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
1999-07-12
2001-05-22
Moore, Margaret G. (Department: 1712)
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
active
06235834
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
FIELD OF THE INVENTION
This invention is directed to emulsions containing silicone particles of large size in which the emulsion is prepared by first emulsifying a silanol endblocked siloxane oligomer to large particles using a dialkyl sulfonic acid as the anionic surfactant, and then polymerizing the emulsified larger particles of silanol endblocked siloxane oligomer to a siloxane polymer of higher viscosity and/or higher molecular weight using a condensation specific acid catalyst.
Dialkyl sulfonic acids are most preferred as the surfactant, as these compounds possess the capability of functioning as the anionic surfactant for purposes of the emulsification, as well as functioning as the condensation specific acid catalyst for purposes of the polymerization.
In another embodiment, a different type of anionic surfactant or a nonionic surfactant could be used in the emulsification step, and the dialkyl sulfonic acid could be used as the condensation specific acid catalyst in the subsequent polymerization step.
BACKGROUND OF THE INVENTION
The advantages of emulsions containing silicones having a large particle size, i.e., 1-100 micron (micrometer/&mgr;m), is well documented in the patent literature, as for example in U.S. Pat. No. 5,302,658 (Apr. 12, 1994). While U.S. Pat. No. 5,302,658 provides for the production of emulsions containing large particle size silicone polymers, it does so by using surfactants to emulsify high viscosity silicone polymers which are difficult to handle and typically in short supply on a commercial scale. By way of contrast, the present invention in the most preferred embodiment, uses an anionic surfactant capable of functioning as an emulsifier to emulsify a silicone oligomer to a large particle size, and capable of functioning as an acid catalyst to polymerize the silicone oligomer, emulsified in the large size particles, to a high viscosity polymer.
These types of disadvantages are also present in U.S. Pat. No. 5,504,150 (Apr. 2, 1996), which while suggesting that a sulfonic acid catalyst can be employed, does not suggest the use of a dialkyl sulfonic acid as the catalyst. U.S. Pat. No. 5,504,150 also requires the use of expensive and complicated equipment including a reaction chamber, shearing and inversion devices, and collection vessels, to convert high molecular weight polymers to emulsions, in comparison to the present invention in which oligomers are first emulsified and then polymerized to higher molecular weight species using simple mechanical agitation.
While U.S. Pat. No. 3,294,725 (Dec. 27, 1966) prepares emulsions containing silicone particles by emulsifying siloxane oligomers using an anionic or a nonionic surfactant, and then polymerizing the emulsified oligomer particles to siloxane polymers of higher viscosity using condensation specific acid catalysts, the catalysts are not dialkyl sulfonic acids. In addition, U.S. Pat. No. 3,294,725 is silent with regard to the particular size of the particles, and where reference is made to the particles, they are merely described as being of “extremely fine particle size” or “so small that they cannot be resolved under an optical microscope”.
Thus, U.S. Pat. No. 3,294,725 teaches against preparing an emulsion as contemplated herein, wherein the particle size is at least one micron (&mgr;n) in diameter, preferably greater than 10 micron (&mgr;m) in diameter. In fact, U.S. Pat. No. 3,294,725 teaches that a small particle size of siloxane reactant, i.e., high surface area, is desirable to get reasonable reaction rates.
Furthermore, it is known that the condensation polymerization rate of an emulsified siloxane oligomer is proportional to the total surface area of the siloxane oligomer particles in water, and therefore inversely related to the particle size. For example, reference may be had to the
Journal of Polymer Science
, Volume 20, Pages 3351-3368, (1982). Because of this, condensation polymerization rates are too slow to be practical in emulsions of siloxane oligomers having a particle size greater than about one micron (&mgr;).
By way of contrast, the present invention is not limited according to such conventional wisdom, as it is believed that the condensation polymerization reaction of the siloxane oligomer occurs inside the particle rather than at the surface. Therefore, fast condensation polymerization rates have been observed according to this invention, and the rate does not decrease with increasing size of the particles.
Similarly, U.S. Pat. No. 4,990,555 (Feb. 5, 1991) fails to teach the use of siloxane oligomers of large particle size, and is further limited to the extent that the amount of water allowed in the process is taught to be less than one percent by weight. The process of the present invention by way of comparison is enabled to use 10-90 times as much water, without suffering any of the disadvantages noted in U.S. Pat. No. 4,990,555.
Thus, U.S. Pat. No. 4,990,555 teaches that the water concentration must be less than one percent by weight in order to obtain fast polymerization rates. In contrast, the polymerization rate in the process according to the present invention does not depend heavily on the water concentration over a very broad range, i.e., 10-90 percent by weight. The reason is that in the present process, an oil-in-water emulsion is formed in which polymerization occurs within and at the surface of the emulsion particles.
Furthermore, the process taught in U.S. Pat. No. 4,990,555 is directed to the bulk polymerization of siloxanes, and is not adapted to function for preparing an emulsion. This is because it is nearly impossible, as a practical matter, to prepare an emulsion in which an oil phase is emulsified in less than one percent by weight of water. The advantage of the present invention, therefore, resides in the ability to carry out the polymerization in water, and this eliminates the common handling problems frequently associated with polymers of high viscosity, i.e., molecular weight. For example, in an emulsion, the viscosity of the polymer forming the dispersed particles has a negligible effect on the viscosity of the emulsion itself. Thus, it is possible to prepare an emulsion containing for example, 50 percent by weight of a one million centipoise (mPa·s) polymer, that has a viscosity of only about 10-100 centipoise (mPa·s). By this means, handling and pumping of high viscosity polymers can be readily facilitated.
BRIEF SUMMARY OF THE INVENTION
This invention relates to a method of preparing an emulsion containing particles of an organopolysiloxane with an average particle diameter of at least one micron (&mgr;). The emulsion is prepared by (i) combining a silanol endblocked siloxane oligomer, water, and a nonionic surfactant or an anionic surfactant; (ii) emulsifying the silanol endblocked siloxane oligomer to form particles in the emulsion with an average particle diameter of at least one micron (&mgr;), by agitating the ingredients or by using a high shear device; (iii) adding a condensation specific acid catalyst to the emulsion of silanol endblocked siloxane oligomer; (iv) polymerizing the silanol endblocked siloxane oligomer to form an organopolysiloxane polymer; and (v) continuing polymerizing step (iv) until the resulting organosiloxane polymer has the desired increase in viscosity, which is preferably a viscosity in the range of about 20,000 to about ten million centipoise (mPa·s).
The condensation specific acid catalyst most preferred is a dialkyl sulfonic acid catalyst such as a dialkyl benzene sulfonic acid, or a dialkyl naphthalene sulfonic acid.
Emulsions prepared according to this invention are capable of functioning as a means of delivering polymers of high molecular weight and tailored rheological properties to the human body, i.e., as in a shampoo base to provide styling and conditioning benefits to human hair, or as a delivery mechanism for use
Gee Ronald Paul
Wrolson Burt Michael
Cesare James L. De
Dow Corning Corporation
Moore Margaret G.
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