EP1546063A1

EP1546063A1 - Method for producing inverse opaline structures

Info

Publication number: EP1546063A1
Application number: EP03798883A
Authority: EP
Inventors: Holger Winkler; Götz HELLMANN; Tilmannn Ruhl; Peter Spahn
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2002-09-30
Filing date: 2003-09-02
Publication date: 2005-06-29
Also published as: CN1684925A; CA2500327A1; US20060254315A1; JP2006501124A; DE10245848A1; TW200418745A; TWI291944B; BR0314827A; WO2004031102A1; AU2003255503A1; KR20050074466A

Abstract

The invention relates to the use of core-shell particles, whose shell forms a matrix and whose core is essentially solid and has an, in essence, monodisperse size distribution. These core-shell particles are used as templates for producing inverse opaline structures. The invention also relates to a method for producing inverse opaline structures while using core-shell particles of this type.

Description

Process for the production of inverse opal structures

The invention relates to the use of core-shell particles as a template for producing inverse opal-like structures and a method for producing inverse opal-like structures.

Three-dimensional photonic structures are generally understood to mean systems which have a regular, three-dimensional modulation of the dielectric constant (and therefore also of the refractive index). If the periodic modulation length corresponds approximately to the wavelength of the (visible) light, the structure interacts with the light in the manner of a three-dimensional diffraction grating, which manifests itself in angle-dependent color phenomena. An example of this is the nature of the E delstein O pal d ar, which consists of a densely packed spherical packing made of silicon dioxide spheres and cavities in between that are filled with air or water. The inverse structure to this arises from the fact that regular spherical hollow volumes are arranged in the densest packing in a solid material. One advantage of such inverse structures over the normal structures is the formation of photonic band gaps with already much lower dielectric constant contrasts (K. Busch et al. Phys. Rev. Letters E, 198, 50, 3896). TiO _{2 in} particular is a suitable material for the formation of a photonic structure because it has a high refractive index.

Three-dimensional inverse structures can be created by template synthesis:

• As a structure-giving template, monodisperse spheres are arranged in the densest spherical packing.

• The hollow volumes between the balls are determined by using

Capillary effects are filled with a gaseous or liquid precursor or a solution of a precursor.

• The precursor is (thermally) converted into the desired material. • The templates are removed, leaving the inverse structure. Many such methods are known in the literature. For example, SiO ₂ spheres can be arranged in the densest packing, the hollow volumes are filled with solutions containing tetraethyl orthotitanate. After several tempering steps, the balls are removed in an etching process with HF, leaving the inverse structure of titanium dioxide (V. Colvin et al. Adv. Mater. 2001, 13, 180).

De La Rue et al. (De La Rue et al. Synth. Metals, 2001, 116, 469) describe the preparation of inverse, consisting of TiO ₂ opals according to the following method: A dispersion of 400 nm polystyrene balls is dried on a filter paper under an IR lamp. The filter cake is suctioned off with ethanol, transferred into a glove box and infiltrated by means of a water jet pump with tetraethyl orthotitanate. Carefully remove the filter paper from the latex-ethoxide composite and transfer the composite to a tube furnace. The calcination takes place in the tube furnace at 575 ° C. for 8 hours in an air stream, whereby titanium dioxide is formed from the ethoxide and the latex particles are burned out. An inverse TiO ₂ opal structure remains.

Martinelli et al. (M. Martinelli et al. Optical Mater. 2001, 17, 11) describe the production of inverse TiO ₂ opals using 780 nm and 3190 nm polystyrene spheres. A regular arrangement in the densest spherical packing is achieved by centrifuging the aqueous spherical dispersion at 700-1000 rpm for 24-48 hours and then decanting, followed by air drying. The regularly arranged balls are moistened with ethanol on a filter on a Buchner funnel and then dropwise provided with an ethanolic solution of tetraethyl orthotitanate. After the titanate solution has soaked in, the sample is dried in a vacuum desiccator for 4 to 12 hours. This filling procedure is repeated 4 to 5 times. The polystyrene balls are then burned out at 600 ° C - 800 ° C for 8 - 10 hours. Stein et al. (A. Stein et al. Science, 1998, 281, 538) describe the synthesis of inverse TiO ₂ opals from polystyrene spheres with a diameter of 470 nm as a template. These are made in a 28 hour process, subjected to centrifugation and air dried. Then the latices template are applied to a filter paper. Ethanol is sucked into the latex template via a Büchner funnel, which is connected to a vacuum pump. Then tetraethyl orthotitanate is added dropwise with suction. After drying in a vacuum desiccator for 24 h, the latices are burned out at 575 ° C for 12 h in an air stream.

Vos et al. (WL Vos et al. Science, 1998, 281, 802) produce inverse TiO ₂ opals by using polystyrene spheres with diameters of 180-1460 nm as templates. A sedimentation technique is used to set the densest spherical packing of the spheres, which is supported by centrifugation for up to 48 h. After slowly evacuating to dry the template structure, an ethanolic solution of tetra-n-propoxy orthotitanate is added to it in a glove box. After about 1 h, the infiltrated material is brought into the air to allow the precursor to react to form TiO. This procedure is repeated eight times to ensure complete filling with TiO ₂ . The material is then calcined at 450 ° C.

The production of photonic structures from inverse opals is very complex and time-consuming according to the processes described in the literature: • lengthy / complex production of the template, or the arrangement of the balls forming the templating structure in a densest packing

• Lengthy / complex, because the cavities of the template structure are often filled with precursors because they have to be repeated several times

• lengthy / complex procedure for removing the template

• only limited or no possibility of producing larger photonic structures with inverse opal structure and transfer from laboratory synthesis to technical production. The disadvantages make it difficult to produce the desired photonic materials with an inverse opal structure. There is therefore a need for an easy-to-implement manufacturing process that is also transferable to the technical scale.

Core-shell particles, the shell of which forms a matrix and the core of which is essentially solid and has an essentially monodisperse size distribution, are described in the earlier German patent application DE 10145450.3

Surprisingly, it was found that core-shell particles of this type are outstandingly suitable as templates for producing inverse opal structures.

A first object of the present invention is therefore the use of the core-shell particles, the shell of which forms a matrix and whose core is essentially solid and has an essentially monodisperse size distribution as a template for producing inverse opal structures.

Another object of the present invention is a method for producing inverse opal structures, characterized in that: a) a dispersion of core-shell particles, the shell of which forms a matrix and the core of which is essentially solid, is dried, b) optionally or more precursors more suitable

Wall materials are added and, c) the cores are subsequently removed.

The use of core-shell particles according to the invention leads in particular to the following advantages:

when drying dispersions from core-shell particles, the crack formation in the template (= arrangement of the balls) can be reduced or even completely prevented when drying, large areas of high order can be obtained in the template,

- Tensions occurring during the drying process can be compensated for by the elastic nature of the jacket,

- If polymers form the sheath, they can intertwine and thus mechanically stabilize the regular arrangement of balls in the template,

- If the sheath - preferably by grafting - is firmly connected to the core via an intermediate layer, the templates can be processed by melting processes.

According to the invention, it is therefore particularly preferred if in the core-shell particles the shell is connected to the core via an intermediate layer.

In order to achieve the optical or photonic effect according to the invention, it is desirable that the core-shell particles have an average particle diameter in the range from about 5 nm to about 2000 nm. It can be particularly preferred if the core-shell particles have an average particle diameter in the range from about 5 to 20 nm, preferably 5 to 10 nm. In this case the nuclei can be called "quantum dots"; they show the corresponding effects known from the literature. To achieve color effects in the visible light range, it is particularly advantageous if the core-shell particles have an average particle diameter in the range of approximately 50-500 nm. Particles in the range from 100 to 500 nm are particularly preferably used, since with particles in this order of magnitude (depending on the refractive index contrast which can be achieved in the photonic structure) the reflections of different wavelengths of visible light differ significantly from one another and thus those for optical effects in the visible range particularly important opalescence particularly pronounced occurs in different colors. In a variant of the present invention, however, it is also preferred to use multiples of this preferred particle size, which then lead to reflections corresponding to the higher orders and thus to a broad play of colors.

The intermediate layer is a preferred one

Embodiment of the invention around a layer of crosslinked or at least partially crosslinked polymers. The networking of

Intermediate layer via free radicals, for example induced by UV radiation, or preferably via di- or oligofunctional monomers. Preferred intermediate layers of this embodiment contain 0.01 to 100% by weight, particularly preferably 0.25 to 10

% By weight, di- or oligo-functional monomers. Preferred di- or oligo-functional monomers are in particular isoprene and allyl methacrylate (ALMA). Such an intermediate layer of crosslinked or at least partially crosslinked polymers preferably has a thickness in the range of

10 to 20 nm. If the intermediate layer turns out thicker, the

Refractive index of the layer chosen so that it either the

Refractive index of the core or the refractive index of the cladding.

If copolymers which contain a crosslinkable monomer, as described above, are used as the intermediate layer, the person skilled in the art does not have any problems in selecting suitable copolymerizable monomers in a suitable manner. For example, corresponding copolymerizable monomers can be selected from a so-called Q-e scheme (cf. textbooks of macromolecular chemistry). Monomers such as methyl methacrylate and methyl acrylate can preferably be polymerized with ALMA.

In another, likewise preferred embodiment of the present invention, shell polymers are directly, via a appropriate functionalization of the core, grafted onto the core. The surface functionalization of the core forms the intermediate layer according to the invention. The type of surface functionalization depends mainly on the material of the core. silica

Surfaces can be suitably modified, for example, with silanes which have correspondingly reactive end groups, such as epoxy functions or free double bonds. In the case of polymeric cores, a styrene functionalized on the aromatic, such as bromostyrene, can be used for surface modification, for example. The growth of the shell polymers can then be achieved via this functionalization. In particular, the intermediate layer can also cause the cladding to adhere to the core via ionic interactions or complex bonds. 5

In a preferred embodiment, the shell of these core-shell particles consists of essentially uncrosslinked organic polymers which are preferably grafted onto the core via an at least partially crosslinked intermediate layer. 0

The jacket can either consist of thermoplastic or elastomeric polymers. The core can consist of various materials. It is only essential in the sense of the present invention that the core and, in one variant of the invention, preferably also the intermediate layer and jacket, can be removed under conditions in which the wall material is stable. The choice of suitable core / cladding / interlayer wall material combinations does not pose any difficulties for the person skilled in the art.

Furthermore, in a variant of the invention, it is particularly preferred if the core consists of an organic polymer, which is preferably crosslinked. 5 In another variant of the invention explained in more detail below, the cores consist of an inorganic material, preferably a metal or semimetal or a metal chalcogenide or

Metal pnictide. As chalcogenides in the sense of the present

Invention denotes those compounds in which an element of the 16th

Group of the periodic table is the electronegative binding partner; as pnictide those in which an element of the 15th group of the periodic table is the electronegative binding partner. Preferred cores consist of metal chalcogenides, preferably metal oxides, or metal pnictides, preferably nitrides or phosphides. Metal in the sense of these terms and also all elements, which can appear as an electropositive partner in comparison to the counterions, like the classic metals of the subgroups or the main group metals of the first and second main group, but also all of them Elements of the third main group, as well as silicon,

Germanium, tin, lead, phosphorus, arsenic, antimony and bismuth. The preferred metal chalcogenides and metal pnictides include, in particular, silicon dioxide, aluminum oxide, gallium nitride, boron and

Aluminum nitride as well as silicon and phosphomitride. In a variant of the present invention, the starting material for the production of the core-shell particles to be used according to the invention is preferably monodisperse silicon dioxide cores, which can be obtained, for example, by the process described in US Pat. No. 4,911,903. The cores are produced by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous-ammoniacal medium, initially producing a sol of primary particles and then bringing the SiO ₂ particles obtained to the desired particle size by continuous, controlled metering in of tetraalkoxysilane , This process can be used to produce monodisperse SiO ₂ cores with average particle diameters between 0.05 and 10 μm with a standard deviation of 5%. Monodisperse cores made of non-absorbent metal oxides such as TiO ₂ are also used as the starting material. ZrO ₂ , Zn0 ₂ , SnO ₂ or Al ₂ O ₃ or metal oxide mixtures can be used. Their production is described for example in EP 0 644 914. Furthermore, the method according to EP 0 216 278 for the production of monodisperse SiO ₂ cores can be transferred to other oxides without further notice and with the same result. Tetraethoxysilane, tetrabutoxytitanium, tetrapropoxy-zirconium or their mixtures are added in one pour with vigorous mixing to a mixture of alcohol, water and ammonia, the temperature of which is adjusted with a thermostat to between 30 and 40 ° C. intensively stirred for a further 20 seconds, a suspension of monodisperse nuclei in the nanometer range being formed. After a reaction time of 1 to 2 hours, the cores are separated off, washed and dried in the customary manner, for example by centrifugation.

In one embodiment of the present invention, the wall of the inverse opal structures obtainable according to the invention is preferably formed from an inorganic material, preferably a metal chalcogenide or metal pnictide. In the present description, this material is also referred to as wall material. For the purposes of the present invention, chalcogenides are compounds in which an element of the 16th group of the periodic table is the electronegative binding partner; as pnictide those in which an element of the 15th group of the periodic table is the electronegative binding partner. Preferred wall materials are

Metal chalcogenides, preferably metal oxides, or metal pnictides, preferably nitrides or phosphides. Metal in the sense of these terms are all elements that can appear as electropositive partners compared to the counterions, such as the classic metals of the subgroups, such as titanium and zirconium in particular, or the main group metals of the first and second main group, but also all elements the third main group, as well as silicon, germanium, tin, lead, phosphorus, arsenic, antimony and bismuth. To the preferred metal chalcogenides include in particular silicon dioxide, aluminum oxide and particularly preferably titanium dioxide.

In principle, all conceivable precursors which are liquid, sinterable or soluble and which can be converted into stable solids by a sol-gel-analogous conversion can be used as starting material (precursor) for the production of the inverse opals according to this variant of the invention. Sinterable precursors are understood to mean ceramic or pre-ceramic particles, preferably nanoparticles, which - as is customary in ceramics - can be processed by sintering, possibly with the elimination of volatile by-products, into a molded part - the inverse opal. Precursors of this type are known to the person skilled in the art from the relevant ceramic literature (e.g. H.P. Baldus, M. Jansen, Angew. Chem. 1997, 109, 338-354). In addition, gaseous precursors that can be infiltrated into the template structure using a known CVD-analog method can also be used. In a preferred variant of the present invention, solutions of one or more esters of a corresponding inorganic acid with a lower alcohol, such as, for example, tetraethoxysilane, tetrabutoxytitanium, tetrapropoxyzircon or mixtures thereof, are used.

In a second likewise preferred variant of the invention, the wall of the inverse opal is formed from the polymers of the shell of the core-shell particles, which are preferably crosslinked with one another. In this variant of the invention, the addition of precursors in step b) can be omitted or replaced by the addition of crosslinking agents. In this variant of the invention, it can be preferred if the cores consist of an inorganic material described above.

In the method according to the invention for producing an inverse opal structure, a dispersion of the core-shell particles described above is dried in a first step. The Drying under conditions that allow the formation of a "positive" opal structure, which then serves as a template in the further process. This can be done, for example, by carefully removing the dispersant, by slow sedimentation, or by applying a mechanical force to a pre-dried mass of the core-shell particles.

The mechanical action of force can, according to the invention, be such a force action that occurs in the usual processing steps of polymers. In preferred variants of the present invention, the mechanical force is applied either: by uniaxial pressing or

Force application during an injection molding process or during a transfer press process, - during a (co-) extrusion or during a calendering process or during a blowing process. If the force is exerted by uniaxial pressing, the shaped bodies according to the invention are preferably films. Films according to the invention can preferably also be produced by calendering, film blowing or flat film extrusion. The various possibilities of processing polymers under the influence of mechanical forces are well known to the person skilled in the art and can be found, for example, in the standard textbook Adolf Franck, "Plastic Compendium"; Vogel-Verlag; 1996 are taken. The processing of core-shell particles by the action of mechanical force, as is preferred here, is also described in detail in the international patent application WO 2003025035.

Then, as described above, a precursor of suitable wall materials is preferably added to the template. In a preferred variant of the method according to the invention for producing inverse opal structures, the precursor is therefore a solution of an ester of an inorganic ortho acid with a lower alcohol, preferably tetraethoxysilane, tetrabutoxytitanium, tetrapro- poxyzircon or mixtures thereof. Lower alcohols such as methanol, ethanol, n-propanol, iso-propanol or n-butanol are particularly suitable as solvents for the precursors.

As has been shown, it is advantageous to allow the precursors or, alternatively, the crosslinking agent to act for some time on the core-shell particle template structure under a protective gas cushion before the condensation of the wall material, in order to bring about a uniform penetration into the cavities. For the same reason, it is advantageous if the template structure is mixed with the precursors or the crosslinking agent under reduced pressure, preferably in a static vacuum at p <1 mbar.

The wall material is formed from the precursors either by adding water and / or by heating the reaction mixture. For the alkoxide precursors, heating in air is usually sufficient. It may be advantageous to briefly wash the impregnated template with a small amount of a solvent in order to wash away the precursor adsorbed on the surface. This step prevents a thick layer of wall material from forming on the surface of the template, which can act as a diffuse spreader. For the same reason, it may be advantageous to dry the impregnated structure under mild conditions before calcining.

The cores can be removed in step c) in various ways. For example, the cores can be removed by removing them or by burning them out. In a preferred variant of the method according to the invention, step c) is a calcination of the wall material, preferably at temperatures above 200 ° C., particularly preferably above 400 ° C. If, according to the variant of the invention described above, a precursor is used to form the Used wall, it is particularly preferred if the entire core-shell particles are removed together with the cores.

If the cores are made of suitable inorganic materials, they can be removed by etching. This procedure is particularly preferred when the sheath polymers are to form the wall of the inverse opal structure. For example, silicon dioxide cores can preferably be removed using HF, in particular dilute HF solution. With this procedure, it can again be preferred if, before the removal of the cores, the jacket is crosslinked, as described above.

However, if the cavities of the inverse opal structure are to be impregnated again with liquid or gaseous materials, it can also be preferred if the jacket is not or only very slightly crosslinked. The impregnation can consist, for example, of storing liquid crystals, as described, for example, in Ozaki et al., Adv. Mater. 2002, 14, 514 and Sato et al., J. Am. Chem. Soc. 2002, 124, 10950.

Those obtainable according to the invention are suitable on the one hand for the use described above as a photonic material, preferably with the impregnation mentioned, but on the other hand also for the production of porous surfaces, membranes, separators, filters and porous supports. These materials can also be used, for example, as fluidized beds in fluidized bed reactors.

On the basis of the considerations set out here, it is expedient if the shell of the core-shell particles according to the invention contains one or more polymers and / or copolymers or polymer precursors and, if appropriate, auxiliaries and additives, the composition of the shell being able to be selected such that it is essentially dimensionally stable and tack-free in a non-swelling environment at room temperature. With the use of polymer substances as a sheath material and possibly core material, the person skilled in the art gains the freedom of their relevant properties, such as. B. to determine their composition, the particle size, the mechanical data, the glass transition temperature, the melting point and the weight ratio of core: shell and thus also the application properties of the core / shell particles, which ultimately also affect the properties of the inverse produced Impact opal structure.

Polymers and / or copolymers which may be contained in the core material or which are made up of them are high molecular weight compounds which correspond to the specification given above for the core material. Both polymers and copolymers of polymerizable unsaturated monomers are suitable, as are polycondensates and copolycondensation products of monomers with at least two reactive groups, such as, for. B. high molecular weight aliphatic, aliphatic / aromatic or fully aromatic polyesters, polyamides, polycarbonates, polyureas and polyurethanes, but also aminoplast and phenoplast resins, such as. B. melamine / formaldehyde, urea / formaldehyde and phenol / formaldehyde condensates.

For the production of epoxy resins, which are also suitable as core material, epoxy prepolymers are usually used, for example by reaction of bisphenol A or other bisphenols, resorcinol, hydroquinone, hexanediol, or other aromatic or aliphatic di- or polyols, or phenol-formaldehyde Condensates, or their mixtures with one another with epichlorohydrin, or other di- or polyepoxides are obtained, mixed with other compounds capable of condensation directly or in solution and allowed to harden.

In a preferred variant of the invention, the polymers of the core material are expediently crosslinked (co) polymers, since these usually only show their glass transition at high temperatures.

These crosslinked polymers can either already in the course of

Polymerization or polycondensation or copolymerization or

Copolycondensation may have been crosslinked or they may be completed the actual (co) polymerization or (co) polycondensation have been post-crosslinked in a separate process step.

A detailed description of the chemical composition of suitable polymers follows below.

For the shell material, as for the core material, in principle polymers of the classes already mentioned are suitable, provided that they are selected or constructed in such a way that they correspond to the specification given above for the shell polymers.

Polymers that meet the specifications for a sheath material are also found in the groups of polymers and copolymers of polymerizable unsaturated monomers, as well as the polycondensates and copolycondensates of monomers with at least two reactive groups, such as. B. the high molecular weight aliphatic, aiiphatic / aromatic or fully aromatic polyesters and polyamides.

Taking into account the above conditions for the properties of the shell polymers (= matrix polymers), selected building blocks from all groups of organic film formers are in principle suitable for their production.

Some other examples may illustrate the wide range of polymers suitable for making the sheath.

If the sheath is to have a comparatively low refractive index, polymers such as polyethylene, polypropylene, polyethylene oxide, polyacrylates, polymethacrylates, polybutadiene, polymethyl methacrylate, polytetrafluoroethylene, polyoxymethylene, polyesters, polyamides, polyepoxides, polyurethane, rubber, polyacrylonitrile and polyisoprene are suitable, for example.

If the sheath is comparatively high-index, are suitable for the

Coat, for example, polymers with a preferably aromatic basic structure such as polystyrene, polystyrene copolymers such as. B. SAN, aromatic-aliphatic polyesters and polyamides, aromatic polysulfones and polyketones, polyvinyl chloride, polyvinylidene chloride, and, with a suitable choice of a high-index core material, also polyacrylonitrile or polyurethane.

In a particularly preferred embodiment of

Core-shell particles, the core consists of cross-linked polystyrene and the shell of a polyacrylate, preferably polyethyl acrylate, polybutyl acrylate, polymethyl methacrylate and / or a copolymer thereof.

Inverse with regard to the processability of the core-shell particles

It is opal structures when the wall material is made of a precursor

Solution results, an advantage if the weight ratio of core to

Sheath in the range from 20: 1 to 1.4: 1, preferably in the range from 6: 1 to

2: 1 and particularly preferably in the range 5: 1 to 3.5: 1. Will the

Wall of the inverse opal structure formed by sheath polymers, it is preferred if the weight ratio of core to mantel in the range from 5: 1 to 1:10, in particular in the range from 2: 1 to 1: 5 and particularly preferably in the range is less than 1: 1.

The core-shell particles which can be used according to the invention can be produced by various processes.

A preferred way of obtaining the particles is a process for the production of core-shell particles, by a) surface treatment of monodisperse cores, and b) application of the shell from organic polymers to the treated cores. In a process variant, the monodisperse cores are obtained in a step a) by emulsion polymerization.

In a preferred process variant, a crosslinked polymeric intermediate layer is preferably applied to the cores in step a) Emulsion polymerization or applied by ATR polymerization, which preferably has reactive centers to which the jacket can be covalently attached. ATR-Polymerization stands here for Atomic Transfer Radicalic Polymerization, as for example in K. Matyjaszewski, Practical Atom Transfer Radical Polymerization, Polym. Mater. Be. Closely. 2001, 84. Encapsulation of inorganic materials using ATRP is described, for example, in T. Werne, TE Patten, Atom Transfer Radical Polymerization from Nanoparticles: A Tool for the Preparation of Well-Defined Hybrid Nanostructures and for Understanding the Chemistry of Controlled / "Living" Radical Polymerization from Surfaces, J. Am. Chem. Soc. 2001, 123, 7497-7505 and WO 00/11043. The implementation of both this method and the implementation of emulsion polymerizations are familiar to the person skilled in the art of polymer production and are described, for example, in the abovementioned references.

The liquid reaction medium in which the polymerizations or copolymerizations can be carried out consists of the solvents, dispersants or diluents customarily used in polymerizations, in particular in processes of emulsion polymerization. The selection is made in such a way that the emulsifiers used to homogenize the core particles and shell precursors can develop sufficient effectiveness. Aqueous media, in particular water, are favorable as a liquid reaction medium for carrying out the process according to the invention.

To initiate the polymerization, for example, are suitable

Polymerization initiators that decompose either thermally or photochemically, form radicals, and thus trigger the polymerization. Among the thermally activatable polymerization initiators, preference is given to those between 20 and 180 ° C., in particular between 20 and

Disintegrate at 80 ° C. Polymerization initiators are particularly preferred Peroxides, such as dibenzoyl peroxide, di-tert-butyl peroxide, peresters,

Percarbonates, perketals, hydroperoxides, but also inorganic

Peroxides, such as H ₂ O ₂ , salts of peroxosulfuric acid and peroxodisulfuric acid, azo compounds, boralkyl compounds and homolytically decomposing hydrocarbons. The initiators and / or

Photoinitiators, which are used depending on the requirements of the polymerized material in amounts between 0.01 and 15 wt .-%, based on the polymerizable components can be used singly or, more advantageously to exploit synergistic effects, in combination ^{w ι} applied together. In addition, redox systems are used, such as salts of peroxodisulfuric acid and peroxosulfuric acid in combination with low-valent sulfur compounds, especially ammonium peroxodisulfate in combination with 5 sodium dithionite.

Appropriate processes have also been described for the production of polycondensation products. Thus, it is possible to disperse the starting materials for the production of polycondensation products in inert liquids and, preferably with low molecular weight reaction products such as water or - e.g. B. when using dicarboxylic acid di-lower alkyl esters for the production of polyesters or polyamides - lower alkanols to condense. 5

Polyaddition products are obtained analogously by reaction with compounds which have at least two, preferably three reactive groups, such as, for. B. epoxy, cyanate, isocyanate, or isothiocyanate 0 groups, with compounds that carry complementary reactive groups. For example, isocyanates react with alcohols to form urethanes, with amines to form urea derivatives, while epoxides react with these complementaries to form hydroxyethers or hydroxyamines. Like the polycondensation reactions, polyaddition reactions can advantageously be carried out in an inert solvent or dispersant. It is also possible to use aromatic, aliphatic or mixed aromatic-aliphatic polymers, e.g. B. polyester, polyurethane,

Polyamides, polyureas, polyepoxides or solution polymers, in a dispersant, such as. B. in water, alcohols, tetrahydrofuran,

To disperse or emulsify hydrocarbons (secondary dispersion) and to condense, crosslink and cure in this fine distribution.

^{, J} As a rule, dispersion aids are used to produce the stable dispersions required for these polymerization-polycondensation or polyaddition processes.

5 Water-soluble, high-molecular organic compounds with polar groups, such as polyvinyl pyrrolidone, copolymers of vinyl propionate or acetate and vinyl pyrrolidone, partially saponified copolymer list of an acrylic ester and acrylonitrile, polyvinyl alcohols with different residual acetate content, cellulose ethers, 0 gelatin, block copolymers are preferably used as dispersants , modified starch, low molecular weight, carbon and / or sulfonic acid group-containing polymers or mixtures of these substances.

⁵ Particularly preferred protective colloids are polyvinyl alcohols with a residual acetate content of less than 35, in particular 5 to 39 mol% and / or vinylpyrrolidone-oleyl propionate copolymers with a vinyl ester content of less than 35, in particular 5 to 30% by weight. 0

Nonionic or ionic emulsifiers, optionally also as a mixture, can be used. Preferred emulsifiers are, where appropriate, ethoxylated or propoxylated, longer-chain alkanols or alkylphenols with different degrees of ethoxylation or propoxylation (for example adducts with 0 to 50 mol of alkylene oxide) or their neutralized based, sulfated, sulfonated or phosphated derivatives. Neutralized dialkylsulfosuccinic acid esters or alkyldiphenyloxide disulfonates are also particularly suitable.

Combinations of these emulsifiers with the protective colloids mentioned above are particularly advantageous since they give particularly finely divided dispersions.

Special processes for producing monodisperse polymer particles have also already been described in the literature (for example BRC Backus, RC Williams, J. Appl, Physics 19, p. 1186, (1948) and can advantageously be used in particular for producing the cores all that is required is to ensure that the polymers are as uniform as possible, in particular by selecting suitable emulsifiers and / or protective colloids or corresponding amounts of these compounds.

By setting the reaction conditions, such as temperature, pressure,

The reaction time and the use of suitable catalyst systems, which influence the degree of polymerization in a known manner, and the selection of the monomers used for their preparation - according to type and proportion - can be set to the desired combinations of properties of the required polymers. The particle size can be set, for example, via the selection and amount of the initiators and other parameters, such as the reaction temperature. The appropriate setting of these parameters does not pose any difficulties for the person skilled in the field of polymerization.

Monomers which lead to polymers with a high refractive index are generally those which either have aromatic partial structures or those which have heteroatoms with a high atomic number, such as, for example, B. halogen Atoms, in particular bromine or iodine atoms, sulfur or metal ions, ie have atoms or groupings of atoms which increase the polarizability of the polymers.

Polymers with a low refractive index are accordingly made

Monomers or monomer mixtures are obtained which do not contain the mentioned partial structures and / or atoms with a high atomic number or only in a small proportion.

^{ι u} An overview of the refractive indices of various common homopolymers can be found e.g. B. in Ulimann's Encyclopedia of Industrial Chemistry, 5th edition, volume A21, page 169. Examples of free-radically polymerizable monomers which lead to polymers with a high refractive index are:

Group a): styrene, alkyl-substituted styrenes in the phenyl nucleus, α-methylstyrene, mono- and dichlorostyrene, vinylnaphthalene, isopropenylnaphthalene, isopropenylbiphenyl, vinylpyridine, isopropenylpyridine, vinylcarbazole, vinylanthracene, N-benzylmethacrylamide, p-hydroxymethacrylamide, p-hydroxymethacrylamide.

Group b): Acrylates which have aromatic side chains, such as, for. B. Phenyl (meth) acrylate (= abbreviation for the two compounds phenyl acrylate and phenyl methacrylate), phenyl vinyl ether, benzyl (meth) acrylate, benzyl vinyl ether, and compounds of the formulas:

In the above formulas and in the formulas below, 5 are to improve clarity and simplify the spelling Carbon chains are only represented by the bonds between the carbon atoms. This notation corresponds to the representation of aromatic cyclic compounds, z. B. the benzene is represented by a hexagon with alternating single and double bonds.

Furthermore, such compounds are suitable which contain sulfur bridges in parts of oxygen bridges, such as, for. B .:

In the above formulas, R represents hydrogen or methyl. The phenyl rings of these monomers can carry further substituents. Such substituents are suitable for modifying the properties of the polymers produced from these monomers within certain limits. They can therefore be used in a targeted manner, in particular in order to optimize the properties of the moldings according to the invention that are relevant in terms of application technology.

Suitable substituents are in particular halogen, NO ₂ , alkyls with one to twenty carbon atoms, preferably methyl, alkoxides with one to twenty carbon atoms, carboxyalkyls with one to twenty carbon atoms, carbonylalkyls with one to twenty carbon atoms, or - OCOO alkyls with one to twenty carbon atoms. The alkyl chains of these radicals can in turn optionally be substituted or by double-bonded ones Heteroatoms or assemblies, such as. B. -O-, -S-, -NH-, -COO-, -OCO- or -OCOO- in non-adjacent positions.

Group c): monomers which have heteroatoms, such as, for. B. vinyl chloride, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, acrylamide and methacrylamide or organometallic compound, such as. B.

Group d): The refractive index of polymers can also be increased by polymerizing in monomers containing carboxylic acid groups and converting the “acidic” polymers thus obtained into the corresponding salts with metals of higher atomic weight, such as, for example, B. preferably with K, Ca, Sr, Ba, Zn, Pb, Fe, Ni, Co, Cr, Cu, Mn, Sn or Cd.

The abovementioned monomers, which make a high contribution to the refractive index of the polymers produced therefrom, can be homopolymerized or copolymerized with one another. They can also be copolymerized with a certain proportion of monomers that make a lower contribution to the refractive index. Such copolymerizable monomers with a lower refractive index contribution are, for example, acrylates, methacrylates, vinyl ethers or vinyl esters with purely aliphatic radicals.

In addition, all bifunctional or polyfunctional compounds which are compatible with the above can also be used as crosslinking agents for producing crosslinked polymer cores from free-radically produced polymers mentioned monomers are copolymerizable, or they can subsequently react with the polymers with crosslinking.

In the following, examples of suitable crosslinkers are presented, which are divided into groups for systematization:

Group 1: bisacrylates, bismethacrylates and bisvinyl ethers of aromatic or aliphatic di- or polyhydroxy compounds, in particular of butanediol (butanediol di (meth) acrylate, butanediol bis-vinyl ether), hexanediol (hexanediol di (meth) acrylate, hexanediol bis- vinyl ether), pentaerythritol, hydroquinone, bis-hydroxyphenylmethane, bis-hydroxyphenyl ether, bis-hydroxymethyl-benzene, bisphenol A or with ethylene oxide spacers, propylene oxide spacers, or mixed ethylene oxide-propylene oxide spacers.

Other crosslinkers in this group are e.g. B. di- or polyvinyl compounds, such as divinybenzene, or also methylene-bisacrylamide, triallyl cyanurate, divinylethylene urea, trimethylolpropane tri- (meth) acrylate, trimethylolpropane tricinyl ether, pentaerythritol tetra (meth) acrylate, pentaerythritol tetra vinyl ethers, and crosslinkers with two or more different reactive ends, such as. B. (Meth) allyl (meth) acrylates of the formulas:

(where R is hydrogen or methyl).

Group 2: reactive crosslinking agents which have a crosslinking action, but mostly have a postcrosslinking action, e.g. B. with heating or drying, and which are copolymerized into the core or shell polymers as copolymers. Examples include: N-methylol- (meth) acrylamide, acrylamidoglycolic acid, and their ethers and / or esters with C ₁ to C ₆ alcohols, diacetone acrylamide (DAAM), glycidyl methacrylate (GMA), methacryloyloxypropyltrimethoxysilane (MEMO), vinyl trimethoxysilane, m-isopropenyl benzyl isocyanate (TMI).

Group 3: Carboxylic acid groups which have been incorporated into the polymer by copolymerization of unsaturated carboxylic acids are crosslinked like polyvalent metal ions. Acrylic acid, methacrylic acid, maleic anhydride, itaconic acid and veneric acid are preferably used as unsaturated carboxylic acids. Mg, Ca, Sr, Ba, Zn, Pb, Fe, Ni, Co, Cr, Cu, Mn, Sn, Cd are suitable as metal ions. Ca, M g and Zn, Ti and Zr are particularly preferred. In addition, monovalent metal ions, such as Well or K.

Group 4: Post-crosslinked additives. This is understood to mean additives which are functionalized to a degree or higher and which react irreversibly with the polymer (by addition or preferably condensation reactions) to form a network. Examples of these are compounds which have at least two of the following reactive groups per molecule: epoxy, aziridine, isocyanate acid chloride, carbodiimide or carbonyl groups, furthermore, for. B. 3.4-Dihydroxy-imidazolinone and its derivatives (®Fixapret @ brands from BASF).

As already explained above, postcrosslinkers with reactive groups, such as. B. epoxy and isocyanate groups, complementary, reactive G groups in the polymer to be crosslinked. For example, isocyanates react with alcohols to form urethanes, with amines to form urea derivatives, while epoxides react with these complementary groups to form hydroxyethers or hydroxyamines. Post-crosslinking is also understood to mean photochemical curing, an oxidative, or an air- or moisture-induced curing of the systems.

The above-mentioned monomers and crosslinking agents can be combined with one another in a targeted manner and (co) polymerized, so that an optionally crosslinked (co) polymer is obtained with the desired refractive index and the required stability criteria and mechanical properties.

It is also possible to use other common monomers, e.g. As acrylates, methacrylates, vinyl esters, butadiene, ethylene or styrene, additionally copolymerize, for example to adjust the glass transition temperature or the mechanical properties of the core and / or shell polymers as required.

According to the invention, it is also preferred if the coating of organic polymers is applied by grafting, preferably by emulsion polymerization or ATR polymerization. The methods and monomers described above can be used accordingly.

The following examples are intended to explain the invention in more detail without limiting it.

Examples

Example 1: Production of the core-shell particles

In a 5 l double-jacket reactor heated to 75 ° C. with a double propeller stirrer, argon protective gas inlet and reflux condenser, a receiver is heated to 4 ° C. and consists of 1519 g demineralized water, 2.8 g 1,4-butanediol diacrylate (MERCK), 25.2 g of styrene (from MERCK) and 1030 mg of sodium dodecyl sulfate (from MERCK) are added and dispersed with vigorous stirring. Immediately afterwards, the reaction is dissolved by successively injecting 350 mg of sodium dithionite (MERCK), 1.75 g of ammonium peroxodisulfate (MERCK) and again 350 mg of sodium dithionite (MERCK), each in about 20 ml of water. started. The injection takes place by means of disposable syringes. After 20 minutes, a monomer emulsion consisting of 56.7 g of 1,4-butanediol diacrylate (from MERCK), 510.3 g of styrene (from MERCK), 2.625 g of sodium dodecyl sulfate (from MERCK), 0.7 g of KOH and 770 g of water are metered in continuously over a period of 120 min via the wobble piston pump.

The reactor contents are stirred for 30 minutes without further addition. Then a second monomer emulsion consisting of 10.5 g allyl methacrylate (MERCK), 94.50 g methyl methacrylate (MERCK), 0.525 g sodium dodecyl sulfate (MERCK) and 140 g water over a period of 30 minutes over the Swash piston pump metered in continuously. After about 15 minutes, 350 mg of ammonium peroxodisulfate (from MERCK) are added and the mixture is then stirred for a further 15 minutes.

Finally, a third monomer emulsion consisting of 200 g of ethyl acrylate (from MERCK), 0.550 g of sodium dodecyl sulfate (from MERCK) and 900 g of water continuously over a period of 240 min

Swash piston pump metered in. The mixture is then stirred for 120 minutes.

Before and after each introduction of monomer emulsions and after

The template is introduced into the double jacket reactor as a protective gas cushion for about one minute.

The next day, the reactor is heated to 95 ° C. and a steam distillation is carried out in order to remove residual, unreacted monomers from the latex dispersion.

The result is a dispersion of core-shell particles in which the shell has a weight fraction of approx. 22%. The polystyrene core is cross-linked, the intermediate layer is also cross-linked (p (MMA-co-ALMA)) and is used to graft the jacket from uncrosslinked ethyl acrylate.

Example 2: Production of an inverse opal structure

To form the templating structure, i.e. H. When the core-shell particles are organized in a dense spherical packing, 5 g of the latex dispersion are poured into a flat glass bowl with a diameter of 7 cm and dried in the air, producing colorful, iridescent tinsel.

Such a tinsel is evacuated in a round bottom flask with the oil rotary vane pump. A precursor solution consisting of 5 ml of tetra-n-butyl orthotitanate in 5 ml of absolute ethanol is then added in a static vacuum so that the dissolved precursor, driven by capillary forces, can penetrate the cavities of the template. An argon cushion is placed over the solution in which the impregnated template is located. This arrangement is left static for a few hours before the impregnated tinsel in the argon protective gas stream removed and calcined in a corundum boat in a tube furnace at 500 ° C.

As a result, inverse structures are obtained which consist of densely packed cavities in TiO ₂ (FIG. 1).

pictures:

Figure 1: Scanning electron micrograph of the inverse opal structure made of titanium dioxide (Example 2). The regular arrangement of the identical hollow volumes can be seen over a large area. The hollow volumes are connected to one another by channels, which results in the possibility of filling via the liquid or gas phase

Claims

claims

1. Use of core-shell particles, the shell of which forms a matrix and whose core is essentially solid and has an essentially monodisperse size distribution as a template for producing inverse opal structures.

2. Use according to claim 1, characterized in that in the core-shell particles, the shell is connected to the core via an intermediate layer.

3. Use according to at least one of the preceding claims, characterized in that in the core-shell particles the weight ratio of core to shell in the range from 20: 1 to 1,

4: 1, preferably in the range from 6: 1 to 2: 1 and particularly preferably in the range from 5: 1 to 3.5: 1.

Use according to at least one of the preceding claims, characterized in that in the core-shell particles the shell consists of essentially uncrosslinked organic polymers which are preferably grafted onto the core via an at least partially crosslinked intermediate layer.

5. Use according to at least one of the preceding claims, characterized in that in the core-shell particles the core consists of an organic polymer, which is preferably crosslinked.

6. Use according to at least one of claims 1 to 4, characterized in that in the core-shell particles, the core consists of an inorganic material and the weight ratio from core to jacket is preferably in the range from 5: 1 to 1:10, in particular in the range from 2: 1 to 1: 5 and particularly preferably in the range less than 1: 1.

7. Process for the production of inverse opal structures, characterized in that a) a dispersion of core-shell particles, the shell of which forms a matrix and the core of which is essentially solid, is dried, ^ι b) optionally one or more precursors are more suitable

Wall materials are added and, c) the cores are subsequently removed.

5 8. A method for producing inverse opal structures according to claim 7, characterized in that in a step a2) the application of a mechanical force to a pre-dried mass of the core-shell particles takes place in step a1).

0

9. A method for producing inverse opal structures according to claim 8, characterized in that the application of a mechanical force by uniaxial pressing or during an injection molding process or during a transfer pressing process 5 or during a (co) extrusion or during a

Calendering process or during a blowing process.

10. The method for the production of inverse o pal structures according to at least one of claims 7 to 9, characterized in that the precursor in step b) is a solution of an ester of an inorganic ortho acid with a lower alcohol.

11. A method for the production of inverse o pal structures according to at least 5 one of claims 7 to 10, characterized in that step b) is carried out at reduced pressure, preferably in a static vacuum with p <1 mbar.

12. A method for producing inverse o pal structures according to at least one of the preceding claims, characterized in that step c) is a calcination, preferably at temperatures above 200 ° C, particularly preferably above 400 ° C.

n ^u 13. A method for for creation H i O nverser palstrukturen according to at least one of claims 7 to 11, characterized in that it preferably is to HF etching to an etching process in step c). 5

14. A method for the production of inverse opal structures according to at least one of the preceding claims, characterized in that the core-shell particles are removed in step c).

0

5

0

5