Room temperature vulcanizable organopolysiloxane compositions and method for making

Room temperature vulcanizable organopolysiloxane compositions are provided which exhibit improved stability and a reduced tendency to corrode copper metal upon contact over an extended period of time. These moisture curable compositions utilize diorganotinaryltriazolate as a condensation catalyst.

Reference is made to copending application of J. H. Wengrovius and T. P. 
Lockhart for Room Temperature Vulcanizable Organopolysiloxane compositions 
Ser. No. 583,530, filed Feb. 24, 1984 now U.S. Pat. No. 4,517,337 and 
copending applications Ser. No. 644,892 of J. H. Wengrovius and L. W. 
Niedrach and Ser. No. 644,891 of J. H. Wengrovius and T P. Lockhart for 
Room Temperature Vulcanizable Organopolysiloxane Compositions and Method 
for Making, filed concurrently herewith, assigned to the same assignee as 
the present invention and incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
The present invention relates to room temperature vulcanizable 
organopolysiloxane compositions having improved shelf stability and a 
reduced tendency to corrode copper metal. More particularly, the present 
invention relates to moisture curable organopolysiloxane compositions 
using a tin condensation catalyst having organo radicals attached to tin 
by carbon tin linkages and whose remaining valences are satisfied by an 
arylotriazolate group, for example, di(n-butyl)tin bis(benzotriazolate). 
Prior to the present invention, as shown by Brown et al., U.S. Pat. No. 
3,161,614, attempts were made to make stable room temperature vulcanizable 
(RTV) compositions employing a polyalkoxy end blocked polysiloxane and a 
monocarboxylic acid metal salt catalyst, such as dibutyltindilaurate. 
These compositions did not cure satisfactorily. Improved results were 
obtained by Beers, U.S. Pat. No. 4,100,129, assigned to the same assignee 
as the present invention, utilizing as a condensation catalyst, a silanol 
reactive organometallic ester having organo radicals attached to metal 
through metal-oxygen-carbon linkages. Experience has shown that in 
instances where silanol reactive organo tin compounds are used as RTV 
condensation catalysts which have organo radicals attached to tin by 
tin-oxygen-carbon linkages, the resulting moisture curable compositions 
are often unstable. 
As utilized hereinafter, the term "stable" as applied to the one package 
polyalkoxy-terminated organopolysiloxane RTV's of the present invention 
means a moisture curable mixture capable of remaining substantially 
unchanged while excluded from atmospheric moisture and which cures to a 
tack-free elastomer after an extended shelf period. In addition, a stable 
RTV also means that the tack-free time exhibited by freshly mixed RTV 
ingredients under atmospheric conditions will be substantially the same as 
that exhibited by the same mixture of ingredients exposed to atmospheric 
moisture after having been held in a moisture resistant and moisture-free 
container for an extended shelf period at ambient conditions, or an 
equivalent period based on accelerated aging at an elevated temperature. 
Further advances were achieved with the employment of silane scavengers for 
eliminating chemically combined hydroxy radicals, water, or methanol, as 
shown by White et al., U.S. Pat. No. 4,395,526, assigned to the same 
assignee as the present invention and incorporated herein by reference. 
However, the preparation of these silane scavengers, such as 
methyldimethoxy-(N-methylacetamide)silane often require special techniques 
and undesirable by-products can be generated during cure. Further 
improvements are shown by Dziark, U.S. Pat. No. 4,417,042 for scavengers 
for one component alkoxy functional RTV compositions and processes, 
assigned to the same assignee as the present invention and incorporated 
herein by reference. 
Organic scavengers for trace amounts of water, methanol and silanol are 
shown by White et al., Serial No. 481,524, for One Package, Stable, 
Moisture Curable Alkoxyterminated Organopolysiloxane Compositions, filed 
Apr. 1, 1983, now Patent No. 4,472,551 assigned to the same assignee as 
the present invention and incorporated herein by reference. Additional 
scavenging techniques for chemically combined hydroxy functional radicals 
are shown by Lockhart in copending applications Ser. No. 481,529, now U.S. 
Pat. No. 4,499,230, Ser. No. 481,527, now U.S. Pat. No. 4,499,229, Ser. 
No. 481,528, now U.S. Pat. No. 4,477,625, and Ser. No. 481,530, now U.S. 
Pat. No. 4,467,063, filed concurrently on Apr. 1, 1983. 
Although the above discussed techniques for improving the stability of room 
temperature vulcanizable organopolysiloxane compositions employing a tin 
condensation catalyst have been found to provide stable, substantially 
acid-free, curable organopolysiloxanes, a separate organic, inorganic, or 
organosilicon scavenger for hydroxy functional radicals is required. 
The present invention is based on a discovery that stable room temperature 
vulcanizable compositions which also exhibit outstanding corrosion 
resistance to copper can be achieved by employing a tin condensation 
catalyst having the formula 
EQU (R).sub.2 Sn(Q).sub.2 ( 1) 
where Q is a monovalent radical selected from a triazole having the 
formula, 
##STR1## 
and an imidazole having the formula, 
##STR2## 
where R is selected from C.sub.(1-18) monovalent hydrocarbon radicals and 
substituted C.sub.(1-18) monovalent hydrocarbon radicals, R.sup.1, R.sup.2 
and R.sup.3 are selected from the same or different monovalent radicals 
selected from hydrogen and R radicals and X is divalent C.sub.(1-50) 
organic radical selected from hydrocarbon radicals and substituted 
hydrocarbon radicals. 
Statement of the Invention 
There is provided by the present invention a room temperature vulcanizable 
organopolysiloxane composition comprising by weight, 
(A) 100 parts of alkoxy terminated organopolysiloxane, 
(B) 0 to 10 parts of polyalkoxy silane, 
(C) 0 to 5 parts of amine accelerator, 
(D) an effective amount of a tin condensation catalyst of formula (1), and 
(E) 0 to 5 parts of a ligand forming material selected from a triazole 
having the formula, 
##STR3## 
and an imidazole having the formula, 
##STR4## 
where X, R.sup.2 and R.sup.3 are as previously defined. 
Also included within the scope of the present invention is a method for 
making room temperature vulcanizable organopolysiloxane compositions which 
comprises mixing together under substantially anhydrous conditions, the 
following ingredients by weight: 
(i) 100 parts of alkoxy terminated organopolysiloxane, 
(ii) 0 to parts of polyalkoxy silane, 
(iii) 0 to 5 parts of amine accelerator, 
(iv) an effective amount of a tin condensation catalyst of formula (1), and 
(v) 0 to 5 parts of ligand forming material as previously defined. 
In a further aspect of the present invention, there is provided a method 
for making a room temperature vulcanizable organopolysiloxane compositions 
which comprises, 
(1) agitating under substantially anhydrous conditions, 
(a) 100 parts of a silanol terminated polydiorganosiloxane, 
(b) 0.1 to 10 parts of alkoxy silane, 
(c) 0 to 5 parts of amine accelerator, 
(d) 0 to 700 parts of filler, and 
(e) 0 to 5 parts of ligand forming material as previously defined, 
(2) allowing the mixture of (1) to equilibrate to produce polyalkoxy 
terminated polydiorganosiloxane, and 
(3) further agitating the mixture of (2) under substantially anhydrous 
conditions with an effective amount of a tin condensation catalyst of 
formula (1). 
Some of the silanol terminated polydiorganosiloxanes which can be used to 
make the stable, substantially acid-free, moisture curable 
organopolysiloxane compositions of the present invention have the formula, 
##STR5## 
where R.sup.3 is a C.sub.(1-13) monovalent substituted or unsubstituted 
hydrocarbon radical, which is preferably methyl, or a mixture of a major 
amount of methyl and a minor amount of phenyl, cyanoethyl, 
trifluoropropyl, vinyl, hydrogen and mixtures thereof, and n is an integer 
having a value of from about 5 to about 5000. 
Polyalkoxy terminated organopolysiloxane which can be used to make the RTV 
compositions of the present invention has the formula, 
##STR6## 
where R.sup.3 and n are as previously defined, R.sup.4 is a monovalent 
radical selected from C.sub.(1-13) hydrocarbon radicals and substituted 
C.sub.(1-13) hydrocarbon radicals, R.sup.5 is a C.sub.(1-8) aliphatic 
organic radical selected from alkyl radicals, alkylether radicals, 
alkylester radicals, alkylketone radicals and alkylcyano or a C.sub.(7-13) 
aralkyl radical and a is a whole number equal to 0 or 1. 
The RTV compositions of the present invention can contain a cross-linking 
polyalkoxysilane having the formula, 
##STR7## 
where R.sup.4, R.sup.5 and a are as previously defined. 
Radicals included within R of formula (1) are, for example, C.sub.(6-13) 
aryl radicals and halogenated aryl radicals, such s phenyl, tolyl, 
chlorophenyl, naphthyl; C.sub.(1-18) aliphatic, cycloaliphatic radicals, 
and halogenated derivatives thereof, for example, cyclohexyl, cyclobutyl; 
alkyl and alkenyl radicals, such as methyl, ethyl, propyl, chloropropyl, 
butyl, pentyl, hexyl, heptyl, octyl, vinyl, allyl, and trifluoropropyl. 
Radicals included within R.sup.1 and R.sup.2 are, for example, hydrogen, 
methyl, ethyl, propyl and mixtures thereof; R.sup.3 and R.sup.4 are 
monovalent radicals selected from R radicals; radicals included within 
R.sup.5 are, for example, C.sub.(1-8) alkyl radicals, for example, methyl, 
ethyl, propyl, butyl, pentyl; C.sub.(7-13) aralkyl radicals, for example, 
benzyl, phenylethyl, alkylether radicals such as 2-methoxyethyl, 
alkylester radicals, for example, 2-acetoxyethyl, alkylketone radicals, 
for example 1-butan-3-onyl, alkylcyano radicals, for example, 
2-cyanoethyl. 
Some of the tin condensation catalysts included within formula (1) are, for 
example, 
di-N-butyltinbis(benzotriazole) 
di-N-butyltinbis(tolyltriazole) 
di-N-octyltinbis(benzotriazole) 
di-N-hexyltinbis(2-methylimidazole) 
Included within the cross-linking polyalkoxysilanes of formula (4) are, for 
example, methyltrimethoxysilane; methyltriethoxysilane; 
ethyltrimethoxysilane; tetraethoxysilane; vinyltrimethoxysilane; etc. 
Among the amine curing accelerators which can be used in the practice of 
the present invention are silyl substituted guanidines having the formula, 
EQU (Z).sub.g Si(OR.sup.5).sub.4-g, (5) 
where R.sup.5 is as previously defined, Z is a guanidine radical of the 
formula, 
##STR8## 
where R.sup.8 is divalent C.sub.(2-8) alkylene radical, R.sup.6 and 
R.sup.7 are selected from hydrogen and C.sub.(1-8) alkyl radicals and g is 
an integer equal to 1 to 3 inclusive. In addition, alkyl substituted 
guanidines having the formula, 
##STR9## 
where R.sup.6 and R.sup.7 are as previously defined and R.sup.9 is a 
C.sub.(1-8) alkyl radical, also can be employed. Some of the silyl 
substituted guanidines included within formula (5) are shown by Takago 
U.S. Pat. Nos. 4,180,642 and 4,248,993. 
In addition to the above substituted guanidines, there can be used various 
amines, for example, di-n-hexylamine, dicyclohexylamine, di-n-octylamine, 
hexamethoxymethylmelamine, and silylated amines, for example, 
.lambda.-aminopropyltrimethoxysilane and 
methyldimethoxy-d-n-hexylaminosilane acts as both a cross-linker and 
curing accelerator. The primary amines, secondary amines, silylated 
secondary amines are preferred and secondary amines, and silylated 
secondary amines are particularly preferred. Silylated secondary amine 
such as alkyldialkoxy-n-dialkylaminosilanes and guanidines such as 
alkyldialkoxyalkylguanidylsilanes which are useful as cure accelerators. 
In addition to the above-described amine accelerators, there is also 
included in the practice of the present invention the use of certain 
sterically hindered diamines which have been found to effect rapid cures 
of the RTV compositions of the present invention when utilized in 
effective amounts as previously defined. These nitrogen bases include, for 
example, di-t-butylethylene diamine (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 
preferable have a viscosity in the range of from about 100 to about 
400,000 centipoise and more preferable from about 1000 to about 250,000 
centipoise when measured at about 25.degree. C. These silanol-terminated 
fluids can be made by treating a higher molecular weight 
organopolysiloxane, such as dimethylpolysiloxane with water in the 
presence of a mineral acid, or base catalyst, to tailor the viscosity of 
the polymer to the desired range. Methods for making such higher molecular 
weight organopolysiloxane utilized in the production of silanol-terminated 
polydiorganosiloxane of formula (2) also are well known. For example, 
hydrolysis of a diorganohalosilane such as dimethyldichlorosilane, 
diphenyldichlorosilane, methylvinyldichlorosilane, or mixtures thereof, 
can provide for the production of low molecular weight hydrolyzate. 
Equilibration thereafter can provide for higher molecular weight 
organopolysiloxane. Equilibration of cyclopolysiloxane such as 
octamethylcyclotetrasiloxane, octaphenylcyclotetrasiloxane, or mixtures 
thereof, will also provide for higher molecular weight polymers. 
Preferable, such polymers are decatalyzed of equilibration catalyst by 
standard procedures prior to use, such as shown by Boot U.S. Pat. No. 
3,153,007, assigned to the same assignee as the present invention. 
Silanol-terminated organopolysiloxanes having viscosities below 1200 
centipoises can be made by treating organopolysiloxanes consisting 
essentially of chemically combined diorganosiloxy units with steam under 
pressure. Other methods that can be employed to make silanol-terminated 
polydiorganosiloxanes are more particularly described in U.S. Pat. No. 
2,607,792 to Warrick and U.K. Pat. No. 835,790. 
In order to facilitate the cure of the RTV compositions of the present 
invention, the tin condensation catalyst of formula (1) can be utilized at 
from 0.1 to 10 part of tin catalyst per 100 parts of the silanol 
terminated or alkoxy terminated polydiorganosiloxane and preferably from 
0.1 to 1.0 part per 100 parts of the polydiorganosiloxane. 
Various fillers, pigments, adhesion promoters, etc., can be incorporated in 
the silanol or alkoxy-terminated organopolysiloxane, such as, for example, 
titanium dioxide, zirconium silicate, silica aerogel, iron oxide, 
diactomaceous earth, fumed silica, carbon black, precipitated silica, 
glass fibers, polyvinyl chloride, ground quartz, calcium carbonate, 
.beta.-cyanoethyltrimethoxysilane, etc. The amounts of filler used can 
obviously be varied within 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 700 parts of 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, such as ground quartz, polyvinylchloride, or mixtures thereof, 
preferably having an average particle size in the range of from about 1 to 
10 microns. 
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 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 silica filler, per 
100 parts of silanol-terminated organopolysiloxane is utilized. 
In the practice of the invention, the room temperature vulcanizable 
compositions can be made by agitating, for example, stirring under 
moisture-free conditions, a mixture of materials which can consist of the 
tin condensation catalyst and the alkoxy terminated polydiorganosiloxane. 
Optionally, cross-linking polyalkoxysilane and amine accelerator can be 
used. 
In instances where silanol terminated polydiorganosiloxane is used in place 
of the alkoxy terminated polydiorganosiloxane it is preferred that 
blending of the filler, for example, fume silica, the silanol terminated 
polydiorganosiloxane and the cross-linking polyalkoxysilane be performed 
and in the absence of the tin condensation catalyst. The tin condensation 
catalyst can be introduced advantageously after the resulting blend has 
been agitated for a period of about 24 hours at room temperature. 
As used hereinafter, the expressions "moisture free conditions" and 
"substantially anhydrous conditions", with reference to making the RTV 
compositions of the present invention, mean 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 0.degree. C. to about 180.degree. C. 
depending upon the degree of blending, the type and amount of filler. 
A preferred procedure for making the RTV compositions of the present 
invention is to agitate under substantially anhydrous conditions a mixture 
of the silanol terminated polydiorganosiloxane or alkoxy terminated 
polydiorganosiloxane, filler and an effective amount of the tin 
condensation catalyst. There can be added to the mixture, the 
cross-linking silane or mixture thereof along with other ingredients, for 
example, the curing accelerator and pigments.

In order that those skilled in the art will be better able to practice the 
invention, the following example is given by way of illustration and not 
by way of limitation. All parts are by weight. 
EXAMPLE 1 
A mixture of 2 grams of dibutyltindimethoxide and 1.62 grams of 
benzotriazole in 20 ml. of methylenechloride was stirred for 15 minutes. 
Reaction volatiles were then removed in vacuo from the resulting solution 
and 3.05 grams of a white non-crystalline solid was obtained. Based on 
method of preparation and NMR spectra of the solid, there was obtained a 
96% yield of dibutyltinbis(benzotriazole). The same procedure was repeated 
except that tolyltriazole was used in place of benzotriazole. The 
resulting dibutyltinbis(tolyltriazole) complex was recovered and 
characterized in an identical manner. 
A base RTV methylpolysiloxane composition was prepared by thoroughly mixing 
under substantially anhydrous conditions, 100 parts of a 
methyldimethoxysiloxy terminated polydimethylsiloxane having a viscosity 
of 30,000 centipoises at 25.degree. C., 0.3 parts of dibutyl amine, 30 
parts of a trimethylsiloxy terminated polydimethylsiloxane having a 
viscosity of 100 centipoises at 25.degree. C., 17 parts of fumed silica 
and 1.4 parts of .beta.-cyanoethyltrimethoxysilane. 
RTV formulations were prepared by mixing under substantially anhydrous 
conditions 100 parts of the above base polymer mixture, 0.3 part of 
dibutyltinbis(benzotriazole), 0.13 part of benzotriazole and 0.67 part of 
methyltrimethoxysilane. A second RTV mixture was prepared by mixing under 
substantially anhydrous conditions 100 parts of the base polymer mixture, 
0.33 part of dibutyltinbis(tolyltriazole), 0.13 part tolyltriazole and 
0.67 part of methyltrimethoxysilane. A third RTV formulation was prepared 
using the same base formulation and 0.35 part of 
dibutyltin(diethylmalonate) in place of the mixture 
dibutyltinbis(benzotriazole) and benzotriazole. 
The above RTV formulations were mixed for 10 minutes in a Semco mixer. Upon 
exposure to atmospheric moisture, the formulations cured to a tack-free 
state in 20 minutes. No change in cure time was observed after heating the 
uncured formulations for 24 hours at 100.degree. C. and then allowing them 
to cure upon exposure to atmospheric moisture. In addition, approximately 
5 grams of the RTV compositions were applied to the surface of a 
2".times.2" section of clean copper metal. The respective RTV compositions 
were then allowed to cure for 7 days. The samples were then exposed to a 
95% relative humidity environment at 20.degree. F. for 28 days. A portion 
of the RTV was removed from the copper and the copper surface was then 
visually examined for corrosion. The copper surfaces in contact with the 
RTV's using the dibutyltinbistriazoles were found to be free of corrosion. 
However, the copper surface in contact with the RTV containing the 
dibutyltin(diethylmalonate) showed evidence of corrosion. Contact 
corrosion to copper also was found when commercial RTV's were evaluated. 
Evidence of corrosion is shown by the presence of a blue film on the 
copper and the presence of blue on the RTV surface in contact with the 
copper. 
Although the above example is directed to a few of the very many variable 
which can be utilized in the practice of the methods of the presence 
invention and the RTV compositions made by such methods, it should be 
understood that the present invention is directed to the use of a much 
broader variety of tin condensation ctalysts as shown by formula (1) as 
well as the use of organopolysiloxane polymer, alkoxysilane and other 
ingredients in the RTV composition as shown in the description preceding 
this example.