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
2001-01-08
2002-11-12
Metzmaier, Daniel S. (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...
C524S266000, C524S588000, C516S055000
Reexamination Certificate
active
06479583
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 and latexes prepared by forming a microemulsion of water, a surfactant, a hydride functional organosilicon oligomer or a mixture of such oligomers, and an alkenyl functional organosilicon oligomer or a mixture of such oligomers, and polymerizing the oligomer containing microemulsion until an emulsion or latex is formed containing polymer particles.
BACKGROUND OF THE INVENTION
Silicone emulsion polymerization is a known technique for preparing silicone emulsions. The technique utilizes organosiloxane precursors, typically cyclosiloxanes or alkoxysilanes, which are substances capable of diffusion into or through water in their original form or when hydrolyzed. In silicone emulsion polymerization, siloxane polymers are formed from siloxane precursors and new emulsion particles are formed containing siloxane polymers formed during the polymerization process.
Confusion often is found in the literature as to what is meant by emulsion polymerization as it pertains to organosiloxane precursors. In this invention, emulsion polymerization means the process where new particles form that are characteristically smaller than the starting droplets of the organosiloxane precursor.
It should be noted that a key component enabling reactions to occur in silicone emulsion polymerization is a surface active catalyst, which has both the properties of a surfactant and a catalyst, described generally as a surfactant-catalyst. It is sometimes described as surfcat for the sake of brevity. Surfcats may be formed in situ in the emulsion polymerization process by ion exchange of a strong acid or base catalyst and an ionic surfactant that is the salt of a surface active strong acid or base, respectively. They can also be prepared beforehand by ion exchange of a strong acid or base catalyst and an ionic surfactant that is the salt of a surface active strong acid or base, respectively, in an aqueous solution.
The purpose of the surfcat is to catalyze the ionic polymerization of organosiloxane precursors to form particles containing siloxane polymers. Silicone emulsions that result from such a process, by design, contain ionic surfactants. The presence of ionic surfactants in silicone emulsions is unsatisfactory in applications where an electric charge on the particles is not desired. Therefore, a need exists for a silicone emulsion polymerization process that does not require a surfcat.
Hydrosilylation is a silicon-based reaction between silicon hydride and an unsaturated carbon bond that does not require an ionic catalyst.
While it's not new to form emulsions and latexes by polymerizing mixtures containing water, surfactants, catalysts, hydride functional organosilicon oligomers, and alkenyl functional organosilicon oligomers, i.e., U.S. Pat. No. 3,900,617 (Aug. 19, 1975) and U.S. Pat. No. 4,248,751 (Feb. 3, 1981), it is not known to polymerize microemulsions containing low molecular weight, low viscosity organosilicon oligomers by the hydrosilylation reaction.
In instances where low molecular weight, low viscosity organosilicon monomers have been used, i.e., U.S. Pat. No. 6,013,682 (Jan. 11, 2000), the monomers contained no more than two reactive sites, and therefore network polymers could not be obtained, nor films of elastomeric or resinous materials upon removal of water.
BRIEF SUMMARY OF THE INVENTION
The invention relates to a method for making emulsions or latexes that contain. polymer particles with a diameter greater than 0.02 micron (micrometer). The steps of the method generally involve the formation of a microemulsion that contains particles of one or more reactive siloxane oligomers having a diameter less than 0.02 micron (micrometer). The microemulsion is formed by combining water, at least one surfactant, a hydride functional organosilicon oligomer, and an alkenyl functional organosilicon oligomer. A catalyst is added to the microemulsion, and polymerization of the oligomers is initiated. Polymerization is allowed to continue until an emulsion or latex is formed containing polymer particles with a diameter greater than 0.02 micron (micrometer).
The oligomers each have a viscosity of 1-50 centistoke (mm
2
/s), and at least one oligomer contains more than two reactive sites.
While it is preferred to form the microemulsion in a single step by combining water, the surfactant, the hydride functional organosilicon oligomer, and the alkenyl functional organosilicon oligomer, and then adding the catalyst to the microemulsion; two separate microemulsions, each containing one of the oligomers, can be prepared and then combined, in which case the catalyst is included in the microemulsion containing the alkenyl functional organosilicon oligomer.
The emulsions and latexes resulting from these processes can be used in various applications such as hair fixative agents, release agents, and as thickening agents for low molecular weight silicone oils.
Cured films may be obtained by removing water from the resulting emulsion or latex. These films can be tailored to contain elastomeric or resinous polymers. Such films have utility as paper coatings, release coatings, and antifouling coatings, for example.
These and other features of the invention will become apparent from a consideration of the detailed description.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
Emulsions and latexes according to this invention are obtained from microemulsions of water, a surfactant, a hydride. functional organosilicon oligomer, and an alkenyl functional organosilicon oligomer, by polymerizing the microemulsion via hydrosilylation to form an emulsion or latex.
Hydrosilylation
Hydrosilylation, as noted above, is a reaction involving addition of a silicon hydride to an unsaturated hydrocarbon to form a silicon-carbon bond. It is used commercially to synthesize organofunctional silicon monomers, to crosslink silicone polymers, and to connect a silicone to an organic polymer block to form a copolymer.
One example is hydrosilylation of an alpha-olefin with a methylhydrogen siloxane according to the general reaction
≡SiH+CH
2
═CH—R→≡SiCH
2
CH
2
—R.
When used for crosslinking, such transition metal catalyzed hydrosilylation reactions typically involve reaction between a low molecular weight polysiloxane containing several Si-H groups and a high molecular weight polysiloxane containing at least two Si-vinyl groups, or vice versa.
Generally, equivalent molar amounts of the ≡SiH groups and the unsaturated groups are employed in the process. It may be necessary, however, to use an excess of the reactant containing unsaturation to totally consume ≡SiH in the siloxane product.
The maximum amount of transition metal catalyst employed is determined by economical considerations, and the minimum amount is determined by the type and purity of the reactants employed. Generally, very low concentrations of a platinum catalyst, such as 1×10
−10
moles catalyst per equivalent of the reactant containing unsaturation, are used when the reactants are extremely pure. However, it is possible to use about 1×10
−8
moles catalyst per equivalent weight of reactant containing unsaturation, and even 1×10
−7
to 1×10
−3
moles of catalyst per equivalent weight of reactant containing unsaturation.
Reaction temperature can vary, and optimum temperatures depend upon the concentration of catalyst and the nature of the reactants. The reaction can be initiated at a temperature below room temperature, i.e., 0° C., and is exothermic once it begins. For purposes of this invention, the temperature should be one at which both reactants are in a liquid state. The maximum temperature is determined by the range in which the microemulsion phase forms. It is preferred to operate th
Halloran Daniel Joseph
Hill Randal Myron
Wrolson Burt Michael
Zimmerman Brett Lee
De Cesare Jim L.
Dow Corning Corporation
Metzmaier Daniel S.
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