Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
1999-12-10
2001-07-10
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06258968
ABSTRACT:
The present invention relates to a process for the production of Si—O—C-linked organofunctional siloxanes and to the use thereof.
Organofunctionally modified siloxanes are widely used for modifying organic polymers. Siloxanes have hitherto been produced by means of two-stage production processes, in which the siloxane skeleton is initially synthesised and the desired organofunctional group is then introduced in a second step.
DE-A 3 334 782 discloses the reaction of an acetoxy end-stopped polysiloxane with dihydroxy compounds with elimination of acetic acid, while U.S. Pat. No. 578 562 describes the reaction of an SiOH end-stopped polysiloxane with diols with elimination of water. U.S. Pat. No. 3,419,634, U.S. Pat. No. 3,821,325 and U.S. Pat. No. 3,832,419 describe processes for reacting Si—Cl end-stopped siloxanes with dihydroxyaryl groups and the use thereof as intermediates for the production of organopolysiloxane/polycarbonate block polymers. This two-stage process is, however, highly complex.
The object of the present invention was to provide a simplified process for the production of organofunctional siloxanes.
It has now been found that organofunctional polysiloxanes may very straightforwardly be produced by reacting cyclic dialkylsiloxanes with at least one compound of the type HO—R′—X, where X═—OH, —COOH, —NH
2
—, —CH═CH
2
and R′ is alkylene or arylene, in the presence of an equilibration catalyst, optionally in a hydrophobic solvent.
The present invention accordingly provides a process for the production of organofunctional polydiorganosiloxanes of the formula (I)
[R
2
(XR′O)SiO
½
]
a
[R
2
SiO
{fraction (2/2)}
]
b
[R
3
SiO
½
]
2-a
where
0<a≦2, preferably 2,
b=0-500, preferably 20-100, and with the proviso that where b=0, a is 2 in the total,
X═—OH, —COOH, —NR″
2
, —CR″═CR″
2
,
R═C
1
-C
18
alkyl, C
6
-C
14
aryl, preferably phenyl, tolyl, C
2
and/or C
3
alkyl, and R′═C
2
-C
18
alkylene, oxyalkylene, such as for example 2,2-bis-hydroxymethyl-l-butenol dialkyl ether, C
6
-C
14
arylene and R″═H and/or C
1
-C
18
alkyl, wherein the [R
2
SiO
{fraction (2/2)}
] units are optionally attached together via O—R′—O linkages,
characterised in that at least one cyclic dialkylsiloxane is reacted with at least one compound of the type HO—R′—X in the presence of at least one equilibration catalyst, optionally in the presence of linear trialkylsiloxy-terminated siloxanes, preferably hexamethyldisiloxane, and optionally in a hydrophobic solvent
at temperatures of between 80 and 220° C., preferably of 130-170° C.
In another preferred embodiment of the process according to the invention, 0.5≦a≦1.5 applies in the organofunctional polysiloxane of the formula (I), i.e. they contain trimethylsiloxy groups. In the case of acid catalysis, the trimethylsiloxy groups are preferably added as hexamethyldisiloxane. In the case of alkaline catalysis, it is preferred to add short-chain trialkylsiloxy end-stopped siloxanes having C
1
-C
18
alkyl, preferably methyl.
Cyclic dialkylsiloxanes having 4, 5 or 6 silicon atoms, preferably 4 or 5 silicon atoms, and bearing methyl residues as the alkyl residues are preferably used in the process according to the invention.
In a preferred embodiment of the process according to the invention, the cyclic dialkylsiloxane used comprises a mixture of cyclic dialkylsiloxane with up to 50 wt. % of short-chain hydroxy-terminated dialkylpolysiloxanes of the formula [HO
½
]
2
[R
2
SiO
{fraction (2/2)}
]
n
where n=2-50. This mixture preferably comprises such a mixture as is obtained from the hydrolysis of chlorosilanes. In this case, water is formed by condensation of the SiOH group as well as the water from the reaction of the compound of the type HO—R′—X with the mixture.
A hydrophobic solvent is preferably additionally used to facilitate removal of the water of reaction.
An equilibration catalyst is taken to be a catalyst which is responsible for both chain synthesis and chain degradation in the reaction.
Equilibration catalysts preferably used in the process according to the invention comprise perfluoroalkylsulfonic acids, preferably C
1
-C
6
perfluoroalkylsulfonic acids, individually or mixed with sulfuric acid, or alkali metal hydroxides, preferably potassium and caesium hydroxide. The equilibration catalyst is here preferably used in quantities of 500-5000 ppm, relative to the quantities of cyclic dialkylsiloxane and the compound HO—R′—X.
Selection of the catalyst is here determined by the functional alcohol used. In the case of aminoalcohols, basic catalysis is accordingly preferred, while in the case of phenolic alcohols or hydroxycarboxylic acids, acidic catalysis is preferred.
In the case of certain compounds of the type HOR′X, acid catalysis brings about not only the desired reaction, but also secondary reactions involving ether and ester formation or cleavage of the compound HOR′X. Ether formation is a particular problem with diols, which may form 5- or 6-membered cyclic ethers, such as for example the formation of dimethyltetrahydrofuran from 2,5-hexanediol. Diol cleavage is in particular observed in bishydroxyphenylalkanes, such as for example in the reaction of 2,2-bis-(4-hydroxyphenyl)propane to yield phenol and isopropenylphenol. These reactions may be partially avoided by suitable catalyst selection. Basic catalysts, such as for example caesium hydroxide, are preferred in this case. The cyclic dialkylsiloxane is preferably used in a ratio of 1 to 500 mol of dialkylsiloxy groups to 2 mol of the compound of the type HO—R′—X.
The hydrophobic solvent used in the process according to the invention preferably has a boiling point of ≧100° C. at atmospheric pressure and/or forms an azeotropic mixture with water. A certain degree of solubility of the compound of the type HOR′X used in the solvent used and/or in the siloxane, is favourable for the performance of the process according to the invention. Xylene, toluene or chlorobenzene are preferably used.
By using a hydrophobic solvent which has a boiling point of above 100° C. and/or a solvent which forms a minimum azeotropic mixture with water, it is possible to remove the water by refluxing in conventional water separators, while simultaneously controlling the rate of reaction. It has proved advantageous if the compound of the type HOR′X used has a boiling point above the solvent used and does not form an azeotropic mixture with water. Preferred combinations in this case are: toluene/hydroquinone, xylene/hydroquinone, xylene/2,2-bis(hydroxymethyl-1-butenol) diallyl ether as well as xylene/2,2-bis-(4-hydroxycyclohexyl)propane.
If compounds of the type HO—R′—X in which X═OH, i.e. dihydroxy compounds, are used in the process according to the invention, O—Si(R
2
)—O—R′—O—Si(R
2
)—O— linkages are also formed. The minimum ratio of Si(R
2
)—OR′—OSiR
2
groups to the desired Si(R
2
)—OR′OH end groups is primarily determined by the alcohol used and the ratio of alcohol to the separated quantity of water. Alcohols in which the OH groups interact by means of conjugated &pgr; electron systems, such as for example hydroquinone, have a stronger tendency to form Si(R
2
)—OR′—OSiR
2
groups in the siloxane chain, than alcohols, such as for example 2,2-bis(4-hydroxycyclohexyl)propane, in which there is no interaction between the OH groups.
In those compounds having a primary and a secondary OH group, the more reactive primary OH group reacts preferentially with the siloxane.
The process according to the invention may be terminated by neutralising the catalyst. Preferred neutralising agents for the neutralisation are those which may be completely removed from the product once the reaction mixture has been worked up. NaHCO
3
, soda and (NH
4
)
2
CO
3
are preferred in the case of acidic catalysis, while (CH
3
)
3
SiCl is preferred in th
Eversheim Hubertus
Schlak Ottfried
GE Bayer Silicones GmbH & Co. KG
Norris & McLaughlin & Marcus
Shaver Paul F.
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