Mixtures Of Cyclic Branched Siloxanes Of The D/T Type And Conversion Products Thereof

Abstract

Mixtures of cyclic branched siloxanes having exclusively D and T units, with the proviso that the cumulative proportion of the D and T units having Si-alkoxy and/or SiOH groups that are present in the siloxane matrix, determinable by .sup.29Si NMR spectroscopy, is less than 2.0 and preferably less than 1.0 mole per cent, are described, as are branched organomodified siloxanes obtainable therefrom.

Claims

1. A mixture of cyclic branched siloxanes having exclusively D and T units, wherein the cumulative proportion of the D and T units having Si-alkoxy and/or SiOH groups that are present in the siloxane matrix, determinable by .sup.29Si NMR spectroscopy, is less than 2 mole per cent, and further comprising at least 5% by weight of siloxane cycles selected from the group consisting of octamethylcyclotetrasiloxane (D.sub.4), decamethylcyclopentasiloxane (D.sub.5), dodecamethylcyclohexasiloxane (D.sub.6) and mixtures thereof.

2. The mixture according to claim 1, wherein the ratio of D to T units is between 10:1 and 3:1.

3. The mixture according to claim 1, wherein the molar mass ratio of the mixture M.sub.w/M.sub.n is in the range of 2<M.sub.w/M.sub.n<50.

4. The mixture according to any of claim 1, wherein the branching T unit derives from alkyltrialkoxysilanes and/or phenyltrialkoxysilanes.

5. The mixture according to claim 1, wherein the branching T unit derives from methyltriethoxysilane.

6. A process for preparing siloxane mixtures according claim 1, comprising (a) an acid-catalysed equilibration of trialkoxysilanes with siloxane cycles and/or ,-dihydroxypolydimethylsiloxane in the presence of at least one acidic catalyst and then b) a hydrolysis and condensation reaction initiated by addition of water, followed by the addition of a silicon-containing solvent, (c) with a subsequent distillative removal of the alcohol released and proportions of the water present in the system, (d) with subsequent addition of toluene and separation of residual water remaining in the system, (e) followed by a neutralization or removal of the acidic catalyst and, if appropriate, removal of any salts formed, (f) with final distillative removal of toluene still present in the system, wherein the silicon-containing solvent preferably comprises the isomeric siloxane cycles octamethylcyclotetrasiloxane (D.sub.4), decamethylcyclopentasiloxane (D.sub.5) and/or mixtures thereof, and mass ratios of silicon-containing solvent to the siloxane having D and T units of 1:1 to 5:1 are advantageously employed.

7. The process according to claim 6, wherein the acidic catalyst is selected from the group consisting of para-toluenesulfonic acid, trifluoromethanesulfonic acid, trichloroacetic acid, sulfuric acid, perchloric acid, phosphoric acid and hexafluorophosphoric acid, in amounts of 0.1 to 2.0 per cent by weight, based in each case on the silicon-containing component of the reaction matrix.

8. The process according to claim 6, wherein the acidic catalyst used is a macrocrosslinked sulfonic acid ion exchange resin, preferably in amounts of 1.0 to 10.0 per cent by weight based in each case on the silicon-containing component of the reaction matrix.

9. The process according to claim 6, wherein the reaction is conducted at temperatures in the range from 20 C. to 120 C.

10. The process according to claim 6, wherein an at least 100% H.sub.2O excess is used, based on the groups to be condensed.

11. The process according to claim 6, wherein the reaction comprises a preliminary equilibration step at temperatures of T >40 C., followed by a condensation initiated by addition of water at temperatures of T >60 C., where the water is added in one portion, in several portions or continuously.

12. A process for preparing branched organomodified siloxanes, wherein in a first step mixtures of cyclic branched siloxanes are provided, preferably according to claim 1, and in a second step the mixtures of cyclic branched siloxanes are acid-equilibrated with silanes and/or siloxanes.

13. A process according to claim 12, characterized in that the silanes and/or siloxanes used are acid-equilibratable silicon compounds, wherein the silanes used are preferably diethoxydimethylsilane, trimethylalkoxysilanes and/or dimethyldichlorosilane, and/or p1 wherein the siloxanes used are preferably tetramethyldisiloxane, -dihydropolydimethylsiloxanes, poly(methylhydro)siloxanes, -dialkoxypolydimethylsiloxanes and/or -divinylpolydimethylsiloxanes.

14. A process according to claim 12, wherein, in the second step, the mixtures of cyclic branched siloxanes are equilibrated with silanes and/or siloxanes in the presence of an acidic catalyst, preferably trifluoromethanesulfonic acid, in an amount of 0.1% by weight.

15. A process according to claim 12, wherein, in the second step in which the mixtures of cyclic branched siloxanes are acid-equilibrated with silanes and/or siloxanes, the equilibration is undertaken over a water-containing macroporous sulfonic acid polystyrene resin, which is preferably used in amounts of 3% to 9% by weight and which has been wetted with 8% to 12% by weight of water, and the specific surface area of which is 35 m.sup.2/g and the mean pore diameter of which is preferably at least 65 nm.

16. A process for preparing branched silicone oils, wherein in a first step cyclic branched siloxanes are provided, preferably according to claim 1, and in a second step the cyclic branched siloxanes are reacted with polydimethylsiloxanes or hexamethyldisiloxane.

17. A starting material for production of stabilizers for PUR foams, for production of defoamers comprising the branched organomodified siloxanes recovered by acidic equilibration, obtainable according to claim 12.

18. The mixture according to claim 1, wherein the ratio of D to T units is between 6:1 and 4:1.

19. The process according to claim 6, wherein the acidic catalyst is selected from the group consisting of para-toluenesulfonic acid, trifluoromethanesulfonic acid, trichloroacetic acid, sulfuric acid, perchloric acid, phosphoric acid and hexafluorophosphoric acid, in amounts of 0.15 to 1.0 per cent by weigh based in each case on the silicon-containing component of the reaction matrix.

20. The process according to claim 6, wherein the acidic catalyst used is a macrocrosslinked sulfonic acid ion exchange resin, preferably in amounts of 2.0 to 6.0 per cent by weight based in each case on the silicon-containing component of the reaction matrix.

Description

EXAMPLES

[0094] 1) Preparation of a cyclic branched siloxane having a target D/T ratio of 6:1 (inventive)

[0095] In a 500 ml four-neck round-bottom flask with a precision glass stirrer and a reflux condenser on top, 52.2 g (0.293 mol) of methyltriethoxysilane were heated to 60 C. together with 65.3 g (0.176 mol) of decamethylcyclopentasiloxane while stirring, 0.400 g of trifluoromethanesulfonic acid was added and the mixture was equilibrated for 4 hours. Then 15.8 g of water and 4.0 g of ethanol were added and the mixture was heated to reflux temperature fora further 2 hours. 10.6 g of water and 65.3 g (0.176 mol) of decamethylcyclopentasiloxane (D.sub.5) were added and the reflux condenser was exchanged for a distillation system, and the constituents that are volatile up to 90 C. were distilled off within the next hour. Gas chromatography analysis (GC) showed that the distillate consists of ethanol/water. 200 ml of toluene were then added to the reaction mixture and the water still present in the system was removed by distillation up to a bottom temperature of 100 C. at the water separator. The reaction mixture was allowed to cool down to about 60 C., the acid was neutralized by addition of 8.0 g of solid sodium hydrogencarbonate, and the mixture was then stirred for complete neutralization for a further 30 minutes. After cooling to 25 C., the salts were removed with the aid of a fluted filter. At 70 C. and with an auxiliary vacuum of <1 mbar applied, the toluene used as solvent was distilled off. Gas chromatography analysis (GC) demonstrated that the distillate consists of toluene to an extent of more than 98%. The distillation bottoms were a colourless mobile liquid, the .sup.29Si NMR spectrum of which shows a D/T ratio of 5.6:1 (target: 6.0:1). Based on the sum total of the Si units detected by spectroscopy, the D and T units bearing Si-alkoxy and SiOH groups respectively, have a proportion of 0.44 mole per cent. The gas chromatography analysis of the liquid also shows a proportion of about 15 per cent by weight of simple siloxane cycles in the form of D.sub.4, D.sub.5and D.sub.6.

[0096] 2) Preparation of a cyclic branched siloxane having a target D/T ratio of 6:1 (inventive)

[0097] In a 10 I four-neck round-bottom flask with a precision glass stirrer and a reflux condenser on top, 783 g (4.39 mol) of methyltriethoxysilane were heated to 60 C. together with 978.7 g (2.64 mol) of decamethylcyclopentasiloxane while stirring, 2.98 g of trifluoromethanesulfonic acid were added and the mixture was equilibrated for 4 hours. Then 237 g of water and 59.3 g of ethanol were added and the mixture was heated to reflux temperature fora further 2 hours. 159.0 g of water and 978.8 g (2.64 mol) of decamethylcyclopentasiloxane (D.sub.5) were added and the reflux condenser was exchanged for a distillation system, and the constituents that are volatile up to 90 C. were distilled off within the next hour. 3000 ml of toluene were then added to the reaction mixture and the water still present in the system was removed by distillation up to a bottom temperature of 100 C. at the water separator. The reaction mixture was allowed to cool down to about 60 C., the acid was neutralized by addition of 60.0 g of solid sodium hydrogencarbonate, and the mixture was then stirred for complete neutralization for a further 30 minutes. After cooling to 25 C., the salts were removed with the aid of a fluted filter. At 70 C. and with an auxiliary vacuum of <1 mbar applied, the toluene used as solvent was distilled off. The distillation bottoms were a colourless mobile liquid, the .sup.29Si NMR spectrum of which shows a D/T ratio of 5.2:1 (target: 6.0:1). Based on the sum total of the Si units detected by spectroscopy, the D and T units bearing Si-alkoxy and SiOH groups respectively have a proportion of 0.43 mole per cent. The gas chromatography analysis of the liquid also shows a proportion of about 15 per cent by weight of simple siloxane cycles in the form of D.sub.4, D.sub.5 and D.sub.6. The GPC has a broad molar mass distribution, characterized by M.sub.w=55258 g/mol; M.sub.n1693 g/mol and M.sub.w/M.sub.n=32.63.

[0098] 3) Preparation of a branched hydrosiloxane having terminal SiH functions from the cyclic branched siloxane from Example 2 with ,-dihydropolydimethylsiloxane and decamethylcyclopentasiloxane (inventive)

[0099] 23.2 g of the product prepared in Example 2, i.e. the cyclically branched siloxane and the simple siloxane cycles, were heated to 40 C. together with 26.7 g of an ,-dihydropolydimethylsiloxane (SiH value: 2.90 eq/kg) and 200.1 g of decamethylcyclopentasiloxane with addition of 0.25 g of trifluoromethanesulfonic acid (0.1 m % based on the overall mixture) in a 500 ml four-neck flask with precision glass stirrer and a reflux condenser on top for 6 hours, then 5 g of sodium hydrogencarbonate were added and the mixture was stirred for a further 30 minutes. With the aid of a filter press (Seitz K 300 filter disc), the salt was separated from the equilibrate. What was obtained was a colourless branched hydrosiloxane having dimethylhydrosiloxy functions in its termini (SiH value: 0.30 eq/kg) and a viscosity of 150 mPas (25 C., Hoppler viscometer). The corresponding .sup.29Si NMR spectrum confirms the target structure.

[0100] 4) Preparation of a branched siloxane having terminal vinyl functions (inventive)

[0101] 97.6 g of the product prepared in Example 2 were heated to 60 C. together with 47.2 g of divinyltetramethyldisiloxane and 105.2 g of decamethylcyclopentasiloxane with addition of 0.25 g of trifluoromethanesulfonic acid (0.1 m % based on the overall mixture) in a 500 ml four-neck flask with precision glass stirrer and a reflux condenser on top for 6 hours, then 5 g of sodium hydrogencarbonate were added and the mixture was stirred for a further 30 minutes. With the aid of a filter press (Seitz K 300 filter disc), the salt was separated from the equilibrate. The corresponding .sup.29Si NMR spectrum confirms, as the target structure, a branched siloxane bearing terminal vinyl functions.