Process for the preparation of polysilanes

Details Process for the preparation of polysilanes Process for the preparation of polysilanes

1999-06-22

2001-01-16

Moore, Margaret G. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S010000, C556S430000

Reexamination Certificate

active

06174982

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for the preparation of polysilanes.
BACKGROUND ART
Polysilanes are attracting attention for their use as ceramic precursors; optoelectric materials such as photoresist, organic photosensitive material, optical waveguide, and optical memory, etc.
Heretofore, a method for producing polysilane is known wherein dialkyldihalosilane or dihalotetraalkyldisilane dissolved in toluene is subjected to reductive coupling in the presence of alkali metals such as metallic sodium with thorough stirring at a temperature over 100° C. (J. Am. Chem. Soc., 103 (1981) 7352). This method, however, including the steps of heating, thoroughly stirring and dispersing alkali metal which is inflammable in the presence of air, has safety problems for industrial-scale production. Further, the quality of the polysilane produced by this method is unsatisfactory; its molecular-weight distribution is polymodal, for example.
To overcome these drawbacks, several new methods for producing polysilanes have been proposed, as described below.
(a) Anionic polymerization of disilenes masked by biphenyl or the like. (Japanese Unexamined Patent Publication No. 23063/1989).
(b) Ring-opening polymerization of cyclic silanes (Japanese Unexamined Patent Publication 170913/1993).
(c) Dehydrogenative polycondensation of hydrosilane in the presence of transition-metal complex catalyst (Japanese Unexamined Patent Publication No. 17753/1995).
(d) Electroreduction of dihalosilane at room temperature or lower temperatures (Japanese Unexamined Patent Publication 309953/1995).
However, the above methods (a) and (b) suffer from various defects: they require complicated processes for producing monomers, the total yield of monomer is low in synthesis, and there are safety concerns due to the alkyl lithium reagent employed in polymerization. The method (c) has yet to be improved in the molecular weight and the structure of resulting polysilane (e.g., formation of crosslinked structure) attributable to the reaction mechanism thereof.
The method (d), on the other hand, is an excellent technique for providing high-molecular-weight and high-quality polysilane safely and efficiently in a high yield. The method, however, requires a special reaction apparatus, i.e., electrolytic cell. Accordingly, the method is not suitable for producing polysilane for less valuable applications although very useful for producing polysilanes for highly valuable applications.
In view of the above, it is a principal object of the present invention to provide a new method for producing desired polysilanes without complicated operations, and safely and economically.
DISCLOSURE OF THE INVENTION
The inventors conducted extensive research and discovered that the prior art problems can be substantially obviated or significantly mitigated by placing halosilane under the action of Mg or Mg alloy in the presence of specific Li salt and specific metal halide.
The present invention provides a method for producing polysilanes as described below:
1. A method for producing polysilanes comprising subjecting a dihalosilane of the general formula
(wherein m is 1 to 3; R represents hydrogen atom, alkyl group, aryl group, alkoxy group, amino group or silyl group and two Rs are the same or different in case of m=1, four Rs are the same or at least two of them are different in case of m=2 and six Rs are the same or at least two of them are different in case of m=3; X represents halogen atom) to the action of Mg or Mg alloy in an aprotic solvent in the presence of Li salt and metal halide, thereby producing polysilane represented by the general formula
(wherein R is as defined above corresponding to the starting material; n is 2 to 1000).
2. The method for producing polysilane according to the item 1 above, wherein Li salt is LiCl.
3. The method for producing polysilane according to the item 1 or 2 above, wherein the metal halide is at least one member selected from the group consisting of FeCl
2
, FeCl
3
, FeBr
2
, FeBr
3
, CuCl
2
, AlCl
3
, AlBr
3
, ZnCl
2
, SnCl
2
, SnCl
4
, COCl
2
, VCl
2
, TiCl
4
, PdCl
2
, SmCl
2
and SmI
2
.
4. The method for producing polysilane according to the item 3 above, wherein the metal halide is FeCl
2
.
5. The method for producing polysilane according to the item 3 above, wherein the metal halide is CUCl
2
.
6. The method for producing polysilane according to the item 3 above, wherein the metal halide is ZnCl
2
.
In the present invention, the halosilane used as the starting material is a dihalosilane represented by the general formula
(wherein m is 1 to 3; R represents hydrogen atom, alkyl group, aryl group, alkoxy group, amino group or silyl group and two Rs may be the same or different in case of m=1, four Rs may be the same or at least two of them may be different in case of m=2 and six Rs may be the same or at least two of them may be different in case of m=3; X represents halogen atom).
The reaction product of the present invention is a polysilane of the general formula
(wherein R is as defined above corresponding to the starting material; n is 2 to 1000).
In the dihalosilane represented by the general formula (1), m is 1 to 3, and hydrogen atom, amino group, organic substituents (alkyl group, aryl group, alkoxy group or amino group), and silyl group which are represented by R may be the same or at least two of them may be different. Stated more specifically, two Rs may be the same or different in case of m=1, four Rs may be the same or at least two of them may be different in case of m=2 and six Rs may be the same or at least two of them may be different in case of m=3.
Preferred compounds represented by the general formula (1) are those in which m is 1 or 2. Examples of the alkyl groups are those having 1 to 10 carbon atoms, among which those of 1 to 6 carbon atoms are preferable. Examples of the aryl groups include, phenyl group, phenyl group substituted with at least one alkyl group of 1 to 10 carbon atoms, p-alkoxyphenyl group, naphthyl group, etc. Examples of the alkoxy groups are those having 1 to 10 carbon atoms, among which those of 1 to 6 carbon atoms are preferred. Examples of the silyl groups are those having 1 to 10 silicon atoms, among which those of 1 to 6 silicon atoms are preferable. When Rs are above-mentioned amino group, organic substituents and silyl group, at least one of hydrogen atoms may be substituted with other functional group such as alkyl, aryl, or alkoxy group. Examples of the functional groups are those as stated above.
In the general formula (1), X represents a halogen atom (Cl, F, Br, I). Cl is more preferable as the halogen atom.
In the method of the present invention, dihalosilanes of the general formula (1) are usable singly or at least two of them can be used in mixture. Dihalosilanes of the highest purity are preferably used. For example, a liquid dihalosilane is preferably dried over calcium hydride and then distilled, and a solid dihalosilane is preferably purified by recrystallization.
Prior to the reaction, dihalosilane is dissolved in a solvent. Examples of useful solvents include a wide variety of aprotic solvents. Specific examples are polar solvents such as tetrahydrofuran, 1,2-dimethoxyethane, propylene carbonate, acetonitrile, dimethylformamide, dimethylsulfoxide, bis(2-methoxyethyl)ether, 1,4-dioxane, methylene chloride, etc.; non-polar solvents such as toluene, xylene, benzene, n-pentane, n-hexane, n-octane, n-decane, cyclohexane, etc. These solvents are usable singly or at least two of them can be used in mixture. Preferably, a single polar solvent, a mixture of at least two of polar solvent, and a mixture of polar solvent and non-polar solvent are used as the solvent. When a polar solvent and a non-polar solvent are used as a mixture, they are preferably in a proportion of the former:the latter=1 to 0.01-20. Preferred polar solvents to be used solely or in combination with other solvents are tetrahydrofuran and 1,2-dimethoxyethane.
Too low a concentration of dih

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