Organometallic polymer and process for production thereof

An organometallic polymer of which the main-chain skeleton consists of a Si-CH.sub.2 bond and a V-O bond and which partly contains a vanadiosiloxane bond, the ratio of the number of silicon atoms to that of vanadium atoms being in the range of from 3:1 to 1000:1, the side-chain group directly bonded to the silicon atom being selected from the group consisting of hydrogen, methyl, ethyl and phenyl, and the vanadium atom being bonded to the silicon atom through an oxygen atom with substantially no side-chain organic group present which is directly bonded to the vanadium atom.

BACKGROUND OF THE INVENTION 
This invention relates to a novel organometallic polymer partly containing 
a vanadiosiloxane bond (V-O-Si) which has excellent heat resistance and 
oxidation resistance and a high residual ratio (percent of weight after 
firing/weight before firing) on firing in a non-oxidizing atmosphere such 
as nitrogen, argon, helium, ammonia and hydrogen. 
Various processes have previously been proposed for the production of 
polycarbosilanes having Si-CH.sub.2 as a main-chain skeleton with an 
organic side-chain group attached to the silicon atom. For example, Fritz 
discloses a process for production of a polycarbosilane from a monosilane 
at page 657 of Angew. Chem., 79 (1967). U.S. Pat. No. 4,052,430 to Yajima 
et al. discloses a process for producing a polycarbosilane from a 
polysilane using an autoclave. Furthermore, U.S. Pat. No. 4,220,600 to 
Yajima et al. discloses a polycarbosilane partly containing a siloxane 
bond which can be produced by a process which does not require an 
autoclave. 
We have now found that a novel organometallic polymer consisting mainly of 
carbosilane and partly containing a vanadiosiloxane bond which has better 
heat resistance and oxidation resistance and a higher residual ratio on 
firing than conventional polycarbosilanes can be obtained by reacting 
polyvanadiosiloxane or a vanadium complex in which a coordination atom 
adjacent to the vanadium atom is oxygen, with a polysilane. 
SUMMARY OF THE INVENTION 
According to this invention, there is provided a novel organometallic 
polymer of which the main-chain skeleton consists of a Si-CH.sub.2 bond 
and a V-O bond and which partly contains a vanadiosiloxane bond, the ratio 
of the number of silicon atoms to that of vanadium atoms being in the 
range of from 3:1 to 1000:1, the side-chain group directly bonded to the 
silicon atom being selected from the group consisting of hydrogen, methyl, 
ethyl and phenyl, and the vanadium atom being bonded to the silicon atom 
through an oxygen atom with substantially no side-chain organic group 
directly bonded to the vanadium atom. 
According to this invention, there is also provided a process for producing 
the aforesaid novel organometallic polymer which comprises mixing 
polyvanadiosiloxane or a vanadium complex in which a coordination atom 
adjacent to the vanadium atom is oxygen, with a polysilane of the formula 
##STR1## 
wherein R.sub.1 and R.sub.2 are identical or different and each represents 
a member selected from the group consisting of hydrogen, methyl, ethyl and 
phenyl, provided that R.sub.1 and R.sub.2 are not both hydrogen; and n is 
a number of not more than 500, and reacting the mixture at a temperature 
of 250.degree. to 500.degree. C. in a non-oxidizing atmosphere.

DETAILED DESCRIPTION OF THE INVENTION 
The process of the invention is first described. 
One starting material used in the process of this invention is a polysilane 
of the formula 
##STR2## 
wherein R.sub.1, R.sub.2 and n are as defined above. This polysilane may 
be of a linear or cyclic structure or a linear-cyclic mixed structure. In 
the above formula, n is usually at least 3 (n.gtoreq.3), preferably 
5.ltoreq.n.ltoreq.100. The sequence of arrangement of the hydrogen, 
methyl, ethyl and phenyl forming the side-chain groups R.sub.1 and R.sub.2 
is optional. 
An especially suitable polysilane used in the process of this invention is 
polysilane consisting only of a structure of the formula 
##STR3## 
or a polysilane in which at least 50% of the side-chains consists of 
methyl and the remainder being phenyl and/or hydrogen. In the case of 
linear polysilanes, the terminal groups are preferably OH or CH.sub.3. 
The other starting material used in the process of this invention to react 
with the polysilane is polyvanadiosiloxane, or a vanadium complex. 
Polyvanadiosiloxane is a polymer which can be produced by the process 
disclosed in U.S. patent application Ser. No. 210,639 filed Nov. 26, 1980 
by Yajima et al., and its main-chain skeleton consists of a Si-O bond and 
a V-O bond. 
The vanadium complex used in the process of this invention is a vanadium 
complex in which a coordination atom adjacent to the vanadium atom is 
oxygen. Examples of such a vanadium complex are as follows: 
##STR4## 
Such a vanadium complex in which a coordination atom adjacent to the 
vanadium atom is oxygen can be produced, for example by the following 
methods. 
(1) By the reaction of an inorganic compound of vanadium with a 
complex-forming agent capable of easily forming a complex with the 
inorganic vanadium compound. Examples of the inorganic compound of 
vanadium include vanadium halides such as VCl.sub.4, VCl.sub.3 and 
VCl.sub.2, oxysulfates of vanadium such as VOSO.sub.4, oxyoxalates of 
vanadium such as VOC.sub.2 O.sub.4, sulfates of vanadium such as V.sub.2 
(SO.sub.4).sub.3, oxyhalides of vanadium such as VOBr.sub.2, and alkali 
metal or ammonium salts of the aforesaid compounds, such as 
Na(VOCl.sub.4), (NH.sub.4)V(SO.sub.4).sub.2 and K[VO(C.sub.2 
O.sub.4).sub.2 ]. Examples of the complex forming agents include C.sub.4 
H.sub.8 O(tetrahydrofuran), CH.sub.3 OH, C.sub.5 H.sub.8 O.sub.2 
(acetylacetone), C.sub.2 H.sub.5 OC.sub.2 H.sub.5, n-C.sub.4 H.sub.9 
OC.sub.4 H.sub.9, (CH.sub.2 OH).sub.2, CH.sub.3 COCH.sub.3, C.sub.5 
H.sub.5 OH, C.sub.5 H.sub.4 O.sub.2 (pyrone), C.sub.7 H.sub.6 O 
(benzaldehyde), C.sub.7 H.sub.6 O.sub.2 (benzoic acid) and C.sub.7 H.sub.8 
O (benzylalcohol). 
Generally, in order to react the vanadium compound with the complex-forming 
agent, it is sufficient only to dissolve the vanadium compound in the 
complex-forming agent with or without heating. In the vanadium complex 
used in the process of this invention, the vanadium atom may have an 
atomic valence of 2, 3, 4 or 5. 
A product obtained by dissolving a complex salt of vanadium, such as 
vanadium acetylacetone complex, in the aforesaid complex-forming agent to 
react it further may be preferably used in this invention because its 
reactivity with the polysilane increases. 
(2) By dissolving an organic compound of vanadium such as V.sub.2 OCl.sub.3 
(OR).sub.3, V(OR).sub.n, VO.sub.x (OR).sub.4-x (wherein R is C.sub.1 
-C.sub.4 alkyl, n is 3, 4, or 5 and x is 1 or 2), VCl(OCH.sub.3).sub.2, 
and VOCl.sub.2 (OC.sub.2 H.sub.5) in a lower alcohol such as methanol, 
ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol and t-butanol, 
the vanadium complex used in this invention can also be produced. 
According to the process of this invention, the organometallic polymer is 
produced by mixing the polyvanadiosiloxane or the vanadium complex in 
which a coordination atom adjacent to the vanadium atom is oxygen, with at 
least one polysilane of the formula 
##STR5## 
and heating the mixture at 250.degree. to 500.degree. C. in a 
non-oxidizing atmosphere to perform polymerization. 
It is necessary that the heating should be carried out in a non-oxidizing 
atmosphere. If the polymerization reaction is carried out in an oxidizing 
atmosphere such as air, oxidation of the starting polysilane takes place 
so that the reaction does not sufficiently proceed. Nitrogen, argon, 
hydrogen and ammonia are suitable as the non-oxidizing atmosphere inert to 
the reaction. Nitrogen, argon and helium are especially preferred because 
of their good ability to be handled. 
Preferably, the polymerization reaction is carried out generally at 
atmospheric pressure or pressures close to it. If the polymerization 
reaction is carried out in vacuum or at highly reduced pressures, 
low-molecular components distill out of the reaction system to reduce the 
yield of the product drastically. Furthermore, it is preferred that the 
polymerization reaction in the process of this invention be carried out 
while introducing the nonoxidizing gas at a fixed flow rate into the 
reactor. This is because by so doing, the pressure in the reaction vessel 
can be maintained nearly at atmospheric pressure, and a rise in 
temperature, or a rise in pressure owing to gases such as methane released 
during the reaction, can be avoided. 
The heating temperature in the process of this invention is usually 
250.degree. to 500.degree. C. If the reaction temperature is below 
250.degree. C., the polymerization does not easily proceed, and if the 
temperature exceeds 500.degree. C., the resulting organometallic polymer 
begins to become inorganic, (namely, liberation of side-chain components 
gradually begins). 
The ratio between the polysilane and the vanadium compound 
(polyvanadiosiloxane or the vanadium complex) is determined so that the 
ratio of the number of silicon atoms to that of vanadium atoms in the 
final organometallic polymer is within the range of 3:1 to 1000:1. 
The time required for the heat polymerization in the process of this 
invention is usually 1 to 10 hours, and the reaction substantially comes 
to an end within 10 hours. 
Practice of the process of this invention requires only a simple reactor 
including a reflux device, etc., and no special device such as a 
pressurized vessel or a flowing-type device capable of permitting 
recycling is required. 
The organometallic polymer obtained by the aforesaid polymerization can be 
purified by dissolving it in a solvent such as n-hexane, benzene, xylene 
or tetrahydrofuran, filtering it, and evaporating the solvent from the 
filtrate. If required, the purified product may further be distilled and 
concentrated under atmospheric pressure or under reduced pressure at a 
temperature of 50.degree. to 450.degree. C. 
A description of the organometallic polymer obtained by the above process 
and partly containing a vanadiosiloxane bond follows. 
The organometallic polymer obtained in hereinbelow Example 1 from 
polydimethylsilane as the starting polysilane shows an infrared absorption 
spectrum given in FIG. 1. For comparison, an infrared absorption spectrum 
of polycarbosilane synthesized by treating polydimethylsilane in an argon 
atmosphere at 470.degree. C. and 36 atmospheres for 36 hours in an 
autoclave in accordance with the method disclosed in U.S. Pat. No. 
4,052,430 to Yajima et al. is shown in FIG. 2. Furthermore, FIG. 3 shows 
an infrared absorption spectrum of polycarbosilane partly containing a 
siloxane bond obtained by mixing 250 g of polydimethylsilane with 10 g of 
polyborodiphenylsiloxane, heating the mixture to 370.degree. C. in a 
nitrogen stream and polymerizing it for 5 hours, by the method disclosed 
in U.S. Pat. No. 4,220,600 to Yajima et al. 
The infrared absorption spectrum given in FIG. 1 shows absorptions of C-H 
at 2950 cm.sup.-1 and 2900 cm.sup.-1, Si-H at 2100 cm.sup.-1, Si-CH.sub.3 
at 1260 cm.sup.-1 and 800 cm.sup.-1, and Si-CH.sub.2 -Si at 1040 
cm.sup.-1, and also exhibits new absorption peaks at 3400 cm.sup.-1, 1600 
cm.sup.-1, 1180 cm.sup.-1, 960 cm.sup.-1, 880 cm.sup.-1, 740 cm.sup.-1, 
and 490 cm.sup.-1 ascribable to the Si-O-V bond. These new absorption 
peaks are not seen in the infrared absorption spectra of the 
polycarbosilane in FIG. 2 and the polycarboxilane partly containing a 
siloxane bond in FIG. 3. 
Observation of the novel organometallic polymer obtained in Example 1 with 
an electron microscope showed that no crystal grain is present in its 
bright field image. The results of measurements by powder X-ray 
diffraction and electron beam diffraction showed no formation of solid 
vanadium oxide. These experimental data led to the determination that 
substantially all of the vanadium atoms are involved in the Si-O-V bond. 
A particular difference of the organometallic polymer of this invention 
from conventional polycarbosilanes is that its main-chain skeleton 
consists of an Si-CH.sub.2 bond and a V-O bond, and when it is fired in a 
nonoxidizing atmosphere, crosslinking through the vanadiosiloxane portion 
proceeds further at 300.degree. to 350.degree. C. to increase its 
crosslinking density and inhibit heat decomposition of the organometallic 
polymer, and therefore its residual ratio on firing is high. This fact is 
clearly shown by the results of thermogravimetric analysis described in 
FIG. 4. Curve (A) in FIG. 4 is a thermogravimetric curve of the 
organometallic polymer obtained in Example 1, and curve (B) is a 
thermogravimetric curve of polycarbosilane partly containing a siloxane 
bond produced by the method described in U.S. Pat. No. 4,220,600 to Yajima 
et al. 
The structure of the organometallic polymer of this invention is complex, 
and complete elucidation of its exact structure is impossible according to 
the present technical level of chemistry. The present inventors, however, 
presume that it has partial structures exemplified hereinbelow. 
##STR6## 
(In the above formulae, R is at least one member selected from the group 
consisting of methyl, ethyl, phenyl and hydrogen.) 
In the above exemplification of the partial structures of the 
organometallic polymer with a main chain skeleton consisting of an 
Si-CH.sub.2 bond and a V-O bond, a trivalent or tetravalent vanadium atom 
is bonded to the silicon atom through an oxygen atom. Generally, in the 
organometallic polymer of this invention, the stable atomic valence of the 
vanadium atom is trivalent or tetravalent, but a divalent vanadium atom 
could exist. 
Powder X-ray diffraction analysis of the organometallic polymer of this 
invention has shown it to be amorphous as are conventional 
polycarbosilanes. When the polymer is fired in a non-oxidizing atmosphere 
such as argon, helium, hydrogen, ammonia and nitrogen gas, it is converted 
mainly to .beta.-SiC containing vanadium. When a fired product obtained by 
firing the novel organic organometallic polymer (obtained in Example 1) in 
an argon stream at 1400.degree. C. for 1 hour is analyzed by powder X-ray 
diffraction using a nickel filter and a Cu target as an X-ray source, 
.beta.-SiC and graphite are mainly identified. Vanadium is detected from 
the resulting product by a wet colorimetric method. 
From the results of elemental analysis of the organometallic polymer 
obtained by this invention, the weight percentages of the individual 
elements in the polymer are generally as follows: 
Si: 30-60, C: 20-60, O: 0.5-3, H: 5-10, 
V: 0.01-15% by weight 
The results of measurement of the molecular weight distribution of the 
polymer by G. P. C. show that the polymer has a molecular weight 
distribution in the range of 500 to 100,000, and its number average 
molecular weight, measured by the vapor pressure method, is 1400 to 2200. 
The organometallic polymers in which the main-chain skeleton consists of an 
Si-CH.sub.2 bond and a V-O bond are thermoplastic substances, which are 
soluble in organic solvents such as n-hexane, xylene, tetrahydrofuran and 
benzene, and melt by heating to 60.degree. to 300.degree. C. Hence, they 
can be molded using various aggregates by utilizing an ordinary monoaxial 
press, isostatic press, injection press, etc. or by extrusion molding. The 
molded article is fired in a non-oxidizing atmosphere at a temperature of 
at least 800.degree. C. to convert a part of the binder to an inorganic 
carbide SiC. Alternatively, a sintered molded article may be obtained by 
impregnating an inorganic fired article prepared separately, with a molten 
mass of the organometallic polymer of the invention obtained by heating in 
a non-oxidizing atmosphere, or a solution of the organometallic polymer of 
the invention in an organic solvent, and firing the impregnated molded 
article at 1300.degree. to 1800.degree. C. in a non-oxidizing atmosphere, 
whereby the pores in the inorganic fired article are filled with SiC. 
The novel organometallic polymer of the invention whose main-chain skeleton 
consists of an Si-CH.sub.2 bond and a V-O bond and which partly contains a 
vanadiosiloxane bond and has excellent heat resistance and oxidation 
resistance is very advantageous for forming continouous filaments, films, 
coated films and powders composed mainly of silicon carbide because its 
residual ratio on firing in a non-oxidizing atmosphere is high. 
Table 1 below summarizes the properties of the novel organometallic polymer 
partly containing a vanadiosiloxane bond shown in Example 1 in comparison 
with those of polycarbosilane synthesized from polydimethylsilane in an 
autoclave at 470.degree. C. for 14 hours with the final pressure in the 
vessel being 110 atmospheres in accordance with the method disclosed in 
U.S. Pat. No. 4,052,430, and polycarbosilane partly containing a siloxane 
bond which is synthesized from polydimethylsilane and 3.85% by weight of 
polyborodiphenylsiloxane at 400.degree. C. for 5 hours in a nitrogen 
atmosphere in accordance with the method disclosed in U.S. Pat. No. 
4,220,600. 
TABLE 1 
______________________________________ 
Polycarbo- 
silane 
partly 
containing 
Novel 
a siloxane 
organo- 
Polycarbosilane 
bond (U.S. 
metallic 
(U.S. Pat. Pat. No. polymer 
Properties No. 4,052,430) 
4,220,600) 
(Example 1) 
______________________________________ 
Number average 
1800 1720 1900 
molecular weight 
Decomposition 
310 350 370 
temperature (.degree.C.) 
Weight increase (%) 
owing to oxidation 
after maintaining 
9.0 6.5 6.0 
at 200.degree. C. for 1 
hour in the air 
Residual ratio (%) 
on firing 
(after maintaining 
49.8 73.8 75.0 
at 1500.degree. C. in argon 
gas for 1 hour) 
______________________________________ 
The results given in Table 1 show that the organometallic polymer of this 
invention has improved properties over prior art polycarbosilanes. 
The following Examples illustrate the present invention. 
EXAMPLE 1 
40 ml of a solution of 25 g of VCl.sub.4 in 500 ml of tetrahydrofuran was 
added to 20 g of a,w-dihydroxypolydimethylsiloxane having an average 
degree of polymerization of 500 in a beaker. The beaker containing the 
above mixture was heated on a hot plate at 190.degree. C., and the heating 
was stopped when the mixture became highly viscous. The mixture was then 
hot-filtered, and tetrahydrofuran was added to the filtrate so that the 
total amount of the mixture reached 100 ml. 
Twenty grams of polydimethylsilane of the formula 
##STR7## 
was weighed into a 200 ml bulb-shaped flask, and 100 ml of the above 
tetrahydrofuran solution was added. They were stirred in a nitrogen 
atmosphere, and the mixture was heated to 200.degree. C. from room 
temperature so as to evaporate the tetrahydrofuran. 
Then, a reflux condenser was attached to a 100 ml. bulb-shaped flask, and 
the bottom of the flask was kept at 400.degree. C. in a nitrogen 
atmosphere. The reaction was performed by heating with an electric 
furnace, and the reaction mixture was maintained at 400.degree. C. for 5 
hours. 
After the reaction, xylene was added, and the solution was filtered at 
atmospheric pressure. The filtration product was transferred to a 200 ml 
roundbottomed separable flask, and a Liebich condenser was attached to the 
flask for distillation. With stirring, nitrogen gas was passed through the 
flask, and the product was heated from room temperature by a mantle 
heater. 
By heating, xylene was distilled at the boiling point (140.degree. C.) of 
xylene, and then the temperature was slowly raised up to 320.degree. C. at 
a rate of 10.degree. C./10 minutes to remove a low-molecular-weight 
organometallic polymer, and concentrate the product. 
The above procedure gave 12 g of a concentrate. Its infrared absorption 
spectrum was measured, and the results are shown in FIG. 1. 
The organometallic polymer was subjected to elemental analysis, and the 
results were as follows: 
Si: 50% by weight 
C: 38% by weight 
H: 6% by weight 
O: 4.8% by weight 
V: 1.0% by weight 
When the organometallic polymer was fired in an atmosphere of argon from 
room temperature to 1500.degree. C., its residual ratio on firing was 75%. 
Powder X-ray diffraction (CuK.alpha.,Ni filter) of the fired product led 
to the determination that the fired product consisted mainly of 
.beta.-SiC, and .alpha.-SiC and graphite were also identified. Vanadium 
was detected from the fired product by a wet colorimetric method. 
The organometallic polymer was found to have a molecular weight 
distribution, measured by GPC, of from 500 to 100,000. The polymer was 
also found to have a number average molecular weight, measured by the 
vapor pressure method, of 1900. 
EXAMPLE 2 
In a 100 ml bulb-shaped flask, 40 g of the same polydimethylsilane as used 
in Example 1 was mixed with 15 ml of a VCl.sub.4 /tetrahydrofuran complex 
obtained by dissolving 25 g of VCl.sub.4 in 500 ml of tetrahydrofuran. 
A rotary evaporator was attached to the bulb-shaped flask, and the 
tetrahydrofuran was evaporated at a water bath temperature of 60.degree. 
C. and a pressure of 50 mmHg produced by a water flow pump. Then, the same 
procedure as in Example 1 was repeated to give an organometallic polymer. 
The polymer was filtered and concentrated to give 26 g of a final product. 
The resulting final organometallic polymer was heated from room temperature 
to 1400.degree. C. at a rate of 5.degree. C./min. The heated product was 
thermogravimetrically analyzed. It was found that the residual ratio on 
firing was 65%. 
EXAMPLE 3 
A solution of 6.5 g of vanadyl sulfate (VOSO.sub.4) in 100 cc of 
acetylacetone was well mixed with 50 g of polysilane in which the ratio of 
methyl groups/phenyl groups in the side chain was 70:30. The acetylacetone 
was evaporated by distillation. Then, the dry powder was put into a 
three-necked flask equipped with a stirrer, and in a stream of argon, the 
bottom of the flask was heated to 500.degree. C. to melt it. Then, it was 
polymerized for 10.5 hours. 
The polymer was dissolved in tetrahydrofuran, and filtered. Then, 
tetrahydrofuran was evaporated in a stream of nitrogen, and the residue 
was then concentrated at 350.degree. C. for 1 hour. 
The resulting organometallic polymer had a number average molecular weight 
of 2013, and when it was fired at 1700.degree. C. for 1 hour in a stream 
of argon, the residual ratio on firing was 70%. 
EXAMPLE 4 
100 g of polydimethylsilane (degree of polymerization 50) and 3 g of 
vanadyl oxalate (VOC.sub.2 O.sub.4) in 50 cc of tetrahydrofuran were mixed 
in a stream of argon. The tetrahydrofuran was evaporated by distillation. 
Then, the mixture was bubbled with nitrogen gas in a stream of nitrogen in 
a reactor equipped with a reflux condenser, and then polymerized at 
370.degree. C. for 6.0 hours. 
The polymer was heated from room temperature to 1400.degree. C. in a stream 
of argon, and a change in weight was measured. The residue was 72%. Powder 
X-ray diffraction analysis of the fired product led to the identification 
of .beta.-SiC and graphite.