Acrylonitrile-silazane Copolymers, Particularly in Fiber Form, Process for Their
Production and Their Use
The present invention pertains to copolymers of acrylonitrile and silazanes that
5 display at least one organic polymerizable double bond, and in particular a vinyl group. The
copolymers are interesting because of the silicon, nitrogen and carbon atom contents, e.g., as
fire-protection materials or as initial materials for pyrolyzed systems of the composition
SiCN (silicon carbonitrides), SiC (silicon carbides) or SiN (silicon nitrides). The materials
may be present in any form, particularly in the form of fibers, both pyrolyzed and also not
10 pyrolyzed.
The above-mentioned systems are suitable as materials for a broad spectrum of
applications since they display high mechanical strengths at high temperatures as well as
good oxidation resistance. The pyrolyzed products have the properties of ceramics and are
used, e.g., in the form of fibers or ceramic matrices as reinforcing elements in structural
15 parts exposed to or are intended to withstand high temperatures and/or corrosive media.
Addition polymers of polysilazanes with isocyanates or isothiocyanates are
described in US 4,929,704, US 5,001,090 and US 5,021,533. Mainly linear product mixtures
are produced with iso(thio)cyanates, in which -N-C(A) groups (with A = 0 or S) are
inserted in Si-N bonds. The reaction of a liquid polysilazane that has reacted with 2,6-
20 toluene diisocyanate leads to a glass-like product with a clearly elevated carbon content. In
these documents, the possibility of reacting polysilazanes with ketenes, thiu^ketenes,
carbodiimide or CS2 is also mentioned. However, one cannot find specific examples of this
or even of the properties of the product. The products have been proposed as the initial
material for ceramic fibers containing silicon nitride.
25 SiC ceramic fibers are often synthesized by starting with silanes/polysilanes. This
synthesis route, however, is not free from problems. Thus, for the - rarely used - dry
spinning process, pyrolysis products from initial materials have been found, which are
soluble, on the one hand, and on the other hand, melt under the influence of the thermal
energy introduced at the time of pyrolysis. Materials that satisfy this criterion, however, are
30 frequently only produced by complicated techniques or else have to be hardened before the
actual pyrolysis. We refer here to the studies at TU Bergakademie Freiburg and the Institute
for Silicate Research of the Fraunhofer Society in Wurzburg.
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2
A melt-spinning process is more commonly used. In such cases, however, the
necessity of having to harden the polymer fibers by electron bombardment is especially of
disadvantage, for which extremely high doses of about 20 MGy are required.
The object of the present invention is to find a material suitable for the field of flame
5 and fire protection that can be fabricated into stable shaped bodies, e.g., self-supporting
fibers. In preferred embodiments, in particular, a pyrolysis should be applied to materials in
the form of stable fibers in order to obtain materials of the composition SiC, SiN or SiCN
To accomplish this object, a copolymer was prepared that was made from (i)
acrylonitrile or of a mixture [consisting ofd acrylonitrile and an organic molecule that can be
10 copolymerized with acrylonitrile and (ii) a silazane material containing a C=C double bond.
The term "silazane" refers in general to compounds that contain the group R1R2R3Si-
N(R4)SiR5R6R7. A very simple representative of this group is disilazane H3Si-NH-SiH3.
Cyclic and linear silazanes contain or consist of -Si(R'R2)-N(R3)- structural units. Starting
with the basic structures, a large number of silazanes have been developed whose
15 substituents on the silicon may be, e.g., besides hydrogen, alkyl, alkenyl or aryl and whose
substituents on the nitrogen may be, besides hydrogen, alkyl or aryl. Oligomeric and
polymeric structures exist, also with incorporation of additional groups such as urea groups,
as well as different rings and multiple rings.
The inventors of the present application were able to discover, surprisingly, that
20 silazanes displaying one or more C=C double bonds can be copolymerized with acrylonitrile
in solvents suitable for this material in the presence of suitable addition polymerization
catalysts to form polymers that remain soluble in the reaction solvents generally used (e.g.,
DMF or another solvent suitable for acrylonitrile). The copolymerizates are generally
soluble in the same solvents as acrylonitrile and polyacrylonitrile. After the removal of the
25 solvent, they are present in solid form at room temperature, but when the temperature is
raised, they become highly viscous. The melt has viscoelastic properties and can accordingly
be drawn into fibers. The latter can be further cross-linked after cooling and optionally
stretching with electron bombardment and thereby made infusible or transformed into a
duroplastic state. A pyrolysis of the fibers can be carried out after such secondary hardening
30 of the fibers.
The copolymerization proceeds according to the formula:
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Kit. N-S,-(A),- CH=CH2 + GH,= - G -= N 11 LM
`-ECH-CH2]_ECH CH2
n
CH-CH2-CH-CH2
P
CN ^X)a CN cX)o
-ESi-NR^ -jSi-NFL}.
CH3 CH3
where X = alkylene
5 o=0or1,
n1= 1, 2, 3 or an arbitrary higher number,
n= 0, 1, 2, 3 or an arbitrary higher number,
p = 0, 1, 2, 3 or an arbitrary higher number,
with the. qualification that m and p cannot simultaneously be 0 and that n and p cannot
10 simultaneously be 0,
y = number of Si-N units in the silazane used,
R = the substituent in the silazane used, generally corresponding to R2 of the formulas (I) to
(III) given below.
The formula above reflects the fact that, depending on the initial material used and
15 the duration of the polymerization / its temperature / the type of catalyst selected, blocks of
the same length or different lengths of oligopolymerizates of acrylonitrile and of the silazane
used are contained in the formed polymer (p = 0), alternating acrylonitrile and silazane
molecules incorporated by polymerization alternate (m and n in each case = 0) or else a
mixed form is created from the two above-mentioned forms with the different constituents
20 (m not equal to 0, n not equal to 0, p not equal to 0). Suitable reaction partners for the
acrylonitrile are all monomeric, oligomeric or polymeric silazanes with one or more alkenyl
groups bound to the silicon.
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The term "oligomeric silazanes" should be understood to mean silazanes with 2 to 10
silicon atoms according to the present invention. Polymeric silazanes are accordingly those
with at least 11 silicon atoms.
5 The silazanes or oligo/poly-silazanes that may be used have general formula (1)
R2 R2' R2 R2'
R1 Si-N - Si-N Si P- i N R5
13 4 13' I4'
,
R3 R3' R4'
10
15
or general formula (II),
R4
R3.
R4'
or general formula (III),
R1
R2,
i NSi-N ICI I
R2 R2,
I
Si-N
R",
i°NIR6
I
R3 R4 R3
I
R4
fl
in which
R2 is alkenyl,
R3 means hydrogen or straight-chained, branched or cyclic, substituted or -preferably -
20 unsubstituted alkyl, the same alkenyl as R2 or a different alkenyl, aryl, arylalkyl, alkylaryl,
alkenylaryl or arylalkenyl, where each of the substituents R2 and R3 in the case when m
and/or o is/are greater than 1 in different units can have a different but preferably the same
meaning,
(a) R2, and R3' are the same or different and mean straight-chained, branched or cyclic,
25 substituted or unsubstituted alkyl, allcenyl, aryl, arylalkyl, alkylaryl, alkenylaryl or
arylalkenyl, where each of the substituents R2'. and R3' in the case when m and/or o
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is/are greater than 1 in different units can have a different meaning but preferably the
same meaning,
or
(b) R2 and R2, have the meaning given above, and in the presence of at least one radical
5 R3 and at least one radical R3, - all or in each case a part of the radicals R3 and R3'
together represent an unsubstituted or substituted, straight-chained or branched
alkylene group with preferably 2 bridging carbon atoms, in which case optionally the
remaining part of the radicals R3 and R3' has the meaning given under (a),
and in which
10 R4 and R4, denote alkyl with preferably 1 to 4 carbon atoms, phenyl or hydrogen, wherein
several radicals R4 and/or R4, in one molecule may be the same or different,
Rl and R5 are the same or different and can have the same meaning as R2 and R3,
respectively, while R5 may also denote Si(R')(R2')(R3') or R1 and R5 together represent a
single bond,
15 R6 denotes Si(R2)(R2')-X-R7-Si(R2)c1(OR2')3_q where X represents either 0 or NR4,
R7 means a single bond or a substituted or - preferably -- unsubstituted, straight-chained,
branched or cyclic alkylene group and q may be 0, 1, 2 or 3,
P is an alkylene group with 1 to 12 carbon atoms, preferably ethylene,
m and p independently of each other denote 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a whole number
20 between 11 and 25,000, preferably between 11 and 200, and
m and p independently of each other denote 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a whole number
between 11 and 25,000, preferably between 11 and 200,
wherein the units placed in square brackets can be distributed in a given molecule,
preferably randomly or instead in blocks and may possibly be distributed alternatively
25 uniformly in each individual molecule.
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The term "units" in connection with the definition of silazanes with the formulas (I)
to (III) pertains to the different parts of the molecule placed in square brackets and with a
subscript stating the quantity of these units in. the molecule (m, n...).
In a first preferred embodiment, R2 in formulas (I) to (III) is a vinyl group.
5 R3 in this embodiment is more preferably alkyl, quite especially preferably methyl or
ethyl.
If n in formulas 1 to 3 is at least 1, the substituents (R2'and R) bound in each case to
a silicon atom of the corresponding units are selected independently of the first preferred
embodiment, preferably as follows: an alkyl radical in combination with a hydrogen atom,
10 another alkyl radical, an alkenyl radical, preferably a vinyl radical or a phenyl radical.
In a third preferred embodiment independent of this, the alkyl or alkenyl radicals in
formulas (I) through (III) display 1 to 6 carbon atoms. Methyl, ethyl and vinyl radicals are
especially preferred. The aryl, arylalkyl, alkylaryl, alkenylaryl or arylalkenyl radicals
preferably have 5 to 12 carbon atoms. Phenyl and styryl radicals are especially preferred.
15 This embodiment is especially preferred in combination with the first embodiment.
In another preferred embodiment of formulas (I) through (III) independent of this, W
and/or R`r' denote alkyl, especially methyl. The carbon fibers produced with such materials
are said to have superior properties.
In a fifth embodiment independent of this, R2, R3, R2'and R3, are preferably selected
20 from among the alkyls, especially those with 1 to 8 carbon atoms.
In a sixth embodiment independent of this one, the substituents R2, R3, R2, and R"
carry fluorine atoms. This embodiment is especially preferred in combination with the
fourth embodiment.
In another independent preferred embodiment of formula (I), the subscript o is equal
25 to 0.
In another independent preferred embodiment of formulas (I) or (II), the subscript in
is always equal to 0.
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In another independent preferred embodiment R1 and R5 together form a single bond.
This embodiment is especially preferred for compounds with formula (I), in which the
subscript o is zero and possibly the subscript m is also zero.
In another independent preferred embodiment, o is equal to 0 and in and n are greater
5 than 1 and preferably lie between 2 and 25,000, especially between 2 and 200. In this case in
and n may be the same or different. In addition or alternatively, the in and n units may be
randomly or uniformly distributed. In this case, they may be arranged in blocks or not.
In another preferred embodiment independent of this one, n and o in formula (I) have
the meaning of zero and R5 has the meaning of Si(Rl)(R2' )(R3' ). An example of this
10 embodiment (here with in = 1) is:
H
Si Si-
15
The single bond mark in these examples can stand especially for alkyl, quite
especially preferably for methyl, but they may also stand for hydride or partially for alkyl
and partially for hydride.
20 In another independent preferred embodiment, in in formula (I) has the meaning of
1, 2, 3, 4 5 or for a whole number between 6 and 50, while n and o are zero, or a mixture of
different silazanes of this type may be involved. In this case the substituents R1 and R5 may
be the same or different and have the same meaning as R3, while R5 may also mean
Si(Rr)(R2')(R) . This or these silazanes may, if necessary, also be present in a mixture with
25 silazanes in which Ri and R5 together represent a single bond.
In another independent preferred embodiment, o in formula (I) is zero and m and n
are the same or different and signify between 2 and 200 and 25,000. In this case the
substituents R1 and R5 may be the same or different and have the same meaning as R3, while
R5 may also mean Si(R1)(R")(R3'). This or these silazanes may, if necessary, also be present
30 in a mixture with silazanes in which R1 and R5 together represent a single bond.
Examples are the following oligomers/polymers:
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8
1
0,5
Ph
SI -°-°--N `T,
33 * L
Si-N
, 033¢ -Si-N-+0133
CH3 H
1
CH3 H
CF13 H
10
where the units in square brackets are arranged randomly in the molecules, or possibly
instead of this are arranged in blocks and in other cases uniformly in the stated ratio to each
other, and the molecules may contain terminal hydrogen atoms or alkyl or aryl groups.
In another independent preferred embodiment, the subscripts n and o are equal to
zero, the subscript m has the meaning 3, and Rl and R5 together represent a single bond.
This embodiment can generally be represented by formula (Ia):
--O
R4 Si R
R3 ^R2
where R2, R3 and W'have the meanings given for formula (I).
In another independent preferred embodiment of formula (I) n and o have the
meaning of 0, m has the meaning of 2, 3, 4, 5, 6, 7, 8, 9, 10 or a higher number and RI and
R5 together represent a single bond.
15 In another independent preferred embodiment of formulas (I) and (II) m and n each
mean 2, 3, 4, 5, 6, 7, 8, 9, 10 or a higher number, and R1and R5 together represent a single
bond. These compounds can be represented (here for o and p equal to 0) in turn, for
example, by formulas such as
r/ CH3
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k
H
Si N-i- SiN+.
11
1 1 0 f- 1 ( O g
CH3 H CH3 H
f Ph ,
Si N
* L
Si_N
I I 0,6 1 I ' 0*5
CH3 H CH3 H
Ph
* I _Ir__Hs
-N -N
i*33
,^Ii I
'033 ` III
CH3 H CH3 H CH3 H
0,33
where, in turn, the units in square brackets are distributed in the molecules either randomly
or in blocks, but also in many cases uniformly, m times or n times or in the case of the last
5 shown formula together (m+n)-times in the stated ratio to each other, but the molecules are
present in a closed chain format. These embodiments can be present especially in the
mixture with corresponding open-chained silazanes and be used for the present invention.
To the extent that the embodiments mentioned above as preferred are not mutually
exclusive, two or more of them may be combined.
10 Silazanes of formula (I) with o equal to 0 are available on the market and can be
synthesized by standard procedures, especially ammonolysis of monohalo i lanes, e.g., as
described in US 4,395,460 and in the literature cited there. In this case, for example, through
the reaction of a monohalosilane with three organic radicals, silazanes of formula (I) are
formed, in which the subscripts n and o are zero, the subscript m means 1, and R5 has the
15 meaning Si(R')(R2')(R3'). The organic radicals are not split off during the reaction.
It is also possible, by analogy with US 6,329,487 BI of the Kion Corporation to
ammonolyze mono-, di- or trihalosilanes in the pressure apparatus in liquid ammonia and
thereby to obtain silazanes of general formula (I).
If halosilanes are reacted at this time with at least one Si-H bond alone and/or in
20 combination with di- or trihalosilanes in an excess of liquid anhydrous ammonia and left in
this medium for a long time, polymerization products are formed in the acidic environment
formed by the forming annnonium halide salt or corresponding acid in the course of time by
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the splitting-off reaction of Si-H bonds, in which the, subscripts in, n and o have a higher
value and/or a different ratio than previously, possibly catalyzed by the presence of
dissolved and ionized ammonium halide.
In US 6,329,487 B1 it is likewise described that corresponding polymerization
5 products can be obtained by the action of sodium dissolved in ammonia.
US 4,621,383 and WO 87/05298 also describe the possibility of synthesis of
polysilazanes by transition-metal-catalyzed reactions.
By the suitable choice of the organic substituents on the silicon atom of the silane
and by a mixture of corresponding initial silanes, by using this procedure a large number of
10 silanes of formula (I) can be generated, in which the subscript o is zero, in which case
frequently a mixture of linear and chain-like polymers is formed.
Regarding the reaction mechanism, also see the dissertation by Michael Schulz at the
Karlsruhe Research Center, Institute for Material Research "Micro structuring of pre-ceramic
polymers by using UV and X-ray deep lithography", November 2003, FZKA 6901. There
15 the production of silazanes of formula (I) is also described, in which the subscript o is zero
and the silicon atoms in the blocks with the subscripts in and n carry different substituents.
It also contains a reference to the production of urea silazanes. If monofunctional
isocyanates are added to silazanes, an insertion reaction of the NCO group into N-H bonds
takes place with formation of a urea group [see the above-described silazanes of formula
20 (II)]. Otherwise, with regard to the production of urea silazanes and poly(urea silazanes)
refer to US 6,165,551, US 4,929,704 and US 3,239,489.
The formation of compounds of formula (III) (alkoxy-substituted silazanes) is known
from US 6,652,978 B2. For the production of these compounds, monomeric or
oligomeric/polymeric silazanes of formula (I), where o is zero, can be reacted with amino or
25 hydroxy-group-containing alkoxysilanes, e.g., 3-aminopropyl triethoxysilane.
A process for production of compounds of formula (I) with o not equal to zero is
proposed in the dissertation by G. Motz (G. Motz, Dissertation, Stuttgart University, 1995)
specifically using the example of ammonolysis of 1,2-bis(dichloromethylsilyl)ethane. The
production of a special representative of these compounds, ABSE, is achieved according to
30 S. Kokott and G. Motz, "Modification of ABSE Polycarbosilazane with Multi-Walled
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Carbon Nanotubes for the Production of Spinnable Compounds," Mat. -miss. u.
Werkstofjtech. 2007, 38(11), 894-900, by hydrosilylation and ammonolysis of a mixture of
MeHSiC12 and McViSiC12.
N-Alkyl-substituted silazanes can, in turn, be synthesized in the same manner for the
5 person skilled in the art directly by bringing the corresponding halosilanes into reaction with
alkylamines, as described in US 4,935,481 and US 4,595,775.
The quantity ratio of silazane used to the acrylonitrile used is basically not critical.
Thus, for example, the molar contents of silazane to acrylonitrile may lie in the range from
100:1 to 1:100. Proportions from 4:1 to 1:20 have been found to be favorable. The molar
10 content of silazane is preferably not above that of acrylonitrile.
The reaction takes place in a solvent suitable for the components. In particular, the
solvents commonly used for polymerization of acrylonitrile such as DMF, 1,3-dioxolan-2-
one, dimethyl acetamide or DMSO may be used. A conventional catalyst for radical
polymerizations, especially polyadditions, may be added. For example, one may resort here
15 to the catalysts known for the production of polyacrylonitrile, e.g., azoisobutyronitrile.
The reaction is usually conducted at elevated temperature, e.g., at 40°C to 100°C
(i.e., at the reflux temperature of the solvent); it is usually completed after a few hours.
Products with linear -C-C- bonds are obtained. If the silazane or silazanes used contain at
least two alkenyl groups, several such bonds may emerge from one silazane molecule or this
20 molecule, respectively. Depending on the steric conditions, these silazancs can therefore be
a starting point for three-dimensional bonds. If oligomeric or even polymeric silazanes are
used, the product formed will also contain chains or rings from Si-N groups, which further
increases the density of the structure.
It is preferred to create the materials according to the present invention exclusively
25 from acrylonitrile and silazane. However, it is also possible for them to contain other
additives.
As additives, for example, organic materials (monomers or other organic molecules)
come into consideration, which can be copolymerized with acrylonitrile. For this purpose,
for example, styrene and/or butadiene and/or vinyl carbazole come into question. In order
30 not to impair the desired properties, especially the flame and fire protection too severely,
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these additives should generally not amount to more than 20 wt.% relative to the content of
the sum of acrylonitrile and organic molecules. The organic substance(s) is/are preferably
mixed with the same solution or charged in it, in which the other components are introduced
in order to cause polymerization.
5 In addition, or instead of this, the material may also contain one or more fillers,
preferably of inorganic nature, but possibly also organically modified, e.g. to facilitate their
being incorporated by polymerization. The filler, depending on requirements, may be added
in a quantity up to about 60 wt.% relative to the weight of the material. Quantities of up to
20 wt.% are preferred. The filler is preferably added before the solvent is removed.
10 The material of the present invention can basically be brought into any desired form.
However, it is preferably used for the production of fibers or'is present in fiber form.
For production of fibers, the solvent is removed from the polymer solution obtained
(e.g., polymer suspension if a filler is added). The product is usually solid at room
temperature. If the temperature is raised, a viscoelastic melt is formed from polymer
15 molecules hooked together. In many cases, the softening point is above 100°C.
From the melt, preferably a melt free of filler, fibers are drawn, preferably by
extrusion through a nozzle head containing a large number of nozzles. The nozzle cross
section is preferably about 150-400 μm. The fibers are then cooled and at the same time
preferably stretched, thus making the diameter clearly smaller; in the case of continuous
20 fiber production, they are then preferably wound [on spools].
The fibers thus obtained are suitable for processing into textile materials, e.g.,
weaving, knitting, laying or for incorporation into polymer materials as a reinforcing agent.
They are especially interesting for use in fire protection since they have fire-inhibiting
properties due to the high content of silicon and nitrogen.
25 In addition, the fibers can be transformed into ceramic fibers by pyrolysis. For this
purpose, the polymer fibers obtained from the melt are first made infusible by conventional
methods, e.g., by bombardment with electron beams. Usually doses in the range of approx.
200 KGy are sufficient for this.
The pyrolysis is usually conducted in a protective gas free of oxygen, e.g., argon.
30 The reaction conditions (gas atmosphere , temperature) can be selected such that the ratio of
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silicon to nitrogen to carbon in the product is held approximately the same (usually,
however, the carbon content diminishes slightly because some methane can form). In this
way, one can arrive at SiCN ceramic fibers. The latter can, if necessary, be transformed by
conventional measures into SiC or SiN fibers, e.g., by heating the fibers to at least 1,450°C,
5 in which case SiC is formed, or by pyrolysis in an ammonia atmosphere, leading to the
formation of methane from the carbon.
The following examples are intended to explain the invention in more detail. The
equivalent ratios given refer to the double bonds (vinyl or acrylic).
Example 1
10 Reaction of divinyl tetramethyl disilazane (DVTMDS) with acrylonitrile (ACN) in a
ratio of 1:1
Under a nitrogen atmosphere, 1.59 g (8.6 mol) of DVTMDS, 0.91 g (17.2 mmol)
ACN and 2.5 g of dimethyl formamide (DMF) are brought together in a three-necked flask
equipped with a reflux condenser with bubble counter, gas feed line and magnetic agitator.
15 To this mixture, 37.5 mg of azoisobutyronitrile (AIBN) are added, followed by stiffing for
five hours at 75°C. Depending on the batch, one will obtain a dark yellow to amber colored
liquid. The vinylic double bond of the silazane has almost totally vanished according to the
Raman spectrum.
Example 2
20 Reaction of divinyl tetramethyl disilazane with acrylonitrile in a ratio of 1:4
Under a nitrogen atmosphere, 0.76 g (4.1 mol) of DVTMDS, 1.74 g (32.8 mmol)
ACN and 2.5 g of dimethyl formamide (DMF) are brought together in a three-necked flask
equipped with a reflux condenser with bubble counter, gas feed line and magnetic agitator.
To this mixture, 37.5 mg of azoisobutyronitrile (AIBN) are added, followed by stirring for
25 five hours at 75°C. Depending on the batch, one will obtain a dark yellow to amber-colored
liquid. The vinylic double bond of the silazane has almost totally vanished according to the
Raman spectrum.
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Example 3
Reaction of a cyclic silazane obtained by ammonolysis of a mixture of 50 mol.%
dichlorovinylmethyl silane and 50 mol.% of dichlorodimethylsilane (VML50) with
acrylonitrile in a molar ratio of 1:1
5 Under a nitrogen atmosphere, 1.82 g of VML50, 0.61 g ACN and 2.5 g of dimethyl
formamide (DMF) are brought together in a three-necked flask equipped with a reflux
condenser with bubble counter, gas feed line and magnetic agitator. To this mixture, 75 mg
of (0.46 mmol) of azoisobutyronitrile (AIBN) are added, followed by stirring for five hours
at 75°C. One obtains a yellow, highly viscous solution.
10 Example 4
Reaction of a cyclic silazane obtained by ammonolysis of a mixture of 50 mol.%
dichlorovinylmethyl silane and 50 mol.% of dichlorodimethylsilane (VML50) with
acrylonitrile in a molar ratio of 1:4
Under a nitrogen atmosphere, 1.04 g (0,66 mmol-equ) of VML50, 1.39 g (26.1
15 mmol) of ACN and 2.5 g dimethyl formamide (DMF) are brought together in a three-necked
flask equipped with a reflux condenser with bubble counter, gas feed line and magnetic
agitator. To this mixture, 75 mg of (0.46 mmol) of azoisobutyronitrile (AIBN) are added,
followed by stirring for five hours at 75°C. After less than two hours, the stirring is halted
by gel formation. A yellow gel is obtained.
20 Example 5 - Production of fibers
-The polymer obtained by polymerization of a vinyl silazane with acrylonitrile is
freed of solvent and heated until a viscous melt is formed. The latter is pressed through a
nozzle plate with several hundred nozzles with diameters of 200 or 300 l.um. The threads
thus formed sink down due to gravity in a space with normal room temperature. The fiber
25 ends are caught and the fiber bundle is wound under tension on a rotating roller, at which
time the fibers are stretched to a thickness of about 10-30 μm.
Example 6 - Secondary stretching of the fibers
The fibers of Example 5 are exposed to electron bombardment of 200 KGy.
Following this, they are duroplastic and are then infusible. * * *
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15

Claims
1. Copolymer obtained by reaction which comprises reacting:
5
(i)
(ii)
acrylonitrile with
at least one monomeric, oligomeric and/or polymeric silazane, where said
silazane contains at least one vinylic double bond.
2. Copolymer in accordance with claim 1, in which the silazane is selected from those of
general formula (I):
of general formula (II),
10
and of general formula (III),
R2
R2'
Si N I iN- R6
R3 1 4 M R3' 14' fl
in which
(a) R2 is alkenyl,
15 R3 means hydrogen or straight-chained, branched or cyclic, substituted or
unsubstituted alkyl, the same alkenyl as R2 or a different alkenyl, aryl,
arylalkyl, alkylaryl, alkenylaryl or arylalkenyl, where each of the substituents
English translation of PCT/EP2010/069196
Fraunhofer Gesellschaft ... e.V., et al.
16
R2 and R3 in the case when in and/or o is/are greater than 1 in different units
has a different or the same meaning,
5
R2 and R3, are the same or different and mean straight-chained, branched or
cyclic, substituted or unsubstituted alkyl, alkenyl, aryl, arylalkyl, alkylaryl,
alkenylaryl or arylalkenyl, where each of the substituents R2, and R3, in the
case when m and/or o is/are greater than 1 in different units has a different
meaning or the same meaning,
or
10
(b) if at least one radical R3 and one radical RYare present, R2 and R2, have the
meaning given above, and (i) all or (ii) in each case a part of the radicals R3
and R3' together represent an unsubstituted or substituted, straight-chained or
branched alkylene group, wherein in variant (ii)'the remaining part of the
radicals R3 and R3, has the meaning given under (a),
and in which
15 R4 and R4, denote alkyl, phenyl or hydrogen, wherein several radicals R4 and/or R4,
present in one molecule of compounds (I) to (III) may be the same or different,
Rl and R5 are the same or different and can have the same meaning as R2 and R3,
respectively, while R5 may also denote Si(Rt)(R2')(RY) or Rt and R5 together represent
a single bond,
20 R6 denotes Si(R2)(R2')-X-R7-Si(R2)n(OR2')3_q where X means either 0 or NR4, R7
means a single bond or represents a substituted or unsubstituted, straight-chained,
branched or cyclic alkylene group, and q may be 0, 1, 2 or 3,
P is an alkylene group with 1 to 12 carbon atoms,
25
m and p independently of each other denote 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a whole
number between 11 and 25000, and
n and o independently of each other denote 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a whole
number between 11 and 25000,
English translation of PCT/LP20'10/069196
Fraunhofer Geseltschaft ... e.V., et at.
17
wherein the units placed in square brackets can be distributed in a given molecule
uniformly, randomly or in blocks.
3. Copolymer in accordance with claim I or 2, obtained exclusively iron acryloni(l'ile
and silazane.
Fraunhofer Ges.... e.V. et al.
12360p; Claims
Replacement page 18
4. Copolymer in accordance with claim 1 or 2 obtained by reacting
i) a mixture of acrylonitrile and an organic molecule that can be copolymerized with
acrylonitrile, said organic polymer being present maximally in a proportion of 20 wt.%
5 in the mixture, and
(ii) a monomeric, oligomeric and/or polymeric silazane, said silazane containing at least
one vinylic double bond.
5. Copolymer in accordance with claim 4, in which the organic molecule is selected from
among styrene, butadiene, vinyl carbazole and a mixture of two or all three of these
10 molecules.
6. Copolymer in accordance with one of the above claims, characterized in that it is filled
with a filler.
7. Copolymer in accordance with one of the above claims, in fiber form.
8. Copolymer in accordance with claim 7, characterized in that it is infusible.
15 9. Use of fiber-like copolymers in accordance with claim 8 or 9 for the production of
ceramic fibers.
10. Process for the production of a copolymer as defined in claim 1, characterized in that
(i) acrylonitrile and
(ii) at least one monomeric, oligomeric and/or polymeric silazane that contains at least
20 one vinylic double bond,
are dissolved in a solvent and copolymerized by means of a catalyst for radical
polymerization.
11. Process in accordance with claim 10, characterized in that a filler is added to the solvent.
Fraunhofer Ges.... e.V. et at.
12360p; Claims
Replacement page 19
12. Process for the production of fibers from a copolymer as defined in claim 1,
characterized in that
(A) (i) acrylonitrile and
(ii) at least one monomeric, oligomeric and/or polymeric silazane that contains at
least one vinylic double bond,
are dissolved in a solvent and copolymerized by means of a catalyst for radical
polymerization,
10
(B)
(C)
the solvent is separated from the copolymer solution obtained,
the product obtained according to (B), if it is not liq qid or viscous at room
temperature; is transformed into a melt, and
(D) the productior melt created from it is extruded through one or more nozzles,
resulting in the formation of fibers.
13. Process in accordance with claim 12, wherein the extruded fibers subsequently are made
15 infusible.
14. Process in accordance with claim 13, wherein the extruded fibers are made infusible by
irradiation with electron beams.
15. Process for the production of SiCN ceramic fibers, characterized in that infusible fibers
produced according to the process of claim 13 or 14 are pyrolyzed under oxygen-free
20 protective gas.
16. Process for the production of SiC ceramic fibers, characterized in that SiCN ceramic
fibers produced as claimed in claim 15 are heated to at least 1,450°C.
17. Process for the production of SiN ceramic fibers, characterized in that SiCN ceramic
fibers produced as claimed in claim 15 are pyrolyzed in an ammonia atmosphere.