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
2002-03-12
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...
C528S038000, C528S042000
Reexamination Certificate
active
06355759
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polydioranosiloxane polyurea 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 hydropnobicity, and good dielectric properties. They also have very good biocompatibility and are of great interest as biomaterials which 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. 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.
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 which include addition cure, cationic cure, and radiation cure systems as well as silicone-containing block copolymers which 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. None of these systems are believed to be hot melt processable. Thus, there is still a need for a silicone-based release coating that is hot melt coatable while retaining the desirable release performance features of the previously mentioned materials.
Block copolymers have long been used to obtain desirable performance characteristics in various products such as elastomers, sealants, caulking compounds, and release coatings.
Physically crosslinked polydiorganosiloxane elastomers usually are segmented copolymers. The mechanical properties of an elastomer generally increase with the molecular weight of the polymer. The molecular weight often can be determined by inherent viscosity measurements. For some uncrosslinked systems, as the molecular weight increases, the polymer becomes less soluble and the inherent viscosity becomes more difficult to measure. The mechanical properties and inherent viscosities of the polydiorganosiloxane polymers can be substantially increased, while most of the desired polydiorganosiloxane properties are maintained, through controlled, solvent-based synthesis of AB, ABA, or (AB)
n
segmented polymers, with a soft polydiorganosiloxane component and a hard component of either a crystalline structure with a high melting point or an amorphous structure with a high glass transition temperature and include, for example, hard segments such as polystyrene, polyamide, polyurethane, polyimide, polyester, polycarbonate, polysulfone and epoxide.
Another class of polydiorganosiloxane segmented copolymers is polydiorganosiloxane polyurea segmented copolymers which may contain blocks other than polydiorganosiloxane or urea. These have some potential process economy advantages because their synthesis reaction is more rapid than those previously mentioned, requires no catalyst, and produces no by-products.
In producing polydiorganosiloxane polyurea segmented copolymers, monofunctional reaction impurities in the polydiorganosiloxane diamine precursor can prematurely terminate 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 which produce materials with low levels of impurities over a wide range of polydiorganosiloxane diamine molecular weights. With this chemistry, polydiorganosiloxane polyurea segmented copolymers have been obtained having inherent viscosities of over 0.8 g/dL measured at 30° C. (using a Canon-Fenske viscometer with chloroform solution at a concentration of 0.4 g/dL) through the use of chain extenders to increase the non-silicone content.
Solution polymerized polydiorganosiloxane polyurea elastomers which do not require a cure step have been described. However, because these compositions are made in solvent, they can have costly handling procedures.
Continuous melt polymerization processes are advantageous and have been used to make compositions such as polyurethane elastomers and acrylate pressure sensitive adhesives. A continuous melt polymerization process for producing polyetherimides, which can contain polydiorganosiloxane segments, has also been described. Recently polyurethane resins have been described which use polydiorganosiloxane urea segments to prevent blocking of film formed from the resin. However, levels of reactive polydiorganosiloxane in the compositions were small, for example, less than 15 weight percent, and potential 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 melt-processable polydiorganosiloxane polyurea segmented copolymer compositions are provided wherein such compositions comprise alternating soft polydiorganosiloxane units, and hard polyisocyanate residue units, (wherein the polyisocyanate residue is the polyisocyanate minus the —NCO groups), and optionally, soft and/or hard organic polyamine units, and such that the residues of the amine and isocyanate units are connected together by urea linkages. Compositions of the present invention typically have inherent viscosities of at least 0.8 dL/g, or are essentially insoluble in common organic solvents such as, for example, chloroform, tetrahydrofuran, dimethyl formamide, toluene, isopropyl alcohol, and combinations thereof
The pr
Mazurek Mieczyslaw H.
Melancon Kurt C.
Nelson Constance J.
Romanko Walter R.
Seth Jayshree
3M Innovative Properties Company
Moore Margaret G.
Peters Carolyn V.
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