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
2000-12-05
2004-11-30
Wyrozebski, Katarzyna (Department: 1714)
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...
C524S501000, C523S334000
Reexamination Certificate
active
06825260
ABSTRACT:
The invention pertains to nanoporous, interpenetrating organic-inorganic networks, to processes for their production, and to their use.
Organic polymers are often characterized by ease of molding and elasticity. For many applications, however, they are not hard or scratch-resistant enough. Ceramic materials, in contrast, are hard and scratch-resistant, but they are usually brittle and inelastic. If it is desired to combine the properties of organic polymers with those of inorganic ceramics, the attempt can be made to produce a material consisting of the most uniform possible mixture of the two different components. Various approaches to achieving this goal are known.
U.S. Pat. No. 4,980,396 describes a composition consisting of organopolysiloxane, a filler of the silicate type, an organosilicon compound of the isocyanurate type, and an organic solvent. The composition is used to bond a fluorosilicone rubber permanently to metal, plastic, and other materials; in this case, the fluorosilicate rubber is to be vulcanized by atmospheric, hot-air vulcanization. The constituents are used in the form of a solution or slurry in an organic solvent such as ethyl acetate, for example.
U.S. Pat. No. 5,342,876 describes a process for the production of porous, spherical particles of silicon dioxide. In this process, polyacrylamide polymers are used as a coagulation growth agent to promote the coagulation of the silica gels. Silica gel coagulates with a pore volume of 0.3-1.0 cm
3
/g are thus obtained. An interpenetrating network of silicon dioxide and polyacrylamide, however, is not formed, which means that the polyacrylamide can be dissolved out of the article produced. The polyacrylamide thus serves to build up the silicon dioxide body but is not a component of an organic-inorganic network.
Various approaches to the problem of obtaining hybrid organic-inorganic materials make use of organosilicon starting compounds. When the very expensive organosilicon compounds are being processed, it is necessary to work in an organic solvent. Both the management of the process and also the starting compounds are extremely expensive, which means that the range of applications open to this process is limited to specialized cases.
Also included among these processes are processes for producing nanocomposite materials, in which alkenylsilanes are polymerized by thermal or photochemical means. After the organic components have been polymerized, an inorganic network is produced by hydrolysis. In this way, bulk materials of high density are accessible. These materials are again extremely expensive.
The task of the present invention is to provide a process for the production of materials with organic and inorganic networks which interpenetrate in very small dimensions, which process makes use of inexpensive starting materials and which leads to products with properties which can be adjusted in many different ways. In particular, the goal is to arrive at aerogels and xerogels of low thermal conductivity and increased sound absorption capacity as well as composite materials which combine the properties of organic polymers with those of inorganic ceramics.
This task is accomplished by a process for the production of materials with interpenetrating organic and inorganic networks with a maximum dimension of 100 nm by:
(1) mixing aqueous solutions or dispersions of organic polymers, polymer precursors, or mixtures thereof which are capable of forming polymer networks in the aqueous phase with silicon dioxide components;
(2) changing the pH of and/or thermally treating the aqueous solution or dispersion to form a gel consisting of interpenetrating organic and silica gel networks; and
(3) drying the gel.
It was discovered as part of the invention that the materials listed above can be obtained by processes for the production of aerogels and xerogels, where organic polymers or polymer precursors capable of forming organic networks under the conditions of the formation of aerogels and xerogels are used in addition to the inorganic starting materials for the production of aerogels and xerogels. In the following, the starting materials are described first, and then the different variants of the process are presented.
Organic polymers, polymer precursors, or mixtures thereof which are able to form networks in the aqueous phase are used to form the organic polymer network.
In principle, any organic polymer which is soluble or dispersible in water can be used; a “polymer” is understood here to be a polymer, a polycondensate, or a polyadduct which can be crosslinked in water. Examples are nonionic polyvinyl alcohol, which can be completely or partially saponified from polyvinyl acetate; polyethylene glycol; anionic polymers such as carboxymethylcellulose and sodium poly(meth)acrylate or other poly(meth)acrylates; or cationic polymers, polyamides, or polyvinylamines as well as mixtures of these. Homopolymers and copolymers of sterols such as bile acid homopolymers, copolymers, or oligomers such as those described in EP-A 0,549,967 or cholesterol can be used. In addition to polyvinyl alcohol or poly(meth)acrylate, it is preferred to use organic polymers or their precursors which are based on formaldehyde or on resins which contain formaldehyde. These include primarily melamine resins, phenolic resins, and resorcinol resins. Especially preferred are melamine-formaldehyde resins, which can possibly contain solubilizers such as sulfamate, and which gel preferably in the pH range of 5-6. These polymers should be crosslinkable in an aqueous medium with standard crosslinking agents such as formaldehyde or glutarodialdehyde. In general, aliphatic and aromatic dialdehydes, especially glutarodialdehyde; aliphatic or aromatic diepoxides; or aliphatic and aromatic diisocyanates can also be used as crosslinking agents for the organic component.
The organic polymer network is preferably obtained by polycondensation in the aqueous phase. Polymers and polymer precursors which can be polymerized by radical polymerization in the aqueous phase, however, can also be used.
Melamine-formaldehyde condensates are described in, for example, U.S. Pat. No. 5,086,085. Resorcinol-formaldehyde condensates are described in, for example, U.S. Pat. No. 4,873,216.
It is preferred to select organic polymers, polymer precursors, or their mixtures which polycondense by adjustment of the pH value or the temperature to a value in the same range as that in which the inorganic (silicate) network condenses.
If polyacrylic acids or bile acid homo- or copolymers according to EP-A 0,549,967 or possibly other derivatives of polyacrylic acids or of polyacrylic acid amide are used, then advantage can also be taken of their enormous swelling capacity, which means that the polyacrylic acids can be used in a form in which they have already been crosslinked and dried. They can be added to a silicic acid sol to swell them. The expression “organic polymers, polymer precursors, or mixtures thereof” thus designates all the components which are required to obtain a polymer network in an aqueous solution or dispersion. In particular, this expression includes polymers, prepolymers, monomers, crosslinking agents, and other substances which play a role in polymerization or crosslinking.
The silicon dioxide components used according to the invention are components which can form polymeric networks in an aqueous solution. The preferred silicon dioxide components are water glass, laminar silicates, or silicic acids. Metal oxides which are suitable for the sol-gel technique are described in, for example, C. J. Brinker and G. W. Scherer:
Sol
-
Gel Science,
1990, Chapters 2 and 3, Academic Press, Inc., New York. Free silicic acid is the preferred component, which can be produced from water glass, for example, by separation of the cations by the use of ion-exchangers. A process of this type is described in, for example, EP-A 0,658,513. Free silicic acid from which the cations have been removed is highly compatible with organic polymers, polymer precursors, or mixtures thereof which can form
Sievers Werner
Zimmermann Andreas
Cabot Corporation
Wyrozebski Katarzyna
LandOfFree
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