RU2296767C1 - Functional metallosiloxanes and method for their preparing - Google Patents

Abstract

FIELD: chemistry of metalloorganic compounds, chemical technology.

SUBSTANCE: invention relates to synthesis of organosilicon compounds. Invention describes novel functional metallosiloxanes of the general formula (I): M[OSiR'R''_n(OAlk)_2-n]_m (I) wherein M means bi- or trivalent metal of the following group: Zr, Zn, Fe (II), Fe (III), Ce, Cu, Cr, Eu and value m corresponds to metal valence; Alk means a substitute -CH₃ or -C₆H₅; R' means substitute -CH₃ or -C₆H₅ or -NH₂(CH₂)₃; R'' means a substitute -CH₂=CH; n = 0 or 1. Also, invention relates to a method for synthesis of functional metallosiloxanes involving interaction of sodium-oxy(alkoxy)organosilane chosen from group sodium-oxy(alkoxy)organosilanes of the formula (II): NaOSiR'R''(OAlk)_2-n (II) wherein R', R'', Alk and n have above given values with metal salt chosen from group of metal salts of the general formula (III): MX_m (III) wherein M and m have above given values; X means Cl or Br or -CH₃COO. Invention provides improving compatibility of synthesized compounds with polymeric compositions and variation of metal type that allows improving their thermostabilizing effects in addition to polymer. Invention can be used in synthesis of different modifying agents of different polymers, in particular, thermostabilizing agents.

EFFECT: improved method of synthesis, improved and valuable properties of compounds.

24 cl, 2 dwg, 1 tbl, 9 ex

Description

The invention relates to the field of chemical technology of organosilicon compounds and may find industrial application in the production of modifiers, in particular thermal stabilizers, of various polymers. More specifically, the invention relates to new functional metallosiloxanes and to a process for their preparation.

The use of metals, in particular salts of organic acids, as thermostabilizing additives to polymer compositions, in particular organosiloxane polymers, is based on their ability to inhibit free radical chain processes occurring during thermal oxidation, deactivating the formation of free radicals or intermediate oxidation products (US patent US 3142655, 1964; auth. Certificate of the USSR No. 369131, 1973). However, for effective thermal stabilization of polymers, it is necessary to solve a number of problems, such as, for example, the possibility of homogeneous introduction of the additive, the absence of its volatility at high temperatures, bringing dispersion of stabilizing additives to nano-sizes, including in rubber compounds, etc.

The addition of organic salts of a number of metals to polymer compositions as thermostabilizing additives is known (see, for example, US patents US 4193885, 1980, US 4528313, 1985). In the descriptions of the patents considered a fairly wide range of metals. However, the poor compatibility of such compounds and polymer matrices and the problems of their dispersion in the polymer significantly reduces their effectiveness and complicates the process of introducing additives.

Heat-resistant and partially functional metallosiloxane compounds are known, obtained by the interaction of 1,4-trimethylsiloxybenzene and sodium hydroxide, followed by the exchange of sodium for aluminum, zinc and calcium (J. Chem. Soc., Dalton trans., 1999, p. 4535-4540). These compounds have poor solubility, contain residual water and their structure is not determinate.

The interaction of copper dichloride and phenylsilanol in the presence of sodium hydroxide and sodium metal is described, which results in the production of phenyl copper sodium siloxane. A nickel-containing metallosiloxane was obtained in a similar manner (Metallorgorgan. Chemistry, 1991, 4, 74; DAN SSSR, v. 325, No. 6, 1992; Eur. J. Inorg. Chem. 2004, 1253-1261). Other radicals of silicon atoms, as well as other metals were not considered. The obtained compounds were not investigated for their thermostabilizing effect in polymer mixtures. The disadvantages of this process are the use of metallic sodium in the process, as well as the content of water and alcohols in the composition of these compounds complicate their use in the following stages.

The closest in structure to the claimed functional metallosiloxane compounds and to the method for their preparation is diethoxyaluminoethylsilicate obtained by the interaction of dialkoxyaluminium bromide and potassiumoxytriethoxysilane (Zhokh, 1995, v.65, issue 4, s.612-615). The resulting compound contains, along with the metal, functional groups at the silicon atom, which allow further transformations. The disadvantage is the absence of organic radicals at silicon atoms, which makes this compound practically inorganic and introduces restrictions on the compatibility of such compounds and polymer matrices. In addition, the proposed method is not universal, it was carried out only with the participation of aluminum-containing compounds, the introduction of other metals has not been studied. The use of the synthesized compound as a thermostabilizing additive to polymer compositions is not described.

The objective of the invention was to obtain a new technical result, which consists in the creation of new functional metallosiloxanes with the set of properties necessary for their effective use as thermostabilizing additives: contain in their structure a certain number of atoms of the corresponding metal, have good solubility in organic solvents and good compatibility with polymer matrix, contain functional groups capable of interacting ju with the components of the polymer composition into which they will be introduced.

In addition, the objective of the invention was to develop a new method for producing the claimed functional metallosiloxanes in acceptable conditions, giving a high yield of a product of a given structure and suitable for use in industrial conditions.

The problem is solved in that metallosiloxanes of the general formula (I) are obtained,

where M is a divalent or trivalent metal from the series: Zr, Zn, Fe (II), Fe (III), Ce, Cu, Cr, Sm, Eu, and the value m corresponds to the valency of the metal;

Alk means a substituent CH ₃ - or C ₂ H ₅ -;

R 'is a substituent of CH ₃ - or C ₆ H ₅ - or NH ₂ (CH ₂ ) ₃ -;

R "means a substituent CH ₂ = CH-;

n is 0 or 1.

In particular, M may mean a divalent metal from the series Zr, Zn, Fe (II), Cu, and n may be 0 or 1.

In particular, M can mean a trivalent metal from the series Fe (III), Ce, Cr, Sm, Eu. Moreover, n can also be 0 or 1.

As in the case of a divalent metal, and in the case of a trivalent metal, Alk may mean CH ₃ - or C ₂ H ₅ -, R 'may mean CH ₃ - or C ₆ H ₅ - or NH ₂ (CH ₂ ) ₃ -. In particular, in cases where n is 0, R "means a substituent CH ₂ = CH-.

Functional metallosiloxanes are prepared by reacting a natrioxy (alkoxy) organosilane of the general formula (II)

where R ', R ", Alk, n have the above meanings, with metal salts of the general formula (III),

,

,

where M and m have the above meanings,

and X means Cl or Br or CH ₃ COO- according to the general scheme:

Functional metallosiloxanes are intended for use as thermostabilizing additives in polymer compositions.

In contrast to the known diethoxyaluminoethyl silicate, the claimed functional metallosiloxanes contain various organic substituents on silicon atoms, as well as various metal atoms. This makes it possible to significantly improve the compatibility of such compounds and polymer compositions of various types, including varnishes and liquids, to obtain various modifications of these compounds using functional groups, and also by varying the type of metal to improve their heat-stabilizing effect when introduced into the polymer.

The problem is also solved by the fact that a method has been developed for the preparation of new functional metallosiloxanes of the general formula (I), which consists in the interaction of the sodium-alkoxy organosilane of the general formula (II)

where R ', R ", Alk, n have the above meanings,

with metal salts of the general formula (III),

,

,

where M and m have the above meanings,

and X is Cl or Br or CH ₃ COO-.

The general scheme of the process can be represented as follows:

where R ', R ", Alk, n, X, M and m have the above meanings.

In particular, the process of interaction of natrioxy (alkoxy) organosilane with a metal salt can be carried out simultaneously with the process of formation of natrioxy (alkoxy) organosilane from sodium hydroxide and alkoxyorganosilane selected from a series of alkoxyorganosilanes of the general formula (V),

,

,

where R ', R ", Alk, n have the above meanings.

In this case, the process is carried out without isolating the sodium oxy (alkoxy) organosilane and the metallosiloxane is obtained in one stage according to the following general scheme:

In both cases, the process of interaction of the components can be carried out in an organic solvent selected from a number of esters: tetrahydrofuran, dioxane, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, or from a number of lower alcohols: methanol, ethanol, propanol. The interaction of the starting components is preferably carried out at a temperature ranging from minus 5 ° to 50 ° C, at their stoichiometric molar ratio and for the time required for the complete conversion of the metal salt.

In particular, the metal salt may be selected from the series of metal salts of the general formula (III), where M is a divalent metal from the series: Zr, Zn, Fe (II), Cu, or the metal salt may be selected from the series of metal salts of the general formula (III) ), where M means a trivalent metal from the series: Fe (III), Ce, Cr, Sm, Eu.

In particular, in the case when M is equal to a divalent metal, the general process scheme can be represented as follows:

In this case, when M is Cu ^{+ 2} , when R 'is CH ₃ -, R "is CH ₂ = CH-, n is 0, the production reaction has the following form:

In particular, in the case when M is equal to a trivalent metal, the general process scheme can be represented as follows:

In the case when M is Fe ⁺³ , R 'is CH ₃ -; Alk is equal to C ₂ H ₅ -, n is 0, the process can be represented by the following scheme:

The resulting compound has the following structure:

In particular, sodium oxymethyldiethoxysilane can be used as the sodium oxy (alkoxy) organosilane, and iron (III) chloride can be used as the metal salt.

In particular, methyl vinylldiethoxysilane or methyl vinyl diethoxysilane can be used as alkoxyorganosilane, and iron (III) chloride or zirconium chloride, respectively, can be used as a metal salt.

Obtained according to the claimed method, functional metallosiloxanes are intended to obtain a statistical cyclolinear structure by the method of hydrolytic polycondensation of functional polymetallosiloxanes.

The structure of the synthesized compounds was proved by elemental analysis, NMR and IR spectroscopy, and chromatographic analysis methods.

According to GPC, the synthesized functional metallosiloxanes have a monomodal molecular weight distribution (see Figure 1). According to GPC data obtained using linear polystyrene standards, the molecular weights of metallosiloxanes correspond to ~ 200 (see figure 1).

The claimed compounds have a structure that is optimal for the introduction of siloxane polymer compositions, due to its polymer nature and the presence of functional groups. In contrast to the known compounds (monomeric, poorly compatible with polymers, or expensive polymeric and lacking functional groups), their use allows polymer-like transformations to further improve compatibility with certain polymer compositions. The presence of chemically bonded transition metal atoms in their structure allows, in particular, the use of these compounds as effective thermostabilizing additives.

A study of the thermal degradation of the functional metal siloxanes themselves showed that their thermal and thermal oxidative degradation is not accompanied by the destruction of the molecular skeleton and the formation of fragments.

Figure 2 shows the TTA curves of a gel-vinylsiloxane oligomer in air and in an inert medium. It can be seen from the above data that the mass loss begins rather early (due to the high concentration of the end groups) - the total loss in argon is less than 10%, and in air about 25%, which is significantly less than the real organic component of metallosiloxane.

The study of thermal stabilization of the polymer in the presence of synthesized metallosiloxane additives was carried out by the DTA method (the procedure is given after the examples). Methylsilsesquioxane resin was used as the polymer of the thermally stabilized polymer. The introduction of metallosiloxane additives in the composition of the resin was carried out by co-dissolution. The obtained results of the DTA tests, shown in the table, show that the activity of the obtained additives as heat stabilizers is high. As a comparative example, the table shows the parameters for silsesquiocane resin without the addition of metallosiloxanes.

In all cases, the amount of added additive was 2-3% calculated on pure metal. As can be seen from the data presented, in all cases, the stabilization effect is observed, so that the temperature of 10% losses with the introduction of methylethoxyzhelezosiloxane shifts by 90 ° C, and in the case of aminopropylethoxyceryl siloxane - by more than 120 ° C towards high temperatures. The coke residue content does not change, however, the maximum position on the DTA curve shifts in the case of the first additive by almost 180 ° C, and in the case of a cerium-containing modifier, by 140 ° C. Aminopropylethoxyzhelezosiloxane turned out to be less effective, but even in this case the properties of the composition are higher than in the comparative system.

Thus, the first series of tests confirmed the promise of using functional metallosiloxanes as thermal stabilizers.

Figure 1 presents the GPC curve of iron-containing methyldiethoxysiloxane.

Figure 2 presents the TGA curves of iron-methylvinyl ethoxysiloxane-siloxane, where curve 1 is heating in argon, 2 is heating in air (heating rate 5 ° C / min).

The table shows the DTA data of methylsilsesquioxane resin in the presence of metallosiloxanes as thermostabilizing additives according to examples 1, 3 and 7. As a comparative example, the DTA data of pure methylsilsesquioxane resin are given.

The invention can be illustrated by the following examples:

Example 1. Synthesis of iron-containing ethoxy-functional methylsiloxane.

To 4.45 g (0.0274 mol) of iron (III) chloride in 200 ml of THF, a solution (0.0822 mol) of sodium oxymethyldiethoxysilane in 70 ml of THF is added dropwise at a temperature of + 5 ° C. The reaction mixture was stirred at 50 ° C for 28 hours. The precipitate of sodium chloride is filtered off, the volatiles are removed in vacuo. Product yield 68%. According to the elemental analysis found: Fe 9.39%; Si 17.41%; C 36.28%; H, 8.02%. Calculated: Fe 11.09%; Si 16.74%; C 35.8%; H 7.75%.

Example 2. The synthesis of samarium-containing ethoxyfunctional methylsiloxane:

7.036 g (0.0274 mol) of samarium chloride, 14.64 g (0.0822 mol) of methyltriethoxysilane and 3.29 g (0.0822 mol) of sodium hydroxide are mixed in 200 ml of THF, at a temperature of 0 ° C, in an inert medium gas. The reaction mixture was stirred for 4 hours at room temperature. The precipitate of sodium chloride is filtered off, ethanol and excess methyltriethoxysilane are removed in an oil pump vacuum. Product yield 79%. GPC: monomodal distribution M _p = 200 according to polystyrene standards). According to elemental analysis, found: Sm 24.52%; Si 14.46%; C 43.03%; H 6.99%. Calculated: Sm 25.11%; Si 14.06%; C 42.19%; H 6.53%.

Example 3. Synthesis of cerium-containing ethoxyfunctional methylsiloxane:

The synthesis is carried out according to the procedure described in example 2, but instead of samarium chloride, cerium chloride in an equimolar amount is used, methanol is taken instead of THF. Product yield 73%. GPC: monomodal distribution M _p = 200 (by polystyrene standards). NMR ¹ H spectrum in CDCI ₃ : δ = 0.13 ppm. (m. 9H, SiCH ₃ ), δ = 1.21 ppm. (t. 18 N, CH ₂ CH ₃ ), δ = 3.79 ppm. (q. 12H, OCH ₂ ).

Example 4. Synthesis of zinc-containing methoxy-functional phenylsiloxane:

The synthesis is carried out according to the procedure described in example 2, but zinc chloride is used instead of samarium chloride and phenyltrimethoxysilane is used instead of methyltriethoxysilane. Product yield 81%. GPC: monomodal distribution M _p ~ 200 (by polystyrene standards). NMR ¹ H spectrum in CDCL ₃ : δ = 3.47 ppm. (m. 6H, OCH ₃ ); δ = 7.2 ppm (m. 5H, C ₆ H ₅ ). Elemental analysis: found,%: Si 11.95; Zn 14.84; C 39.06; H 4.87. Calculated,%: Si 12.99; Zn 15.16; C 38.94; H 5.09

Example 5. Synthesis of iron-containing ethoxy-functional methylvinylsiloxane:

The synthesis is carried out according to the procedure described in example 2, but instead of samarium chloride, iron (III) chloride is used, instead of methyltriethoxysilane, methylvinyl diethoxysilane is used, all in an equimolar amount. The yield of 82.2%. GPC: monomodal distribution M _p = 200 (by polystyrene standards). NMR - ¹ H spectrum in CDCl ₃ : δ = 0.15 ppm. (p. 9H); δ = 1.2 ppm (m. 9H); δ = 3.71 ppm (m. 6H); δ = 5.92 ppm (m. 9H). Elemental analysis: found,%: Si 22.68; Fe 13.39; C 29.76; H, 5.71. Calculated,%: Si 18.75; Fe 12.46; C 40.06; H, 7.35.

Example 6. Synthesis of zirconium-containing methoxy-functional siloxane:

The synthesis is carried out according to the procedure described in example 2, but instead of samarium chloride, zirconium chloride is used; instead of methyltriethoxysilane, methylvinyl diethoxysilane is used, all in an equimolar amount. The product yield of 89.5%. GPC: monomodal distribution M _p = 200 (by polystyrene standards). NMR - ¹ H spectrum in CDCl ₃ : δ = 0.15 ppm. (p. 9H); δ = 1.2 ppm (m. 9H); δ = 3.71 ppm (m. 6H); δ = 5.92 ppm (m. 9H). Elemental analysis: found,%: Si 17.66; Zr 27.79; C 14.66; H, 5.71. Calculated,%: Si 17.20; Zr 28.04; C 14.76; H 5.5.

Example 7. Synthesis of iron-containing γ-aminopropyl diethoxysiloxane:

Under stirring, under a stream of argon, 1.62 g (0.010 mol) of iron (III) chloride, 4.43 g (0.020 mol) of γ-aminopropyltriethoxysilane, 0.8 g (0.020 mol) of sodium hydroxide are mixed in 50 ml of methyl tert-butyl ether. The reaction is carried out for 2 days at room temperature. The precipitate of sodium chloride is filtered off, volatile compounds are removed in a vacuum oil pump. GPC: M _r ~ 200. NMR ¹ H in CDCI ₃ : δ = 0.6 ppm. (m. 4H, SiCH ₂ ), δ = 0.84 ppm. (d. 4H, NH ₂ ), δ = 1.22 ppm. (m. 6H, CH ₂ CH ₃ ), δ = 1.67 ppm. (broad s. 4H, CH ₂ ), δ = 3.33 ppm. (q. 2H, CH ₂ NH ₂ ), δ = 3.8 ppm. (m. 4H, CH ₂ O).

Example 8. The synthesis of chromium-containing methoxy-functional siloxane:

The synthesis is carried out according to the procedure described in example 2, but instead of samarium chloride, chromium chloride is used, instead of methyltriethoxysilane, methylvinyl diethoxysilane is used, all in an equimolar amount. The product yield of 75.3%. GPC: monomodal distribution M _p = 200 (by polystyrene standards). NMR - ¹ H spectrum in CDCl ₃ : δ = 0.15 ppm. (p. 9H); δ = 1.2 ppm (m. 9H); δ = 3.71 ppm (m. 6H); δ = 5.92 ppm (m. 9H). Elemental analysis: found,%: Si 20.61; Cr 12.71; C 34.96; H, 6.71. Calculated,%: Si 20.84; Cr 12.90; C 35.73; H, 6.70.

Example 9. Synthesis of poly (copper) methylvinylsiloxane:

11.9 g (0.04 mol) of copper-containing methoxyfunctional methylvinylsiloxane Cu [OSiMeVinOMe] _{2 is} dissolved in 100 ml of THF and 0.08 ml (0.004 mol) of water is added with stirring in a ratio of 1 mol of metallosiloxane / 0.05 mol of H ₂ O. After After 10 hours stirring at room temperature, the volatiles are removed in vacuo. Product yield 73%. GPC: wide monomodal distribution M _p ~ 100000 (by polystyrene standards). NMR - ¹ H spectrum in CDCl ₃ : δ = 0.15 ppm. (p. 3H); δ = 3.71 ppm (m. 3H); δ = 5.92 ppm (m. 3H).

Test procedure for the thermostabilizing action of metallosiloxanes.

A solution of 0.7 g of methylsilsesquioxoxane resin in 6.5 ml of methyl tert-butyl ether (MTBE) and a solution of 0.14 g of tris (diethoxymethylsiloxy) iron (or other synthesized metallosiloxane) in 2 ml of MTBE (1.8% Fe weight of resin). The resulting homogeneous solution is kept in air in a thin layer until the solvent dries. The obtained uniform transparent film is heated in a vacuum oven at a temperature of 200 ° C for 2 hours. Analyze the obtained sample by DTA and compare with the DTA data of methylsilsesquioxane resin without the addition of metallosiloxanes. The results of a number of tests are shown in the table.

Table Example No. Type of additive metallosiloxane T _10% , ° C % coke. rest The maximum position on the DTA curve, ° C one Fe [OSiCH ₃ (OC ₂ H ₅ ) ₂ ] ₃ 620 88 620 3 Ce [OSiCH ₃ (OC ₂ H ₅ ) ₂ ] ₃ 650 89 567 7 Fe [OSi (OC ₂ H ₅ ) ₂ (CH ₂ ) ₃ NH ₂ ] ₃ 575 86 467 Comparative example no 533 88 437

Claims (24)

1. Functional metallosiloxanes of the general formula (I)

where M means a divalent or trivalent metal from the series Zr, Zn, Fe (II), Fe (III), Ce, Cu, Cr, Sm, Eu, and the value m corresponds to the valency of the metal; Alk means a substituent CH ₃ - or C ₂ H ₅ -; R 'is a substituent of CH ₃ - or C ₆ H ₅ - or NH ₂ (CH ₂ ) ₃ -; R "means a substituent CH ₂ = CH-; n is 0 or 1. 2. Functional metallosiloxanes according to claim 1, characterized in that M means a divalent metal from the series Zr, Zn, Fe (II), Cu. 3. Functional metallosiloxanes according to claim 2, characterized in that n is 0. 4. Functional metallosiloxanes according to claim 2, characterized in that n is 1. 5. Functional metallosiloxanes according to claim 1, characterized in that M means a trivalent metal from the series Fe (III), Ce, Cr, Sm, Eu. 6. Functional metallosiloxanes according to claim 5, characterized in that n is 0. 7. Functional metallosiloxanes according to claim 5, characterized in that n is 1. 8. Functional metallosiloxanes according to claim 2 or 5, characterized in that Alk means CH ₃ -. 9. Functional metallosiloxanes according to claim 2 or 5, characterized in that Alk means C ₂ H ₅ -. 10. Functional metallosiloxanes according to claim 2 or 5, characterized in that R 'means CH ₃ -. 11. Functional metallosiloxanes according to claim 2 or 5, characterized in that R 'means C ₆ H ₅ -. 12. Functional metallosiloxanes according to claim 2 or 5, characterized in that R 'is NH ₂ (CH ₂ ) ₃ -. 13. Functional metallosiloxanes according to claim 3 or 6, characterized in that R "means a substituent CH ₂ = CH-. 14. Functional metallosiloxanes according to any one of claims 1 to 7, characterized in that they are intended for use as thermostabilizing additives in polymer compositions. 15. The method of obtaining functional metallosiloxanes according to any one of claims 1 to 13, which consists in the interaction of natrioxy (alkoxy) organosilane selected from a series of natrioxy (alkoxy) organosilanes of the general formula (II)

where R ', R ", Alk, n, M and m have the above meanings, with a metal salt selected from a number of metal salts of the general formula (III)

where M, m have the above meanings; X is Cl or Br or CH ₂ COO-. 16. The method according to p. 15, characterized in that the process of interaction of natrioxy (alkoxy) organosilane with a metal salt is carried out simultaneously with the process of formation of natrioxy (alkoxy) organosilane from sodium hydroxide and alkoxyorganosilane selected from a series of alkoxyorganosilanes of the general formula (V)

where R ', R ", Alk, n, have the above meanings. 17. The method according to p. 15 or 16, characterized in that the interaction of the components is carried out in an organic solvent selected from a number of ethers: tetrahydrofuran, dioxane, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, or from a number of lower alcohols: methanol, ethanol, propanol. 18. The method according to 17, characterized in that the interaction of the components is carried out at a temperature of from minus 5 to 50 ° C, with a stoichiometric molar ratio of the starting components and for the time required for the complete conversion of the metal salt. 19. The method according to p. 15 or 16, characterized in that the metal salt is selected from a series of metal salts of the general formula (III), where M is a divalent metal from the series Zr, Zn, Fe (II), Cu. 20. The method according to p. 15 or 16, characterized in that the metal salt is selected from a series of metal salts of the general formula (III), where M is a trivalent metal from the series Fe (III), Ce, Cr; Sm; Eu. 21. The method according to claim 20, characterized in that sodium oxymethyldiethoxysilane is used as the sodium oxy (alkoxy) organosilane, and iron (III) chloride is used as the metal salt. 22. The method according to claim 20, characterized in that methyl vinylldiethoxysilane is used as the alkoxyorganosilane, and iron (III) chloride is used as the metal salt. 23. The method according to claim 20, characterized in that methyl vinylldiethoxysilane is used as the alkoxyorganosilane, and zirconium chloride is used as the metal salt. 24. The method according to any of paragraphs.15, 16, 18, 21-23, characterized in that the obtained functional metallosiloxanes are intended to produce a statistical cyclolinear structure by the method of hydrolytic polycondensation of functional polymetallosiloxanes.

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