Process for preparing mixtures of linear organopolysiloxanes

Details Process for preparing mixtures of linear organopolysiloxanes Process for preparing mixtures of linear organopolysiloxanes

1999-10-06

2001-05-15

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...

C556S450000

Reexamination Certificate

active

06232423

ABSTRACT:

TECHNICAL FIELD
The invention relates to a process for preparing mixtures of linear organopolysiloxanes.
BACKGROUND ART
The preparation of organopolysiloxanes by hydrolysis and condensation of halosilanes is known. Organopolysiloxanes are also frequently prepared starting from mixtures of low-molecular-weight and high-molecular-weight organopolysiloxanes, which are equilibrated to give low-molecular-weight mixtures by adding a suitable catalyst. However, the latter method is not an adequate solution for preparing organopolysiloxanes with a very low degree of condensation. The known preparation processes are also particularly directed at forming cyclic organopolysiloxanes with a ring size of from 3 to 6 siloxane units.
No processes are known for directly preparing mixtures of linear low-molecular-weight siloxanes with a low proportion of hexamethyldisiloxane and of cyclic siloxanes, but the targeted products can be prepared by mixing the individual components in a very time-consuming and costly manner.
A continuous process for hydrolyzing organochlorosilanes is described in DE-C 954 198. This reaction is carried out in a loop reactor. The concentration of the discharged hydrochloric acid produced during the reaction is at least 25%. This high concentration leads to a crude hydrolysate with unhydrolyzed and undesirable Si—Cl units.
DISCLOSURE OF INVENTION
The object on which the invention is based is to provide a process which allows the cost-effective production of linear, low-molecular-weight organopolysiloxanes with a defined makeup and a reduced proportion of hexamethyldisiloxane, in which very little cyclic low-molecular-weight organopoly-siloxanes and organopolysiloxanes containing Si—Cl units are produced.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention provides a process for preparing mixtures of linear organopolysiloxanes of the general formula 1
R
3
SiO—(SiR
2
O)
n
—SiR
3
  (1)
in which organochlorosilanes of the general formula 2
R
4−y
SiCl
y
  (2)
where
R is identical or different and is a hydrogen atom or an unsubstituted or substituted hydrocarbon radical having from 1 to 18 carbon atoms,
y is 1 or 2, and
n is 0 or an integer from 1 to 50,
are reacted continuously in a closed circulation system with water which may, if desired, have been acidified with hydrochloric acid, where the HCl concentration in the hydrochloric acid discharged is less than 25% by weight.
Using the present process, the proportions of cyclic, low-molecular-weight organopolysiloxanes achieved in the product are not more than 1% by weight, in particular not more than 0.5% by weight.
The radical R is preferably a hydrocarbon radical having from 1 to 18 carbon atoms and unsubstituted or substituted with fluorine, chlorine or cyano radicals and preferably free from ethylenically or acetylenically unsaturated bonds.
Examples of hydrocarbon radicals R are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl and tert-pentyl radicals, hexyl radicals such as the n-hexyl radical; heptyl radicals such as the n-heptyl radical; octyl radical s such a s the n-octyl radical, and isooctyl radicals, such as the 2,2,4-trimethylpentyl radical; nonyl radicals such as the n-nonyl radical, decyl radicals such as the n-decyl radical; dodecyl radicals such as the n-dodecyl radical; octadecyl radicals such as the n-octadecyl radical; cycloalkyl radicals such as cyclopentyl, cyclohexyl and cycloheptyl radicals and methylcyclohexyl radicals; aryl radicals, such as the phenyl, naphthyl and anthryl and phenanthryl radicals; alkaryl radicals, such as o-, m- and p-tolyl radicals, xylyl radicals and ethylphenyl radicals; aralkyl radicals, such as the benzyl radical and the alpha- and the &bgr;-phenylethyl radicals.
Examples of substituted hydrocarbon radicals R are cyanoalkyl radicals, such as the &bgr;-cyanoethyl radical, and halogenated hydrocarbon radicals, for example haloalkyl radicals, such as the 3,3,3-trifluoro-n-propyl radical, the 2,2,2,2′,2′,2′-hexafluoroisopropyl radical and the heptafluoroisopropyl radical, and haloaryl radicals, such as the o-, m- and p-chlorophenyl radicals.
R is preferably a linear alkyl radical, in particular having from 1 to 10 carbon atoms, particularly from 1 to 6 carbon atoms. Particularly preferred radicals R are ethyl and, in particular, methyl radicals.
n is preferably not more than 20, in particular not more than 10.
The mixtures preferably have the following makeup:
n=0: the proportion is from 0 to 99 percent, preferably from 0 to 80 percent, and in particular from 0 to 60 percent.
n=1: the proportion is from 0 to 99 percent, preferably from 10 to 70 percent, and in particular from 20 to 65 percent.
n=2: the proportion is from 0 to 99 percent, preferably from 5 to 50 percent, and in particular from 10 to 35 percent.
n=3: the proportion is from 0 to 99 percent, preferably from 0 to 20 percent, and in particular from 2 to 15 percent.
n=4: the proportion is from 0 to 99 percent, preferably from 0 to 10 percent, and in particular from 0 to 5 percent.
n=5: the proportion is from 0 to 99 percent, preferably from 0 to 5 percent, and in particular from 0 to 3 percent.
n=6: the proportion is from 0 to 99 percent, preferably from 0 to 5 percent, and in particular from 0 to 2 percent.
n=7: the proportion is from 0 to 99 percent, preferably from 0 to 5 percent, and in particular from 0 to 1 percent.
n=8: the proportion is from 0 to 99 percent, preferably from 0 to 5 percent, and in particular from 0 to 1 percent.
n=9: the proportion is from 0 to 99 percent, preferably from 0 to 5 percent, and in particular from 0 to 0.5 percent.
n=10: the proportion is from 0 to 99 percent, preferably from 0 to 5 percent, and in particular from 0 to 0.5 percent.
Preferred organochlorosilanes of the general formula 2 are vinylmethyldichlorosilane, phenylmethyldichlorosilane, divinyldichlorosilane, diphenyldichlorosilane, methyldichlorosilane, vinyldimethylchlorosilane, dimethyldichlorosilane and trimethylchlorosilane. Particularly preferred organochlorosilanes of the general formula 2 are dimethyldichlorosilane and trimethylchlorosilane.
The organochlorosilanes of the general formula 2 are preferably used in stoichiometrically molar amounts in the process. Preference is given here to proportional amounts of R
3
SiX:R
2
SiX
2
of from 1:100 to 100:1, in particular from 1:20 to 1:1. It is, however, also possible to use amounts of organochlorosilanes which differ from this.
The process is preferably carried out at temperatures of from 20 to 150° C., in particular from 30 to 100° C. The pressure used is preferably that of the surrounding atmosphere, i.e. 1020 hPa (abs.) or about 1020 hPa (abs.). However, higher or lower pressures may also be used if desired, preferably from 100 to 10,000 hPa (abs.), in particular up to 6000 hPa (abs.).
In the reaction, hydrolysis with water and condensation of the organochlorosilanes of the general formula 2 take place simultaneously. In the closed circulation system the reaction mixture is preferably circulated by a pump. Fresh water and the organochlorosilanes are fed continuously. Likewise, an appropriate portion of the reaction mixture composed of organopolysiloxanes of the general formula 1 and acid-enriched water are continuously discharged from the process and separated.
The concentration of HCl in the hydrochloric acid discharged is preferably from 18 to 24% by weight, in particular from 20 to 23% by weight. The HCl formed during the hydrolysis of the organochlorosilanes is converted to an aqueous hydrochloric acid by metering in water, and the concentration of the hydrochloric acid in the reaction vessel is preferably thus held constant.
If desired, a portion of the low-molecular-weight, linear organopolysiloxanes, in particular those in which n=0, is separated off, by batchwise or continuous distillation, from the organopolysiloxanes of the general formula 1 discharged,

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