Note: Descriptions are shown in the official language in which they were submitted.
~ -~ 60SI 965
PREPAR~TION OF HIG~ STRENGTH, HIGH APPLICATION
RATE SILICONE RTV RUBBER
~ _ __ _ _
This invention relates to titanium catalyzed alkoxy
end-stopped polydiorganosiloxane RTY rubbers. 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.
Background of the Invention
Early types of one-component RTV ruhber compositions are,
for instance, disclosed in Ceyzeriat, U.S. Patent No.
3,133,891, and Bruner, U.S. Patent No. 3,035,016. Such patents
disclose the use of acyloxy funotional silanes as cross-linking
agents for hydroxy end-stopped organopolysiloxane 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
polydiorganosiloxane 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
~ ,;'', ' ~ ' ~'
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alkoxy end-capped polydiorganosiloxane. The titanium
condensation catalyst will promote ~he end-capping reaction as
well as promote the ure reaction 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 catalyst. 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 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 RTV rubber in two mixing steps
but without preparing the alkoxy end-stopped
polydiorganosiloxane beforehand.
It is another obJect of the present invention to produce
titanium catalyzed one-component RTY rubbers having improved
properties including improved application properties and
improved properties of the vulcanized rubber such as hardness~
tensile strength, and elongation.
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Description of the Invention
Briefly, according to the present invention, there is
provided a method for production of titanium catalyzed alkoxy
end-stopped RTY rubbers having superior properties, which
method comprises:
(a) reacting a mixture comprising:
(i) a silanol terminated polydiorganosiloxane,
(ii) an end-capping agent having the formula:
RmSi(OR )4-m
~ 10 wherein m has a value of from O to 2, and R and
Rl are hydrocarbyl, halohydrocarbyl, and cyano
lower alkyl radicals having up to about l2 carbon
atoms, and
(iii) an end-capping catalyst sel~cted from Lewis acids,
Lowry-Bronsted acids and mixtures of 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 invention can be represented by
the formula~ R2
(l) HQ SiO - H
~ R3 n
. . . . . .. ., ~ . ,. . .. ~ , . . . . ., . . . . . .. . . ~ .. .. . . . .. . . .
.
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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 lS,000 or more.
The silanol chain-stopped polydiorganosiloxanes are well
known in the art and include compositions 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,
diphenylsiloxane units and methylphenylsiloxane units or, for
example, copolymers of dimethylsiloxane units,
methylphenylsiloxane units and methylvinylsiloxane units.
Preferably, at least 50X 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, ben2yl, tolyl, xylyl
and ethylphenyl; halogen-substituted mononuclear aryl9 such as
2,6-di-chlorophenyl, 4-bromophenyl, 2,5-di-fluorophenyl,
2,4,6-trichlorophenyl~ and 2,5-dibromophenyl; alkyl such as
methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl,
isobutyl, tertbutyl, amyl, hexyl, heptyl, octyl; alkenyl such
as vinyl, allyl, n-butenyl, n-pentenyl-2, n-heptenyl; alkynyl
such as proparayl, 2-butynyl; haloalkyl such as chlorome~byl,
iodomethyl, bromomethyl, fluoromethyl, chloroethyl, iodoethyl,
bromoethyl, fluoroethyl, trichloromethyl, di-iodoethyl,
tribromoethyl, trifluoromethyl, dichloroethyl, chloro-n-propyl,
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bromo-n-propyl, iodoisopropyl, bromo-n-butyl, bromo-tert-butyl,
1,3,3-trichlorobutyl~ 1,3,3-tribromobutyl, chloropentyl,
bromopentyl, 2,3-dichloropentyl, 3,3-dibromopent~l~
chlorohexyl, bromohexyl, 1,4-dichlorhexyl, 1,3-dibromohexyl,
bromooctyl; haloalkenyl such as chlorovinyl bromovinyl,
chloroallyl, bromoallyl, 3-chloro-n-butenyl-1,
3,chloro-n-pentenyl-1, 3-fluoro-n-heptenyl-1,
1,3,3-trichloro-n-hepteny1-5, 1,3,5-tri-chloro-n-octenyl-6,
2,3,3-trichloromethylpentenyl-4; haloalkynyl such as
chloropropargyl, bromopropargyl; cycloalkyl, cycloalkenyl and
alkyl and halogen substituted cycloalkyl and cycloalkenyl such
_ as cyclopentyl~ cyclohexyl,cycloheptyl, cyclooctyl,
6-methylcyclohexyl,3,~-dichlorocyclohexyl,
2,6-dibromocycloheptyl,l-cyclopentyl,
3-methyl-1-cyclopentenyl,3,4-dimethyl-1-cyclopentenyl,
5-methyl-5-cyclopentenyl,3,4-dichloro-5-cyclopentenyl,
5-(tert-butyl)l-cyclopentenyl,l-cyclohexenyl,
3-methyl-1-cyclohexenyl, 3,4-dimethyl-1-cyclohexenyl; and cyano
lower alkyl such as cyanomethyl, beta-cyanoethyl,
gzmma-cyanopropyl, delta-cyanobutyl, and gamma-cyanoisobutyl.
A mixture of various silanol chain-stopped
polydiorganosiloxanes also may be employed. The silanol
chain-stopped materials useful in the RTV compositions of this
jnvention have been described as polydiorganosiloxanes but such
materials can also contain minor amounts, e.g., up to about 20%
of monoorganosiloxane units such as monoalkylsiloxane units,
e.g., monomethyls;loxane units and monophenylsiloxane units.
The technology involved in incorporating monoalkylsilQ~ane
un~ts into RTV compositions is disclosed in U.S. Pat. 3,332,205
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~3f Beers ( 19 6 8 ) . . The silano 1 chain- s topped . materi al s
may also contain triorganosiloxane units, such as
trialkylsiloxane units, e.g., trimethylsiloxane units,
- tributylsiloxane units and triphenylsiloxane units. The
s i 1 anol chain-stopped materials may also contain
t-alkoxysiloxane units, e.g., t-butoxysiloxane units,
t-pentoxysiloxane units, and t-amyloxysiloxane 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 polymer having a ratio of t-alkoxysiloxane units to silanol
of 0.05 to 0.9 and preferably 0.2 to 0.8
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~5. Pat. 3,438,930,
Beers, which issued April 15, 1969, and is assigned to the
General Electric Company .
The siianol chain stopped polydiorganosiloxanes employed in
the practice of the present invention 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:
2 5 RmSi(ORl)4 m
wherein m has a value of from O to 2, preferably 1, and R and
,
,
fl rp~ r~
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Rl 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 suitable end-capping
agents include:
CH35i(OCH3)3
_ CH3Si(OCH2CH3)3
(CH3)2Si(OCH3)2
Si(OCH3)4
CH3cH2cH2cH2cH2cH2cH2cH2si(ocH3)3
CF3CH2Si(OCH3)3
NCCH2CH2Si(OCH3)3
(CH3)Si(OCH2CH2CH2CH3)3
The amount of the end-capping agent admixed with the
silanol chain-stopped polydiorganosiloxane 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 grou~s in
.
,
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JWH:mz/60SI-g~$/02~3p
the silanol chain-stopped polydiorganosiloxanes. 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
using more than 10 msles of the silane per mole of the
polydiorganosiloxane 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, Lowry-Bronsted acids, and 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 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 jn 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 anhyride, propionic anhydride, butyric
anhydride, valeric anhydride, etc.; the acyloxy silanes, such
,
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as, methyltriacetoxy silane, ethyltriacetoxy silane, phenyltri-
acetoxy silane, dimethyldiacetoxy silane, methyltributyroxy
silane, 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 include, for
example, AlC13, BaS04, BC13, TiBr3.
Although the above acids may be used alone, it has been
found to be advantageous to employ an amine co-catalyst 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=NC3~6Si(OMe)3~ H2Nc3H6si(oEt)3~
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 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
Silicone Products Division, General Electric Company,
Waterford, N.Y., C-204 Test Method should be at least 0.~-and
should not exceed 15.
, ~ .. ,.. ,, . ..... , .... . . "..... . .. ~ . .. .. .
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Briefly, the C-204 Test Method consists of taking a 250 ml.
flask and adding 100 ml. of isopropanol and 0~25 ml. of phenol-
phthalein 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
(solution in methanol) to the pink end point. The volume of
KOH in methanol used in the titratium is recorded as Yt. The
total acid number is then calculated from the following formula:
Vt(NKOH) (56.1)
Total Acid Number = Sample wt.
-
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 polydi-
organosiloxane polymer. Uhere ~mines are utilized with the
above acids as co-catalysts, they are used in a concentration
of anywhere from about 0.1 to about O.S parts by weight per 100
parts by weight of the silanol end-stopped polydiorganosiloxane
polymer. Further teaching concerning these end-capping
catalysts is unnecessary. Their use is well known ~n the art.
End-capping catalysts as taught above, are described in U.S.
Patent No. 4,51~,932~
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, for example, 1,3-propanedioxytitanium bis(ethyl-
acetoacetate), 1,3-propanedioxytitanium bis (acetylacetonate),
and diisopropuxytitanium bis (acetylacetonate). Additional
.
~, s ~ 5 r ~ ~ ~,
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titanium chelates are disclosed in Unit~d States PatE~nt---
Numbers 3,689,~54 and . which issued
~ . The titanates may be selected from
titanium naphthenate, tetrabutyl titanate, tetra-2-ethylhexyl-
titanate, tetraphenyl titanate, tetraoctadecyltitanate, ethyl-
triethanolaminetitanate, etc. In addition, betadicarbonylti-
tanium 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 O.OOl to about 2.0 parts by
weight per lO0 parts by weight of the silanol terminated
polydiorganosiloxane.
Various fillers and pigments can be incorporated in the
silanol or alkoxy-terminated organopolysiloxane, such as for
example, titanium dioxide, zirconium silicate, silica aerogel,
iron oxide, diatomacèous 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 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 lO0
parts of organopolysiloxane can be employed. In such
applications, the filler can consist of a major amount of
.
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extending materials, such as ground ~uartz, polyvinylchloride,
or mixtures thereof, preferably having an average particle size
in the range Df from about 1 to 10 microns. Preferably,
however, from about ~ to about 30~ parts by weight of filler
5 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 application for which the organopolysiloxane
10 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
15 organopolysiloxane is utilized. -
The preferred filler, fumed or precipitated silica, may be
treated or untreated. Treated silica fillers include fillers
treated with hydrolyzate, i.e. treated with a mixture of cyclic
and hydroxy end-stopped silanol fluids; fillers treated with
20 silane fluids9 such as trimethyl silyl; and fillers treated
with a silazane, i.e. hexamethyldisilazane~ Treatment of the
filler affects the wet out of the filler~ compatibility of the
filler, and other properties, such as hydroxy group content of
the filler.
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.
. . ~ . ... .... .. _... ., , .. .. .. . , . . . ...... , . . ...... , . .. ~ . . . .
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Fillers treated with, silane fluids, for example, trimethyl-
silane or with silazanes, such as hexamethyldisilazane, will
have relatively low hydroxy group contents It is preferred
that low-hydroxy content fillers be employed herein.
Hydroxy or methanol scavengers may be used in the instant
application to extend shelf life. These scavengers are
disclosed in Uni ted States Patent Numbers 4, 39 5, 5 2 6
and 4,417,042.
As used hereinafter, the expressions "moisture free
conditions" and "substantially anhydrous conditions", with
reference to making the RTY 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 0C to about l80~C, 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 sllanol terminated 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:
Rmsi(oR )4-m
wherein m has a value of from l to 2, and R and
.. . .. .. . . ~ . . , ~ ., ... . . , . ., ~ . . .. .. . . . . . .. .
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Rl 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-Br~nsted acids and mixtures of the
acids with amine cG-catalysts;
(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
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 exceèd about 180C. Where a sufficiently fast
end-capping reaction cannot be achieved below 180C, then
end-capping catalyst or end-capping agent should be varied in
order to speed the reaction.
Following the reaction step, the titanium condensation
catalyst should be admixed. Where a viscosity risç is
experienced following such admixture, then jnsufficient
end-capping has been performed. This may be a result of ~ ot
enough end-capping agent being employed or insufficient
reaction time or conditions to complete end-capping.
. _ , _ . . .... . . .. . . .. . . . . . . . . . . . ........ .. . . . . ... . ... . .
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There can also be added other ingredients, including cure
accelerators, pigmentsp flame retardants, fungicides;
plasticizers and the like. These ~TV 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 application 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 fbr the
purpose of limitation. All parts in the Examples are by weight.
Examples
.
Example 1
A base composition was prepared by mixing 100 parts of
silanol end-stopped polysiloxane having a viscosity of about
12,000 cps at 25C and a phenyl on chain content of about 5
mole X, 25 parts of a trimethylsilyl treated fumed silica
filler and 1.0 parts of titanium dioxide as a pigment.
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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(ethylacetoacetate).
5 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 75F and
50% R.H. excepting of course application rate which was
-10 measured at 90 p.s.i. through a 1/8" opening. Results of this
testing are listed in Table I.
Comparative Examp_e 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
15 and 2.0 parts of diisopropoxytitanium bis(ethylacetoacetate).
The catalyzation was characterized by a large but temporary
viscosity rise making the mixing of the ingredients difficult.
The resultant RTY rubbers were applied and cured with the
physical properties being taken as in Comparative Example A.
20 Results of this teiting are listed in Table I.
Table I
Comparative Example A B
Shore A 25 22
. Tensile Strength (p.s.i.) 357 B63
Elongation (X) 375 390
Application Rate (g/min.) 162 126
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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 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
_ 10 of a solution containing 3.0 parts methyltrimethoxysilane and
1.5 parts of diisopropoxytitanium bis(ethylacetoacetate). The
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.
Examp_e 3
To 100 parts of the modified base composition of Example 2
was added 5.0 parts of a solution of 3.0 parts
methyltrimethoxysilane and 2.0 parts of diisoproxytitanium
bis(ethylacetoacetate). Again, the catalyzation went smoothly
with no viscosity rise. This RTV rubber was tested as
described in Comparative Example A, and resluts are listed in
Table II.
.
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Table II
_ _
Example 2 3
Shore A 36 36
Tensile Strength (p.s.i.) 655 685
Elongation (%) 286 276
_ Application Rate (g/min.) 252 252
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.
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.
.. . . . ... .
.
