Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2002-03-15
2004-03-09
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C556S435000, C528S025000, C528S031000, C528S032000, C528S043000, C528S481000, C528S483000
Reexamination Certificate
active
06703519
ABSTRACT:
“This application is a national phase of PCT/FR00/02562 which was filed on Sep. 15, 2000, and was not published in English.”
The present invention relates to poly(ethynylene phenylene ethynylene silylene) polymers with a determined molecular weight, to a method for preparing said polymers and to hardened products which may be obtained by a heat treatment of said polymers. The polymers according to the invention may notably be used in matrices for composites.
The technical field of the present invention may be defined as being that of heat stable plastics, i.e. polymers which may withstand high temperatures which may attain up to 600° C., for example.
The industrial needs for such heat stable plastics have enormously increased during the last decades in particular in the field of electronics and aerospace.
Such polymers were developed for finding a remedy to the defects of materials used earlier in similar applications.
Indeed, it is known that metals such as iron, titanium and steel, are thermally very resistant, but they are heavy. Aluminum is light but not very heat resistant i.e. up to about 300° C. Ceramics such as SiC, Si
3
N
4
and silica are lighter than metals and very heat resistant but not moldable. This is why a large number of plastics have been synthetized which are light, moldable and have good mechanical properties; these are carbon-based polymers essentially.
Polyimides have the highest heat resistance of all plastics with a heat deformation temperature of 460° C., however the compounds which are listed as being the most stable known presently are very difficult to apply. Other polymers such as polybenzimidazoles, polybenzothiazoles and polybenzooxazoles have an even greater heat resistance than that of polyimide, but they are not moldable and they are flammable.
Silicon-based polymers, such as silicones or carbosilanes, have also been investigated extensively. The latter, such as compounds of poly(silylene ethynylene), are generally used as precursors of ceramics of the silicon carbide SiC type, resist compounds and conducting materials.
It was recently shown in document [4] that poly[(phenyl sylylene), ethynylene-1,3-phenylene ethynylene] (or MSP) prepared by a synthesis method involving a polymerization reaction by dehydrocoupling between phenylsilane and m-diethynylbenzene, exhibited a remarkably high heat stability. This is confirmed in document [1] which generally demonstrates the excellent heat stability properties of poly(silyl ethynylene phenylene ethynylene)s which include a recurrent unit represented by the following formula (A):
Synthesis of polycarbosilanes including a silane function and diethynylbenzene by conventional methods with metal catalysts leads to low purity polymers containing significant traces of metal catalyst largely detrimental to their thermal properties.
Other enhanced synthesis methods are presented in document [2]: these are syntheses catalyzed by palladium which in fact are only applied to a very limited number of specific polymers wherein silicon bears two phenyl or methyl groups, for example.
In particular, it will be noted that the compounds with the recurrent unit described earlier by formula (A), cannot be synthetized by this method. Now, it is found that the SiH bonds of such compounds, particularly difficult to obtain, are of high interest as they are extremely reactive and may produce multiple rearrangements and reactions.
Another cross dehydrocoupling method for silanes with alkynes in the presence of a catalyst system based on copper chloride and an amine is described in document [3]. This method is however also limited to a few polymers and results in compounds with a partly cross-linked structure and a very high weight average molecular weight (10
4
-10
5
). These structural defects seriously affect both the solubility properties and thermal properties of these polymers.
Another synthesis method for overcoming the drawbacks of the method described above, and for preparing pure compounds, without any traces of metals, and with excellent and well-defined properties, notably heat stability, has been suggested in document [4] already mentioned above. This method essentially provides synthesis of compounds of formula (A) above, wherein the silicon atom bears a hydrogen atom. The method according to [4] is a polycondensation with dehydrogenation of a functionalized hydrosilane with a compound of the diethynyl type in the presence of a metal oxide such as MgO according to the following reaction scheme (B):
This method leads to weakly cross-linked polymers with, as illustrated above, an excellent heat stability, but for which the weight distribution is however very wide.
In another more recent publication [1], the same authors prepared a polymer series including the —Si(H)—C≡C— unit by method (B) and by another more advantageous method, involving the condensation reaction of dichlorosilane and organomagnesium reagents, and subsequently the reaction of the obtained product with a monochlorosilane followed by hydrolysis according to the following reaction scheme (C):
Unlike method (B), with method (C) polymers without any structural defects may be obtained in good yields and with a narrow weight distribution.
The compounds obtained by this method are perfectly pure and have perfectly characterized thermal properties. These are cross-linkable thermoplastic polymers.
This document also discloses the preparation of the aforementioned polymers reinforced by glass, carbon or SiC fibers.
A patent relating to polymers comprising the most general recurrent unit (D):
wherein R and R′ relate to a large number of known groups in organic chemistry, was granted to the authors of documents [1] and [4], this is document EP-B1-0 617 073 (corresponding to U.S. Pat. No. 5,420,238).
These polymers are essentially prepared by the method of scheme (C) and optionally by the method of scheme (B), and they have an average molecular weight from 500 to 1,000,000. This document also describes hardened products based on these polymers and their preparation by heat treatment. It is shown that the polymers of this document may be used as a heat stable polymer, a fire-resistant polymer, a conducting polymer, a material for electroluminescent and linear components. In fact, it seems that such polymers are essentially used as organic precursors of ceramics.
The excellent heat stability of the polymers, as notably prepared in document EP-B1-0 617 073, enables them to make up the resin forming the organic matrix of heat stable composite materials with organic matrices.
Numerous techniques for producing composites exist.
Very broadly speaking, the different methods require injection techniques, (notably resin transfer molding (RTM)), or techniques for compacting prepregs.
Prepregs are semiproducts, with a small thickness, formed of fibers impregnated with resin. Prepregs which are for making high performance composite structures, contain less than 50% of fiber in volume.
Also, during application, the matrix shall have a low viscosity in order to penetrate the reinforcing sheet and properly impregnate the fiber in order to prevent its distortion and to preserve its integrity. The reinforcement fibers are impregnated either with a resin solution in a suitable solvent, or with pure molten resin, this is the so-called “hot melt” technique. The technology for manufacturing prepregs with a thermoplastic matrix is essentially determined by the morphology of the polymers.
Injection molding is a method which consists of injecting liquid resin in the textile reinforcement positioned beforehand in the cavity formed by the mold and the counter-mold. The most important parameter is viscosity which should be between 100 and 1,000 mPa.s at the injection temperature which is generally from 50 to 250° C.
For these two techniques, viscosity is therefore the critical parameter which conditions the applicability of the polymer.
Now, amorphous polymers correspond to
Buvat Pierrick
Jousse Franck
Levassort Christian
Barts Samuel
Commissariat a L' Energie Atomique
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