SE427665B - 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 liquid. Such thermally stabilized liquids are particularly suitable for use as heat transfer agents in a non- oxidative water-free environment.

Description

veossos-å 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 cross-linking 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. For example, Rode and others, Vxsokomol. sgvgd.

All: Nr. 7, 1529-1538 § 12 studied the thermal degradation and stabilization of polydimethylsiloxane and the absence of oxygen and found that the thermal degradation rate of a hydroxy-end blocked polydimethylsiloxane against cyclotrisiloxane formation could be reduced by reacting the hydroxyl end groups with the hydroxyl end groups. iron or zirconium in m-cresol. They have also found that the thermal stability of the hydroxy end-blocked polydimethylsiloxane fluids could be improved by simply adding additives such as aluminum acetylacetonates. zinc, cobalt, copper, iron, and zirconium and titanium tetrabutoxylate; but intense cross-linking and gelation of the treated siloxane occurred even at vsoszos-2 low temperatures. Rode and others also noted that if trimethylsiloxane end-blocked polydimethylsiloxane 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 in the process of 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. McNu1ty 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 heat 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 alkoxide 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-terminated polydimethylsiloxanes against siloxane-arrangement, no vsoszøs-2 is taught therein regarding the stabilization of hydrocarbon-methyl-end-polysaccharides. siloxane composition in the absence of moisture using only the aforementioned titanium or zirconium compounds. It has 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 into the methylpolysiloxane small amounts of certain titanium, zirconium or hafnium compounds.

It has further been discovered that said rate of thermal -siloxane anom arrangement can be further reduced and substantially eliminated by mixing an organosilicone hydride compound with methylpolysiloxane, which has 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 siloxane array arrangements at high temperature 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 heating it. 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 methyl polysiloxane possesses increased resistance to siloxane aggregation under anhydrous pre-water conditions at high temperature if its metal content has a value of from 0.001 to 0.1% by weight. Metal-containing methyl polysiloxanes having more than 0.1% by weight of metal are thermostable additives and can be mixed with additional end-blocked methyl polysiloxane 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 in SiOH, contained in trace amounts in the end-blocked methylpolysiloxane and which cause siloxane anomal 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 bond 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 comprising (A) mixing components consisting essentially of (i) a trimethylsiloxane end-blocked methylpolysiloxane fluid having on average from 1.9 to less than 3.0 methyl groups of silicone and (ii) an organometallic compound in an amount sufficient to give more than 0.1 but not more than 10.0 parts by weight of the metal per 100 parts by weight of the mixture of (i) plus (ii), said organometallic compound is selected from the group consisting of organotitanium, organozirconium, and organohafnium compounds, each organic group consisting of carbon, oxygen and hydrogen atoms and which is bonded to the metal with at least one metal-oxygen-carbon bond and (B) heating the mixture of (i) plus (ii) in an inert atmosphere to decompose the organometallic compound.

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 a different viscosity or siloxane unit. The end-blocked methylpolysiloxane fluids (i) to be used in the process of the invention consist essentially of siloxane units selected from the group consisting of (CH 5) 3 SiO 1/2, (CH 3) 2 SiO 2/2, CH 3 SiO 5/2 and SiO 4/2. each siloxane moiety in (i) is such that the average of methyl groups per silicone in the methylcycloxyloxane has a value of from about 1.9 to less than 3- In general, the majority of (CH 3) 5 SiO 1/2 and / or (CH 3) 2 SiO 2/2 siloxane units in (i). Preferably methyl polysiloxane (i) contains at least 90 mol% of (CH3) 3SiO1 / 2 units and (GH3) 2SiO2 / 2 units and not more than 10 mol% of CH3SiO3 / 2 units and SiO4 / 2 units- Most preferably methyl polysiloxane (i) substantially free, from CH 3 SiO 3/2 units and SiO 4/2 units- Examples of preferred endblocked methylpolysiloxanes (i) are linear trimethylsiloxane endblocked polydimethylsiloxane fluids, which have fomeih (cn fi šsio Kcff 3) 5, cs @ has an average value greater than zero; Linear end-blocked methyl polysiloxane fluids are well known in the polymer art and are commercially available in a wide range of viscosities ranging from moving liquids to slow flowing rubbers. They can be prepared by methods well known in the art. Trace amounts of boundary siloxane 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, which contain more than trace amounts of CH 3 SiO 3/2 and SiO 4/2 SiO such as methipolysiloxanes of known, simple structure such as [(CH5) 3SiQ73SiCH3 and [(GH3) 3SiQZSi and more complex siloxanes, which often have an unknown structure, which are conveniently described by the Gen formula of ger-m) 5siol / 2¿7m¿ ( cr13) 2sio2 / 2 jn ßnñsioz / egg [š1o4 / ZÄ, where m, h, p and q denote mol% of the indicated siloxane unit and whose total value is 100 mol%. As stated above, the sum of m plus n generally comprises more than 50 and is suitably at least 90-Branched. methyl polysiloxane fluids can be prepared by any suitable method which will give substantially complete endblocked fluids which are substantially free of silicone bonded hydrolyzable bar groups such as hydroxyl. Typically, branched filaments can be prepared by cohydrolysis of appropriate amounts of the appropriate hydrolysable silanes and / or alkoxysilanes, such as (o fi3) 3 sicl, (c fl ögsiocnä and (oH3) 2si (ocH3) 2, and køhaeheatiøh of the resulting silanols in the well known manner. Endblocked methyl polysiloxane fluids, which are prepared, often contain low molecular weight ) 3Si72O and cyclopolysiloxanes of the formula [(CH3) 2SiQ73_10, which may or may not be removed from the fluid as desired. In any case, the end-blocked methylpolysiloxane fluids, especially the higher molecular weight fluids which are likely to contain trace amounts of catalytic species such as silanol, undergo rearrangement reactions at high temperature to produce additional amounts of said lower molecular weight species.

Bette rearrangements are of particular importance with certain fluids, such as the trimethylsiloxane end-blocked polydimethylsiloxane linear fluids exemplified hereinbefore, which have a viscosity of from 10 to 100 millipascal seconds at 2500. These fluids are of particular value. as a heat transfer medium, in which use they are often subjected to temperatures in excess of 300 ° 0- 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 pressures 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 low molecular weight formation of siloxanes.

While the end-blocked methyl polysiloxane fluid (i) consists essentially of siloxane units bearing only methyl groups, 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 end-blocking groups.

The viscosity of the endblocked methylpolysiloxane (i) is not critical and may have any value- Low viscosity having methylpolysiloxane fluids, e.g. up to 10 pasolal seconds, are relatively easy to handle in such operations as holding, piping, mixing and stirring, but very low viscosity fluids, e.g., up to 10 millipascal seconds, may have low boiling points, which may make pressure equipment necessary for their accommodation during heating operations.

Higher viscosity having methylpolysiloxane liquids, e.g. from 10 to 100 pascalseconds, and rubbers, e.g., from 0.1 to 10 kilopascalseconds, may be more difficult to handle but may not require pressure equipment during heating operations due to their higher or non-existent boiling points. The process and compositions of the invention are effective. the same for all viscosities of (i).

By fluid is meant here 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), which are mixed with the methylpolysiloxane (1), are derivatives of group 4A metals in the periodic table of the elements, ie titanium, zirconium and hafnium. 78 083 05 -2 e While derivatives of each element are active 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. that zirconium and hafnium are substantially identical in 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 hafnium, or zirconium mixed with less 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 gel to give 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. Suitably the organometallic compound is soluble in the methylpolysiloxane (i), although this is not necessary. i g A preferred and readily available class of organometallic compounds (ií) are zirconium soaps, which are longer chain acid derivatives of zirconium, such as zirconium okman0qt, which is well known as a wiper in color preparations. The organozirconium compounds and organotitanium compounds are well known in the dye and polymer art 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 bond 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 at the maximum 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 joined by the same or different silicone radicals in the molecule. Any silicone valence in (v) which is not satisfied with an oxygen-metal bond or by said hydrocarbon radicals is satisfied with divalent oxygen atoms which join 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 R 1, Zr or Hf atoms, or by oxygen-bound organic radicals , A type of siloxy-metal compounds (v) are the polydimethylsiloxy-metal compounds of the general formula (-O [(CH3) 2SiQ7y) 4M, where M represents mi, Zr or Hf, y is an integer greater than zero and the insignificant 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 listed in Pode, and others in the above reference. Another type of siloxy metal compounds (v) are tetrakistrimethyl siloxy metal compounds of the formula [(CH3) 5SiQZM, where M represents Ti, 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 form * for (v) should be taken as reference 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 tetrakistrimethylsiloxymethyl compounds, it may be present in (v) small amounts of partially hydrolyzed and condensed molecules bearing less than 4 trimethylsiloxy groups per liter. The degree of axillary hydrolysis and condensation would not be so great as to render the siloxy metal compound (v) insoluble in the methyl polysiloxane (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).

When 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 to form a metal-rich thermostability additive having more than 0.1% by weight of 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, the organometallic do 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 of the invention, it may also be admixed 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 then can 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 giloxy 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 to siloxane arrangement.

In the process of the invention, the desired amount of the organometallic compound (ii) or the siloxy-metal compound (v) is to 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 can be used: in the well-known manner to facilitate mixing. All solvents would be unreactive with (i) or (ii) and conveniently removed from the mixture prior to thermal decomposition of the organometallic compound (ii) ° Thermal decomposition of the organometallic compound (ii) is done by heating the mixture of (ii) i (i) in an inert atmosphere under appropriate 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 organomevallic 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 reaching ) for a period of from 6 to 24 hours. Preferably, 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 sols must be removed Precipitation products such as G02, hydrocarbons, acids and alcohols, are suitably removed before the stabilized methylpolysiloxane 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 can 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. an organosilicone anhydride compound (iv) in the process of the invention is optional. A methyl polysiloxane fluid with improved resistance to siloxane arrangement at high temperature 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 method.

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

The organosilicon anhydride compound (iv) may be any silane, siloxane or silk web which carries at least one silicone-bonded hydrogen atom per molecule and which is soluble in the methylpolysiloxane (i). Preferably, the organosilicone 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, isopropyl, 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, alkoxy, and halogen. For maximum thermostability, the organosilicone compound (iv) carries only silicone-bonded food, hydrogen and divalent acid radicals.

Examples of organosilicone anhydride compound (iv) include silanes such as C6H5 (CH3) 2SiH, CH3 (C6H5) 2SiH and (Q§2) 4§i (CH) H, silk webs such as man) '2sicn2cs2si (c1¶3) 2a and enoxanes such as us; en) 2s1g73s1 (o1¶3) 21¶, s1¿ös1 (cs3) 2s_74, s1¿ösi (cs3) (c6æz4) n74, cösssi si (cH¿) 2H_73, ¿fi (cs) s1o_74, H (cH3) 2sio ¿Ñ (cH3) s1g730s1 (cH3) 2H and (ca5) d3sio¿ïcnö) zsio_7z (css) sio_75si (æš) 3. .

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) to be used in the process of the invention to achieve appreciable improvement in thermostability is any amount sufficient to give up to 0.05 parts by weight of silicone-bonded hydrogen for every 100 parts by weight of the thermostabilized methylpolysiloxane containing from 0.001 to 0.1% by weight of metal. However, the amount of (iv) added would not be so large as to form a gel structure in the composition. The degree of improvement in thermostability will vary directly with the amount of Sv (iv) used. Optimal improvement in thermostability can be obtained by using enough (iv) to give at least one silicone-bonded hydrogen from (iv) for each active: hydrogen atom. , such as SiOH, in the methylpolysiloxane (i) to be stabilized. 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" 1; 7808305-2 by A. Lee Smith, Publisher John Wiley and Sons, Inc-, N-Y-, U-S-A-, pp. 136-38 The ethylpolysiloxane fluids prepared by the process of the invention are useful as non-curing heat transfer fluids in high temperature, non-oxidative substantially anhydrous environments. Conventional additives for heat transfer fluids such as lubricants, and anti-wear additives may be mixed with the thermally stabilized fluids of the invention, if desired. In particular, anti-oxidants may be mixed with said fluids to increase 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 can escape from it despite the environment being maintained as 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 may be prepared directly from the appropriate amounts of methylpolysiloxane (i) and organometallic compound (ii) or siloxymetal compound (v).

Alternatively, the thermally stabilized methylpolysiloxane can be prepared indirectly by mixing a previously prepared thermostable additive of the invention with an appropriate 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 For example, a thermally stabilized fluid of 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 a heat source. , such as a solar collector, an electric heating element and a flame, a heat exchanger, and the following components. Alternatively, in the in-situ process, a methyl polysiloxane fluid (i) may be placed in said system and an appropriate amount of organometallic compound ( ii) or siloxy-metal compound (v) is then added with the methylpolyeiloxane ( in); or a mixture of the methyl polysiloxane (i) and organometallic compound (ii) or siloxy-metal compound (v) can be prepared and placed in said system. Decomposition of the organometallic compound (ii) can then be carried out in said system. 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 any case, each organosilicone hydride compound (iv) can be added to the thermally stabilized methylpolyleoxane 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 methylpolysiloxane thermostability additive by mixing sufficient zirconium okbanoate with a trimethylsiloxane turn-blocked polydimethylsiloxane fluid to give about 3% by weight of zirconium in the mixture and heat the resulting mixture under a nitrogen blanket for at least 6 hours at 35000. 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 zirconium 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 trimethylsiloxane end-blocked polymethylhydrogensiloxane fluid. 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, moisture, 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 by way of illustration and non-limiting invention, which are properly described in the appended claims. All parts and percentages are by weight unless otherwise indicated viscosities are measured in centipoise 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 by 135.3224 and rounded off e vsoszos-z 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 possible ninerei prite at 120 ° C and 6.67 kg of pressure and the ateretea was cooled, 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 vessel was purged with nitrogen, then sealed and the mixture heated for 24 hours.The pressure in the reaction vessel was noted to increase for 24 hours ar »The hot reaction vessel was slowly vented to atmospheric pressure to remove gaseous products and the product, 6.59 parts, was cooled to room temperature and filtered 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 200 / minute using a nitrogen flow of 200 cm 3 / min. so% a 90% vikxferiuet occurred, feathers 415 ° c, 4e7 ° c, a 5o3 ° c. reepexei- ve. The analysis 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 according to the invention gained weight percentages of 10% at 495 ° C. so% at 5a1 ° c een go f at 62800, thereby showing the improvement in thermostability achieved by the process of the invention- This is an example of a thermally stabilized methylpolyleoxane fluid in an open system- Example 3 Trimethylsiloxane end-blocked polydimethylsiloxane 2 was mixed with the following organometallic compounds 8, the siloxymethyl compounds and the thermostability additives of the invention in sufficient quantity to give 0.02% of Group 4A metal; (1) A thermostability additive prepared from tetrakis (2-ethylhexyl) titanate (2.25% Ti) as in Example 1; (2) Tetrakis (2-ethylhexyl) titanate; (3) Tetrakis- (trimethylsiloxy-kon-ironium; (4) Zirconium-octanoate (69ê Zr) in mineral spirits; (5) Iron-octo-för 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 mixtures were evaluated for improved thermostability using thermogravimetric analysis (TGA-) as in Example 2. in Table I, and except for comparison fluid, they are arranged according to an increase of 10% weight loss temperature. noticeably better overall results (10, 50, and 90% by weight) were obtained from compositions prepared from thermostability additives, dowel-s- (1), (7) and (8). All compounds except zirconium acetylacetonate were soluble in the fluid. Compounds (2), (4), and (6) were thermally decomposed during TGA analysis to thereby form a thermally stabilized methylpolysiloxane of the invention. Example 4 A trimethyl end-blocked polydimethylumoxyl the viscosity of 10 mPa-s at 25 ° C was analyzed by gas-liquid chromatography (GL.C.) to determine the total amount of cyclopolydimethylsiloxanes in the fluid, The fluid was then heated for 25 hours, 100 hours, and 400 hours v1 < 1035o ° ci tetaae pipes possibly stainless steel. The bar was opened and the contents re-examined as above to determine the new cyclopolydimethylsiloxane content. An increase in% by weight of cyclopolydimethylsiloxanes was noted in each case. The experiment was repeated with the following compositions according to the invention based on the above 10 mPa-s. the fluid: (QJ Fluidum + 0.75% of the zirconium octanoate additive in Example 1, (100 Fluidum + 0.75% of tetrakis (trimethylsiloxy) zirconium, (ll) Composition (9.) + trimethylsiloxane end-blocked polymethylhydrogensiloxane, (l2¿ Composition (9-) + hexamethylethylhydrocyclotetrasiloxane, (133 Composition (10.) + Trimethylsiloxane end-blocked polymethylhydrogensiloxane- After heating at 350 ° C for 25, 100 ooh 400 hours in sealed stainless steel tubes, the above minor compositions of the invention were subjected to increase in cyclopolydimethylsiloxane formation than the comparator. This shows the increased thermal stability of the fluid in a closed system with the process of the invention. numbered in Table II- The composition (11) (12), and (13-) had a concentration of silicone-bonded hydrogen of 0.004% based on the weight used of the composition (9-), (9-) and (10- ) respectively.

Example 5 The experiment of Example 4 was repeated with two trimethylsiloxane end-blocked polydimethylsiloxane fluids having viscosities of 20 and 50 mPa 3, respectively. A composition according to the invention was prepared in each case as follows: (14-) 20 mPa ° fluid + 0.75% of the zirconium octanoate additive in Example 1, (l5.) Kbmposition (l4.) + trimethylsiloxane end-blocked polymethylhydrogensiloxane, (16.) 50 mPa fluid + 0.75% of the zirconium octanoate additive in Example 1, (17-) Kbmposition (16-) + trimethylsiloxane end- 17 78Û83Û5'2 blocked polymethylhydrogensiloxane- The results are summarized in Table III. Compositions (15th) and (17th) had a concentration of silicone-bonded hydrogen of 0.004% based on the weight used of compositions (14-) and (16-) 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 / cm2, pipeline for transferring the heat transfer fluid between the heat source and the heat exchanger and associated control and monitoring equipment was charged with the comparison fluid of Example 4 as the heat transfer fluid. The fluid was allowed to circulate during a nitrogen purge in the heat transfer loop at 21 ° C for 24 hours to dry and release the fluid from oxygen. The temperature of the fluid was then increased to 36 ° 0 for 800 hours. The fluid was tested after 25, 100, 400 and 800 hours and analyzed by G-L.C- as in Example 4 for cyclopolydimethylsiloxane content. The test was repeated with composition (9) according to Example 4 as heat transfer fluid, instead of the control fluid, except that the test temperature was increased to 370 ° C. While the control 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% of cyclopolydimethylsiloxane, respectively. 18 vsossos-2 N fl ø fi wo Heø mæm acw www Nmm www mom o \ o om cßm @ ßm Nam Hem qøm øwm owe Nam noe o \ o om o \ d 000 h fl anhø E0uua5Hàßha3 fi>. <. 5.BH H fl mmää .fl waøucwon fl unnßm fi man * * o \ a ~ o + o »nu pø flfi møm d fl e ° \ a Hø.o * www www owe mmv New» Ne o fi e wow wav OH nævwæ fl ANVHN ñ @ U »NH axnmvom ñ ^ nv ~ N_ så., _« ~ Hv fi @: øw: H ^ w: flfl uhwuv H fi nuøä 4: anshø '7808305-2 19 nui fl u »N ** uusa fl u w.Hmn *« «°. <> HH w ~. = Ñm fi ví @HH> m. = Mm. = ñ ~ Hv «« °. <> HH. @ ~. ° AHHU> m. ~ M <.H @ ~ .c _ ~ = Hv w @. ~ M <.H «« @@. ° _ hav «ßm.ßH ~ mw ¶ @ <. M ^ m .ums o fi v wm fl wpmuswh .E fi u Oo: .Eau 00 .... .Eau mw ~ wv_uoomn v «>« um fl: uH fi ncuxo flfi u fi huua fl uwmmao fl shu = c «» fl m ° aaou HH flfi wßß m 5-2 Hv. . ~ mm.NN © m.m flfl æ.o wn.o mm.m. æm.HN ~ .mN oo.oH .Eau Oøà .Eda OCH <~. = mæ.H mm.m ~ <. = m ~ .HH @ .m åmmawm ~ w »ooomn ud» wsmmu fifi ncuxo flfi m fi hvun fl un fi oma fi xho HHH flfl øâdß ñß ñß ñß ñß æmä omv mm fl mhwwsmw fi m fi u ñe fi v nm-mmë owv om fl ohæusmw .HUCOHÜHMOQÉOX

Claims (2)

21 PATENT REQUIREMENTS A process for the preparation of a thermoatable methylpolyeiloxane additive, characterized by (A) mixing components consisting essentially of (i) a trimethylsiloxane end-blocked methylnolysiloxane fluid having an average of from 1.9 to less than 3.0 methyl bases. silicone, and (ii) an organometallic compound in an amount sufficient to give more than 0.1 but not more than 10;) parts by weight of the metal per 10% by weight of the mixture of (i) blouse (ii), said organometallic compound being selected from consisting of organotitanium, organoacirconium and organohafnium compounds, each organic primer consisting of carbon, oxygen and hydrogen atoms and bound to the metal by at least one metal-oxygen-carbon bond and (B) heating the mixture of (i) blouse (ii) in an inert atmosphere to decompose the organometallic compound. A process according to claim 1, characterized in that the organometallic compound is zirconium octanoate and the mixture of (1) nina (ii) is heated via about 35 ° C for at least 6 hours. 7808305-2 7808305-2 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 especially useful as the heat transfer fluid in non-oxidative, anhydrous environments.