Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2000-01-25
2002-11-26
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C556S440000
Reexamination Certificate
active
06486338
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for the preparation of organosilicon compounds (P) containing &agr;,&bgr;-unsaturated carboxylic acid radicals, to polymers of the organosilicon compounds (P), to compositions comprising organosilicon compounds (P), and to optically anisotropic layers produced by alignment and polymerization of liquid-crystalline organosilicon compounds (P).
BACKGROUND ART
The syntheses and applications of crosslinkable organosiloxanes and organosilanes, in particular siloxanes and silanes containing methacryloyl groups, are described in large number in the literature. Frequently used materials, which are, for example, employed for coatings, are alkoxy-substituted silanes, which, besides the methacryloyl groups, usually also contain methoxy or ethoxy groups. Owing to the relatively low reactivity of the methacryloyl groups, however, the crosslinking density of the polymerized layers produced from these compounds is comparatively low. In many applications, an increase in the crosslinking density could produce better material properties, for example an improvement in the solvent stability, an improvement in the adhesion to the surfaces to be coated, or an increase in the hardness of the coatings. Possible solutions to the preparation of highly crosslinked structures of this type are to increase the number of polymerizable groups, and to use polymerizable groups of higher reactivity than that of the methacryloyl groups, for example acryloyl groups. However, the processes disclosed hitherto for the preparation of such organosiloxanes and organosilanes containing polymerizable groups of high reactivity can only be carried out with difficulty on an industrial scale, or do not give the desired result for reasons associated with the method of production. This is particularly true in the case of acryloyl groups.
It is known that crosslinked organosiloxanes having a liquid-crystalline structure are frequently insufficiently stable to external influences, such as exposure to certain organic solvents. U.S. Pat. No. 5,362,315 discloses, for example, pigments comprising liquid crystalline substances having a chiral phase which are distinguished by the fact that their color depends on the viewing angle. These pigments are employed in various transparent media, such as coatings, binders or plastics. However, EP-A-724005 discloses that when these pigments are prepared from liquid-crystalline organosiloxanes in which the polymerizable groups are exclusively methacryloyl groups, they then, depending on the processing conditions and the medium into which the pigments are incorporated, exhibit color changes which cannot be tolerated in a large number of applications. A solution to this problem, or at least a reduction in its magnitude, can likewise be achieved by increasing the network density of the aligned and crosslinked liquid-crystalline structure.
Various methods are known for the preparation of organosiloxanes and silanes containing methacryloyl groups. A process which is frequently used on an industrial scale comprises the hydrosilylation of di-unsaturated compounds containing double or triple bonds of different reactivity. The aim in this process is for an &ohgr;-olefinically unsaturated group to be the target of Si—H attack, while the second unsaturated group is not hydrosilylated. To this end, the reactivity of the group which is not to be hydrosilylated must be lower than the reactivity of the other unsaturated groups. The unsaturated group of lower reactivity is preferably the methacryloyl double bond, but, in principle, the methacryloyl double bond can also be hydrosilylated. In general, more than 10% of side-reactions of methacryloyl groups with Si—H groups take place, the proportion of these side-reactions corresponding to the concentration of the methacryloyl double bonds. In general, the competing hydrosilylation of the two different unsaturated systems thus necessitates that undesired byproducts, for example, dimers, are always produced in such processes, in a proportion which generally depends on the nature of the unsaturated groups and on the manner in which the reaction is carried out.
If the polymerizable groups to be used are &agr;,&bgr;-unsaturated carboxylic acid radicals of relatively high reactivity, such as, for example, the acryloyl double bond, the competition with &ohgr;-olefinically unsaturated groups is significantly higher than in the case of methacryloyl double bonds under the conditions of the hydrosilylation reaction. Organosiloxanes or silanes containing acryloyl groups are therefore not readily accessible in the manner described above, since the high proportion of side-reactions results in partial crosslinking even during the hydrosilylation reaction, or in the case of siloxanes or silanes containing only one hydrogen atom bonded directly to silicon, in double addition of the siloxane or silane moiety to the di-unsaturated compound. If the organosiloxanes contain mesogenic side groups, the consequent increase in the viscosity usually reduces the mobility of the mesogens so much that a uniformly aligned liquid-crystalline phase can form only with difficulty, if at all.
U.S. Pat. No. 5,211,877 therefore describes, as an alternative method for the preparation of liquid-crystalline organosiloxanes or silanes containing methacryloyl or acryloyl groups, a multistep synthesis in which the methacryloyl or acryloyl group is introduced subsequently, by esterification using a reactive methacryloyl or acryloyl compound after hydrosilylation of a precursor containing a hydroxyl group protected by a protecting group, and subsequent removal of the protecting group. Owing to the large number of reaction steps necessary, however, this method tends to be more practicable for small laboratory syntheses. It is unsuitable for the production of highly crosslinkable organosiloxanes and organosilanes on an industrial scale.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a process which can be implemented on an industrial scale for the preparation of crosslinkable organosilicon compounds containing &agr;,&bgr;-unsaturated carboxylic acid radicals in high selectivity.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention relates to a process for the preparation of organosilicon compounds (P) containing &agr;,&bgr;-unsaturated carboxylic acid radicals, of the general formula (1)
—A—O—C(O)—CR═CH
2
(1),
in which, in a first step,
organosilicon compounds (H) containing hydrogen atoms bonded directly to silicon are reacted with olefinically unsaturated compounds (U) containing a terminal double or triple bond, of the general formula (2)
&OHgr;-O—C(O)—CRH—CH
2
—Z (2),
in the presence of metals or compounds from the platinum group as catalyst, to give organosilicon compounds (E) containing radicals of the general formula (3)
—A—O—C(O)—CRH—CH
2
—Z (3),
and, in a second step, H—Z compounds are eliminated from organosilicon compounds (E), where
A is a divalent organic radical,
&OHgr; is a monovalent organic radical containing a terminal double or triple bond,
R is an H atom or a methyl radical, and
Z is Cl, I, Br or 4-methyltoluenesulfonyl.
The process proceeds in high selectivity in both steps and therefore gives very pure organosilicon compounds (P) since the undesired hydrosilylation of the &agr;,&bgr;-unsaturated radical —CR═CH
2
in the general formula (1), and premature polymerizations caused thereby, are avoided.
The elimination of the H—Z compounds is preferably carried out by means of a base, such as a tertiary amine, for example triethylamine or tributylamine, or a basic metal salt of an acid, such as, for example, K
2
CO
3
, Na
2
CO
3
, KHCO
3
, NaHCO
3
, Na acetate and KOC(O)C(CH
3
)═CH
2
. The H—Z compound is then chemically bound to the base as a salt.
The organosilicon compounds (H) employed are, in particular, organosiloxanes, which may be linear, branched, or crosslinked organosiloxanes, or which may be in the form of organosilsesquioxanes, or organosilanes.
T
Häberle Norman
Hanelt Eckhard
Sandmeyer Frank
Schindler Wolfram
Brooks & Kushman P.C.
Consortium fur Elektrochemische Industrie GmbH
Shaver Paul F.
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