JPH055261B2 - - Google Patents

Description

[Detailed description of the invention]

PRESENTATION OF RELATED APPLICATIONS This application is filed under U.S. patent application Ser.
No. 583,530 (filed February 24, 1984) and U.S. Application No. 644,892 to Wenglobius et al., filed on the same date as the U.S. patent application on which this application is based, entitled "Room Temperature Curable Organopolysiloxane Compositions and Process for Preparing the Same" It is related to BACKGROUND OF THE INVENTION The present invention relates to room temperature curable (RTV) organopolysiloxane compositions with excellent storage stability and corrosion resistance. More particularly, the present invention provides RTV organopolysiloxane compositions employing an effective amount of a specific tin condensation catalyst in which the organo groups are attached to the tin via carbon-tin bonds and the remaining valences are filled with dicarboxylate groups. relating to things. For example, di-n-butyltin-diethylmalonate can be used in combination with the amine curing accelerator di-n-butylamine. Prior to the present invention, RTV organolysis was performed using polyalkoxy-endcapped diorganopolysiloxanes and monocarboxylic acid metal salt catalysts, such as dibutyltin dilaurate, as disclosed in Brown et al., U.S. Pat. No. 3,161,614. Polysiloxane compositions have been produced. These compositions did not cure satisfactorily. U.S. Pat. No. 4,100,129 to Beers, assigned to the present applicant, discloses the use of silanol-reactive organometallic esters in which the organo group is attached to the metal via a metal-oxygen-carbon bond as a condensation catalyst. The results were obtained. Experience has shown that when silanol-reactive organotin compounds in which the organo group is bonded to tin via tin-oxygen-carbon bonds are used as RTV condensation catalysts, the resulting moisture-curable compositions are often unstable. As used below, the term "stable" as used for the one-package polyalkoxy-terminated organopolysiloxane RTV of the present invention refers to the moisture-curable mixture being excluded from atmospheric moisture. The elastomer can remain substantially uncured, meaning that it can be cured into a tack-free elastomer even after extended storage periods. More stable RTV
is based on the tack-free time exhibited by freshly mixed RTV ingredients under atmospheric conditions and when a mixture of the same ingredients is stored in a moisture-proof, moisture-free container under ambient conditions for extended periods of storage or accelerated aging at elevated temperatures. It means that the tack-free time when exposed to atmospheric moisture after holding for an equivalent period of time is substantially the same. RTV stability is determined by the use of silane scavengers to remove chemically bound hydroxy groups, water or methanol, as shown in commonly assigned U.S. Pat. No. 4,395,526 to White et al. This was further improved by using a scavenger. However, the production of these silane scavengers, such as methyldimethoxy-(N-methylacetamido)silane, often requires specialized techniques and undesirable by-products can be generated during curing. Further improvements in scavenging agents for one-component alkoxy-functional RTV compositions and methods for making RTV compositions are disclosed in commonly assigned U.S. Pat. No. 4,417,042 to Dziark. . Organic scavengers for removing traces of water, methanol and silanols are disclosed in U.S. Patent Application No. 481,524 to White et al., assigned to the present applicant.
No. (filed April 1, 1983) "One-Package Stable Moisture Curing Alkoxy-Terminated Organopolysiloxane Composition". Another scavenging technique for scavenging chemically bonded hydroxy functional groups is disclosed in Lockhart U.S. Patent Application No. 481,530.
No. (filed April 1, 1983). Although it has been established that the above techniques for improving the stability of room temperature curable organopolysiloxane compositions using tin condensation catalysts result in stable, substantially acid-free curable organopolysiloxanes. , an organic, inorganic or organosilicon scavenger for the hydroxy functionality is required separately. Using silanol-terminated or alkoxy-terminated polydiorganosiloxanes and tin condensation catalysts (which may be further combined with alkoxysilane crosslinkers and optionally amine promoters), such as scavengers for hydroxy-functional materials, It would be desirable to produce stable room temperature curable organopolysiloxane compositions without the use of additional materials. The present invention was made based on the discovery that a stable, rapidly curable RTV composition can be obtained by using a tin condensation catalyst having the following formula: (R) ₂ Sn[Y] (1). Here, Y is the following formula: is a dicarboxylate group having a divalent C _(1-18) hydrocarbon group and a monovalent substituted C _(1-18) hydrocarbon group, and R ¹ is a dicarboxylate group having a divalent C ₍ 1-18) hydrocarbon group; _-18) hydrocarbon group and divalent substituted C _(1-18) hydrocarbon group,
a is an integer having a value of 0 or 1. Some silanol-terminated polydiorganosiloxanes that can be used to prepare the stable, substantially acid-free, moisture-curable organopolysiloxane compositions of the present invention have the formula: Here, R ² is a monovalent C _(1-13) hydrocarbon group or a substituted hydrocarbon group, preferably methyl, or a large amount of methyl and a small amount of phenyl, cyanoethyl, trifluoropropyl, vinyl, hydrogen or these. and m is an integer having a value of about 5 to about 5,000. The polyalkoxy-terminated organopolysiloxane that can be used to make the RTV compositions of the present invention has the formula: Here, R ² and m are as defined above, and R ³ is
A monovalent group selected from a C _(1-13) hydrocarbon group and a substituted C _(1-13) hydrocarbon group, R ⁴ is an alkyl group,
It is a C _(1-8) aliphatic organic group or a C _(7-13) aralkyl group selected from an alkyl ether group, an alkyl ester group, an alkyl ketone group, and an alkyl cyano group, and a is as defined above. The RTV composition of the present invention has the following formula: It may also contain a crosslinking polyalkoxysilane having the following. Here, R ³ , R ⁴ and a are as defined above. DISCLOSURE OF THE INVENTION According to the present invention, on a weight basis, (A) 100 parts of an organopolysiloxane consisting essentially of chemically bonded diorganosiloxy units terminated with polyalkoxysiloxy units; (B) 0 to 10 parts of A room temperature curable composition is provided containing a polyalkoxysilane of formula (4), (C) 0 to 5 parts of an amine promoter, and (D) an effective amount of a tin condensation catalyst of formula (1). Also included within the scope of the present invention is a method of making a room temperature curable organopolysiloxane composition, which method comprises: (i) 100 parts by weight of formula (3) under substantially anhydrous conditions; an alkoxy-terminated organopolysiloxane, (ii) 0 to 10 parts by weight of a polyalkoxysilane of formula (4), (iii) 0 to 5 parts by weight of an amine promoter, and (iv) an effective amount of a tin condensate of formula (1). It consists of mixing together the catalysts. A method of making a room temperature curable organopolysiloxane composition according to yet another aspect of the invention comprises: (1) under substantially anhydrous conditions: (i) 100 parts of a silanol-terminated polydiorganosiloxane of formula (2); (ii) 0.1 to 10 parts of the alkoxysilane of formula (4), (iii) 0 to 5 parts of the amine promoter, and (iv) 0 to 700 parts of the filler; (2) step (1); equilibrating the mixture to form a polyalkoxy-terminated polydiorganosiloxane; and (3) stirring the mixture of step (2) under substantially anhydrous conditions with an effective amount of a tin condensation catalyst of formula (1). including. Examples of groups included in R in formula (1) are C _(6-13)
Aryl, halogenated aryl and alkylaryl groups such as phenyl, tolyl, chlorophenyl, ethyl phenyl and naphthyl; C _(1-18)
Aliphatic, cycloaliphatic groups and their halogenated derivatives such as cyclohexyl, cyclobutyl, alkyl and alkenyl groups such as methyl, ethyl, propyl, chloropropyl, butyl, pentyl, hexyl, heptyl, octyl, vinyl, allyl and trifluoropropyl. . Examples of groups included in R ¹ include methylene, dimethylene, trimethylene, tetramethylene, alkyl-substituted alkylene groups such as dimethylmethylene, diethylmethylene, α-dimethylethylene, 2,2-dimethylpropylene, etc.; alicyclic groups For example, cyclobutylene,
Cyclopentylene, cyclohexylene, cyclooctylene, etc.; C _(6-13) arylene groups such as phenylene, tolylene, xylylene, naphthylene, etc., and the above R ¹ group is further a monovalent group such as halogen, cyano, ester, amino , silyl and hydroxyl. The groups contained in R ³ are all the monovalent C _(1-13) groups shown for R, and in this case R and R ³ may be the same or different. Groups contained within R ⁴ may be methyl, ethyl, propyl, butyl, etc., benzyl, phenylethyl, 2-methoxyethyl, 2-acetoxyethyl, 1-butan-3-onyl, 2-cyanoethyl, among others. Some examples of tin condensation catalysts included in formula (1) include di-n-butyltin diethyl malonate, di-
n-octyltin succinate, di-n-octyltin oxalate, di-n-butyltin hexahydrophthalate, dimethyltin adipate, di-n-butyltin glutamate, di-n-propyltin (2-
cyanoglutarate), di-sec-butyltin adipate and di-n-pentyltin phthalate. The crosslinking polyalkoxysilane of formula (4) includes, for example, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, tetraethoxysilane, vinyltrimethoxysilane, and the like. Among the amine cure accelerators that can be used in the practice of this invention are silyl-substituted guanidines having the formula: (Z) _g Si (OR ⁴ ) _4-g (5). here
R ⁴ is as defined above, and Z is the following formula: is a guanidine group, R ⁷ is a divalent C _(2-8) alkylene group, R ⁵ and R ⁶ are selected from hydrogen and C _(1-8) alkyl group, and g is equal to 1 to 3 is an integer. In addition, the following formula: Alkyl-substituted guanidines can also be used.
Here, R ⁵ and R ⁶ are as defined above, and R ⁸ is C _(1-8)
It is an alkyl group. Some of the silyl-substituted guanidines included in formula (5) are shown in Takago US Pat. Nos. 4,180,642 and 4,248,993. In addition to the substituted guanidines mentioned above, various amines such as di-n-hexylamine, dicyclohexylamine, di-n-octylamine, hexamethoxymethylmelamine and silylated amines such as δ-aminopropyltrimethoxysilane and methyldimethoxy -di-n-hexylaminosilane may also be used. methyldimethoxydi-n
-Hexylaminosilane acts both as a crosslinker and as a curing accelerator. Primary amines, secondary amines, and silylated secondary amines are preferred, and among these, secondary amines and silylated secondary amines are particularly preferred. Silylated secondary amines such as alkyldialkoxy-n-dialkylaminosilanes and guanidines such as alkyldialkoxyalkylguanidylsilanes are useful as curing accelerators. In addition to the amine promoters described above, the practice of this invention also encompasses the use of certain sterically hindered diamines. When these sterically hindered diamines are used in the effective amounts described above, they can be used in the present invention.
The RTV composition was found to cure quickly.
These nitrogen bases include, for example, di-t-butylethylenediamine (DBEDA), 1,5-diazabicyclo[4,3,0]non-5-ene (DBN),
and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU). Silanol-terminated polydiorganosiloxanes of formula (2) are well known and preferably have viscosities in the range of about 100 to about 400,000 centipoise, particularly in the range of about 1000 to about 250,000 centipoise, measured at about 25°C. These silanol-terminated fluids can be prepared by treating a high molecular weight organopolysiloxane, such as dimethylpolysiloxane, with water in the presence of a mineral acid or basic catalyst to change the viscosity of the polymer to the desired range. Methods for producing such high molecular weight organopolysiloxanes used in the production of silanol-terminated polydiorganosiloxanes of formula (2) are also well known. For example, a low molecular weight hydrolyzate can be produced by hydrolyzing diorganohalosilanes such as dimethyldichlorosilane, diphenyldichlorosilane, methylvinyldichlorosilane or mixtures thereof. Higher molecular weight organopolysiloxanes can be produced by subsequent equilibration. Higher molecular weight polymers should also be obtained by equilibration of cyclopolysiloxanes such as octamethylcyclotetrasiloxane, octaphenylcyclotetrasiloxane or mixtures thereof. Such polymers are preferably stripped of equilibration catalyst prior to use by standard methods such as those set forth in commonly assigned US Pat. No. 3,153,007 to Boot. Silanol-terminated organopolysiloxanes with viscosities below 1200 centipoise can be made by treating organopolysiloxanes consisting essentially of chemically bonded diorganosiloxy units with pressurized steam. Another method that can be used to make silanol-terminated polydiorganosiloxanes is described in U.S. Pat. No. 2,607,792 to Warrick.
and British Patent No. 835790. To accelerate the curing of the RTV compositions of the present invention,
The tin condensation catalyst of formula (1) can be used in an amount of from 0.1 to 10 parts of tin catalyst per 100 parts of silanol-terminated or alkoxy-terminated polydiorganosiloxane, preferably from 0.1 to 1.0 parts of tin catalyst per 100 parts of polydiorganosiloxane. Various fillers, pigments, adhesion promoters, etc. can be incorporated into the silanol- or alkoxy-terminated organopolysiloxane, such as titanium dioxide,
Zirconium silicate, silica aerogel, iron oxide,
Silica earth, humid silica, carbon black,
Examples include precipitated silica, glass fiber, polyvinyl chloride, quartz powder, calcium carbonate, and β-cyanoethyltrimethoxysilane. It is clear that the amount of filler used can vary within wide limits depending on the intended use. For example, the curable compositions of the present invention can be used without fillers in certain sealant applications. For other uses, for example when the curable composition is used in the production of binder materials, on a weight basis:
As much as 700 parts or more of filler per 100 parts of organopolysiloxane can be used. In such applications, the filler may consist primarily of bulking agents such as quartz powder, polyvinyl chloride, or mixtures thereof, preferably having an average particle size in the range of about 1 to 10 microns. The compositions of the invention can also be used as architectural sealants and caulks. The exact amount of filler will therefore depend on factors such as the intended use of the organopolysiloxane composition, the type of filler used (ie, the density and particle size of the filler). It is preferred to use a proportion of 10 to 300 parts of filler per 100 parts of silanol-terminated organopolysiloxane, which filler may contain up to about 35 parts of reinforcing filler, such as fumed silica filler. In the practice of the present invention, room temperature curable compositions can be prepared by agitating, e.g. stirring, a component mixture of the tin condensation catalyst and the alkoxy-terminated polydiorganosiloxane under moisture-free conditions. Crosslinking polyalkoxysilanes and amine promoters can be used if desired. If a silanol-terminated polydiorganosiloxane is used instead of an alkoxy-terminated polydiorganosiloxane, the blending of the filler, such as fumed silica, the silanol-terminated polydiorganosiloxane, and the crosslinking polyalkoxysilane is carried out in the absence of a tin condensation catalyst. preferable. Advantageously, the tin condensation catalyst is introduced after the resulting blend has been stirred for about 24 hours at a similar temperature. The expression "moisture-free conditions" or "substantially anhydrous conditions" as used herein in connection with the manufacture of the RTV compositions of the present invention refers to the use of vacuum to remove air;
This refers to mixing in a dry box or sealed container, which is then purged with a dry inert gas, such as nitrogen. The temperature can vary from about 0°C to about 180°C depending on the degree of blending and the type and amount of filler. A preferred method for making the RTV compositions of the present invention is to stir a mixture of a silanol-terminated polydiorganosiloxane or an alkoxy-terminated polydiorganosiloxane, a filler, and an effective amount of a tin condensation catalyst under substantially anhydrous conditions. It is. A crosslinking silane or mixture thereof can be added to this mixture along with other ingredients such as accelerators and pigments. To enable those skilled in the art to practice the invention, the following examples are included by way of illustration and not by way of limitation. All parts are by weight. Example 1 A mixture of 300g dibutyltin oxide, 193g diethylmalonic acid and 500ml toluene was refluxed for 1 hour. 21 g of water was collected in a Dean Stock trap by azeotropic distillation.
The reaction mixture was then filtered hot and allowed to cool to ambient temperature. Removal of the solvent under vacuum gave 460 g (98% yield) of dibutyltin diethyl malonate as a white crystalline solid. product identification
Confirmed by NMR, IR and FD-MS analysis. Viscosity of 100 parts total: approximately 40,000 centipoise (25℃)
methyldimethoxysiloxy-terminated polydimethylsiloxane, 0.3 parts dibutylamine, 17 parts fumed silica, 30 parts viscosity 100 centipoise (25
Base by thoroughly mixing trimethylsiloxy-terminated polydimethylsiloxane (°C) and 1.4 parts β-cyanoethyltrimethoxysilane.
An RTV composition was produced. To 100 g of the above basic RTV composition was added 0.35 g dibutyltin diethylmalonate and 0.30 g methyltrimethoxysilane. The resulting RVT composition was blended in a Semco mixer under substantially anhydrous conditions for 15 minutes. Half of this RTV composition was then heat aged at 100°C for 48 hours.
The other half of the RTV composition was stored at 25°C. Both RTVs were evaluated under substantially anhydrous conditions in sealed containers. When exposed to atmospheric moisture, both heat-aged and non-aged RTV
It cured to a tack-free state in minutes. The following table shows aged and non-aged RTV
The physical properties of the cured product obtained after 12 days of curing are summarized. "H" is hardness (Shore A), "T" is tensile strength (psi), "E" is elongation (%), and "M" is elastic modulus (psi).

[Table] These RTVs meet the US military standard (Military
It was also confirmed that it passed the vapor phase corrosion test for copper metal described in Specification) No. 46146A. Furthermore, it was confirmed that both RTVs did not yellow. Example 2 A mixture of 161.4 g of dibutyltin oxide and 100 g of hexahydrophthalic anhydride was heated under reflux in 100 ml of toluene for 2 hours. During this period, dibutyltin oxide quickly dissolved and formed a yellow homogeneous solution. After cooling, the reaction mixture was filtered.
The solvent was removed under vacuum to give a yellow glassy solid in quantitative yield. Based on the method of preparation and NMR spectrum, this solid was dibutyltin hexahydrophthalate. 100 parts dimethoxymethylsiloxy-terminated polydimethylsiloxane with a viscosity of 20,000 centipoise (25°C) under anhydrous conditions, 1 part β-cyanoethyltrimethoxysilane, 20 parts fumed silica,
20 parts 100 centipoise viscosity trimethylsiloxy-terminated polydimethylsiloxane, 1 part 1,3,
5-tris(trimethoxysilylpropyl)isocyanurate, 0.08 parts di-n-butylamine,
An RTV composition was prepared by mixing together 0.25 parts of the di-n-butyltin hexahydrophthalate condensation catalyst and 0.3 parts of methyltrimethoxysilane. A portion of this RTV composition was cured at ambient conditions under atmospheric humidity. The tack-free time was about 20 minutes. Other parts of the RTV composition under sealed conditions
Heated to 70°C for 120 hours. When cured under atmospheric conditions, the tack-free time was 25 minutes. Example 3 A mixture of 1000 g dibutyltin oxide, 587.2 g adipic acid and 500 ml toluene was refluxed for 3 hours. 72 g of water was obtained by azeotropic distillation. The reaction mixture was then filtered hot and the resulting bright yellow liquid was freed from the solvent under vacuum. After drying,
1501 g of dibutyltin adipate was obtained with a yield of 99.1%. The melting point of the product was 128-130°C. Product identity was further confirmed by NMR spectra. under substantially anhydrous conditions 100 parts methyldimethoxysiloxy endcapped polydimethylsiloxane of Example 2, 20 parts fumed silica, 20 parts trimethylsiloxy endcapped silicone oil, 1.4
part of β-cyanoethyltrimethoxysilane, 1 part of 1,3,5-tris(trimethoxysilylpropyl)isocyanurate, 0.3 part of dibutyltin adipate, 0.05 part of di-n-butylamine and
The RTV composition was prepared by mixing together 0.3 parts of methyltrimethoxysilane. A portion of this RTV composition was cured under atmospheric conditions and had a tack free time of 15 minutes. 70 different parts of RTV composition
Heat aged at ℃ for 120 hours. This tack-free time was 30 minutes. Example 4 As shown in U.S. Application No. 644,892, compositions of the present invention exhibit reduced corrosiveness to copper when in contact with copper for extended periods of time under ambient conditions as described below. be able to. Viscosity of 100 parts by weight under substantially anhydrous conditions 40,000
Methyldimethoxysiloxy-terminated polydimethylsiloxane in centipoise (25°C), 0.3 parts dibutylamine, 30 parts viscosity 100 centipoise (25°C)
of trimethylsiloxy-terminated polydimethylsiloxane, 17 parts fumed silica and 1.4 parts β-
The basic RTV formulation was prepared by mixing together the cyanoethyltrimethoxysilane. An RTV composition was prepared by blending together 100 parts of the base polymer mixture, 0.35 parts of dibutyltin (diethyl malonate), and 0.30 parts of methyltrimethoxysilane under substantially anhydrous conditions (Mixture 1). . A mixture of 100 parts of base polymer was also blended with 0.30 parts of dibutyltin diethylmalonate, 0.13 parts of benzotriazole and 0.30 parts of methyltrimethoxysilane (Mixture 2). 100 parts base polymer, 0.37 parts dibutyltin diethylmalonate,
A third mixture was made using 0.02 parts of Reomet 39 (a benzotriazole derivative from Ciba Geigy) and 0.66 parts of methyltrimethoxysilane (Mixture 3). These three formulations were compounded under substantially anhydrous conditions and mixed in a Semco mixer for 15 minutes.
Five grams of each RTV formulation was applied to the surface of a 2 inch by 2 inch section of clean copper metal. All RTV formulations were cured in contact with a copper metal surface for 7 days. The samples were then heated for 28 days at 120 °C and 95% relative humidity. A portion of the RTV sample was then peeled away from each copper substrate and the exposed substrate was visually inspected for corrosion. Ivy made from mixture 1
RTV leaves a blue film on the copper substrate, indicating that corrosion of the copper surface has occurred. RTV samples made from Mixtures 2 and 3 showed no evidence of any changes to the copper surface as indicated by a clean metallic appearance. Although the above examples involve only a few of the numerous embodiments that can be used to make the room temperature curable compositions of the present invention, the room temperature curable compositions of the present invention can be used in a very wide variety of Prepared from a tin dicarboxylate salt of formula (1), a silanol-terminated polydiorganosiloxane of formula (2), a polyalkoxysilane of formula (4), and all of the other components listed herein. be able to.

Claims (1)

[Scope of Claims] 1 (A) 100 parts by weight of polydiorganosiloxane having terminal polyalkoxysiloxy units, (B) 0 to 10 parts by weight of polyalkoxysilane, (C) Primary amines, secondary amines, silyl Amine promoter selected from the group consisting of substituted alkylguanidines and alkyl-substituted guanidines
0.05 to 5 parts by weight, (D) Up to 700 parts by weight of filler, and (E) The following formula: (R) ₂ Sn[Y] (However, Y in the formula is the following formula: is a dicarboxylate group, R is a monovalent C _(1-18) hydrocarbon group and a monovalent substituted
selected from C _(1-18) hydrocarbon groups, R ¹ is a divalent C _(1-18) hydrocarbon group and divalent substitution
selected from C _(1-18) hydrocarbon groups, and a is an integer of 0 or 1), in a moisture-proof, moisture-free container under ambient conditions. A stable, moisture-curing formulation that maintains virtually the same tack-free time as when freshly mixed even after extended storage periods, and is substantially free of organic solvents and scavengers for hydroxy-functional materials. Room temperature curable organopolysiloxane composition. 2 The tin dicarboxylate condensation catalyst is di-n-butyltin diethylmalonate, di-n-octyltin diethylmalonate, di-n-octyltin succinate, di-n-octyltin oxalate, di-
n-Butyltin hexahydrophthalate, di-n-
Butyltin glutamate, di-n-butyltin (2-
2. The composition of claim 1, wherein the composition is selected from the group consisting of di-n-pentyltin phthalate (cyanoglutarate), di-n-pentyltin phthalate and dimethyltin adipate. 3. The composition of claim 2, wherein the tin dicarboxylate condensation catalyst is di-n-butyltin diethyl malonate. 4. The composition of claim 2, wherein the tin dicarboxylate condensation catalyst is di-n-octyltin diethyl malonate. 5. Claim 2, wherein the tin dicarboxylate condensation catalyst is di-n-octyltin succinate.
Compositions as described in Section. 6. Claim 2, wherein the tin dicarboxylate condensation catalyst is di-n-octyltin oxalate.
Compositions as described in Section. 7. The composition according to claim 2, wherein the tin dicarboxylate condensation catalyst is di-n-butyltin hexahydrophthalate. 8. The composition of claim 2, wherein the tin dicarboxylate condensation catalyst is di-n-butyltin glutamate. 9. The composition according to claim 2, wherein the tin dicarboxylate condensation catalyst is di-n-butyltin (2-cyanoglutarate). 10 Tin dicarboxylate condensation catalyst is di-n-
Claim 2 which is pentyltin phthalate
Compositions as described in Section. 11. The composition according to claim 2, wherein the tin dicarboxylate condensation catalyst is dimethyltin adipate. 12. The composition of claim 1, wherein the polydiorganosiloxane having terminal polyalkoxysiloxy units is produced in situ by an equilibrium reaction between a silanol-terminated polydiorganosiloxane and a polyalkoxysilane.