Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2000-05-24
2003-07-15
Lovering, Richard D. (Department: 1712)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C427S221000, C427S387000, C428S398000, C501S012000, C502S171000, C502S527240, C516S100000, C516S111000, C523S209000, C528S403000
Reexamination Certificate
active
06592991
ABSTRACT:
DESCRIPTION
This application is a 371 of PCT/EP 98/05585 filed Sep. 3, 1998.
The invention relates to a process for preparing structured organic-inorganic hybrid materials using amphiphilic block copolymers as templates. The process of the invention can also be used to prepare macroscopically anisotropic formed pieces, mesoporous solids and inorganic formed pieces in the nanometer range. The invention also comprises the materials prepared and their use, in particular in separation technology and in heterogeneous catalysis, and in the microelectronics industry.
Organic-inorganic hybrid materials with structures in the nanometer range are a class of materials with varied and interesting properties. Materials of this type are used in catalysis, membrane technology and separation technology, and also in developing nanoscopic structures. In particular materials in which the structures have a large length range are likely to have varied applications.
Conventional processes for preparing structured materials use self-assembling surfactants as structuring templates. The morphology of the inorganic materials is determined here by the way the surfactant molecules organize. Processes of this type have been used in particular to prepare inorganic mesoporous materials, and the surfactants used here have had low molecular weight (N. K. Raman et al., Chem. Mater. 8 (1996), 1682; U.S. Pat. Nos. 5,057,296; 5,108,725; 5,098,684 and 5,102,643). However, the aim of these processes has been to form mesoporous inorganic solids rather than an organic-inorganic hybrid material. In addition, control of structure during the conduct of the process is extremely difficult due to phase changes. Using surfactants as templates, furthermore, it is only possible to obtain mesoporous solids with relatively small pores in the range from 2 to 10 nanometers. Already at pore sizes above about 5 nanometers the inorganic solids described begin to become mechanically unstable and collapse, due to insufficient wall thicknesses. A further disadvantage is that the mesoporous solids obtained by this process can be obtained only as fine powders.
The use of lyotropic liquid-crystalline phases of low-molecular-weight surfactants has recently been described for preparing mesoporous solids (Attard et al., Nature 378 (1995), 366-367). Strict separation between aqueous (polar) and hydrophobic (nonpolar) regions in lyotropic liquid-crystal phases of this type permits the formation of an ordered structure. Polycondensation of an inorganic water-soluble monomer consolidates the inorganic material and produces a copy of the liquid-crystal structure. This makes it possible to form not only fine-grained powders but also nanostructured mesoporous monoliths. Moreover, these processes, too, serve to prepare a mesoporous material rather than an organic-inorganic hybrid material. The low-molecular-weight surfactants used moreover give only relatively low pore diameters.
The use of a lyotropic liquid-crystal phase made from amphiphilic block copolymers as a template has also been proposed for preparing mesoporous inorganic materials (C. G. Göltner et al., Adv. Mater. 9(5) (1997), 431-436). Stable mesoporous materials with pore sizes of from 7 to 15 nanometers could be obtained in this way. However, no further details concerning suitable amphiphilic block copolymers have been disclosed.
It was therefore an object of the invention to provide a process for preparing structured organic-inorganic hybrid materials while overcoming at least some of the disadvantages of the prior art.
The invention achieves this object by means of a process for preparing structured organic-inorganic hybrid materials, comprising the steps:
(a) forming a mixture comprising at least one mesophase of an amphiphilic organic block copolymer having at least one hydrophilic block and at least one hydrophobic block as template and comprising at least one precursor which can be reacted to give an inorganic solid,
(b) reacting the precursor,
(c) optionally removing any volatile constituents from the reaction mixture, and
(d) obtaining the organic-inorganic hybrid material,
wherein a hydrophobic block of the amphiphilic block copolymer has a glass transition temperature Tg≦50° C.
According to the invention a mixture is first formed which comprises at least one mesophase of an amphiphilic block copolymer as template and comprises at least one precursor which can be reacted to give an inorganic solid. An amphiphilic block copolymer is composed of at least two blocks of different polarity, of which one is hydrophobic and the other hydrophilic, in particular water-soluble. Reacting the precursor gives an inorganic solid, either surrounding the amphiphilic block copolymers present as template of being embedded into these. During the reaction of the precursor to give the solid any volatile constituents which may have been produced are removed from the reaction mixture so that they cannot interfere with the mesophase.
Surprisingly, it has been found that use of an amphiphilic block copolymer with a glass transition temperature Tg≦50° C. allows for controlled establishing of various structures by varying the amount of precursor added. Using a polymer of this type allows an equilibrium morphology to be obtained, and suitable selection of the amounts of the starting compounds can therefore predetermine the structures. Increasing the proportion by volume of the inorganic precursor in relation to the polymer gives the morphologies predicted from the phase diagram of diblock copolymers. The process according to the invention provides therefore a controllable route to the preparation of new and improved structured materials. Combining inorganic constituents in a hybrid material with organic block copolymers in the nanometer size range gives products with interesting mechanical properties. Since the chemistry of the block copolymers (e.g. their composition, chain length, structure, etc.) can be modified in a know manner it is possible to prepare composites with specific predetermined properties in the manner which has been known for many years for polymers.
Using block copolymers it is further possible to obtain microstructures whose order of size is within the characteristic range of lengths of the polymer chains, i.e. within a size range of from 5 to 100 nanometers. The range of lengths of the structured hybrid materials may be adjusted directly via the molecular weight of the block copolymer used.
The amphiphilic block copolymers used according to the invention as template have at least one hydrophobic and one hydrophilic block. The amphiphilic block copolymers used preferably have A-B, A-B-A or B-A-B structure, particularly preferably A-B structure, where A is a hydrophobic block and B is a hydrophilic block. Each of the individual blocks comprises ≦5 monomer units, preferably ≦10 monomer units.
Block copolymers frequently have a further structural unit linking the different blocks to one another. Other amphiphilic polymers preferably used for forming the mesophase therefore have the structure A
n
-C
m
-B
n,
A
n
-C
m
-B
n
-C
m
-A
n
or B
n
-C
m
-A
n
-C
m
-B
n
, where A is a hydrophohic structural unit, B is a hydrophilic structural unit and C is a low- or high-molecular-weight, hydrophobic or hydrophilic structural unit, and n, independently each time it occurs, is an integer ≧5 and m, independently each time it occurs, is an integer from 0 to 20. C is frequently a coupling molecule or a coupling group linking the individual blocks to one another. A coupling molecule of this type may be used to form a block copolymer by linking a hydrophilic polymer block to a hydrophobic polymer block. It is also possible to begin by polymerizing one of the two blocks, e.g. the hydrophobic block, and then to attach to this block a coupling molecule or a coupling group in order to modify the reactivity of the polymerized block with respect to the monomers, for example by changing the basicity, and then to continue the polymerization with another monomer, e.g. with a hydrophilic monomer.
T
Templin Markus
Wiesner Ulrich Bernd
Lovering Richard D.
Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V.
Rothwell Figg Ernst & Manbeck
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