EP1709092A1

EP1709092A1 - Use of statistical copolymers

Info

Publication number: EP1709092A1
Application number: EP04803997A
Authority: EP
Inventors: Matthias Koch; Victor Khrenov; Markus Klapper; Klaus Muellen
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2004-01-27
Filing date: 2004-12-17
Publication date: 2006-10-11
Also published as: TW200540191A; WO2005070979A1; KR20070004599A; CA2554335A1; JP2007519786A

Abstract

The invention relates to the use of statistical copolymers, comprising at least one structural unit with hydrophobic groups and at least one structural unit with hydrophilic groups, as emulsifiers, in particular, for the synthesis of nanoparticles and a production method for such particles with the steps a) production of an inverse emulsion containing one or several water-soluble precursors for the nanoparticles, or a melt, from a statistical copolymer of one monomer with hydrophobic groups and at least one monomer with hydrophilic groups and b) the generation of particles.

Description

Use of statistical copolymers

The invention relates to the use of statistical copolymers as emulsifiers, in particular in the synthesis of nanoparticles, and to production processes for such particles.

The incorporation of inorganic nanoparticles in a polymer matrix can not only the mechanical properties such. B. impact strength, affect the matrix, but also changes their optical properties, such as wavelength-dependent transmission, color (absorption spectrum) and refractive index. Particle size plays an important role in mixtures for optical applications because the addition of a substance with a refractive index that differs from the refractive index of the matrix inevitably leads to light scattering and ultimately to opacity. The decrease in the intensity of radiation of a defined wavelength when passing through a mixture shows a strong dependence on the diameter of the inorganic particles.

The development of suitable nanomaterials for dispersion in polymers requires not only the control of the particle size, but also the surface properties of the particles. A simple mixing (eg by extrusion) of hydrophilic particles with a hydrophobic polymer matrix leads to an uneven distribution of the particles throughout the polymer and also to their aggregation. For the homogeneous incorporation of inorganic particles into polymers, their surface must therefore be at least hydrophobically modified. In addition, the nanoparticulate materials in particular show a great tendency to form agglomerates, which remain even after a subsequent surface treatment. Surprisingly, it has now been found that nanoparticles can be precipitated directly from emulsions with a suitable surface modification almost without agglomerates if certain statistical copolymers are used as emulsifiers.

A first subject of the present invention is therefore the use of statistical copolymers containing at least one structural unit with hydrophobic residues and at least one structural unit with hydrophilic residues as an emulsifier, in particular in the synthesis of nanoparticles from emulsions.

Another object of the present invention is a method for producing polymer-modified nanoparticles, which is characterized in that in step a) an inverse emulsion containing one or more water-soluble precursors for the nanoparticles or a melt, with the aid of a statistical copolymer of at least one Monomer with hydrophobic residues and at least one monomer with hydrophilic residues is produced and particles are generated in a step b).

The emulsion technique for the production of nanoparticles is known in principle. This is how M. P. describes Pileni; J. Phys. Che. 1993, 97, 6961- 6973 the production of semiconductor particles such as CdSe, CdTe and ZnS in inverse emulsions.

However, the syntheses of the inorganic materials often require high salt concentrations of precursor materials in the emulsion, the concentration additionally fluctuating during the reaction. Low molecular weight surfactants react to such high salt concentrations that the stability of the emulsions is at risk (Paul Kent and Brian R. Saunders; Journal of Colloid and Interface Science 242, 437-442 (2001)). In particular, the control of the Particle sizes are only possible to a limited extent (M.-H. Lee, CY Tai, CH Lu, Korean J. Chem. Eng. 16, 1999, 818-822).

K. Landfester (Adv. Mater. 2001, 13, No. 10, 765- 768) suggests the use of high molecular weight surfactants (PEO-PS block copolymers) in combination with ultrasound to produce nanoparticles in the particle size range from about 150 to about 300 nm from metal salts.

The selection of statistical copolymers from at least one monomer with hydrophobic residues and at least one monomer with hydrophilic residues has now made it possible to provide emulsifiers which enable the production of inorganic nanoparticles from inverse emulsions while controlling the particle size and particle size distribution. At the same time, the use of these new emulsifiers enables the nanoparticles to be isolated from the dispersions almost free of agglomerates, since the individual particles form a polymer coating immediately. In addition, the nanoparticles obtainable with this method can be dispersed particularly easily and uniformly in polymers, with in particular an undesirable impairment of the transparency of such polymers in visible light being largely avoided.

The statistical copolymers to be preferably used according to the invention show a weight ratio of structural units with hydrophobic radicals to structural units with hydrophilic radicals in the statistical copolymers in the range 1: 2 to 500: 1, preferably in the range 1: 1 to 100: 1 and particularly preferably in the range 7: 3 to 10: 1. The weight-average molecular weight of the statistical copolymers is usually in the range from M _w = 1000 to 1,000,000 g / mol, preferably in the range from 1,500 to 100,000 g / mol and particularly preferably in the range 2,000 to 40,000 g / mol.

It has been shown that in particular copolymers which correspond to formula I, wherein

X and Y correspond to the residues of conventional nonionic or ionic monomers and R ¹ stands for hydrogen or a hydrophobic side group, preferably selected from the branched or unbranched alkyl residues with at least 4 carbon atoms in which one or more, preferably all, H atoms are replaced by fluorine atoms , and R ² stands for a hydrophilic side group, which preferably has a phosphonate, sulfonate, polyol or polyether radical, and wherein within one molecule -XR ¹ and -YR ^{2 can} each have several different meanings, the inventive Meet requirements in a special way.

Polymers in which —YR ² stands for a betaine structure are particularly preferred according to the invention.

Polymers of the formula I in which X and Y independently of one another are - O-, -C (= 0) -O-, -C (= 0) -NH-, - (CH ₂ ) _{n are} again particularly preferred -, phenyl, naphthyl or pyridiyl. Polymers in which at least one structural unit contains at least one quaternary nitrogen atom can also be used, where R ² preferably represents a side group - (CH2) _m - (N ⁺ (CH ₃ ) 2) - (CH2) n-S0 ₃ - or a side group - (CH ₂ ) m- (N ⁺ (CH ₃ ) ₂ ) - (CH ₂ ) n-P0 ₃ ^{2 "} , where m stands for an integer from the range from 1 to 30, preferably from the range 1 to 6, particularly preferably 2, and n stands for an integer from the range from 1 to 30, preferably from the range 1 to 8, in particular preferably 3, use advantageously.

Statistical copolymers to be used with particular preference can be prepared according to the following scheme:

The desired amounts of lauryl methacrylate (LMA) and dimethylaminoethyl methacrylate (DMAEMA) are free-radically copolymerized by adding AIBN using known methods, preferably in toluene. A betaine structure is then obtained by reacting the amine with 1,3-propanesultone using known methods.

Alternative preferred copolymers may contain styrene, vinylpyridone, vinylpyridine, halogenated styrene or methoxystyrene, these examples being no limitation. In another likewise preferred embodiment of the present invention, polymers are used which are characterized in that at least one structural unit is an oligomer or polymer, preferably a macromonomer, polyether, Polyolefins and polyacrylates are particularly preferred as macromonomers.

Water-soluble metal compounds, preferably silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron, yttrium and / or zirconium compounds, can be used as precursors for the inorganic nanoparticles Precursors, preferably for the production of corresponding metal oxide particles, are preferably reacted with an acid or alkali. Mixed oxides can be obtained in a simple manner by suitable mixing of the corresponding precursors. The choice of suitable precursors is not difficult for the person skilled in the art; all compounds are suitable which are suitable for precipitating the corresponding target compounds from aqueous solution. An overview of suitable precursors for the production of oxides is, for example, in Table 6 in K. Osseo-Asare "Microemulsion-mediated Synthesis of nanosize Oxide Materials" in: Kumar P., Mittal KL, (editors), Handbook of microemulsion science and technology, New York: Marcel Dekker, Inc., pp. 559-573, the content of which expressly belongs to the disclosure content of the present application.

Hydrophilic melts can also serve as precursors for nanoparticles in the sense of this invention. In this case, a chemical conversion to produce the nanoparticles is not absolutely necessary.

In particular, alkali metal or alkaline earth metal silicates, preferably sodium silicates, can also be reacted as precursors with acid or alkali to give silicon dioxide. In likewise preferred embodiments of the present invention, at least one soluble compound of a noble metal, preferably silver nitrate, is converted to the metal with a reducing agent, preferably citric acid.

To produce nanoparticulate metal sulfides, which is also preferred according to the invention, a soluble metal compound, preferably a soluble Pb, Cd, Zn compound, is reacted with hydrogen sulfide to give the metal sulfide.

In another embodiment of the present invention, a soluble metal compound, such as preferably e.g. B. calcium chloride, implemented with carbon dioxide to a nanoparticulate metal carbonate.

Nanoparticles which are particularly preferably produced are those which essentially consist of oxides or hydroxides of silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron, yttrium and / or zirconium.

The particles preferably have an average particle size determined by means of dynamic light scattering or

Transmission electron microscope from 3 to 200 nm, in particular from 20 to 80 nm and very particularly preferably from 30 to 50 nm. In particularly preferred embodiments of the present invention, the distribution of particle sizes is narrow, i.e. the fluctuation range is less than 100% of the mean, particularly preferably a maximum of 50% of the mean.

In the sense of using these nanoparticles for UV protection in polymers, it is particularly preferred if the nanoparticles are a Have absorption maximum in the range 300-500 nm, preferably in the range up to 400 nm, particularly preferred nanoparticles absorbing radiation, particularly in the UV-A range.

The emulsion process can be carried out in various ways:

As already stated, particles are usually produced in step b) by reacting the precursors or by cooling the melt. Depending on the process variant selected, the precursors can be reacted with an acid, an alkali, a reducing agent or an oxidizing agent.

To generate particles in the desired particle size range, it is particularly advantageous if the droplet size in the emulsion is in the range from 5 to 500 nm, preferably in the range from 10 to 200 nm. The droplet size in the given system is adjusted in the manner known to the person skilled in the art, the oil phase being individually matched to the reaction system by the person skilled in the art. For the production of ZnO particles, for example, toluene and cyclohexane have proven to be an oil phase.

In certain cases it can be helpful here if, in addition to the statistical copolymer, a further co-emulsifier, preferably a non-ionic surfactant, is used. Preferred co-emulsifiers are optionally ethoxylated or propoxylated, longer-chain alkanols or alkylphenols with different degrees of ethoxylation or propoxylation (e.g. adducts with 0 to 50 mol of alkylene oxide).

Dispersing aids can also be used advantageously, preferably 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, gelatin, block copolymers, modified starch, low molecular weight, carbon and / or sulfonic acid groups or mixtures of these substances can be used.

Particularly preferred protective colloids are polyvinyl alcohols with a residual acetate content of less than 40, in particular 5 to 39 mol% and / or vinylpyrrolidone-aminopropionate copolymers with a vinyl ester content of less than 35, in particular 5 to 30% by weight.

By setting the reaction conditions, such as temperature, pressure and reaction time, the desired combinations of properties of the required nanoparticles can be set. The corresponding. Setting these parameters presents no difficulties for the person skilled in the art. For example, normal pressure and room temperature can be used for many purposes.

In a preferred process variant, a second emulsion in which a reaction partner for the precursors is emulsified is mixed with the precursor emulsion from step a) in step b). This 2-emulsion process allows the production of particles with a particularly narrow particle size distribution. It can be particularly advantageous if the two emulsions are mixed together by the action of ultrasound.

In another, likewise preferred process variant, a precipitant is added to the precursor emulsion in step b) which is soluble in the continuous phase of the emulsion. The precipitation then takes place by diffusing the precipitant into the Micelles containing precursor. For example, titanium dioxide particles can be obtained in this way by diffusing pyridine in micelles containing titanyl chloride or silver particles by diffusing long-chain aldehydes in micelles containing silver nitrate.

The nanoparticles according to the invention are used in particular in polymers. Polymers into which the nanoparticles according to the invention can be readily incorporated are in particular polycarbonate (PC), polyethylene terephthalate (PETP), polyimide (PI), polystyrene (PS), polymethyl methacrylate (PMMA) or copolymers which contain at least a proportion of one of the polymers mentioned.

Incorporation can be carried out by customary methods for the production of polymer preparations. For example, that

Polymer material with nanoparticles according to the invention, preferably in an extruder or kneader, are mixed.

Depending on the polymer used, kneaders can also be used.

A particular advantage of the particles according to the invention is that for the homogeneous distribution of the particles in the

Polymer only a small compared to the prior art

Energy input is required.

The polymers can also be dispersions of

Polymers, such as paints. Here you can

Incorporation is carried out by usual mixing processes.

The polymer preparations according to the invention containing the nanoparticles are also particularly suitable for coating surfaces. So that the surface or that under the Protect coating material, for example, from UV radiation.

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

Examples

Example 1: Synthesis of Macro Surfactants.

The first step involves the synthesis of a statistical copolymer of dodecyl methacrylate (lauryl methacrylate; LMA) and dimethylaminoethyl methacrylate (DMAEMA). Control of the molecular weight can be achieved by adding mercaptoethanol. The copolymer thus obtained is modified with 1,3-propane sultones to add saturated groups.

For this purpose, 7 g of LMA and DMAEMA, in an amount corresponding to Table 1 below, are initially introduced into 12 g of toluene and polymerized under free radicals under argon at 70 ° C. after the start of the reaction by adding 0.033 g of AIBN in 1 ml of toluene. The chain growth can be controlled by adding 2-mercaptoethanol (see Table 1). The crude polymer is washed, freeze-dried and then with 1,3-propanesultone, as in V. Butun, CE Bennett, M. Vamvakaki, AB Löwe, NC Billingham, SP Armes, J. Mater. Chem., 1997, 7 (9), 1693-1695.

The characterization of the resulting polymers can be found in Table 1.

Table 1: Amounts of monomers used and characterization of the polymers obtained

Example 2: Precipitation of ZnO particles

ZnO particles are precipitated using the following method: 1. Preparation of an inverse emulsion of an aqueous solution of 0.4 g of Zn (AcO) ₂ * 2H ₂ 0 in 1, 1 g of water (emulsion 1) and 0.15 g of NaOH in 1 , 35g water (emulsion 2) using ultrasound. Emulsion 1 and Emulsion 2 each contain 150 mg of a random copolymer E1 - E5 from Table 1. 2. Ultrasound treatment of the mixture of Emulsion 1 and Emulsion 2 and subsequent drying. 3. Purification of sodium acetate by washing the solid obtained with water. 4. Drying and redispersion of the powder functionalized by the emulsifier on the surface by stirring in toluene.

FT-IR spectroscopy and X-ray diffraction demonstrate the formation of ZnO. Furthermore, no reflections of sodium acetate are visible in the X-ray diagram. Thus, example 2 leads to a product consisting of the synthesized macro surfactant and zinc oxide particles.

Comparative Example 2a: Use of the ABIL EM 90 ® emulsifier

The implementation according to Example 2 with the commercially available emulsifier, ABIL EM 90 ^® (Cetyl Dimethicone copolyol, Fa. Goldschmidt) instead of the random copolymer of Example 1 does not lead to a stable emulsion. The particles obtained have diameters between 500 and 4000 nm.

Example 3: Precipitation of silicon dioxide

The precipitation of Si0 ₂ particles is carried out according to the following method: I. Production of an inverse emulsion of an aqueous solution of Na2Si0 ₃ (emulsion 1) and H ₂ S0 ₄ (emulsion 2) by means of ultrasound (concentrations according to Table 2). 2. Ultrasound treatment of the mixture of emulsion 1 and emulsion 2 and subsequent drying. 3. Purification by washing the solid obtained with water. 4. Drying and redispersion of the powder obtained. FT-IR spectroscopy and X-ray diffraction demonstrate the formation of SiO ₂ and the absence / absence of sodium silicate. Thus, the step leads to a product consisting of the synthesized macro surfactant and silica particles.

Table 2: Composition of the emulsions and characterization of the products Example 4: Polymer preparation

A dispersion of the particles from Example 2-E1 in PMMA lacquer is produced by mixing, applied to glass substrates and dried. The ZnO content after drying is 10% by weight. The films show a barely perceptible cloudiness. Measurements with a UV-VIS spectrometer confirm this impression. Depending on the layer thickness, the sample shows the following absorption values (the percentage of the incident light that is lost in transmission is indicated)

Layer thickness UV-A (350nm) VIS (400 nm)

1.2μm 35% 4%

1.6μm 40% 5%

2.2μm 45% 7%

Comparison:

(ZnO (reinst., Fa. Merck) in PMMA lacquer as above)

2μm 64% 46%

Claims

claims

1. Use of statistical copolymers containing at least one structural unit with hydrophobic radicals and at least one structural unit with hydrophilic radicals as an emulsifier.

2. Use according to claim 1, characterized in that the copolymers are used as an emulsifier in the synthesis of nanoparticles from emulsions.

3. Use according to at least one of the preceding claims, characterized in that the weight ratio of structural units with hydrophobic radicals to structural units with hydrophilic radicals in the statistical copolymers in the range 1: 2 to 500: 1, preferably in the range 1: 1 to 100: 1 and particularly preferably in the range 7: 3 to 10: 1.

4. Use according to at least one of the preceding claims, characterized in that the weight-average molecular weight of the statistical copolymers in the range from M _w = 1000 to 1 000 000 g / mol, preferably in the range from 1 500 to 100 000 g / mol and particularly preferably is in the range 2,000 to 40,000 g / mol.

5. Use according to at least one of the preceding claims, characterized in that the copolymers correspond to formula I, wherein

X and Y correspond to the residues of conventional nonionic or ionic monomers and R ¹ stands for hydrogen or a hydrophobic side group, preferably selected from the branched or unbranched alkyl residues with at least 4 carbon atoms in which one or more, preferably all, H atoms are replaced by fluorine atoms may be, and R ² stands for a hydrophilic side group, which preferably has a phosphonate, sulfonate, polyol or polyether radical, and wherein within one molecule -XR ¹ and -YR ^{2 can} each have several different meanings.

6. Use according to claim 5, characterized in that X and Y independently of one another represent -O-, -C (= 0) -0-, -C (= 0) -NH-, - (CH ₂ ) n-, Phenylene or pyridiyl.

7. Use according to at least one of the preceding claims, characterized in that at least one structural unit contains at least one quaternary nitrogen atom, wherein R ² preferably represents a side group - (CH2) m- (N ⁺ (CH3)) - (CH2) n- S0 ₃ ^" or a side group - (CH ₂ ) m- (N ⁺ (CH3) 2) - (CH2) n-P0 ₃ ^2" , where m represents an integer from the range from 1 to 30, preferably from the Range 1 to 6, particularly preferably 2, and n stands for an integer from the range 1 to 30, preferably from the range 1 to 8, particularly preferably 3.

8. Use according to at least one of the preceding claims, characterized in that at least one structural unit is an oligomer or polymer, preferably a macromonomer, polyethers, polyolefins and polyacrylates being particularly preferred as macromonomers.

9. A process for the preparation of polymer-modified nanoparticles, characterized in that in a step a) an inverse emulsion containing one or more water-soluble precursors for the nanoparticles or a melt, with the aid of a statistical copolymer of at least one monomer with hydrophobic residues and at least one monomer is produced with hydrophilic residues and particles are produced in a step b).

10. The method according to claim 9, characterized in that the generation of particles in step b) is carried out by reacting the precursors or by cooling the melt.

11. The method according to claim 10, characterized in that the precursors are reacted with an acid, an alkali, a reducing or oxidizing agent.

12. The method according to claim 11, characterized in that a sodium silicate is reacted as a precursor with an acid or alkali to form silicon dioxide.

13. The method according to claim 11, characterized in that a soluble compound of a noble metal, preferably silver nitrate, is reacted with a reducing agent, preferably citric acid to the metal.

14. The method according to claim 11, characterized in that a soluble metal compound, preferably a soluble Pb, Cd, Zn compound is reacted with hydrogen sulfide to the metal sulfide.

15. The method according to claim 11, characterized in that a soluble metal compound, preferably calcium chloride, is reacted with carbon dioxide to form a metal carbonate.

16. The method according to at least one of the preceding claims, characterized in that the droplet size in the emulsion is in the range from 5 to 500 nm, preferably in the range from 10 to 200 nm.

17. The method according to at least one of the preceding claims, characterized in that in step b) a second emulsion in which a reaction partner for the precursors is emulsified is mixed with the precursor emulsion from step a).

18. The method according to claim 17, characterized in that the two emulsions are mixed together by the action of ultrasound.

19. The method according to at least one of the preceding claims, characterized in that the one or more precursors are selected from water-soluble metal compounds, preferably silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron -, Yttrium or zirconium compounds and the precursors are preferably reacted with an acid or alkali.

20. The method according to at least one of the preceding claims, characterized in that a co-emulsifier, preferably a non-ionic surfactant is used.