Disilanols containing in-chain perfluoroalkyl and aromatic groups and the process by which they were prepared are discussed. The disilanols, when reacted with a diaminosilane and cured, produce polymeric material resistant to hydrocarbon fuels and stable at elevated temperatures

Morris, D. E.

Patterson, W. J.

English

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United States Patent Office 3,763,204Patented Oct. 2, 1973
3,763,204
POLYMERIZABLE DISILANOLS HAVING IN-
CHAIN PERFLUOROALKYL GROUPS
William J. Patterson, Madison, and Donald E. Morris,
Huntsville, Ala., assignors to the United States of Amer-
ica as represented by the Administrator of the National
Aeronautics and Space Administration
No Drawing. Original application Dec. 22, 1970, Ser. No.
100,774, now Patent No. 3,666,718. Divided and this
application Jan. 20, 1972, Ser. No. 219,590
Int. Cl. C07f 7/08
U.S. Cl. 260—448.2 D 4 Claims
ABSTRACT OF THE DISCLOSURE
Disilanols having the formula
R R
HO—Si—Ar— (CF2),—At— Si—OH
R R
where R is a monovalent hydrocarbon radical, Ar is an
arylene group and x is from 2 to 8 and a process for
preparing the same are discussed The disilanols, when
reacted with a diaminosilane and cured, produce poly-
meric material resistant to hydrocarbon fuels and stable
at elevated temperatures.
10
sion of titanium alloys, probably because of elimination
of hydrogen and fluorine from adjacent carbon atoms in
the form of HF, and in their marginal thermal stability.
Polymenzable fluorine-containing compounds, tailored to
provide fuel resistance and thermal stability without hav-
ing a structure likely to release HF, are accordingly
needed.
SUMMARY OF THE INVENTION
The present invention is directed to disilanols having
the formula
15
20
25
ORIGIN OF THE INVENTION
The invention described herein was made by employees
of the United States Government and may be manufac-
tured and used by or for the Government for govern-
mental purposes without the payment of any royalties
thereon or therefor.
CROSS REFERENCE TO RELATED APPLICATIONS
The invention described herein is a division of applica-
tion Ser. No. 100,774, filed Dec 22, 1970, now U.S Pat.
No. 3,666,718.
BACKGROUND OF THE INVENTION
This invention relates to fluorine-containing organosili-
con compounds and more particularly to disilanols hav-
ing in-cham perfluoroalkyl groups.
The successful development of hypersonic aircraft and
certain types of reusable space shuttle vehicles will re-
quire the availability of improved high-temperature seal-
ant materials. 'Fuel-tank sealants for such applications
must be resistant to hydrocarbon fuels and stable under
thermo-oxidative environments at elevated temperatures
such as 450° F to 500" F. for extended periods In ad-
dition, candidate sealant materials must not contribute to
stress corrosion of the titanium alloys used for fuel tank
construction
Previously available sealant materials generally fail
to meet one or more of the above criteria. Sealants which
are resistant to hydrocarbon fuels have relatively low
thermal stability and materials which show better ther-
mal stability lack the required fuel resistance. Fuel re-
sistance consistent with some improvement in thermal
stability has been obtained in newly developed polymer
systems which incorporate fluorine atoms along the poly-
mer backbone or in pendant groups However, most of
the previous fluorine-containing sealant polymers have
been deficient in their tendency to promote stress corro-
30
35
45
50
55
60
65
R
HO-S1-.Ar— (CF2)
J-fc
,—Ar— Si—'OH
R R
where R is a monovalent hydrocarbon radical, Ar is an
arylene group and x is from 2 to 8 and to a process for
preparing the same by hydrolysis of the corresponding di-
hydride compound, which in turn is prepared by reaction
of a dibromoaryl perfluoroalkane with a monochloro
silane. Disdanols of the formula given above are useful
for preparation of polymers by reaction with diamino-
silanes. Upon curing with ethyl silicate the polymers are
converted to elastomenc material showing superior resist-
ance to hydrocarbon fuels, favorable thermal stability
and a minimum tendency to promote corrosion of titani-
um alloys This combination of properties is believed to
result from incorporation of perfluoroalkyl groups be-
tween arylene groups in the polymer backbone by means
of the novel disilanols
It is therefore an object of this invention to provide
polymenzable disilanols containing in-chain perfluoro-
alkyl groups and aromatic groups.
Another object is to provide a process for preparing
such disilanols
Still another object is to provide polymeric sealant ma-
terial that is resistant to hydrocarbon fuels and is stable
at elevated temperatures.
Other objects and advantages of the invention will be
apparent from the following detailed description and the
appended claims.
DESCRIPTION OF THE PREFERRED
EMBODIMENT
Disilanols embodying the present invention are repre-
sented by the formula
R R
HO—Si—Ar— (CF8K— Ar— SI—OH
R R
where R is a monovalent hydrocarbon radical, Ar is an
arylene group and x is a whole number from 2 to 8. The
monovalent hydrocarbon radical designated by R can be
an alkyl radical such as methyl, ethyl, propyl, butyl and
the like; an aryl radical such as phenyl, xylyl, tolyl, etc.;
an aralkyl radical such as phenylethyl or benzyl, a cyclo-
aliphatic radical such as cyclohexyl, or any other mono-
valent aliphatic or aliphatic radical. The simpler disilanols
having methyl or phenyl groups at these sites are pre-
pared for use in polymer preparations The arylene group
designated by Ar can be any divalent aromatic group ex-
emplified by p-phenylene, m-phenylene, biphenylene,
naphthalene, phenylene ether, diphenylmethylene and di-
phenylpropylene.
Disilanols having the formula given above can be pre-
pared by hydrolysis of the corresponding dihydride com-
3,763,204
pound, which in turn is prepared by reaction of a di-
bromoaryl perfluoroalkane with a monochloro silane. In
a preferred process sequence a perfluoroalkyl diiodide is
first prepared by reacting the appropriate perfluoro di-
acid chloride with potassium iodide Such reaction can .
be carried out by heating a mixture of these reactants °
in a stirred pressure vessel at a temperature of 200° C.
and a pressure of 500 to 600 p s i. for 6 hours, using a
modification of the procedure given by Krespan, J Org
Chem 23, 2016 (1958) The perfluoroalkyl diiodide is
 1Q
then reacted with an lodobromo arylhahde to form the
dibromoaryl perfluoroalkane. This reaction is carried
out by slurrying two moles of the lodobromo arylhahde
with one mole of the dnodo compound in an aprotic sol-
vent such as N.N-dimethylformamide m the presence of
an activated copper-bronze catalyst
The dibromoaryl perfluoroalkane is then reacted with
a monochloro silane having the formula
Cl—Si-H
R
r R R' ~|
-j-Si—Ar—(CFj).—Ar—Si-O-Si—0-j-
|_R R R' J
15
20
where R is a monovalent hydrocarbon radical as defined
above to produce the precursor hydride compound The 25
silane-dibromide reaction can be carried out by slowly
adding one mole of the dibromide in a solvent such as
tetrahydrofuran to a mixture of magnesium turnings and
two moles of the silane in the same solvent under condi-
tions of stirring and slight heating The resulting di- 30
hydride is converted by hydrolysis to a disilanol of the
formula given above. Hydrolysis can be carried out by a
modification of the procedure given by Merker et al., J.
Polymer Sci., A, 2, 15 (1964) for preparation of non-
fluormated silanols. Such procedure involves hydrolysis
with a caustic solution in an alcohol solvent system. Best
results are obtained by first contacting the dihydride with
a solution of sodium ethoxide m ethanol and then adding
a solution of sodium hydroxide in methanol, along with
 40
an aqueous sodium hydroxide solution Other hydrolysis
methods can also be used
Disilanols prepared as described above are useful for
preparation of curable polymers having repeating units
of the formula 45
50
where R, Ar and x have the meaning given above and R'
is a monovalent hydrocarbon radical defined for R or a
fluorine-substituted monovalent hydrocarbon radical Such
polymers are prepared by reacting the disilanol with a
diammosilane having the formula
R'
RiN—Si-
R<
•NRj
60
where R is a monovalent hydrocarbon radical, and pref-
erably a methyl radical, and R' is a monovalent hydro-
carbon radical, defined herein to include fluorine-substi-
tuted radicals such as 65
0-(CF,),-CFt
70
where y=0, 1 or 2 By using a diamino silane having fluo-
rine-substituted pendant radicals at these sites, additional
fuel resistance can be imparted into the polymer 75
Polymerization proceeds readily upon heating an equi-
molar mixture of these reactants in a dry solvent such as
toluene to a temperature of 90 to 100° C. The resulting
polymer is a viscous oil having a degree of polymerization
up to about 100, which polymer can be cured to form a
tough, flexible thermoset elastomer. Curing can be car-
ried out at room temperature by addition of an ethyl
silicate cross-linking agent and a metal salt catalyst such
as dibutyltin diacetate at proportions of 10 and 2 weight
percent, respectively. Other curing agents and catalysts
can also be used
The invention is further illustrated by the following
specific example.
Example I
The following procedure exemplifies the preparation of
a disilanol wherein R in the formula given above is
methyl, Ar is 1,4-phenylene and x is 3. Perflouoro-glutaryl
chloride (2000 grams, 0722 mole) was treated with
potassium iodide (3200 grams, 1.93 moles) in a stirred
pressure vessel for six hours at 200° C and 500-600 p s i
The product 1,3-dndo-l,1,2,2,3,3-hexafluoropropane, b.
105° C./350 mm, was obtained in 45 percent yield The
dndo compound (1400 grams, 0347 mole) was then
reacted with p-iodobromobenzene (216.0 grams, 0763
mole) in the presence of 198 grams of an activated cop-
per-bronze catalyst by slurrying m N,N-dimethylform-
amide. The product l,3-bis-(p-bromophenyl)-l,1,2,2,3,3-
hexafluoropropane was purified as a crystalline solid, m.
124-5° C. in 60 percent yield
Analysis—Calcd for Ci5H8Br2F6 (percent) C, 38 99,
H, 175, Br, 34.59. Found (percent). C, 382, H, 2.2;
Br, 338.
The resulting dibromide (130 grams, 0282 mole) was
slowly added as a solution in tetrahydrofuran to a mix-
ture of magnesium turnings (150 grams, 0564 mole)
and dimethyl chlorosilane (53 3 grams, 0.564 mole) in
100 ml of tetrahydrofuran, which was stirred and heated
slightly The product, l,3-bis[p-(dimethylsilyl)phenyl]-
1,1,2,2,3,3-hexafluoropropane was isolated by extraction
with cyclohexane and recovered in 50% yield by dis-
tillation, b. 170° C/2.5 mm.
Analysis—Calcd for CigH^FgS^ (percent) C, 54 36,
H, 528, Si 13.34. Found (percent): C, 53.7, H, 5.05, Si,
141.
The resulting dihydride was hydrolyzed by treatment
with an ethanol-sodmm ethoxide solution, and a water-
sodium hydroxide-methanol solution The crude diol was
precipitated in potassium hydrogen phosphate and re-
crystallized from carbon tetrachloride in 30% yield, m.
118° C., as l,3-[p-(hydroxymethylsilyl)phenyl]-l, 1,2,2-
3,3-hexafluoropropane.
Analysis.—Calcd for Cigl^FeOjtS^ (percent)- C,
5042 H, 491, Si, 1240 Found (percent) C, 488, H,
454, Si, 11 8
The disilanol was then reacted with an equimolar
amount of bis(dimethylamino)dimethylsilane by heating
to a temperature of 90-100° C in dry toluene to form a
viscous polymer having an inherent viscosity of 0 5 at
a concentration of 1 gm./dl. in tetrahydrofuran at 30°
C A sample of the polymer was cured by addition of
ethyl silicate and dibutyltin diacetate at proportions of
10 and 2 weight percent respectively to produce tough,
flexible thermoset elastomeric material The elastomenc
material showed no degradation, color change or loss of
mechanical properties upon being boiled in water for 24
hours. Soaking the sample for 24 hours in JP-4 aviation
fuel resulted m swelling of 30% of its original volume, as
compared to 150% for conventional silicones
It is to be understood that the above example is merely
illustrative and that modifications and changes in the pro-
cedures and reaction conditions described therein can
be employed without departing from the spirit and scope
of the invention.
3,763,204
-Si—OH
R
What is claimed is:
1 A compound having the formula
R R
HO—SI—Ar—(CFj)»—Ai
R
where R is a monovalent hydrocarbon radical selected
from the group consisting of methyl, ethyl and phenyl,
Ar is a phenylene group and x is a whole number from
2 to 8.
2. The compound of claim 1 wherein R is a methyl
radical.
3. The compound of claim 2 wherein Ar is p-phenyl-
ene.
4. The compound of claim 3 wherein x is 3.
2,561,429
3,647,740
3,666,718
References Cited
UNITED STATES PATENTS
7/1951 Sveda 260—448.2 D
3/1972 Loree et al 260—448.2 D X
•5/1972 'Patterson et al. _ 260—448.2 D X
OTHER REFERENCES
Merger et al., J. Polymer Sci., A, 2, p. 15, 1964.
!0 DANIEL E. WVMAN, Primary Examiner
P. F. SHAVER, Assistant Examiner
U.S. Cl. X.R.
15 260—46.5 E, 448.2 E


Polymerizable disilanols having in-chain perfluoroalkyl groups

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