Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1993-11-02
1996-09-17
Bleutge, John C.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524102, 524130, 524173, 501 88, 501 90, C08K 534, C04B 3552
Patent
active
055569013
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
The present invention concerns polysilane-based compositions which are particularly useful for producing silicon carbide. The field of the invention is that of the stabilisation in air, particularly in oxygen, and/or at a temperature, of such polysilane-based compositions or mixtures of polysilanes.
Polysilanes are polymeric materials, the linear skeleton of which is constituted by silicon atoms connected together. These silicon-rich materials have been applied in numerous technical fields. They are used in the industries of electronics and composites, particularly as photoconductors, semiconductors, materials constituting the image in xerography and microlithography and, as indicated above, as ceramic precursors in silicon carbide (CHEM. REV. 1989, 89, 1410).
More specifically, polysilanes are thus mainly used: ceramics, ceramic fibres, composition is used as a matrix, with carbon or ceramic fibres or, as a binder, with ceramic powders), composite carbon-carbon materials or carbon fibres, are coated with said polysilane and the latter is pyrolysed), as materials for filling the pores of a porous ceramic material, and with the aim of improving the mechanical properties of such a material,
PRIOR ART
Polysilanes can be obtained in various ways such as, for example, by condensing halogenosilanes such as chlorosilanes with alkaline metals, as described in patents U.S. Pat. Nos. 4,783,516 and 4,537,942, as well as in the publication CHEM. REV. 1989, 89 (6), 1359, or by coupled dehydrogenation reactions involving catalysts, as described in the publications J. AMER. CHEM. SOC. 1986, 108, 40/59 or J. ORGANO-METALLIC CHEM., 1985, 2079, C11, or by redistribution reactions, as disclosed in patents U.S. Pat. Nos. 4,814,919 and 4,310,651, or else by chemical modification of simple polysilanes as described, in particular, in the publication POLYM. REPRINTS, 1987, 28, 222.
The polysilanes considered in the context of the present invention are those having the general formula: ##STR1## in which the R groups can be identical or different, independent from one another along the whole length of the polymer chain and chosen from the following groups: carbon atoms, functional groups containing nitrogen, oxygen, phosphorus or boron weight greater than 50 units of mass.
The present invention concerns, more particularly, polysilanes having on their skeleton hydrogen groups (Si--H) and/or olefin groups preferably having 1 to 18 carbon atoms and, more preferably still, a further 2 carbon atoms, this corresponding to the vinyl group (Vi:--CH.dbd.CH.sub.2).
By way of example, the following may be cited: polymethylhydrogensilanes, hereinafter termed PMSs, and vinyl groups in their skeleton and hereinafter termed PVSs. U.S. Pat. No. 4,783,516.
In all applications of polysilanes involving crosslinking, including in particular ceramisation, and which are those with which the present invention is concerned in preference, it is necessary to constitute polysilane chains reactive by hydrosilylation.
Hydrosilylation is a radicalar addition reaction involving a hydrogen group (Si--H) and an olefin group (Si--Vi).
The compositions used in these applications must therefore include polysilane chains comprising at least two hydrogen and/or olefin groups per molecule.
According to a variant, use may be made of crosslinking additives (or bridging agents) of the organic or organosilicic compound type, with or without a polymeric structure and also comprising at least two hydrogen and/or olefin groups per molecule.
Consequently, all the polysilanes with which the invention is concerned, including in particular PVS and PMS, are subject to unwanted oxidation (Si--H) and/or crosslinking (Si--H with Si--Vi) reactions in the presence of air.
In contact with the ambient air (and therefore with oxygen), PMS polymethylsilanes are subject to rapid incorporation of oxygen within the polymer skeleton, which leads to polysiloxane-type products (MeHSiO).sub.n. Such parasite products are quite undesirable when it is intended to ceramise the
REFERENCES:
patent: 5025048 (1991-06-01), Barnier
Bleutge John C.
Dean Karen A.
Flamel Technologies
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