Note: Descriptions are shown in the official language in which they were submitted.
4*` `j 1304~75
pct 36503
Docket No. 36503
The present invention relates to a process for preparing
silicon-containing preceramic polymers that is particularly useful
for making silicon nitride and silicon nitride/silicon carbide and
silicon oxynitride ceramics and for their pyrolysis to such ceramic
materials.
There is a great deal of interest in preceramic polymer
; materials, which can ba pyrolyzed to yield silicon carbide, silicon
nitride, silicon oxynitrida and other silicon-based cera~ic
materials. R.W. Rlce, mer~ Ce~ oc,,_Bull~, 62: 889-892 tl983).
Applications for such polymers include, among others:
1. formation into complex shapes and subsequent pyrolysis to
give a ceramic material of the same shape,
I-j 2. spinning into contlnuous fibers whose subsequent pyrolysis
I yields ceramic fibers;
3. as a matrix material for carbon or ceramic fibers, or as a
binder for ceramic powders (with subsequent pyrolysis to form a
ceramic body);
4. oxidation-resistant coatings on otherwisc oxidlzable materials
(such as carbon/carbon composites) - after the polymer coating is
made, it can be pyrolyzed to gi~e the resistant ceramiclcoating
. S. infiltration of porous ceramic bodies such as ones obtained ;~
~ from reaction-sintered silicon nitr~de by the polymer itself (if
-~
!
.
~:~04~37S
liquid) or by a solution of the polymer, with subsequent pyrolysis to
form a ceramic, resulting in better strength, oxidation resistance,
etc., of the body; and
6. formation of thin films of the c~ramic material for
electronics applications.
For instance, Penn et al., ~ pl. Polvmer Sci.. 27: 3751-61
(1982) describe tha preparation of silicon carbide-silicon nitride
fibers from a polycarbosilazane precursor. Tris(N methylamino)
methylsilane monomer was formed by reaction o~ monomethylamine and
methyltrichlorosilane in dry petroleum ether and a polycarbosilazane
resin was formed by passing the monomer over glass Raschig rings at
520C. The brittle polymer was soluble in methylene chloride and
chloroform, etc. This product was spun into fibers, crosslinked in
air and then pyrolyzed to give ceramic fibers.
Other polymer precursors for forming silicon carbide and silicon
nitride ceramics have been described in U.S. Pat. Nos. 3,108,935;
3,853,567; 3,892,583; 4,310,651 and 4,312,970. These linear or
crosslinked polymers and processes :Eor producing ceramic materials
have generally been found to be deficient in one or more ways.
S. Yajima, Amer. Ceram. Soc. Bull , ~2: 893-898; 903 (1983)
discloses using (CH3)2SiC12 as a starting material for a
preceramic polymer for the preparation of SiC-containing cer~mics.
The polymer of Ya~ima is prepared by sodium metal condensation of
(CH3)2SiC12 to result i~ a polysilane, -[(~H3)2Si]n- (n
is approximately 30). This polysilane can then iorm either a "Mark
I" polymer or a "Mark III" polymer depending upon the treatment
used. Heating in an autoclave under argon at 100 kPa at
450-470C for 14 hours results in a Mark I polymer while adding
a few percent of a polyborodiph~nylsiloxane and heating under
nitrogen at ambient pressure at 350C for 10 hours results in the
Mark III polymer. In either case, the polysilicon backbone is
;
~ -2-
~3~7S
converted to a polymeric chain in which the main repeat unit is:
ICsH3
[- i-CH2]- (I)
The Mark I pol~mer also contains some -[(CH3)2SiCH2]- units. The
Mark III polymer contains some Si-Si bonds in the form
-[(CH3)2si-si(cH3)2]n((n-2-8) units and a low percentage of
[(C6H5~2SiO] units. l'hese preceramic polymers can be processed
to give ceramic fibers containing SiC, some free carbon and some
Si02. However, there are problems associated with these
polycarbosilane-derived ceramics. They have a tendency to crystallize
below 1200C, they have a SiO2 content as a result of an oxidative
cure step, and free carbon and a relatively low ceramic yield is
obtained upon their pyrolysis for a commercial product. While the
ceramic yield for the Mark III polymer is 68~, the yield for the Mark I
polymer is only 54%.
Silicon oxynitrides are another important group of ceramics. This
ceramic material has most of the same advantages as sillcon nitride,
but is expected to have a better oxidation stability. These are high
refractory materials able to withstand temperatures up to about
1500C before decomposing. Although K. Okamura et al, Chem. Lett,
(1984): 2059-2060 (See also K. Okamura et al, Fifth Int. Conf, on
Composite Materials, July 29 - August 1, 1985, Proceedings: 535-S42),
reported obtaining silicon oxynitride fibers after pyrolysis under
ammonia, of SiO2-containing polycarbosilanes ~having
CH3Si(H)CH2] as the major repeat unit), this was an expensive and
inef~icient process.
U.S. Patent 4,482,669 issued November 13, 1984, describes
organopolysilazane preceramic polymers whose pyrolysis gives a mixture
of silicon carbide and silicon nitride wherein, generally, neither
component is in large excess over the other. These polymers were
obtained by the reaction of a base (such as an alkali metal hydride,
amide, etc.) with the ammonolysis product of a dihalosilane, for
-3-
s
~xampla, CH3S~HC12 whlch result3 in a pol~m~rization proc~3~
balieved to in~lude th~ Dyt~r~ UiLLI ~ (DHCD) reactiDn ~hown
in ~q. A.
ba~s / N ~
2 -~L-~- ~ ~ 2 ~2 ~/si Si / (A)
H H N
The action of a catalytic smount of the bs3a on thos~ cyclic
oligom~r~ link3 thom toge~h~r ~ia such cy~lodl~ilazan~ units l~to
sh~t-lik~ array. Tr~atm~nt of, for ex~mple, th~ CH3SL~C12
a~onolysis product by th~ bas~, usually KH (0.5-4 mol percen~ ba~t
on CH3SiH~H uni~s), providas a polysil~zana inten~adiate of ~ypo
[(CH3s~H~l)a~cH3s~N)b(cH3slxNK)cln~ l.o. a nll~in~"
poly~ar which ~ill con~ains re~ctive 3ilylamlds functlons. Thl~
~li~ing" poly~ilazano $n~rm~dlat~ can b~ ~ra~sd wit~ a suit2bl~
alec~rophlle, such a3 CH3I or 8 chloro~ilan~, to "nautralizo~ th~
r~acti~ silyl~ida functlon~. Ulti~at~ly, on pyrDlyYia in a~ in~rr
ga~ s~rea~ (N2 or Ar~ to lOOO~C, the yield o~cer~ic re~iduo i~
high (80-85~, A ~ical compo~it~o~ o such a c~ra~ic matari~l is
0.9 Si3N~ + 1.3 51C ~ 0.75 C or, o~ n welg~t ~ b~s, 67
Si~Nh, 283 S~C and.5~ C.
U.S. Patents Nos. 4,645,807 issued February 24, 1987
and 4,650,837 issued March 17, 1987, deæcribe methods for
converting organosilicon polymers containing Si-H repeat units
to new and useful preceramic polymers and ceramic materials.
The preceramic polymers, which are prepared by reacting either
~; an organopolysilane or a polycarbosilane with a silylamide
result in preceramic polymers whose pyrolysis gives a mixture
of silicon carbide and silicon nitride ceramic materials, which
are generally rich in silicon carbide.
It would be useful to have a polymer precursor that is
formed from readily available and relatively inexpensive
starting materials, that is stable at room temperature, is
fusible and/or soluble in..... ~... ,.............. ~
D
~3~'1L875
organic solvents and whose pyrolysis can provide a high
yield of ceramic products. It would also be useful to be
able to ha~e such a polymer precursor which forms a ceramic
material upon pyrolysis that i~ rich in the silicon nitride
component.
Summary of the Invention
We have found that reaction of a polymeric
silylamide, which is the intermediate formed from the
dehydrocylodimerization reaction (DHCD) of the
coammonolysis product of [RlSiHX2] and [R2SiX3~ where R1,
R and X are as defined above, with an organosilicon
pol~mer containing Si-~ repeat units yields new polymeric
organosilicon compounds which are useful preceramic
materials. Upon pyrolysis these "hybrid" polymers
typically qive ceramic yields significantly better than
obtained for the original organosilicon polymer compound
alone. The polymeric silylamide may be preformed and
added to the Si-H containing organosilicon polymer.
Alternatively, one may prepare the silylamide in situ, in
the presence of the organosilicon compound.
The above polymeric silylamide is generated by
treating the coammonolysis product of R1SiHX2 and R2SiX3
(R and R are as defined above) with a basic catalyst
capable of deprotonating the hydrogen from a nitrogen atom
adjacent to a silicon atom also referred to as
dehydrocylodimerization. With either preformed
polysilylamide or an ln situ silylamide procedure, the
reaction mixture containing the organosilicon polymer
having Si-H repeat llnits and the polysilylamide is stirred
at room temperature and preferably heated at reflux in a
suitable solvent such as tetrahydrofuran to complete the
reaction. The resulting solution is then cooled and
quenched typically with an organic halide or a silicon
halide to produce the preceramic organosilicon polymers of
the present invention. Preferably the organosilicon
polymer is a polysilane compound of the formula
-- 5 --
~13~487S
[(RSiH)X(RSi)y3n, (where x ~ y ~ 1, n i~ an integer greater
than 1, R is a lower alkyl group having from 1 to about 6
carbon atoms, a lower alkenyl group having from 2 to about
6 carbon atoms, a substituted or unsubstituted lower aryl
group having from 6 to about 10 carbon atoms~ or a tri
(lower)alkyl- or di(lower)alkylsilyl group), a poly-
carbosilane polymer containing repeat units o the formula
[RaSi(H~-(CH2)q], i.e.,
a~
~~i~(CH2)q~ (II)
(where q is an integer 1 or greater, Ra is H, a lower
alkyl group having from 1 to about 6 carbon atoms, a
cycloalkyl group having Prom 3 to about 6 carbon atoms, a
substituted or unsubstituted lower alkenyl group having
from 2 to about 6 carbon atoms or a substituted or un-
substituted lower aryl group having from 6 to about 10
carbon atoms), or an organohydrogen-siloxane polymer
containing repeat units of formula [RbSi(H)o]n/ i.e.,
~ Rb
-~i-O- (III)
~where n is an integer 1 or greater, Rb is a lower alkyl
group having from 1 to about 6 carbon ~toms, a cycloalkyl
group having from 3 to about 6 carbon atoms, a substituted
or unsubstituted lower alkenyl group having from 2 to
about 6 carbon atoms or a substituted or unsubstituted
lower aryl group having from 6 to about 10 carbon atoms).
Aryl-substituted polymers of the type [RaSi(H)-
(CH2)q~, '[RSiH]n and [RbSi(H)o]n (e.g., where R, Ra or Rb
is phenyl), react in the same way as ths above described
polycarbosilanes, organopolysilanes and polysiloxanes to
give new polycarbosilane/organopolysilazane, organopoly-
silane/organopolysilazane and polysiloxane/organopoly-
silazane hybrid polymers, respectively.
- 6 -
~ ~,
: "
~L3~a~S
The polymer~ formed by thi~ method can then bepyrolyzed to yield cera~ic materials in high yield.
~çtailed Descrip~ion of the Inven~ion
The following description of the invention includes
not only the method ~or preparing preceramic polymers by
reacting a polymeric silylamide with an organosilicon
polymer, to which the present application is directed, but
also a method for preparing preceramic organosilicon
polymers comprising thP ~teps of reacting in solution
anhydrous ammonia with a mixture of RlSiHX2 and RSiX3,
thereby forming a mixture of precursor polymers; and
reacting the precursor polymers in the presence of a basic
catalyst capable of deprotonating the NH ~unctions in the
precursor polymers to form the preceramic polymer. The
latter method is being made the subject o~ a divisional
application.
We have now discovered that by using the coam-
monolysis product of a mixture of a dihalosilane and a
trihalosilane, one can obtain a preceramic polymer whose
pyrolysis results in a ceramic material richer in silicon
nitride than the polymer obtained by using the. ammonolysis
product of the corresponding dihalosilane alone. ........
r~ ~ 7 --
~13~
.
Additionally, the coammonolysls product i9 often more soluble than
the ammonolysis product of the corresponding trihalosllane, and
because an important requirement for a useful preceramic poly~er is
that it be processable, i.e., fusible, and/or soluble ln organic
solvents, the coammonolysis product is preferable.
Preferably, the dihalosllane is of the formula R15iHX2,
wherein Rl is a lower alkyl group having from 1 to about 6 carbon
atoms, a substituted or unsubstituted cycloalkyl group hav~ng from 3
to about 6 carbon atoms, a substituted or unsubstituted lower alkenyl
group having ~rom 2 to about 6 carbon atoms, or a substituted or
unsubstituted lower aryl group having from 6 to about 10 carbon
atoms, while X is a halogen, preferably, fluorine, chlorine, bromine
or iodine. More preferably, Rl is a lower alkyl group. Nost
preferably, Rl is CH3. X is preferably chlorine.
Preferably, the trihalosilane has the formula RSiX3,
wherein R is hydrogen, a lower alkyl group having from 1 to about 6
carbon atoms, a substituted or unsubstituted cycloalkyl group having
from 3 to about 6 carbon atoms, a substituted or unsubstituted lower
alkenyl group having from 2 to about 6 carbon atoms, or a substituted
or unsubstituted lower aryl group having from S to about 10 carbon
atoms and X is a halogen, preferably, fluorine, chlorine, bromine or
iodine. Nore preferably, R is a hydrogen or a lower alkyl group.
Still more preferably R is hydrogen or CH3. Most preferably, R ls
hydrogen. X is preferably chlorine.
The coammonolysis reaction is carried out in any organic solvent
in which ~he two reactants are soluble. Solvents which may be used
include ethers such as dialkyl ethers, particularly diethyl ether
(Et20); cyclic ethers such as tetrahydropyran, l,~-dioxane,
preferably tetrahydrofuran (THF); glycol ethers; aliphatic
hydrocarbons such as pentane, hexane; and aromatic hydrocarbons such
as benzene, toluene, xylenes. Other useful solvents are well known
to the person of ordinary skill in the art, based upon this
disclosure. The RlSiHX2/RSiX3 mixture is then reacted with
sm=onia in such a sol~ent to tffoct ~he coa:monolysis teaotion.
:,
.',,
~304~S17~;
In a pref0rred embodiment of the present invention, the
coammonolysis product is treated with catalytic quantities oE a base
capable of deprotonating the NH functions in the resultant
coammonolysis product, for example, KH, in an organic solvent. A
dehydrocyclodimerization reaction (DHCD) takes place, which results
in a preceramic polymer that gives high ceramic yields upon
pyrolysis. Preferably, the base is an alkali me~al, an alkal$ metal
hydride, an alkaline earth metal hydride, an alkali metal amid0, an
alkaline earth metal amide, a complex alkali metal hydride, e.g. KB
(sec-Bu)3H, LiAlH4, etc., alkali and alkaline earth metal
silylamides, an alkali metal organic compound and the like. More
preferably, the base is KH. Only small amounts of the base are
necessary (0.1-10 mole percent based upon the NH containing repeat
unit) because the reaction is catalytic.
The coammonolysis product is reacted with the base in any organic
solvent, in which the coammonolysis product is soluble without
reaction. Such organic solvents include ethers, such as dialkyl
ethers, preferably diethyl ether; cyclic ethers, for example,
preferably, THF; glycol ethers, aliphatic hydrocarbons such as
alkanes, arenes ? and combinations thereof.
The temperature at which this reaction takes place generally
ranges from about -10C to about +30C. After the reaction is
complete, the mixture may be quenched with an electrophile, EX,
capable of reaction with residual silylamide functions. E is any
organic group, preferably, a lower alkyl group or silyl group; X is
preferably a halide, sulfate or sulfonate. The electrophile can be
an alkyl halide, sulfate or sulfonatz; a halosilane; or the like.
Typically, CH3I or a chlorosilane is used although other equivalent
electrophiles well-known to those skilled in the art can also be
used. This quenching limits the reactivity of the "living" polymer
intermediate.
l3l~a7s
The preceramic polymer produced by the DHCD reaction typically is
a white solid, which is produced ln virtually quantitative yield.
When Rl was CH3, X was Cl and R was H, the proton NMR spectra of
the products showed an increase in the SiCH3/SiH + NH proton ratio,
while the relative SiH/NH ratio was unchanged. This indicates that a
hydrogen loss had taken place.
In the DHCD reactions, the molecular weight of the qolid product
was greater than that of the starting coammonolysis product, thus a
polymerization reaction had occurred. The conversion of the oils
which typically are formed in the coammonolysis reactions to the
solids of the present invention results in a material that is more
easily handled.
Pyrolysis of the white solid obtained in these base-catalyzed,
DHCD reactions under argon from 50 to 950C, typically produces
black ceramic residues. The ceramic yields were generally
excellent. These ceramic materials have a rich silicon nitride
content.
Relatively pure silicon nitride material can be formed when the
preceramic polymer is pyrolyzed in a stream of = onia rather than of
an inert gas such as nitrogen or argon. The ammonia reacts with the
polymer at higher temperatures to cleave methyl groups from silicon,
so that essentially all carbon is lost. For example, where ~1 is
CH3 and R is H, the pyrolysis of the preceramic polymer derived
from the DHCD product of the 1:1 co = onolysis (in THF) product to
1000C in a stream of ammonia produced a white ceramic residue in
high yield containing only 0.29~ by weight C, with the remainder
being silicon nitride. When both Rl and R were C~3, the
pyrolysi~ of the preceramic polymer derived from the DHCD product of
the 6:1 coammonolysis (in Et20) product to 1000C in a stream of
ammonia produced a white ceramic residue containing only 0.36~ by
wei~ht of carbon. Similarly, pyrolysis of a 3:1
CH3SiHC12:C2H5SiC13 (co = onolysis product in Et20)
KH-catalyzed DHCD (in THF) product to 1000C in a stream of ammonia
produced an essentially pure white residue with a very faint brown
-10-
`` ~30~'7S
tinge. However, alkenyl groups appear to be more intimately involved
with the pyrolysis chemistry. Pyrolysis oE a control ammonolysis
product of CH2-~HSiC13 to 1000C in a stream of ammonia
produced a brown ceramic residue, while pyrolysis of a 3:1
CH3SiHC12:CH2-CHSiC13 (coammonolysis in THF) KH-catalyzed
DHCD (in THF) product in a stream of ammonia produced a ceramic that
was black with touches of white and brown.
A wide range of RlSiHX2:RSiX3 ratios can be used in
preparing the coammonolysis product, the mole ratio can be for
example from about 20:1 to 1:20, it preferably ranges from about 8:1
to 1:7. Generally, the higher the mole % of dihalosilane used, the
more soluble is the coammonolysis product. However, this product
generally forms a ceramic material in lower yields. In addition, at
a high mole % oi trihalosilane, the DHCD reaction has less effect.
The DHCD reaction at high mole ~ of trihalosilane should be limited
to the soluble reaction product. For certain halosilanes, however,
the coammonolysis product obtained with high levels of trihalosilane
has properties that are quite useful without a subsequent DHCD
reaction. ~hen a DHCD reaction is contemplated, the mole ratio of
RlSiHX2:RSi~3 is preferably from about 8:1 to about 1:6, more
preferably from about 8:1 to about 1.2, even more preferably about
6:1 to about 1:1. A higher mole ratLo of dihalo~ilane to
trihalosilane, such as about 6:1 to 3:1, provides a coammonolysis
product that is typically soluble, which, when sub;ected to a DHCD
reaction, results in a preceramic polymer that provides excellent
yields of ceramic material. However, a ratio of about 2:1 to 1:2,
preferably about 1:1, produces a preceramic polymer whose pyrolysis
in an inert atmosphere, typically, results in a greater percent of
silicon nitride in the ceramic material than obtained on using the
higher mole ratio of dihalosilane. Thus, depending upon the desired
end product and reaction sequences, the mole ratio of
dihalosilane:trihalosilane will vary. The particular ratio to use in
a given situation can readily be determined empirically by the
desired end use based upon the present disclosure.
-11-
~3~L875
For example, ammonolysis of HSiCl3 alone gives mostly
insoluble, highly cross-linked products. The highest yield oP
soluble products (47~) was obtained when the HSiC13 ammonolysls was
carried out at -20C (at 0C the yield of soluble product was
17%, at -78C it was 20%). However, these lnitially soluble
silazanes become insoluble after the solvent is removed. Since the
main requirement of a preceramic polymer is that it must be
processable, i.e., uslble and/or soluble in organic solvents,
ammonolysis of HSiCl3 alone is not satisfactory.
When R is H, and Rl is CH3 and X is Cl, the preferred ratio
of RlSiHX2:RSiX3 ranges from about 8:1 to about 1:4; more
preferably, the ratio is about 6:1 to about 1:2 when a DHCD reaction
is used; more preferably about 6:1 ~o about 3:1 when one is concerned
with the solubility of the starting materials; and about 3:1 to about
1:2, more preferably about l:l when one is interested in the
resultant weight percent of the ceramic residue obtained after
pyrolysis in an inert atmosphere; and l:l to about 1:4, most
preferably about 1:3 when the coammonolysis product without a DHCD
reaction is desired.
In either Et20 or THF, the 6:1 and 3:1 ratios used in the
co = onolysis produced polysilazane oils with molecular weights in
the range 390-401 g/mol and 480 g/mol, respectively. When a l:l
reactant ratio was used, waxes of somewhat higher (764-778 g/mol)
molecular weights were obtained in both solvents. In the l:l
reaction carried out in Et20 the yield of soluble product was only
40%, but in THF it wa~ nearly quantitativ~.
The oils produced in the 6:1 and 3:1 reactions in Et20 are
stable on long-t~rm storage at room temperature in the absence of
moisture (e.g., in an inert atmosphere box). However, the waxy
product of 1:1 reactions in (Et20) and all the coammonolysis
products prepared in THF formed gels (i.e., became insoluble) after
3-4 weeks at room temperature, even when stored in a nitrogen-filled
dry box. (See Tables l and 2).
. ' ............. '
:
,
' ., ;'""'`''', '''''''''"' '"' " ' ''' ~
~30487S
T~BLE l
COAMMONOLYSIS OF METHYLDI_HLOROSILANE 4ND
TRICHL~ ILA~E I~ DIETHYL ETHER MEDIUM.
DEHY~ROCYCLODIMERIZATION OF THE PRODUCTS~
CH3~Ç12 Ceramlc
HSiC13 _ Yield by
ReactionMolar Ratio . Product Yield~%)_~W TGA. ~ -
6 oil 74 390 33
Coammonolysis
in Et20 3 oil 79 484 41
1 wax 40 778 72
. _
6 solid 1001300 85
DHCD Reaction,
1~ KH in THF 3 solid 99 1250 88
1 solid 931630 87
-13-
.,, !
~3~ '7S
CoAMyç~LoLysIs oE ~ETHx~D~yL8a~
TRICHLOROSI19E~ i~ T~E_~enI~.
DEHYDROCYCLODIMERIZATION QF ~E_PRoDUCTS.
CH3SiH 2 Ceramic
HSiC13 _ Yield
Reaction _ MoLsr RatiQ_ Product Yield(~) M~ b~ TÇA~
6 oil 91 401 28
Co = onolysis
in THF 3 oil 85 482 67
1 wax 94 764 78
_ _ _ _
6 solid 961094 82
DHCD Reaction,
1% XH in THF 3solid97 942 82
1 solid 931620 86
-14-
., .. ~
~30~a7s
The integrated proton NMR spectra of the various coammonolysis
products establish their approximate constitutions:
Ç~3sl~cl2~ 3 ~io Ap~roximflte Eorm la
6:1 [CH3SiHNH]l.o[Hsi(NH)l.5]o.l7
3:1 [CH3SiHNH]l.o[Hsi(NH)l.5]o.33
1:1 [CH3SiHNH]l.o[Hsi(NH)l.5]o.37
These formulas carry no structural implications, they merely are
average formulations. The HSiC13 component probably
introduces both SiNHSi bridglng and SiNH2 terminal groups
into the structure. From these approximate formulas one can
calculate expected % C, H, N and Si compositions and, in
general, the agreement of observed % C, H and N for the 6:1 and
3:1 products with these values is good (+ 0.55~). (Analyses
were not obtained of the wa~es prepared in the 1:1 reactions).
The pyrolysis of these coammonolysis products was studied.
The 6 CH3SiHC12:1 HSiC13 ammonolysis product gives low
ceramic yields on pyrolysis. Pyrolysis of the 3:1 products
gives incr ased ceramic yields, whi:Le pyrolysis of the most
highly cross-linked 1:1 ammonolysis products gives quite good
ceramic yields*, 72~ for the product prepared in Et20, 78% for
that prepared in THF.
*Ceramic yield is defined as
wei~ht of residue x_100 _
weight of sample pyrolyzed
-15-
:
~L3~4~7~
Sub;ecting these co = onolysis products to the DHCD
reaction, using KH as a base resul~ed in white solids in
virtually quantitative yield. The solids are easier to handle
and store than the oils. Pyrolysis of the white solids
obtained in these KH-catalyzed DHCD reactions (under argon from
50-950C) produced black ceramic residues, with the exception
of the 1:1 THF ammonolysis-deri~ed solid which left a brown
residue. The ceramic yields were excellent (all greater than or
equal to 82~, with the highest being 88~).
Analysis of bulk samples of the ceramic materials produced
ln the pyrolysis of the various XH-catalyzed DHCD products shows
that a hlgher Si3N4/SiC ratio has been achieved (Table 3):
for the 1:1 coammonolysis products-derived polymers, 86
Si3N4, ~ SlC and 5% C (TH~ coammonolysis) and ~3~
Si3N4, 11% SiC and 6~ C (Et20 coammonolysis); for the 3:1
and 6:1 coammonolysis products-derived polymers: 77~ Si3N4,
18-19~ SiC and 4-5~ C (Et20 co { onolysis) and 74% Si3N4,
20~ SiC and 5-6% C (THF coam~onolysis).
However, the KH-catalyzed DHCD reactions with the 1:3
coammonolysis-derived polymer were slow, producing soluble
products in poor yields. Pyrolysis of this material produced a
black ceramic.
There are situations where one desires a ceramic material
and/or preceramic polymer that contains differing amounts of
silicon carbide and silicon nitride. The present process can ba
used to result in a preceramic polymer that will typically
produce a ceramic material that is enriched in silicon nitride
when compared to reactions in which the precursor dihalosilane
is used alone a~ the initial starting material.
For example, when Rl was CH3, X was Cl, and R was CH3,
CH2~CH or C2H5, the Eollowing results were obtained.
As control experi~ents, the ammonolysis of CH3SiC13
alone was studied. Ammonolysis of this precursor in Et20 gave
~L3~ '7S
a 46~ yield of soluble solid product, molecular weight 70Z
g/mol, ceramic yield (by TGA to 950C) 56~. A similar
CH3SiCl3/NH3 reaction in THF gave soluble solid produat in
82~ yield, molecular weight 672 g/mol, ceramic yield (by TGA)
69%. By proton NMR (C_3Si/N_ integration), the Et20 product
may be for~ulated as [CH3Si(NH)1 3]x~ the THF product as
[CH3Si(NH)1 6]x (This is only a rough approximation
because integration of the broad N~ signals is rather
: inaccurate~. The results o-f the coammonolyses of CH3SiHC12
: -17-
`` ~L341~ 7S
PRQDUCTS OF THE REACTIQNS IN TABLES 1 AND 2
CH3SiHC12/
HSiC13 Molar
Ratio _ Product C.~ H.~ _ N.% _ S~
of a~monolysis 17.75 7.53 25.80
in Et2O
6 of DHCD 20.05 6.73 25.82
ceramica 10.36 30.94 58.92
--
of } onolysis
in Et2O 16.19 7.31 27.04
3 of DHCD 17.61 6.46 25.85
ceramicb 9,35 30.79 59,99
1 of DHCD 14.10 6.12 27.60
ceramicC 9.10 0.70 32.56 56.52
__
of am~onolysiS
; in THF 18.22 7.89 25.21
6 of DHCD 19.89 6.85 25.08
cerAmicd 11.72 29.71 59.03
of ammonolysis
in THF 16.10 7.45 25.51
3 of DHCD 18.00 6.71 27.32
- ceramice 11.21 29.77 59.09
1 of DHCD 12.42 5.97
ceramicf 7.74 0.54 34.29 57.17
aCalc. 77% (by weight) Si3N4, 18% SiC, 5% C
bCalc. 77% Si3N4, 19% SiC, 4% C
Calc. 83~ Si3N4, 11% SiC, 5.7~ C
dCalc. 74~ Si3N4, 20% SiC, 6% C
eCalc. 74% Si3N4, 20% SiC, 5~ C
fCalc. 87~ Si3N4, 8% SiC, 5.4% C
~304B'75
and CH3SiCl3 are gi~en in Tables 4 and 5. In all cases,
whether the solvent was Et20 or THF, oils ware obtained in
high yield. These were of low (300-500) molecular weight and
their pyrolysis gave only low ceramic yields. The KH-catalyzed
DHCD reaction of these coammonolysis products gave white solid
products of higher (ca. two-to-threefold) molecular weight.
Based upon the lH NMR analysis, th~ following formulations
of the products were generated:
cH3siHcl2/
CH3SiC13 Reaction
L_~3~lQ Solv_nt Formula
6 Et20 [CH3SiHNH]1 o[CH3Si(NH)1.5]0.26
THF [CH3SiHNH]1 o[CH3Si(NH)2.1]0.27
3 Et20 [CH3SiHNH]1 o[CH3Si(N~l)l.1]0.29
THF [CH3SiHNH]1 o[CH3Si(NH)1.1]0.29
Et20 [CH3SiHNH]1 o[CH3Si(NH)1.5]0.63
THF [CH3SiHNH]1 o[CH3Si(NH)1.8]0.80
These are only approximate constltutions, but agreement of combustion
analysas (C, H, ~) was fairly good for the for~ulations given. The
ceramic yields obtained on pyrolysis of these polymers were high:
78-82% for the products generated by initial coammonolysis in THF. In
all cases, a black ceramic residue resulted when the pyrolysis to
950C was carried out in a strPam of argon. As expected, the carbon
content (in the for~ of SiC and free C) was hi~her than that of the
CH3SiHC12/HSiC13-derived ceramics (Table 6): 12-18~ SiC, up to
9.5% carbon. Nonetheless, higher S13N4 contents than those
obtained when CH3SiHCl2 is used alone ( 67~) were obtained.
DHCD products of polysilazanes from a~onolysis in Et20:
75-76% Si3N4; 15-18% SiC; 7-9~ C.
-19-
~3~8~75
~ .
w~a~
METH~LTRICH~OROSILANE IN DIE~ ET~ER AND
DEHYDROCYCLODTMERIZATION OF THE PRODUCTS
Ceramic
CH3SiHC12/CH3SiC13 - Yield
Reaction _ Molar Ratio _ Product _ Yield(~) MW bv TGA.
Coammonolysis
in Et20 6 oil 75 376 21
3 oil 80 373 40
1 oil 81 526 44
1/3wax 89 627 --
1/6white solid 65 642 --
DHCD Reaction,
1% KH in THF 6solid 97 1260 82
3solid 100 795 78
1solid 98 786 78
1/3white solid 95 850 58
1/6white solid 90 1012 56
-20-
~3(~ 7S
TABLE_5
QND METHyLTRICHLOROSILANE IN THF~
DEHYDROCYCLODIMERIZATION OF THE PRODUCTS
Ceramic
CH3siHC12/C~3siC13 Yield
Reaction __ Molar Ratio Product Yield(~) MW _bv TGA.%
6 o~l 81 311 26
Coam~onolysis
in THF 3 oil 91 363 31
1 oil 89 484 44
1/3white solid 88 --- --
1~6white solid 98 --- --
6solid 72 1171 86
DHCD Reaction,
1~ KH in THF 3 solid 84 1170 83
1solid 100 838 82
.
1/3white solid 92 1180 76
1/6white solid 95 925 71
-21-
.
~;3g~48~5
TABLE 6
PRODUCTS OF THE REACTIONS OF TABLES 4 AND 5.
CH3siHcl2/
CH3SiC13 Analysis
Molar Ratio _ . _ Product C.% H.% N.% Si,~
of ammonolysis
in Et2O 20.248.02
6 of DHCD 21.85 7.09
ceramica 12.16 0.51 30.4457.23
_ _
of ammonolysis
in Et2O 20.01 7.90
3 of DHCD 21.67 7.26
ceramicb 13.04 0.72 31.0555.30
. _ . _
of ammonolysis
in Et2O 19.66 7.49
1 of DHCD 21.04 7.29 22.20
ceramicC 11.36 0.61 31.9056.35
of ammonolysls
in THF 20.26 8.06 23.79
6 of DHCD 21.85 7.02
ceramicd 12.87 0.60 29.3553.94
of ammonolysis
in THF 20.13 7.93
3 of DHCD 22.05 7.03
ceramice 12.36 0.63 29.5756.77
9..~ 8'75i
of ammonolysis
in THF 19.53 7.42
1 of DHCD 22.35 7.24
ceramicf 11.19 0.63 31.01 56.36
aCalcd. 76~ (by weight) Si3N4, 16~ SiC, i~ C
bCalcd. 78~ Si3N4, 12~ SiC, 9~ C
CCalcd. 80~ Si3N4, 12~ SiC, 8~ C
dCalcd. 76~ Si3N4, 154 SiC, 9~ C
eCalcd. 75~ Si3N4, 18~ SiC, 7% C
fCalcd. 79% Si3N4, 14~ SiC, 7~ C
gL3~17~
Changing the "monomer" ratio from 6 to 3 to 1 does not vary the
compositions of the final ceramic materials very much: the Si3N4
content varies by only 5~, while the SiC content shows a 6~ range and
the carbon content is within 2~ for all the materials.
To produce a ceramic material containing only Si3N4, the white
solid polysilazane derived from the DHCD of the oil obtained by
ammonolysis of 6:1 CH3SiHC12/CH3SiC13 in Et20 medium was
pyrolyzed in a stream of ammonia (to 1000C). A white ceramic
residue containing only 0.36~ by weight C resulted.
Essentially the same reactions were carried out using
vinyltrichlorosilane in place of methyltrichlorosilane
tCH3SiHC12/CH2-CHSiC13 molar ratios of 6, 3 and 1; ammonolysis
in Et20 and THF medium; subsequent KH-cataly~ed DHCD in THF: see
Tables 7, 8, and 9). Control experiments involving the ammonolysis of
CH2-CHSiC13 alone, in Et20 and in THF medium, were also
perfor~ed. In both solvents, glassy white solids were obtained. The
yield of soluble products in Et20 was low (61%); in THF it was
quantitative. The molecular weights were relatively high (1165 and
1185, respectively) and the ceramic yields obtained on pyrolysis to
950C were high (76% and 82~, respectively). This is a result, at
least in part, of a greater incorporation of carbon. Analysis of the
ceramic obtained in the pyrolysis of the CH2-CHSiC13 ammonolysis
(in THF) product showed a composition 71% Si3N4, 29% C.
The coammonolysis of CH3SiHC12 and CH2~CHSiC13 in ~t20
i
-24-
i 3~D~!37~i
~ '.
COA~ONOLYSIS QF METHYLDICHLOROSILANE AND
VIN L~RICHLOROSIL4NE I~ DIETHYL ET~
PEHYDROCYCLODIMERIZATIQN OF THE PRODUCTS
CH3SiHC12/ Ceramic
CH2;CHSiC13 ~ Yield
Reaction Molar Ratio Product Yield~? . MW_ by TGA.
Coammonolysis
in Et20 6 oil 86 305 43
3 oil 87 333 53
1 oil 90 605 74
DHCD Reaction,
1~ KH in T~F 6 solid 99 880 83
: 3 sol$d 98 999 84
1 solid 98 970 78
_ _ .
-25-
~3~8~7~
TABLE 8
C AMMONOLYSIS OF METHYI.~ICHLOROSILANE AND
VINyLTRTcHLoRos L~E__N_~E
D~HYDROCyCLODIMERIZA~ION OF THE PROD~
CH3SiHCl2/ Ceramic
CH2-CHSiC13 Yield
Reaction Molar Ratio _ Product _ Yield(~) MW _ bv TGA,~
Coammonolysis
in THF 6 oil 89 350 47
3 oil 92 361 57
1 oil 94 536 74
- DHCD Reaction,
1~ KH in THF 6solid 88 773 84
3 solid 100 716 78
- 1solid 99 777 85
.
,
-26-
`` ~3~'48~S
TABLE 9
PRODUCTS OF THE REACTIONS OF T4BLES 7 AND 8
CH3SiHCl2/
CH2-CHSiC13 Analysis
olar Ratlo _ _~roduet C% _ _H~ _ N% Si~ _
of ammonolysis
in Et20 22.80 7.86 23.91
6 of DHCD reaction 24.486.86 23.51
eeramiea 17.06 28.33 54.62
of ammonolysis
in Et20 24.39 7.65 24.59
3 of DHCD reaction 26.216.89 23.31
eeramieb 17.21 28.43 54.91
of ammonolysis
in Et20 26.83 7.08 24.73
1 of DHCD reaetion 27.666.48 25.14
eeramieC 20.87 29.09 49.85
_
aCaled. 71% (by weight) Si3~4, 17% SiC, 12% C
bCaled. 71% Si3N4, 17~ SiC, 12% C
CCaled. 73% Si3N4, 9% SiC, 18% C
dCaled. 69~ Si3N4, 19~ SiC, 12% C
eCalcd. 70~ Si3N4, 16~ SiC, 13% C
fCalcd. 71~ Si3~4, 11% SiC, 18~ C
~304~7S
and in THF medi~n gavs polysilazane oils in high yield, molecular
weights 300-600 g/mol. Pyrolysis of the coammonolysis products gave
higher ceramic yields, the higher the C~2-CHSiC13 content in the
chlorosilane mixture. Application of the K~-catalyzed DHCD reaction
to the ammonolysis products in all cases gave white solids of higher
molecular weight whose pyrolysis to 950C gave high (78-85~)
ceramic yields. However, their Si3N4 content was lower and their
carbon content (as SiC + free C) was higher than observed in the
ceramics from the CH3SiHC12/HSiC13 and CH3SiHCl~/
CH3SiC13 systems: For the CH3SiHC12/CH2-C~SiC13 ratio ~
6 and 3 products: 69-71% Si3N4; 16-19~ SiC; 12-13% C. For the
1:1 products: 71-73% Si3N4; 9-11~ SiC; 18~ C.
A mixture oE CH3SiHC12 and C2H5SiC13 (3:1 molar ratlo)
was treated wlth ammonia in Et20 and in THF at 0C. In both
cases, silazane oils, MW 360-370, were obtained in high yield.
Their cerc~nic yields on pyrolysis to 950C were low (15% and 23~,
respectively). Application of the DHCD reaction (1% KH in THF) to
these oils in both cases gave white solids with increased MW (972 and
860, respectively) and increased cer~nic yield on pyrolysis to
950C (81% and 78%, respectively). 'Fhe pyrolysis product in each
case was a black foam when the pyrolysis gas stream was argon.
Analysis of the ceramic products gave ~ C, N and Si values from which
compositions of about 71-73~ Si3N4, 14-17~ SiC and 11-12% C could
be calculated. Thus, there is essentially no difference between
thsse results and the calculated composition of the ceramic product
of the corresponding 3:1 CH3SiHC12/CH2-CHSiC13 system ~70-71
Si3N4, 16-17% SiC, 12-13~ C).
In the case of the present polymers, as is seen in Table 10, some
were self-curing and on pyrolysis gave ceramic fibers (those noted
"yes"). Others melted when heated, so that the fibers were destroyed
(those noted "no"). Conversion of the meltable fiber to an infusible
iiber by a cure step prior to pyrolysis will enable one to melt spin
these materials into fibers.
-28-
~3~ 75
TABLE 10
CERAMIC FIBERS AND_SiC POWDER COMPOSITES
Molar Ammonolysis Fiber on
Chlorosilanes_ _ Ratio _ Solvent ~3~ _PYroly~__a_
CH3SiHCl2/
CH2-SiC13 6/1 Et20 xb Yes
'~ 3/1 Et2O x No
" 1/1 Et2O x No
" 6/1 THF x Yes
n 3/1 THF x No
" 1/1 THF x Yes
CH3SiHC12/
HSiC13 6/1 Et20 x Yes
.. 3/1 Et2O x Yes
n1/1 Et2O x Yes
n6/1 THF x No
n3/1 I~F x No
"1/1 I'HF x Yes
-
CH3SiHC12/
CH3SiC136/1 E:t2O x Yes
n 3/1 Et2 x No
~ t2o x No
-
" 6/1 THF x Yes
3/1 THF x No
" 1/1 THF x Yes
a Yes - Fibers remained after heating to 1000C under Ar.
No - Fibers did not remain after pyrolysis to 1000C.
b x means a bar was made and pyrolyzed to obtain a ceramic bar.
-29-
~L39~4B7~
The "cure" step prior to pyrolysis can be accomplished when either
R or Rl is alkenyl by curing the fiber through hydrosilylation. This
reaction can be induced by ultraviolet and other hlgh energy radiation,
as well as by chemical free radical sources and transition metal
catalysts. These compounds can readily be selected by the person of
ordinary skill in the art and include H2PtC16 6H20, peroxide
and azo compounds, preferably organic peroxides, such as benzoyl
peroxide, more preferably azo compounds such as azobisisobutyronitrile
and the like. Preferably, a radiation source is used.
W irradiation, irradiation with an electron beam or an X-ray
source, etc. will cure the alkenyl containing polymer. Subjecting the
preceramic fiber to W irradiation (Rayonet Reactor) for 2 hours
results in an infusible fiber that does not melt upon subsequent
pyrolysis under argon, producing ceramic fibers. By incorporating C C
into the coammonolysis product, this strategy can be broadly applied to
the present invention. The addition of a third compound containing an
unsaturated functionality to the ammonolysis mixture results in a
mixture of ollgomers. The particular amount to be added to the
coammonolysis mixture will depend upon the desired US2 and compounds
being used.
Fibers were prepared in the following manner: In the dry box, a
few drops of toluene was added to a polymer sample and the resulting
mixture stirred with a glass rod until a sticky residue resulted from
which fibers could be drawn. These fibers (1/4" to 2" in length) were
placed in a boat, taken out of the dry box and placed in a tube furnace
flushed with Argon. The fibers were heated to 1000C at
10C~minute. The poly~ers listed in Table 10 were used in preparing
fibers.
The present polymers can be used as binders for SlC powder
processing.
Ceramic composite bars were prepared in the following manner:
In the dry box, a 100 ml, one-necked, round-bottomed flask was
charged with 0.6 g polymer and 2.4 g of commercial Fujima SiC powder.
-30-
~3~ 75
The flask was removed from the dry bo~ and charged with 25 ml of
toluene. me flask was placed in an ultrasonic bath for at least 15
minutes. The toluene was then removed on a rotary evaporator and the
residue then dried under vacuum at 0.03 mm Hg for at least 1/2 hour.
The SiC/polymer residue was ground with a mortar and pestle to produce
a fine powder. This powder was pressed in a 1.5" x 0.5" x 0 ln dle at
6000 lbs. for 5 minutes. The bar was then isostatically pressed at
40,000 lbs. Finally, the bar was pyrolyzed under Ar in a tube furnace
to 1000C.
The polymers shown in Table 10 were used to form composite bars.
All bars retained their rectangular shape upon pyrolysis.
In a different embodiment, the polymeric silylamide which is the
intermedlate formed from the DHCD reaction of [RlSiHX2] and
[R2SiX3] (wherein Rl, R2 and X are as defined above) can be
used to form another preceramic polymer. This poly~eric silylamide is
the intermediate formed aEter the DHCD reaction and prior to treatment
with an electrophile, such as Ch3I. This intermediate species
(sometimes also reierred to as a ~reactive 'living' polymer",
si].ylamide, poly(silylamide) or alkali metal sllylamide)n) can react
with electrophiles other than CH3I. We have discovered that the
reaction o this silyamide with an organosilicon polymer containing
Si-H repeat units (referred to as an Si-H containing organosilicon
polymer) results in novel preceramic polymers.
The Si-H containing organosilicon polymer is preferably a
polysilane compound of the formula ~(RSiH)X(RSi)y]n, (where x ~ y
1, n is an integer greater than 1, R is a lower alkyl group having
from 1 to about 6 carbon atoms, a substituted or unsubstituted lower
alkenyl group having from 2 to about 6 carbon atoms, a substituted or
unsubstituted lower aryl group having from 6 to about 10 carbon atoms,
or a tri(lower)alkyl- or di(lower)alkylsilyl group) (See U.S. Paten~
Application Serial No. 756,353 filed July 18, 1985), a polycarbosilane
polymer containing repeat units of the ormula
[RaSi(H)-(CH2)q],i.e.,
~a
-~i-(CH2)q~ (II)
(where q is an integer 1 or greater, Ra is H, a lower alkyl group
-31-
, .
~304~375
having from 1 to about 6 carbon atoms, a cycloalkyl group having
from 3 to about 6 carbon atoms, a substituted or unsubstituted
lower alkenyl group having from 2 to about 6 carbon atoms or a
substituted or un~ubstituted lower aryl group having from 6 to
about 10 carbon atoms) (See the aforementioned U.S. patent No.
4,650,837), or an organohydrogensiloxane polymer containing
repeat units of the formula C RbSi ( ~ ) ] b~,i.e.,
-~i-0- (III)
(where n is an integer 1 or greater, Rb is a lower alkyl group
having from 1 to about 6 carbon atoms, a cycloalkyl group having
from 3 to about 6 carbon atoms, a substituted or unsubstituted
lower alkenyl group having from 2 to about 6 carbon atoms or a
substituted or unsubstituted lower aryl group having from 6 to
about 10 carbon atoms) (See U.S. Patent Application Serial No.
849,390 filed April 8, 1986).
In accord with the present invention, treatment of, for
example, organopolysilanes with the silylamide will provide
higher molecular weight preceramic materials and improve the
ceramic yield.
We have now found that organopolysilanes such as
methylpolysilanes ([(CH3SiH)X(CH3Si)y]n) obtained in the above
reactions, upon treatment with catalytic quantities of
silylamides in accord with the present invention, yield
preceramic polymers of higher molecular weight which upon
pyrolysis give significantly higher ceramic yields. Such
polymers, when prepared as described herein, are soluble in
organic solvent.
Polycarbosilane polymers that are used in the prsent
invention preferably contain a multiplicity of repeat units of
the formula [R~Si(H)~(CH2q~ (where q and R~ are as defined above(
(hereinafter polymers containing such repeat units are referred
to as "polycarbosilanes"). The reaction of these
- 32 -
-~` i3(~4~
polycarbosilanes with an alkali metal silylamide results in
novel preceramic polymers. Typically, the prolysis of this new
polymer gives a black ceramic ................................
~i ,
: ~:
., 1 `
,. .
.~
- 3~ -
... :~ '
, ' '"~ ~ ' `' "
.. '. :': . .
"' .
.
l3~al~s
solid in a yield that is greater than that obtained on pyrolysis of the
parent polycarbosilane.
The polycarbosilane polymer should contain at least 25 mol~ % of
repeat units of the formula II, i.e. [RaSi(H)-(CH2)q], in addition
to other repeat units, such as [Ra2Si(CH2~q] (e.g. the Yajima
polymers). Preferably the polycarbosilane polymer contains at least 35
mole % of repeat units of formula II. More preferably, the polymer
contains at least 50 mole ~ repeat units of formula II.
The polymer may also contain a mixture of repeat units of the above
described formula, e.g., both [RaSi(H)-(CH2)q] and
[Ra'Si(H)-(CH2)q'] (Ra' and q' are defined the same as Ra and
q, respectively, but Ra' may be dif~erent than Ra and q'may be
different than q). Ra is pr~ferably a lower alkyl group, more
preferably Ra is CH3. Preferably q is equal to 1 - 3, more
preferably it i5 equal to one.
The polycarbosilane and silylamide are typically added in a weight
ratio o polycarbosilane: silylamide o~ about 10:1 or less. Preferably
this ratio is about 5:1 or less. More preferably the ratio is about
3:1 or less. Most preferably the ratio is about 1:1.
Additionally, the reaction of organohydrogensiloxane polymers
containing a plurality of repeat units of the formula [RbSi(H)O]n
~where n and Rb are as defined above) (hereinafter polymers
containing such repeat units are referred to as "polysiloxanes"), with
a poly(silylamide) also results in a novel preceramic polymer.
- The pyrolysis of this new preceramic polymer under a stream oi`
ammonia typically results in a hi~h yield of a white ceramic material.
By choos.ing the correct stoichiometry one is readily able to obtain a
ceramic material that is virtually only silicon oxynitride. This
process provides silicon oxynitrides at high yield and at low costs.
The pyrolysis of the preceramlc polymer of the present invention under
an inert atmosphere such as nitrogen or argon typically results in a
black ceramic solid in high yield. This black ceramic material
generally contains SiC, Si3N4 and SiO2 and can be used as a
binder or coating.
-33-
~30~L8~5
The polysiloxane polymer used in the present invention can be
readily obtained by the hydrolysis of the appropriate RbSiHC12
(where Rb is as defined abo~e). The hydrolysis may be steered to
give a high yield of cyclic [RbSi(H)O]n oligomer or to produce
higher molecular weight linear [RbSi(H)O] polymers. They yield o
cyclic oli~omers (n - 4, 5, 6,...) may be maximized by using the method
taught by Seyferth, D., Prud'homme, C; and Wiseman, G.H., Inor~. Chem ,
22: 2163 2167 (1983). Additionally, ona can use commercially available
[RbSi(H)O]n polymers.
The polysiloxane polymers useful in the present invention encompass
polymers having a wide range of [RbSi(H)O] repeat units. The number
of repeat units contained in the polymer will vary depending upon the
desired end product.
Preferably, the polysiloxane polymer should contain at least 25
mole g of repeat units of the formula III, i.e. [RbSi(H)O]n, in
addition to other repeat units, for example, [RbRb SiO],
[Rb Rb SiO], Rb and Rb are defined the same as Rb;
and Rb, Rb , and Rb may be the same as or different from each
other. More preferably the polysiloxane polymer contains at least 35
mole ~ of repeat units of formula III. Even more preferably, the
polymer contains at least 50 mole ~ repeat units of formula III. Most
preferably, the polymer contains at least 75~ mole repeat units of
formula III.
~ ith respect to the silylamide used, Rl is preferably a lower
alkyl group, more preferably CH3, while R2 is preferably H or a
lower alkyl group, more preferably H or CH3. X is pre~erably
chlorine, fluorine, bromine or iodine. The dihalosilane can be added
to the trihalosilane over a wide range, but preferably the mole ratio
of RlSiHX2:RSiX3 is about 20:1 to 1:20, more preferably it is
from about 8:1 to about 1:6, still more preferably about 8:1 ~o about
1:2, and even more preferably from about 6:1 to about 1:1.
This silylamide when pyrolyzed will typically produce a ceramic
material that is richer in silicon nitride than that obtained on
pyrolysis of the polysilazane DHCD product obtained from the
-34- .~
. .
~ 8~
corresponding dihalosilane alone.
The use of the above polymeric silylamide in one embodiment of the
present invention upgrades the Si-H containing organosllicon polymer,
for example, the organopolysilanes, the polycarbosilanes and the
polysiloxanes to new polymers which give a high ceramic yiel.d on
pyrolysis. When this silylamide is reacted with an Si-H containing
organosilicon polymer, the reaction product after treatment with a
suitable electrophile such as an organic or a silyl halide,
incorporates both starting materials. When this reaction product is
pyroly7ed, the ceramic yield is significantly greater than that of the
"parent" organosilicon polymer. Additlonally, the silicon
nitride/silicon carbide ratio of the resulting material can be varied
depending upon the particular dihalosilane and trihalosilane, ratio of
dihalosilane to trihalosilane and Si-H organosilicon polymer used. The
ratios to use to obtain a particular result can be determined
empirically by the skilled artisan based upon the ~resent disclosure.
The weight ratio of Si-H containing polymer to polymeric silylamide
can ~ary widely. For example, mole ratios of organopolysilane:
polymeric silylamide from about 4:1 to about 1:4, and preferably from
2.5:1 to 1:2 typically provide useful results. Weight ratios of
polycarbosilane: polymeric silylamide from about 10 to about 1; and
preferably from 5:1 to 1:1 typically provide useful results. Ueight
ratios of polysiloxane: polymeric silylamide of 1:1 and 1:5 typically
provided useful results. Ueight ratios of polysiloxane: polymeric
silylamide from about 15 to about 1 to about 1 to about 15, should also
provide useful results. Preferably the weight ratio of polysiloxane:
polymeric silylamide ranges from abo~t 5:1 to 1:5, and more preferably,
from 5:1 to 1:1. Howe~er, in all three cases other ratios can be used
depending on the particular starting materials and their pyrolysis
characteristics.
The organosilicon polymers thus formed by reaction of the
organosilicon polymer containing Si-H repeat units with the preformed
silylamide "living intermediate" followed by treatment with an
electrophile, henceforth will be referred to as "graft" polymers.
-35-
~L3~ 37S
Polysilanes of type (RSiH)n (i.e., the general case where y 0,
x - 1) also react with the polymeric silylamides that are the DHCD
reaction product of ths coammonolysis of a dihalosilane and
trihalosilane. Thus, a reaction of (C6H5SiH~n with the
silylamide "living intermediate" (l:l molar ratio) in THF at room
temperature gives a new organosilicon polymer which is an effective
ceramic precursor, giving a Si3N4/SiC/C ceramic product in high
yield upon pyrolysis to 1000C.
Additionally, use of the reaction product of organopolysilanes or
polycarbosilanes with the polym~ric silylamide results in a product
that is self-curing as the temperature is raised in the production of
ceramic material. Consequently, with these polymers it is possible to
avoid the formation of SiO2 which results when an oxidative cure step
is used. This again is an improvement over pyrolysis of the precursor
silane compound alone.
In this system, R or Ra is preferably a lower alkyl, more
preferably, R or Ra is CH3. However, R or Ra need not be the
same and, as aforesaid, mixtures of Si-H con~aining organosilicon
compounds and~or repeat units, e.g., [(RSiH)X(RSi)y~n and
[ (R SiH)X, ~R Si)yl ]n'~ [RaSi(H)~(CH2)q] Rnd
[Ra Sl(H)-(CH2)q'], and [~RSiH)x(RSi)y]n and
[RaSi(H)-(CH2)q] can be used to obtain further flex~bility in
tailorlng the properties of the aforesaid product. Similarly, mixed
polymers of the type [(RSiH)a(RSi)b(~R Si)c]m (where a, b,
m and R are as defined above, and R is defined as is R above and
R may be the same or diferent than R) can be used as well.
Preferably, at least one of the grouping R, R', Ra, and Ra for
each mixture is CH3.
The polysiloxane polymer may also contain a mixture of repeat units
of the above described formula, e.g., both [RbSi(H)O] and [Rb
Si(H)O] (Rb is defined the same as Rb but Rb' may ba different
than Rb). Rb is preferably a lower alkyl group, more preferably
Rb is CH3.
Further, these aforesaid mixtures of compounds can be used to obtain
-36-
. .. .
~IL3~ S
additional flexibility in tailoring the properties of the aforesaid
product.
Mixtures of polysilazanes, for example where R2 i9 H and R2 is
CH3 also may be used.
As indicated above, this invention also includes the case of
(RSiH)x(RSi)y~n~ where x~l, y O, with R as defined abo~s. Thus,
[(RSiH)]n ma~ be a linear or a mixture o~ cyclic species, or a hybrid
of both types. For example, [PhSiH]n (Ph is a phenyl group), cf,
Aitken, C. et al., J. Org~nomet. Chem., ~ Cll-C13 (1985), reacts in
the same way as the above-described organopolysilanes to provide new
organopolysilane/organopolysilazane hybrid polymers. These mixtures
will be particularly useful in attempts to avoid excess free silicon or
carbon. Similarly, aryl-substituted repeat units of either
IRaSi(H)-(CH2)q] or [RbSi(H)O], for example, where Ra or Rb
is a phenyl or substituted phenyl group, and Ra and * can be a
lower aryl group is also included.
The preceramic product one obtains by using these silylamides, even
in only catalytic amounts, differs from the starting organosilicon
compound. Thls difference in products apparently arises because both
Si-H and Si-Si bonds are reactive towards nucleophilic reagents.
The ~'graft" polymer is for~ed by combining the already formed
polymeric silylamide with the Si-H containing organosilicon polymer,
for example, the organopolysilane i~ varying proportions in an organlc
solvent. Thereafter, the mixture is stirred at room temperature for
sufficient time for the two compounds to react. In one embodiment, the
polysilo~ane, ~or example, [C~3Si(~)O]n oligomers with a high
cyclic content, is added slowly to an organlc solution such as THF
containing the preformed silylamide. An immediate reaction with some
gas evolution occurs. Thereafter, the mixture is stirred at room
temperature for sufficient time for the two compounds to more
completely react.
Any organic solvent in which both polymer systems are soluble
without reaction can be used. Such organic solvents include, for
example, THF, diethyl ether, glycol ethers, alkanes, arenes and
-37-
!
., ' .' '`;'.'' , ~, ''` ` '`' , '
~3~7S
combinations thereof. The mixture may be heated above room
temperaeure, and can be refluxed to sp0ed up the completion oE the
reaction. After refluxing, the mixture is quenched with an
electrophile, E-21, to form the organosilicon "graft" polymer. The
electrophila can be an alkyl halide, sulfate, or sulfonate; a
halosilanc; or the like. Typically, CH3I or a chlorosllane is used,
although oth0r equivalent electrophiles well-known to those skilled in
the art can also be usQd. E is preferably a lower alkyl group or silyl
group; Xl is preferably a halide, sulfate or sulfonate.
The organosilicon polymer formed by the present ("graftn) process
with the organopolysilane is typically obtained in yields greater than
85% based on weight of the starting materials with a variable molecular
weight, typical values being in the 1600-2200 g/mol range. This
preceramic organosilicon polymer can then by pyrolyzed under inert
atmosphere conditions (As used herein, nitrogen will be considered an
inert gas, argon is another example) to result in a ceramic material in
high yield. Pyrolysis under nitrogen gave ceramic products in a yield
75-85~.
~ he organosilicon preceramic polymers formed by the present
(ngraft") process when polycarbosilane is used were produced in high
yields (as high as 95%). Pyrolysis of this preceramic polymer gave
ceramic products in a yield of 75-85% (based on weight of the starting
materials).
The resultant preceramic polymer when polysiloxane was used were
produced in good yields, typically better than 70%. The
polysiloxane-derived preceramic organosilicon polymers can then by
pyrolyzed under nitrogen or other Inert atmosphere to result in
ceramlc materials in high yield. Typically, pyrolysis under nitrogen
gave black ceramic products in a high yield (as high as 88%). More
significantly, pyrolysis under ammonia will give a white ceramic solid
ln high yield. The white ceramics contain little, if any, carbon.
What is referred to herein as an "~ situ" polymer can be obtained
by carrying out the DHCD reaction of the dihalosilane and trihalosilane
coammolysis product in solution in the presence of the Si-H containing
-3~-
. . ~ . . ~ . . , , ~ . .
.
,
,
~3~ 7S
organosilicon polymer. In this method, the organopolysilane or
polycarbosilane is added to an organic solvent. Afterwaxds, the
mixture (generated b~ reacting in solution anhydrous = onia with the
dlhalosilane and trihalosilane) is added. The polysiloxane i8 added to
the coammonolysis mixture which is in an organic solvent.
One then adds to the solution a basic catalyst capable of
daprotonating the hydroge~ from a nitrogen atom ad~acent to a silicon
atom. See U.S. ~atent No. 4,482,669. The reaction mixture gradually
changes color and hydrogen is evolved. The resultin~ solution ls then
stirred at room temperature for sufficient time for the silylamide
intermediates and the Si-H containing organosilicon polymer to react.
It can be heated above room temperature, and can be heated at reflux to
speed the completion of the reaction. Afterwards, the reaction mixture
is allowed to cool to room temperature, if required, and quenched with
an electrophile such as CH3I or a halosilane, such as a chlorosi~ane,
to produce the organosilicon "in situ" polymer. The molecular welght
of the "~ sitU" polymer is variable. On pyrolysis this material
provides a high yield of a black ceramic material.
On pyrolysis the polycarbosilane-derived material provides a yield
of a black ceramic material, that is typically greater than that
obtained on pyrolysis of the polycarbosilane alone.
On pyrolysis under nitrogen or argon tbe polysiloxane-derived
material provides a yield of a black ceramic material, that is
typically greater tha~ that obtained on pyrolysis of the polysiloxane
alone. Pyrolysis under ammonia typically rPsults in silicon oxynitrides
in high yields.
The organosilicon polymer formed by either of the above "graft" or
"ia situ" methods usually is separated from solution. The solvent is
removed by using techniques well known to a person of ordinary skill in
the art. One standard method is distillation, preferably trap-to-trap
distillation. The polymer, typically a white powder that is soluble in
an organic solvent, is thereby obtained. One may also combine
trap-to-trap distillation with centrifuging, followed by trap-to-trap
distillation to separate the polymer from solution.
-39-
`` 13~1~87S
The "in situ" preceramic polymer differs physically rom the
"gra~t" preceramic polymer. ~a;or differences will be observed in
their proton NMR spectra and in the form of their thermogravimetric
analysis ~TGA) curves. both types of polymers are useful as preceramic
materials.
The use of coammonolysis-derived, DHCD-catalyzed silylamide
described herein not only improves the ceramic yield of the
organopolysilanes, but, more significantly, when this silylamide is
reacted with organopolysilane of the formula [(RSiH)X(RSi)y]n in
ths appropriate stoichiometry, the reaction product of
[tRSiH)X(RSi)y]n and the "living intermediate" silylamide after
treatment with a suitable electrophile such as an organic or a silyl
halide, incorporates both starting materials. When this reactlon
product is pyrolyzed, the excess silicon normally obtained in the
pyrolysis of the organopolysilane alone and the excess carbon normally
obtained in the pyrolysis of the quenched polymeric silylamide alone
combine so that there is no substantial excess of either element in the
ceramic product. Consequently, one can obtain a ceramic material
preferably with less than about 1~ free silicon or free carbon, more
preferably less than about 0.5~ free carbon and less than 0.5~ free
silicon, and most preferably with less than about ~.1% of free sillcon
and less than about 0.1~ of free ~arbon, i.e., a ceramic material
containing substantially no free carbon a~d no free silicon. The exact
combination o the two compounds necessa~y to result in the desired
stoichiometry can readily be calculated by a person of ordinaxy skill
ln the art on the basis of the results of the analyses of the ceramic
products obtained in the pyrolysis of the separate polymers. Mole'
ratios of organopolysilane: metal silyla~ide from about 4:1 to about
1:4, and preferably from 2.5:1 to 1:2 should provide useful results.
However, other ratios can be used depending on the particular starting
materials and their pyrolysis characteristics.
The excess of free carbon, which can be a problem with the starting
polycarbosilanes, can be dealt with by using a ternary system of: (1)
the polycarbosilane; (2) the polysilazane (as the polymeric silylamide,
-43-
,
.. -~ ~'"'` `
~L3~ 375
either preformed or generatad n situ) and (3) a polysilane whose
pyrolysis alone gives a ceramic product which contains an excess of
silicon. ~xamples of such polysilanes are organopolysilane~ as
described`above, for example, those which ara produced by the sodium
condensation of methyldichlorosilaDe. In these reactions the
organopolysilane is preferably as defined above, i.e
[(RSiH)X(RSi)y]n. More preferably R is a lower alkyl group, most
praferably R is CH3. Using an appropriate mixture of the three
polymers (which can be calcul~ted from the results of the analyses of
the ceramic products of the pyrolysis of each individual polymer, e.g.,
the CH3I- quenched polymer in the ca~e of the polymeric silylamids),
one can obtain a ceramic product which contains a minimal excess of
either element, carbon or silicon. Such hybrid ternary preceramic
polymers are soluble in organic solvents and, depending on component
ratios used, are of variable molecular weight. Their yyrolysis gives
black ceramic products in high (generally > 80%) yield.
In the preceramic polymer which results from a combination of a
polysiloxane polymer (A) and an alkali metal (poly)silylamide (B), the
ratio of Si/O/N of the resultant ceramic material can be broadly varied
by ad~usting the stoichiometry of the preceramic polymer, i.e. the A:B
ratio. For example, at one extreme, the pyrolysis of a
CH3I-quenched silylamide derived from the coammonolysis o~
CH3SiHC12 and HSiC13 and subsequent DHCD reaction under a NH3
atmosphere produced white silicon nitride. By appropriate selection of
reactant stoichiometry it should be possi~le to obtain a ceramic
product that is virtually pure silicon oxynitride.
For example, it should be possible to obtain distinct crystalline
phase Si20N2 after pyrolysis under a stream of ammonia from a
preceramic polymer one obtains by the in situ process. In this
instance the weight ratio of polysiloxane:alkali metal poly(silylamide)
is about 1:1 and R and Rl are CH3 and R2 is H or CH3. In the
above-described system, deviating from a 1:1 ratio results in a ceramic
polymer having some Si3N4 when you usa more poly(silyamide) or some
SiO2 when you use more polysiloxane. It is simple to empirically
-41-
'
~3~41 3~7S
determine the appropriate weight ratio for a desired ceramic
product with the use of any of the claimed starting materials.
The polysiloxane and silylam:ide are typically added in
a weight ratio of polysiloxane: silylamide from 15:1 to 1:15.
Preferably this ratio is about 5:1 to 1:5. More preferably the
ratio is about 3:1 to 1:3. Most preferably the ratio is about
1 : 1 .
Physical blends of Si-H containing organosilicon
polymers, for example the organopolysilane, the polycarbosilane
polymers containing repeat units of [R~Si(H)~(CH2)q]~ for
example, the Yajima polycarbosilane or the polysiloxane
containing repeat uni~s of [RbSi(H)o]n, with the "quenched"
organosilazane polymer of U.S. patent No. 4,720,532 (issued
January 19, 1988) can be used since these will react when they
are heated together. When approximately equal molar quantities
of the polymers where R, R~ or Rb = CH3, Rl = CH3, R = H or CH3,
are mixed and finely ground together and then subjected to
pyrolysis to 1000 C, ceramic yields are obtained which are
approximately the average of the ceramic yields when the
organopolysilane and the organosilazane polymers are pyrolyzed
separately, are significantly higher than that which results
when the polycarbosilane is pyrolyzed separately and is still
higher than that which results when the polysiloxane is
pyrolyzed separately.
When polycarbosilane/organosilazane mixtures are
heated, in the absence of a solvent at 200 C under nitrogen,
white foamy solids are obtained which are insoluble in nonpolar
organic solvents. When organosilane/organosilazane mixtures are
heated, either in the absence of a solvent at 100 C under
nitrogen or in a toluene solution at reflux, white powders are
obtained which are insoluble in nonpolar organic solvents.
Ternary blends of the polycarbosilane, the polysilazane
and the [(CH3SiH)y(CH3Si)y]n polysilane behave similarly.
The combined polymers obtained by the "graft," "in
situl' and physical blend methods can be converted to black
ceramic fibers. Pyrolysis of pressed bars of the combined
polymers to ~000 C provides................................
~3
~3~7~
a black solid product. In other experimants, silicon carbide powder is
dispersed in a toluene solution containing 25% by weight of the
combined organosilane/organosilazane polymers. The solvent i5
eYaporated and the residue, a fine powder of silicon car~lde with
combined polymer binder is pressed into bars and pyrolyzed at 1000C.
A ceramic bar is obtained showing a low weight loss and slightly
shrunken size.
Similarly, when silicon carblde powder is dispersed in toluene
solutions of the combined polycarbosilane/organosilazane polymers, the
solvent evaporated and the residue, a fine powder of silicon carbide
with combined polymer binder, is pressed into bars and pyrolyzed at
1000C, a ceramlc bar is obtained showing a low weight loss and
slightly shrunken size.
Pyrolysis of bars of the combined polysiloxane-organosilazane
polymers under am~onia results in a white rectangular body. Pyrolysis
under either pyrolysis condition results in ceramic bars showing low to
moderate weight loss and slightly shrunken size.
The invention will be further illustrated by the examples that
follow:
I. General
All reactions and manipulations were carried out under a dry
nitrogen atmosphere using standard Schlenk techniques or a Vacuum
Atmospheres dry box. All solvents were distilled under nitrogen:
diethyl ether and tetrahydrofuran from sodium ben2ophenone ketyl, and
he~ane from lithium aluminum hydride. Chlorosilanes were obtained from
Petrarch Systems, Inc. or Silar Labs., Inc. and were distilled from
magnesium filings prior to use. Anhydrous ammonia (Matheson) was dried
by passing through a KOH-filled drying tube. Methyl iodide was
distilled under nitrogen from P205. Potassium hydride (Alfa) was
obtained as a 40% slurry in mineral oil which was filtered, washed with
hexane and dried prior to use.
Proton ~MR spectra were obtained on either a Jeol FX-9OQ (90 MHz)
or a Bruker WM-250 (250 MH7) using a CDCl3 reference (7.24 ppm
-43-
. .
. .~
.
~L3~
shit). Infrared spactra were obtained on a Perkin-Elmer Model 1430
infrared spectrophotometer.
Nolecular weights were determined by cryoscopy ln benzene.
Thermogravimetric analysis (TGA) yields were obtained using a
Perkin-Elmer TGS-2 system. Samples were heated from 50C to 950C
under an argon atmosphare at 10C/min. Large-scale tube furnace
pyrolyses to produce gram quantities of ceramics were performed in a
Lindberg Model 59344 tube furnace with controller. Samples were heated
from 200C to 1000C at 10C/minute in an argon atmosphere.
Analyses of all oils and polymers were performed by Scandinavian
Microanalytical Labs, Herlev, Denmark. Ceramic analyses were performed
by Galbraith Labs, Knox~ille, Tennessee.
II. Ammono~ysis Reactions
~ typical reaction is described. All other ammonolyses of the
RSiC13 alone or of mixtures of CH3SiHC12 with RSiC13 (R D H,
CH3, CH2 CH) were carried out using the same general procedure.
For each CH3SiHC12/RSiC13 molar ratio used, separate reactions
were carried out in Et20 and in THF medium. The yields of soluble
products (soluble in the reaction medium), the molecular weights, the
ceramic yields (by TGA under argon) obtained on their pyrolysis and
their analyses are given in the appropriate Tables (1-9).
A 1000 ml three-neGked, round-bottomed flask equipped with a Dry
Ice condenser, an overhead mechanical stirrer and a rubber septum was
flame-dried while a stream of dry nitrogen was passed through. Dry
diethyl ether (600 ml) was added and then 33.6 ~ (0.'292 mol) of
CH3SiHC12 and 6.B g (0.05 mol) of HSiC13. The solution was
cooled to 0C (ica bath). The ori~inal septum was replaced with
another septum through which a one~foot gas inlet tube passed.
Gaseous a~monia then was bubbled into the solution at a moderate rate
for 4.5 hours until ammonia was obser~ed condensing on tha -7BOC
condenser. The a~monia inle~ tube was replaced with a rubber septum
after the addition of ammonia had been stopped.
.
. ,
,~ ~
,
' .
.~, . , j, . ..
` ~L3()4a75
The reaction mixture was allowed to warm to room temperatura and
stirred under nitrogen overnight. Filtration (in the dry box)
removed NH4Cl and any other insoluble products of the resction.
The solids were washed with three 50 ml portions of ether.
Trap-to-trap distillation of the solvent (25C, Q.l mm Hg) from the
combined ether phases left a clear, mobile oil (15.0 g, 74~ based on
the (CH3SiHNH) and [HSi(NH)l 5] components). The oil was
characterized by analysis (Table 3), by IR and lH NMR
spectroscopy. The molecular weight was measured (cryoscopy in
benzene) and a thermogravimetric trace was obtained (50-950C,
10C per minute).
H NMR (250 MHz, in CDC13): ~ 0.17 (broad m, 2.6 H, CH3Si),
0.85 (broad m, 1.3, NH), 4.37 (broad s, 0.25 H, SiH), 4.63 (broad s,
0.41 H, SiH) and 4.81 (broad s, 0.33 H, SiH).
IR (thin film, cm 1): 3380 (s), 2960(s), 2900(w), 2140-2120
(broad,s), 1545(w), 1405(m), 1255(s), 1200-1150 (broad, vs), 980-750
(broad, vs).
MW: 390 g/mol
TGA: 33% by weight ceramic residue, black solid
Anal.(Based on NMR-derived formula [CH3SiHNH][HSi(NH)1 4]0 li)
alcd for CH5.41Nl.24Sil.l7, C, 17.7; H, 8.05; N, 25.7
Found: C, 17.75; H, 7.53; N, 25.80.
III. -Catal~zed Dehydrocyclod~merizstion Reactions
One such experiment is described in order to pro~ide details of
the procedure used. All reactions were carried out in THF using 1
moL % of the KH catalyst. In all cases, the white solid polymer
obtained after the CH3I quench was characterized by analysis and IR
and lH NMR spectroscopy. The molecular weight was measured by
cryoscopy in benzene and a thermal analysis trace (TGA, 50-950
at 10C/minute, under argon) was obtained. The results of these
experiments are gi~en in the Tables.
A 250 ml, three-necked, round-bottomed flask was equipped with a
-45-
. '
'
.. . ~ ~; -
,.
-` ~30413~5
magnetic stir-bar, a gas inle~ tube and two rubber sspta and charged
with KH (0.04 g, 1.0 mmol). The flask then was connected to the
nitrogen line. Dry THF (100 ml) was added by syringe and then 6.355
g (0.1 mol, based on CH3Si~ + [HSi(NH)l 5] units) oE the
polysilazane oil (obtained by ammonolysis of a l:l molar ratio
mixture of CH3SiHC12 and HSiC13 in diethyl ether) dissolved in
20 ml of THP. The latter solution was added dropwise over a period
of 20 minutes. Gas evolution (H2) was observed. The requlting
clear solution was stirred at room temperature under nitrogen for 1
hour. Subsequently, methyl iodide (0.46 g, 3.2 m~ol) was added by
syringe. An immediate white precipitate of KI formed. The mi~ture
was stirred for 30 minutes at room temperature and then the solvent
was removed by trap-to-trap distillation. To the residue was added
70 ml of benzene and the mixture was centrifuged to remove
insolubleq. The solution phase was trap-to-trap distilled (25C,
0.03 mm Hg) to remove the benzene, leaving a white or~anic-soluble
solid (5.41 g, 93~ yield). (Generally, in all other such reactions,
the reaction mixture was stirred for 1-18 hours at room temperature
after the initial gas evolution was observed. In the present case,
such longer reaction times led to formation of insolubles.)
lH N~R (250 NHz, in CDC13): ~ 0.17 (broad m, 2.5 H,
CH3Si), 0.94 (broad, 1.2 H, NH), 4.82 (broad s, 1.0 H, SiH).
IR(CC14, cm 1): 3480 (w), 3400(s), 2960(s), 2900(w), 2120(s),
1540(w), 1410(m), 1250(s), 1180-1130(broad,s), 1030(s),
970-850(broad,vs).
MW: 1630 g/mol
TGA (50-950C, 10C per minute, under argon): 87~ ceramic
yield (black solid).
Anal. Found: C, 14.10; H, 6.12; N, 27.60.
A 3 g sample of this product was pyrolyzed in a tube furnace under
-46-
130~87S
argon, leaving a residue of 2.4 g (80%) in the form of a chunk of
black solid.
Anal. Found: C, 9.10; H, 0.70; N, 32.56; Si, 56.52.
Assuming that all nitrogen is present as Si3N4, that the rest
of the silicon is present as SiC and that the remaining carbon is
present as free carbon, one can calculate from this analysis the
composition 1.0 Si3N4 + 0.46 SiC + 0.81 C or, by weight, 83
Si3N4, 11% SiC and 6~ C.
Pyrolysis of the white solid obtained from another such
preparation (1:1 CH3SiHC12/HSiC13 ammonolysis in THF
followed by KH-catalyzed DHCD and CH3I quench; a 3.53 g sample)
in a fused silica boat in a tube furnace in a stream of ammonia
(25-1000C within 3 hours~ gave a white powder residue in
84~ by weight yield (100~ yield based on the silicon content of
the polysilazane). Analysis indicated a carbon content of only
0.29~.
IV. Preparation of Organosilicon Compounds
1. Preparation of ~(CH3SiH~x(CH3Si~
~all operations under nitrogen) ~
a. In THF Medium.
A 500 ml, three-necked, round-bottomed flask equipped with a
stir-bar, a dropping funnel and a reflux condenser was charged
with 50.5 g (2.20 g atom~ of Na metal. The flask was attached
to a Schlenk manifold, evacuated and refilled with nitrogen
three times. THF (200 ml) was added and the dropping funnel was
charged with 65 ml (0.625 mol) of CH3SiHC12. The silane was
added to the stirred Na suspension during the course of 45 min.,
after which time the reaction mixture was cloudy and slightly
warm. The mixture was stirred for 16 hours at room temperature
and 48 hours at reflux; it then was cooled to room temperature.
Hexane (60 ml) was added. The mixture was transferred by
cannula to a heavy-walled centrifuge bottle and centrifuged.
-47-
~L3~4a'7S
The supernatant layer was transferred to a 1 liter
round-bottomed flask (under nitrogen). THF (50 ml) and hexane
(30 ml) were added to the residual solid and the resulting
suspension WA9 centrifuged. The supernatant layers were combined
and solvents were removed by trap-to-trap distillation ln vacuum
until the residual liquid volume was about 100 ml. This liquid
was cannulatcd into a 250 ml single-necked Elask and the
remaining solvent was removed in vacuo to leave 13.2 g (0.30 mol,
48~ yield) of a white, glassy solid. On being heated in a sealed
capillary (in vacuo) this solid sotened around 40C and "m~lted"
between 130-140C with gas evolution, leaving a thick gum. There
was no further change up to 300C except for a gradual increase
in viscosity. The product W8S poorly soluble in hexane, only
somewhat soluble in benzene (precluding measurement o~ its
cryoscopic molecular weight in this solvent) and quite soluble in
THF.
NMR (90 MHz, in CDC13): ~ 0.10-0.61 (m, SiCH3, 7.5H) and
3.55-3.90 (m, SiH, lH). Based on the reasonable assumption that
every Si atom bearing a H substituent also bears a CH3
substituent, the integrated CH3Si and SiH intensities lead to a
ccnstitution [(CH3SiH~o 4(CH3Si)o 6]n-
Anal. Calcd for CSiH3 4: C, 27.60; H, 7.87.
Found: C, 27.18; H, 7.17.
IR (KBr, Nujol): 2170(sh), 2100(s, Si-H), 1408(m), 1260(m,
Si-CH3), 1249(s, Si-CH3), 1060(br), 1019(s), 931(s), 865(vs,
Si-CH3), 770(vs), 685(vs~, cm 1.
TGA(25-1000C, 10C/min.): 60~ yield o a gray-black ceramic
solid. A tube furnace pyrolysis of 3.20 g of this material to
1500C gave 1.52 g (48%) of a gray ceramic powder.
Anal. of the Ceramic Po~der. Found: C, 22.56; Si, 78.42; H,
0.01; N, 0.009%. (SiC requires C, 29.94; Si, 70.06~; actual
-48-
~30~1L8~75
composition: SiC + 0.49 Si). X-ray powder diffractlon (do~
A): 1.315(s) (~ -sic), 1.542(s) (~ -sic), l.91(m)
(si), 2.181(m), (~ -sic), 2.52(vs) (~ -sic), 3.13(m)
si) .
A mass spectral analysis of the pyrolysis gas in another
experiment showed the following: no gaseous products were
observed up to 385C, then fragment ions corresponding wcll with
the reported fragmentation of CH3SiH3. At 445C, CH3SiH3
was still observed and a peak at
~ m/~ - 16 (CH4) began to grow in. By 580c, when weight loss
was about over, only the methane peak was observable.
b. In Hexane/THF Medium
In a dry box, a 1 liter three-necked, round-bottomed flask equipped
with a stir-bar, a dropping funnel and a reflux condenser was charged
with 75.0 g (3.26 mol) of sodium metal. The flask was attached to a
Schlenk manifold, evacuated and flushed with nitrogen. THF (70 ml) and
hexane (420 ml) were added and the dropping funnel was charged with 150
ml (1.44 mol) of methyldichlorosilane. Methyldichlorosilane was added
slowly into the flask over a 3 hour period. The reaction solution
turned purple and by the end of the addition was st gentle reflux. The
reaction mixture was stirred at room temperature for 2 hours and then
heated at reflux for 16 hours. After it had been cooled to room
temperature, the reaction mixture (except for the large NaCl crystals)
was transferred via cannula into a heavy-walled glass bottle. The
mixture was centrifuged and the clear, colorless supernatant layer
transferred by cannula into a 1 liter round-bottomed flask equipped
with a stir-bar. Hexane (200 ml) and THF (20 ml) were added to the
remaining solids, the mixture again was centrifuged, and the
supernatant liquid combined with the supernatant solution previously
separated. Solvent was removed by~ trap-to-trap distillation until the
volume of the residue was about 100 ml, and the remaining liquid was
transferred by cannula into a weighed 250 ml round-bottomed flask.
-49-
'
~oa~ 75
Remaining solvent was removed by trap-to-trap distillation at
approximately 0.05 mm Hg at room temperature to give 51.2 g (81~, 1.16
mol) of a cloudy whit~ oil.
H NMR (90 MHz, C6D6~:~ 0.37 (broad, SiCH3, 3.74H)
3.92 (broad, SiH, 1 H).
NMR integration of the product gave a constitution oi
[(CH3SiH)o 8(CH3Si)0,2]n.
IR (thin film, cm 1): 2967(s), 2900(s), 2800(w), 2099(vs), 1410(s),
1385(w), 1249(s), 1055(br), 933(s), 865(vs), 770tvs), 685(br), 650(sh),
585(w).
Molecular weight (cryoscopic in benzene): 600 g/mol.
Anal. (material from another similar preparation3. Calcd. for
CSiH3 76; C, 27.39; H, 8.55; Si, 64.05. Found: C, 27.49; H, 8.98;
Si, 61.58~.
TGA (25-1000C, 10C/min): 20% yield of a gray-black ceramic solid.
Pyrolysis of a sample from another preparation in a tube furnace gave a
gray-black ceramic solid in 36% yield (by weight).
Anal. of Ceramic. Found: C, 22.93; Si, 75.99%.
The pure liquid obtained by this procedure is very air-sensitive,
particularly when its effective surface area ig high, as when in
contact with a fritted funnel or a paper or cloth towel (in which cases
spontaneous inflammation may occur).
Other, similar reactions have given 62-75% yields of
(CH3SiH)x(CH3Si)y~ Nolecular we~ght determinations of several
preparations ranged from 520-740 g/mol. All products had ~ery similar
lH NMR spectra, but with different SiCH3:SiH ratios. Physical data
of these products are listed in Table 11.
-50
~3~
TABLE 11
P~SICAL DATA FOR ~(CH3SiH)~(CH3Si~y~ _~Y~
Sample ~ Polymer M.W.a SiCH3:SiHb CeramicC x y
Yield (%~ i91~_L3~ _
YFY III-l 81 600 3.74:1 20 0.80 0.20
YFY II-40 74 740 3.56:1 16 0.84 0.16
YFY II-25 73 650 3.51:1 26 0.85 0.15
YFY II-12 66 520 3.27:1 16 0.91 0.09
YFY I-73 73 680 3.48:1 27 0.86 0.14
~Cryoscopic in ben~ene.
b lH ~MR integration ratio.
CUnder nitrogen gas, 25-1000C, 10C/min (TGA)
~3~375;
For the purpose of slmplifying calculation, an average formula
weight value 44 was assigned for the unit (CH3SiH)X(CH3Si)y.
Therefore, in each of the following experiments, tha numb&r of moles of
the reaction unit (CH3SiH) was calculated from the weight of the
polymer used divided by 44.
The product formed in the THF solution glves a 60% ceramic yield,
but it is of limited solubility in organic solvents and its conversion
to ceramic fibers requires a curing step of photolysis/oxidation.
Preparation of the [(CH3SiH)X(CH3Si)y]n in a hexane/THF
mixture of approximately 6 to 7:1 resulted in satisfactory yields of a
soluble product. However, pyrolysis of this material resulted in very
low ceramic yields, ranging from 16 to 27%.
2. Characteri~ation of the Polycarbosilane,
The polycarbosilane, a white solid, was purchased from Dow Corning
Corporation. The following data were collected on it:
H NMR (90 MHz, C6D6): 6 4.52 (broad, Si_, lH)
0.26 (broad, SiCH3 and
SiCH2SI, 8.6H)
IR (KBr, NU3O1, cm 1~ 2104(s~, 1253(s), 1014(s, broad), 845(s,
broad), 734(s).
Molecular Weight (cryoscopic in benzene): 1210 g/mol
TGA (25-1000C, 10C/min): 58% yield of a black ceramic solid.
Tl/2 ~ 510C
3 Preparation of Slloxanes
a. Pre~_ration of ~CH3~ Qln~
A 500 ml three-necked, round-bottomed flask equipped with a
stir-bar, a reflux condenser, and a serum cap was charged with 90 ml
(0.87 mol) of CH3SiHC12 and 250 ml of CH2C12. To the solution
was added slowly (syringe pump) 20 ml (1.11 mol) of H20 over a two
hour period. The reaction mixture was stirred at room temperature for
24 hours. Eight 100 ml portions of H2O were added to the reaction
-52-
~l3~ 75
mixture. The CH2C12 layer was washed with two 100 ml portions of
H20 and dried over MgS04. The solvent was removed by rotary
evaporation to give 44.5 g (85% yi~ld based on (CH3Si~H)0) unit) of a
clear oil.
H ~ (90 MHz, C6D6):6 4.71, 4.69 (broad, SiH, 1 H)
0.23, 0.21 (broad, SiÇH3, 3 H)
(neat, cm~l): 2976(s), 2918(w), 2162(s), 1410(w),
1260(s), 1030-1140 (broad,s),
830-920 (broad,s), 769(s), 715(w).
This is the procedure described by D. Seyferth, C. Prud'hom~e and
G.H. Wiseman (Inor~. Chem., 22 (1983) 2163) in the hydrolysis of
CH3SiHC12. A good yield of cyclic [CH3Si(H)O]n oligomers was
reported, mostly n~4, 5 and 6, but some higher n (up to n 22) was also
obtained in lower yield. The cera~ic yield of these oligomers is low
and wlll vary from 0 to 5 ~ depending upon the W rolysis conditions and
the particular oligomer used.
b . Preparatlon of Mixed Siloxane
r (cH3~ Q~ 3)2sio)s ~
A 500 ml three-necked, round-bottomed flask equipped with a
stir-bar, a reflux condenser, and a serum cap was charged with 100 ml
(0.96 mol) o~ CH3SiHC12, 50 ml (0.41 ~ol) of (CH3)2SiC12, and
250 ml of CH2C12. To the solution t:here was added 60 ml (3.33 mol)
of H20 (slowly by syringe pump) over a 4 hour period. Reaction
occurred immedia~ely. The réaction mixture was stirred at room
temperature for 24 hours and then was washed with fifteen 200 ml
portions of H20 until the h20 washings were neutral pH. The
CH2C12 layer was dried over MgS04 and the solvent was removed by
rotary evaporation to give 64.7 g (87~ yield by weight) of a clear oil.
H NMR (90 MHz, C6D6):~ 4.99 (broad, SiH, 1 H)
0.22, 0.16 (broad, SiCH3, 6H)
IR (neat, c~ 2972(s~, 2168(s), 1410(w), 1260(s),
1030-1120 (broad,s), 880(s), 836(s),
804(s), 769(s), 708(w)
~ '
:
13~4B75
C. Characterization of Commercial ~CH3Si(H)Ol~(Petrarch_
PS-122~
IR (neat): 2982(m), 2171(s), 1413(w),
1262(s), 1030-1140 (s,broad),
860;905 (s,broad), 765(s), 718(w)
cm
H NMR (C6D6):~ 0.25 (broad s, SiCH3, 3.4H), 5.04 (broad
s, SiH, lH)
Y9~ L~ LL~L~y~h~: 4500-5000 (vendor data)
Ceramic Yield: (TGA, 25-1000C., 10C./minute): 13~ (black solid)
V. Graft Reactions
A. Graft Reaction of the Coammonolvsis Product of
Methyldichlorosilane and Vin~ltrichlorosilane (3:1 Ratio. THF) and
Polvmethvlhvdridosiloxane (PS 122) with Potassium Hydride in THF.
A 100 ml, three-necked, round-bottomed flask was~equipped with a
reflux condenser with gas inlet tube on top, a stir-bar and two septa
and oven-dried for 1 hour. (This wilI be termed the ~standard reaction
apparatus".) The apparatus W8S taken into the dry box and charged with
potassium hydride (0.02 g, 0.50 mmol) and was then connected to a
nitrogen line, and charged with 50 ml of THF. The oil (1.64 g, 26.0
mmol) from the coa~monolysis of CH3';i~C12 and CH2-CHSiCl3 (3:1
ratio) in THF was added dropwise by syringe over 15 minutes. Gas
evolution was observedO The reaction mixture was stirred for an
additional hour at room temperature. By syringe,
polymethylhydridosiloxane tPetrarch Systems, Inc. PS 122) (1.59 g, 26.5
mmol) was added to the reaction mixture. After stirring 35 minutes,
methyl iodide (0.46 g, 3.2 mmol) was added and an immediate white
precipitate formed. The solvent was removed by trap-to-trap
distillation (25C, 0.03 mm Hg) and the residue extracted wlth 40 ml
of hexane. The reaction mixture was centrifuged and the supernatant
liquid cannulated into a 100 ml flask. Removal of the hexane by
trap-to-trap distillation left a white solid (2.44 g, 75%).
-54-
`~ ~.. 3~ 7S
H NMR (CDC13, 250 MHz): 6 0.17 (broad, 9.7 H, SiCH3),
0.99 (broad, 3.0 H, NH), 4.38 (broad, 0.07 H, SiH), 4.74 (broad, 0.93
H, SiH), 5.91 (broad, 2.1 H, SiCH~CH2).
IR (CC14, cm 1): 3400(s), 3050(m), 3010(sh), 2960(s), 2900(sh),
2140-2120 (broad, s), 1595(m), 1405(s), 1270-1250 (broad, vs),
1200-1020 (broad, vs), 990-840 (broad, vs).
MW (cryoscopy in benzene): 1340 g/mol.
TGA (10C/min, Ar, 50-950C): 86~ ceramic yield, black residue.
B. Graft Reaction of the Coa~monolysis_Product of
Methy~dichl_rosilane and Vin~ltrichlorosilane (3 1 Ratio. THF) and
PolymethylhYdridosilane with Potassium Hydride in THF.
The standard reaction apparatus was charged with potassium hydride
(0.02 g, 0.50 mmol) and 50 ml THF as previously described. The oil
(1.70 g, 27.1 mmol) from the coammonolysis of CH3SiHC12 and
CH2~CHSiC13 (3:1 ratio) in THF was added dropwise over 15 minutes.
Gas evolution was observed. The reaction mixture was stirred an
additional hour at room temperature. Polymethylhydridosilane (1.24 g,
28.2 mmol) from the reaction of CH3SiHC12 and excess sodium in a
6:1 hexane/THF solvent mixture was added by syrlngs. The reaction
mixture became orange and then afte:r 10 minutes turned yellow. The
reaction mixture was stirred an addltional 35 minutes at room
temperature and then methyl iodide (0.46 g, 3.2 mmol) was added by
syringe. An immediate white precipitate formed and the yellow color of
the reaction mixture was discharged. The solvent was removed by
trap-to-trap distillation and the residue extracted w~th 40 ml hexane.
The reaction mixture was centri~uged and the supernatant liquid
cannulated into a 100 ml flask. Removal of the hexane by trap-to-trap
distillation left a white solid (2.74 g, 93~).
H NMR (CDC13, 250 MHz): 6 0.28 (broad, 3.1 H, SiCH3), 1.25
(broad, 0.55 H, ~H), 3.65 (broad, 0.21 H, SiH), 4.38 (broad, 0.35 H,
SiH), 4.76 (broad, 0.44 H, SiH), 5.95 (broad, 0.53 H, SiCH-CH2).
IR (CC14, cm 1): 3390(w), 3150(w), 3050(m), 2960~s), 2900(m),
-55-
~L304a7S
2160-2140 (broad, vs), 1410(s), 1260~s), 1190-1140 (broad, s), 1040-840
(broad, vs), 710 (vs), 590(w).
MW (cryoscopy in benzene): 1612 g/mol.
TGA (10C/min., Ar, 50-950C): 86~ csramic yield, black solid
residue.
C. ~aft Reacton o the Coam~onolYsis Product of MethYldichlQxs~__ne
and Vinyltrichlorosilane (3:1 Ratio. THF~ and Polycarbosilane (Dow
Cornin~_~9-6348) with Potassiwn HYdride l~ THF.
The apparatus was charged with potassium hydride (0.02 g, 0.50
mmol) and 50 ml of THF. The oil (1.65 g, 26.0 ~mol) from the
coammonolysis of CH3SiHC12 and CH2-CHSiC13 (3:1 ratio) in THF
was added dropwise by syringe over 15 minutes. Gas evolution was
observed. The reaction mixture was stirred for an additional hour at
room temperature. Polycarbosilane (1.64 g, 28.0 m~ol, Dow Corning
X9-6348) was ground to a fine powder with a mortar and pestle and
placed in a 25 ml, one-necked flask. The flask was degassed and then 10
ml of THF was added. The resulting solution was cannulated into the
reaction mixture. After stirring for 35 minutes., methyl iodide (0.46
g, 3.2 mmol) was added and an immediate white precipitate formed. The
solvent was removed by trap-to-trap distillation (25C, 0.03 mm Hg)
and the residue extracted with 40 ml of hexane. The reaction mixture
was centrifu~ed and the supernatant liquid cannulated into a 100 m~
flas~. Removal of the hexane by trap-to-trap distillation le~t a white
solid (3.04 g, 92~).
~'
H NMR (CDC13, 250 MHz): ~ 0.16 (broad, 5.6 H, SiCH3), 0,95
(broad, 1.25 H, ~H), 4.16 (broad, 0.3 H, SiH), 4.71 (broad, 0.7 H,
SiH), 5.91 (broad, 0.8 H, SiCH~CH2).
IR (CC14, cm~l): 3400(s), 3050(m), 3010(sh),. 2960(s), 2900(m),
2120-2100 (broad, s), 1600(w), 1410(s), 1360(m), 1270-1250 (broad, vs),
1190-1130 (broad, vs), 1050-840 ~broad, vs).
MU (cryoscopy in benzene): 862 g/mol.
-56-
~ 3~ il7S
TGA (10C/min., Ar, 50-950C): 85~ ceramic yleld, black solid
residue.
D. Graft Reacti~ of the Coammonolysi~ duct of ~ethYldichlorosilane
and Trichlorosilane_(3:1 Rat~o. THF~ and P~olvmethylhvdridosiloxane (PS
122) with Potassiu~ Hydride in THF
A three-necked round-bottomed flask was equipped with a gas inlet
tube, a stir-bar and two septa, oven-dried for 1 hour and then was
charged with potassium hydride (0.02 g, 0.50 ~mol). The apparatus was
then connected to a nitrogen line and 50 ml of THF was added. The oil
(1.64 g, 0.029 mol) from the coammonolysis of CH3SiHCl2 and
HSiC13 (3:1 ratio) in THF, was added over 5 minutes. Gas evolution
was observed. The reaction mixture was stirred for an additional 45
minutes at room temperature. By syringe, polymethylhydridosiloxane
(1.58 g, 0.026 mol., Petrarch Systems, Inc., PS 122) was added to the
reaction mixture. Aiter stirring 30 minuteq, methyl iodide (0.46 g,
3.2 mmol) was added and an immediate white precipitate formed. The
solvent was removed by trap-to-trap distillation (25C, 0.1 m~ Hg)
and the residue extracted with 40 ml of hexane. The reaction mixture
was centrifuged and the supernatant liquid cannulated into a lO0 ml
flask. Removal of ths hexane by trap-to-trap distillation left a white
solid (2.30 g, 71%).
H NMR (CDC13, 250 MH~): 6 0.10 (broad, 4.5 H, SiCH3), 0.93
(broad, 2.0 H, NH), 4.84 (broad, 1.0 H, SiH).
IR (CC14, cm 1): 3490(w), 3400(s), 2960(s), 2900(w), 2870(sh),
2820(w), 2130(s), 1580(w), 1425(m), 1265 (broad, s), 1200-1020 (broad,
vs), 980-850 (broad, vs).
MW (cryoscopy in benzene); 1855 g/mol
TGA (10C/min, Ar, 50-950C): 88~ ceramic yield, black solid
residue.
-57-
~3~ S
E. Graft Reaction of the Coammmono~ysis Product of
~ichlorosilane and Trichlorosilane f3:1 Ratio ~THF)_and
Polymethvlhydridosilane with Potassium Hvdride in T~E~
The apparatus wa~ charged with KH (0.02 g, 0.50 mmol) and 50 ml of
THF. The oil (1.77 g, 0.031 mol) from tha coammonolysis of
CH3SiHCl2 and HSiCl3 (3:1 ratio) in THF was ~dded o~er 5
minutes. Gas evolution was obQerved. The reaction mlxture was stirred
an additional 45 minutes at room temperature. Polymethylhydridosilane
(1.30 g, 0.030 mol) fxom the reaction of CH3SiHC12 and excess
sodium in 6:1 hexane/THF was addcd. The reaction mixture became orange
and then after 10 minutes turned yellow. The reaction mixture was
stirred an additional 30 minutes at room temperature and then methyl
iodide (0.46 g, 3.2 mmol) was added. An immediate white precipitate
formed and the yellow color of the mi~ture was discharged. The solvent
was remov~d by trap-to-trap distillation and the residue extracted wtin
40 ml of hexane. The reaction mixture was centrifuged and the
supernatant liquid cannulated into a lO0 ml flask. Removal of the
hexane by trap-to-trap distillation left a white solid (2.70 g, 88%).
H NMR (CDC13, 250 NHz): ~ 0.30 (broad, 2.6 H, SiCH3), 1.23
(broad, 0.58 H, MH), 3.65 (broad, 0.19 H, SiH), 4.4 (broad, 0.28 H,
SiH), 4.8 (broad, 0.53 H, SiH).
IR (CC14, cm~l: 3670 (broad, w), 3490 (m), 3150 (s), 3060 (s),
2960(s), 2900(w), 2280(s), 2150 (broad, vs), 1815(s), 1670(w), 1415(s),
1265(s), 1190 (broad, w), 1050-1020 (broad, vs~, 980-350 (broad, vs),
700(w).
MW (cryoscopy in benzene): 2200 g/mol
TGA (10C/min., Ar, 50-950C): 75% ceramic yield, black solid
residue.
-58-
` ``" ~3t~ 7~i
F. Graft Reaction of the Coammonol~sis Product of MethYldichlorosllane
and Trichlorosila~e t3:1 Ratio, THF) and Polycarbosilane (Do~ Cornin~
X9-6348) with Potassium Hydride in THF~
The apparatus was charged with KH (0.02 g, 0.50 mmol) and 50 ml oE
THF. Th~ oil (1.61 g, 0.028 mol) from the coammonolysis of
CH3SiHC12 and HSiC13 (3:1 ratio) in THF was added over 5
minutes. Gas evolution was observed. The reaction mixture was stirred
an additional 30 minutes at room temperature. Polycarbosilane (1.45 g,
0.025 mol, DGW Corning X9-6348) was ground to a fine powder and placed
in a 25 ml one-necked flask. The flask was degassed and then 10 ml of
THF was added. This solution was then cannulated lnto the reaction
mixture. After stirring for 30 minutes, methyl iodide (0.46 g, 3.2
mmol) was added and an immediate white precipitate formed. The solvent
was removed by trap-to-trap distillation (25C, 0.1 mm Hg) and the
residue extracted with 40 ml of hexane. The reaction mixture was
centrifuged and the supernatant liquid cannulated into a 100 ml flask.
Removal of ~he hexane by trap-to-trap distillation left a whlte solid
(2.97 ~, 95~)-
H NMR (CDC13, 250 MHz): ~ 0.16 (broad, 5.0 H, SiCH3), 0.95(broad, 0.8 H, NH), 1.24 (0.7 H, ~H), 4.4 (broad, 0.3 H, Si~), 4.8
(broad, 0.7 H, SiH).
IR (CC14, cm 1): 3490(w), 3400~s), 2960(s), 2900(m), 2875(sh),
2120 (broad, s), 1460(w), 1415(m), 1365(m), 1260(s), 1175 (broad, vs),
1030 (broad, s~, 1080-850 (broad, vs).
MW (cryoscopy in benzene): 845 g/mol
TGA (10C/min., Ar, 50-950C): 76~ ceramic yield, black solid
residue.
c
-59-
~L3q~487~i
TABLE 12
~L~
Ceramlc
_ Yield
Reaction Product Yield.~ _ MW _ _bY TGA.
3:1 CH3SiHC12/
ViSiCl3 (THF)
with KH/PS 122 solid 75 1340 86
3~1 CH3SiHCl2/
ViSiC13 (THF) solid 92 862 85
with KH/D.C. Polycarbosilane
3:1 CH3SiHC12/
ViSiC13 (THF) solid 93 1612 86
with KH/(CH3SiH)0.7g
(CH3si)0~22
3:1 CH3SiHC12/
HSiC13 (THF)
with KH/PS 122 solid 71 1855 88
3 1 CH3SiHCl2/
HSiC13 (THF) solid 95 845 76
with KH/D.C. Polycarbosilane
3-1 CH3SiHCl2/
HSiC13 (THF) solid 88 2200 75
with KH/(CH3siH)0.78
C~13Si) o . 22
* V~ vinyl
-6~-
:: . .. ; . . .: . . .
~L3~ S
VI . n In-Situ Procedure"
A. Reaction of a Coammonolysis Mixture of_CH~SiHC~2~ 3
and ~CH3SiH~ 3~ n with KH_5~aly~5_
1. Usin~ Coammonolysis Product PrePared in Dieth~l Ether
In a dry box, a 250 ml round-bottomed flaqk equipped with a
stir-bar, reflux condenser and a serum cap is charged with 0.10 g of KH
(0.0025 mol). THF (50 ml) is added to suspend the KH. A separate 250
ml Schlenk flask is charged with 2.0 g of a CH3SiHC12/HSiC13
coammonolysis mixture that is prepared as described in section II.
Thls mixture is prepared by ammonolysis of CH3SiHC12 and HSiC13
in ether solution, and then combined with 2.2 g of
[(CH3SiH)X(CH3Si)y]n (0.05 mol, x ~ 0.74, y ~ 0.26), and 100
ml of THF. The mixed polymer solution is transferred by cannula into
the KH suspension. The reaction mixture gradually changes color to
light orange and hydrogen gas is slowly evolved. The resulting
solution is stirred at room temperature for 14 hours and is then heated
at reflux for 1 hour. The light orange color of the solution
persists. The reaction mixture is allowed to cool to room temperature
and 0.5 ml (7.9 mmol) of CH3I is added to form a white precipitate.
The solvent i5 removed by trap-to-trap distillation. The product is
extracted with 200 ml of hexane and the insoluble residue is removed by
centrifugatlon.
The clear, colorless supernatant layer is transferred via cannula
into a weighed 250 ml round-bottomed flask The hexane is removed by
trap-to-trap distillation leaving 3.8 g (91~ by weight) of a white
- powder. The latter is soluble in THF, benzene, and hexane.
2. Usin~ a Coammonolysis mixture of CH3SIHC12/HSiC13 Prepared in
THF
- According to the procedure described above, the reaction between
O.1 g of KH (0.0025 mol), 2.0 g of the coammonolysis product of
CH3SiHC12/HSiC13 (prepared in THF solution), and 2.2 g of
-61-
.~ ...
~75
[(CH3SiH)~(CH3Si)y]n (x ~ 0.74, y - 0.26) is carried out
under nitrogen. The resulting reaction mixture also gradually changes
color to light orange with 910w evolution of hydrogen gas. The
~olution is stirred at room temperature for 14 hours and then 0.5 ml
(7.9 mmol) of CH3I is added. Work-up as described in the previous
experiment leaves a white, soluble solid.
B. Reactio~s of a Mixture of a Coammonolys~ i3~ and
Polycarbosilane with KH Catalyst.
1. Usin~ a Coammo~ol~sis Mixture o~ 3SiHC12/HSiC13_
Pre~ared fro~ Diethyl Ether,
c. Polycarbosilane~Coa~monolysis Mixture in l:l weieht
ratiQ
In a dry box, a 250 ml round-bottomed flask equipped with a
stir-bar, reflux condenser and a serum cap is charged with 0.15 g of KH
(3.75 mmol). THF (50 ml) is added to suspend the KH. A separate 250
ml Schlenk flask is charged wtih 5.0 g of the coammonolysis product of
CH3SiHC12 and HSiC13 prepared in ether solution, and 5.0 g of
polycarbosilane, and 150 ml of THF. The mixed polymer solution is
transferred by cannula into the KH suspension in THF. The reaction
mixture gradually turns clear and hydrogen gas slowly evolves. The
resulting solution is stlrred at room temperature for 2 hours and is
then heated at reflux for 24 hours. The reaction mixture ls allowed
to cool to room temperature and 0.5 ml (7.9 mmol) of CH3I is added
and the mixture is heated for several hours. The solvent is removed by
trap-to^trap distillation. The product is extracted with 200 ml of
hexane and the insoluble residue is removed by centrifugation. The
clear, colcrless supernatant layer is transferred via a cannula into a
weighed 250 ml round-bottomed flask. The hexane is removed by
trap-to-trap distillation le~ving a white powder. The white powder is
soluble in THF, benzene, and hexane.
C. Reacti ns of a Mixture of a Coa~monolYsis Mixtu~e and cy~_ic
L~_3Si(H~O1n with KH catalyst
-62-
~04~7S
1. L~3Si~H)Oln/Coa~onolYsi.s Mixture oE
_3~iHC12~H__~_3 in 1:1 wei~ht ratlo
In a dry box, a 250 ml round-bottomed flask equipped with a
stir-har, reflux condenser, and a serum cap is charged with 0.1 g of KH
(2.50 mmol). THF (100 ml) is added to suspend the KH. A separate 250
ml flask is charged with 4.0 g of the product, prepared by
coammonolysis of CH3SiHCl2 and HSiC13 in THF solution, and 3.6 g
of [CH3Si(H)O]n, and 50 ml of THF. This solution i3 transferred by
cannula into the KH suspension in THF. The reaction mi~ture gradually
turns clear and hydrogen gas is slowly evolved. The resulting solution
is stirred at room temperature for 4 hours and then 0.5 ml (7.9 mmol)
of CH3I is added. The solvent is removed by trap-to-trap
distillation. The residual solid is treated with 80 ml of hexane and
the insoluble residue is removed by centrifugation. The clear,
colorless supernatant layer is transferred via cannula into a weighed
100 ml round-bottomed flask. The hexane is removed by trap-to-trap
distillation leaving of a white powder. The latter is soluble in THF,
benzene, and hexane.
This invention has been described in detail with reference to the
preferred embodiMents thereof. However, it will be appreciated that
those skilled in the art, upon consideration of this disclosure, may
~ake modificatlons and improvements within the spirit and scope of the
invention.
-63- ;
,
. .
