FR2565234A1 - New unbranched polysilanes, their preparation and their application - Google Patents

Abstract

New polysilanes containing units of formula: which are substantially unbranched and substantially free from halogen bonded to silicon; their preparation consisting chiefly in subjecting a silane of formula: SiH2 to a polymerisation by the catalytic action of an organometallic titanium or zirconium derivative.

Description

 The present invention relates to new unbranched polysilanes, their preparation and their application.

We know that the plastics industry uses molecules consisting essentially of long chains of carbon atoms,
Although silicon is in the same family of elements as carbon and has some similar chemical properties, polysilanes are a practically non-existent class of polymer. This is mainly due to the lack of a simple and inexpensive method of preparation.

 US patents 2,563,005 and 4,260,780 describe in particular the preparation of methyl- and / or phenyl-polysilanes by reduction of corresponding dichlorosilanes, using an alkali metal. The polymers obtained also contain chlorine, in a proportion which can range up to 0.8 atom of chlorine per atom of silicon. In addition, the industrial application of this process raises difficulties because the alkali metals are reactants whose use is dangerous (see in this regard Example II of US Pat. No. 4,260,780).

 We have now discovered a catalytic process for the polymerization of silanes which makes it possible to selectively obtain new unbranched polysilanes with a high yield.

caracterise par le ralt que lesdits polysilanes sont non ramifiés et sont pratiquement exempts d'halogène.The process of the invention makes it possible to prepare new polysilanes containing units of formula I

characterized by the fact that said polysilanes are unbranched and are practically free of halogen.

dans laquelle R1 et R2, qui peuvent être égaux ou différents l'un de l'autre, représentent chacun un groupement alkyle, cycloalkyle, cycloalkyl-alkyle, aralkyle ou aryle, ou bien l'un des groupements R ou R peut représenter en outre -H ou un groupement hydrocarboné insaturé, étant entendu que lesdits 1 R1 et 2 groupements R et R peuvent être éventuellement substitués et/ou comporter un ou plusieurs hétéroatomes.The subject of the invention is in particular polymers as defined above, characterized by the fact that they contain units a of formula IA

in which R1 and R2, which may be equal or different from each other, each represent an alkyl, cycloalkyl, cycloalkyl-alkyl, aralkyl or aryl group, or else one of the groups R or R may also represent -H or an unsaturated hydrocarbon group, it being understood that said 1 R1 and 2 R and R groups may be optionally substituted and / or contain one or more heteroatoms.

 The degree of polymerization of the polymers of the invention varies in particular depending on the structure of the starting materials. In general, it corresponds to an average molecular weight, measured by osmometry, which can be greater than approximately 800 Daltons.

 In the products of formula IA, when R and / or R2 represent an alkyl, a cyclo-alkyl or an aryl, said alkyl is an alkyl having for example from 1 to 12 carbon atoms, and in particular from 1 to 8 atoms carbon; the aryl of the aryl or aralkyl group is in particular a phenyl optionally substituted for example by lower alkyl groups the cycloalkyl group is preferably a 5 or 6-membered group optionally substituted, for example a cyclopentyl or cyclohexyl group optionally substituted for example by lower alkyl groups; when one of the substituents R1 or R2 represents an unsaturated hydrocarbon group, it is in particular a hydrocarbon group comprising from 2 to 10 carbon atoms, in particular from 2 to 6 carbon atoms.

 The invention relates in particular to polymers comprising units of formula IA, with the exception of those for which R1 and / or R2 represent methyl and / or phenyl.

dans laquelle R représente un groupement alkyle, cycloalkyle, cycloalkyl-alkyle, aralkyle ou aryle, ledit groupement pouvant être éventuellement substitué et/ou comporter un ou plusieurs hétéroatomes.t1 invention relates in particular to the polysilanes characterized by the fact tools contain units of formula IB

in which R represents an alkyl, cycloalkyl, cycloalkyl-alkyl, aralkyl or aryl group, said group possibly being optionally substituted and / or comprising one or more heteroatoms.

 The present invention also relates to a process for the preparation of polysilanes of formula I, IA or IB.

è l'action catalytique d'un dérivé organométallique de titane ou de zirconium puis que l'on transforme, si désiré, le polymère obtenu en polymère modifié correspondant.This process is characterized by the fact that a silane of general formula II is subjected:

è the catalytic action of an organometallic derivative of titanium or zirconium then that the polymer obtained is transformed, if desired, into the corresponding modified polymer.

In particular embodiments, the method of the present application may also have the following characteristics, taken individually or in combination
- said organometallic derivative is a derivative of formula III
X2 (R ') 2 (III) in which M represents Ti or Zr,
X represents a 75-cyclopentadienyl group optionally substituted with 1 to 5 substituents such as for example lower alkyl substituents (in particular methyl) and
R ′ represents an alkyl, aralkyl or aryl group,
- said organometallic derivative is a derivative of formula IV
(X2 Ti H) 2H (IV) in which X is defined as above
- The proportion of catalyst varies from 0.5 to 2% in moles compared to the silane used as starting material
- R 'represents an alkyl group having 1 to 5 carbon atoms, an aralkyl group, in particular phenylalkyl in which the alkyl part has 1 2 5 carbon atoms
- one operates for example at a temperature which can range from 0 to 150pu, in particular from 10 to 30 "C, generally at room temperature
- operating in the presence of an inert hydrocarbon solvent
- Said solvent is chosen from alkanes which are liquid at reaction temperature, benzene or an alkylated derivative of benzene;
- After the polymerization reaction, the polymer is purified by chromatography to remove the catalyst.

 The catalyst of formula X2-M (R ') 2 can be prepared for example by the action of a derivative of formula R' ti on a compound of formula X2M (Hal) 2, Hal being a halogen atom such that 'a chlorine atom.

The catalyst of formula (X2 Ti H) 2R can be prepared by reacting the catalyst of formula III (M = Ti) with certain alkyl-, aryl-, or alkoxy-silanes in an inert solvent according to the reaction 4 X2 Ti (R ' ) 2 + 8 (R3) 3 Silo 2 (X2 Ti H) 2H + 6 (R3) 3 Si R'2 + (R3) 6 Si2 + 2 R2H in which,
R 'and X are defined as above, and the groups R3, which may be different in the same compound of formula V
(R3) 3 SiH ('W) represent -H or an alkyl, aryl or alkoxy group.

 It can be seen that in the case where the product of formula V is equivalent to a product of formula IA, the catalyst of formula IV is formed in situ during the polymerization reaction of the silane in the presence of the starting catalyst of formula III.

 In practice, the process of the invention is carried out using a large excess of starting silane. It is possible to operate without added solvent, and in this case it is the starting silane which constitutes the solvent for the polymer, or else, preferably, it is operated in the presence of a hydrocarbon solvent such as, for example, hexane, benzene, toluene, etc ...

Since the release of hydrogen is in some cases very vigorous, it is generally useful to stir the reaction mixture, possibly by bubbling an inert gas, for example argon, to regularize the
evolution of hydrogen and accelerate the reaction. After a time which is generally a few hours at room temperature, the viscosity of the reaction mixture increases sharply due to the accumulation of the polysilane formed. After the end of the evolution of hydrogen, the polysilane formed can be collected by column chromatography, for example a Florisil column (registered trademark for a magnesium silicate). This chromatography makes it possible to separate the polymer and the catalyst. The solvent can then be removed by evaporation under reduced pressure.

 The polymerization reaction is carried out in the absence of air, since many polysiloxanes oxidize easily on contact with air.

 The evolution of the polymerization reaction can be followed by infrared or R.M.N. These methods make it possible to observe, for example in the case where the starting product is a primary silane, a rapid disappearance of the starting product and the appearance of a new product having an absorption characteristic of the Si-H trisubstituted compounds (at neighborhood of 2090 cl).

 The polymers formed also exhibit intense absorption in the near ultraviolet, in the vicinity of 270 nm, characteristic of the Si-Si bond.

 the spectrum R.M.N. polymers show a complex solid in the Si-fl region.

The DEPT study (short for "Distortionless Enhancement by
Polarization Transfer ") made on polymers obtained from primary silanes containing the 29Si isotope has shown that practically all silicon atoms have an Si-E bond.

In other words, the polymers obtained by the process of the present application are essentially unbranched polymers,
The molecular weight of the polymers obtained according to the process varies in particular depending on the purity of the starting materials, the reaction time, etc.

 Of course, the invention is not limited to polymers whose degree of polymerization varies within a particular range. It may be noted, however, that in general, the average molecular weight, measured by osmometry, is greater than 800 Daltons. it can vary for example from 800 to 50,000 Daltons approximately.

 It should be noted that the secondary silanes react much more slowly than the primary silanes.

 To transform the polysilanes obtained in particular those having units of formula IB into other polysilanes of units of formula TA, the polymer of formula IB can be subjected to a reaction with unsaturated ethylenic or acetylenic derivatives. It has in fact been discovered that polymers with units IB give, with the unsaturated carbon derivatives, a reaction analogous to the known reaction known as hydrosilylation reaction observed with silanes. This reaction is carried out in the presence of known hydrosilylation catalysts based on platinum (in particular octadiènediméthylplatine) or catalysts of the ZIEGLER type. This gives polysilanes of corresponding formula IA (with R = R and R = group corresponding to the unsaturated derivative used ). In the case where this reaction is carried out with dienes, acetylenics, or polyunsaturated derivatives, derivatives of formula IA are obtained with one of the substituents R or R representing an unsaturated hydrocarbon derivative.

 The polysilanes of the invention can be used in particular to form fibers or coatings of silicon carbide by thermal decomposition (pyrolysis). In addition, it is possible to give a shape to these polymers before pyrolysis and in this case it is possible to obtain parts of any shape in silicon carbide.

 The polymers of the invention can also be used in the preparation of photoconversion devices based on amorphous silicon, in particular solar energy photoconversion devices, because of their high absorption in the near ultraviolet.

 In addition, the polymers of the invention can be doped by copolymerization with phosphorus, arsenic or boron derivatives so as to modify their properties. The polymers of the invention can also be mixed with base materials for ceramics in order to obtain new materials for ceramics.

Examples of uses of polysilanes that may be mentioned include the applications which are described in particular in the following publications:
- S. YAJIMA et al, Nature, London, 1976, Vol. 261, p. 683;
- R. WEST, J. of Am. Chem. Soc., 1981, 103, p. 7352.

 Finally, the polymers of formula IB can serve as an intermediate product for the preparation of other polysilane derivatives by replacing the hydrogen bonded to the silicon with other groups, in particular by catalytic hydrosilylation, as indicated previously.

The following examples illustrate the invention without however limiting it
EXAMPLE 1 Preparation of the polyphenylsilane (formula IA with one of the
substituents R and R2 representing - H and the other representative
a phenyl group)
a) A solution of 2 ml of C 6H5-SiH3 in 3 ml of toluene is subjected to degassing, then the solution is saturated with argon. 40 mg of
dimethyltitanocene and the solution is added vigorously by passing a stream of argon for 24 hours. It is evaporated under repeated pressure at room temperature until dry. The residue is redissolved in a toluene-hexane mixture (1: 2 v / v) and the solution is chromatographed on a column of
Florisil (trademark). Eluted with the same toluene-hexane solvent.

 The polyphenylsilane obtained is in the form of a friable glassy solid of white color.

-l
Infrared spectrum: bands at 2090 and 2085 cm -1 (Si-H bond).

 Spectrum R.M.N. : a massive complex at # = 4 to 5 ppm in the Si-R region with a ratio of 1/5 by comparison with the protons of the phenyl groups.

5-
Similarly, using di-P cyclopentadienyl dimethyl zirconium as catalyst as the catalyst in place of dimethyltitanocene, a polyphenylsilane is obtained, starting from phenylsilane.

The product obtained can then be transformed into polyphenylhexylsilane (formula IA with one of the substituents R and R representing a phenyl group and the other a hexyl group) in the following manner
b) 1 g of the polyphenylsilane obtained above is dissolved in a mixture of 5 ml of benzene and 5 ml of hexene-1. 5 mg of cyclooctadièiméiméthylplatine are added and the mixture is stirred at room temperature under an argon atmosphere for 24 hours. The reaction is followed by the evolution of the infrared spectrum which shows the disappearance of the absorption band corresponding to the binding Si-fl. After removal of the solvent by evaporation under reduced pressure, the polyphenylhexylsilane is obtained, the study of the NMR spectrum of which shows the presence of phenyl and hexyl groups in equivalent proportions, and the absence of Si-fl bond.

EXAMPLE 2 Preparation of polyhexylsilane (compound of formula IA with one of the substituents R and R representing -H and the other representing a hexyl group)
The starting product is a 50% solution of hexylsilane in hexane containing 1% of the same catalyst as that used in Example 1. The mixture is brought to reflux for 3 days. After purification of the product obtained in a similar manner to that described in Example 1 a), the product indicated is obtained in the form of a very viscous oil.

Claims (11)

1. New polysilanes, characterized in that they contain units of formula I:

 and that said polysSlanes are substantially non-branched and are substantially free of halogen bonded to silicon.  2. New polysilanes, characterized in that they contain units of formula IA

 in which R1 and R2, which may be equal or different from each other, each represent an alkyl, cycloalkyl, cycloalkyl-alkyl, aralkyl or aryl group, or else one of the groups R or R may also represent -H or an unsaturated hydrocarbon group, it being understood that said 1 R1 and 2 R and R groups may be optionally substituted and / or contain one or more heteroatoms.  3. New polysilanes, characterized in that they contain units of formula IB

 in which R represents an alkyl, cycloalkyl, cycloalkyl-alkyl, aralkyl or aryl group, said group possibly being substituted and / or comprising one or more heteroatoms.  4. Polysilanes according to any one of claims 2 and 3, characterized in that when R1 and / or R2 represent an alkyl, a cycloalkyl or an aryl, said alkyl has from 1 to 12 carbon atoms, the aryl of aryl or aralkyl group is in particular a phenyl optionally substituted for example by lower alkyl groups; the cycloalkyl group is preferably an optionally substituted 5 or 6-membered group, for example a cyclopentyl or cyclohexyl group optionally substituted for example by lower alkyl groups when one of the substituents R1 or R2 represents an unsaturated hydrocarbon group, it s' acts in particular of a hydrocarbon group comprising from 2 to 10 carbon atoms.  5. Process for the preparation of a polymer as defined in any one of claims 1 to 4, characterized in that a silane of general formula II is subjected

 to the catalytic action of an organometallic derivative of titanium or zirconium, then that lton transforms, if desired, the polymer obtained into the corresponding modified polymer.  6. Method according to claim 5, characterized in that said organometallic derivative is a derivative of formula:  X2 M (R ') 2 in which X represents a 7 5-cyclopentadienyl group optionally substituted with 1 to 5 substituents and R' represents an alkyl, aralkyl or aryl group.  7. Method according to claim 5, characterized in that said organometallic derivative is a derivative of formula  (X2 Ti H) 2H in which X is defined as in claim 6.  8. Method according to any one of claims 5 to 7, characterized in that the proportion of catalyst varies from 0.5 to 2% by mol relative to the silane used as starting material.  9. Method according to any one of claims 5 to 8, characterized in that one operates at a temperature which can range from 0 to 15O0C.  10. Method according to any one of claims 5 to 99 characterized in that after the polymerization reaction, the polymer is purified by chromatography to remove the catalyst.  11. Method according to any one of claims 5 to 10, characterized in that the polymer obtained, of formula IB, is subjected, if desired, to a reaction with unsaturated carbon derivatives, in the presence of a hydrosilylation catalyst, to form corresponding polysilanes of formula IA (with R1 = R and R2 = group corresponding to the unsaturated derivative used).