating the mixture in order to decompose the organic compound introduced. The thermal stability of the liquid can be further improved by admixing a small amount of an organosilicon hydride to the titanium-, zirconium- or hafnium-containing fluid. Such thermally stabilized liquids are particularly suitable for use as heat transfer agents in a non- oxidative water-free environment.

Description

8000051-6 rings.

Although organopolysiloxanes, especially methylpolysiloxanes, are well known for their thermal stability, considerable effort has been expended by the prior art to obtain improvements in this regard. The high temperature instability of the organopolysiloxane has to do with reactions in silicone-bonded organic radicals, such as cooling and oxidation, which often lead to crosslinking and gelation of the organopolysiloxane, and rearrangement of the reactions in siloxane linkages, which often leads to depolymerization of the siloxane and the formation of lower molecular weight siloxanes. A large part of the older technology relates to stabilization of organopolysiloxanes for radical fission and oxidation at high temperature. The present invention relates to a process for improving the stability of an end-blocked methylpolysiloxane to high temperature siloxane arrangement in the absence of more than. trace amounts of moisture and compositions obtained therefrom.

Organopolysiloxanes are known to readily undergo siloxane anomal arrangements in the presence of acidic and alkaline catalysts to produce another arrangement of siloxane linkages. For example, a trimethylsiloxane endblocked polydimethylsiloxane should give rise to cyclopolydimethylsiloxanes such as the corresponding cyclotrisiloxane and cyclotetrasiloxane and shorter chain trimethylsiloxane endblocked polydimethylsiloxane methanes, including sulfuric acid or sodium hydroxide.

Many organopolysiloxanes, in which no catalyst according to the invention has been added, also undergo siloxane arrangements to some extent at high temperature. This rearrangement is thought to be due to the presence of silanol in the siloxane. So, for example, Rode and others, Vysokomol. ggygd.

All: Nr. 7, 1529-1538 l2§2 have studied the thermal degradation and stabilization of polydimethylsiloxane and the absence of oxygen and have found that the thermal degradation rate of a hydroxy-end-blocked polydimethylsiloxane against cyclotrisiloxane formation could be reduced by reacting the hydroxyl end group with the hydroxyl end group. iron or zirconium in m-cresol. They have also found that the thermal stability of the hydroxy endblocked polydimethylsiloxane fluids could be improved by adding thereto only additives such as acetylacetonates of aluminum, zinc, cobalt, copper, iron, and zirconium and titanium tetrabutoxylate; but intense cross-linking and gelation of the treated siloxane took place even at low temperatures. Rode and others also noted that if trimethylsiloxane end-blocked plyldimethylsiloxane also undergoes siloxane anomal arrangements to form cyclotrisiloxane, they did not suggest a solution to this problem.

Britt, U.S. Patent No. 3,759,970 stabilizes polysiloxane fluids by replacing contaminant groups such as SiCl, SiH, and SiOH with a fluoride group. Britt talks about the problem of oxidative instability detected by gel formation of the polysiloxane fluid in the air at high temperature, but states in96t about inhibiting the siloxane anomer arrangement in the absence of air. Organic titanium and zirconium compounds have found use in organopolysiloxane compositions. For example, Ceyzeriat and others in U.S. Patent No. 3,151,099 use large amounts of titanium alkoxides or zirconium alkoxides as a component of a moisture curing composition. Brown and others in U.S. Patent No. 3,745,129 use several siloxane organometallallocene compounds to protect polydiorganosiloxane fluids from oxidation. Hunter and others in U.S. Patent No. 2,728,736 use large amounts of zirconium alkoxides in organopolysiloxane compositions suitable for the treatment of leather. McNulty and Others in U.S. Pat. 2,687,388 uses small amounts of zirconium salt of an organic acid which is soluble in polyorganosiloxanes to act as a hardener for the polyorganosiloxane. Swiss in U.S. Pat. 2,465,296 uses small amounts of certain metal chelates to stabilize organosilicon oxide polymers against oxidation at high temperatures. Swiss further teaches that the solution of metal chelate and organosilicon oxide polymer would be heated to 2000 - 250 ° C to provide better oxidation resistance to the composition. It is also known that certain cerium-containing thermal stability additives for organopolysiloxanes which have improved precipitation resistance can be prepared by reacting certain alkali metal siloxanolates with cerium salts and at least one organic carboxylic acid salt or alkoxy derivative of zirconium, titanium or iron. .

While the above prior art teaches that organic titanium or zirconium compounds can be used in organopolysiloxanes for many reasons, including stabilization of hydroxy-end-blocked polydimethylsiloxanes against siloxane-arrangement, no aoooo51-6 is taught therein regarding the stabilization of hydrocarbon-methyloxyl-methyl-terminated hydrocarbon siloxane arrangement in the absence of moisture using only said titanium or zirconium compounds; It has now been discovered that the rate of thermal siloxane arrangement occurring in an end-blocked methylpolysiloxane under anhydrous conditions can be reduced to a low level by incorporating small amounts of certain titanium, zirconium or hafnium compounds into the methylnolvic siloxane.

It has further been discovered that said rate of thermal siloxane arrangement can be further reduced and substantially eliminated by mixing an organosilicon hydride compound with methyl polysiloxane having incorporated therein said titanium, zirconium or hafnium compounds. It is an object of the invention to provide a process for improving the stability of end-blocked methylpolysiloxanes against high temperature siloxane arrangement in an inert atmosphere. It is another object of the invention to provide a process for the preparation of a titanium, zirconium or hafnium containing thermostable additive to reduce siloxane arrangement in methylpolysiloxanes.

These and other objects are achieved by the process of the invention, the resulting compositions and their use in a heat transfer system, which process briefly comprises producing a metal-containing methylpolysiloxane, wherein the metal is titanium, zirconium, or hafnium and using it as a heat transfer medium. . The metal-containing methyl polysiloxane can be prepared by mixing certain siloxy-titanium, zirconium or hafnium compounds with a methyl polysiloxane or by mixing certain organotitanium, zirconium or hafnium compounds with a methyl polysiloxane and heat the resulting mixture. The heating is carried out in an inert atmosphere at a temperature sufficient to decompose the organotitan, zirconium or hafnium compound.

The resulting metal-containing methylpolysiloxane possesses increased resistance to siloxane reactions under anhydrous conditions at high temperature if its metal content has a value of from 0.001 to 0.1% by weight. Metal-containing methylpolysiloxanes having more than 0.1% by weight of metal are thermostable additives and can be mixed with additional end-blocked methylpolysiloxane to achieve the desired stabilizing metal concentration indicated above.

While we do not wish to limit the invention to theory, we believe that metal-oxygen-silicone bonds, either added as a siloxy-metal compound or formed during the heating step of the above process, serve to inactivate or attenuate certain active hydrogen atoms, such as SiOH, contained in trace amounts in the end-blocked methylpolysiloxane and which cause siloxane arrangements at high temperature, unless inactivation or removal occurs. It is clear that the metal-containing methylpolysiloxane prepared from the siloxymetal compounds may or may not have the same type of metal-oxygen-silicone bonding structure as metal-containing methylpolysiloxane prepared from organometallic compounds.

For further improvement in resistance to siloxane anomers, an organosilicone hydride compound can be added with the metal-containing methyl polysiloxane having from 0.001 to 0.1% by weight of metal. It is theorized that the silicone-bonded hydrogen atoms in the organosilicone hydride compound react with the inactivated or attenuated hydrogen atoms in the metal-containing methylpolysiloxane to remove them from the composition.

This invention relates to a process for the preparation of a thermostable methylpolysiloxane additive, said process being characterized by mixing components consisting essentially of (i) a trimethylsiloxane end-blocked methylpolysiloxane fluid having on average from 1.9 to less than 3.0 methyl grouperger silicone and a siloxymetallic compound in an amount sufficient to give more than 0.1 parts by weight of the metal Der 100 parts by weight of the mixture of (i) plus (v), said siloxymetallic compound being selected from the group consisting of organosilicone compounds which has at least one silicone-acid-titanium, silicone-acid-zirconium or silicone-acid-hafnium bond.

It is clear that the process according to the invention comprises the preparation of a thermally stabilized metal-containing methylpolysiloxane having the desired metal concentration in the range of 0.001 to 0.1% by weight or the preparation of a thermostable additive containing more than 0.1% by weight. % of the metal, which can be added with additional methylpolysiloxane (iii) to lower the concentration of the metal to a value of from 0.001 to 0.1% by weight. Said additional methylpolysiloxane (iii) may be only additional amounts of methylpolysiloxane (i) used to prepare the additive or- (iii) may be another methylpolysiloxane (i) such as one having another viscosity or other siloxane unit content. The end-blocked methyl polysiloxane fluids (i) to be used in the process of the invention consist essentially of siloxane units selected from the group consisting of (CH 3) 3 SiO 2/2, (GH 3) 2 SiO 2/2, CH 3 SiO 3/2 and SiO 4/2. each siloxane unit in (i) is such that the average of methyl groups per silicone in the methylpolysiloxane has a value of from about 1.9 to less than 3 »I, generally the majority of (CH 3) 3 SiO 1/2 and / or (CH 3) 2 SiO 2 / 2 siloxane units in (i). Suitably methyl polysiloxane (i) contains at least 90 moles fi of (CH3) 3SiO1 / 2 units and (GH3) àSiO2 / 2 units and not more than 10 mol% of CH5Si05 / 2 units and Si0¿ / 2 units. Most preferably, methylpolysiloxane (1) is substantially free of CH5SiO3 / 2 units and S104 / 2 units. ) 5, wherein x has an average value greater than zero, e.g. -x = 1 to 2,500 or more. Linear end-blocked methyl polysiloxane fluids are well known in the polymer art and are commercially available in a wide variety of viscosities. Liquids for slow flowing rubbers- They can be prepared by methods well known in the art- Trace amounts of gensiloxane units, such as CH 3 SiO 3/2 and SiO 4/2 units may be present in said linear fluids as impurities- Further examples of end-blocked methylpolysiloxanes (i) are branched fluids, more than trace amounts of CH3SiO3 / 2 and SiO4 / 2 siloxane units, such as methylpolysiloxanes of known, simple structure such as [fCH3) 3SiQ73SiCH3 and ¿fCH3) 3SiQZSi and m are complex siloxanes, often having an unknown structure, which are conveniently described by the general formula fl csš) 5sio1 / 2] m¿ (cf13) 2sio2 / 2 jn [Hasioš / zå [š1o4 / 2Å, var: m, n, p and q represents mol% of the indicated siloxane unit and its total value is 100 molø. As stated above, the sum of m plus n generally comprises more than 50 and is suitably at least 90. Branched. methylpolysiloxane fluids can be prepared by any suitable method which will yield substantially complete endblocked fluids which are substantially free of silicone bonded hydrolyzable groups such as hydroxyl. Typically, branched fluids are prepared by co-hydrolysis of appropriate amounts of the appropriate hydrolyzable silanes, such as chlorosilanes and / or alkoxysilanes, such as (cn3cycyl, (cH3) 3siOcH3 and (cn3) zsi (oc fl3) z, and cone expansion of the resulting silanol End-blocked methylpolysiloxane fluids, which are prepared, often contain low molecular weight siloxanes, such as βfCH3) 3Si720 and cyc10p ° 1y siloxanes of the formula [{GH3) 2SiQ73_10, which can be removed or not removed from the fluid. In any case, the end-blocked methyl polysiloxane fluids, especially the higher molecular weight fluids which are likely to contain trace amounts of catalytic species such as silanol, will undergo high temperature rearrangement reactions to produce additional amounts of said lower molecular weight species.

This rearrangement is of particular importance with certain fluids, such as the trimethylsiloxane end-blocked polydimethylsiloxane linear fluids, as exemplified hereinbefore, having a viscosity of from 10 to 100 millipascal-seconds - at 25 ° C. special value as a heat transfer medium, in which use they are often exposed to temperatures exceeding 300 ° C- In such use it is convenient to remove and prevent the further formation of said low molecular weight siloxanes from the fluid to avoid the formation of high pressure in a closed system or loss of fluid from an open system due to the high volatility of the low molecular weight siloxanes. The process of the invention greatly reduces and in some cases substantially stops this formation of low molecular weight siloxanes. While the end-blocked methyl polysiloxane fluid (i) consists essentially of siloxane units bearing only methyl group It is within the scope and spirit of the invention to allow up to one mole% of said methyl groups in (i) to be replaced by other hydrocarbon groups, such as phenyl, vinyl, and ethyl, especially in the endblocking groups. The viscosity of the endblocked methylpolysiloxane (i) ) is not critical and can have any value. Low viscosity exhibiting methylpolysiloxane fluids, e.g. up to 10 pascals seconds, are relatively easy to handle in such operations as pouring, piping, mixing and stirring, but very low viscosity exhibiting fluids, e.g. up to 10 millipascal seconds, may have low boiling points, which may make pressure equipment necessary for their containment during heating operations.

Higher viscosities having methylpolysiloxane fluids, e.g., from 10 to 100 pascalseconds, and rubbers, e.g., from 0.1 to 10 kilopascalseconds, may be more difficult to maintain but may not require pressure equipment during heating operations due to their higher or non existing boiling points. The process and compositions of the invention are effective for all viscosities of (i) - By fluid is meant herein a substance which can float at room temperature.

Of course, liquid fluids flow quickly, but rubber fluids can require from several minutes to several hours to undergo flow.

The organometallic compounds (ii) and the siloxy-metal compounds (v) mixed with the methylpolysiloxane (i) are derivatives of group 4A metals in the periodic table of the elements, i.e. titanium, zirconium and hafnium-aoooosv-6 B Itidane derivatives of each element are effective in the process of the invention¿ the derivatives of zirconium and hafnium are preferred because they are less volatile and less prone to hydrolysis than the corresponding derivatives of titanium. It is well known that zirconium and hafnium are substantially identical to their chemical behavior. and that all zirconium in nature contains small portions of hafnium. For these reasons, it is clear that the use of the word zirconium herein is intended to denote optional zirconium, free of hafhium, or zirconium mixed with minor amounts of hafnium. Similarly, the use of the word hafnium is here to be understood as meaning optional hafnium, free of zirconium, or hafnium mixed with minor amounts of zirconium. The organometallic compounds (ii) carry organic radicals containing atoms of carbon, hydrogen and oxygen and which are bonded to the metal atoms by one or more metal-acid-carbon bonds. Examples of suitable organic radicals which are so bonded include carboxylates such as propionate, butyrate, crotonate, octanoate, laurate, naphthenate, and benzoate; hydrocarbon oxides, such as ethoxide, propoxide, butoxide, and phenoxide, which give rise to compounds otherwise known as esters such as tetraethyl titanate and tetrabutyl zirconate; the enolates such as acetonates; and chelates such as acetylacetonates, succinates, phthalates and maleaters.

A preferred and readily available class of organometallic compounds (ii) are zirconium soaps, which are longer chain acid derivatives of zirconium, such as zirconium octanoate, which is well known as a desiccant in dye compositions. The organozirconium compounds and the colorothrite compounds and polymer techniques such as curing agents and catalysts; many are commercially available. Information on the preparation of suitable organozirconium compounds and organohafnium compounds can be found in "The Chemical Behavior of Zirconium", by Warren B. Blumenthal, D. van Nostrand Company, New York, U.s.A. Cape. 8 and 9.

The siloxy-metal compounds (v) are organosilicone compounds which have at least one siloxy-metal bond, i.e. at least one silicone-oxygen-titanium, silicone-oxygen-zirconium or silicone-oxygen-hafnium admixture per molecule and which are soluble in the methylpolysiloxane (i) - suitably the siloxy-metal compound is non-volatile at room temperature and most preferably it is non-volatile. volatile at the maximum operating temperature of the thermally stable fluid.

Silicone-bonded groups in (v) may be monovalent hydrocarbon radicals, such as aliphatic radicals such as methyl, ethyl, isopropyl, vinyl, benzyl, and cyclohexyl, and aromatic radicals such as phenyl, tolyl and xenyl; And polyvalent hydrocarbon radicals such as alkylene radicals such as methylene, ethylene, propylene, butylene, and cyclohexylene and arylene radicals such as phenylene and xenylene. Polyvalent hydrocarbon radicals may be combined with the same or different silicone radicals in molecules which are not silicone. with an oxygen-metal bond or by said hydrocarbon radicals are satisfied with divalent oxygen atoms which combine the silicone atoms to form siloxane linkages.

The titanium, zirconium or hafnium atoms in the siloxy-metal compounds (v) have at least one organosiloxy group attached thereto and may have only organosiloxy groups attached thereto. All Ti, Zr or Hf valences in the siloxy metal compounds (v) which are not satisfied with siloxy groups are satisfied with oxygen atoms, either simple or combined with other Ti, Zr or Hf atoms, or by oxygen-bonded organic radicals present in the organometallic compound (ii) above A type of siloxy-metal compounds (v) are the polydimethylailoxy-metal compounds of the general formula (-0 [(CH3) 2SiQ7y) 4M, where M represents Ti, Zr or Hf, y is an integer greater than zero and the unspecified oxygen valence may be satisfied with an end-blocking radical such as trimethylsiloxy or with an M-atom. Examples of siloxy-metal compounds and references describing their preparation are included in Pode, and others in the Another type of siloxy-metal compounds (v) are tetrakistrimethylsiloxymeal compounds of the formula fl oæmbsigzra, where m represents mi, Zr or Hf. It is clear that in view of the tendency of M to coordinate, as well as to combine, with oxygen atoms, the above formula for (v) should be taken as referring to the monomeric tetrakis-trimethylsiloxy-metal compound and any coordinated polymeric compound , which has the above formula as a monomeric repeat unit.

Furthermore, in view of the easy hydrolysis of the tetrakistrimethylsiloxy-metal compounds, there may be in (v) small amounts of partially hydrolyzed and condensed molecules bearing less than 4 trimethylsiloxy groups per I - The degree of hydrolysis and condensation mentioned would not be so. large that the siloxy-metal compound (v) is made insoluble in the methylpolysiloxane (i).

The amount of organometallic compound (ii) or siloxy-metal compound (v) to be mixed with the end-blocked methylpolysiloxane (i) to give improved thermal stability is the amount which will give from 0.001 to 0.1 parts by weight of the metal for every 100 parts by weight of the mixture of (i) plus (ii) or the mixture of (i) plus (v). where the organometallic compound (ii) is used in the process of the invention and thereby requiring a heating step to decompose the organometallic compound, it is convenient to mix excess organometallic compound (ii) with (i) and to heat the mixture SÛÛOÛS 1-6 «10 for to form a metal-rich thermostability additive having more than 0.1 weight in: metal, which can be shipped and / or stored and then mixed with additional quantities of (i) - However, to avoid degradation of (i) during the heating step, it would the organometallic compound does not give more than 10, preferably not more than 5% by weight of the metal in the mixture to be heated. When the siloxy metal compound (v) is used in the process according to the invention, it may also be mixed in excess with (i) to form a metal-rich thermostability additive having more than 0.1% by weight of metal which can be shipped and / or stored and can then be mixed with additional amounts of (i). In this case, however, the concentration of metal in the additive may exceed 10% by weight if desired, since no heating to decompose the siloxy metal compound is required as with the thermostability additives prepared from the organometallic compound (ii). Said subsequent dilution of either thermostability additive would use a sufficient amount of (i) to reduce the metal concentration to a value of from 0.001 to 0.1% by weight, as indicated above, to give a methylpolysiloxane which has improved stability In the process of the invention, the desired amount of the organometallic compound (ii) or the siloxy-metal compound (v) should be mixed with an appropriate amount of the end-blocked methylpolysiloxane (i) in any suitable manner to give a substantially homogeneous mixture.

Solvents, heat, shear and the like could be used -in the well known manner to facilitate mixing- All solvents would be inactive with (i) or (ii) and conveniently removed from the mixture before thermal decomposition of the organometallic compound (ii).

Thermal decomposition of the organometallic compound (ii) is done by heating the mixture of (ii) in (i) i 'an inert atmosphere under suitable conditions of time and temperature. By an inert atmosphere is meant an environment such as a vacuum or a nitrogen blanket or purification which will not react with the components of said mixture at the temperature used to decompose the organometallic compound.

Conditions of time and temperature which are suitable for decomposition of the organometallic compound will vary depending on the particular organometallic compound used and are impossible to predict with accuracy. They would be determined for each particular combination of (i) and (ii) by simple experimentation. For example, the mixture of (i) plus (ii) may be heated in a closed, inert state. system equipped with a device for measuring system pressure. A temperature at which an increase in pressure with time is noticed in the system indicates a suitable decomposition temperature. For the purposes of the invention. Alternatively, the organometallic compound (ii) to be used in the process according to the invention may be subjected to thermogravimetric analysis or differential thermoanalysis. In an inert atmosphere to determine a decomposition temperature which can be used in the process of the invention. As a limiting example, the mixture of (i) plus (ii) may be heated to a temperature close to but not attaining the thermal decomposition temperature of the methylpolysiloxane (in ) for a period of from 6 to 24 hours, suitably the decomposition of the organometallic compound would be substantially complete, thereby providing a thermally stabilized fluid or a thermostability additive which can be used at elevated temperatures without undergoing further decomposition. In the process according to the invention, all volatile and / or insoluble s decomposition products such as CO 2, hydrocarbons, acids and alcohols, are conveniently removed before the stabilized methyl polysiloxane fluid is used in high temperature application. Preferably, said decomposition products are removed while being formed in the heating step or shortly thereafter.

Decomposition products could be removed by any suitable method, such as distillation, evaporation, filtration, centrifugation, decantation and absorption. The metal-containing methyl polysiloxane would be kept under anhydrous conditions. Preferably, the process of the invention would be carried out completely under anhydrous conditions and the resulting compositions would be stored and used under anhydrous conditions.

The process of the invention further comprises mixing an organosilicon anhydride compound (iv) with a thermally stabilized methylpolysiloxane of the invention. This use of an organosilicon anhydride compound (iv) in the process of the invention is optional. A methyl-polysiloxane fluid with improved resistance to high temperature siloxane arrangement will be obtained if (iv) is omitted from said process, but even greater improvement in resistance to siloxane arrangement can be achieved by its use in said process.

The organosilicone hydride compound (iv) would not be added to a metal-containing methyl polysiloxane of the invention containing more than 0.1% by weight of metal; ie a thermostability additive according to the invention, since loss of silicone-bonded hydrogen and release of hydrogen gas can occur, especially in the presence of moisture. The organosilicon hydride compound (iv) is suitably mixed with the thermally stable methylpolysiloxane containing from 0.001 to 0.1% by weight of metal or with the additional methylpolysiloxane (i), which is mixed with a thermostability additive according to the invention.

The organosilicone hydride compound (iv) may be any silane, siloxane or silk carbane bearing at least one silicone-bonded hydrogen atom per molecule and a soluble in the methylpolysiloxane (i). suitably organosilicone - v The hydride is non-gaseous at room temperature. The organic groups in (iv) may be monovalent hydrocarbon radicals such as aliphatic radicals such as methyl, ethyl; iopropyl, vinyl, allyl, benzyl, and cyclohexyl and aromatic radicals such as phenyl, tolyl and xenyl; and polyvalent hydrocarbon radicals such as alkylene radicals such as methylene, ethylene, propylene, butylene, and cyclohexylene and arylene radicals such as phenylene and xenylene. Polyvalent hydrocarbon radicals may be joined to the same or different silicone atoms in the molecule. All silicon valences in (iv) which are not satisfied with hydrogen or with said hydrocarbon radicals are satisfied with divalent oxygen atoms which combine silicone atoms to form siloxane linkages. The organosilicone hydride compound (iv) is substantially free of hydrolyzable radicals such as hydroxyl, alkyl, halogen- For maximum thermostability, the organosilicone compound (iv) carries only silicone-bonded methyl, hydrogen and divalent oxygen radicals. Examples of organosilicone hydride compound (iv) include silanes, such as C 6 H 5 (CH 3) 2 SiH, CH 3 (C 6 H 5) 2SiH and (Q fi2) 4§ i (CH HL ailcarbanes as but) 2sic112cf12si (c1 = 13) 2l: and cönßiuzsš) _; and eiloxanes such as C53 m5) 2slg73si (cæ13) 2s, sl¿ösl (cs3) 2s_74, sl¿ösi (cz_l3) (c6r1¿) g74, c6r15si¿osi (c113) 211_73, ¿fi (cz13) slo_74, H (cH3 ) 2slo¿í: (cH3) s197¿0si (cH3) 2H och (m3) 3slo¿ (cfr3) 2sio_72¿ñ (cs3) sio_75sl (01x93.

A trimethylsiloxane end-blocking polymethylhydrogensiloxane is preferred as the organosilicone hydride compound (iv) because it is a relatively rich source of silicone-bonded hydrogen and can be made in various viscosities. Such a source of silicone-bonded hydrogen will provide the desired amount of hydrogen from a relatively small amount of (iv) and will also allow the adjustment of the viscosities of the methylpolysiloxane (i) and the organosilicone hydrogen compound (iv) if desired. The amount of (iv) is used in the process of the invention to provide appreciable improvement in thermostability is any amount which is sufficient to give up to 0,05 parts by weight of silicon-bonded hydrogen for every 100 parts by weight of the thermostabilized methylpolysiloxane containing from 0, ool to 0, 1 by weight of metal.However, the amount of (iv The degree of improvement in thermostability will vary directly with the amount of (iv) used in the composition. ptimum improvement in thermostability can be obtained by using sufficient (iv) to give at least about one silicone-bonded hydrogen from (iv) for each active hydrogen atom, such as SiOH, in the methylpolysiloxane (i) to stabilize. The number of said active hydrogen atoms in the methylpolysiloxane (i) can be determined by any suitable analytical method. Particularly suitable analytical methods for the determination of active hydrogen can be found in "Analysis of Silicones" 8000051-6 13 by A. Lee Smith, Publisher John Wiley and Sena, Inc-, NY-, US-Ih, pp. 136-138.

The methylpolysiloxane fluids prepared by the process of the invention are useful as non-curing high temperature non-curing friend transfer fluids, non-oxidative substantially anhydrous environment- Conventional additives for heat transfer fluids such as lubricants, and anti-wear additives may be mixed with the thermally stabilized fluids if desired. In particular, anti-oxidants may be mixed with said fluids to extend their usefulness to oxygen-containing environments. High temperature, non-oxidative, substantially anhydrous environments, as mentioned above, may be of the closed or open type. An environment is open if volatile materials Imnna resign. from there despite the fact that the environment is maintained non-oxidative and anhydrous. An example of an open environment is the enclosed space of a nitrogen-purified, ventilated system.

An environment is closed when volatile materials can neither leave nor enter it.

In the practice of the invention, a thermally stabilized methylpolysiloxane can be prepared directly from the appropriate amounts of methylpolysiloxane (i) and organometallic compound (ii) or siloxymethyl compound (v).

Alternatively, the thermally stabilized methylpolysiloxane can be prepared indirectly by mixing a previously prepared thermostable additive of the invention with a suitable amount of a methylpolysiloxane (i).

It is clear that a thermostable additive or a thermally stabilized methylpolysiloxane according to the invention can be prepared and then placed in the environment for the intended use, but it is also within the spirit and scope of the invention to produce said thermostability additive or said thermally stabilized methylpolysiloxane in situ, i.e. in the environment for its intended use.

For example, a thermally stabilized fluid according to the invention may be prepared, directly or indirectly as indicated above, and then placed and used as a heat transfer fluid in a system, either open or closed, comprising an angular source, such as a solar collector, an electric heating elements and a flame, a heat exchanger, and accompanying components. Alternatively, in the in situ procedure, a methyl polysiloxane fluid (i) may be placed in said system and an appropriate amount of organometallic compound (ii) or siloxy-metal compound (v) may then be added with the methyl polysiloxane (i); or a mixture of the methylpolysiloxane (i) and organometallic compound (ii) or your eiloxi metal compound (v) may be prepared and placed in said system. Decomposition of the organometallic compound (ii) can then be carried out in said system.

When used in in situ procedures, it is preferred to remove all volatile decomposition products from the system before the thermally stabilized methylpolysiloxane fluid is used as the heat transfer fluid. In each case, each organosilicone anhydride compound (iv) may be added to the thermally stabilized methyl polysiloxane at the proper time as described above. It is believed at this time that the best way to practice the invention is to prepare a methyl polysiloxane thermostability additive by mixing sufficient zirconium octanoate. with a trimethylsiloxane end-blocked polydimethylsiloxane fluid to give about 5% by weight of zirconium in the mixture and heat the resulting mixture under a nitrogen blanket for at least 6 hours at 350 ° C. The resulting fluid, after being freed from gaseous and solid materials, can then be mixed with a methylpolysiloxane to be thermally stabilized so that the zizunnium concentration is reduced to a value from 0.015 to 0.030% by weight.

The resulting thermally stabilized methylpolysiloxane can be used in a high temperature, non-oxidizing, substantially anhydrous environment without siloxane arrangement and the concomitant low molecular weight siloxane formation to the same extent as with zirconium-free methylpolysiloxane in the same environment. further resistance to siloxane anomer arrangement, the above thermally stabilized methylpolysiloxane may be mixed with an equivalent amount of a trimethylsilozane blockade polymethylhydrogenoxane fluid. By an equivalent amount is meant an amount which will give about a silicone-bonded active hydrogen atom up to 0.05 in the mixture of thermostability additive plus methylpolysiloxane.

It is preferred that the thermostable additive and its mixture with methylpolysiloxane and its mixture with methylpolysiloxane plus polymethylhydrogensiloxane be retained anhydrous to preserve their full effectiveness as a thermostable additive and thermally improved siloxanes- However, trace amounts of, e.g. . up to 10 parts by weight per million parts of the fluid are absorbed by the fluid without adversely affecting its stability against rearrangement. The following examples are included as illustrative examples and non-limiting invention, which is properly described in the appended claims.

All parts and percentages are by weight unless otherwise indicated viscosities are measured in centipois and converted to pascal seconds (Pa ° s by multiplying by 0.001. Pressure was measured in millimeters of mercury and converted to pascal (Pa) by multiplying with 1 33.3224 and rounded off with solvents. Example 1 Four parts of a solution of zirconium octanoate in mineral spirits, containing 6% zirconium, placed in a reaction vessel and freed from 2.64 parts of mineral spirits at 120 ° G and 6.67 kPa Then, 7.55 parts of a trimethylsiloxane end-blocked polydimethylsiloxane fluid were mixed with a viscosity of about 20 mPa ° s at 25 ° C with a portion of the cooled residue. The reaction tube was purged with nitrogen, then sealed for 24 hours and the mixture was heated for 24 hours. - The pressure in the reaction vessel was noted to increase for 24 hours- The hot reaction vessel was slowly vented to atmospheric pressure to remove gaseous products and the product, 6.59 parts, ky Allow to cool to room temperature and filter under a nitrogen atmosphere. The resulting product, 5.96 parts, was a clear, dark brown thermostability additive, containing about 3.1% zirconium, according to elemental analysis.

Example 2 A trimethyl end-blocked polydimethylsiloxane fluid having a viscosity of 10 Pa's was analyzed by thermogravimetric analysis by heating the fluid from room temperature in a nitrogen atmosphere at 2 ° C / minute using a nitrogen flow of 200 cm 3 / min. %, so ef, a 90 a: viktreriuet ekeaae, vem 415%, 467%, a 503% .. respectively. The assay was repeated on another portion of the fluid except that the thermostable additive of Example 1 was added in an amount sufficient to give a zirconium content of 0.02%. The resulting composition of the invention had weight losses of 10% at 493 ° C, 50% at 581 ° C and 90% at 628%, resulting in the improvement in the yield obtained by the process of the invention. This is an example of a mechanically stabilized methylpolysiloxane fluid in an open system. Example 3 The trimethylsiloacane end-blocked polydimethylsiloxane fluid of Example 2 was mixed with the following organometallic compound amyloxy metal compounds and the thermostability additives of the invention in varying quantities to give 0.02 m of group 4A attenuated moiety (1). (Z-ethylhexyl titanate (2.25 so Ti) as in Example 1; (2) Tetrakis (2-ethylhexyl) titanate; (3) Tetrakis (trimethylsiloxy) zirconium; (4) Zirconium octanoate (694 Zr) in mineral spirits; (5 Iron octanoate for comparison (6) Zirconium acetylacetonate; (7) Zirconium octanoate additive (3.1% Zr) in Example 1; (8) A thermostability additive prepared from hafnium octanoate (0.5% Hf) as in Example 1. The resulting the mixtures were evaluated for improved thermostability 8000Û51 ~ 6 16 using thermogravimetric analysis (TG-AJ) as in Example 2.

The results are summarized in Table I, and in addition to comparative fluids, they are arranged according to an increase of 10% weight loss temperature-significantly better overall results (10, 50, and 90 * few weight loss) were obtained from compositions prepared from thermostability additives, i.e. ( 1), (7) and (8) - All compounds except zirconium acetylacetonate were soluble in the fluid. Compounds (2), (4), and (6) were thermally precipitated by ¶.GA analysis thereby forming a thermal stability. Example 4 A trimethyl end-blocked polydimethylsiloxane fluid having a viscosity of 10 mPa-s at 25 ° C was analyzed by gas-liquid chromatography (GLC) to determine the total amount of cyclopolydimethylethane siloxide. for 25 hours, 100 hours, and 400 hours at 35,000 in sealed stainless steel tubes. The tubes were cooled, opened and the contents re-examined as above to determine the new cyclo-polydimethylsiloxane content. ts% of cyclopolydimethylailoxanes were noted in each fail.

The experiment was repeated with the following compositions according to the invention based on the above 10 mPa-s fluid: (9J Fluidum + 0.75% of the zirconium octanoate additive in Example 1, (10J Fluidum + 0.75% of tetrakis (trimethylsiloxy) zirconium, (ll) Composition (9.) + trimethylsiloxane ~ endblocked polymethylhydrogensiloxane, (l2¿) Composition (9.) + hexamethylethylhydrocyclotetrasiloxane, (130 Composition (10.) + trimethylsiloxane endblocked polymethylhydrogensiloxane , 100 and 400 hours in sealed stainless steel tubes, the above compositions of the invention underwent a smaller increase in cyclopolydimethylsiloxane formation than the comparative fluid. This shows the increased thermostability of the fluid in a closed system with the process of the invention. The results are summarized in Table II. .) (12-), and (13-) had a concentration of silicone-bonded hydrogen of 0.004% based on the weight used of compositions (9.), (9.) and (10.), Respectively. The experiment of Example 4 was repeated with two trimethylsiloxane end-blocked polydimethylsiloxane fluids having viscosities of 20 and 50 mPa, respectively. A composition according to the invention was prepared in each case as follows: (14-) 20 mPa's fluid + 0.75% of zirconium octanoate example 1, (15.) Composition (14) + trimethylsiloxane end-blocked polymethylhydrogensiloxane, (16-) 50 mPa's fluid + 0.75% of the zirconium octanoate-1 additive in Example 1, (17.) Composition (16-) ) + trimethylsiloxane-end- æv ~ ---.... __, _. .-...., _ _ .. _ P 8000051-5 I blocked polymerylhydrogensiloxane. Results aummëraë: death-ell inf Compositions (l5.) And (l7.) Had a concentration of eiliknn-bound hydrogen of 0.004% based on the weight used of compositions (14-) and (l6.) Respectively Example 6 A dynamic transfer loop with a volume of about 60 liters and comprising an electric heating element, fluid-to-water heat exchanger, fluid pump, nitrogen purified, room temperature expansion tank ventilated to the atmosphere through a valve of 0.5 kg / cm 2, pipeline for transferring the heat transfer fluid between the heat source and the heat exchanger and associated control and monitoring equipment was filled with the comparison fluid of Example 4 as the heat transfer fluid. The fluid was circulated under a nitrogen purge in the heat transfer loop at 120 ° 0 for 24 hours to dry and then release the fluid from the fluid. 31 ° C for 800 hours. The fluid was tested after 25, 100, 400 and 800 hours and analyzed by G.L.0. as in Example 4 for cyclopolydimethyl-ailoxane content- The test was repeated with composition (9) according to Example 4 as heat transfer fluid, instead of the comparison fluid, except that the sample temperature was increased to 370 ° O. While the comparison fluid gained 0.74, 1.6, 3.3, and 4.2% cyclopolydimethylsiloxane at 25, 100, 400, and 800 hours, respectively, the composition (9) of the invention gained only 0.47, 0.75. , 1.15 and 1.6% cyclopolydimethylsiloxane respectively- nmJ .__ 8ÜOÛÜ51'6 18 mao Hwo Hwo mæm Hwm mmm Nmm www mom o \ d om cum øßm Nmm Hwm vom www owe Næm see o \ @ om o \ 6 H QQmm .fl wawøummm fl w fi w fi em fi nmk apo fl m ** ° \ a¶ ~ o $ o amg pw fifi wpw fl fi e o \ c Hø ~ o * www www www mme New “Ne o fi v wow m fi w ca 000 hdu fl nm Emäum5Hhwwux fl>. <. ub ^. nøuhw xæ fi muom AQUHN ^ mv »N ^ ~ U fl ß æn fi v fl e GOWSH ^ mc fi cm% wmv H fl ußms 4: nasnø i. _. 8000051-6 19 «Qo. <M fl. H *« ov ßm.N mo.N * ßm.hH .Eau 00% ”NM umomn v fl> wc fl sø flfi pcuxo fl Hm fl hvwa fl uz fl ono fi xäv ßH.H ßm.o ß fi. H me.H m. M. .æ .E fl ß OOH m ~ .o nm.ow ~ .co> .o «% æa.o oe.m .Ban mm HH H fi mndä nuss fi» »N ** nnas fl p w.Hmm * ñm fi u fi ~ Hv ñ flfl v. ñc fl v _ nav ^ m.wms o fl v wm fi wpßwamw co fl u fl moaëow åÜÛÛ051- “6 20 Hmfo» ~. = H «.«. wm. ~ mm.- @ m.nH H @. ° «m. ° mm.m. _ wm. fi ~ N. »~ @ Q. ° H .Eau oo: .Eau oo fl ^ wv ooomn vw» wø fl nu fifl nn fl xo fifi m fi h fi ws fi øh fi ømo fi ghu vH.o mæ.H mm.m ~ eo mN.H fi ø.w ° E H m u mw Away ^ m. «@ S Qmv .ww fl whwwsww ñm fl v fi q fi u _. ^ m.mmE owv um fl w fi wmšmw .HNQOHßHWO E03

Claims (1)

1. soooo51-5 21 PAWÉNTKRÅV Processes for the preparation of a thermostable methylPolysiloxane additive, characterized in that it comprises mixing components consisting essentially of (i) a trimethylsiloxane end-blocked methylnolysiloxane fluid having from less than 1,1. 3.0 methyl samples of silicone, and (ii) a siloxy-metal compound in an amount sufficient to give more than 0.1 parts by weight of the metal per 100 parts by weight of the mixture of (i) nlua (ii), said siloxy-metal compound being selected from gm flfi a consisting of oreano-eilicon compounds, which have at least one silicone-oxygen-titanium, silicone-agyre-zirconium- or er: failicon-acid-hafnium bond. 8000051-6 Summary: End-blocking methylpolysiloxane fluids, such as trimethylsiloxane end-blocking polydimethylsiloxanes, are made more resistant to thermally formed siloxanomers by incorporating titanium, zirconium, or hafnium-containing compounds therein. The incorporation of these compounds can be accomplished either by mixing organosiloxide derivatives of Ti, Zr, or Hf with the fluid or by mixing certain organic derivatives of Ti, Zr or Hf with the fluid and heating the mixture to decompose the added organic derivative. Further improvements in the thermostability of the fluid can be obtained by mixing the titanium, zirconium or hafnium-containing fluid with a small amount of an organosilicon hydride compound. The thermostabilized fluids are particularly useful as the heat transfer fluid in non-oxidative, anhydrous environments.