Catalyst for preparing organosiloxanes or polyorganosiloxanes

Details Catalyst for preparing organosiloxanes or polyorganosiloxanes Catalyst for preparing organosiloxanes or polyorganosiloxanes

1996-01-11

1998-06-30

Caldarola, Glenn

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

502150, 502158, 502159, 502162, 528 28, 528 23, C08G 7706

Patent

active

057735484

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to a catalyst for preparing organosiloxanes or polyorganosiloxanes which are obtained primarily by polycondensation processes. The catalyst of the invention is a reaction product of SiO(R.sub.2 SiO).sub.m !.sub.3 P.dbd.O (I), where R are, independently of one another, identical or different, unsaturated and/or saturated monovalent hydrocarbon radicals having from 1 to 6 carbon atoms or hydrogen, with the proviso that only one hydrogen atom is bound to each silicon atom and m has a value between 0 and 1000. Volatile chlorine-containing silicon compounds formed during the reaction can, if required, be completely or partially removed. Organosiloxanes and polyorganosiloxanes are important intermediates and final products of silicon chemistry.


PRIOR ART

For the preparation of organosiloxanes and polyorganosiloxanes, two different basic chemical processes are essentially known for industrial applications.
One process is the ring-opening polymerization of cyclic polysiloxanes, combined with the incorporation of mono-, di- and/or trifunctional silicon compounds, also known as equilibration. However, this reaction proceeds only to a chemical equilibrium at which about 87% by weight of linear polysiloxanes and about 13% by weight of cyclosiloxanes are present. These have to be separated in a subsequent process step.
In the second process, the starting materials are low-molecular-weight (oligomeric) siloxanes containing OH groups, and these are subjected to a polycondensation reaction. Here too, the incorporation of mono-, di- and/or trifunctional silicon compounds is possible. Attempts are made to counteract the formation of cyclic siloxanes by means of suitable catalysts, so as to avoid additional removal of the cyclic compounds.
For both process methods, use is customarily made of basic or acid catalysts. Known basic catalysts are, inter alia, potassium hydroxide, potassium siloxanolates or ammonium and phosphonium siloxanolates. The group of acid catalysts includes, for example, sulphuric acid, trifluoromethanesulphonic acid, acid ion exchange resins, acid-activated Fuller's earths and phosphonitrilic chlorides.
Most catalysts which are of importance for polycondensation reactions of silanols and siloxanols also cause a more or less rapid equilibration reaction, which results in the formation of cyclic siloxanes.
Owing to their high activity in addition to a good selectivity, almost no equilibration takes place, phosphonitrilic chlorides are very suitable as catalysts for polycondensation reactions of silanols and siloxanols.
Phosphonitrilic chlorides and compositions containing them are known (Nitzsche et al. DE-B 12 79 019, Nitzsche et al. U.S. Pat. No. 3,839,388). Solvents which are proposed are, for example, benzene, toluene, petroleum ether, halogenated hydrocarbons, ethers and ketones (Triem et al. U.S. Pat. No. 3,652,711).
However, phosphonitrilic chlorides are only very slightly soluble in non-polar solvents such as, for example, aliphatic and aromatic hydrocarbons. This has the disadvantage that the phosphonitrilic chlorides are, owing to their very low concentration in the solutions, particularly susceptible to impurities or to hydrolysis. For this reason, such solutions often have only a low storage stability, and the activity of the catalyst drops quickly.
Solvents such as ethers, ketones and esters are not completely inert to the phosphonitrilic chlorides, which likewise leads to deactivation of the catalyst with the entire solution becoming dark in colour.
A further variant for preparing phosphonitrilic chloride solutions is the addition of surfactants or crown ethers as solubilizers, for example ethyl acetate (Schuster, J. et al. EP 381 204). This makes the preparation of the catalyst solution a complicated, multistage process. In the subsequent preparation of the polyorganosiloxanes, the surfactants or crown ethers used remain in the product and can interfere in the further processing of the polymer. In addition, long storage of the catalyst solution resul

REFERENCES:
patent: 3652711 (1972-03-01), Triem et al.
patent: 3839388 (1974-10-01), Nitzche et al.
patent: 5099051 (1992-03-01), Beck et al.
patent: 5210131 (1993-05-01), Gilson et al.
patent: 5420221 (1995-05-01), Razzano et al.
patent: 5534608 (1996-07-01), Thomposon et al.

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