Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-02-26
2003-03-18
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C525S477000, C528S028000, C528S033000, C528S036000, C528S038000
Reexamination Certificate
active
06534184
ABSTRACT:
TECHNICAL FIELD
This invention relates to block copolymers and more particularly to polysilazane/polysiloxane block copolymers and their preparation.
BACKGROUND OF THE INVENTION
The growth of the silicone industry since its beginnings can be attributed to the unique physical and chemical properties of the polysiloxanes. Silicone materials are now being used in almost all aspects of industrial processing and products, consumer goods and in many medical applications. Silicones are now used as paint and printing ink additives for flow control, leveling, pigment dispersion and gloss improvement, as plastics additives to improve flow, in textile processing applications to impart water Is repellency, oil resistance, and to provide a soft “finish”, in cellular plastics as silicone-polyether copolymers to improve bubble formation and to provide for uniform cell size for polyurethanes and other foamable plastics, in consumer products such as furniture and car polish, iron spray, eyeglass lens paper, shaving lotion, hair care preparations, milk cartons, as antifoam agents in the food processing, wine fermentation, and chemical processing industries.
Many expanding technologies and major businesses are highly dependent on tailor-made products based on organosilicon chemistry. For example, today's billion dollar urethane foam market was made possible by the development in the late 1950's of silicone surfactants. The development of silicone-coated release agents was critical to the success of pressure-sensitive adhesives. Silicone coatings provide long term weather and thermal protection for a variety of environmentally severe conditions on earth and in outer space.
Silicone resins have also been used as vehicles for heat resistant paints, and in recent years silicone-organic copolymers have been developed using alkyds, polyesters, epoxies and acrylics. Characterized by outstanding weathering gloss retention and heat resistance, these vehicles are widely used for coil coating and maintenance paints. In addition, frying and baking pans, release-type paper coatings, coatings for plastics and a large number of other end-uses have been commercialized by using silicones in combination with common organic coatings resins.
While such silicone-organic copolymers are now well known in the art, the combining of silicones and inorganic polymers such as polysilazanes to prepare copolymers is not as well known. U.S. Pat. No. 5,288,795, for instance, issued to H. Fujiki, discloses blending siloxanes with silazane surface-treated silica particulates. Coatings comprising random copolymers of siloxanes and silazanes are disclosed by U.S. Pat. No. 4,678,688 to Itoh, et al. These compositions are prepared by subjecting a mixture of monomeric chlorosilanes first to a base hydrolysis step to effect partial conversion of the chlorosilanes to siloxanes, and second to an ammonolysis step to effect conversion of the residual silicon-chlorine bonds to silazanes. A random siloxane/silazane copolymer is obtained because of the random nature of the hydrolysis/ammonolysis reactions which form the polymer. However, such random configurations of Si—O and Si—N bonds in a copolymer results in homogeneous compositions which exhibit a weighted average of the two families of materials.
While silazanes are noted for their excellent heat resistance, corrosion resistance, and adhesive properties, these attractive characteristics are compromised by their random copolymerization with silicones. Thus, as a rule, the random copolymerization of two families of materials results in properties which are a weighted average of the properties of each of the materials employed.
The above mentioned random copolymer may thus be effective in certain applications, but is unsatisfactory for providing the optimum in derivative performance based on the attractive features of each family of materials.
SUMMARY OF THE INVENTION
The present invention has an object to provide novel polysilazane/polysiloxane block copolymers which exhibit excellent heat resistance, corrosion resistance, and adhesion derived from their polysilazane blocks, as well as superior gloss, durability, oil and water resistance, and release characteristics derived from their polysiloxane blocks. Accordingly, block copolymers of the invention comprise at least one polysilazane with at least one polysiloxane. The polysilazane comprises a plurality of Si—N groups.
Another object of the present invention is to provide a block copolymer of a polysilazane and a polysiloxane which exhibits optimum benefits from each of the components, rather than an averaging of their properties.
Still another object of this invention is to prepare novel polysilazane/polysiloxane block copolymers where each block segment is at least 10 wt % of the copolymer weight.
It is a further object of this invention to prepare novel polysilazane/polysiloxane block copolymers that form attractive and durable protective coatings on metal, glass, and polymeric substrates.
Still yet another object of this invention is to prepare block copolymers which are not hampered by the comonomer reactivity ratio restriction found in random copolymers.
It is still another object of this invention to prepare novel block copolymers from a polysilazane and a different polymer having nucleophilic substituents. This would include a polysiloxane comprising at least one nucleophilic group. The nucleophilic group would preferably be a member selected from the group consisting of hydroxyl, an amine and mixtures thereof.
These and further objects are accomplished by the novel compositions of the present invention which comprise reaction mixtures comprising a polysilazane (A) and a polysiloxane (B) copolymerized to form a polysilazane/polysiloxane block copolymer. The sequential arrangement of the block copolymers of the present invention can vary from simple A-B structures containing only two segments, to A-B-A and B-A-B triblock structures, and multi-block systems possessing many segments -(A-B)-
n
. Many intermediate arrangements can be made of the block copolymers of the present invention wherein the polymeric segments of the polysilazanes and polysiloxane are attached end to end and/or in branched configuration and/or graft configuration in which a plurality of siloxane chains are pendant to the silazane backbone, so that the physical and chemical characteristics of each of the separate sequences are asserted individually in the block copolymer.
Accordingly, for purposes of this invention the expression “block copolymer” as appearing in the specification and claims is intended to include both block copolymers and graft copolymer variations thereof.
Preferably, the block copolymers are prepared by copolymerizing a polysilazane with a polysiloxane. More particularly, polymer condensation techniques are utilized employing functional ended polysilazanes and polysiloxanes. As such, the separate polymer blocks are pre-formed under conditions affording the maximum degree of control over their compositions and then linking the blocks by standard methods of organic and organosilicon chemistry chosen to result in effectively quantitative conversion of the functional groups.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As described above, the polysilazane/polysiloxane block copolymers of this invention are made by copolymerizing at least one polysilazane with at least one polysiloxane.
The base ingredients in the inventive compositions include polysilazanes and polysiloxanes. Any polysilazane or a mixture of polysilazanes known in the art or commercially available, having repeating units of Si—N linkages, can be used to prepare the block copolymer. By “polysilazane” is meant any oligomeric or polymeric composition comprising a plurality of Si—N repeat units. By “oligomer” is meant any molecule or chemical compound which comprises several repeat units, generally from about 2 to 10 repeat units. “Polymer”, as used herein, means a molecule or compound which comprises a large number of repeat units, generally greater than about 10 repeat unit
Abel Albert E.
Knasiak Gary J.
Lukacs III Alexander
Mouk Robert W.
Dawson Robert
Ellis Howard M.
Kion Corporation
Robertson Jeffrey B.
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