Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2000-05-18
2001-10-16
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S015000, C528S031000, C528S037000, C556S451000
Reexamination Certificate
active
06303729
ABSTRACT:
This invention relates to a process for preparing a partially added cyclic organohydrogensiloxane which is useful as a crosslinking agent in addition cure type silicone compositions.
BACKGROUND OF THE INVENTION
In the prior art, a partially added cyclic organo-hydrogensiloxane is prepared by partially adding a compound having an aliphatic unsaturated hydrocarbon group to a cyclic organohydrogensiloxane in the presence of a catalyst such as a platinum compound. In this process, the addition reaction product is isolated by distillation, often in low yields.
More particularly, a partially added cyclic organo-hydrogensiloxane is prepared by partially adding a compound having an aliphatic unsaturated hydrocarbon group of the general formula (4) to a cyclic organohydrogensiloxane of the general formula (3) in the presence of a platinum compound catalyst according to the following reaction scheme.
Herein, R is a monovalent hydrocarbon group, n is 3 to 5, and m is 1 to 2. This process, however, suffers from the phenomenon that when the reaction mixture is heated for isolating the reaction product by distillation, ring-opening reaction occurs on both the reactant and the product whereby the isolation yield of the end product becomes very low.
The ring-opening reaction upon heating takes place through the following mechanism. The platinum compound added as the addition reaction catalyst catalyzes ring-opening reaction with a minor amount of water in the system to form silanol compounds, which trigger ring opening of the cyclic organohydrogensiloxane (reactant) and the partial addition compound (reaction product).
To restrain the ring-opening reaction, JP-B 51-33540 proposes to control the catalytic activity of a platinum compound by adding a nitrogen, phosphorus or sulfur-containing compound which becomes a catalyst poison.
The inventor found that even after the catalytic activity is lost, some molecules can exceed the activation energy barrier during heating. As isolation by heat distillation is continued for a long time, ring-opening reaction slowly takes place. Because of this phenomenon, the method is unsatisfactory.
Therefore, for the preparation of a partially added cyclic organohydrogensiloxane, it has been desired to have a technique capable of improving the yield of distillative isolation.
SUMMARY OF THE INVENTION
An object of the invention is to provide a process for preparing a partially added cyclic organohydrogensiloxane so that the end product may be obtained in high yields after distillative isolation.
A partially added cyclic organohydrogensiloxane is prepared by mixing (A) a cyclic organohydrogensiloxane having at least two Si—H bonds in a molecule with (B) a cyclic or acyclic organic unsaturated compound having an aliphatic unsaturated double bond in a molecule such that the moles of Si—H bonds in component (A) may be excessive relative to the moles of aliphatic unsaturated double bonds in component (B), effecting addition reaction in the presence of a platinum catalyst, and isolating the reaction product by distillation. The inventor has found that if a silylating agent is added to the reaction system at the end of addition reactions, but prior to the distillative isolation, the silanol compounds, which are present in the reactions system at the end of addition reaction and can trigger ring-opening reaction undergo silylation reaction with the silylating agent whereby the silanol compounds are converted into siloxane compounds. This effectively prevents ring-opening reaction from taking place on the residual reactant and reaction product and thus significantly improves the yield during distillative isolation. Therefore, the end partially added cyclic organohydrogensiloxane is obtained in high yields.
Accordingly, the invention provides a process for preparing a partially added cyclic organohydrogensiloxane, comprising the steps of:
mixing (A) a cyclic organohydrogensiloxane having at least two Si—H bonds in a molecule with (B) a cyclic or acyclic organic unsaturated compound having an aliphatic unsaturated double bond in a molecule such that the moles of Si—H bonds in component (A) may be excessive relative to the moles of aliphatic unsaturated double bonds in component (B),
effecting addition reaction between components (A) and (B) in the presence of a platinum catalyst to form a partially added cyclic organohydrogensiloxane,
adding a silylating agent to the reaction mixture, and
isolating the partially added cyclic organohydrogen-siloxane from the reaction mixture by distillation.
REFERENCES:
patent: 3992427 (1976-11-01), Chandra et al.
patent: 4736049 (1988-04-01), Suzuki et al.
patent: 4892918 (1990-01-01), Ryang
patent: 5227448 (1993-07-01), Durfee
patent: 5409995 (1995-04-01), Iwahara et al.
patent: 6087523 (2000-07-01), Bank et al.
Dawson Robert
Millen White Zelano & Branigan PC
Shin-Etsu Chemical Co. , Ltd.
Zimmer Marc S.
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