Process for producing polysiloxanes and use of the same

Details Process for producing polysiloxanes and use of the same Process for producing polysiloxanes and use of the same

2002-12-02

2004-11-16

Peng, Kuo-Liang (Department: 1712)

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

Synthetic resins

From silicon reactant having at least one...

C528S020000, C528S032000, C528S041000, C528S042000

Reexamination Certificate

active

06818721

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to processes for the production of polysiloxanes, and in particular to processes which yield siloxanes through the condensation of a silanol (SiOH) with an alkoxy compound (SiOR).
BACKGROUND
Polysiloxanes (alternating Si—O backboned polymers) have found use in a variety of fields. However, their good light transmission properties, substrate adhesion and mechanical and chemical stability over an extended temperature range make them attractive targets for use in optical materials such as optical waveguides and devices. Of particular interest is the fact that the mechanical, optical and chemical properties of polysiloxanes can be controlled and modified by variation of the starting monomer compositions and by control of reaction conditions.
One method commonly employed for the preparation of siloxanes involves the hydrolysis of silicon alkoxides in organic solution with stoichiometric amounts of water in the presence of catalytic quantities of acid. Such reaction conditions often result in significant residual quantities of OH groups (either from water or Si—OH or both) in the reaction mixture which are often difficult to remove. This is especially problematical in the field of polymer optics, where a low OH content is highly desirable in any polymeric light transmissive material. OH groups have a high near-IR absorption (3500 cm
−1
) that impacts negatively upon optical transparency at 1550 nm. Uncondensed Si—OH groups can also continue a slow reaction over the service life of the polymeric material, which can lead to cracking and loss of adhesion.
One alternative route to polysiloxanes of controlled functionality is via the condensation of a silanol bearing molecule, SiOH, with an alkoxy silanol, SiOR. This route is an attractive one, compared to the condensation of two silanols, because it is an asymmetric condensation. Asymmetric condensations can often be advantageous—for example by the “head to tail” condensation of a single compound bearing both silanol and alkoxysilane groups, or the alternating condensation of diols and dialkoxy compounds. Both these approaches allow a degree of regularity to be imparted into a polysiloxane by the use of a simple choice of starting monomers. It also allows ready introduction of a variety of functionalities into condensates.
A further advantage of the condensation of silanols with alkoxy silanes is the preparation of branched or linear highly functionalised compounds. One system of particular interest is the preparation of polycondensates as disclosed in PCT Publication No. WO/0104186. In particular, these condensations are between an organically modified silane diol (the silanol) and an organically modified silane (the alkoxy silane) and which may be represented by the following scheme:
n
Ar
2
Si(OH)
2
+n
RSi(OR′)
3
→Polycondensate+2
n
R′OH
Theoretically, each silicon is capable of being either di-branched (from the silanol) or tri-branched (from the alkoxy silane), although in reality, steric influences mean that most silicon atoms are di-branched and so a number of Si—OR′ groups may be found in the polycondensate. This reaction is of particular interest because of the physical properties of the condensates generally and because it allows functionality to be introduced into the polycondensate by either substitution on the Ar group, or substitution on the R group. Functionality can include such things as cross-linkability etc, as disclosed in U.S. patent application Ser. Nos. 10/151,710 and 10/167,068, the disclosures of which are incorporated herein by reference.
However, one weakness of the approach has been the nature of the catalyst required to carry out the condensation and form the cross-linked polysiloxane backbone of the polycondensate. A variety of catalysts have been employed for condensation reactions including, for example, sulphuric acid, hydrochloric acid, Lewis acids, sodium or potassium hydroxide and tetramethylammonium hydroxide. These catalysts can be chemically severe and when involved in the condensation of silanols with alkoxy silanes have been found to cause bond scission and random rearrangement. This problem was addressed, for example, in GB 918,823 which provided condensation catalysts for the production of organosilicon compounds without siloxane bond scission and rearrangement.
The solution provided by GB 918,823 is, however, not entirely satisfactory from the point of view of polymer optical materials. GB 918,823 discloses the use of amine salts of phosphoric or carboxylic acids as condensation catalysts. While these may promote condensation without rearrangement, they are inherently unsuitable for use in the production of optical materials because they are usually liquids and/or are not readily removable from the product. The use of these compounds as catalysts for polymers in optical applications is also further hindered because they degrade at high temperatures, so any residual catalyst remaining within the polymer matrix would degrade during possible subsequent heat treatment.
The production of optical materials based on organosilicon compounds requires that the chemical structure of the components be well known and controlled. In order to achieve high optical performance, the structures need good reproducibility and predictability. Further, fine-tuning the physical properties by chemical modification requires very precise control of the chemical structure and also precise control over other components which may remain in the material as artefacts of production. From this point of view, not only must random rearrangements within the polymer be kept to a minimum, but also large residual amounts of catalyst or catalyst degradation product are clearly unacceptable.
U.S. Pat. No. 5,109,094 discloses the synthesis of siloxanes from the condensation of silanols (or via the self condensation of a disilanol) via the use of magnesium, calcium, strontium and barium hydroxides, however, as mentioned above, in the present circumstances the silanol-silanol condensation is not such an interesting reaction as the condensation of silanols with alkoxy silanes. U.S. Pat. No. 5,109,093 by the same inventors, discloses the synthesis of siloxanes from a condensation of silanol and alkoxysilane, but stipulates that the reaction proceeds only in the presence of a barium or strontium catalyst. This narrower range of catalysts suggests that the reaction of alkoxy silanes with silanediols is more catalyst sensitive than the reaction of two silanediols.
A specific drawback with the use of barium or strontium hydroxide catalysts is their relative toxicity. Barium hydroxide, for example, has an oral LD50 in rats of 308 mg/kg, whereas the LD50 for calcium hydroxide is 7300 mg/kg, ie barium hydroxide is around 20 times more toxic than the corresponding calcium salt. Even in circumstances where barium exposure to humans is not likely to be an actual problem, it could well be perceived by the market place as such. Further, close consideration also needs to be given to the disposal options for the strontium or barium compounds removed from the siloxane after preparation.
According to a first aspect, the invention provides a process for the preparation of an organosilicon condensate which comprises reacting together:
(A) at least one silicon containing compound having at least one silanol group; and
(B) at least one silicon containing compound having at least one —OR group wherein R represents an alkyl group having from 1 to 8 carbon atoms, or an alkoxyalkyl group having from 2 to 8 carbon atoms in the presence of
(C) a calcium or magnesium catalyst selected to allow the reaction to proceed and
(D) at least one solvent.
The organosilicon condensate is a siloxane, and most preferably a polysiloxane.
Compounds (A) and (B) may independently be monomeric, dimeric, oligomeric or polymeric compounds.
The at least one silicon containing compound (A) is advantageously a silanol having between one and three unsubstituted or substituted hydrocarbon groups hav

Affiliated with

Also associated with

Rating

Process for producing polysiloxanes and use of the same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for producing polysiloxanes and use of the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing polysiloxanes and use of the same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3328856