Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1998-12-23
2001-03-06
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C524S837000, C524S858000, C525S474000, C525S477000, C528S012000, C528S031000, C528S033000, C528S034000, C528S039000
Reexamination Certificate
active
06197914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
This invention relates to a method for preparing a polyorganosiloxane that contains mono- and tetrafunctional units, by hydrolysis and condensation of a mixture of alkyl silicates and alkylsilanes and/or their hydrolyzates and compounds containing SiCl groups.
2. Discussion of the Related Art
Methods for preparing polyorganosiloxanes that consist of monofunctional M-units (R
3
SiO
½
) and tetrafunctional Q-units (SiO
{fraction (4/2)}
) are known. Most of the methods use tetraalkyl silicates as the source of Q-units. The M-units are usually introduced in the form of hydrolyzable trialkylsilanes. The hydrolysis/condensation reaction taking place must be catalyzed in order to obtain the desired products. Acidic compounds have proved to be especially suitable for that purpose. The reaction is usually carried out in an organic solvent. A method described in U.S. Pat. No. 2,857,356 starts with a mixture of tetraalkyl silicate and a trialkylchlorosilane in a solvent immiscible with water, and the mixture is reacted with water, with the resin solution being separated from the alcoholic hydrochloric acid by phase separation. The reaction is difficult to control because of the two-phase system. Additional drawbacks include the production of large amounts of concentrated alcoholic hydrochloric acid and the shift of the stoichiometric balance by the formation of volatile byproducts, and the siloxanes containing Q-units dissolved in the aqueous hydrochloric acid. The resins contain a large fraction of OH groups bonded to silicon.
To minimize the production of alcoholic hydrochloric acid, the use of a trialkylalkoxysilane and/or of its disiloxane and aqueous hydrochloric acid instead of trialkylchlorosilanes is proposed in EP 195 936. In this case, the alkyl silicate is added to the heterogeneous mixture of silanes and hydrochloric acid. Usable products are obtained by this method when the mixture contains at least 5 wt. % HCl. For this reason, hydrochloric acid with at least 10 wt. % hydrogen chloride has to be used. Volatile oligomers are also formed, which adversely affect the stoichiometric balance. Since the system is heterogeneous throughout the entire time of reaction, the reaction is difficult to control.
For this reason, it has been suggested to react triorganoalkoxysilanes and/or their hydrolyzates with tetraalkyl silicates in the presence of strongly active catalytic compounds, which can then be used in smaller amounts. Thus, EP 529 547 describes the use of alkyl silicate and disiloxane in combination with a strong proton acid, such as a sulfuric or phosphoric acid, with concentrated hydrochloric acid as catalyst. EP 294 277 uses a sulfonic acid and phosphonitrile chloride for the reaction of alkyl silicates with oligomeric siloxanes. In EP 604 847, a multi-proton acid, preferably sulfuric or phosphoric acid, is used, which is neutralized in several stages. Again, EP 640 109 describes the use, in particular, of hydrochloric acid, but only in catalytic amounts (preferably 0.2 to 50 mmoles based on 1000 g of reaction mixture), which usually makes it possible to carry out the procedure in a homogeneous phase. The infeed (addition) of small amounts of hydrochloric acid, and especially its homogeneous distribution in the reaction mixture, seems to be a problem (in Example 1, 1.9 g of 20% hydrochloric acid is used in relation to 1475 g of reaction mixture), since, according to EP 640 109, homogeneity is not achieved when the acid concentration is raised.
The critical drawback to such methods, in which the catalytically active compounds are fed into the silane and/or siloxane mixture, consists of the fact that partially high catalyst concentrations occur at the point of infeed, either because of the insolubility of water or aqueous acids in the siloxanes used, or because of the usual infeed, which leads to uncontrollable reactions taking place at this point. The catalyst can be distributed through the entire reaction mixture only after the formation of silanols with solubilizing action, and the catalyst is present in the specified (average) concentration only thereafter.
SUMMARY OF THE INVENTION
The purpose of this invention is to make available a method for preparing polyorganosiloxanes that contain mono- and tetrafunctional units that guarantees very good reproducibility, that starts with tetraalkyl silicate and alkylalkoxysilanes and/or their hydrolyzates, and that avoids locally high catalyst concentrations.
The object of the invention is a method for preparing polyorganosiloxanes that contain mono- and tetrafunctional units that is characterized by the fact that in step 1, a mixture of
(a) at least one silane with the formula:
Si(OR)
4
(I),
wherein R can be identical or different and represents a monovalent alkyl group with 1 to 4 carbon atoms, or its partial hydrolyzate,
(b) at least one silane with the formula:
R
1
3
SiOR (II),
and/or its hydrolyzate with the formula:
R
1
3
SiOSiR
1
3
(III),
wherein R has the meaning given above and R
1
can be identical or different, and represents for hydrogen, branched and/or unbranched, saturated and/or unsaturated, substituted and/or unsubstituted, linear, cyclic, aliphatic, and/or aromatic hydrocarbon groups with 1 to 18 carbon atoms; and
(c) at least one monomeric and/or oligomeric compound that has at least one SiCl group, is reacted with the equivalent amount of water based on the hydrolyzable groups and then in step 2, an aqueous alcohol phase is separated from the homogeneous reaction mixture obtained by adding water and/or a solvent immiscible with water.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The monomeric compound that has at least one SiCl group can conform to the formula:
R
1
y
SiCl
4-y
(IV),
wherein R
1
has the meaning given above and y is a number between 0 and 3, and wherein preferred R
1
groups are methyl, vinyl, or ethyl groups, for example with silicon tetrachloride, methylvinyldichlorosilane, and/or trimethylchlorosilane, or other trialkylchlorosilanes being used, whose alkyl groups can be long-chained and/or substituted.
The oligomeric compound that has at least one SiCl group can conform to the formula:
Cl
a
(R
1
)
3-a
Si(OSiR
1
2
)
m
OSi(R
2
)
3-b
Cl
b
(V),
wherein R
2
represents trimethylsiloxy or alkyldimethylsiloxy groups, wherein the alkyl group may contain OR
1
and/or R
1
substituents, “m” has a value between 0 and 1,000, and “a” and “b”, independently of one another, have values between 0 and 3, provided that (a+b) is at least 1. The R
1
in this case is an alkyl group such as methyl, vinyl, or ethyl group, with methyl group being particularly preferred. For example, bis(trimethylsiloxy)methylchlorosilane or tris(trimethylsiloxy)chlorosilane can be used, or also a tetramethyldichlorosilane or a linear siloxane with dimethylchlorosiloxy end groups.
The content of Cl groups bonded to silicon in the starting mixture is preferably from 0.1 to 5 wt. %.
No infeed of acidic catalyst is necessary in the method of the invention. The catalyst needed for the hydrolysis and/or condensation is formed in situ with the addition of water, by hydrolysis of the SiCl groups. Since the concentration of SiCl groups in the starting mixture is low compared to the amounts of silanes used, and they are accordingly distributed homogeneously, it is possible to make the reaction take place controllably by the rate of water addition, and thus to control it.
Tetraalkoxysilanes, for example, tetraethoxysilane, and/or its commercial partial hydrolyzates, for example, with an SiO
2
content of 40 wt. %, are preferably used as silane (a) with the formula (I) that forms Q-units.
Trialkylalkoxysilanes in which the trialkylsilyl group, for example, represents a trimethyl-, dimethylvinyl-, and/or dimethylhydrogensilyl group, or their hydrolyzates, and/or hexaalkyldisiloxanes or vinylalkyldisiloxanes are preferably used as silane (b) with the formulas (II) and (III) that form M-units.
The ratio of silane (a) to silane
Hoffmann Sabine
Kaeppler Klaus
Lehnert Robert
Schoeley Toni
Dawson Robert
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Robertson Jeffrey B.
Wacker - Chemie GmbH
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