Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1997-09-26
2002-08-27
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
Reexamination Certificate
active
06441118
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polydiorganosiloxane oligourea segmented copolymers and a process for making same.
BACKGROUND OF THE INVENTION
Polydiorganosiloxane polymers have unique properties derived mainly from the physical and chemical characteristics of the siloxane bond. Typically, the outstanding properties of polydiorganosiloxane polymers include resistance to ultraviolet light, extremely low glass transition temperature, good thermal and oxidative stability, good permeability to many gases, very low surface energy, low index of refraction, good hydrophobicity, and good dielectric properties. They also have very good biocompatability and are of great interest as biomaterials that can be used in the body in the presence of blood. Polydiorganosiloxane elastomers have been widely used because of these many excellent properties. But, their limited tear resistance and poor resistance to low polarity solvents have made them unsuitable in many other applications.
Elastomers possess the ability to recover their initial shape from deformation produced by an imposed force. Traditional polydiorganosiloxanes show elastomeric behavior only when they are chemically or physically crosslinked. Even extremely high molecular weight polydiorganosiloxane gums (greater than 500,000 grams per mole) exhibit cold flow when uncrosslinked. However, chemical crosslinking results in polymers with poor mechanical properties relative to other organic materials. Thus, to be useful in most commercial applications, traditional polydiorganosiloxanes must be further filled with up to 50 weight percent fillers such as finely divided high surface area silica, fumed silica, titanium dioxide, alumina, zirconia, pigment-grade oxides, carbon blacks, graphite, metal powders, clays, calcium carbonates, silicates, aluminates, fibrous fillers, and hollow glass or plastic microspheres, depending on the desired properties, for example, to maintain their mechanical strength and reduce swelling in solvents. Since polydiorganosiloxanes do not lose their mechanical strength as abruptly as other organic materials at elevated temperatures, they find particular use in high temperature applications.
For many uses such as in insulated wire, rods, channels, tubing, and similar products, polydiorganosiloxane compounds are extruded in standard rubber extrusion equipment. The extruded material must immediately be heated to set the form. Usually, hot-air vulcanization at 300-450° C. or steam at 0.28-0.70 MPa (40-100 psi) for several minutes is needed. Final properties can be developed by oven curing or by continuous steam vulcanization.
For many other uses such as in elastomers, caulking, gaskets, sealants, and release coatings, polydiorganosiloxane compounds are applied as liquids or deformable semi-solids at room temperature and require intimate mixing if two part systems are used. Final properties are developed after lengthy cure times and are generally inferior. Often a delay occurs before the next sequence in manufacture or repair can proceed.
In recent years, free radically cured and moisture cured liquid polydiorganosiloxane compositions have been disclosed that cure rapidly and completely under exposure to radiation or moderately elevated temperatures with excellent properties. Thus, subsequent manufacturing or repair steps are often delayed until some degree of curing occurs. Also, thick constructions cannot be made without temporary support until curing is accomplished and irregularly shaped surfaces can be difficult to coat adequately. Therefore, there is still a need for polydiorganosiloxane compositions with green strength, i.e., strength in the uncured state, and controlled flow properties.
Silicone-based release coatings have been used commercially for some time, predominantly in such applications as release liners for adhesives. Generally, these materials are coated from solvent or a carrier and thermally crosslinked at high temperatures. Recently, silicone release technologies have been disclosed that include addition cure, cationic cure, radiation cure, and moisture cure of monomer, oligomer or polymer systems as well as silicone-containing block copolymers that do not require curing. Some of these systems can be coated without solvent, e.g., by roll coating. Others can be coated from organic solvents or water. There is still a need for a silicone-based coating with controlled flow properties and good green strength while retaining the desirable release performance features of the previously mentioned materials.
Physically crosslinked polydiorganosiloxane polyurea segmented copolymers, that may contain blocks other than polydiorganosiloxane or urea, are elastomers that are synthesized in and coated out of solvent. These copolymers have some potential process economy advantages because their synthesis reaction is rapid, requires no catalyst, and produces no by-products.
In producing polydiorganosiloxane polyurea segmented copolymers, monofunctional reaction impurities in the polydiorganosiloxane diamine precursor can inhibit the chain extension reaction and limit the attainment of optimum molecular weight and tensile strength of the polymer. Because the early processes for making the polydiorganosiloxane diamines resulted in increasing levels of monofunctional impurities with increasing molecular weight, it was not possible to achieve elastomers having satisfactory mechanical properties for most elastomer or adhesive applications. More recently, processes have been developed that produce low levels of impurities over a wide range of polydiorganosiloxane diamine molecular weights. With these processes polydiorganosiloxane polyurea segmented copolymers have been obtained that have good mechanical properties through the use of chain extenders to increase the non-silicone content. However, these systems, with or without chain extender, do not flow at room temperature.
Continuous melt polymerization processes have been used to produce polyurethane elastomers and acrylate pressure-sensitive adhesives. Polyetherimides, which can contain polydiorganosiloxane segments, have also been produced in a continuous melt polymerization process. Recently polyurethane resins have been described that use polydiorganosiloxane urea segments to prevent blocking of films formed from the resin. However, levels of reactive polydiorganosiloxane in the compositions were small, for example, less than 15 weight percent, and incomplete incorporation of the polydiorganosiloxane into the backbone was not detrimental since easy release was the intent. Unincorporated polydiorganosiloxane oil can, however, act as a plasticizing agent in elastomers to reduce tensile strength or detackify and reduce shear properties of pressure-sensitive adhesives. This unincorporated oil can also bloom to the surface of an elastomer or adhesive and contaminate other surfaces with which it is in contact.
SUMMARY OF THE INVENTION
Briefly, in one aspect of the present invention, polydiorganosiloxane oligourea segmented copolymers are provided wherein such copolymers comprise soft polydiorganosiloxane diamine units, hard polyisocyanate residue units, wherein the polyisocyanate residue is the polyisocyanate minus the —NCO groups, optionally, soft and/or hard organic polyamine units, wherein residues of the isocyanates amine units are connected by urea linkages, and terminal groups, wherein the terminals groups are non-functional endcapping groups or functional endcapping groups.
The present invention further provides polydiorganosiloxane oligourea segmented copolymer compositions comprising the reaction product of
(a) at least one polyisocyanate;
(b) an endcapping agent having a terminal selected from polydiorganosiloxane monoamines and non-siloxane containing endcapping agents having a terminal portion reactive with an amine or isocyanate and a terminal portion that is non-functional or that can react under moisture-cure or free-radical conditions,
with the provisos (1) that if no polydiorganosiloxane monoamine is present, then at least one polyamin
Everaerts Albert I.
Leir Charles M.
Mazurek Mieczyslaw H.
Nelson Constance J.
Romanko Walter R.
Moore Margaret G.
Peters Carolyn V.
Sherrill Michael S.
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