Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-03-07
2002-06-18
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S555000, C524S916000, C523S105000, C523S223000, C523S342000
Reexamination Certificate
active
06407161
ABSTRACT:
This invention relates to polymers made from water soluble ethylenically unsaturated monomer or monomer blend, and in particular to dry granular polymers and their uses.
There are various ways of making such polymers including, for instance, precipitation polymerisation, bulk gel polymerisation and reverse phase polymerisation. Precipitation polymerisation has the disadvantage that the molecular weight of the polymers (if made in the absence of cross linker) tends to be rather low (for instance not more than intrinsic viscosity 1 dl/g) with the result that cross linked polymers made by this technique have an undesirably short chain length between adjacent cross links.
Bulk gel polymerisation is a convenient technique but it involves comminution and gives a wide spread of particle sizes.
Reverse phase polymerisation has the advantage that it can give a more uniform particle size. Unfortunately the products are always contaminated with hydrophobic materials.
Reverse phase polymerisation processes comprise providing a dispersion of droplets of an aqueous monomer phase dispersed in a continuous phase in which is dissolved a polymeric stabiliser for the droplets, and polymerising the monomer in the droplets to produce a dispersion of aqueous polymer droplets in the continuous phase.
When the droplets are large (typically above 100 &mgr;m) this is a bead polymerisation process and the aqueous polymer droplets are dried and separated from the dispersion as substantially individual dry beads.
When the aqueous monomer phase droplets are emulsified into the continuous phase the product is a substantially stable emulsion of the aqueous polymer droplets (having a size substantially all below 10 &mgr;m and often below 3 &mgr;m) in the continuous phase. The emulsion can be subjected to dehydration so that the droplets which are dispersed in the continuous phase are substantially dry.
If the emulsion (with or without dehydration) is used as such, its use necessarily carries the continuous phase with the polymer into the environment where the polymer is being used.
It is known to recover dry polymer droplets as a powder from the continuous phase of the emulsion. For instance spray drying is mentioned in GB-A-905,779 and U.S. Pat. No. 4,035,317 and will lead to granular aggregates above 10 &mgr;m in size formed of the primary polymer particles which are below 10 &mgr;m in size.
Irrespective of whether the dry polymer is recovered as large beads or as granular aggregates, the polymer is always contaminated by contaminants from the production process. In practice, the polymeric stabiliser is always insoluble in water, irrespective of the pH of the water, and is typically a copolymer of, for instance, a relatively large amount of stearyl methacrylate together with some methacrylic acid. This stabiliser will have concentrated at the interface of the aqueous monomer droplets and the continuous phase, and thus the polymer beads or granules are always contaminated by significant amounts of it. Also the continuous phase is usually a hydrophobic liquid such as a hydrocarbon and residues of this are normally trapped in or on the granules or beads, and so cause further hydrophobic contamination. The granules made from the emulsions are usually further contaminated by water-in-oil, non-polymeric surfactant, such as sorbitan oleate, which is used to promote the emulsification of the aqueous monomer phase into the continuous oil phase.
These various hydrophobic and relatively water insoluble contaminants therefore tend to interfere with the performance of the granules or beads when they are mixed into water. For instance they tend to reduce the wettability of the granules or beads with water, which can be undesirable, and they tend to carry into the resultant aqueous composition contaminants which are unwanted and in some instances undesirable. For instance it can be undesirable deliberately to introduce surfactant into the aqueous composition, for instance when the polymer is to be used as a flocculant. It can be undesirable to include water immiscible components into the aqueous composition when the visual appearance of the resultant aqueous composition is important. For instance, in unpublished research we have established that aqueous gels made from such granules tend to be opaque because of the residual stabiliser and continuous phase and surfactant.
A known polymeric thickener for making clear aqueous gels for cosmetics and other purposes is a cross linked anionic polymer powder having a very small particle size made by precipitation polymerisation. Although a reasonably clear gel is obtained under pH conditions where the polymer is ionised, the polymer gives an inferior gel and inadequate performance at lower pH values, since the polymer is not then fully ionised. Since the pH of the human skin is around 5.5, it follows that these precipitated anionic polymers do not provide optimum clarity and performance in compositions which are convenient and suitable for application to the skin. Also the low molecular weight obtainable by precipitation polymerisation tends to detract from their performance.
In the invention, we now provide a novel reverse phase polymerisation process which can be conducted as a bead polymerisation process but is preferably conducted as an emulsion polymerisation process and we provide dry polymeric products obtainable from this process and which avoid the contamination which is conventionally associated with products made by reverse phase polymerisation.
According to the invention we provide a product comprising dry polymer particles which are substantially spherical and are formed of a polymer of water soluble ethylenically unsaturated monomer or monomer blend and which carry contamination by 2 to 30%, based on the dry weight of the polymer, of contaminants, wherein the contaminants are water miscible and include at least 2% (based on the dry weight of polymer) by weight of a stabiliser polymer containing ionisable groups whereby the stabiliser is soluble in water when substantially ionised but substantially insoluble in water when the ionisable groups are substantially non-ionised, and the contaminants are substantially free of materials which are not soluble in water at the pH at which the ionisable groups are substantially ionised.
The dry polymer particles can be polymer beads made by reverse phase bead polymerisation, in which event they normally have a size at least 90% above 50 &mgr;m, and generally below 1000 &mgr;m.
Preferably, however, the dry polymer particles are particles which have a size at least 90% by weight below 10 &mgr;m which are primary particles in dried granules which have a size at least 90% by weight above 10 &mgr;m and which are formed of the primary polymer particles and the contaminants. These dried granules are preferably made by spray drying the reverse phase emulsion but can be made by other techniques for recovering dry particles from such an emulsion, for instance precipitation and/or, preferably, film drying.
When the granules are to be used as viscosifiers, especially for cosmetics, the granules including the contaminants preferably provide a gel having a clarity of less than 25 NTU when mixed with deionised water to provide a composition containing 1% by weight of the granules and having a pH at which the ionisable groups are sufficiently ionised for the stabiliser to be soluble in that gel.
The invention also includes the clear gel made by mixing the granules with water and compositions (such as household and cosmetic, pharmaceutical or other personal care compositions) incorporating such a gel.
When the granules are to be used for other purposes, such as flocculants or other uses where they are to be dissolved into a large amount of water, the contaminants are preferably such that they do not deleteriously interfere with the dissolution of the granules into water to form the aqueous solution of flocculant, viscosifier, or other functional polymer.
Except where stated otherwise in this patent specification, solubility is judged in the cont
Ciba Specialty Chemicals Corporation
Mansfield Kevin T.
Yoon Tae H.
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