Organic compounds -- part of the class 532-570 series – Organic compounds
Reexamination Certificate
1998-02-20
2003-04-29
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
C532S001000, 53, 53
Reexamination Certificate
active
06555662
ABSTRACT:
This invention relates to a process for making siloxane compositions, more specifically compositions wherein high viscosity polysiloxanes are dispersed in volatile, cyclic polysiloxanes (also known as cyclosiloxanes).
Cyclosiloxanes are critical intermediates in the silicone industry, primarily as starting monomers for polymerisation. Several general routes are known for the preparation of cyclosiloxanes. Together with hydroxy-endblocked linear polydiorganosiloxanes, they are formed as a product of hydrolysis of the corresponding diorganodihalosilanes. Mixtures of cyclic and/or linear polydiorganosiloxanes can also be equilibrated or “cracked ” by reaction in the presence of a catalyst such as a base to form an equilibrium mixture of more desired cyclics and linears.
Various catalysts are known for the polymerisation of cyclosiloxanes. Examples are alkali metal hydroxides, alkali metal alkoxides or complexes of alkali metal hydroxides and an alcohol, alkali metal silanolates, and phosphonitrile halides (sometimes referred to as acidic phosphazenes). Such polymerisations can be carried out in bulk, in solvents (such as non-polar or polar organic solvents) or in emulsion. An endblocking agent may be used to regulate the molecular weight of the polymer and/or to add functionality. Polymerisation may be terminated by using a neutralizing agent which reacts with the catalyst to render it non-active. In most cases catalyst residues remain in the polymer product and are desirably removed, such as by filtration.
Dispersions of high viscosity polysiloxanes in cyclic polysiloxanes have been known for some time and have been commercially available. These dispersions have a variety of useful characteristics and are important ingredients in many cosmetic compositions. They are generally prepared by physically mixing high viscosity siloxanes into a medium of cyclic siloxanes which have a low viscosity. This method is tedious and requires a lot of energy to ensure a more or less homogeneous dispersion as the high viscosity materials may have a viscosity which amounts to several m
2
/s. It is possible to dissolve the high viscosity materials in a solvent prior to the dispersion in the cyclic siloxanes in order to reduce the handling viscosity and hence ease the dispersion. However, this leaves the manufacturer with the added disadvantage that a solvent is present and needs to be removed. This disadvantage is all the more serious since the cyclic siloxane materials are volatile to some extent and could be at least partially removed when the solvent is removed.
EP-A-0 503 825 discloses a method of making a dispersion of high viscosity siloxanes in volatile cyclosiloxanes by selectively condensing hydrolysable siloxanes in the presence of volatile cyclosiloxanes using catalysts which are phosphonitrile halides or selected metal compounds. This suffers from the disadvantage that there is a need to make a first dispersion of the hydrolysable siloxane in volatile cyclosiloxanes, and filtration of the eventual product is required to remove catalyst residues.
We have now found that a dispersion of high viscosity siloxanes in volatile cyclosiloxanes can be made in a single step by the ring-opening polymerisation of cyclosiloxanes catalysed by phosphazene bases.
Phosphazene bases are known to be extremely strong bases. Numerous phosphazene bases and routes for their synthesis have been described in the literature, for example in Schwesinger et al, Liebigs Ann. 1996, 1055-1081.
The use of a phosphazene base catalyst for the ring-opening polymerisation of a cyclosiloxane on a laboratory scale has been described in Molenberg and Möller, Macromol Rapid Commun. 16, 449-453 (1995). Octamethylcyclotetrasiloxane(D4, where D denotes an —Si(CH
3
)
2
O— unit) was polymerised in toluene solution in the presence of methanol and the phosphazene base I (FIG.
1
), used as a 1 molar solution in hexane. All the components were carefully dried before the reaction, which was carried out under an argon atmosphere containing less than 1 ppm O
2
and H
2
O. The methanol was deprotonated by the phosphazene base to form methoxide ions which initiate the reaction. A similar reaction system has been used by Van Dyke and Clarson in Poly Prep ACS Div Polym Chem 1996, 37, 668. In this case, tetraphenyltetramethylcyclotetrasiloxane, the phenylmethyl analog of D4, was polymerised. The catalyst system was the same as in Molenberg and Möller, and again all the reaction components were carefully dried beforehand. The phosphazene base catalysts were used in an amount of more than 800 ppm based on the weight of D4.
We have found that the phosphazene base-catalysed polymerisation can be adapted to produce a blend of a high viscosity polysiloxane dispersed in volatile cyclosiloxanes. We have also found that the hexane/methanol activated catalyst can give erratic polymerisation behaviour. We have therefore additionally sought a catalyst medium that gives reproducible polymerisation, preferably without the need for solvent. We have surprisingly found that it is also possible to carry out the ring-opening polymerisation of cyclosiloxanes with a phosphazene base catalyst in the presence of water. In the simplest case, sufficient water can be provided simply by taking no special steps to dry the cyclosiloxane starting material. To ensure the presence of water it is sufficient to avoid totally anhydrous conditions. Very small amounts of water, e.g. a few molecules, have been found to suffice to allow the polymerisation to take place. Furthermore, we have found that it is not essential to form a methoxide ion, e.g. by using methanol, in contrast to the prior art teaching.
The present invention thus provides a process for making a dispersion of a high viscosity siloxane in a volatile cyclosiloxane, which comprises effecting the ring-opening polymerisation of a volatile cyclosiloxane under catalysis by a phosphazene base, and stopping the polymerisation reaction before completion of the ring-opening polymerisation of the cyclosiloxane has occurred.
The high viscosity siloxane in the dispersion produced according to the invention may typically be a gum with a molecular weight of from 100,000 to 5,000,000 more preferably from 500,000 to 1,000,000. Where molecular weight is used in this specification, number average molecular weight is intended unless otherwise indicated. The percentage by weight of gum in the dispersion is preferably from 5% to 40%, more preferably from 15% to 35%. In the case of dispersions containing about 15% gum, the viscosity of the composition may be from 5,000 to 10,000 mm
2
/s at 25° C.
If the desired composition is to contain 15% gum, 85% of the cyclosiloxane starting material has to be unpolymerised. We have surprisingly found that it is possible to form a gum size polymer after only 15% conversion of cyclosiloxane has been polymerised. A molecular weight of greater than 350,000 is needed to reach a targeted viscosity higher than 5,000 mm
2
/s at 25° C. for a dispersion with only 15% of polymer in the blend.
High molecular weight polymers can be achieved only when the initial concentration of catalyst is low.
The phosphazene base reacts with trace quantities of water present to form highly active hydroxide ions which initiate the polymerisation. The phosphazene base will also react with certain other chemical groups which may be present, e.g. silanol or alcohol, to form similarly active polymerisation-initiating species. The phosphazene base may be in ionic form, with a strong anion such as fluoride or hydroxide, which is active in initiating polymerisation.
As the phosphazene base is a very powerful catalyst for the polymerisation, it can be present in a relatively low proportion, for example from 1-500 ppm by weight, based on the weight of cyclosiloxane. A preferred range is 2-200 ppm, more preferably 5-50 ppm. The proportion of catalyst actually used will be selected depending on the polymerisation product that is sought.
The proportion of water present in the reaction is generally at least 0.5 mol per mol of phosphazen
Bischoff Remy
Taylor Richard
Dow Corning Ltd.
Shaver Paul F.
Warren Jennifer S.
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