GB2298429A

GB2298429A - Silicone equilibration catalyst

Info

Publication number: GB2298429A
Application number: GB9603822A
Authority: GB
Inventors: Slawomir Rubinsztajn
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1995-03-02
Filing date: 1996-02-23
Publication date: 1996-09-04
Also published as: FR2731227A1; DE19607264A1; JPH08311203A; GB9603822D0

Description

SILICONE EQUILIBRATION CATALYST

Background of the Invention

2298429 The present invention relates to a silicone equilibration catalyst in the form of a reaction product of a silicone fluid having terminal triorganosiloxy units and a linear phosphonitrilic halide (LPNO), where 0 is a halogen atom and preferably chloro. More particulady, the present invention relates the use of an LPNO-silicone catalyst to effect the condensation and/ or equilibration of silanol fluids and mixtures thereof with silicone fluids having terminal triorganosiloxy units.

Silicone gums have been made by equilibrating diorganosiloxane cyclics, such as octamethylcyclotetrasifoxane, with triorganosiloxy terminated polydiorganosiloxanes such as hexamethyidisifoxane. Equilibration can be effected by using a strong base or acid such as sulfuric acid as a catalyst. Although valuable results have been achieved by such procedures, the resulting chain-stopped higher molecular weight polydiorganosiloxanes often have to be stripped of undesirable oligomeric cyclic species resulting from adverse catalytic side reactions.

Alternative procedures for equilibrating organopolysiloxanes can employ an 1-PNO catalyst, and particularly a linear phosphonitrilic chloride (LPNC) having the formula C13P(WC12)nNPC13.PC16, (1) where n is 0-4 and preferably 1 or 2. The LPNC's can be made by procedures shown in U.S. Patent 3,839,388 incorporated herein by reference. Silanol-terminated polydiorganosiloxanes can be intercondensed employing an LPNQ catalyst. Mixtures of such silanol-terminated polydiorganosiloxanes and diorganosiloxanes having terminal triorganosiloxy units can be equilibrated with LPNQ D-23543 catalyst, such as LPNC of formula (1). For example, U.S. Patent 2,990,419 shows a method for making organopolysiloxane oils by equilibrating a hyd roxy-e nd blocked diorganosiloxane and a triorganosi ly I-endb locked diorganosiloxane using a phosphorus nitrogen compound such as a phosphonitrilic halide. Although effective results are achieved using this method, it has been found necessary to blow air continuously through the mixture for several days at different temperatures to stabilize the siloxane oil. As shown in U.S. Patent 3,835,388, other procedures use a phosphonitrilic halide as an equilibration catalyst to effect the condensation and/or equilibration of silanol fluids and mixtures thereof which involve the use of vacuum to facilitate condensation.

U.S. Patent 5,008,229 is directed to solutions of phosphonitrile chlorides in an organic solvent, and the use of such compositions to accelerate the condensation and/or equilibration of hydroxy-endblocked diorganosiloxanes. Although improved results are achieved, an organic solvent such as ethyl acetate is used to facilitate the dissolution of the phosphonitrile chloride. As a result, environmental problems can be created. German patent application 3,725,377 eliminates the use of an organic solvent by employing as the catalyst a reaction product of a phosphorus- nitrogen chloride and a cyclic diorganosiloxane such as octamethylcyclotetrasiloxane.

However, experience has shown that phospho rus- nitrogen chloride octamethylcyclotetrasiloxane reaction products often have viscosities exceeding several thousand centipoise, which can render such materials less suitable as catalysts for extruder reactor polymerizations.

It would be desirable, therefore, to provide equilibration catalysts and improved procedures for equilibrating polydiorganosiloxanes which would minimize environmental concerns.

W-23543 The present invention is based on the discovery that a linear phosphonitrilic chloride (LPNC) of formula (1) can be reacted with a linear siloxane oil having the formula R(R1)2Si[OSi(R1)21MOSi(R1)2R, (2) wherein R is hydrogen or a Cl-18 monovalent organic group, R1 is a Cl-13 monovalent organic group and preferably methyl, vinyl or phenyl and m is a whole number equal to 0 to 100 inclusive, to produce a LPNC-siloxane catalyst in the form of a uniform mixture. In addition, unlike the reaction product of German patent application 3,725,377, the reaction product of formulas (1) and (2) does not result in a substantial viscosity increase. Further, the resulting L1PNCsiloxane reaction product has been found to be effective as an equilibration catalyst for making organopolysiloxanes.

Summary Of The Invention

One aspect of the present invention is a silicone equilibration catalyst having a viscosity in the range of about 1 -1000 centistokes in the form of a reaction product of about 0.1-3.0 parts by weight of a phosphonitrilic halide per 100 parts of a linear siloxane oil of formula (2) A further aspect of the invention is a method for polycondensing and/or rearranging silanol-containing organosiloxanes having an average ratio of from 1.9 to about 2.1 organic groups per silicon atom attached to silicon by carbon-silicon bonds, comprising:

(1) agitating a mixture comprising silanol-containing organosiloxane and about 2-200 ppm by weight of an equilibration catalyst at a temperature of about 30-15011C, and (2) quenching the equilibration catalyst in the mixture of (1) when the desired silanol level has been achieved, ID-23543 said equilibration catalyst being a silicone having a viscosity in the range of about 1 - 1 OOO.centipoise in the form of a reaction product of 0.1-3.0 parts of a phosphonitrilic halide per 100 parts of a linear siloxane oil of formula (2).

Detailed Description; Preferred Embodiments

Among the organo groups shown for R of formula (2), there are included C18 alkyl radicals, for example methyl, ethyl, propyl, butyl, and haloalkyl radicals such as trifluoropropy]. In addition, R can be C1-8 alkenyl, such as vinyl and allyl; C3-8 cycloalkyl, such as cyclopropyl; and cycloalkenyl, such as cyclopenty]. R also includes C6-13 aryl radicals such as phenyl, tolyi, xylyl and naphthyl, as well as haloaryl, for example chloropheny]. R is preferably methyl, vinyl or phenyl. Radicals which are included within R1 of formula (2) are all of the aforementioned Cl-13 monovalent organic radicals of R.

The expression usilanol-containing organosiloxane" as used in the description of the present invention includes polydiorganosiloxane fluids having the formula

HO-[Si(R1)2-0lxH, (3) and mixtures thereof with polydiorganosiloxane fluids of the formula R%R1)2SiOlyH, (4) where x and y are integers having values of about 5-10,000 inclusive and preferably about 20-1,000 inclusive. These fluids can have viscosities in the range of about 5-500,000 and preferably about 10 30,000 centipoise. The fluids of formula (3) can be made by hydrolyzing a diorganosilane such as di methyldich lorosi lane with a controlled amount of water in the presence of a suitable acid or base catalyst. The fluids of formula (4) can be made by equilibrating a mixture of compounds with triorganosiloxy and diorganosiloxy units.

The fluids of formulas (3) and (4) can contain about 0.02-8.0% (by ID-23543 weight) hydroxy radicals attached to silicon. Methods for making the fluids of formulas (3) and (4) are shown in U.S. Patent 3,541,044 incorporated herein by reference.

The linear siloxane oil of formula (2) can be made by equilibrating a mixture of a cyclic polydiorganosiloxane and a trio rganosi loxy-e ndb locked disiloxane in the presence of a standard equilibration catalyst such as a strong acid, for example sulfuric, or an alkali metal hydroxide such as potassium hydroxide.

The equilibration catalyst, or LPNO-siloxane, of the present invention can be made by heating and vigorously agitating a mixture of the linear siloxane oil and the 1-PNO for 1 to 8 hours at 901400C. it is preferred to conduct the reaction under an inert atmosphere; for example, under an inert gas like nitrogen. Upon the formation of a clear solution, volatiles can be removed under reduced pressure. In place of linear phosphonitrilic chloride (I-PNCI), the equilibration catalyst can comprise linear phosphonitrilic bromide(LPNBr) and linear phosphonitrilic fluoride(I-PNF).

Equilibration, or polycondensation, of the silanol-containing organosiloxane of formulas (3) and (4) can be achieved by employing an effective amount of the LPNO-siloxane as previously defined. While it is preferred to initially heat the silanol-containing organosiloxane to a temperature in the range of 90-1 401C prior to the addition of the LPNOsiloxane, the order of addition of the respective ingredients is not critical. It also has been found advantageous to agitate the mixture under reduced pressure, such as 0.1-10.0 torr, while heating the mixture. Afterareaction period of about 2-20 minutes, the reaction can be terminated by the addition of a quencher for the LPNO-siloxane catalyst. A suitable catalyst quencher can be used at 10-200% by weight of the 1PNQ- siloxane catalyst. Among useful catalyst quenchers, there ar e included organosilazanes such as hexamethyidisilazane, the lithium salt of hexamethyidisilazane, lithium trimethylsilanolate, silylamines, and amines such as triethylamine, pyridine and butylamine.

D-23543 The organopolysiioxanes, such as silicone gums and fluids, made in accordance with the practice of the invention can be used as filament lubricants, converted to elastomers, and used in the production of platinum-catalyzed silicone room temperature 5 vulcanizable compositions.

The invention is illustrated by the following examples. All parts are by weight unless otherwise indicated.

Example 1

A mixture of 20.5 g of phosphorus pentachloride, 2.7 g of ammonium chloride and 50 mi of tetrachloroethane was stirred and refluxed over 8 hours. The mixture was then poured into petroleum ether; a light yellow precipitate was formed. After removing traces of solvent under vacuum, there was obtained 14 g of light yellow crystals. Based on method of preparation, the product was a linear phosphonitrilic chloride (I-PNCI).

A mixture of 100 g of a trimethylsiloxy-terminated polydimethylsiloxane oil having a viscosity of 100 centistokes and 2.0 g of LPNCI was vigorously stirred for 8 hours at 1 OWC under a nitrogen atmosphere. When a clear homogenous mixture was formed, the low boiling materials were removed by heating the mixture at 1000C under reduced pressure (1.0 torr) for 15 minutes. There was obtained 97 g of a clear oil, referred to hereinafter as the "LPNCI- tdmethyisiloxy catalyst".

Example 2

The procedure of Example 1 was repeated, except that a vinyidimethyisifoxy-terminated polydimethylsiloxane fluid having a viscosity of 250 centistokes was substituted for the trimethyisiloxyterminated polydimethylsiloxane fluid. There was obtained 96 g of a clear "LPNCI-vinyidimethyisiloxy catalyst".

ID-23543 Example 3

A mixture of 60 g of a silanol-terminated polydimethylsiloxane having a viscosity of 1,000 centistokes and 1 g of decamethyltetrasiloxane was heated to 1 OWC. There was then added to the mixture 20 ppm (60 gi) of the LPNCI-tdmethyisiloxy catalyst. The mixture was stirred under a pressure of 1 torr at 1 OOOC. There was an initial rapid increase in viscosity followed by a reduction in viscosity. After 5 minutes, the catalyst was quenched with 0.002 g of hexamethyidisilazane. The effectiveness of the LPNCI- trimethylsiloxy catalyst as an equilibration catalyst was shown by the formation of 60 g of a trimethyisiloxy-terminated polydimethylsiloxane having a viscosity of 200 centistokes and less than 50 ppm of silanol terminal groups.

Example 4

The procedure of Example 3 was repeated, except that 20 ppm of the LPNCIvinyidimethyisiloxy catalyst was substituted for the LP NCI -tri methyl si loxy catalyst. There was obtained a substantially equivalent amount of the trimethyisiloxy-terminated polydimethylsiloxane having a viscosity of 200 centistokes and less than 50 ppm of silanol terminal groups.

D-23543

Claims

CIAIMS

1. A silicone equilibration catalyst having a viscosity in the range of about 1-1000 centistokes in the form of a reaction product of about 0. 1 3.0 parts by weight of a phosphonitrilic halide per 100 parts of a linear siloxane oil of the formula R(R1)2SifOSi(R1)21MOSi(R1)2R, (2) wherein R is hydrogen or a Cl-18 monovalent organic group, R1 is a Cl-13 monovalent organic group and m is a whole number equal to 0 to 100 inclusive.

2. A silicone equilibration catalyst in accordance with claim 1 wherein the phosphonitrilic halide is a phosphonitrilic chloride.

3. A silicone equilibration catalyst in accordance with claim 1 wherein the linear siloxane oil is a tri.methyisiloxy-terminated polydimethylsiloxane.

4. A silicone equilibration catalyst in accordance with claim 1 wherein the linear siloxane oil is a vinyidimethylsifoxy-terminated polydi met hylsi loxane.

5. A method for polycondensing and/or rearranging silanol-containing organosiloxane having an average ratio of from about 1.9 to about 2.1 organic groups per silicon atom attached to silicon by carbon-silicon bonds, comprising:

(1) agitating a mixture comprising silanol-containing organosiloxane and about 2-200 ppm by weight of an equilibration catalyst at a temperature of about 30-1500C, and (2) quenching the equilibration catalyst in the mixture of (1) when the desired silanol level has been achieved, D-23543 said equilibration catalyst being a"silicone having a viscosity in the range of about 1-1000 centipoise in the form of a reaction product of 0.1-3.0 parts of a phosphonitrilic halide per 100 parts of a linear siloxane oil of the formula R(R1)2Si[OSi(R1)21MOSiffil)2R, (2) wherein R is hydrogen or a Cl-18 monovalent organic group, R1 is a Cl-13 monovalent organic group and m is a whole number equal to 0 to 100 inclusive.

6. A method in accordance with claim 5 wherein the equilibration catalyst is a reaction product of a phosphonitrilic chloride.

7. A method in accordance with claim 6 wherein the equilibration catalyst is a reaction product of a trimethylsiloxy-terminated polydimethylsiloxane.

8. A method in accordance with claim 6 wherein the equilibration catalyst is a reaction product of a vinyidimethyisiloxy-terminated polydimethylsiloxane.

9. A method in accordance with claim 5 wherein the catalyst is quenched with an organosilazane.

10. A method in accordance with claim 9 wherein the organosilazane is hexamethyidisilazane.