GB2196014A

GB2196014A - Titanium catalyzed RTV polysiloxane rubbers

Info

Publication number: GB2196014A
Application number: GB08719571A
Authority: GB
Inventors: John Joseph Dziark
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1986-08-22
Filing date: 1987-08-19
Publication date: 1988-04-20
Also published as: KR880002898A; CA1284544C; GB8719571D0; KR940003886B1; JPS6399236A; DE3727565A1; FR2604713A1

Description

GB2196014A 1

SPECIFICATION

Preparation of high strength, high application rate silicone RTV rubber This invention relates to titanium catalyzed alkoxy end-stopped polydiorganosiloxane. RTV rub- 5 bers. More particularly, this invention relates to a process for producing such rubbers whereby the application properties of the compositions are improved as well as the properties of the cured rubber, including hardness, tensile strength and elongation.

Early types of one-component RTV rubber compositions are, for instance, disclosed in Ceyzer- iat, U.S. Patent No. 3,133,891, and Bruner, U.S. Patent No. 3,035,016. Such patents disclose 10 the use of acyloxy functional silanes as cross-linking agents for hydroxy end-stopped organopo lysiloxane gums. The compositions of Ceyzeriat were packaged in a substantially anhydrous state and upon exposure to atmospheric moisture, cured to a silicone elastomer.

Two methods for the manufacture of one-component RTV rubbers have been employed. The object of each method is to produce a mixture of moisture free alkoxy end- stopped polydiorga- 15 nosiloxape rubber and condensation catalysts. Of course, the mixture must also contain the usual additives, including fillers, plasticizers, pigments, etc.

In the first method, additives, silanol end-stopped polydiorganosiloxane, alkoxy silane and titanium condensation catalyst are mixed in a single step under anhydrous conditions. The silane will end-cap the silanol to produce an alkoxy end-capped polydiorganosiloxane. The titanium 20 condensation catalyst will promote the end-capping reaction as well as promote the cure reac tion when water is introduced. This method of preparation suffers from the disadvantage that a large viscosity rise occurs during catalyzation of the base due to temporary coupling of the silanol polymers with the titanium condensation catayst. This method is exemplified in U.S.

Patent Nos. 3,689,454 and 3,779,986 issued to Smith, et al., and assigned to the instant 25 assignee.

In the second method, a pre-prepared alkoxy end-stopped polydiorganosiloxane is mixed with- additives and a condensation catalyst. This method suffers from the need to prepare beforehand the alkoxy end-stopped material.

Thus, it is an object of the present invention to produce a titanium catalyzed one-component 30 RTV rubber in two mixing steps but without preparing the alkoxy end- stopped polydiorganosilox ane beforehand.

It is another object of the present invention to produce titanium catalyzed one-component RTV rubbers having improved properties including improved application properties and improved pro perties of the vulcanized rubber such as hardness, tensile strength, and elongation. 35 Briefly, according to the present invention, there is provided a method for production of titanium catalyzed alkoxy end-stopped RTV rubbers having superior properties, which method comprises:

(a) reacting a mixture comprising:

(i) a silanol terminated polydiorganosiloxane, 40 (ii) an end-capping agent having the formula:

Rm Si(ORI)4-m wherein m has a value of from 0 to 2, and R and RI are hydrocarbyl, halohydrocarbyl, and cyano lower alkyl radicals having up to about 12 carbon atoms, and (iii) an end-capping catalyst selected from Lewis acids, Lowry-Bronsted acids and mixtures of 45 the acids with amine co-catalysts; and (b) further admixing at least one titanium condensation catalyst.

These titanium catalyzed alkoxy end-stopped RTV rubbers have superior application properties as well as superior properties in the vulcanized state.

The silanol chain-stopped polydiorganosiloxanes useful in the RTV compositions of this inven- 50 tion can be represented by the formula, R 2 1 55 HO sio-- H (1) 1 3 R; n 60 wherein R2 and R3 are each organic radicals of not more than 12 carbon atoms selected from the group consisting of hydrocarbyl, halohydrocarbyl and cyano lower alkyl and n is a number of from 10 to about 15,000 or more.

The silanol chain-stopped polydiorganosiloxanes are well known in the art and include compo- 65 2 GB2196014A 2 sitions containing different R2 and R3 groups. For example, the R2 groups can be methyl, while the R3 groups can be phenyl and/or beta-cyanoethyl. Furthermore, within the scope of the definition of polydiorganosiloxanes useful in this invention are copolymers of various types of diorganosiloxane units, such as silanol chain-stopped copolymers of dimethylsiloxane units, di phenylsiloxane units and methylphenylsiloxane units or, for example, copolymers of dimethylsilox- 5 ane units, methylphenylsiloxane units and methylvinylsiloxane units. Preferably, at least 50% of the R2 and R3 groups of the silanol chain-stopped polydiorganosiloxanes are methyl groups.

In Formula 1, the hydrocarbyl, halohydrocarbyl and cyano lower alkyl radicals represented by R2 and R3 can be, for example mononuclear aryl, such as phenyl, benzyl, toly], xylyl and ethylphenyl; halogen-substituted mononuclear aryl, such as 2,6-di- chlorophenyi, 4-bromophenyl, 10 2,5-di-fluorophenyi, 2,4,6-trichlorophenyi, and 2,5-dibromophenyl; alkyl such as methyl, ethyl, n propy], isopropyl, n-butyl, sec-butyl, isobutyl, tertbuty], amyi, hexyi, heptyl, octyi; alkenyl such as vinyl, allyl, n-butenyl, n-pentenyl-2-, n-hepteny]; alkynyl such as proparayl, 2-butynyl; haloalkyl such as chloromethyl, iodomethy], bromomethyl, fluoromethyl, chloroethyl, iodoethyl, bromoethyl, fluoroethyl, trichloromethyl, dHodoethyl, tribromoethyl, trifluoromethyl, dichloroethyl, chloro-n-pro- 15 pyi, bromo-n-propyl, iodoisopropyl, bromo-n-butyi, bromo-tert-butyl, 1,3, 3-trichlorobuty], 1,3,3 tribromobutyl, chloropentyl, bromopentyl, 2,3-dichloropentyl, 3,3dibromopentyi, chlorohexy], bro mohexyl, 1,4-dichlorohexyi, 1,3-dibromohexy], bromoocty]; haloalkenyl such as chlorovinyl bro movinyl, chloroallyl. bromoally], 3-chloro-n-butenyi-l-, 3,chloro-n- pentenyi-l, 3-fluoro-n-heptenyi 1, 1,3,3-trichforo-n-hepteny]-5, 1,3,5-tri-chloro-n-octenyl-6, 2,3,3- trichloromethylpentenyl-4; haloalkynyl such as chloropropargyl, bromopropargy]; cycloalkyl, cycloalkenyl and alkyl and halogen substituted cycloalkyl and cycloalkenyl such as cyclopentyl, cyclohexy], cycloheptyl, cyclooctyl, 6-methylcyclohexyl, 3,4-dichlorocyclohexyi, 2,6-dibromocyqioheptyi, 1- cyclopentyl, 3-methyl-1-cy clopentenyl, 3,4-dimethyi-l-cyclopentenyi, 5-methyi-5-cyclopenteny], 3,4- dichloro-5-cyclopentenyl, 5-(tert-butyl)l-cyclopentenyi, 1-cyclohexenyi, 3-methy]-1-cyclohexenyi, 3, 4-dimethyi-l-cyclohexe- 25 nyi; and cyano lower alkyl such as cyanomethyl, beta-cyanoethy], gamma- cyanopropyi, delta cyanobuty], and gamma-cyanoisobutyl.

- A mixture of various silanol chain-stopped polydiorganosiloxanes also may be employed. The silanoi chain-stopped materials useful in the RTV compositions of this invention have been described as polydiorganosiloxanes but such materials can also contain minor amounts, e.g., up 30 to about 20% of monoorganosiloxane units such as monoalkylsiloxane units, e.g., monomethylsi ioxane units and monophenylsiloxane units. The technology involved in incorpoating monoalkylsi loxane units into RTV compositions is disclosed in U.S. Pat. 3,382, 205 of Beers (1968), which is hereby incorporated into the present application by reference. The silanol chain-stopped materials may also contain triorganosiloxane units, such as trialkylsiloxane units, e.g., trimethylsi- 35 loxane units, tributylsiloxane units and triphenylsiloxane units. The silanol chain-stopped materials may also contain t-alkoxysiloxane units, e.g., t-butoxysiloxane units, t- pentoxysiloxane units, and t-amyioxysiloxane units. Effective results can be obtained if sufficient t-alkoxysiloxane is utilized in combination with the silanol-terminated polydiorganosiloxane of Formula 1 to provide a poly mer having a ratio of t-alkoxysiloxane units to silanol of 0.05 to 0.9 and preferably 0.2 to 0.8 40 tert-alkoxydialkylsiloxy units per silanol. Many of the t-alkoxysiloxanes useful as part of the silanol chain-stopped materials are described and claimed in U.S. Pat. 3, 438,930, Beers, which issued April 15, 1969, and is assigned to the General Electric Commpany, the disclosure of which is expressly incorporated herein by reference.

The silanol chain-stopped polydiorganosiloxanes employed in the practice of the present inven- 45 tion may vary from low viscosity thin fluids to viscous gums, depending upon the value of n and the nature of the particular organic groups represented by R2 and R3.

End-capping agents suitable for use herein have the general formula:

RmSi(OR1),,, 50 wherein m has a value of from 0 to 2, preferably 1, and R and R' can be hydrocarbyl, halohydrocarbyl, and cyano lower alkyl radicals having up to about 12 carbon atoms and selected from, for example, the same group as those listed above for R2 and R3.

Preferred end-capping agents contain alkoxy groups, preferably methoxy groups. Examples of 55 suitable end-capping agents include:

3 GB2196014A 3 CH3Si(OCH.).

CH,Si(OCH2CH,), (CH3)2Si(OCH3)2 Si(OCH3)4 5 CH3CH2CH2CH2CH2CH2CH2CH2S'(OCH,)3 CF,CH2Si(OCH3)3 NCCH,CH2Si(OCH3)3 (CH3)Si(OCH2CH,CH2CH3)3 10 The amount of the end-capping agent admixed with the silanol chain- stopped polydiorganosi- loxane can vary within wide limits. However, for best results, it is preferred to add an excess of one mole of the silane per mole of silanol groups in the silanol chainstopped polycliorganosilox anes. Satisfactory curing can be obtained, for example, with from 1.0 to 10 moles of the silane per mole of silanol groups in the polydiorganosiloxane. No particular detriment is suffered from 15 using more than 10 moles of the silane per mole of the polycliorganosiloxane except for a more resinous product being formed and slowing down the cure. The temperature at which the silane and the silanol chain-stopped polydiorganosiloxane are admixed is not critical and a room temperature addition is usually employed.

Suitable end-capping catalysts are selected from Lewis acids, LowryBronsted acids, and 20 mixtures of these two acids with amine co-catalysts. Lewis acids and Lowry-Bronsted acids are not exclusionary. Lewis acids have the broader definition of being defined as a compound which is an electron acceptor in a reaction with another compound. A more formal definition is to be found in Van Nostrand Rheinhold Publishing Company, Condensed Chemical Dictionary, 8th Ed., Revised by G.G. Hawley, (1971), in which a Lewis acid is defined as "any molecule or ion that 25 can combine with another molecule or ion by forming a covalent chemical bond with two electrons from the second molecule or ion. A narrower definition is applied to Lowry-Bronsted acid which in the foregoing Van Nostrand Rheinhold dictionary is defined by inference as, a substance that can give up a proton to form a new compound with a covalent bond.

Suitable Lowry-Bronsted acids include the acid anhydrides, such as, acetic anhydride, propionic 30 anhydride, butyric anhydride, valeric anhydride, etc.; the acyloxy silanes, such as, methyltriace toxy silane, ethyltriacetoxy silane, phenyltriacetoxy silane, dimethyldiacetoxy silane, methyltributy roxysilane, etc.; inorganic acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, etc.; and organic acids, such as, formic acid, acetic acid, propionic acid, palmitic acid, maleic acid, etc. Suitable Lewis acids broadly encompass the above acids, but additionally 35 include, for example, A;C13, BaSO, BCI, TiBr3Although the above acids may be used alone, it has been found to be advantageous to employ an amine co7catalyst with these acids. Basically, any primary, secondary, or tertiary amine will function as a co-catalyst but such amines having fewer than about 12 carbon atoms are preferred. Suitable amines for use as the co-catalyst include diethyl amine, (Me2N)2C=NC3H- 40 6Si(OMe),, H2NC3H6Si(OEt)31 piperidine, N,N-dimethylethylenediamine, N- hexylamine, tributylamine, dibutylamine, cyclohexylamine, etc.

The concentration of the acid utilized should be at least an effective amount necessary to promote the end-capping reaction. The concentration of the acidifying agent should not be so high as to cause or catalyze the rupture of any of the siloxane bonds in the silanol-containing 45 oganopolysiloxane that is to be end-capped. Another way of saying the same thing, preferably the acid number of the acidifying agent in the reaction medium is such that the acid number as determined by Silicon Products Division, General Electric Company, Waterford, N.Y., C-204 Test Method should be at least 0.1 and should not exceed 15.

Briefly, the C-204 Test Method consists of taking a 250 mi. flask and adding 100 mi. of 50 isopropanol and 0.25 mi. of phenolphthalein indicator to the flask. The sample whose acid number is to be determined is then weighed and added to the flask. The resulting solution is then titrated with 0.1 N KOH (soolution in methanol) to the pink end point. The volume of KOH in methanol used in the titratium is recorded as V, The total acid number is then calculated from the following formula: 55 Vt(NKOH) (56. 1) Total Acid Number= Sample wt.

60 Generally in the case of acetic acid, this range is equivalent to a range of from about 0.01 to about 0.10 parts by weight acetic acid to 100 parts by weight silanol end- stopped polydiorga nosiloxane polymer. Where amines are utilized with the above acids as co- catalysts, they are used in a concentration of anywhere from about 0.1 to about 0.5 parts by weight per 100 parts by weight of the silanol end-stopped polycliorganosiloxane polymer. Further teaching concerning 65 4 GB2196014A 4 these end-capping catalysts is unnecessary.Their use is well known in the art. End-capping catalysts as taught above, are described in U.S. Patent No. 4,515,932, hereby incorporated by reference.

The present invention is directed to titanium catalyzed RTV rubbers. Suitable titanium catalysts include both the titanium chelates and the titanates. The titanium chelates may be selected from, 5 for example, 1,3-propanedioxytitanium bis(ethylacetoacetate), 1,3- propanedioxytitanium bis (acetylacetonate), and diisopropoxytitanium bis (acetylacetonate). Additional titanium chelates are disclosed in U.S. Patent No. 3,,689,454 and U.S. Serial No. 889,598 filed July 22, 1986, hereby incorporated by reference. The titanates may be selected from titanium naphthenate, tetrabutyl titanate, tetra-2-ethyfhexyltitanate, tetraphenyl titanate, tetraoctadecyltitanate, ethyltriethanolami- 10 netitanate, etc. In addition, betadicarbonyltitanium compounds as shown by Weyenberg, U.S.

Patent No. 3,334,067 can be used as condensation catalysts in the present invention.

The amount of condensation catalyst utilized should be at least an effective amount to facilitate the cure of the RTV composition. Generally the titanium condensate catalyst should be used in an amount of from about 0.001 to about 2.0 parts by weight per 100 parts by weight 15 of the silanol terminated polydiorganosiloxane.

Various fillers and pigments can be incorporated in the silanol or alkoxyterminated organopoly- siloxane, such as for example, titanium dioxide, zirconium silicate, silica aerogel, iron oxide, diatomaceous earth, fumed silica, carbon black, precipitated silica, glass fibers, polyvinyl chloride, ground quartz, calcium carbonate, etc. The amounts of filler used can obviously be varied within 20 wide limits in accordance with the intended use. For example, in some sealant applications, the curable compositions of the present -invention can be used free of filler. In other applications, such as the employment of the curable compositions for Making binding material on a weight basis, as much as 300 parts or more of filler, per 100 parts of organopolysiloxane can be employed. In such applications, the filler can consist of a major amount of extending materials, 25 such as ground quartz, polyvinylchloride, or mixtures thereof, preferably having an average particle size in the range of from about 1 to 10 microns. Preferably, however, from about 300 parts by weight of filler are per 100 parts by weight organopolysiloxane.

The compositions of the present invention also can be employed as construction sealants and caulking compounds. The exact amount of filler, therefore, will depend upon such factors as the 30 application for which the organopolysiloxane composition is intended, the type of filler utilized (that is, the density of the filler and its particle size). Preferably, a proportion of from 10 to 300 parts of filler, which can include up to about 35 parts of a reinforcing filler, such as fumed siica filler, per 100 parts of silanol-terminated organopolysiloxane is utilized.

The preferred filler, fumed or precipitated silica, may be treated or untreated. Treated silica 35 fillers include fillers treated with hydrolyzate, i.e. treated with a mixture of cyclic and hydroxy end-stopped silanol fluids; fillers. treated with silane fluids, such as trimethyl silyl; and fillers treated with a silazane, i.e. hexamethyldisilazane. Treatment of the filler affects the wet out of the filler, compatability of the filler, and other properties, such as hydroxy group content of the filler. 40 Hydroxy group content of the filler may lead to end-capping reactions taking place on the filler surface as well as at the end of the silanol chain. Untreated fillers or fillers treated with hydrolyzate have relatively high hydroxy group contents. Fillers treated with, silane fluids, for example, trimethylsilane or with silazanes, such as hexamethyldisilazane, will have relatively low hydroxy group contents. It is preferred that low hydroxy content fillers be employed herein. 45 Hydroxy or methanol scavengers may be used in the instant application to extend shelf life.

These scavengers are disclosed in U.S. Patent Nos. 4,395,526 and 4,417, 042 hereby incorpo ated by reference.

As used hereinafter, the expressions "moisture free conditions" and "substantially anhydrous conditions", with reference to making the RTV compositions of the present invention, mean 50 mixing in a dry box, or in a closed container which has been subjected to vacuum to remove air, which thereafter is replaced with a dry inert gas, such as nitrogen. Temperatures can vary from about O'C to about 180C, depending upon the degree of blending, the type and amount of filler.

The procedure for making the RTV rubber requires that the end-capping of the silanol termi- 55 nated polydiorganosiloxane be accomplished prior to incorporating the titanium condensation catalyst. Obviously, this may be done by (a) mixing (i) a silanol terminated polydiorganosiloxane, - (ii) an end-capping agent having the formula: 60 RmSi(OR'),-m wherein m has a value of from 1 to 2, and R and RI are hydrocarbyl, halohydrocarbyl, and cyano lower alkyl radicals having up to about 12 carbon atoms, and (iii) an end-capping catalyst selected from Lewis acids, Lowry-Bronsted acids and mixtures of the acids with amine co-catalysts; 65 GB2196014A 5 (b) reacting the resultant mixture; and (c) further admixing an effective amount of at least one titanium condensation catalyst.

The mixing step should be performed under substantially anhydrous conditions. It is preferred that any fillers, particularly fumed silica fillers, be added in the initial mixing step, prior to the reacting step. The reacting step, i.e. end-capping step, may require several minutes or even 5 hours, depending upon the temperature, end-capping agent, and end-capping catalyst employed.

Temperature of the reacting step, which may be carried out simultaneously with the mixing step, should not exceed about 180'C. Where a sufficiently fast end-capping reaction cannot be achieved below 1800C, then end-capping catalyst or end-capping agent should be varied in order to speed the reaction. 10 Following the reaction step, the titanium condensation catalyst should be admixed. Where a viscosity rise is experienced following such admixture, then insuffucient end-capping has been performed. This may be a result of not enough end-capping agent being employed or insufficient reaction time or conditions to complete end-capping.

There can also be added other ingredients, including cure accelerators, pigments, flame retar- 15 dants, fungicides, plasticizers and the like. These RTV rubbers will cure upon exposure to moisture and to avoid cure, must be kept in an anhydrous state.

The titanium catalyzed, alkoxy end-stopped polydiorganosiloxane RTV rubbers so produced exhibit improved hardness, improved tensile strength, improved elongation, and improved appli cation rates. Such RTV rubbers find use in household caulking applications and industrial applications such as on buildings, factories, automotive equipment, and in applications where adhesion to masonry, glass, plastic, metal and wood is required.

The Examples below are given for the purpose of illustrating the present invention. They are not given for the purpose of limitation. All parts in the Examples are by weight.

25 Examples

Example 1

A base composition was prepared by mixing 100 parts of silanol endstopped polysiloxane having a viscosity of about 12,000 cps at 25"C and a phenyl on chain content of about 5 mole %, 25 parts of a trimethylsilyl treated fumed silica filler and 1.0 parts of titanium dioxide as a 30 pigment.

Comparative Example A To 100 parts of the base composition of Example 1 was added 4.5 parts of a solution of 3.0 parts of methyltrimethoxysilane and 1.5 parts of diisopropoxy titanium bis(ethylaceloacetate). 35 The catalyzation was characterized by a large but temporary viscosity rise making the mixing of the ingredients difficult.

The resultant RTV rubber was applied and cured. Physical property measurements were taken after a 7-day cure at 75'F and 50% R.H. excepting od course application rate which was measured at 90 p.s.i. through a 1/8" opening. Results of this testing are listed in Table 1. 40 Comparative Example B To 100 parts of the base composition of Example 1 was added 5.0 parts of a solution of 3.0 parts of methyltrimethoxysilane and 2.0 parts of diisopropoxytitanium bis(ethylacetoacetate). The catalyzation was characterized by a large but temporary viscosity rise making the mixing of the 45 ingredients difficult.

The resultant RTV rubbers were applied and cured with the physical properties being taken as in Comparative Example A. Results of this teiting are listed in Table 1.

Table 1 50

Comparative Example A B Shore A 25 22 Tensile Strength (p.,9.i.) 357 363 Elongation (%) 375 390 Application Rate (g/min.). 162 126 55 Example 2

This example demonstrates the present invention. To 126 parts of the base composition of Example 1 was added 3.3 parts of a solution of 2.5 parts methyltrimethoxy silane, 0.1 parts of 60 diethylamine and 0.05 parts of acetic acid. This composition was heated at 80-100C for 20 minutes. A vacuum was then applied for approximately 20 minutes, and the mixture was cooled to give a modified base composition.

To 100 parts of the modified RTV base was added 4.5 parts of a solution containing 3.0 parts methyltrimethoxysilane and 1.5 parts of diisopropoxytitanium bis(ethylacetoacetate). The 65 6 GB2196014A 6 catalyzation went smoothly with no viscosity rise. The RTV rubber obtained was tested as described in Comparative Example A, and the results are listed in Table II.

Example 3

To 100 parts of the modified base composition of Example 2 was added 5.0 parts of a 5 solution of 3.0 parts methyltrimethoxysilane and 2.0 parts of diisoproxytitanium bis(ethylacetoa cetate). Again, the catalyzation went smoothly with no viscosity rise. This RTV rubber was tested as described in Comparative Example A, and results are listed in Table 11.

Table // 10

Example 2 3

Shore A 36 36 Tensile Strength (p.s.i.) 655 685 Elongation (%) 286 276 Application Rate (g/min.) 252 252 15 According to the present invention, a viscosity rise during catalyzation is avoided and a higher application rate material is produced which cures to a stronger elastomer compared to the RTV rubbers of the Comparative Examples.

20 Comparative Example C To 136 parts of the modified base of Example 2 was added 4.62 parts of a solution of 4.2 parts methyltrimethoxysilane and 0.42 parts dibutyltindiacetate. After 10 minutes of mixing, the RTV rubber gelled in the tube and could not be extruded from the tube. This is in sharp contrast to Examples 2 and 3 where a titanium catalyst was used. 25

Claims

1. A method for production of titanium catalyzed alkoxy end-stopped RTV rubbers having superior properties, which method comprises:

(a) reacting a mixture comprising: 30 (i) 100 parts by weight a silanol terminated polydiorganosiloxane, (ii) at least one mole per mole of silanol group in (a)(i) of an end- capping agent having the formula:

RmSi(OR'),-m wherein m has a value. of from 0 to 2, and R and RI are hydrocarbyl, halohydrocarbyl, and 35 cyano lower alkyl radicals having up to about 12 carbon atoms, and (iii) an effective amount of an end-capping catalyst selected from Lewis acids, Lowry-Bronsted acids and mixtures of said acids with amine co-catalysts; and (b) further admixing an effective amount of at least one titanium condensation catalyst.

2. The method of claim 1 wherein said mixture of said reacting step further comprises from 40 about 5 to about 70 parts by weight treated silica filler.

3. The method of claim 2 wherein said silica filler is treated with agents selected from the group consisting of hydrolyzate, silane fluids, and silazane.

4. The method of claim 1 wherein said end-capping agent is selected from the group consisting of 45 CH3S'(OCH,), CH3Si(OCH,CH3)3 (CH3)2Si(OCH3)2 Si(OCH3)4 50 CH3CH,CH2CH,CH2CH2CH,CH2Si(OCH3)3 CF3CH,Si(OCH3)3 NCCH2CH2Si(OCH3)3 (CH3)Si(OCH2CH2CH2CH3)3 55

5. The method of claim 4 wherein said end-capping agent is CH3Si(OCH3)3.

6. The method of claim 1 wherein said Lewis acids and said Lowry-Bronsted acids are selected from the group consisting of organic acids.

7. The method of claim 6 wherein said organic acids are selected from the group consisting of formic acid, acetic acid, propionic acid, palmitic acid, and maleic acid. 60

8. The method of claim 7 wherein said organic acid is acetic acid.

9. The method of claim 1 wherein an amine co-catalyst is present.

10. The method of claim 9 wherein said co-catalyst is selected from the group consisting of diethyl amine, (Me,N),C=N_C3H.Si(OMe)3, H,NC,H6Si(OEt)3, piperidine, N,N- dimethylethylenediam ine, Whexylamine, tributylamine, dibutylamine and cyclohexylamine. 65 7 GB2196014A 7

11. The method of claim 9 wherein said co-catalyst is diethylamine.

12. A substantially anhydrous RTV rubber comprising:

(a) the reaction product of a mixture comprising:

(i) 100 parts by weight a silanol terminated polydiorganosiloxane, (ii) at least one mole per mole of silanol group in (a)(i) of an end- capping agent having the 5 formula:

R,nSi(0R'),_m wherein rn has a value of from 0 to 2, and R and RI are hydrocarbyl halohydrocarbyl, and cyano lower alkyl radicals having up to 12 carbon atoms, and 10' (iii) an effective amount of end-capping catalyst selected from Lewis acids, Lowry-Bronsted 10 acids -and mixtures of said acids with amine co-catalysts; and (b) an effective amount of at least one titanium condensation catalyst.

13. The composition of claim 2 wherein said reaction product further comprises from about to about 70 parts by weight treated silica filler.

14. The composition of claim 13 wherein said silica filler is treated with agents selected from 15 the group consisting of hydrolyzate, silane fluids, and silazane.

15. The composition of claim 12 wherein said end-capping agent is selected from the group consisting of:

CH3Si(OCH3)3 20 CH3S'(OCH2CH3)3 (CH3)2Si(OCH3)2 Si(OCH3)4 CH3CH2CH2CH2CH2CH2CH,CH2Si(OCH3)3 CF3CH2Si(OCH3)3 25 NCCH2CH2S'(OCH3)3 (CH3)Si(OCH2CH2CH2CH3)3

16. The composition of claim 15 wherein said end-capping agent is CH3S'(OCH3)3, -

17. The composition of claim 12 wherein said Lewis acids and said Lowry- Bronsted acids are 30 selected from the group consisting of organic acids.

18. The composition of claim 17 wherein said organic acids are selected from the group consisting of formic acid, acetic acid, propionic acid, palmitic acid, and maleic acid.

19. The composition of claim 18 wherein said organic acid is acetic acid.

20. The composition of claim 1 wherein an amine co-catalysts is present. 35

21. The composition of claim 20 wherein said amine co-catalyst is selected from the group consisting of diethyl amine, (Me2N)2C=N_C3H,Si(0Me6 H2NC3H,Si(OEt)31 piperidine, N,N-dimethy lethylenediamine, N-hexylamine, tributylamine, dibutylamine and cyclohexylamine.

22. The composition of claim 21 wherein said co-catalyst is diethylamine.

23. A method for the production of titanium catalyzed alkoxy and endstopped RTV rubbers 40 as claimed in claim 1, substantially as described in any one of the examples.

24. A RTV rubber when produced by a method as claimed in any one of claims 1 to 11 and 23.

25. A RTV rubber as claimed in claim 12, substantially as hereinbefore described in any one of the examples. 45 Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BF15 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.