Note: Descriptions are shown in the official language in which they were submitted.
WO 90/12835 '`, '., . 2;0,2 8 3 ~ 2 PCl'/US90/D1638
HYDR I DVS I LOXANES AS
PRECURSORS TO CERAMIC PRODUCTS
Description
Technical Field
This invention relates generally to preceramic ~ - -
polymers and preparation of ceramic products therefrom.
More particularly, the invention relates to the use of
hydridosiloxanes as precursors to ceramic products such
as silica, silicon oxynitride, silicon carbide, and
metal silicates.
Backqround Art
The invention relates primarily to- (1) the
preparation of polymers that are useful as precursors to
ceramic materials (i.e., which serve as ~preceramic"
polymers); and (2) catalytic activation of si-H bonds.
- The invention also concerns, in one embodiment, the use
f sol-gel processing techniques.
The sol-gel process is an important route for
advanced metal-oxide glasses and ceramics. The method
is currently used or of potential for protectiv2, --
optical and electronic coatings, optical fiber preforms,
nonlinear optical devices, dielectrics or supercon-
- ductors, display materials, and structures. The sol-gel
technique provides a relatively low~temperature,
controlled method of; producing a~large variety of shapes , ~-
such as monodispersed~particles,~runiform coatings,
~ _ T, , , ` -`
' ' ' . ~
~' -'''' ." ':
~_.
I .,:
WO90/12835 ~ 2 0`2 8 8 ~ ~ PCT/US9OlO1638 ~
fibers, densë;br porous articles, and mixed metal oxides
having controlled stoichiometry and purity at the
molecular level.
The sol-gel process has been based mostly on
the same group of starting materials, the metal
alkoxides, carboxylates and diketonates. These
precursors are hydrolyzed, then condensed in the
presence of an alcohol/water solution to form a gel
which is dried and fired to give the final product.
Chemical control of product formation is manipulated by
temperature, type of catalyst and pH as well as by the
type and ratio of reactants in solution. See, e.g.,
C.J. Brinker et al., in "Ultrastructure Processing of
Ceramics, Glasses and Composites I" (1984), at pp. 43 et
seq.
Thus, the reaction procedure controls to a
large extent the morphology of the final gel, and,
therefore, the final ceramic microstructure as well.
Low water content and/or acidic conditions will give
spinnable gels because the precursor polymer will, as
noted above, be substantially linear. Higher water
content will give slightly crosslinked, coatable gels,
while a very high water content and/or basic conditions
will give highly crosslinked gel products that are
useful in casting processes and for powder formation.
See B.J.J. Zelinski et al., J. PhYs. Chem. Solids
45:1069 (1984), and L.C~ Klien et al., Ann. Rev. Mat.
Sci. l5:227 (lg85)~
It~has recently been su~gested that àlkoxide-
~ siloxane oligomers may sérve as molecular building ~blocks for unique ceramic siiica structures (V.W. Day et
al.,-J. Am.:Chem. Soc. 107:8264 (1985)). A rigid cubic
alkoxysesquisiioxane, [SigO12](0~H3)g, offers the e
poss~ibility of generâting-porous materials, yet rigid
due to the molecular block s~ructure.
,
.
~;
: ' - . .
WO90/12835 r'2,~j28;$~,2 Pcr/usgo/nl~38
As noted above, the inver.tion also relates to
preparation of preceramic polymers, i.e., polymers which
may be converted upon pyrolysis to ceramic products.
The present invention provides preceramic siloxane
S polymers which are useful for preparing a wide variety
of silicious ceramic materials and articles, e.g.,
articles such as fibers, films, shaped products, and the
like, comprising materials such as silica, silicon
oxynitride, silicon carbide, or metal silica~e.
The preceramic polymers, or "ceramic
precursors", of the invention are prepared by catalytic
activation of Si-H bonds. To date, catalytic activation
of Si-H bonds has mainly been used for hydrosilylation
reactions of unsaturated compounds, as illustrated by
reactions ~1) and (2~:
R3Si-H + M --~ R3S~-M-H (1)
R3Si-M-H + R2C=X~ R2CH-XSiR3 ~ M t2)
( X = O, CR2 )
Over the past 25 years, numerous homogeneous and
heterogeneous catalysts have been found which promote
these reactions. See, e.g., J.L. Speier et al., J. Am.
Chem. Soc. ?9:97~ (1957). Typical applications of -~
these reactions have been in organic synthesis or in the
crosslinking of silicon rubbers (J.P. Collman et al., in
"Principles and Applications of Organotransition Metal
Chemistryn, pp. 38~-392, University Science Books,
1~80). Only recently have such reactions been found
....
useful in another application, crosslinking of pre~
ceramic polymers, as described in commonly assigned PCT
;-
,
.,,, ~ ~ ', '
WO90~12835 2 0 ~ 8 & 5 2 4 PCT/US90/01638
Application No. PCT/US86/02266, published ll September
1987 as w~87/0529a. ~:
Related reactions involving substitution at an
Si-H bond have been used to form compounds containing
Si-Y groups wherein Y i~, for example, halogen, alkoxy,
or substituted or unsubstituted amino: . .
.
R3Si-H + H-Y~ R3Si-Y + H2 (3)
catalyst
L.H. Sommer et al., J. Ora. Chem. 32 :4270 (1967). Only
mono- and di-substituted aminosilanes, halosilanes and
alkoxysilanes have been synthesized by this method.
Surprisingly, there have been virtually no attempts to :~
enlarge the po~ential capability of reaction (3). For
example, the inventors herein are unaware of any work .
invol~ing reaction of compounds containing multiple Si-H
bonds with water to form oligomeric or polymeric
siloxane products.
Investigators at SRI, the assignee of the
present.application, have recently discovered that .
catalytic activation of Si-H bonds is extremely useful
in the synthesis of polysilazane ceramic precursors,
according to reaction (4)~
R2SiH2 + RNH2 -~ [R2SiNR]X + H2 (4).
. - catalyst~ ~ :
-~
.
- (R=H, alkyl)
~ ~ . ......... . .
.To date,- however, efforts have not been focl~sed on
. -enlarging the scope of;the analogoùs reaction in the
:- ~ presence of--water, i.~e., instead of using ammonia or
; 35 monoalkylamines. Preliminary research indicates that
. .
-
.
~ .
~: ' ' ' , .
WO90/12835 ~~~ ;' PCT/US90/01638
similar reactions (as illustrated by reactions (5) and
~6)) will occur in the presence of water, to produce
monomeric, oligomeric or polymeric siloxanes, at room
temperature, or lower:
30C
R3SiH + H20 -~~ R3SiOH + R3SioSiR3 ~ H2 (5)
RU3(cO)l2
30C
R2SiH2 + H2O ~ R2SiO]X + H2 (6)
RU3(cO)l2
The present invention is directed to a new
approach to polymer processing, and involves combining
the fields of research summarized hereinabove: (a)
preparation of preceramic polymers useful in making
ceramic materials: and (b) reaction of hydridos;loxane
compounds by catalytic activation of the Si-H bonds con-
tained therein. In a preferred embodiment, the inven-
tion also involves the use of (c) sol-gel processing
techniques. Gels or preceramic polymers produced usin~
the present method are highly "processable" and, upon
pyrolysis, give the desired ceram-ic material in
relatively high yield.
Disclosure of the Invention
~ Accordingly, it is a primary object of the
invention to use catalytic Si-H bond activation to
produce precursors to ceramic products. --
It is another object of the invention to use
~catalytic Si-H bond activation, in conjunction with
-~~
~: , , - , ' : . : : ' '
O90/1283~ 2 0 ~ 2 PCT/US90/01638
sol-gel processing and/or other crosslinking or coupling
techniques, to produce ceramic precursors.
It is still another object of the invention to
prepare preceramic polysiloxanes using a ~wo-step
process whirh involves: (a) replacing hydrogen atoms of
a hydridosiloxane starting material with non-hydro~en
substituents, via catalytic si-H bond activation, and
(b) crosslinking the substituted intermediate so
provided using sol-gel processing or a related
crosslinking technique. It is also possible to treat
the starting material with water under sol-gel reaction
conditions, prior to introduction of non-hydrogen
moieties at Si-H sites.
It is yet another object of the invention to
provide such a method of making preceramic polymers in
which catalytically activated Si-H bonds in the
hydridosiloxane starting material are replaced with
Si-C, Si-N, Si-O, Si-Metal, or other linkages.
It is a further object of the invention to
provide a method of making silicious ceramic products by
pyrolyzing preceramic polymers synthesized via catalytic
Si-H bond activation of hydridosiloxane starting
materials.
- It is stilI a further object of the invention
to provide a method of making silica, silicon
oxynitride, silicon carbide, and/or metal silicates by
pyrolyzing various preceramic- polymers as described
herein.
Additional ob3ectsj--advantages-and novel - ~-
30 features of the invention wili b;e set forth in part in
the description which follows, and in part will become
apparent to those skilled in thë art upon examination of
the following, or may be learned by practice of the
~ invention.~
~: -
- ' i
I
:, ' ' . . , . , " '' . ' ' ,' ~ " ' ' ' '' ' ~ ';'," ' . ' ' ' ' ' ` `" ': ~ ',
WO90/1283~ 20~8 ~!S~ PCT/US90/01638
In one aspect of the invention, a method is
provided for preparing a ceramic precursor, which
comprises: (a) providing a hydridosiloxane polymer
containing one or more Si-~ bonds per mer unit; and (b)
reacting said hydridosiloxane polymer with a hydroxyl-
containing compound R'-OH, wherein R' is hydrogen,
Cl-Clo alkyl, or aryl of 1-2 rings tand may be
substituted with one or more substituents which do not
significantly hinder the reaction), in an inert atmos- -
phere in the presence of a catalyst effective to acti-
vate Si-H bonds, to give a ceramic precursor in which
hydrogen atoms have been replaced by -OR' moieties.
Crosslinking may then be effected using sol-gel or other
suitable techniques.
In other aspects of the invention, ceramic
precursors are provided using a similar method, i.e.,
one which involves catalytic activation of Si-H bonds in
a hydridosiloxane starting material, but which provides
preceramic polysiloxanes in which the "activated"
2~ hydrogen atoms have been replaced with non-hydrogen,
non-alkoxy substituents, e.g., nitrogen-containing,
carbon-containing, or organometallic groups.
In still other aspects of the invention,
silicious ceramic materials are prepared by: (l)
catalytic activation of Si-H bonds in a hydridosiloxane
starting material; (2) replacement of the activated
hydrogen atoms by non-hydrogen substituents; (3)
optional crosslinking using sol-gel processing or some
other suitable technique (e.g., reaction with an amine
crosslinker); and (4) pyrolysis at a selected
temperature and in a selected atmosphere, to give the
desired ceramic product. Depending on the pyrolysis
tempera$ure, the particular polysiloxane preceramic, and
on the pyrolysis atmosphere, ceramic materials may be
;~
" '''".''
. .
, . :
WO9Otl283~ 2 0 2 8 8 ~ 2 PcT/vsgOJol638
provided which comprise silica, silicon oxynitride,
silicon carbide, metal silicates, or mixtures thereof.
In many aspects of the invention, the
hydridosiloxane starting material of the aforementioned
processes, and/or the substituted intermediate, is
treated with water in the presence of an acid or base
catalyst after an initial catalytic Si-H bond activation
reaction. Such a step is in conformance with standard
sol-gel processing techniques, and extends the degree of
polymerization in or crosslinks the product. Typically,
this step provides a polymeric gel.
Modes for Carrvinq Out the Invention
A. Definitions.
nHydridosiloxanes" as used herein are
compounds which con~ain one or more silicon-hydrogen
bonds and one or more silicon-oxygen bonds. The term ic
intended to include oligomeric, cyclomeric, polymeric
and copolymeric hydridosiloxanes.
The term "polymer" is intended to include both
oligomeric and polymeric species, i.e., compounds which
include two or more monomeric or cyclomeric
hydridosiloxane units.
The "ceramic yield" of a compound upon
pyrolysis indicates the ratio of the weight of the
ceramic product after pyrolysis to the wei~ht of the
compound before pyrolysis.
A "lower alkyl" or "lower alkoxy" group is an
alkyl or alkoxy-group, respectively, having 1-6 carbon
atoms, more typically 1-4 carbon atoms, therein.-
"Silyl" as used herein is~an
" -
S i x ~
,
WO90/12835 ; ~; 2.~ 2 8 8 ~ 2 PCT/US90/01638
-SiX2- or -SiX3 moiety wherein X is hydrogen, lower
alkyl, lower alkenyl or amino, unsubstituted or substi
tuted with 1 or 2 lower alkyl or lower alkenyl groups.
The "silyl" moiety may be part of a silicon-containing
oligomer, cyclomer or polymer.
Hydridosiloxane "coupling agents" as used
herein are intended to include any chemical reagent
which is capable of bridging two hydridosiloxane units.
The coupling agent typically has the formula HZH,
wherein Z is oxygen, sulfur, phosphoro, amino
(unsubstituted or substituted with one or more lower
alkyl or silyl groups), -O-, -O-Y-O-, -NX-NX-, or
-NX-Y-NX-, where Y is a linking group, typically lower
alkyl or silyl, and X is typically lower alkyl, silyl,
or hydrogen -Z- bridges between silicon atoms of two
hydridosiloxane monomeric or cyclomeric units.
B. Preparation of Ceramic Precursors.
~.l. Overview:
The method of the present invention involves
preparation of polysiloxane ceramic precursors by
catalytic Si-H bond activation of a hydridosiloxane
starting material. While a number of different types of
reactions and products are encompassed by the present
method, each reaction involves catalytic activation of
Si-H bonds in the selected hydridosiloxane material, and
replacement of the activated hydrogen atoms therein.
Table l illustrates the various pathways and
products of the invention:
WO 90~12835 ` 2 d ~ g r 2
PCT/US~0/01638 ,~.
Table l
Starting material: Polymer containing
the structure [RSiHO~n
PathwaY __ Primarv Product
Pyrolyze directly SiO2/SiCJC,
si2o~2
(dependin~ on R,
temperature and
pyrolysis atmosphere)
. . -- ~ _ :
$I.
A. Substitute with alkoxy groups lRsiHo]l[Rsio1m
OR': react with R'OH OR'
B. Sol-gel: prepare by cata- tRSi~o]l~RSio]~
lytically reacting product of O .
. A . wi th wa~cer - - [ Rs iHo ~ l ~ R~ io ]m
.,.
. .. ' -
~: 35 ~ . ~
:~ !
` 2028~2
: ~O90/~2835 b~ '` . '~' ` ~ PCT/US90/01638
11
. _ .... . . ., :
Pathway _ PrimarY Product - ~.
C. Pyroly7e product of II.A. or
II.B.
l. Under inert atmosphere SiO2/SiC/C
2. Under reactive amine
atmosphere si2oN2/sio2
3. under 2 SiO2
l III.
A. Sol-gel: prepare by [RSiHO~l[RsiO]m ::.
catalytically reacting with OH
water
B. Pyrolyze product of III.A.
directly
l. Under inert atmosphere SiO2/SiC/C .
2. Under reactive amine : .
atmosphere si20N2/Si~2
3, Under 2 sio2 -:.
C. React product of III.A. [RSiHO]l[RsiO]m
with an organometallic LbM-O
complex MLa,in the pres- :
ence of a catalyst
D. Pyrolyze product of-III.C.
l. Under ~2 MXSiyOz
2. Under reactive amine MXsiyozNw . ~.
atmosphere (e.g., ~Sialon")
~ . .
~, , ,~ " . _ .. . .. ... = ,
.
~ 35 : .
' ` : . ' ' '
:
- -':
. ' ': . - .
~. ..
-: . . : -.- - . .. .. , . . , ,. ., . . . , ., ., ~, . . . .. . .. .
WO 90/~Z83~ . ~` 2 ~ 2 8 ~ ~ 2 PCT/US90/01638 ,_
12
_ ,
IV.
A. Substit~te with hydrocarbon: [RSiHOll[RSioim
ca~alytically react with a ~ :
compound containing an un- R
satur~ted carbon-carbon
~ond
B. Pyrolyze
1. Under inert atmosphere SiO2~SiC~C
2. Under reactive amine
atmosphere Si2ON2/siO2
3. Under 2 SiO2
V.
A. Substitute with amine: [RSiHO]l[RSio~m
catalytically react with a NR~2
secondary amine NR~2H
: 25 B. Crosslink with amine:
catalytically react with [RSiHO]l[RSIiO]m
primary amine NR~2 or N-
ammonia [RSiHO]l[~siO]m
C. Pyrolyze
o 1. Under in~rt atmosphere Si2ON2/SiO2/SiC/C
2. Under reactive amine
atmosphere SiON2/siO2
3. under 2 SiO2
' . .. : :. ': : ' ' ~ ... ''.. : . :. . .. .
WO 90/1283~ ~`
2 0 2 ~ 8 ~ 2 PC~/US90/01~38 ::
13
5 --~_
VI.
A. Substitute with organometallic
group: ~RsiHo]l[Rsio~m : -
1. Ca~alytically react with LMLa-
~La or
,
[RSiHO]l(R~iO]m .~ -
MLb
2. Catalytically react with [RSiHO]l~RsiO]m
LaM-VH OMLb
B~ Pyrolyze produc~s of either
VI.A.1. or VI.A.2.
1. Under 2 MXSiyOz ~ - .
~. Under reactive amine
a~mosphere MXsiyozN
. . .
VII.
React with coupling agent ~-Z-H
1. ~RSiHO]~ [RSiO]
z :
[ RS i o ~
2. Cyclomeric starting material -- .
/o - SiHR r O-SiHR RHSi-O~ z~ . ~ .
- R~iSi C~ I ~i' `I 01' S~~
,, i SiHR ' l- ~)` j~'Si~z~si`~si~R i '~ '
RHS i--O - ~ n -:
. .
; -^ ^---- - . :
3 5
''
WO90/12835 ~ ~- 2?~52 PCT/US90/01638 ^
~ he;hydridosiloxane starting material is a
polymer which contains recurring mer units having the
structure -[RSiHO]-, i~e., ~[RSiHO]n- wherein n
indicates the number of recurring mer units in the
polymer, and wherein R is selected from the group
consisting of: hydrogen; hydroxyl; Cl-Clo alkyl or
alkoxy, which may be either unsubstituted or substituted
with hydroxyl, lower alkyl, lower alkoxy, halogeno,
silyl, or NR"2 groups, wherein R" is hydrogen or lower
alkyl; aryl of 1-2 rings, which may be similarly
substituted; NR2n; silyl; and MLa, OMLa, or NR"MLa,
wherein MLa is an organometallic compound, and may be an
oligomer or cluster. This hydridosiloxane starting
material will frequently be commercially available, or
it may be synthesized from an unsubstituted monomeric or
polymeric hydridosiloxane using the catalytic Si-H bond
activation/substitution reaction described herein.
Cyclomers such as
,. O--SiHR
RHS~ ~
OSiHR
RHS i--0/
2S
may be used as well, as may hydridosiloxane copolymers.
Suitable hydridosiloxane copolymers include the mer unit
-~RSiHO]-, as above, combined with other types of
monomers to impro~e polymeric and pyrolytic properties.
Any such copolymers are considered to be equivalent, for
purposes of the invention, to the homopolymer
~tRSiHo]n-. Preferred monomer units for incorporation
into a hydridosiloxane copolymer include but are not
limited to, the following structures (wherein R is~as -
defined above):
-
.' . '
7r ' '
WO 90~2835 ` 15 2 0 2 8 ~ ~ 2 PCrJuS9olol63g
R 0 0
-Si- -O-Si-O- $
~ , o and R
It is required that the aforementioned
reactions for preparing ceramic precursors be carried
out in the presence of a catalyst. Virtually any
catalyst may be used, so long as it does not actively
interfere in the reaction and is effective to ~he
activate Si-H bonds of the precursor. Suitable
catalysts include acid catalysts such as HCl, H2So4,
HBr, NH4Cl, NHgBr, AlC13, BC13 and H3PO4, basic
catalysts such as NaOH, KOH, Ca(0~2, NH3 ~nd pyridine,
and metal catalysts, particularly transition metal
catalysts such as those indicated in Tables 2 and 3
below. Table 2 sets forth homogeneous catalysts which
dissolve in the reactants. Heterogeneous catalysts such
as those of ~able 3 may also be used, as can mixtures of
homogeneous catalysts and/or heterogeneous catalysts.
(It should be pointed out here that the "homogeneous"
and heteroseneous" classifications are made on the
basis of solubility in common organic solvents such as
alcohols. However, it is not uncommon that during the
reactions, homogeneous catalysts may be converted to a
heterogeneous form and vice versa.) These catalysts may
include any number of ligands, usually 1-6, including
carbonyl, amino, halo, silyl, hydrido, phosphine, arsine
and organic ligands.
3 ~The reaction involving catalytic activation of
Si-H bonds in the hydridosiloxane starting material
-~RSiHO]n- is preferably carried out under an inert
atmosphere, e.g., under argon, nitrogen, or the like.
Also, since~the reaction can be an aggressive, it is
preferred that it be carried out at temperatures of 0C
wo gO/12835 2 0 2 8 8a 2 PCT/US90/01638
to lOO~C, more preferably 0C to 40C. The use of an
inert organic solvent, is optional.
The catalyst(s) may be supported on a polymer,
inorganic salt, carbon or ceramic material or the like.
The heterogeneous catalyst may be provided in a
designated shape, such as in particles, as porous
plates, etc.
The concentration of catalyst will usually be
less thAn or equal to about 5 mole percent based on the
total number of moles of reactants, usually between
about O.l and 5 mole percent. In some instances,
however, catalyst concentration will be much lower, on
the order of 20 to 200 ppm.
Table 2, Homoqeneous CatalYsts
HgRu4(CO)12, Fe(CO)s, Rh6(C)16~ C2(C)8,
(Ph3P)2Rh(CO)H, H2PtCl6, nickel
cyclooctadiene, Os3(co)l2~ Ir4(C)l2~
(Ph3P)2Ir(CO)H, NiCl2, Ni(oAc)2, ~p2TiCl2,
(Ph3P)3RhCl, H2Os3(CO)lo~ Pd(Ph3P)4,
Fe3(CO)l2, RU3(CO)12~ transition metal
hydrides, transition metal salts (e.g., ZnCl2,
RuCl3, ~a~Ru3(CO)ll) and derivatives, PdCl2,
Pd(OAc)2, (~CN)2PdCl2, [Et3SiRu(CO)4]2,
(~e3Si)2Ru(CO)4, [Me2SiXSiMe2]Ru(CO)4, and
mixtures thereof.
.
Table 3, Heteroqeneous Catalys_ -
Pt~C, Pt /~a50~, Cr, Pd/C, Co/C, Pt black, Co
black, Ru black, Ra-Ni, Pd black, Ir~Al2O3,
Pt-/Sio2, Rh/TiO2; Rh~La2O3, Pd/Ag alloy,
LaNis, PtO2, and mixtures thereof.
35 ~
~,
-. - - . . . : .: .- . , . . , -., . .. ,; ~.. . ~ . -: . . .
W090/12835 ~.~` 2 02$ ~ S 2
17 ~CT/US90/01638
~.2. Substitution of -~RSiHo]n- with .:
alkoxy moieties: . -
The preferred method of the present invention
involves preparation of a polysiloxane preceramic by
reaction of a hydridosiloxane polymer with an alcohol,
either prior to or following sol-gel processing. The .1
reaction involves catalytic activation of Si-H bonds in
the hydridosiloxane starting material, and replacement
of the "activated~ hydrogen atoms therein with alkoxy
groups, as indicated in Section II of Table l.
The hydridosiloxane may be represented as
containing one or more mer units having the structure .-
-Hx ~ .1.
_ - si-o_ _
R2-x : ~
wherein x is l or 2. Reaction of this starting material
with a hydroxyl-containing reactant R'OH, wherein R' is .-
hydrogen or a lower alkyl moiety and is different than :
R, yields the polysiloxane preceramic .
~ 5~- ~ [ I
R2 - x R2 - x ' :
,, .
~.in which, as may be deduced from the structure, hydrogen
atoms of the hydridosiloxane starting material have been
- replaced by new, OR', alkoxy moieties. The relative ` ~ .
amounts of.unsubstituted.and alkoxy-substituted mer
. units are indicated;by;the subscripts }~and m, . ¦~
~,}~
''" :
~1, ' ''
I ~
'"'`' " . ',','`'''"''.<' ., ;,"', ' ' ' ;'
WOg 835 . ~; - 2 ~ 8 ~2
0/12 . 18 PCT/US90/01638
respectively. (Reaction with water, i.e., wherein R' is
hydrogen, is described in Section B.6. below.)
This preceramic may be pyrolyzed directly to
give the products enumerated in Table l. Alternatively,
it may be processed prior to pyrolysis according to the
sol-gel method described in Section B.5., below, to give
a preceramic gel (see Section II of Table l). The gel,
while yielding the same ceramic product as its linear
precursor, provides higher ceramic yields and does not
lQ melt upon pyrolysis.
In a related reaction, the hydridosiloxane
starting material is monomeric rather than polymeric,
and initially substituted with alkoxy groups, i.e., it
is a monomeric silane substituted with one, two or three
alkoxy groups "ORln. The monomeric silane may thus be
represented by the formula HmSi(oRl)4_m wherein m is l,
2 or 3. In a first type of reaction involving this
monqmeric starting material, the compound is reacted
with an alcohol R20H in the presence of a catalyst ~
effective to activate Si-H bonds so that activated ~ :
hydrogen atoms are replaced by new alkoxy moieties
"OR2n. Rl and R2 are typically Cl-Clo alkyl or alkoxy
moities, or aryl of 1-4, preferably 2-3 rings, more
typically lower alkyl groups, and may be either
unsubstituted or substituted as for the substituent "R",
d;scussed above. The resulting structure may be
represented as Si(ORl)~-m(OR2)m.
This latter compound may be hydrolyzed to give
a polysiloxane ceramic precursor; hydrolysis will again
be.carried out in the presence of`a catalys~ effective
to actavate Si-H bdnds. The differential in hydrolysis
. rates of the two different types of alkoxy moieties -O
and -oR2 is useful in.:dictating the type of polymer
which result upon-:gelation:(i.e.,~upon hydrolysis).
Where there is a substantial difference in hydrolysis
WO90/12835 7 '` '; I ~` 0 2 8 8 ~ 2 PCT/US90/01638
19
rates, a more linear polymer will be produced, while if
hydrolysis rates are approximately the same (for
example, when Rl and R2 represent the same
substituents), a crosslinked structure will result.
S (A second type of reaction involving the
aforementioned monomeric silane is simple hydrolysis to
give a polymeric alkoxy-substituted siloxane, containing
pendant -oRl moieties.)
B.3. Introduction of additional carbon: ~hen
the ceramic product ultimately desired is to include
car~on, e.g., as silicon carbide, it is preferred that
the polysiloxane ceramic precursor be modified to
increase the mole fraction of carbon therein. In such a
case, as illustrated in Section IV of Table l, the
hydridosiloxane starting material -~RSiHO]n- is reacted,
in the presence of a catalyst effective to activate Si-H
bonds, with a compound containing an unsaturated -
carbon-carbon bond. Sol-gel processing is optional and ~ -
may be carried out either before or after th~
substitution reaction. The compound may be alkenyl or
alkynyl, and of any size and containing any number and
kind of substituents, so long as potential steric
interference is minimized and the substituents do not
hinder the reaction. In general, the reaction may be
represented as introducing pendant -(CH2)2-R species in
place of the activated hydrogen atoms, by reaction with
-CH=CH-R (or -C_C-R) with R as defined hereinabove.
Pyrolysis of the carbon-rich polysiloxane
precursor will give-ceramic products as indicated in ~ -
Table l, Section IV.
. Bo4~ Amine substitution: When it is desired
that the ceramic material include nitrogen, e.g., as
silicon nitride or silicon oxynitride, the
hydridosiloxazane starting material -[RSiHO]- is reacted
35 with ammonia or a primary or secondary amine in which
.. -. . . : . .. ~ : . . . . .
W090~283s ' ; -;- 2 0 2 8 8 5 2
- PCT/US90/01638 -
the substitutents, if any, are lower alkyl, in the
presence of a catalyst effective to activate Si-H bonds.
When the amine reactant is a secondary amine, the
reaction will result in a structure in which the
linearity of the siloxane polymer is substan~ially
maintained, but in which the activated hydrogen atoms in
the starting material have been replaced by pendant
amine groups. In the preferred embodiment, the amine
reactant is ammonia or a primary amine, and a
crosslinked siloxazane structure in which polysiloxane
chains are joined through -NH- or -NR"- linkages results
(Section V of Table l). Additional information
concerning this latter reaction may be found in PCT .:
Publication No. W087/0529a, cited above.
Pyrolysis of either the linear or crosslinked
ceramic precursor in which nitrogen-containing moieties
have been incorporated as above will result in: (l) a -
mixture of silicon oxynitride, silica, silicon carbide
and carbon, when pyrolysis is conducted in an inert
atmosphere, (2) a mixture of silicon oxynitride and
silica, when pyrolysis is conducted in a reactive amine ..
atmosphere, e.g., in ammonia or methylamine; (3) silica,
when pyrolysis is conducted in oxygen.
B.5. Substitution with organometallic
species: In an equally important embodiment of the
present invention, organometallic species are introduced
into the polysiloxane precursor prior to pyrolysis. .: .
Pyrolysis will then give.metal silicates, which
(depending on the pyrolysis-atmosphere) may or may not
contain nitrogen. - -: .
Several routes may be taken to introduce :
organometallic species into the polysiloxane precursor.
~irst, the hydridosiloxane starting material -~SiHO]n- -
may be directly reacted.with an or~anometallic compound
MLa, wherein M i~ a metal atom, L represebts one or more - '
1,
i ~ ` '
W O 90/12835 ` ~ 2 0 2 8 8 ~ 2 PC~r/VS90/01638
: 21
ligands associated therewith, and "a~ represents the
mole ratio of L to M in the compound. "MLa" may be
monomeric or oligomeric: it may also represen~ a
cluster. As above, the reaction is carried out in the
S presence of a catalyst effective to activate Si-H bonds,
so that the activated hydrogen atoms are replaced with
the organometallic species. Depending on the particular -: -
metal and ligand, the activated silicon atoms may bind
either to the metal or to the ligand, to give either
Si-M or Si-L bonds in the resultant ceramic precursor.
Examples of representative "M" elements
include lithium, sodium, potassium, magnesium, calcium,
boron, aluminum and phosphorus, as well as the transi- -
tion metals, lanthanides and actinides. Examples of
suitable ligands include carbonyl, cyanocyclopentadienyl
(nCpn), phenyl (nPhn), halide, metal clusters, alkoxy,
and ~C-C~, where ~ is alkyl, particularly lower alkyl,
or aryl, such as phenyl.
Second, the hydridosiloxane starting material
-[RSiHO~n- may be reacted: (1) with water, as described
above, to give pendant hydroxyl groups in the ceramic
precursor; and subsequently (2) with the organometallic
compound MLa. In this case, in contrast to the reaction
just described, the organometallic species bind to the
silicon atoms of the polysiloxane chain via oxygen
bridges, i.e., Si-H bonds are replaced by Si-OMLb
linkages, wherein b represents the mole ratio of L to M
in these pendant groups.
~ ~ Third, the hydridosiloxanë starting material
; 30 ~LRsi~o]n- may be directIy reacted with a compound
MLa-OH or M-OH~ i.e., a metal-containing compound which
includes one or more hydroxyl groups. As before, the
~ ~reaction is carried out in the~prèsence of a catalyst
,~e.~ , effective to activate Si-H bonds.--Thè cer~am~c precursor
- which results here is similar to that obtainéd in thë
. ~ . ,.. , . ,:............. .. ~ ''
0288~2
WO90~12835 - -
22 P~US90/01638
reaction just~;described, in which Si-H bonds are
replaced by Si-OMLb linkages. Examples of
metal-containing compounds suitable for this reaction
include CpFeCp OH, Cp2Ti(oH~2, NaOH, KOH, R3Si-oH~
R2B-OH, and the like, wherein R is as defined earlier
herein. -
Pyrolysis of ceramic precursors which have
been modified to include organometallic groups yields
metal silicates that may be represented by the formula
MXSiyOz. Pyrolysis under an amine atmosphere, or of a
precursor that has been additionally modi~ied to include
nitrogen (as described above), will yield a metal-
containing silicious ceramic material that additionally
contains nitrogen, MXSiyOzNw, wherein x, y, z and w
represent the combining proportion of M, Si, O and N in
the ceramic product.
B.6. Sol-gel processing: The alkoxy-
substituted hydridosiloxane prepared in Section B.2.
may, if desired, be processed using sol-gel techniques.
The reaction is a hydrolysis step carried out using con-
ventional sol-gel processing methodology as described,
for example, by C.J. Brinker et al., in "Better Ceramics
Through Chemistry", eds. C.J. Brinker et al., Mat. Res.
Soc. Symposium Proceedings 32 (1984), at page 25, cited
above. Hydrolysis introduces pendant hydroxyl groups
into the polysiloxane structure as well as some degree
of coupling or cross-linking. The produc~ obtained may
be either pyrolyzed directly Isee Section C) or
substituted as described in the preceding sections.
As with the reactions described in Sections
B.2. throu~h B.5., hydrolysis is typically carried out
at a temperature in the range of about 0C to 40C,
preferably at room ~emperature-or lower. The reaction
~^ ; medium~is typically aqueous alcohol, and the preferred
mole~ratio of water to hydridosiloxane starting material
WO90/~835 -~ ~ 2 0 2 8 8 ~ 2 PCT/US90/01638
is on the order of O.l to 8, more preferably O.l to ~,
most preferably O.l to 2. Increasing the amount of
water present will typically give a more crosslinked
product, while reducing the amount of water will
correspondingly give a more linear product. The
reaction is carried out catalytically, with Lewis acid
or base cataly~ts preferred. Examples of suitable
catalysts for this reaction are as set forth above.
B.7. Reaction wiith a coupling agent: If
desired, the polymer obtained upon catalytic Si-H bond
activ~tion and substitution may be further reacted with
a coupling agent H-Z-H as defined above. Such a -
reaction provides -Z- bridges between hydridosiloxane
units (which may be either oligomeric, polymeric or
cyclomeric), either extending the degree of polymer-
ization of or crosslinking the product.
Alternatively, a monomeric, oligomeric or
cyclomeric hydridosiloxane starting material, (e.g., a
cyclomeric material as described in Section B.l.), may
be directly treated with a couplin~ agent H-Z-H in a
dehydrocouplin~ reaction to give a coupled hydrido-
siloxane product. The coupled product may be pyrolyzed
as is, substituted first using the reac~ions of B.2.
through B.5., or processed via a sol-gel method as
~5 described in Section B.6.
These latter two reactions are illustrated
schematically in Section VII of Table l.
C. Pyrolysis.
Another important advantage of the
compositions and methods of the present invention is the
specificity and deyree of ceramic yield upon pyrolysis.
Generally, an increase in the--oxygen content of the
ceramic precursor will-:result;in a higher oxygen content
- 35 . in the ceramic product, whilè-an increase in the carbon
. ~- `2~288~2
Woso/~2835 ` -- PCT/US90/01638
content of the precursor will result in a higher carbon
content in the ceramic product. In addition to the
chemical composition of the ceramic precursor, the
atmosphere in which pyrolysis is conducted (as ~ell as
the pyrolysis tempera~ure) also dictates the composition
of the ceramic product. Ceramic materials which may be
obtained by the present method include, inter alia,
silica, silicon carbide, silicon nitride, silicon
oxynitride, and metal silicates. In a particularly
preferred embodiment, silica is prepared in
substantially pure form.
Silica will be provided by pyrolysis of a
ceramic precursor containing Si and O in oxygen or in an
oxygen-containing atmosphere. Carbon-free polysiloxanes
which may be prepared according to the method disclosed
herein will provide silica of very high purity, i.e.,
98-99~ or higher.
The ceramic preeursors prepared according to
the metnods described in Section B may also be pyrolyzed
to give silicon nitride, silicon oxynitride, silicon
carbide, and metal silicates, as described above and as
outlined in Table l.
Procedurally, pyrolysis is preferably carried
out as follows. A ceramic precursor prepared as
described in Section B is heated in the selected
atmosphere at a predetermined heating rate. If it is
desired that the composition of the pyrolysis product
correspond substantially to the composition of the
precursor, pyrolysis should be carried out in an inert
atmosphere. If desired, pyrolysis may be carried out in
a reactive atmosphere, e.g., under 2, NH3, H2O2j, H2O,
N20, H2, an alkylamine or the like. Pyrolysis in a
reactive amine atmosphere (i.e., under ammonia-or an
alkylamine gas? will typically give more nitrogen in the
ceramic product, e.g., in the form of--silicon nitride or -
WO90~12835 '`;` '-`-" 2~28852 PCT/US90/01638
silicon oxynitride. Preferred heatin~ rates for bulk
pyrolysis are in the range of about O.lC to lOC per
minute, preferably about 0.5C to 2C per minute, with a
particularly effective heating rate, optimizing ceramic
yield, of about 0.5C per minute. In some applications,
flash pyrolysis may be preferred (e.g., in coating
applications).
Pyrolysis is carried out at temperatures of at
least about 500C, preferably at temperatures in the
range of about 500C to about 900C. The pyrolysis
products set forth in Table l represent the ceramic
materials obtained by pyrolyzing in this temperature
range. In some cases, it may be desirable either to '
initially pyrolyze at a higher temperature, e.g., l200aC
or higher, or to carry out an additional high tempera-
ture pyrolysis step (again, at greater than about1200C) after the initial, 500C-900C, pyrolysis. Such
a procedure is useful to remove residual carbon, and in
carborizing or crystallizing the product. Where
mixtures of silicious ceramic products (e.g., silica,
silicon oxynitride) and carbon are-obtained upon
pyrolysis in the 500~C to 900C range, a subsequent high
temperature pyrolysis step will give silicon carbide in
high yield. Silicon carbide will also be obtained in
fairly high yield upon initial high temperature
pyrolysis of the carbon-containing ceramic precursors
disclosed hereinabove.
The heating process may include one or more
isothermal holding steps, in order to'"control the
3~ pyrolysis, to provide more crosslinking at-moderate
temperatures (less than about 400C) and to further '
increase the yield of the final product. '~
- ;. After pyrolysis at-'a relatively-'low'~ '
;~ tèmperaturej-i.e~ in~the 'range of'500C to'900C, a
high temperature pyrolysis-step may be-carrièd out to
WO90/22835 ~.-, 2b 2 8 8 ~ 2 PCT/US9OlO1638 .-
convert mixtures of silica and carbon to silicon carbide
or to crystallize an amorphous ceramic product Mix-
tures of silica and carbon are obtained, for example, by
low temperature pyrolysis of the preCUrSQrS of Section
B.l. and 3.2. If desired, pyrolysis may be carried out
in the presence of a catalyst; examples of suitable
catalysts are set forth in Tables 2 and 3.
Optionally, pyrolysis may be carried out only
partially, i.e., in applications where it is not
necessary to obtain a fully pyrolyzed material. Such
"partial pyrolysis" or partial curing may be carried out -
at temperatures lower than 500C.
D. Ceramic Coatings.
The ceramic materials provided herein are
useful in a number of applications, including as coat-
ings for many different kinds of substrates.
Silica, silicon nitride and silicon carbide
coatings may be provided on a substrate, for. example, by
a variation of the pyrolysis method ~ust described. A
substrate selected such that it will withstand the high~ :
temperatures of pyrolysis (e.g. metal, glass, ceramic,
fibers, graphite) is coated with the preceramic ~el
material. The ceramic precursor is then pyrolyzed on ~:
the substrate by heating according to the pyrolysis ~.
procedure outlined above. In such a method, pyrolysis
can be conducted relatively slowly, i.e., at a heating
.rate between about 0.1C-and 10.0C per minute, in order ~:
.to allow evolved gas to.escape gradually, and can
30 ... include one or more isothermal holding steps. In some ~ :
1nstances, for example, with- relatively temperature-
sensitive..mater:iaLs,. or..where a rapid-coating process is
desired, a~flash pyrolysis step may be preferred. Flash
j .~pyrolysiis -involves;either:di:rect exposure of-a coated :
,~3 substrate to a hiqh temperature,~ or application of thé
WO90/1~835 ~ji ; `2`0 2 PCT/VS90/01638
coating material to the surface of a heated substrate.
Repeated, multiple coatings may be applied where a
thicker layer of material is desired, with partial
curing or gradual or flash pyrolysis following each
individual coating step.
The pyrolysis temperature will vary with the
type of coating desired. Typically, temperatures will
range from about 350C tc about 1100C. Lower tempera-
tures, below about 500C, can result in only partially
pyrolyzed polymer.
The above coating procedure is a substantial
improvement over the conventional, chemical vapor depo-
sition (CVD) method of producing silicious coatings in
which the appropriate compounds (e.g., SiH4 and NH3 or
volatile silazane) react in the vapor phase to form the
ceramic which deposits on the target substrate. CV~ is
typically a time-consuming process which requir~s costly
and specialized equipment that is limited in size. The
procedure described above for producing coatings con-
taining silica, silicon nitride, silicon oxynitride,
and/or silicon carbide can be done with a conventionalfurnace. Further, the method leads to heat-stable,
wear-, erosion-, abrasion, and corrosion-resistant
silicious ceramic coatings. Because these silicon- ~-
containing coatings have desirable electronic and
optical properties, and are resistant to most chemicals
as well as to extremes of temperature, many applications
2f the coating process are possible. One specific
application is in gas turbine engines, on parts which
-are particularly susceptible to wear, corrosion, or
heat. Also, the coating process could be used to make
~the dielectric material of capacitors, or for providing
insulating coatings in the electronics industry. Other
applications are clearly-possible.
WO90/12835 2 0 2 8 ~ ~ 2 pcT/usso/ol638 .-
E. Fabrication of Molded Ceramic ~odies
The ceramic precursors prepared as described
hereinabove may also be used to form three-dimensional
articles by injection- or compression-molding using
procedures substantially as described in PCT Publication
No. W087/05298, cited above. The results as
demonstrated in the examples of that application
indicate that the procedure may also be successful in
the absence of sintering agents.
F. Preparation of Fibers
The ceramic precursors can also be used for
preceramic fiber spinning.
Three general spinning techniques are commonly
used: ta) melt spinning, in which the polymer is spun
from its melt and solidified by cooling; ~b) dry
spinning, in which the polymer is at least partially
dissolved in solution and pulled out through the spin-
neret into a heat chamber, then solidified b~ solvent
evaporation; and (c) wet spinning, in which a
concentrated polymer solution is spun into a coagulation
or regeneration bath containing another solvent in which
the polymer is not soluble. In addition, gel-type
polymers can be spun from very viscous solutions. These
tractable polymers rapidly gel and crosslink upon ~-
removal of solvent after spinning due to high latent
reactivity. Polymeric fibers so-formed are intractable.
Additional, relatively small quantities
(O.l-S.0 wt. %) of a very high molecular weight substan-
tially linear organic polymer (100,000-5,000,000D) may
be mixed with the inorganic polymer to support and
improve the fiber strength after spinning, as taught in,
e.g., U.S. Patent Nos. 3,853,567 to Verbeek and
3,B92,533 to Winter et:al.
. . , . :: , ~ : . , ~ -, , -
woso/l283s `~'~ 2 Q 2 8 $ ~ 2
PCT/US90/01638
The supporting technique is especially useful
when low molecular weight and/or nonlinear polymers
having a very low degree of chain entanglement are used.
One problem encountered in ceramic fiber
fabrication derives from the fusability of inorganic
polymers during pyrolysis. This fusability results in
structural problems in the spun fiber. Polymers pro-
duced by the present invention, however, may overcome
the fusability problem, providing that the catalytic
process as described herein is actually incorporated
into the fiber-spinning process. For example, a high
molecular weight polysiloxane may be mixed with a
homogeneous catalyst and heated in a spinneret or in a
curing chamber to cause Si-H bond activation to occur
and increase the degree of crosslinking in the fiber. ',
Alternatively, the spinneret can itself be a catalytic '~
bed. Coupling or crosslinking agents may also be ~,
included in the fiber-spinning process. Latent reactive
groups (e.g., free amino moieties) may be present as
~ well.
G. Other Applica~ions
Many other applications of the novel polymers
of the invention are clearly possible.'^ ~'
Combining the polysiloxane gels prepared in
Section C with other ceramic powders (e.g., SiC, BNr
BgC) may be carried out in order to produce composite
articles. Such a composite of, e.~., a siloxane ~-
polymer/SiC powder mixture may give an article having
improved oxidation resistance. -Another application -
would be to use the polymer gels-as binders combined
,with ceramic powders so as to provide a fluid polymer/
powder solution.
;~,, It is,to,be:understood that'~while the inven-
,t,ion has been described-in conjunction with'the ''
:: : ' ," : ' ;,: 1: ' :, ' " ' .:: ' ' .: ': , . '-' '' ', . ~
Wo90/l2~3~ - '2 0 2 ~ 8 ~ 2 PCT/US90/~1638 -
-~ :
preferred specifi'c embodiments thereof, that the
foregoing description as well as the examples which
follow are intended to illustrate and not limit the
scope of the invention, which is defined by the scope of
the appended claims. Other aspects, advantages and
modifications within the scope of the invention will be
apparent to those skilled in the art to which the inven-
tion pertains.
Ex~ es
Experimental: Unless otherwise indicated, the reagents
used were obtained from the following sources: silanes, '
from Petrarch Systems, Inc., Bristol, Pennsylvania
organic reagents including amines, from Aldrich Chemical
Co., Milwaukee, Wisconsin; gases, from Matheson,
Seacaucus, New Jersey; and catalysts, from Strem,
Newburyport, Massachusetts.
Examele l
Reactions of Oliqo and PolYmethvlsiloxane with Ammonia
a. 0.05 mmol (32 mg) Ru3(CO)l2 was added to
l00 mmol (6.0 g) ~CH~SiHo]4 and the solution was heated
at 60C under 200- psi of ammonia. Gas evolution gave a
pressure of 400 psi in l9 hours and hard rubber was
formed. The product's elemental analysis showed the
presence of 5.55% N which indicated a nitrogen-silicon
ratio of 0.28 (Table 3). The ratio of oxygen to silicon
was found to be about 1.29. Some of the oxygen excess '-
was believed to be a- result-of''oxygen contamination
found in the commercial starting material and detected
by an NMR intensity:ratio of'Si-H/Si-CH3 absorbance
(0.8:1.0). '
~ The product was pyroly2ed at 850C under and
35- atmosphere first-,-of::nitrogen'and then, of ammonia.
' :
. .
., - : . .
WO90/12835 ~ ~ 0 2 ~ ~ ~ 2 PCT/US90/01638
Elemental analysis of the pyrolyzed material suggested a
mixture of the following ceramic components (mol ratio):
SiO2(0.63); Si3~4(0.23); SiC~0.14), C(0.58)~ It is not
clear whether the N content derived from silicon nitride
or from silicon oxynitride. The mol ratios of 0, N and
Si in the ceramic material were similar to those of the
preceramic polymer, i.e., prior to pyrolysis. Pyrolysis
under a slow stream of ammonia reduced, almost totally,
the carbon content, as well as reducing some of the
oxygen excess. Correlatively, pyrolysis under ammonia
increased significantly the nitrogen content.
Very similar results were observed when the
cyclotetramer was replaced by polymethylsiloxane having
a number average molecular weight (Mn) of 18~0D (degree
of polymerization is 29~ as shown in Tables 4 and 5. A
comparison of the cyclo- and polysiloxane reactions
reveals that less nitrogen interacts with the polymer
than with the cyclomer, and that the SiC fraction in the
product obtained by pyrolysis under nitrogen is higher
for the polymer reaction. However, no real difference
was seen when both were pyrolyzed under ammonia. The
ceramic yields were found to be very high for all types
of reactions and pyrolysis procedures. (see Table 4).
b. A solution of 100 mmol ~6.0 g) ECH3SiHo]4
and 25.0 ~mol (8 mg) RU3(CO)12 was heated at 60C under
100 psi of ammonia. After 2 hours 220 psi of pressure
were formed, and the product was a viscous liquid having
Mn = 1230 D. The pressure was released and the reaction
mixture was recharged with additional lO0 psi of
ammonia. 200 psi of gas were evolved in a 2-hour
period, and the viscous liquid converted to a soft
rubber.
lH-NMR integration revealed that 41% of the
Si-H bonds were replaced by ammionia to form Si-NH2 and
Si-NH groups.
,
i .
.. :: :,.... . , ,. ., ,,,, ~
WO90/~2835 '' ' 2 0 ~ 8 ~ ~ 23
~ 32 P~T/us9o/ol638 .-
Elemental analysis showed the incorporation
ratio of 0.24 nitrogen per carbon atom, whi~h indicated
the formation of cyclosiloxane chain polymer bridged by
ammonia.
Indeed, a dimer of two cyclotetramers brid~ed
by a single -NH was the major product found by GC-MS
analysis.
IR of CC14 solutions showed new sharp stretch
peaks at 3421 (w) r 3380 (m), cm~l together with new
shoulders at 1240 and 1160 cm~l.
lH NMR (CDC13, ~, Ref CHC13: Si-H (4.69,
0.59H), NH (l.10, 0.16H) CH3 (0.22, 3H).
The elemental analysis of the product was as
follows: C, 19.91 (mol ratio 1.003: H, 6.14 (mol ratio ~ ~-
3.70); N, 5.39 (mol ratio 0.24); S, 42.23 (mol ratio
0.91).
:
~
- ' .
..
. . - ,'
.
":
, ~. :
- - . . _, ,- . .:
J;~
,:..
-r ~
, 7 ^ t
WO90/1283S ' 202~2
. PC~/US90/01638
33
Table 4
The Elemental AnalYsis of Polymers and Ceramics
Obtained in a Catalyzed Reaction Between
Methylsiloxanes and _ _
Product Si AnalYsls % (mol ratio)
C~clotetramer reaction ,:
Polymer 40.70 29.855.5518.02 5~88
(1.00) (1.29)(0.28)(1.03) (4.06)
Ceramic material 45.73 32.536.9414.10 0.79
under N2 (1.00) (1.25)(0.31)(0.72) (0.48)
Ceramic materi~l 47.76 28.2621.811 35 0 57
under NH3 (1.00) (1.04)(0.91)(0 06) (0 33)
PolYmer Reaction
Polymer 42.47 27.804.0619.67 6.00
(1.00) (1.1~)(0.19)(1.07) (3.95)
Ceramic material 48.12 32.815.0213.65 0 76 -
under N2 - (1.00) (1.19)(0.21)(0~6S) (0 44) -
Ceramic material 49.29 28.3521.011.75 0.54 ~ -
under NH3 (1.00) (1.03)(0.87)(0.09) (0.31
able 5
Ceramic Yield of the PYrolYzed Polymers
Obtalned in a CatalYtic Reaction ~etween
MethYlsiloxanes and Ammonia
8~95~Qn~ PYr-olysis Conditions Ceramic Yield
Cyclotetramer - N2 77
Cyclotetramer N~3 8
,
Polym~er N2 - ~- 75
; : ~ Polymer -:. . NH3 . ^ 88
sJ - ; ¦
3 5 . ; ~ t . -
I
~ ~ I
,' `
- '' ' . , I
-. 202~2
WosO/12835 ~; 34 PCTtUS9OtO1638
Evidence for Si2ON2: X-ray powder diffraction
analyses of the ceramic products obtained by the above
procedure showed clear spectra pattern of orthorhombic
Si20N2, when the polymeric produc~s were pyrolyzed under
NH3. Pyrolysis under N2 gave poor crystallization under
the same conditions. When the amorphous ceramic product
produced by pyrolysis under N2 at 900C was reheated to
1600C (also under N2), however, X-ray powder diffrac- ~ -
tion analysis of the product again indicated ortho-
~rhombic Si2ON2. No other types of ceramic crystallites
were observed in the X-ray powder diffraction spectra.
Example 2
Reactions of MethYisiloxanes [CH3SiHO]
With DimethYlamine
a. [CH3SiHO]4: To 6.0 g (100 mmol)
[CH3SiHO]4 were added 32 mg (0~05 mmol) of Ru3(CO)12 and
the solution was charged with approximate~y 100 psi of
dimethylamine. The reaction was carried out at 60C and
detected by the observed pressure formed in the reactor.
The pressure was released every 0.5-1 hour and the
reactor recharged with fresh dimethylamine. After 6
hours, a total pressure of 1100 psi was char~ed into the
reactor and a total pressure of 770 psi was formed. No
more gas-evolution was observed. 8.1 9 of viscous oily
products were obtained, indicating a 49% yield of amine -~
~ubstitution. This yield correlated with the lH-NMR
~analysis of the solution, which showed 53% amine
substitution and 29% Si-H groups. GC-MS analysis showed
that bis- and tris-substituted cyclotetramers were the
màjor products when mono and tetrakis appear only in
small guantîties.
b. ~CH ~ 31: The reaction was run with . :~
the same amounts and under the same conditions as the
reaction with the tetramer. Only 50 psi of
WO 90/12835 r., ~ 2~n 2 8~ ; 2 PCI`/US91)/01638
dimethylamine could be charged into the reactor each
time. A total pressure of 500 psi was charged and 375
psi of gas evolved after 6 hours. 7.4 9 of a very
viscous polymer was obtained (33% yield of amine
substitution) which is correlated to the lH-NMR analysis
showing similar results (36~ amine substitution and 45%
Si-CH3 groups).
Example 3
Reactions of MethYlsiloxanes ~CH3~ X
a. [CH3SiHO]4: To 6.0 g (100 mmol)
[CH3SiHO]4 were added 0.40 9 water and Ru3~CO~12 as
above. The reaction was carried out at 60C under
nitrogen and detected by the observed hydrogen pressure
formed in the reactor. After ~ hour, a total pressure
of 440 psi was formed. After 2 hour, a total pressure
of 520 psi was observed. No more gas evolution was ob-
served. Pyrolysis was carried out at a rate of 5C/min
up to 900C. Pyrolysis under nitrogen gave a 70% yield,
while pyrolysis under ammonia gave a 77.3% yield.
Elemental analysis of the product before pyrolysis gave
the following: C, 19.91 (mol ratio 1.03); H, 5.67 (mol
ratio 3.81) N, 0.10: Si, 41.63 (mol ratio 1.00), O,
22.16 ~mol ratio 0.93). Elemental analysis of the
~5 product after pyrolys-is under nitrogen gave: C, 12.66
(mol ratio 0.65); H, 0.98 (mol ratio 0.60); N, 0.74 (mol
ratio 0.03); Si, 45.74 (mol- ratio 1.00); O, 40.27 (mol
ratio 1.54). The mole ratio of SiO2:SiC:C was derived
to be approximately 0.77:0.23:0.42.
~ b. ~CH3SiHO]2g: To 6.0 g (100 mmol)
LcH3siHo]4 were added 0.18 ~ water and Ru3(CO)12 as
above. The reaction was carried out at 60C under
nitrogen and,. as-in Section (a), detèc~ed by the
- . observed ;pressùré formed in the reactor. After ~ hour,
.35 a total pressurè of 150 psi was formed. After 2 hour,
Woso/~2835 -- 2 0 2 8 g 5 26 PCT/US90/01638
a total pressure of 180 ksi was observed. No msre gas
evolution was observed. Pyrolysis was carried out at
900C. Pyrolysis under nitro~en gave a 44% yield, while
pyrolysis under ammonia gave a 86.7% yield. Elemental
analysis of the product before pyrolysis gave the
following: C, 20.69 (mol ratio 1.13): H, 6.70 (mol ratio
4.41); N, 0.24 Si, 4~.78 (mol ratio 1.00); O, 26.81
(mol ratio 1~07). Elemental analysis of the product
after pyrolysis under nitrogen gave: C, 12.73 (mol ratio
1.06); ~, 0.82 (mol ratio 0.82); N, 0.80 (mol ratio -
0.06); Si, 45.53 (mol ratio 1.63); O, 40.41 (mol ratio
2.52).
c. To 10 grams of cyclotetrahydridomethyl-
siloxane (CH3SiHo)4, in 20 9 tetrahydrofuran (THF) were
added 0.67 9 H2O and 20 mg Ru3~CO)12, and the solution
was heated to 60C under nitrogen. The reaction was
followed by observing the total pressure in the reactor.
After 15 minutes, the total pressure observed was 280
psi; after 3 hours, the increase in pressure stopped and
the evolution of gas (H2, a5 above) was thus completed.
After removal of solvent, a viscous, waxy polymer,
polycyclohydridomethylsiloxane (PHMSO) was obtained,
removed from the reactor, and diluted to give a 5 wt.%
solution. The polymer 510wly continued to crosslink and
converted to a solid product which was still soluble in
THF. The resulting polymer can be pyrolyzed under
nitro~en or oxygen to give a high yield of an amorphous
ceramic composition comprising silica and potentially
carbon, and is useful in the fabrication-of ceramic
coatings, shaped products, fibers, films, and the like.
Exam~le 4 i ~ -
Reactions of Diethylsilane with Water
a. To 0.~8 g diethylsilane-~were added 0.18 g
H2O and 50 mg triethylamine as catalyst.:_The reaction
_. .,
,~
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,, . ~,, , . ., . , ., ,.- . , . ~ . ; . . , , . " ... .. . .
- ~028~2
WO90/12835 '' ~J pcT/usso/o1638
37
was carried out under nitrogen at 60C and de~ected by
the o~served pressure formed in the reactor. After l
hour, a total pressure of 5 psi was observed. After 22
hours, 78% of the diethylsilane was converted to linear
and cyclic oligomers of [Et2Sio]n (Et = ethyl), wherein
n is 2-9.
b. To 1.76 g diethylsilane were added 0.36 9
water and 16 mg Ru3(CO)l2 as catalyst. The reaction was
carried out under nitrogen at 60C and de~ected by the
observed pressure in the reactor. After l hour, a total
pressure of 150 psi was observed; a pressure of 150 psi
remained after 3 hours. l.75 g product was obtained.
After l hour, a series of
Exam~le 5
As described in Section B.2., it will
sometimes be desired to introduce additional carbon into
the preceramic polysiloxane so that a higher fraction of
carbon will be present in ~he ceramic product, e.g., as
follows.
a. Reaction of tCH3Si~O]4 with an alkene or
alkyne: To ~CH3SiHO]4 in a suitable solvent such as THF
is added a predetermined amount of the selected alkene
or alkyne. The amount will vary depending on the mole ,'
fraction of carbon desired in the ultimate ceramic
product. A catalyst such as H2PtCl6 is added, and the
solutioh is heated to about 60C under an inert
atmosphere such as nitrogen. The-resulting hydro-
silylation product, in which hydrogen atoms of activated
Si-~ bonds have been replaced by carbon-containing
groups, may or may not be isolated at this point.
Hydrolysis is then carried out to polymerize this
t ~ . product, according,:to the method of the preceding
examples. ~ate,r isiadded-,,along with'a-cataIyst, and
35 ~ the reaction,i~ carried out at-about'60C~unde~r
..~,~,... .
. , . ~ . . . . . ....... . .. ..
W090/12835 _ 2 0 2 8 ~ ~ 2 PCT/US90/01638 --
nitrogen. As in~he preceding examples, the reaction is
monitored by obsërving the increase in pressure during ~'
the reaction. When the pressure increase stops, the
reaction may be presumed to be complete. Pyrolysis of
the resulting polymer will give a product which contains
a relatively high fraction of carbon, as either silicon
carbide or unbound carbon. To increase the fraction of
silicon carbide in the ceramic product, an additional
1200C pyrolysis step may be carried out. This
procedure is useful for making ceramic articles,
coatings, and the like, having a high carbon content.
b. In an alternative procedure, [CH3SiHO]4
may be hydrolyzed to give a polysiloxane as described in
Example 3, followed by reaction with an alkene or alkyne
to give subs'tantially the same preceramic polymer as ''- '
obtained in the Section (a). The catalyst may or may ~
not be the same as that used in Section (a). ' '
c. Aryl groups may also be introduced into
the polymer using this method. For example, [CH3SiHO~4
may be reacted with styrene using essentially the same
procedure as described in Section (a), to introduce '
pendant aromatic groups into the-polysiloxane precursor. '
Alternatively, [CH3SiHO]4 may first be reacted with
water, followed by reaction of the resulting polymer
with styrene, along the lines of the procedure outlined
in Section (b). In either case, the ceramic precursor
produced will have a higher carbon content than that of
the hydridosiloxane starting material, in turn giving'
rise to a ceramic product of higher carbon content (aryl
groups are readily transformed to give graphite carbon). ':
Exam~le 6 - - ~
~ ~ Ceramic products comprised-'of metal silicates '~
_ j may be prepared by;reacting~a:hydridosiloxaneistarting
material with a-metal-containing compound', as-follows;
WO90/12835 3g2 Q ~ 8 ~ 5 2 Pcr/us~o/0l638
predetermined amount of aluminum bis(glycolate). The
amount will vary depending on the mole fraction ofiron
desired in the ultimate ceramic product. A catalyst
such as Ru3(CO)12 is added, and the solution is heated
to about 60~C under an inert atmosphere such as
nitrogen. The resulting product, in which Si-H groups
have been replaced by
10 Si ~ - Al\ ~
groups, may or may not be isolated at this point.
Pyrolysis of the resulting polymer will give an iron
silicate ceramic product, i.e., one which contains
silicon, iron and oxygen.
b. In an alternative procedure, a linear
polyhydridosiloxane starting material is subjected to
hydrolysis in dilute solution to form Si-OH ispecies.
The product is then reacted with Ti(OR)~ or (RO)xTiCl4_x
to form Si-O-Ti groups.
c. The aforementioned procedures may also be
used to prepare "SiAlON", a ceramic product containing
aluminum, i.e., in addition to silicon, oxygen and
nitrogen. The method of Sections (a) or (b) are
followed using an aluminum-containing reactant such as
tRAlNH]3, ~RO)3Al or tRAlO]3 instead of aluminum
bis(glycolate), with pyrolysis carried out under
ammonia.
.. . . . .
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