 |
Description  |
|
|
BACKGROUND OF THE INVENTION
This invention relates to organosilicon compositions and more particularly
to polyolefin filled-organopolysiloxane compositions.
Heat vulcanizable and room temperature vulcanizable polyorganosiloxane
compositions are well known. Generally, these compositions, whether they
be of the one-package or two-package type, are composed of an
organopolysiloxane base material, crosslinking agents, such as alkyl
silicates, alkyltriacyloxysilanes, etc., and curing or crosslinking
catalysts, such as organic peroxides, metals salts of carboxylic acids,
etc.
It is also well known to incorporate various additives into these
organopolysiloxane compositions to improve their properties. Included
among these additives are inorganic filler materials, such as silica
aerogel, diatomaceous earth, calcium carbonate, iron oxide, etc. The use
of filler materials of this nature, however, has not met with complete
satisfaction, since often the improvement in the properties of the
organopolysiloxane composition realized by their presence may be
outweighed by the high cost and formulation problems which they present.
This is particularly the case when employing certain silica fillers.
Other methods to improve the properties of organopolysiloxane compositions
have also been used in the past. For example, U.S. Pat. No. 2,965,593 to
Dietz discloses that a water-repellant polyorganosiloxane composition is
provided by dispersing a polyorganosiloxane in a vinyl monomer base and
polymerizing the mixture. The resultant material is disclosed therein as a
mixture of the polyorganosiloxane in a thermoplastic high polymer matrix.
Further attempts to improve the properties of the organopolysiloxanes are
disclosed, for example, in U.S. Pat. Nos. 3,631,087, 3,627,836, 3,580,971,
3,441,537, 3,436,252, 3,070,573, 2,959,569 and 2,958,707. These patents
disclose the use of grafted organopolysiloxanes, i.e., organopolysiloxanes
which are chemically grafted with polymeric side chains. As discussed, for
example, in U.S. Pat. No. 3,627,836, while graft-modified polymers have
some desirable properties, they are inadequate in others, and accordingly
have not met with total satisfaction.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide novel improved
organopolysiloxane compositions.
Another object of this invention is to provide improved organopolysiloxane
compositions which, without necessarily utilizing conventional inorganic
filler materials, provide equal or improved physical properties to
products formed therefrom when compared with conventionally filled
organopolysiloxane compositions.
Still another object of this invention is to provide improved
organopolysiloxane compositions which are essentially free of grafted
organopolysiloxane.
These and other objects are accomplished herein by providing
organopolysiloxane compositions which are characterized as
polyolefin-filled-organopolysiloxane stable dispersions comprised of two
phases:
(i) a continuous phase comprising an essentially ungrafted
organopolysiloxane fluid and intimately dispersed therein,
(ii) a discontinuous phase comprising finely divided solid particles of an
ungrafted polymer prepared from an organic monomer having aliphatic
unsaturation or mixture of such monomers polymerized in the presence of
said orgaopolysiloxane fluid.
DETAILED DESCRIPTION OF THE INVENTION
The polyolefin-filled organopolysiloxane dispersions of the present
invention are prepared by the in-situ polymerization of an organic monomer
or monomers in an organopolysiloxane fluid material in the presence of a
free-radical initiator. Surprisingly, the resulting composition is a
stable dispersion wherein a discontinuous phase of discrete finely divided
solid particles of a homopolymer or copolymer of the starting organic
monomer or monomers are intimately dispersed in a continuous matrix phase
of essentially ungrafted and essentially unaltered organopolysiloxane
fluid.
The finely divided solid particles of homopolymer or copolymer which are
formed in-situ are of a small enough diameter so that they act as
reinforcing or semi-reinforcing fillers or, in some cases, extending
fillers for the organopolysiloxane matrix material, resulting in an
improved stronger silicone elastomer. Generally, the major portion of
these solid particles of homopolymer or copolymer have an average diameter
of less than about 10-15 microns, with some having a diameter of less than
one micron.
While the polyolefin-filled organopolysiloxane dispersions of the present
invention may be prepared by simply heating the preformed mixture of
components, namely, the organic monomer or monomers, the
organopolysiloxane fluid material and the free-radical initiator, other
procedures are also contemplated herein. For example, the organic monomer
or monomers may be added gradually in increments to a preformed heated
mixture of the organopolysiloxane composition and free-radical initiator.
Another procedure contemplated herein is gradual incremental addition of a
preformed mixture or solution of the organic monomer or monomers and
free-radical initiator to the heated organopolysiloxane material.
Regardless of which of the above procedures is employed, the organic
monomer or monomers are polymerized or copolymerized in-situ, i.e., in the
presence of the organopolysiloxane fluid material, and surprisingly,
essentially no grafting, condensation, polymerization or other alteration
occurs with regard to the organopolysiloxane material.
In all of the hereinabove described processes for preparing the present
dispersions, the polymerization catalyst, i.e., the free-radical
initiator, may be any of the well-known or conventional free-radical
initiators. Among these are included, for example, organic peroxides, such
as benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dialkyl peroxides, like
di-tert-butyl peroxide and dicumyl peroxide; hydroperoxide, and decylene
hydroperoxide; cyclic peroxides, such as ascaridole and
1,5-dimethylhexane-1,5-peroxide; peresters, such as tert-butylperbenzoate,
tert-butyl-peroxyisopropyl carbonate, tert-butylperoctoate and
tert-butylperacetate. The well-known are compounds are also useful herein
as free-radical initiators. These include, for example, those azo
compounds containing tertiary carbon atoms (that is, carbon atoms having
no hydrogen attached thereto) attached to each nitrogen atom of the azo
linkage. The remaining valences of the tertiary carbon are satisfied by
nitrile radicals, carboxyalkyl radicals, cycloalkylene radicals, alkyl
radicals and radicals of the formula YOOC in which Y is an alkyl radical.
Specific examples of such azo compounds are:
MeEt(NC)CN.dbd.NC(CN)MeEt
MeEt(NC)CN.dbd.(CN)MeEt
Et.sub.2 (NC)CN.dbd.NC(CN)Et.sub.2
Pr.sub.2 (NC)CN.dbd.NC(CN)Pr.sub.2
AmMe(NC)CN.dbd.NC(CN)MeAm
(HOOCCH.sub.2 CH.sub.2)Me(NC)CN.dbd.NC(CN)Me(CH.sub.2 CH.sub.2 COOH)
(meOOC)Me.sub.2 CN.dbd.NCMe.sub.2 (COOMe)
(EtOOC)Me.sub.2 CN.dbd.NCMe.sub.2 (COOEt).
The symbols Me, Et, Pr and Am represent methyl, ethyl, propyl, and amyl,
respectively. Preferred free-radical initiators within the scope of the
present invention are benzoyl peroxide, tert-butyl peroctoate, and
azobis(isobutyronitrile).
The temperature of the in-situ polymerization reaction of the present
invention may vary. Generally, however, the temperature should be
sufficient to form free radicals at a rate such as to effect the
polymerization of the organic monomer or monomers in a reasonable length
of time, but insufficient to result in grafting of the organopolysiloxane
with polymeric side chains. Specifically, these temperatures are from
about 35.degree. C. to about 135.degree. C. and preferably from about
45.degree. C. to about 125.degree. C.
Because of the free radical nature of the polymerization process, it is
important that the reaction be maintained in an oxygen-free environment,
such as by sweeping the reaction vessel with nitrogen. Furthermore,
solvents for dissolving the free-radical initiator and/or organic monomer
or monomers such as acetonitrile, chain transfer agents or other
conventionally employed polymerization additives may be present during the
reaction to modify the reaction and/or to modify the product.
Moreover, the in-situ polymerization process of the present invention can
be carried out at subatmospheric, atmospheric or superatmospheric
pressure. Preferably, atmospheric pressures are employed. Depending upon
the particular conditions employed, the polymerization reaction is
generally completed in about 30 minutes to about 10 hours. If it is
desired to perform the in-situ polymerization reaction of the present
invention by incremently adding the organic monomer or monomers to the
reaction vessel containing the oranopolysiloxane, the portion of
increments used and time used may vary. Generally, however, incremental
addition is completed in about 10 minutes to about 5 hours.
The organic monomers which are useful to prepare the polyolefin-filled
organopolysiloxane dispersions of the present invention may be any
olefinic monomer or monomers which have aliphatic unsaturation and which
are polymerizable. Examples of suitable monofunctional olefinic compounds
are low molecular weight straight chain hydrocarbons, such as ethylene,
propylene, butylene and the like; halogenated straight chain hydrocarbons
like vinyl halides, such as vinyl chloride; vinyl esters, such as vinyl
acetate; vinyl containing aromatics, such as styrene, ring substituted
styrenes; other aromatics such as vinylpyridine and vinylnaphthalene;
unsaturated acids, such as acrylic acid and derivatives thereof including
salts, esters, such as ethyl acrylate, butyl acrylate, methylmethacrylate,
amides and unsaturated nitriles, such as acrylonitrile; N-vinyl compounds,
such as N-vinylcarbazole, N-vinylpyrrolidone, and N-vinyl caprolactam.
Moreover, disubstituted ethylenes of the type CH.sub.2 .dbd.CX.sub.2 may be
used, including vinylidene fluoride, vinylidene chloride, vinylidene
cyanide, methacrylic acid, and compounds derived therefrom such as salts,
esters and amides as well as methacrolein, methacrylonitrile, and the
like.
Disubstituted ethylenes of the type CHX.dbd.CHX, such as vinylene carbonate
and various monomers which polymerize best in the presence of other
monomers, e.g., maleic anhydride, esters of maleic acid and fumaric acids,
stilbene, indene and coumarone are also useful herein.
Examples of suitable polyfunctional olefinic monomers, i.e., having at
least two olefinic linkages, are esters, such as allyl methacrylate, allyl
acrylate, diallyl adipate, methallyl acrylate, methallyl methacrylate,
vinyl acrylate, vinyl methacrylate; hydrocarbons such as divinylbenzene
and vinyl cyclohexene; polyol esters of acrylic and methacrylic acid,
e.g., ethylene dimethacrylate, tetramethylene diacrylate, and
pentaerythritol tetramethacrylate; and conjugated diolefins such as
1,3-butadiene, isoprene and chloroprene.
Any of these olefinic monomers mentioned hereinabove may be used singly or
in combination in the practice of the present invention.
Any of the well-known organopolysiloxane fluid compositions, which are
substantially free of aliphatic unsaturation and silanic hydrogen, may be
used in the practice of the present invention. The term "substantially
free," as employed herein, means that the material may contain traces of
the undesirable ingredients which are normally present in commercially
available organopolysiloxane materials. For example, organopolysiloxane
resins and polymers often contain traces of silicon-bonded hydrogen as an
impurity. These trace amounts do not interfere with the reaction of the
present invention.
Included among the organopolysiloxane fluid materials useful in the
practice of this invention are compounds of the type which have structural
units of the formula
R.sub.a R'.sub.b SiX.sub.c O.sub.(4-a-b-c)/2
such as disclosed in U.S. Pat. No. 2,958,707, incorporated herein by
reference. In these compounds a has a value from 1 to 3, b has a value
from 0 to 3, c has a value from 0 to 3, and the sum of a + b + c has a
value not greater than 3. R is an alkyl radical, such as methyl, ethyl,
propyl, butyl, isobutyl, etc., or aryl, such as phenyl, naphthyl, tolyl
and the like, and R' is any monovalent hydrocarbon or halogenated
hydrocarbon radical attached to the silicon by a silicon carbon bond,
which is free of aliphatic unsaturation, such as alkyl or haloalkyl,
including methyl, ethyl, propyl, isopropyl, butyl, chlorobutyl,
trifluoropropyl, hexyl, octadecyl; cycloalkyl, or halogenated cycloalkyl,
such as cyclohexyl, cyclopentyl, and chlorocyclohexyl; aryl radicals and
halogenated aryl radicals such as phenyl, tolyl, chlorophenyl, xylyl,
bromophenyl; aralkyl radicals such as benzyl, phenethyl and the like;
organofunctional radicals such as carboxyphenyl, gamma-hydroxypropyl,
gamma-aminopropyl and any other hydrocarbon radicals having aldehyde,
ketone, nitrile, nitro, carboxy, amide, hydrosulfide or other functional
groups attached thereto. Preferably R and R' are methyl.
X is an hydrolyzable or condensable group such as hydroxyl, acyloxy, amino,
sulfide, halogen or OR'", wherein R'" is a monovalent hydrocarbon radical
free of aliphatic unsaturation, such as methyl, ethyl, octadecyl,
cyclohexyl, phenyl, tolyl, benzyl, etc.
Among the organopolysiloxane materials useful in the practice of the
present invention, as defined by the formula R.sub.a R'.sub.b SiN.sub.c
O.sub.(4-a-b-c)/2, the most preferred are the linear fluid
diorganopolysiloxanes having terminal silicon-bonded hydroxyl groups and
being substantially free of aliphatic unsaturation and silanic hydrogen
such as those disclosed in U.S. Pat. No. 2,843,555 to Berridge, U.S. Pat.
No. 3,065,194 to Nitzsche et al, U.S. Pat. No. 3,127,363 to Nitzsche et
al, U.S. Pat. No. 2,857,356 to Goodwin and U.S. Pat. No. 2,814,601 to
Currie et all, all of which are incorporated herein by reference.
For the purposes of this invention, these linear fluid
diorganopolysiloxanes having terminal silicon-bonded hydroxyl groups have
a viscosity generally in the range of from about 100 to 10,000,000,
preferably from about 500 to 3,000,000 centipoise at 25.degree. C. Most
particularly preferred among these are the silanol terminated dimethyl
polysiloxanes.
Preparation of these diorganopolysiloxanes may be carried out by any of the
well-known procedures. In particular and for example, these polysiloxanes
can be produced by following a procedure involving hydrolysis of one or
more hydrocarbon substituted dichlorosilanes in which the substituents
consist of saturated hydrocarbon groups to produce a crude hydrolyzate
containing a mixture of linear and cyclic polysiloxanes. The crude
hydrolyzate is then treated with a suitable catalyst such as KOM so that
it can be depolymerized to form a mixture of low boiling, low molecular
weight cyclic polymers and undesirable materials such as the
monofunctional and trifunctional organosiloxanes. The resulting
composition is fractionally distiled and there is obtained a pure product
containing the low boiling, low molecular weight cyclic polymers free of
any significant amount of monofunctional and trifunctional groups.
In order to depolymerize the crude hydrolyzate there is added to said
hydrolyzate a strong base such as KOH and the mixture is heated at a
temperature in the range of 150.degree. C. to 175.degree. C. under an
absolute pressure of 100 mm of Hg. to produce and remove by evaporation a
product consisting of low molecular weight cyclic polysiloxanes
comprising, for example, about 85 percent of the tetramer and 15 percent
of the mixed trimer and pentamer. Among the cyclic polymers that may be so
produced are hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane and
decamethylcyclopentasiloxane.
Various pure cyclic polysiloxanes are mixed in the desired proportions to
obtain the desired mixture. Then the mixture of the cyclic polysiloxanes
is subjected to an equilibration procedure to obtain a linear
diorganopolysiloxane. The equilibration is preferably carried out at
temperatures of about 125.degree. C. to 150.degree. C. in the presence of
a small amount of rearrangement catalyst such as potassium hydroxide,
tetrabutyl phosphonium hydroxide, etc. The amount of catalyst used will
depend on the extent of the polymerization desired. Generally, 40-50 ppm
(parts per million) of the catalyst is sufficient for the polymerization
to produce diorganopolysiloxane polymers of a viscosity of 5 .times.
10.sup.5 to 1.0 .times. 10.sup.7 centipoise measured at 25.degree. C.
There is also present in the reaction mixture 15-150 ppm (parts per
million) of water based on the cyclic polymer so as to supply the hydroxy
groups which function as chain-stoppers for the linear
diorganopolysiloxane material that is formed. After the equilibration
reaction has proceeded for two hours there is reached an equilibration
point wherein the mixture contains about 85% linear polymers and the
amount of linear polymers being formed from the cyclic polymers is equal
to the cyclic polymers being formed from the linear polymers.
When this equilibration point has been reached there is added to the
mixture a sufficient amount of an acid donor that will neutralize the KOH
catalyst so as to stabilize the polymerization product. Preferably, enough
acetic acid is added to the reaction mixture to react with and neutralize
the KOH. The cyclicdiorganosiloxanes in the reaction mixture are then
distilled off to leave the polydiorganosiloxane polymer which is useful in
the present invention. The resulting linear diorganopolysiloxanes are
chain-stopped primarily with hydroxy groups and have a viscosity of 5
.times. 10.sup.5 to 1.0 .times. 10.sup.7 centipoise at 25.degree. C.
Then high molecular weight diorganopolysiloxanes having a viscosity of 5
.times. 10.sup.5 centipoise at 25.degree. C. and above can be treated with
water and various catalysts to arrive at low molecular weight
diorganopolysiloxanes having a viscosity of 100 to 90,000 centipoise at
25.degree. C. This may be accomplished by blowing steam across the surface
of the high molecular weight product or through the polymer for a
sufficient length of time to obtain the low molecular weight component
having the desired silanol content. Thus, it may be desirable to obtain
the low molecular weight diorganopolysiloxane from a portion of the high
molecular weight diorganopolysiloxanes by the above water treatment which
is well known to those skilled in the art so as to reduce the number of
diorganosiloxy units from above 5,260 to a value in the neighborhood of
300. The use of steam in this fashion will cause a decrease in the
viscosity of the polymer while at the same time the formed linear
polysiloxane will have terminal silicon-bonded hydroxy groups.
Alternatively, the low molecular weight diorganopolysiloxanes can be
produced from the high molecular weight diorganopolysiloxane by adding
water to them and heating the resulting composition at elevated
temperatures of 150.degree. C. to 170.degree. C. so as to break up the
long chain polymers into smaller chains. The amount of water used will
vary depending upon such factors as the molecular weight of the polymer
being treated, the time and the temperature at which the mixture of high
molecular weight diorganopolysiloxanes are heated and the desired
viscosity. These conditions may readily be determined. For example, a high
molecular weight diorganopolysiloxane having a viscosity of 2,000,000
centipoise at 25.degree. C. may be heated to 150.degree. C. with 0.5
percent by weight of water and a catalyst for two hours to arrive at a low
molecular weight diorganopolysiloxane having a viscosity of 2,000
centipoise. Preferably, the low molecular weight organopolysiloxane is
produced so that it has a viscosity of 1,000 to 90,000 centipoise at
25.degree. C.
The amounts of the materials employed in the processes and dispersions of
the present invention can vary with wide limits. Thus, for example, the
amount of free-radical initiator used in the in-situ polymerization is not
critical and in general is from 0.1% to 10% by weight of the total
admixture of organic monomer or monomers and organopolysiloxane compound.
The amounts of organic monomer or monomers used herein can also vary and
are generally within the range of from about 5% to about 70% by weight of
the total composition and preferably from about 10% to about 60% by weight
of the total dispersion. The amount of organopolysiloxane material
employed herein is generally from about 30% to about 95% by weight of the
total composition and preferably from about 40% to 90% by weight of the
total dispersion.
The polyolefin-filled organopolysiloxane dispersions of the present
invention are useful in the manufacture of silicone elastomers, resins and
fluids, which are useful for electrical insulation, solvent-resistant
hoses, protective coatings, caulking compositions and other uses for which
organosilicon compositions of this type are known, such as in coating of
paper, textiles and other substrates.
The polyolefin-filled organopolysiloxane dispersions of the present
invention are particularly well suited for application in heat and
room-temperature vulcanizable compositions.
Thus, heat vulcanizable compositions employing polyolefin-filled
poly(diorganosiloxane) gums are within the scope of the present invention.
Typical gums may be prepared by condensing the fluid organopolysiloxane of
the dispersion with any of the well-known condensing agents, e.g., ferric
chloride hexahydrate, phenyl phosphoryl chloride, alkaline condensing
agents, such as potassium hydroxide, sodium hydroxide, and the like. These
heat vulcanizable polyolefin-filled poly(diorganosiloxane) gums are in
turn cured by the application of heat and preferably in the presence of a
heat vulcanization catalyst such as an organic peroxide or organic
per-esters like benzoyl peroxide, t-butyl peracetate, dicumyl peroxide,
di-t-butyl peroxide, 2,4,-dichlorobenzoyl peroxide and the like.
Moreover, the polyolefin-filled organopolysiloxane dispersions of the
present invention wherein the organopolysiloxane either contains terminal
silicon bonded condensable groups, such as hydroxyl groups, or may be
readily modified to contain such condensable groups, are particularly
useful in one and two component room temperature vulcanizable compositions
and these too are within the scope of the present invention.
For example, a one-package toom temperature vulcanizable system within the
scope of the present invention which is vulcanizable upon exposure to
moisture is comprised of (1) an essentially water-free polyolefin-filled
organopolysiloxane dispersion, as prepared by the present invention,
wherein the organopolysiloxane component is an essentially ungrafted
linear fluid diorganopolysiloxane substantially free of aliphatic
unsaturation and silanic hydrogen, containing terminal silicon bonded
hydroxyl groups and having a viscosity of 100 to 10,000,000, preferably
500 to 3,000,000 centipoise at 25.degree. C.; (2) an essentially
water-free crosslinking agent selected from the group consisting of (A) an
organotriacyloxysilane having the formula R.sup.3 Si(OY).sub.3 wherein
R.sup.3 is selected from the group consisting of a monovalent hydrocarbon
radical, a halogenated monovalent hydrocarbon radical, an
alkoxysubstituted monovalent hydrocarbon radical, and a cyanoalkyl
radical, and Y is selected from the group consisting of a saturated
aliphatic monoacyl radical of a carboxylic acid and (B) a monomeric
organosilicate having the formula
(R.sup.3 O).sub.3 SiR.sup.4
wherein R.sup.3 is as defined above and R.sup.4 is selected from the group
consisting of alkyl, haloalkyl, arylhaloalkyl, alkenyl, cycloalkyl,
cycloalkenyl, cyanoalkyl, alkoxy, and aryloxy; and (C) liquid partial
hydrolysis products of the aforementioned organosilicates. These
one-component systems, upon exposure to moisture, are cured to elastomers
from a few minutes to several hours or days. The curing may be accelerated
by the presence therein of a crosslinking catalyst which will be described
in more detail hereinbelow with reference to two-component
room-temperature vulcanizable compositions.
A preferred two-component, room-temperature vulcanizable composition within
the scope of the present invention is comprised of, for example:
(1) a polyolefin-filled poly(organosiloxane) dispersion as prepared by this
invention, wherein the poly(organosiloxane) component is an essentially
ungrafted linear fluid diorganopolysiloxane having terminal silicon-bonded
hydroxyl groups, being substantially free of aliphatic unsaturation and
silanic hydrogen and having a viscosity of 100 to 10,000,000, preferably
about 500 to 3,000,000 centipoise at 25.degree. C.;
(2) a crosslinking agent selected from the group consisting of (A) a
monomeric organosilicate corresponding to the formula (R.sup.3 O).sub.3
SiR.sup.4 wherein R.sup.3 and R.sup.4 are as defined above, and (B) a
partial liquid hydrolysis product of the aforementioned organosilicate;
and
(3) a crosslinking catalyst selected from the group consisting of a metal
soap, a metal chelate, metal salts of mono- and dicarboxylic acids, metal
salts of a thiol, metal salts of a dithiolcarbamic acid, metal oxides,
organo-metal compounds, amines, amine salts, imines, organic acids,
organic bases and mixtures thereof. The metals which are conventionally
part of the aforementioned metal containing crosslinking agents include
lead, tin, zirconium, zinc, antimony, iron, cadmium, barium, calcium,
titanium, bismuth and manganese. Thus, these crosslinking catalysts
employed in the one and two-package room temperature vulcanizable
compositions of the present invention may be any of those conventionally
employed for that purpose.
Particularly useful crosslinking catalysts which are within the scope of
the present invention are the titanium chelate catalysts and the other
catalyst systems disclosed in U.S. Pat. Nos. 3,708,467 and 3,689,454 to
Smith et al, and U.S. Pat. No. 3,341,486 to Murphy, which are incorporated
herein by reference.
These room temperature vulcanizable compositions of the present invention
are formulated in the usual manner for preparing siloxane elastomers of
this type. In the case of a one-component system, all the ingredients may
be mixed prior to use and stored in the absence of moisture. In the case
of a two-component system, the crosslinking agent and/or catalyst are
stored in a separate package from the polyolefin-filled-organopolysiloxane
dispersion. In other words, the polyolefin-filled-organopolysiloxane
dispersion, crosslinking agent, and, if desired additional additives, may
be compounded in one package and the crosslinking curing catalyst added
thereto just prior to use. In another method, the
polyolefin-filled-organopolysiloxane dispersion, crosslinking curing
catalyst and, if desired, other additives, may be formulated in one
package, and the crosslinking agent added thereto just prior to use.
The amounts of crosslinking agent and crosslinking catalysts employed in
the vulcanizable compositions of the present invention are not critical
and are generally the same amount that is conventionally used in room
temperature vulcanizable compositions of this nature. In particular, the
crosslinking agents are generally present in amounts varying from about
0.1 to about 15% by weight based on the weight of the organopolysiloxane,
while the crosslinking catalysts are generally present in amounts from
about 0.1 to 5% by weight based on the weight of the organopolysiloxane.
As a result of the presence of the polyolefin-filled organopolysiloxane
dispersions of the present invention, these heat and room-temperature
vulcanizable compositions are convertible to cured rubbers having physical
strength properties, such as tensile, tear, elongation, etc., which are
equivalent to or better than those employing more expensive and difficult
to handle conventional inorganic reinforcing fillers. Moreover, the
present heat and room-temperature vulcanizable compositions provide
different and improved densities and surface appearances in comparison to
compositions employing conventional fillers.
If desired, however, the incorporation of conventional fillers into the
polyolefin-filled organopolysiloxane dispersions and vulcanizable
compositions of this invention is also contemplated herein. These include,
for example, fumed silica, high surface area precipitated silicas, silica
aerogels, as well as coarser silicas, such as diatomaceous earth, crushed
quartz and the like; other fillers include carbon black, metallic oxides,
titanium oxide, ferric oxide, zinc oxide; organic fillers having a
thixotropic effect, such as lithium stearate and other additives such as
pigments, antioxidants, process aids, plasticizers, viscosity control
agents, and ultraviolet absorbers also may be employed.
In order that those skilled in the art may better understand how the
present invention may be practiced, the following examples are given by
way of illustration and not by way of limitation.
EXAMPLE 1
This example illustrates the preparation of a polyvinyl
acetate-silanol-terminated poly(dimethylsiloxane) dispersion, containing
40% by weight solid particles of polyvinyl acetate, according to this
invention.
180 grams of linear fluid silicon-bonded hydroxy-terminated
poly(dimethylsiloxane) having a viscosity of 2,660 centipoise at
25.degree. C. is placed in a one-liter flask equipped with a stirrer,
reflux condenser, addition funnel, nitrogen inlet, and oil bath. A
solution of 0.45 grams of azobis(isobutyronitrile) and 12 grams of
acetonitrile in 120 grams of vinyl acetate monomer is put in the addition
funnel. A nitrogen gas flow is allowed to enter the reaction flask and is
maintained throughout the reaction. The oil bath is heated to about
95.degree.-100.degree. C. The vinyl acetate solution is added dropwise
into the reaction flask containing the silicon-bonded hydroxy-terminated
poly(dimethylsiloxane) over a period of about 100 minutes. The reaction
mixture becomes white and thicker during the addition. After addition is
completed, heat is then applied to the hot mixture for one-half hour to
remove unreacted and low boiling materials. 294 grams (98% yield) of a
white, viscous field dispersion is obtained.
EXAMPLE 2
This example illustrates the preparation of another polyvinyl
acetate-silanol-terminated poly(dimethylsiloxane) dispersion, containing
40% by weight solid particles of polyvinyl acetate, according to this
invention.
Using the equipment and reaction conditions of Example 1, a solution of 0.9
grams azobis(isobutyronitrile) in 240 grams of vinyl acetate is added to
360 grams of silicon-bonded hydroxy-terminated-poly(dimethylsiloxane)
having a viscosity of 2,660 centipoise at 25.degree. C. A white, viscous
fluid (589 grams, 98% yield) having a Brookfield viscosity of 11,900
centipoise at 25.degree. C. is obtained. This white viscous fluid
dispersion shows no signs of phase separation after one month.
EXAMPLE 3
This example illustrates the preparation of a polyvinyl
acetate-silanol-terminated poly(dimethylsiloxane) dispersion, containing
60% by weight solid particles of polyvinyl acetate, according to this
invention.
Using smaller equipment, but similar reaction conditions as in Example 1, a
solution of 0.2 grams of azobis(isobutyronitrile) and 6 grams of
acetonitrile in 60 grams vinyl acetate monomer is added to 50 grams of
silicon-bonded hydroxy-terminated poly(dimethylsiloxane) having a
viscosity of 2,660 centipoise at 25.degree. C. A very viscous fluid (96%
yield) is obtained.
EXAMPLE 4
This example illustrates the preparation of a polyvinyl
acetate-silanol-terminated poly(dimethylsiloxane) dispersion, containing
12% solid particles of polyvinyl adetate and also containing an additional
filler, namely, calcium carbonate, according to this invention.
Using the equipment of Example 1, but without the use of the addition
funnel, 211 grams of silicon-bonded hydroxy-terminated
poly(dimethylsiloxane) having a viscosity of 2,660 centipoise at
25.degree. C., 29 grams of vinyl acetate, 0.3 grams
azobis-(isobutyronitrile) and 72 grams of calcium carbonate filler powder
is stirred and heated in 70.degree.-80.degree. oil bath for five hours. A
viscous, flowable dispersion is obtained.
EXAMPLE 5
This example illustrates the preparation of a polyvinyl
acetate-silanol-terminated poly(dimethylsiloxane) dispersion, containing
40% solid particles of polyvinyl acetate, according to this invention.
Using the equipment and conditions of Example 1, a solution of 0.9 grams
azobis(isobutyronitrile) in 2.7 grams of acetonitrile is added to 369
grams of silicon-bonded hydroxy-terminated poly(dimethylsiloxane) having a
viscosity of 17,600 centipoise at 25.degree. C. and preheated to
79.degree. C. Then 240 grams of vinyl acetate monomer is added over a
period of about 3 hours. A very viscous, white fluid dispersion (573 grams
having a viscosity of 73,000 centipoise at 25.degree. C.) is obtained.
EXAMPLE 6
This example illustrates the preparation of a polyvinyl
acetate-silanol-terminated-poly(dimethylsiloxane) dispersion, containing
40% solid particles of polyvinyl acetate, according to this invention.
Using the equipment and reaction conditions of | | |
