Note: Descriptions are shown in the official language in which they were submitted.
TITLE: A PROCESS FOR T~E PREPARATION OF
P3LY(DISILYL)SILAZANE POLYMERS AND THE PO~YMERS THEREFROM
Background of the Invention
This invention relates to the preparation of
silazane polymers. These polymers are useful as chemical
intermediates to synthesize organosilicon compounds. They
are also useful, when fired at high temperatures, to form
silicon carbide and silicon carbide containing ceramic
materials.
What i5 disclosed herein is a novel process to
obtain novel silazane polymers. ~he process con~ists of
contacting and reacting chlorine-containlng di~ilane with
disilazanes in an inert, essentially anhydrous atmosphere
while distilling volatile by-products.
As is well-known in the art, halosilane monomers
will react with ammonia and most organic compounds
containing a primary or secondary amino group ~o give a
variety of silazanes. For example, the reaction of
trim~thylchlorosilane and ammonia produces
hexamethyldisilazane, a silazane monomer, while
dimethyldichlorosilane and ammonia produce dimethylcyclic
silazanes. These two reactions probably constitute the
majority of commercial ~ses of the silazane chemistry.
Silazanes in general have been academic
curiosities for ~any years and a variety of such silazanes,
including monomers, oligomers, cyclics and even low
molecular weight resins and linear polymers have been
prepar~d by a varie~y of methods. For example, L. W. ~reed
et al., ln the Journal of Organic Ghemistry, 27, 1114(1962)
report the ~ormation of silazanes from the polymerization
o sterically hindered silazane oligomers, while in the
Journal of Polymer Science, A 2 45(1964~, cyclic trimer and
~etramer silazanes are reported to be thermally cracked
using catalysts to give linear polymers.
In contrast, fluids, rubbery polymers and resins
prepared from C~3SiC13, (C~3)2SiC12 and excess ammonia have
been reported by Kruger et al. in the Journal of Polymer
Science, A 2 3179~1964) and Redl, Silazane Polymer,
ARPA-19, Advanced Research Projects Agency, October, 1965.
The patent literature also contains disclo~ures of
the preparation of silazanes. Cheronis, in U.S. Patent
2,564,674, issued August 21, 1951 discloses the preparation
of low molecular weight linear silazane polymers by the
reaction of halosilanes with excess ammonia in`a solvent
solution. Bausma, et al., in U.S. Patent 3,809,713 issued
May 7, 1974, discloses a similar reaction scheme with the
added modifica~ion of removing the by-produced solid
ammonium halide using ethylene diamine.
More recently, Verbeek, et al., in U.S. Patents
3,853,567 issued December 10, 1974, and U.S. Patent
3,892,583 issued July 1, 1975, disclosed that mixtures of
CH3SiC13 and (C~3)2SiC12 can be treated with ammonia or
organoamines to form materials that can be pyrolyzed to
yield SiC/Si3N4 ceramics.
~18~8~
As should ~e recognized by those skilled in the
art, the present invention differs in at least one respect
from all of the above art in that the present invention is
based on chlorine-containing disilanes as opposed to the
use of chlorine containing monosilanes.
In another segment of the prior art, the ~se of
disilanes in the preparation of silazane polymers has been
limited to the formation of relatively low molecular weight
materials. In one example, Wannagat et al., Ang. Chem.
75~7) 345(1963~, reported the reaction of
tetramethyldichlorodisilane with gaseous ammonia to give a
six-membered cyclic silazane, {(CH3)2SiSi(CH3)2N~}2, rather
than the expected linear silazane polymer and Hengge et
al., Montash. Chem. lOlI(2)325(1970), prepared
dime~hylamino substituted mixtures o disilanes from
dimethylamine and the chlorine-containing disilane mixture
obtained from the Direc~ Process ~or the preparation o
chlorosilanes.
What has been newly discovered is the coreaction
between chlorine-containing disilanes and disilazanes to
give high molecular weight silazane polymers.
The Invention
The instan~ invention c~ncerns a new class o~
silazane polymers pr~pared from chlorodisilanes. In
essence, a single chlorine-containing disilane or a
specified mixture of chlorine-containing disilanes is
treated with a disilazane, as the nitrogen source, in
sufficient amounts to react with all o the chlorine on the
chlorine-containing disilanes. This is usually an
e~uimolar amount of disilazane based on the chlorine
content of the disilane. The inventor does not wish to be
he}d to such a theory but it is believed that when the
mixture is heated, usually in the absence of solvent and in
an essentially anhydrous atmosphere, the reactions
-Si-SiCl ~ R'35iNHSiR13~ Si-Si-NHSiR'3 ~ R'3SiCl,
~ '
. . . . .
-Si-Si-Cl + -Si Si-N~SiR'3 ~ ~Si-Si-NH-Si-Si- ~ R'3SiCl
and
2-Si-Si-NHSiR'3 ~ -Si-Si-N~-Si-Si * R'3SiNHSiR'3
take place.
The advantage of this process is the ability to
stop the reaction at any point by cool ing the reaction mass
thus giving polymers with any desirable viscosity, hence
any desirable molecular weight. The silazane polymers
range in physical appearance from liquids, to high
viscosi~y liquids, to hard glassy materials. The m~terials
are therefore very easy to handle. They are essentially
hydrolytically stable.
~ hus, this invention consists of a process ~or
preparing an R' 3SiN~- containing silazane polymer which
consists of contacting and reacting in an inert,
essentially anhydrous, atmosphere, a chlorine-containing
disilane or a mixture of chlorine-containing disilanes, of
the general formula
(ClaRbSi)2
with a disilazane having the general formula
(R~3si)~NH
at a temperature in the range of 25C to 300C while
distilling by-produced volatile products~ wherein R is
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon
atoms or the phenyl group; a has a value of 0.5-3; b has a
value of 0-2.5 and the sum ~f a I b is equal to three.
This invention also deals with a new and novel
composition of matter which is an R'3SiNH- containing
silazane polymer which is prepared by contacting and
reacting in an inert, essentially anhydrous, atmosphere, a
chlorine containing disilane or a mixture o
chlorine-containing disilanes, of the general formula
( ClaRbS i ) 2
with a disilazane having the general formula
(R'35i)2NH
at a temperature in ~he range of 25C to 300C while
distilling by-produced volatile products, wherein R is
vinyl, an alkyl group o~ 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon
atoms or the phenyl group, a has a value of 0.5-3; b has a
value of 0-2.5 and the sum of a ~ b is equal to three.
This invention further deals with a process ~or
preparing an R'35iNH- containiny silazane polymer which
consists of contacting and reacting in an ine~t,
essentially anhydrous, atmosphere, a chlorine-containing
disilane or a mixture of chlorine-containing disilanes,
wherein the number of diorgano-substituted silicon atoms
does not exceed the number of monoorgano substituted
silicon atoms, of the general formula
(ClaRbSi)2
with a disilazane having the genera} formula
(~l3Si)2NH
at a temperature in the range of 2SC to 300C while
distilling by-produced volatile products wherein R is
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrosen, an alkyl group of 1~3 carbon
atoms or the phenyl group; a has a value of 0.5-3; b has a
value o~ 0-2.5 and the sum of a ~ ~ is equal to three.
This invention also deals with a new and novel
composition of matter which is an R'3SiNH- cont~ining
silazane polymer which is prepared by contac~ing and
reacting in an inert, essentially anhydrous ~ atmosphere, a
chlorine-containing disilane or a mixture o~
chlorine-containing disilanes wherein the number of
diorgano-substituted silicon a~oms does not exceed the
number of monoorgano-substitu~ed silicon atoms of the
general formula
(ClaRbSi32
wi~h a disilazane having the general formula
(Rl3si)2NH
at a temperature in the range of 125C to 300C while
distilling by-produced volatile products, wherein R i5
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon
atoms or the phenyl group; a has a value of 0.5-3; b has a
value of 0-2.5 and the sum of a ~ b is equal to three,
Still further, this invention deals with a method
of preparing a silicon carbide containing ceramic material
which consists of heating a silazane polymer in an inert
aumosphere or in ~ vacuum to at least a temperature of
750C until the silazane polymer is converted to silicon
carbide ceramic material, which silazane pol~mer is
obtained by a process which consists of contacting ancl
reacting in an inert, essentially anhydrous, atmosphere, a
chlorine-containing disilane or a mixture of
~L~L~8~
chlorine-containing disilanes, wherein the number of
diorgano-substituted silicon atoms does not exceed the
number of monoorgano-substituted silicon atoms, of the
general formula
~ ClaR~Si32
with a disilazane having ~he general formula
~ R'3Si)2NH
at a temperature in the range of 125C to 300C while
distilling by-produced volatile products, wherein R is
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon
atoms or the phenyl group; a has a value of 0.5-3; b has a
value of 0-2.5 and the swm of a ~ b is equal to three.
Yet another object of this invention is a method
o~ preparing a silicon carbide containing ceramic article
which consists of (A) forming an ~rticle of the desired
shape from a silazane polymer; (B) heating the article
formed in (A) in an inert atmosphere or in a vacuu~ to an
elevated temperature of at least 750C until the silazane
polymer is converted to silicon carbide containing ceramic,
which silazane polymer is obtained by a process which
consists of contacting and reacting in an inert,
essentially anhydrous, atmosphere, a chlorine-containing
disilane or a mixture of chlorine-containing disilanes,
wherein the number of diorgano-substituted sil.icon atoms
does not exceed ~he number of monoorgano-substituted
silicon atoms, of the general formula
(~laRbSi)2
with a disilazane having the general formula
(R'3~i)2N~
at a te~perature in the range of 125C to 300C while
dist:illing by-produced volatile products, wherein R is
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon
atoms or th~ phenyl group; a has a value of 0.5-3; b has a
value of 0-2.5 and the sum of a ~ b is equal to three.
Still another object of this invention is a method
for preparing a filled ceramic article which consist of
(A) mixing a silazane polymer with at least one
conventional ceramic filler, ~B) orming an a~icle o~ the
desired shape from the mixture of silazane polymer and
filler and ~C~ heating the article formed in (~) in an
inert atmosphere or in a vacuum to an elevated temperature
of at least 750C until the silazane polymer is converted
to a silicon carbide containing ceramic, which silazane
polymer is obtained by a process which consists of
contacting and reacting in an inert, essentially anhydrous,
ab~osphere, a chlorine-containing disilane or a mix~ure of
chlorine-containing disilanes, wherein the number of
diorgano-substituted silicon atoms does not exceed the
number of monoorgano-substituted silicon atoms, of the
general formula
. . . . . . .
_ . . .
(ClaRbSi~2
with a disilazane having the gencral ormula
(R'3Si)2NH
at a temperature in the range of 125C to 300C while
distilling by-produced volatile products wherein R is
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
yroup; R' is vinyl, hydrogen, an alkyl group of 1 3 carbon
atoms or the phenyl sroup; a has a value of 0.5-3; b has a
value of 0-2.5 and the sum of a ~ b is equal to three.
Still ~urther, it is an object of this invention
to prepare an article coated with a silicon carbide ceramic
material which method consists of (A) mixing a silazane
polymer with at least one conventional ceramlc iller, tB)
coating a substrate with the mlxture o~ silazane pol~ner
and filler and, (C) heating the coa~ed su~strate in an
inert atmosphere or in a vacuum to an elevated temperature
of at least 75QC until ~he coating is converted to a
silicon carbide ceramic material, whereby a silicon carbide
containing ceramic coated article is obtained, which
~ilazane polymer is obtained by a process which consists o~
contacting and reacting in an inert, essentially anhydrous,
atmosphere, a chlorine-containing disilane or a mixture of
chlorine-containing disilanes, wherein the number of
diorgano-substituted silicon atoms does no~ exceed the
number o monooryano~substituted silicon atomæ, of the
general formula
~ClaRbSi)2
with a disilazane having the general formula
~ R13Si)2N~I
at a temperature in the range of 125C to 3~0C while
distilling by-producPd volatile products, wherein R is
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon
atoms or the phenyl group; a has a value of 0.5-3; b has a
value of 0 2.5 and the sum of a ~ b is equal to three.
A further object of this invention is a process
for preparing an article coated with a silicon carbide
ceramic material which consists of (A) coating a substrate
with a silazane polymer, (B) heating the coated substrate
in an inert atmosphere or in a vacuum to an elevated
temperature o~ at least 750C until the coating is
converted to a silicon carbide ceramic material, whereby a
silicon carbide containing ceramic coated article is
obtained, which silazane polymer is obtained by a process
which consists of contacting and reacting in an inert,
essentially anhydrous, atmosphere, a chlorine-~ontaining
disilane or a mixture of chlorine-containing disilanes,
wherein the number of diorgano-substituted silicon atoms
does not exceed the number of monoorgano-substituted
silicon atoms, of the general formula
~ ClaRbSi)2
with a disilazane having the general formula
.
.
(
~2
(R'3Sij2NH
at a temperature in the range of 125C to 30~C while
distilling by;produced volatile produc~s wherein R is
vinyl, an alkyl group of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 car~on
atoms or the phenyl group; a has a value of 0.5 3; b has a
value of 0~2.5 and the sum of a + b is equal to three.
A final object of this invention is a process for
preparing an R'3SiNH- containing silazane polymer which
consists of contacting and reacting in an inert,
essentially anhydrous atmosphere, a disilazane having the
general formula
(R~3Si)2NH
with (i) a mixture of a chlorine-containing disilane having
the general formula
(ClaRbSi) ;2
and a chlorine-containing monosilane having the gen~ral
formula
R'nSicl4-n;
~ii) a mixture of chlorine-containing disilanes having the
general formula
(ClaRbSi)2
mixed with a chlorine-con~aining monosilane having the
general formula
R'nSlcl4-n
or (iii) a mixture of chlorine-con~aining disilanes having
the general formula
13
Cl aRbs i 2
mixed with a mixture of chlorine-containing monosilanes
having ~he general formula
R'nSicl4-n
at a temperature in the range of 25C to 300C while
distilling by-produced volatile products, wherein R is
vinyl, an alkyl radical of 1-3 carbon atoms or the phenyl
group; R' is vinyl, hydrogen, an alkyl group of 1-3 carbon
atoms or the phenyl group; a has a value of 0.5-3; b has a
value of 0-2.5; n has a value of 0, 1, 2 or 3 and the sum
of a ~ b is equal to three.
The inventions described herein result in new
compositions of matter which are an improvement in ~he art,
in that, essentially hydrolytically stable, easy to handle
silazane polymers can be prepared. Further, the silaæane
polymers lead to an improvement in the art of formation o~
silicon carbide and they can be used as binders in ceramic
materials.
The invention results from reacting disilazanes
~ith chlorine-containing disilanes or mixtures of disilanes
with monosilanes in an inert, essentially anhydrous
atmosphere and then firing the resulting si~azane polymer
to get silicon carbide or silicon carbide containing
ceramic materials.
14
The chlorine-containing disilanes of this
invention are those disilanes having the yeneral formula
(ClaRbSi)2-
In this formula, R is vinyl, an alkyl radical containing
1-3 carbon atoms or the phenyl group. Thus, those groups
which are contemplated as being useful in this invention
are methyl, ethyl, propyl, vinyl and phenyl. For purposes
of this invention, the R groups can all be the same or they
can be different. The chlorine-containing disilanes can be
those found in the residue from the Direct Process for
producing halosilanes (Eaborn, C., ~Organosilicon
Compounds", Butterworth Scientific Publications, London,
1960, pg. 1). Whenever the symbols 0, Me, Et and Vi are
used herein, their meaning is phenyl, methyl, ethyl and
vinyl, respectively.
For purposes of this invention, the value of a and
b is f~om 0.5-3 and 0-2.5 respectively and the sum of a + b
is equal to three. Examples of chlorine-containing
disilanes useful in this invention are {Cl(CH3~2Si}2,
{C12CH3si}2r {cl2c2H5si}2r {Cl(C6Hs)2Si}2
and {cl2cH2=c~si}2-
Monosilanes useful in admixture with the disilanesof this invention can be for example CH3SiC13, (CH3)2SiC12,
~(CH3)2SiCl, (CH3)3SiCl, (CH2=CH)(CH3)2SiCl, (C2Hs)2SiCl~,
C6H5siC13~ (c6H5)2sicl2 and (C6Hs)3SiCl.
Also considered within the scope of this invention
is the use of mixtures of chlorine-containlng disilanes.
One aspect of ~-his invention requires that whenevPr certain
chlorine-con~aining disilane mixtures are required, the
n~ber of units of diorgano-substituted silicon atoms
should not exceed the number of units of
monoorgano-substituted silicon atoms. Even though silazane
polymers can be formed from chlorine-containing disilane
mixtures wherein the number of diorgano-substituted units
does exceed the number of monoorgano-substituted units, it
has been found that these polymers do not have the handling
properties for formability because of low viscosities.
The second reactant in this invention is a
disilazane of the general formula ~R'3Si)2NH. For purpo~es
of this invention, R' is vinyl, hydrogen or has the same
meaning as R above. Thus, R' in this ~ormula i5 vinyl,
hydrogen or an alkyl radical of 1-3 carbon atoms or the
phenyl group. Therefore, R', for purposes of this formula
is represented by hydrogen, methyl, ethyl, propyl, vinyl
and phenyl. As set forth above, each Rl group in this
formula can be the same or they can be different. Examples
of compounds contemplated within the scope of this
invention include: {(CH3~3Si}2NH, tC6H5(CH3)2si}2~
l'l~OB'O
16
{(c6H5)2cH3si}2NH~ {C~2-CH(CH3)2si}2NH'
{C~ H5C~3)C6~5si}2~ (CH2=CH~tC6H5)2Si}2N~,
{CE~25C~(C2H5)2si};~N~I~ {(C~2-C~)C6H51C2H5)5i} 2NH~
{~(CH3)2si}2N~t {~2(c~3)si}2NH and lHc6~scH3si}2N~.
These reactants are brou~ht together in an inert,
essentially anhydrous atmosphere. For purposes of this
invention what we mean by n iner~" is that the reaction is
carried out under a blanket of inert gas, such as, argon or
nitrogen or helium. What we mean by ~essentially
anhydrous~ is that the reaction is preferably carried out
in an abso}utely anhydrou~ atmosphere but minute amounts of
moisture can be tolerated.
When the reactants are contacted with each other,
the reaction begins which forms an intermediate disilane
amino compound i.e.
-Si-Si-Cl ~ (R'3Si)2NH ~ -Si-Si-NH5iR'3 + R'3SiCl.
Upon heating, additional disilane amino compound
is formed and upon continued heating, R'3SiC1 is disti}led
from the reaction mixture and a disilylsilazane polymer is
formed i.e.
~BO
Si-Si-Cl ~ -Si-Si-NH5iR'3~ -Si-Si-~H-Si-Si- ~ R13SiCl
.
.. ~, .. ..
2-Si-Si NHSiR'3~ Si-SiNH-Si-Si + R'3SiNHSiR'3.
The order of addition of the materials does not appear to
be critical. AS the temperature is raised higher, more
condensation takes place and crosslinking occurs, with
residual R'3Si- that is not distilled from the mixture,
acting as a chain-stopper. This control allows one to stop
the reaction at any point to obtain almost any desired
viscosi~y. The desirable temperature range for this
reaction is 25C to 300C. The most preferred range :is
125C to 300C. The length of time ~hat the reaction
requires depends on the temperature and the viscosity one
wishes to achieve.
What is meant by "volatile products" are the
distillable by-produced products that are formed by the
reactions set forth above. These materials can be
represented by (CH3)3SiCl, (CH2-CH~(C6Hs)2SiCl,
3(C6H5)2siCl~ (cH3~2c6~ssiu ~ HtcH3)25icl and
(CH2=C~)(C~3)2SiCl. Sometimes, these materials require the
use of a vacuwm along with the heat in order to remove them
from the reaction mixture.
18
The sila~ane polymers are then essential}y ready
to use. The silazane polymers are pyrolyzed in an inert
atmosphere or in a vacuum at temperatures o:f at least 750C
to give a silicon carbide containing materi,al. If the
polymer is of sufficient viscosity, it can be shaped first
(such as an extruded fiber) and then pyrolyzed to give a
silicon carbide containing fiber or the silazane polymers
can be filled with ceramic type fillers (if desired) and
then fired to at least 750C to obtain silicon carbide
ceramic materials or silicon carbide ceramic material
GOntaining ceramic articles.
When mixtures of chlorine-containing disilanes are
to be used, it is best if the chlorine-containing disilanes
are mixed prior to contacting and reacting with the
disilazanes.
As mentioned above, some of the resulting polymers
can be extruded to give various shapes such as fibers. It
has been found that the polymers of this invention that
have the handleability that enables one to extrude or form
them are those polymers in which the number of
diorgano-substitu~ed silicon atoms do not exceed the number
of monoorgano-substituted silicon atoms. Thus, if the
polymer is to be extruded or otherwise formed, it should be
prepared from disilanes and disilazanes wherein the
diorgano-substituted silicon atoms do not exceed the nu~ber
of monoorgano-substituted silicon atoms.
As mentioned above, the polymers of this invention
can be used in both the filled and unfilled state,
depen~ing on the application. Thus, it is contemplated
wi~hin the scope of this invention ~o coat substrates with
~illed and unfilled polymers and heat the s~bstrates to
pr~duce silicon carbide containing ceramic ~oated artic}es.
Fillers and adjuvants can be milled on 3 roll mills by
simply mixing the polymers of this invention with the
fillers and making several passes on the mill. In the
alternative, the polymers can be plac~d in solvents and the
fillers and adjuvants can be added thereto and after mixing
the solvent can be removed to give the filled polymer.
The coating can be carried out by conventional
means. The means used depends on the polymer and
substrates used and the application one has in mind. ~hus,
these materials can be brushed, rolled, dipped or sprayed.
In the filled stated, it is sometimes necessary to trowel
the polymer onto the substrate.
Whenever the polymers are converted to the ceramic
state, it i5 done by pyrolyzing the polymer to a
temperature of at least 750C in an inert atmosphere or in
a vacuum.
Attempts to pyrolyze at or above 750C without an
inert atmosphere lead to undes:irable side reactions and
therefore, caution should be exercised ~o be ~ure to
exclude moisture and other potential reactants.
. . . _ ,
0
Now so that those skilled in the art can better
appreciate and understand the invention, the following
examples are given. The examples are for purposes of
illustration only and are not to be regard~ed as
limitations.
In ~he following examples, the analytical methods
used were as follows:
Thermogravimetric analyses (TGA) were carried out
on a Netzsch STA 429* (2400C) TGA instrument manufactured
by Netzsch Instruments, Selb, West Germany. Sample sizes
averayed 11 mg., program rate was 10C/min., gas flow rate
was 200 cc/min. The scale setting was 50C/in. ~ 0.5C/in~
Differential Thermal Analyses (DTA) were carried
out on the Netzsch instrument using samples averaging 13.S
mg., a flow rate of 200 cc/min., a program rate of lO~C/min
and a scale setting of 50C/in + 0.5C/in.
Percent Silicon was determined by a fusion
technique which consis~ed of converting the silicon
material to soluble forms of silicon and the soluble
material is quantitatively determined as total silicon by
atomic absorption spec~rometry. Solubilization takes place
by weighing the sample into a Parr-type* fusion cup (about
0.3 gm), adding 15.0 gms of Na peroxide, heating for about
90 sec. and ~uenching in cold water. The material is
placed in a nickel beaker containing 150-200 ml. of
distilled water. 55 ml. of reagent grade acetic acid is
added and diluted with water to 500 ml. volume.
Trademark
(
21
Percent Chlorine tresidual) was cletermined ~y Na
peroxide decomposition and titration with silver nitrate.
Fusion of ~he halides with Na peroxide is followed by
potentiometric titration with standard silver nitrate by
weighing a sample into a gelation capsule~ placing about
1.5 gm. of Na2O~, about 0.7 gm of ~NO3 and about 0.15 gm of
sug~r into a clean, dry reaction cup and burying the
capsule in the mixture. The cup is filled with Na2O2 and
placed in a reaction vessel. It is heated for 1-1 1/2 minO
and quenched in cold water. The cup and vessel are washed
and ~he washings are collected. The washings are heated to
dissolve any solids. 15 ml. of cold 50~ aqueous H2SO4 is
added and allowed to stand 15-20 sec. This solution is
neutralized with additional H2SO4 and titrated.
Carbon and hydrogen were determined by
microcombustion by weighing 10 to 20 mg. of sample into a
micro platinum boat and treating it in an A. H. Thomas
co~bustion apparatus, Catalog No. 6447-E, Philadelphia, PA.
In the reactions carried out below, the reaction
apparatus was essentially the same in each case and
consisted of a 500 ml., glass, round-bottomed flask
equipped with a mechanical stirrer, gas inle~ tube,
distillation apparatus and a thermocouple to record
temperature. The distillation apparatus was equipped to
use a vacuum if needed.
.,
8~
22
A mixture of 50 gms of chlorine-cont:aining
di~ilanes consis~ing of 57.6 wPight percent of
tetrachlorodimethyldisilane; 32 weight percerlt of
trichlorotrimethyldisilane and 10.4 weight percent of
dichlorotetramethyldisilane were added dropwise to a
reaction vessel described above which contained 120 gms of
hexamethyldisilazane. The reaction vessel was then slowly
heated to 275C under argon and held at that ~emperature
~or two hours. The distillate that was collected during
~he heating pariod was found ts contain ~CH3)3SiCl, some
hexamethyldisilazane and a small amount of NH4Cl. The
polymer residue in the flas~ weighed 29.6 gms and when
cooled was a hard, colorless, glassy solid. The material
was fired in an Astro Industries Furnace lOOOA water cooled
graphi~e heated model 1000.3060-FP-12 to 1200C under Argon
for a yield of 46.29%. The material contained 29% carbon,
7-8% hydrogen, 45% silicon and 8.1% nitrogen. Infra red
analysis showed the presence of -Si-NH-Si- but no
-Si-O-Si-. X-ray analysis of samples fired at various
temperatures showed the following:
tem~ type of material
1200C Amorphous ~aterial
1400C Amorphous material
1600C beta-SiC l~oA and Moissanite SiC
18~0C beta-SiC o ~2000~ and Moissanite SiC
2000C beta-SiC of > 2000~ but no Moissanite
Ebulliometry gave 3125 gm/mole.
23
~ examethyldisilazane (214 gms) and S9.90 gms of
Si~C16 were placed in a reaction vessel described above.
Upon mixing, the reaction exothermed to 57GC and the
mixture turned cloudy white. Distillation began at about
77~C and the reaction mass cleared and turned a faint
yellow color when the flask reached 110C.
The reaction mass proceeded to foam and the foam
level was controlled by increasing stirrer speed and
maintaining the temperature at 160-165C for 1 hour. The
temperature was raised to 170C with rapid stirring and
then to 265C where the reaction mass foamed excessively.
The temperature was decreased to about ~15C ~or a short
while and then the pot was allowed to cool. When cooled
the material was a glassy, clear solid which was easily
removed from the inside surface of the reaction flask. A
small amount of gummy liquid was also removed from the
flask. Infra red analysis showed the presence of NH and
Si(CH3)3 with some -SiCH3 and -Si-N-Si. %Si was 42.3%.
X-ray diffraction on a sample fired to 1600C showed the
major phase to be beta-silicon car~ide with a minor phase
of beta-Si3N4. The average crystallite size of the
beta-silicon carbide was 130A.
~.~8$~
~4
~e~
Tetrachlorodimethyldisilane (32.7 gms) and 17.3
gms of trichlorotrlmethyldisilane were mixed with 168.3 gms
of hexamethyldisilazane in a reaction vessel equipped as
des~ribed above. This mixture was gradually heated to
~65C under argon and held there for about 10 min.
Distillate was removed during this period of time. ~hen
cooled~ the residue was a polymer which was a hard,
colorless resin. The yièld was 65.7%. Thermal gravimetric
analy~is to 1000~C yielded 54% silicon carbide.
Differen~ial thermal analysis in air to 500C gave an
exotherm at 93C. ~TA in argon to 500C showed no ~hermal
break. Residual chlorine content was 1.44 weight % and %Si
was 47.4. Infra-red analysis showed the presence of NH,
NH4Cl, SiC~3, Si-N-Si. X-ray diffraction studies on a
sample fired at 1600C showed beta-silicon carbide having
a particle size of 120~ and a small amount of alpha-silicon
carbide. The polymer was analyzed by derivatization gas
chromatography and found to contain 7.5 weight % (C~13)3Si-,
15.0 weight ~ (CH3)2SiS and 68.5 weight ~ of CH3Si~.
Derivatization gas chromatography is an analysis wherein
the polymer is treated with tetraethoxysilane and KOH to
give the organoethoxysilane derivatives of the individual
polymeric units~ Gas chromatography is then used to
determine ~he content and relative ratios o~ the various
units present in the mixture. This procedure is carried
out by weighing about 0.3 gm of the polymer sample into a
50 ml. round-bottomed flask. To this flask is added 8O0
ml. of Si(OC2~s)4. One pellet of XO~ is added and the
flask is heated to initiate the reaction and it is then
reflllxed for 45 min. to one hour. An additional 2.0 ml. of
Si(OC2Hs)4 is added and then about 1/2 teaspoon of
pulverized CO2 is added to neutralize the KO~. The sample
i5 centrifuged to separate the phases. The silane layer is
then analyzed by gas chromatcgraphy which has been
standardized.
}~
Tetrachlorodimethyldisilane (45.6 gms) was mi.xed
with 129.1 yms of hexamethyldisilazane under argon. The
reaction vessel was equipped as in Example 1. This
reaction mass was heated to 240C and held for a few
minutes and then cooled to room temperature. The resulting
material was a solid whit~ powder and 26.6 gms were
obtained. The % yield was 58~3%o TGA to 1000C in argon
gave 27~ weight loss. DTA in air to 500C gave an exotherm
at 140C and DTA in argon to 500C gave no thermal break.
% residual chlorine was 4~83 weight ~ and weight % Si was
44.4, Infra-red analysis showed the presence of ~H4Cl,
Si-N-Si and -SiCH3. A yield of 62.6 weight ~ was obtained
when the material was fired to 1200C and 78.1 weight % was
obtained on firing from 1200C up to 1600C.
Deriva~ization using Si(OC2Hs)4 gave the following: 6.4
weight % (C~3)3Si-, 2.0~ of (CH3)2Si= and 68.0% of CH3Si3.
26
Exam~le S
Trichlorotrimethyldisilane (45.8 gms) was mixed
wi~h 196~84 gms of hexamethyldisilazane in a reaction lask
equipped as described above. This mixture was hea~ed under
argon to 280 The material was maintained at this
temperature for a few minutes and then cooled to room
temperature. The polymer obtained was 33.4 gms of a gummy,
white solid in a yield of 72.9 weight %. A TGA in argon to
lOOO~C gave 87.5% weight loss. DTA in air to 500C gave ,an
exotherm at ~5C and a DTA in argon to 500C showed an
endotherm from room temperature to 140C. The residual
chlorine was 2.29 weight %. ~Si was 45.2. Infra-red
analysis showed the presence of -NH, NH4Cl, SiCH3, Si N-Si
and a small amount of Si-O-Si. Astro firing gave a ~0.2~
weight loss at 1~00C and 16.2% weight loss on firing from
1200-1600C. X-ray dif~raction studies on the 1600C fired
sample showed beta-silicon carbide of 120~ particle size
plus a small amount of alpha-silicon carbide.
Derivatization analysis showed 4.0% (CH3)3Si-, 31~0%
(CH3~2Si= a~d 32% C~3Si-.
ExamE~e 6
A mixture of 25 mole % te~rachlorodimethyldisilane
and 75 mole % tetramethyldichlorodisilane totaling 55.3 gms
was mixed with 113.0 gms of hexamethyldisilazane under
argon and heated to 275C in a reaction vessel equipped as
described above. The temperature was held for 1/2 hour and
27
then the reaction mass was allowed to cool. Thirty-one and
seven tenths grams of a clear yellow liquid were obtained
for a yield o~ 57.3~ of the ceramic materia]L. TGA in argon
to :1000C gave a 7.0% yield. DTA in air to 500C gave an
exothenm at 90C and a DTA in argon at 500C showed no
thermal break. ~ residual chlorine was 3.06% and the %si
was 43Ø Firing in the ~stro furnace at 1200C gave a 7~6
weigh~ % yield o~ the ceramic material and firing at
1200-1600C gave a 75.8 weight ~ yield. Gas chromatography
of the material from derivatization gave 3.5% of (CH3)3Si,
44.1~ (CH3)2Si= and 25.4% of CH3SiYo
Example 7
Tetramethyldichlorodisilane (56.3 gms) was mixed
with 113.3 gms of hexamethyldisilazane under argon and
heated over 1 1/2 hours to 250C and held there for 1 hour.
The reaction vessel was equipped as described above. The
bulk of the material distilled from the reaction vessel
leaving only 16.1 gms of a light yellow oil which turned
colorless on cooling. $he % yield of ceramic materi~1 was
28.6. TGA to 10~0C in argon gave 0% yield of ceramic
material. DTA in air to 500C gave an exotherm at 85C and
DTA in argon to 500C gave an endotherm from room
temperature ~o 200C. The % residual chlorine was 7.47%
and % Si was 39. Infra-red showed the presence of NH, SiCl
and Si(CH3)3. The inventor was unable to fire this
28
material in the Astro furnace because of it:s high
volatility. Deriva~ization ~as chromatography showed 5.6
(C~13)3Si-, 6896 (C~13~2Si- and 9.0~6 CH3Si--.
~.~
A polymer was prepared from a disilane mixture
similar in composition to that set forth in Example 1. The
material was heated under argon for 1 hour. This material
was made into a filled, molded ceramic material by
combining 35.0~ gms of 320 mesh silicon carbide powder and
15.06 gms of the above polymer in a toluene solution. The
material was then vacuum evaporated to dryness and then
ball milled to give a fine powder. The powder was then
press molded at 200C at 7500 psi for 30 minutes to make a
pellet which was qlassy and very smooth. ~he resulting
pellet was fired in the Astro furnace described abov~e at
1200C for 6 hours to a ceramic material with very low
porosity. The yield was about 85%.
Example 9
The polymer from Example 8 was mixed in a ratio of
10 weight % with 90 weight % of 500 mesh Norton crystolon
powdered silicon carbide. The mixture was prepared in
hexane and then vacuum evaporated to dryness and ball
milled for 45 min. to give a fine powder. Six grams of the
powder was subjected ~o the following conditions to prepare
each pellet.
* Trademark
O
29
Pellet Preparation
Pressed at a Pressure TLme
: (Rsi~_ (min?
A 175 8,05)0 12
B 250 8,000 10
C 250 10 9 0~)0 10
D 17~ 10,000 10
E 300 8,000 10
F 250 8,000 3Q
G 250 10,000 30
All of the samples formed nice, even pellets
except Sample E whirh delaminated. When fired in the Astro
furnace these materials give ceramic pellets.
Example 10
The polymer of Example 1 was mixed in a 40/60
weight ratio with 320 mesh Norton Crystolon beta-~ilicon
carbide powder using a solution-evaporation-grinding
technique. Thus, 20.64 gms of polymer was dissolved in 80
ml of hexane to which was added 30.25 gms of 320 mesh
silicon carbide. It was then evaporated to dryness to give
a soft material which was ground to a powder using a mortar
and pestle rather than the ball mill, The fine powder was
then molded in a pellet mold at 175C under 7500 psi for 30
minutes. The resulting pellet was a smooth, very nice
pellet. When heated in the Astro furnace, this material
gave a ceramic material.
Example 11 - Preparation of a polymer from a mixture of
disilanes and a monosilane
A disilane mix~ure similar in composition to that
found in Example 1 (42.0 gms) and 41. 6 gms of C~3SiC13 were
mixed in a 500 ml., 3-necked, round-bottomed glass flask
equ:ipped as in Example 1. ~examethyldisilaæane (237 gms)
was added under an argon blanke~ with stirring. After
stirring about 10 minutes at room temperature, the reaction
mixture was hea~ed over 1 hour, 15 minutes to 275C and
held there for about 30 minutes. The reaction mixture
turned cloudy at about 95-100%C but cleared again at
135C. After cooling to room temperaturel there resulted a
pale yellow, clear, hard, glassy resin~
This material was fired in the furnace in a
graphite crucible to 1200C over a 2 1/2 hour period. The
ceramic resulting from this firing was obtained in 53
weiyht % yields. It was a lo~ density foam-like ceramic.
Example 12 - Preparation of an article coated with a
filled ceramic
A polymer prepared similar to Example 1 was mixed
with Norton 1000* mesh beta-silicon carbide in a weight
ratio of 10 gms to 10 gms. This material was then mixed
with lO0 gms of dry hexane. This slurry was evaporated
under vacuum until a paint-like viscosity of the slurry was
obtained. A graphite disc was dip coated with the slurry
and allowed to air dry. It was then heated in air at 125C
* Trademark
31
for 30 minutes and at 150C for 30 minutes to dry the
coating. The coated disc was then heated to 1200C in an
ine~t a~mosphere over a 2 1/2 hour period a~ld then allowed
to cQol~ The filled ceramic coating had remained intact
during the pyrolysis, showing large areas o:E a smooth,
uniform continuous coating. In the areas where the coating
was thic~er~ it was pock-marked.
- Ceramic fibers from a silazane polym4r
A polymer was prepared similar to ~hat ~ound in
Example 1. This material, a clear solid hard resin, was
melted and extruded into fibers using conventional fiber
extruding equipment. The fibers were then fired in the
furnace under argon to 1200C after being treated as
follows:
treatment result
~ none
B heat at 200C solid clear
1 hour iber
C 15 min. dist L H2O ~lear fiber turned
at 75C then heat opaque-soft
1 hr. at 200C
D 15 min in 0.1 N HCl dissolved in acid
at 75C
E 15 min. in dist. clear fiber turned
H2O at 25C then opaque-soft
1 hour at 200C.
F 15 min. at 100C heat -~
100~ hu~idity
32
All samples were given mild heat treabment :Eor 18 hours,
then fired.
After 1- ~
result
A Fibers retained shape/good quality
B Fibers retained shape/excellent
quality
C Fibers rPtained shape/poor quality
E Fibers retained shape/poor quality
F Fi~ers retained shape/good quality
Example 14
A polymer similar to that found in Example 1 was
prepared and melt extruded into small diameter fibers of
about 12~. These straight fibers were placed on a 6" x 4"
piece of graphite which had been previously baked out at
1500C for three hours in vacuo and the graphite was rolled
up in such a manner that the fibers were main~ained
straight and held snugly in place. This roll wa~ then
placed in a graphite crucible and fired to 1200C under
argon to g ive hara, dark colored fibers.
When the polymer was extruded into small diameter
fibers and heat treated in air prior to firing at
1200C.according to the schedule below, the resulting
fibers were soft and pliable.
33
Schedule
1 hr/75C
0O5 hr/125C
0.5 hrflS0C
1.~ hr~l75~C
1.0 hr/200C
1.0 hr/225C
1.0 hr/250C
0.33 hr/275C
Exam~le 15
The polymer of Example 1 was mixed in a 30/70
weight ratio with 320 mesh Norton Crystolon beta-silicon
carbide using the solution-evaporation-ball mill technique.
The material was then press molded at 10,000 psi and 175C
for 30 min. to give a very ~mooth glassy surfaced pellet.
This pellet was fired to 1200C over a 6 hour period to
give a ceramic pellet with a binder char yield of 50~.
