Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
The present invention relates to
fluorosilicone elastomers. More particularly, it
relates to curable fluorosilicone copolymer compositions
winch provide superior physical properties and are
suitable for the manufacture of nigh quality electrical
connectors.
BACKGROUND OF TUBE INVENTION
Platinum catalyzed fluorosilicone/
organosilicone blends and low molecular weight silicone
copolymer compositions such as those described in US.
4,122,247 Evans), US. 4,157,337 (Evans), and US.
4,317,899 (Blue stein et at) have found use as low energy
molding compounds in the aerospace industry for making
high quality electrical connectors and other molded
silicone rubber inserts. Such compounds, which cure via
nydrosilation addition reaction in the presence of
platinum, display the advantages of rapid processing,
fast deep section curing, low rejection rate, and good
mechanical properties. However, in spite of these
advantages, the addition cure systems are susceptible lo-
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koalas. poisoning, e.g., from small amounts of
compounds such as carborl monoxide or sulfur or amine,
which tie up platinum; the ratio of silicon hydra tee to
olefin functionality for optimal properties must fall
within a narrow range; a critical range of inhibitor to
catalyst is necessary to provide rapid cure along with
adequate working shelf life; and the systems are also
susceptible Jo organic contaminants which can adversely
affect the thermal stability of the cured parts.
In order to secure better thermal aging
properties, many electrical connector manufacturers have
tested peroxide-cured fluorosilicone systems made by
blending heat-curable fluorosilicone compounds with
polydimethylsiloxane gums. Because of the nature of tune
curing reaction, addition cure compositions do not fully
cure initially, and further curing in response to hush
temperatures encountered by the compositions in use ma
lead to shrinkage of the molded component, making it
23 unsuitable for continued used. Greater dimensional
stability is provided by peroxide-curable systems which
fully cure and so do not shrink in use. It has been
observed that the peroxide-curable blends, however,
require a higher overall average fluorine content to
provide sufficient solvent resistance. Consequently,
their has been a need for a peroxide-curable
fluorosilicone copolymer gum which exhibits the
desirable process ability of the addition cure systems
while providing better thermal aging and good resistance
to solvent swell.
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SUMMARY OF TOE INVENTION
Accordingly, it is an object of the present
invention to provide a fluorosilicone copolymer gum that
is curable in the presence of provide catalysts.
It is a further object of the present
invention to provide a peroxide-curable fl~orosilicone
copolymer composition useful for the manufacture of high
quality electrical connectors.
It is a further object of the present
invention to provide a curable fluorosilicone composition
which, wren compounded and cured exhibits superior
physical properties, including low solvent swell and
goon thermal aging.
These and other objects are accomplished
herein by a peroxide-curaole sullenly- or
alkenyl-endstopped diorganopolysiloxane coplanar oil or
gum comprising units of the formulae RR'SiO and R" So,
wherein R is fluoroalkyl of from 3 to 8 carbon atoms, R'
is alkyd of from l to 8 carbon atoms or phenol, and each
R" is independently, alkyd of from l to & carbon atoms,
alkenyl of from 2 to 8 cordon atoms, or phenol, and
wherein sufficient RR'SiO units are present to provide
at least about q5 mole percent fluorosilicone content
and sufficient R" So units containing alkenyl
substituents are present to provide up to about 0.5
30 weight percent vinyl content (as I I along the
polysiloxane chain.
Also contemplated is a curable fluorosilicon~
composition comDrisins PA) a silanol-endstopped or
35 alkenyl-endstopped diorganpolysiloxane copolvmer oil Ox
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gum comprising units of the foretell Rio and R" So,
wherein R is fluoroalkyl of from 3 to 8 carbon atoms, R'
is alkyd of from 1 to 8 carbon atoms or phenol, and each
R" is, independently, alkyd of from 1 to 8 carbon atoms,
alkenyl of from 2 to 8 carbon atoms, or phenol, and
wherein sufficient RR'SiO units are present to provide
at least about 45 mole percent fluorosilicone content
and sufficient R" So units containing alkenyl
substituents are present to provide up to about 0.5
weight percent vinyl content (as OH I along the
polysiloxane chain; and By a peroxide catalyst.
Processes for preparing the copolymers and
compositions of the present invention are Allah
contemplated.
DETAILED DESCRIPTION OF THE INVENTION
The fluorosilicone copolymers of the present
invention may be compounded and cured in conventional
ways in the presence of a peroxide catalyst to provide
dimensionally stable cured parts having exceptional
resistance to solvent swell, superior thermal aging
properties and mechanical properties which exceed strict
industrial aerospace specifications.
The R, I' and R" substi~uents defined above
are representative of monovalent hydrocarbon radicals
and halogenated monovalent hydrocarbon radicals that are
well known as attachments to silicon atoms. Preferably,
the fluoroalkyl substituent, R, contains 3 or more
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carbon atoms and 1 or more fluorine atoms, the radicals
including, for example, 3-fluoropropyl, 3,3-difluorcpro-
Pyle 3,3,3-trifluoropropyl, and the like up to 8 carbon
atoms. More preferably, the R radical is a substituted
alkyd group such as, -OH OH R , wherein R is perfluoro-
alkyd containing from 1 to 6 carbon atoms, such as
perfluorome,hyl, perfluoroethyl, perfluorohexyl, and the
like. Most preferably, the R radical is trifler-
propel. R' it preferably methyl; R" is preferably
methyl or vinyl, with at least 1 vinyl group being
present along the copolymer chain but no more vinyl
groups being present than would provide about 0.5 weight
percent vinyl, as vinyl, the rest of the R" groups being
methyl.
The copolymers of the present invention may
De synthesized from diorganodihalogensilanes of the
formulae RR'SiX and R"2SiX2, wherein OR and R" are as
previously defined, and X is halogen, such a chlorine or
bromide (preferably chlorine), as described in the
aforementioned Evans patents, United States Patent
Number 4,122,247 and United States Patent No. 4,157,337.
The diorganodihalogensilanes, at a purity of at least
99~ by weight, are added to water at room temperature,
e.g., 20-25C to provide from about 2 to 10 moles of
water per mole of dior~anodihalogensilane. After the
diorganodihaIogensilanes have been added to the water it
will contain about 20% by weight of Hal.
Optionally, hydrolysis may be carried out in
the presence of a water-immiscible solvent such as, for
example, Tulane, zillion, Bunsen, and the like. The
use of a solvent facilitates the separation of the
hydrolyzate from the aqueous acid solution. Preferably,
a water-immiscible organic solvent is added to tune waxer
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prior to the addition of the diorganodihalogensilanes.
The diorganodihalogensilanes, preferably at greater than
99% purity, are added to the water (or water/water-
immiscible solvent mixture) over a one-half to two hour
period, with agitation. Where a solvent is used, the
hydrolyzate is seen to dissolve in the solvent phase,
and this is then separated from the water phase. The
hydrolyzate is finally neutralized with a mild base,
such as sodium bicarbonate, to a pi of about 7 to 8.
Alternatively, the hydrolyzate may be washed repeatedly
with water until a neutral pi is reached.
The hydrolyzate product is a mixture
containing mostly cyclic polysiloxanes of from 3 to 10
silicon atoms and low molecular weight linear sullenly-
end stopped diorganopolysiloxanes. This raw hydrolyzateis useful as a treating agent for fumed silica fillers
as described in US. Patent No. 4,529,774, issued
July 16, 1985 to Evans et at.
Heating the hydrolyzate at elevated temperatures
removes any solvent by overhead distillation. The
hydrolyzate is then cracked by a procedure comprising
adding from 0.1 to 5% by weight (preferably 0.1 to 2%
by weight) of a cracking catalyst, such as potassium
hydroxide or sesame hydroxide, then heating.
The cracking procedure is typically
carried out at temperatures between 150 and 200C,
and preferably heating is carried out under a vacuum of
1 to 100 millimeters of mercury for a period of from
about 1 to 5 hours. A mixture of cyclic polysiloxanes,
specifically cyclic trimmers, tetramers and pen tamers
viol be continually distilled overhead. The cracking
procedure is utilized to maximize the formation of the
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cyclic triter from the broad range in the headrest.
This permits conversion of about us% by weight of the
hyarolyzate to cyclic trisiloxanes, cyclic tetrasiloxanes,
and cyclic pentasiloxanes, predominantly cyclic
trisiloxanes. The cyclic polysiloxanes may be separated
by known distillation procedures from the other cyclic.
It is preferred that there be less than 10
parts per million of water in the composition of cyclic
selections to be utilized with the catalyst to make
polymers. Removal of all but traces of water may be
accomplished by heating to 100C or above, with a
nitrogen purge. This effectively reduces the water
content of the cyclic selection composition to less than
10 parts per million. It has been found that if there
is substantially more than this amount of water present,
the desired copolymer gum will not be formed in
commercially attractive yields.
To prepare the copolymers of the invention,
cyclic polysiloxanes of the formulae (RR'SiO) and
I So) , where OR and R" are as previously define
an x an y are integers from 3 to 6, are placed in a
reaction vessel. An alkali metal hydroxide polymerization
catalyst (preferably KIWI) in amounts to provide about 5
to 500 parts per million of the catalyst are added to
the cyclic mixture. Polymerization is then carried out
by heating at a temperature of from 20 to 160C for a
period of from hour to 20 hours, during which time
equilibrium is reached. At this point, 70 to 88% by
weight or more of the cyclic selections will have been
converted to the desired diorganopolysiloxane copolymer
oil or gum. The reaction mixture can be cooled, e.g.,
to under 25C, and the catalyst neutralized.
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A number of conventional neutralizing agents
may be used, however neutralizing agents preferrer for
the purposes herein include phosphoric acid,
tris(2-chloroethyl)phosphite, and sill phosphate (See,
e.g., United states Patent Number 4,177,200
(Rosen et at), and also orgànohalosilanes or
halosilanes of the formulae R Six , wherein R is
alkyd, cycloalkyl, vinyl or phenol, the alkyd and
cycloalkyl groups having from 1 to 8 carbon atoms; b is
an integer from 1 to 3; and wherein X is bromide or
chlorine. These Solon compounds include, e.g.,
trimethylchlorosilane.
After neutralization, the reaction mixture
is heated at elated temperatures, e.g., 150 to 200C
under a vacuum of 1 to 100 millimeters of mercury to
strip the unrequited cyclic polysiloxanes to viola the
diorganopolysiloxane copolymer oil or gull.
In accordance to known procedures, the
viscosity of the copolymer may be controlled by adding a
chain stopper to the composition of co-monomers and
polymerization catalyst. Such chain stoppers can be, for
example, disiloxanes or low molecular weight
diorganopolysiloxanes having, preferably, either sullenly
( Sigh) or vinyl terminal units. the organ substituents
in such chain stoppers are typically alkyd of from l to 8
carbon atoms, vinyl, phenol, cycloalkyl of from 4 to 8
carbon atoms, or haloalkyl, especially fluoroalkyl, such
30 as trifluoropropyl. Preferred5c6hainstoppers for the
purposes herein include, HERR R Sue, where R is
alkyd and R it 3,3,3-trifluoropropyl, and
VitMe)2-~MeR So) Messiah) Si-(Me)2Vi,6wherein x=23,
yo-yo, Vi is vinyl, Me is methyl, and R is 3,3,3-
35 trifluoropropyl.
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Generally, the amount of chain stopper
introduced to the equilibration mixture will be selected
to produce the desired final molecular weight or
viscosity of the diorganopolysiloxane copolymer oil or
gum. sigher amounts of chain stopper will produce lower
molecular weights, and smaller amounts will produce
higher molecule weights. For the purposes of the
present invention, it is generally preferred to use
sufficient chain stopper to provide a copolymer having a
Williams Plasticity I minute reading) of about 160 to
220, or to provide a copolymer having a molecular weight
of f rum about 400,000 to 600,000.
As mentioned previously the fluorosilicone
copolymers should have a fluorosilicone content of at
least 45 mole percent in order to exhibit a desired high
resistance to solvent swell. Preferably the
fluorosilicone content of the copolymer will fall in Tao
range of 45-65 mole percent, more preferably 50-60 mole
20 percent, and most preferably 52-57 mole percent.
Obviously, where solvent swell is not a concern of the
practitioner, the fluorosilicone content of tube
copoiymer may be varied within wider limit.
In addition, sufficient, alkenyl-functional
starting materials should be adder to the polymerization
mixture to provide up to about 0.5 weight percent vinyl
content (as I SHEA-), preferably 0.02-0.2 weight
percent, and most preferably 0.03-0.1 weight percent
30 vinyl along the copolymer chain. This on-chain alkenyl
functionality allows for a Tighter" cure and thereby
contributes to the higher dimensional stability of the
cured compositions according to this invention.
however, higher levels of.on-chain-unsaturation than
35 about 0.5 weight percent (as I act-) leads to too tight
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a cure, adversely affecting other mechanical properties
of the cured compositions, e.g., compression set.
The aforementioned copolymers are curable in
the presence of peroxide catalysts which initiate a
cross linking hydrogen abstraction reaction between the
pendant alkenyl groups and pendant saturated hydrocarbon
groups or possibly a halogen abstraction reaction, in
the case of pendant fluorocarbon groups) of the copolymer
chains. This type of free-radical initiated abstraction
is promoted by small amounts, such as about 0.01~ by
weight of the more active organic peroxide inflators.
Greater amounts, such as up to about 5.0% by weight or
more of the initiator may be used, but amounts in excess
of about 1.5~ by weight may promote coupling reactions
which undesirably increase the viscosity of the reaction
mixture.
The most suitable peroxide initiators are
compounds of the formula, POOH or AYE, in which A is an
organic radical, especially those compounds in which at
least one peroxide oxygen is attached to a tertiary
carbon atom. Preferred such initiators include t-butyl
hydroperoxide, cumin hydroperoxiae, decline
hydroperoxide, di-t-butyl peroxide, dicumyl peroxide,
2,5-dimethyl-2,5-di-~t-butyl peroxy)hexane; also cyclic
peroxides such as ascaridole and l,5-dimethylhexane-1,5-
peroxide, per esters such as t-butyl-perbenzoate,
t-butylperoxyisopropylcarbonate and t-butyl peroctoate,
and kitten peroxides such as acetone peroxide and
cyclohexanone peroxide. The peroxides containing tertiary
alkoxy radicals have been found to be more efficient in
abstracting hydrogen or halogen) atoms from the pendant
organic groups linked to the silicon atoms, and the are
therefore preferred. 2,5-dimethyl-2,5-di-(t-butyl
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peroxy)hexane is most preferred and is available
commercially, e.g., at 45~ by weight on an inert filler
under the trade names, VAROX- (RUT. Vanderbilt Co., Inc.)
and LUPERCO- 101XL (Lucidly Division, Penlight Corp.).
The fluorosilicone copolymer oils or gums of
the present invention, when combined with the
aforementioned peroxide curing catalysts form curable
- compositions having superior physical properties, compared to prior addition cure silicone compositions. Obviously,
the copolymers can be formulated, e.g., by mixing with
reinforcing fillers, such as fumed silica or precipitated
silica; extending fillers, such as zinc oxide, titanium
oxide, diatomaceous earth, and the like; heat aging
additives, such as iron oxide; pigments or dyes; flame
retardants, such as platinum (as platinum or in
combination with other materials such as
triallylisocyanurate); adhesion promoters, such as
organic soullessness, which promote bonding between fillers
JO and the gum; and other additives, including anti-oxidants,
processing alas (e.g., sullenly fluids), compression set
resistance promoters (e.g., curium hydroxide),
supplementary curing agents (e.g., materials that provide
additional vinyl curing sites) such as trimethylol
propane trimethacrylate (Sartomer- 350; Sartomer Co.),
triallyl trimellitate tSipomer- TAT; Alcoholic, Inc.),
1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane,
1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiiloxane,
and the like.
A particularly useful filler for the
compositions described herein is a silica filler,
preferably fumed silica, that has been treated with the
raw hydrolyzate containing mixed cyclic polysiloxanes
and low molecular weight linear polysiloxanes described
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above. Such fillers are disclosed in the aforementioned
US. Patent Jo. 4,529,773.
The copolymer gums, mixed into a uniform
mass to which is added a peroxide curing agent,
may be cured at elevated temperatures, for example
from about 100 to 300C, or by exposure to radiation,
to produce fluorosilicone elastomers having tune
aforementioned superior physical properties,
including exceptional resistance to solvent swell
and excellent thermal aging characteristics.
In order that persons skilled in
this art may more readily practice the present
invention, the following examples are provided
by way of illustration, and not by way of limitation.
All measurements are by weight.
EXAMPLES 1-3
Sample 1
1716 parts by weight of methyl-3,3,3-tri-
fluoropropylsiloxane cyclic triter, 821 parts
by weight of dim ethyl selection cyclic tetramer,
and about 850 parts per million (Pam)
HO-(MeCH2CH2CF3SiO)3-H chain stopper were added to
a clean, dry polymerization vessel equipped with
stirrer, nitrogen inlet, and thermometer. The
25 mixture was heated to 150-160C and with a
nitrogen spurge, 115 parts by weight of dim ethyl-
selection cyclic tetramer were removed to
azeotropically dry (to fewer than 10 Pam of moisture)
the reaction mixture. While maintaining a positive
atmosphere of nitrogen, the vessel was allowed
to cool to 135-142C, at which point 3.1 parts
by weight of methyl vinyl selection cyclic triter
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(99~ purity) and sufficient potassium hydroxide* to
provide 25 Pam (as potassium hydroxide) were added. The
resulting exotherm cause a 16~C temperature rise within
about 30-35 seconds, which subsided over a 50-minute
period to the 135-145C range.
A gum began to form after 30 minutes, and
the polymerization was continued for 4-6 hours before
the catalyst was neutralized with silylphosphate. The
unrequited cyclic and other volatile were removed by
heating to 160C while agitating and maintaining a
strong Newton purge. When the level of volatile
reached about 0.8 (+0.5) weight percent in the copolymer
solution, the copolymer was discharged from the
neutralization vessel to give 1897 parts by weight
~81.6% yield) of a clear gum with a Williams Plasticity
(3 minute value) of 178, specific gravity of 1.1708 at
77F, and a refractive index of 1.3810 D . Nuclear
magnetic resonance (NOR) indicated a fluorosilicone
content of 56.9 mole percent and a dimethylsiloxy content
of 43.1 mole percent; Fourier Transform infrared assay
(FIR) indicated a vinyl content of 0.04 weight percent.
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*OWE is collided in 1,3,5,7-octamethylcyclotetrasiloxane
and dried over a AYE molecular solve.
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Sample 2
A fluorosilicone copolymer was prepared
according to the procedure described above for Sample 1.
A copolymer having a Williams Plasticity (3 minute
value) of 208 was obtained; the fluorosilicone content
it methyltrifluoropropyl-siloxy content) was 50.4
weight percent and the dimethylsiloxy content was 49.6
weight percent. The vinyl content was 0.03 weight
percent.
Sample 3
A vinyl-terminated fluorosilicone copolymer
was prepared according to the procedure described for
Sample 1. The product (82~ yield) was a clear gum
having a Williams Plasticity (3 minute value) of 193.
The copolymer vinyl content was 0.042 weight percent.
The three copolymers were compounded with a
number of conventional ingredients and an organic
peroxide curing agent as follows:
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FORMULATION
Ingredient Amounts Parts weight)
Copolymer 100
5 Fluorosilicone
hydrolyzate treated
fumed silica 2 40
Silica filler 6
Sullenly fluid processing aid 3 5
10 Bis-dimethylvinylsilazane 0 1
Iron octet 0 04
Curium hydroxide 0 40 -
Curing co-agent 1 0
Red pigment 5 1 7
15 Curing catalyst (1 5 parts/100 of
total compound)
... . . _ _ _ . _ _
Treated filler according to cop ending U S Application
Serial No 410,004, filed August 20, 1982
Cab-O-Sil- ~S-5(Cabot Crop )
Silanol-terminated polydimethylsiloxane ~PDMS) fluid
having the formulae, ~O-(Me2SiO) -
owe 4
Trimethylol propane trimethacrylate (Sartomer- 350;
Sartomer Co.)
Varox- (R T Vanderbilt, In 45% 2,5-dimethyl-2,5-
35 di(t-butvlperoxy)hexane on inert fillers
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A control composition was also prepared
according the same formulation using 100 parts of a
blend of fluorosilicone h4mopolymer with a polydimethyl-
selection gum. The three sample formulations and the
control were press cured 15 minutes at 350F and post
baked 4 yours at 400DF. The following properties were
observed in the cured elastomers:
Control
Physical Properties Sample 1 Sample 2 Sample 3 (blend)
Fluorosilicone
Content, m% 56.9 50.4 50 66
Shore A 56 56 57 51
Tensile, psi 1070 1035 1060 1050
15 Elongated, 420 410 430 450
Die B Tear, pi 102 100 117 107
Specs Go. 1.3595 1.3300 1.3350 1.345
Ashore . 35 - - -
Coup. Set, method B.
22 hrs./350F, % 17.5 13.6 12.7 25
Fuel Immersion, Fuel B 22 hrs./RT
Volume Swell 87.6 108 121.5 91.
teat Age, 7Q hrs.~43? F
Store Change 0 +1 +2
% Tensile Change -9.6% -7% -5%
% Elongation Change -14~2% -15~ -16%
Dimensional Change 1.1% 1.3~ 1.4%
It is seen that in identical formulations
the copolymers of the present invention show comparable
or superior physical properties, with a significantly
US lower fluorosilicone content, when compared to a
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conventional fluorosilicone/PDMS blend. Especially
promising results are obtained in the important areas of
compression set, solvent swell and dimensional stability
after heat aging. The samples prepared in accordance
with the invention, especially Sample 1, are believed to
meet the strictest current aerospace industry
specifications.
Modifications and variations in the present
invention are obviously possible in light of the foregoing
disclosure. It is understood, however, that incidental
changes made in the particular embodiments of the
invention as ascribed herein are within the full
intended scope of the appended claims.
