GB2252969A

GB2252969A - Phosphonitrile halide adducts as polymerisation catalysts

Info

Publication number: GB2252969A
Application number: GB9203217A
Authority: GB
Inventors: Jean-Marc Gilson; Jean De La Croi Habimana
Original assignee: Ow Corning S A
Current assignee: Ow Corning S A
Priority date: 1991-02-21
Filing date: 1992-02-14
Publication date: 1992-08-26
Also published as: CA2061006A1; KR920016472A; AU1108092A; KR100239611B1; JPH04328128A; ITTO920135A1; ITTO920135A0; GB9103656D0; IT1256673B; DE4205200A1; ES2046103B1; FR2676063A1; GB9203217D0; FR2676063B1; ES2046103A1; JP3207905B2; NL9200225A

Abstract

A phosphonitrile halide catalyst for use in polymerising organopolysiloxanes has the general formula [X(PX2=N)nPX3]<+> [MX(v-t+x)Rt]<->wherein X is halogen, M is an element with an electronegativity of from 0.1 to 2.0, e.g. Al or Sb, R is C1-12 alkyl, n is 1 to 6, v is the valence or oxidation state of M and t has a value of from 0 to v-1. A method for making the catalyst and its use in the polymerisation process of siloxanes especially by condensation is also claimed.

Description

CATALYST FOR POLYMERISATION This invention relates to catalysts, more

specifically catalysts which are used in polymerisation reactions, especially the polymerisation of organosiloxanes.

The polymerisation or copolymerisation of organo- siloxanes has been known for some time and is a well known step in the production of commercial siloxanes. Organo polysiloxanes have been prepared for example by contacting low viscosity organosiloxanes, especially cyclic polysi loxanes, low viscosity siloxanols or a mixture thereof in the presence of an acidic or basic catalyst. For example organopolysiloxanes may be prepared by condensation of organosiloxanes having reactive groups at terminal silicon at.. -.g. silicon-bonded hydroxyl groups, silicon-bonded hydrocarbonoxy groups and mixtures of one or more of these.

Organopolysiloxanes may also be made by rearrangement of linear and/or cyclic organosiloxanes. For each of the polymerisation processes a range of catalysts have been developed, some being more effective than others. Known catalysts for such polymerisation reaction include sulphuric acid, hydrochloric acid, Lewis acids, sodium hydroxide, potassium hydroxide, tetra-methylammonium hydroxide, tetrabutylphosphonium silanolate and amines.

A number of patent applications discloses phosphonitrile halide catalysts. G.B. Patent Specification 765 744 discloses that preferred phosphonitrile halides for the polymerisation of liquid organosiloxanes having an average degree of substitution of from 1.9 to 2.1 organic groups attached to silicon per silicon atom are polymeric chlorides represented by the formula (PNC1 2)n, wherein n is an integer of at least 3, most preferably 3 to 6. The process is described as being especially valuable for the production of polymerised organosiloxanes to be used for the manufacture of silicone rubber. G.B. Patent Specification 910 513 discloses phosphonitrile halide catalysts for use in a process for the manufacture of stabilised high viscosity organopolysiloxane oils, which comprises preparing a fluid mixture of the halides with a hydroxylterminated diorganopolysiloxane and a triorganosilyl endblocked diorganopolysiloxane with a viscosity from 1 to 10,00OMM2/S' followed by bringing the mixture in contact with a stream of air at room temperature until thp viscosity is stabilised and thereafter bringing the mixture in contact with a stream of air at a temperature of from 100 to 2000C until the viscosity is stabilised. In U.S. specification 3,549,680 phosphonitrile halide catalysts are employed in rearrangement reactions, e.g. a method of preparing organohalogenosilicon compounds in which organohalogenosiloxane compounds containing at least one halogen atom bonded to silicon per molecule and organosiloxanes free from halogen substituents having a viscosity of less than 100,00Omm2/s are mixed with the halides. E.P. Patent Specification 319 978 describes chlorophosphonitrile catalysts for use in a process for the preparation of diorganopolysiloxanes containing a silicon-bonded hydroxyl group in each of the terminal units in which a cyclic diorganopolysiloxane and/or diorganochlorosilane-hydrolysis product is reacted with a diorganochlorosilane, followed by the treatment with water or an aqueous solution and separating the low boiling substituents and the aqueous phase

There is a continuing search for catalysts which will have improved activity in the polymerisation of organosiloxanes.

We have now found that if phosphonitrile catalysts include certain Lewis acid-based parts an improved catalyst for making organopolysiloxanes is obtained.

According to the invention there is provided a phosphonitrile halide catalyst for use in polymerising organosiloxanes, having the general formula EX(PX 2 =N) n PX 31 + [MX (V-t+l) Rt]- (1) wherein X denotes a halide atom, M is an element having an electronegativity of from 1.0 to 2.0 on Paulingfs scale, R is an alkyl group having up to 12 carbon atoms, n has a value of from 1 to 6, v is the valence or oxidation state of M and 0:5 t < v.

Some phosphonitrile halide compounds which are useful as a catalyst in the polymerisation of organosiloxanes have been described in the literature, but their use as a catalyst has hitherto not been known.

U.S. Specification 3,449,091 describes metal halide modified phosphonitrile chloride polymeric compositions which are useful as high temperature lubricants. The disclosed materials have the general formula [Cl[PC1 2 -=N] n PC1 3]+[EX (v+1)]-, wherein E is an element having an electronegativity value of from 1.2 to 2 and differs in electronegativity from the halogen portion of the halide by a maximum of 2.5, X is a halogen, v is the valence of element E and n is from 1 to 10 inclusive. Exemplified E elements include Zn, Al, B, Ti, Sn, Sb, Th and Fe. Although several of the described compounds may be useful as catalysts for the polymerisation of organosiloxanes, not all are effective and some compounds are more preferred than others. Nothing in the art indicates the usefulness of some of these compounds as catalysts and nothing indicates which of these compounds would be useful as catalysts for the polymerisation of organosiloxanes.

Catalysts according to the invention have a cationic phosphonitrile part and an anionic part which has been derived from a Lewis acid. The phosphonitrile part is a linear oligomeric or polymeric phosphonitrile halide having the general formula [X(PX 2 =-N) n PX 31 + wherein n denotes an integer having a value of from 1 to 6. It is preferred that the halogen X is a chlorine atom. Phosphonitrile halide cationic parts with a value for n which is higher than 6 are less suitable as catalysts. Most preferred are the phosphonitrile halide parts in which the value of n is from 2 to 4. It is sometimes difficult to separate the polymeric phosphonitrile halides having different n values and mixtures are often used. It is particularly preferred that the amount of phosphonitrile halide polymer, in which n has a value of 2, is as high as possible as this gives the most active catalyst. Particularly preferred is a catalyst which exclusively consists of compounds according to the invention in which the value of n is 2.

The anionic part of the catalyst is derived from a Lewis acid and has the formula [MX(v_t+,)Rt] Although it is preferred that the value of t is zero alkyl groups may be included. Preferably the Lewis acid based anion contains a halide X which is the same as the halide of the phosphonitrile cationic part, i.e. most preferably a chlorine. The element M of the Lewis acid part is an electropositive element having an electronegativity value according to Pauling's scale C-L -from. I to 2, preferably from 1.2 to 1.9, most prefera;-dy 1.5 to 1.9. Suitable elements are found in Groups Ib, IIa, IIb, IIIa, IVa, IVb, Va, Vb, VIb, VIIb and VIII of the Periodic Table. They include Al, B, Be, Mg, Sb and Si. It is preferred that the difference in electronegative value between the phosphorus atom of the phosphonitrile part of the catalyst and the M element is as large as possible within the preferred range, giving improved catalytic activity when this value is larger. The presence of the anionic Lewis acid based part in the catalyst improves the catalytic activity of the catalyst in the polymerisation reaction of organosiloxanes. It also tends to make the catalyst more stable in itself, thus preventing it from cyclisation and from polymerisation with other phosphonitrile compounds, even at higher temperatures.

A particularly suitable compound is the one where the Lewis acid derived portion is based on antimony, especially SbC1 3 or SbC1 5' An example of such suitable catalyst has the formula [Cl 3 P=N-(PC1 2 =N) s_PCl 3]+[SbC'63-1 wherein s has a value from 1 to 4. Another suitable compound is the one where the Lewis acid derived portion is based on aluminium.

Phosphonitrile halide catalysts according to the invention may be made by reacting a phosphorus pentahalide, an ammonium halide and a Lewis acid. Preferably they are made by reacting in the presence of an aromatic hydrocarbon or more preferably of a chlorinated aliphatic or aromatic hydrocarbon, e.g. toluene, sym- tetrachloroethane or 1,2,4trichlorobenzene, as inert solvent, the phosphorus penta- g. phosphorus pentachloride, the ammonium halide, ium chloride and the selected Lewis acid.

jewis acids are those which are based on an _Lectropositive element M having an electronegativity value according to Pauling's scale of from 1 to 2. Examples of suitable Lewis acids are SbCl 31 SbCl,, AlCl3' S'C'41 MgC'21 BC1 3 and BF 3 The reaction may be carried out at a tempe rature between 100 and 2200C followed by separating the reaction products from the solids and the volatile compo nents, thus isolating the liquid reaction product. At temperatures below 1000C the reaction does not occur or is so slow as not to be economically feasible. Mere mixtures of the reagents do not give satisfactory polymerisation rates. Temperatures above 2200C may be used provided that - 6 pressure is applied to maintain the solvent in the system; however, temperatures above 220C are not generally recommended because of the tendency of the products to darken at elevated tempera- tures. Preferred temperature range is the refluxing temperature of the inert solvent used in the reaction, for example 120 to 1600C. The reagents may be added in any order although it is preferred that no Lewis acid is added before a suitable solvent has been introduced in the reaction vessel. The reagents may be contacted for any period of time but preferably a period which may vary from 2 to 10 hours. It is preferred to continue the reaction for a period in excess of 6 hours. It is preferred to react the reagents till a fair amount of the phosphonitrile halides produced are oligomers with more than 2 units. This can be observed easily as phosphonitrile halide dimers are not soluble in the solvents. If the remaining reaction product contains dimers, it is preferred that these dimers are separated and refluxed in a solvent in order to be transformed into higher oligomers, preferably in the presence of traces of ammonium halide. Preferably the reaction conditions are adapted to provide a high level of linear trimers and tetramers. The yield of linear phosphonitrile halides versus cyclic phosphonitrile halides can be increased by using a stoichiometric excess of phosphorus halide, which is the preferred method. In such preferred method from 0.1 to 1 mole, more preferably 0.3 to 0.6 mole of the selected Lewis acid is provided for each mole of phosphorus pentahalide.

Representative chlorinated aliphatic or aromatic hydrocarbons that are inert solvents and can be used in the present invention include symmetric tetrachloroethane, monochlorobenzene, o- dichlorobenzene and 1,2,4-trichlorobenzene. The amount of chlorinated hydrocarbon used as 1 7 solvent seems not to be critical provided a sufficient amount is used to dissolve at least a portion of the solid reactants, i.e. phosphorus pentahalide and ammonium halide. Of course the reaction rate improves substantially when a significant portion of the solid reactants is in solution. The use of large quantities of solvent, however, is not recommended because of the necessity of subsequent removal of the solvent from the reaction product. The manner of recovering the desired modified phosphonitrile halide polymeric composition is not critical. If any solid material is present in the reaction mixture it may be removed by any conventional method, e.g. hot filtration, decantation, centrifugation etc. The volatile materials e.g. the solvent, may be also removed by conventional methods, e.g. distillation. A preferred method of recovering the catalyst includes the removal of the reaction solvent and the addition of a solvent in which only the most preferred compounds are soluble, e.g. dichloromethane. Other compounds can then be filtered off.

The catalyst according to the invention can be conveniently stored in solvent, preferably under a blanket of nitrogen. The invention accordingly also includes catalyst compositions which comprise a catalyst according to the invention. The other parts of the composition may include a solvent, a carrier, a support and some unreacted materials which were used for making the catalyst. It is also possible that some compounds according to formula (1) are present but wherein the value of n is 0 or larger than 6. Preferably the amount of such compounds is kept to a minimum.

Concentrations of the catalyst in such compositions may range from 1 to 50% by weight. Preferably from 5 to 20% as this facilitates its use in polymerisation processes.

The catalysts of the invention are useful for the polymerisation of organosiloxanes. The invention accordingly also provides the use of phosphonitrile halide catalyst of formula (1), as defined above, in the process of polymerising organosiloxanes. They are particularly useful as condensation catalysts but are also suitable as rearrangement catalysts. Thus they will be useful for a process of making organopolysiloxanes having units of the general formula R' SiO (2) wherein R' denotes a hydrogen a 4-a 2 atom, a hydrocarbon group having from 1 to 18 carbon atoms, a substituted hydrocarbon group having from 1 to 18 carbon atoms or a hydrocarbonoxy group having up to 18 carbon atoms and a has on average a value of from 1.8 to 2.2. R' is substituents may be alkyl, e.g. methyl, ethyl, propyl, isobutyl, hexyl, dodecyl or octadecyl, alkenyl, e.g. vinyl, allyl, butenyl, hexenyl or decenyl, alkynyl, e.g.

propargyl, aryl, e.g. phenyl, aralkyl, e.g. benzyl, alkaryl, e.g. tolyl or xylyl, alkoxy, e.g. methoxy, ethoxy or butoxy, aryloxy, e.g. phenoxy, substituted groups, e.g.

trifluoropropyl, chloropropyl or chlorophenyl. Preferably at least 80% of all R' groups are alkyl or aryl groups, more preferably methyl groups. Most preferably substan tially all R' groups are alkyl or aryl groups, especially methyl groups. The organopolysiloxanes are preferably those in which the value of a is 2 for practically all units, except for the endblocking units, and the siloxanes are substantially linear polymers of the general formula R? [R' 2 Sio] p SiRl 2 R 2 (3) wherein R' is as defined above, R2 is a group R' or a hydroxyl group and p is an integer. It is, however, also possible that small amounts of units wherein the value of.a denotes 0 or 1 are present. Polymers with such units in - 9 the chain would have a small amount of branching present. Preferably R2 denotes a hydroxyl group or an alkyl or aryl group, e.g methyl or phenyl. The viscosity or the organopolysiloxanes which may be produced by the process using a catalyst according to the present invention may be in the range of from 1000 to many millions M1n2/s, depending on the reaction conditions and raw materials used in the method of the invention. Suitable organosiloxanes for use as reagents in a polymerisation process in which the catalysts of the invention are used include polydiorganosiloxanes having terminal hydroxydiorganosiloxane units, e.g.

hydroxyldimethyl siloxane endblocked polydimethylsiloxanes, hydroxyldimethyl siloxane endblocked polydimethyl poly --'-",,"phenyl siloxane copolymers, triorganosiloxane ked polydimethylsiloxanes, e.g. trimethylsiloxane ---ed polydinethylsiloxanes and cyclic polydiorgano --,loxanes, e.g. polydimethylcyclosiloxanes.

The catalysts of the invention may be used at a concentration of from 1 to 50Oppm by weight based on the total weight of the organosiloxanes used as reagents in a polymerisation process. Preferably from 5 to 15Oppm by weight are used, most preferably from 5 to 5Oppm. The amount of catalyst used in the method of the invention may be reduced when the temperature at which the organosilicon compounds and the catalyst are contacted is increased. The method of the invention may conveniently be carried out at room temperature. The temperature may also be as high as 2500C. Preferably, however, the temperature range is from to 1500C, most preferably from 50 to 1200C.

Catalysts according to the invention may be neutra lised at the end of the polymerisation reaction in order to stabilise the reaction product, e.g. in respect of its viscosity. The neutralisation may be done at any stage of observed.

the polymerisation process, e.g. as soon as the desired viscosity of the organopolysiloxanes is reached. Neutralisation agents for the catalysts are alkaline materials, preferably lightly alkaline materials. Examples of suitable neutralisation agents are diethylamine, propylamine, ammonia and hexamethyldisilazane.

There now follow a number of examples which illustrate the invention and its usefulness. Parts and percentages are by weight unless otherwise mentioned.

ExamDle 1 2 parts of NH 4 Cl, 5 parts of PC1 5 and 1 part of A1C1 3 were mixed together and stirred under a nitrogen blanket at 1800C for 3 hours in 1,1, 2,2, tetrachloroethane as solvent. A white solid was obtained which was soluble in dichloro- methane but insoluble in diethyl ether. The reaction product has the average formula EPC1 3_=N-PC12 =N-PC1 31 + [A1C1 41-- Example 2

0.12 mole of PCl., 0.08 mole of NH 4 Cl and 0.04 mole of SbCl 5 were allowed to react together in 60m1 of symtetrachloroethane at its refluxing temperature of 1470C for 3.5 hours. After the reaction the solution was filtered to remove insoluble compounds followed by removal of the solvent under reduced pressure. A bright yellow liquid was obtained which slowly crystallised upon cooling. The resulting catalyst was analysed by NMR (nuclear magnetic resonance) spectroscopy. It was found to be a 50/50 mixture of [PC1 3 =N-PC1 2 =N-PC1 3]+[SbC163 - and [PC1 =N-(PC1 =N) -PC1] + [SbCl]_ while no [PC1 63 anion was 2 2 3 6 ExalnDle 3 The preparation method of Example 2 was repeated except that instead of SbCl 5 SbCl 3 was used. The resulting 1 1 catalyst was a so/5o mixture of EPC1 3 =N-PC1 2 =N-PC1 31 + [SbCl 4] and [PC1 3 =N-(PC1 2 =N) 2-PC131 + [SbCl 41-ExamDle 4 The procedure of Example 2 was followed except that after 3 hours the compounds of the formula [PC1 3 =N-PC1 3]+[SbC161 which were insoluble in dichloromethane were separated. A part (A) was retained and the rest was refluxed in sym-tetrachloroethane to yield a pure compound (B) of the formula [PC1 3 =N-(PC1 2 =N) 2-PC131 +[SbC161_ Example 5

The procedure of Example 2 was followed except that the reaction was continued for 8 hours. The resulting is mixture was 35% [PC1 3 =N-PC1 2=N-PC1 3 + [SbCl 61 and -N-(PC1 2 =N) 2-PC131 + ISbCl 63 x-,--,miDle 6 When 150ppm of the catalyst of Example 1 were added to 1500g of dimethylsilanol endblocked polydimethyl siloxane having a viscosity of 10OMM2/s, and the mixture stirred at a reduced pressure of 20 mbar for 15 minutes at room temperature (18OC), a very high viscosity polydi methylsiloxane was obtained.

Example 7

The catalysts of Examples 2 and 3 were used in the polymerisation of hydroxyl endblocked polydimethylsiloxanes and were compared with a prior art catalyst prepared by the reaction of 0.4mole of PC1 5 and 2 mole of NH 4 Cl 1 resulting in a mixture of 75% [PC1 3 =N-PC1 2 =N-PC1 33+1PC163 and 25% [PC1 3 =N-(PC1 2 =N)2-PC133+1PC161 3 batches of 1500g of dimethylsilanol endblocked polydimethylsiloxane having a viscosity at 250C of 10OMM2/S were dried under reduced pressure for 10 minutes to remove all traces of water.

- i.w - 12ppm of the catalyst of Example 2, 12ppm of the catalyst of Example 3 and 24ppm of the prior art catalyst were added respectively to the first, second and third batch of poly dimethylsiloxane under stirring. The first batch reached a viscosity of 200, OOOMM2/s after only 23 minutes, of which the first 20 were an induction period. The second batch had an induction period of 18 minutes and reached a visco sity of 200,OOOMM2/s after 21 minutes, while the third batch had an induction period of 30 minutes and did not 10, reach a viscosity of 200,OOOM1n2/S until after 35 minutes.

Example 8

This example shows the improved heat stability of polymers which are prepared by using catalysts according to the invention which are neutralised with amines. The results are compared with stability of polymers prepared with traditional polymerisation catalyst KOH neutralised with CO 2 4 batches of polydimethylsiloxanes were prepared. Batches 1 and 2 used 35ppm. of the catalyst prepared in Example 2 at room temperature whilst batches 3 and 4 used KOH as a catalyst. Batches 1 and 2 were neutralised with diethylamine upon reaching a viscosity of 41000 and 1400Omm21s respectively. Batches 3 and 4 were neutralised with CO 2 after having reached a viscosity of 40800 and 1420Omm2/s respectively. All batches were then stored at 1600C for a period of up to 122 hours and the viscosity was measured. As can be seen in the Table below the viscosity of Batches 1 and 2 was much more stable than that of Batches 3 and 4.

is TABLE Viscosity in MM2/S Time Batch 1 Batch 2 Batch 3 Batch 4 (hours) 0 41,000 14,000 40,800 14,200 22 51,500 - 80,000 25,500 29.5 - 99,000 30,700 51,500 - 300,000 73,500 - 20,000 500,000 122,000 122 63,500 - - - Example 9

40kg of dimethylsilanol endblocked polydimethyl siloxane was mixed with 5Oppm of the catalyst of Example 2 and the mixture was reacted at a temperature of 800C for 5 minutes, at which time 60ppm of diethylamine was added to neutralise the catalyst. A viscosity of 300,OOOMM2/S was obtained. ExamDle 10 Part A of Example 4 was tested as condensation catalyst by mixing it in with dimethylsilanol endblocked polydimethyl siloxane, but showed no catalytic activity even when the mixture was heated.

ExamDle 11 Part B of Example 4 and the catalyst of Example 5 were each mixed in with 40g of dimethylsilanol endblocked polydimethyl siloxane at a concentration of 12ppm and the mixture was reacted at 500C and a pressure of 20 mbar. The reaction went faster with the Catalyst of Example 5, showing that the presence of a compound of the formula [PC1 3 =N-PC1 2 N-PC1 3]+[SbC 163 improves the catalytic activity of the catalyst.

ExamiDle 12 40g of octamethylcyclotetrasiloxane was loaded to a flask together with 120ppm of the catalyst of Example 5. After 4 hours of reaction at 1400C at atmospheric pressure, almost 50% of the cyclic siloxane was polymerised into longer chain polydimethylsiloxanes, showing that the catalyst of the invention is also an active rearrangement catalyst.

- is -

Claims

A phosphonitrile halide catalyst for use in polymerising organopolysiloxanes having the general formula [X(PX 2 =N) n PX 31 + [MX (V-t+l) RJ, wherein X denotes a halogen atom, M is an element having an electronegativity of from 1.0 to 2.0 according to Pauling's scale, R is an alkyl group having up to 12 carbon atoms, n has a value of from 1 to 6, v is the valence or oxidation state of M and t has a value of from 0 to v-1.
2. A phosphonitrile halide catalyst according to Claim 1 wherein each group X denotes a chlorine atom.
3. A phosphonitrile halide catalyst according to Claim 1 or 2 wherein n has a value of from 2 to
4.

-nitrile halide catalyst according to Claim 3,.ue of n is 2.
5. A phosphonitrile halide catalyst according to any one of the preceding claims wherein the value of t is 0.
6. A phosphonitrile halide catalyst according to any one of the preceding claims wherein M is selected to have an electronegativity value according to Pauling's scale of from 1.2 to 1.9.
7. A phosphonitrile halide catalyst according to any one of the preceding claims wherein M is selected to have an electronegativity value according to Pauling's scale of from 1.5 to 1.9.
8. A phosphonitrile halide catalyst according to any one of the preceding claims wherein M is selected to maximise the difference in electronegativity value according to Pauling's scale between the phosphorus atom of [X(PX 2 =N) n PX 31 + and M.
9. A phosphonitrile halide catalyst according to any one of the preceding claims wherein M is Sb.
10.. A phosphonitrile halide catalyst according to any one of Claims 1 to 8 wherein M is Al.
11. A method of making a phosphonitrile halide catalyst which comprises reacting together a phosphorus pentahalide, an ammonium halide and a Lewis acid.
12. A method according to Claim 11 wherein the reaction takes place in the presence of a chlorinated aliphatic or aromatic hydrocarbon.
13. A method according to Claim 12 wherein chlorinated hydrocarbon is tetrachloroethane.
14. A method according to anyone of Claims 11 to 13 wherein the reaction is carried out at a temperature between 1000C and 2200C.
15. A method according to any one of Claims 12 to 14 wherein the reaction is carried out at the reflux temperature of the chlorinated aliphatic or aromatic hydrocarbon.
16. A method according to any one of Claims 11 to 15 wherein the reagents are contacted for a period of from 2 to 10 hours.

2
17 - 17. A method according to any one of Claims 11 to 16 wherein a stoichiometric excess of phosphorus pentahalide is used over the Lewis acid.
18. A method according to Claim 17 wherein from 0.3 to 0.6 mole of the Lewis acid is used for every mole of phosphorus pentahalide.
19. A catalyst composition comprising a phosphonitrile halide ca talyst according to anyone of Claims 1 to 10 and one.or more of a solvent, a carrier or a support for said catalyst.
20. A catalyst composition according to Claim 19 comprising from 5 to 20% by weight of the catalyst and 80 to 95% by weight of a
21. A catalyst composition according to Claim 19 or 20 wherein the solvent is dichloromethane.
22. The use of a phosphonitrile halide catalyst according to any one of Claims 1 to 10 in the process of polymerising organosiloxanes.
23. The use of a catalyst composition according to any one of Claims 19 to 21 in the process of polymerising organosiloxanes.
24. A phosphonitrile halide catalyst substantially as described in any one of Examples 1 to 5.