KR20070004599A - Use of statistical copolymers - Google Patents

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. ® KIPO & WIPO 2007

Description

Use of Statistical Copolymers {USE OF STATISTICAL COPOLYMERS}

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

Incorporation of inorganic nanoparticles into the polymer matrix not only affects the mechanical properties of the matrix, such as, for example, impact strength, but also optical properties such as, for example, wavelength-dependent transmission, color (absorption spectrum) and refractive index. Reform. In mixtures for optical applications, the particles play an important role, since the addition of materials with refractive indices different from the refractive index of the matrix inevitably results in light scattering and eventually light opacity. The decrease in wavelength irradiation intensity of the retreat when passing through the mixture indicates a high dependence on the diameter of the inorganic particles.

The development of nanoparticles suitable for dispersion in polymers requires control of the particle size as well as the surface properties of the particles. Simple mixing (eg, by extrusion) of the hydrophilic particles with the hydrophobic polymer matrix results in an inhomogeneous distribution of the particles throughout the polymer, and also agglomeration thereof. Thus, for homogeneous incorporation of the inorganic particles into the polymer, its surface must be at least hydrophobicly modified. In addition, nanoparticle materials are particularly prone to forming aggregates, which remain in subsequent surface treatments.

Surprisingly, it has now been found that when certain statistical copolymers are used as emulsifiers, the nanoparticles can be precipitated directly from the emulsion with little aggregates, with suitable surface modification.

Accordingly, the present invention first relates to the use of statistical copolymers containing one or more structural units containing hydrophobic radicals and one or more structural units containing hydrophilic radicals as emulsifiers, in particular in the synthesis of nanoparticles from emulsions. do.

The present invention further relates to a process for the preparation of polymer-modified nanoparticles, wherein in step a) an inverse emulsion containing at least one of the melt or the water soluble precursor of the nanoparticles contains hydrophobic radicals. Characterized in that it is prepared by a statistical copolymer of at least one monomer and at least one monomer containing a hydrophilic radical, and particles are prepared in step b).

Emulsion techniques for the production of nanoparticles are generally known. Thus, M.P. Pileni; J. Phys. Chem. 1993, 97, 6961-6973 describe the preparation of semiconductor particles such as CdSe, CdTe and ZnS in reverse emulsion.

However, the synthesis of inorganic materials often requires high salt concentrations of the precursor material in the emulsion, which concentrations change additionally during the reaction. Low molecular weight surfactants respond to such high salt concentrations and are therefore at risk for emulsion stability (Paul Kent and Brian R. Saunders; Journal of Colloid and Interface Science 242, 437-442 (2001)). In particular, particle size can only be controlled to a limited extent (M. H. Lee, C. Y. Tai, C. H. Lu, Korean J. Chem. Eng. 16,1999, 818-822).

K. Landfester (Adv. Mater. 2001, 13, No. 10, 765-768) is a high molecular weight surfactant (PEO-PS) for the production of nanoparticles of particle size ranging from about 150 to about 300 nm from metal salts. Block copolymers) together with ultrasound.

The selection of statistical copolymers of one or more monomers containing hydrophobic radicals and one or more monomers containing hydrophilic radicals, emulsifiers which now facilitate the preparation of inorganic nanoparticles from inverse emulsions, with control of particle size and particle-size distribution To make available. At the same time, the use of these novel emulsifiers makes it possible to isolate the nanoparticles from the dispersion substantially without aggregates since each particle is formed directly with the polymer coating. In addition, the nanoparticles obtainable in this way can be particularly easily and homogeneously dispersed in the polymer, which in particular makes it possible to sufficiently prevent unwanted transparency damage of such polymers in visible light.

The statistical copolymers to be preferably used according to the invention are in the statistical copolymers in the range from 1: 2 to 500: 1, preferably in the range from 1: 1 to 100: 1 and particularly preferably in the range from 7: 3 to 10: 1. And the weight ratio of the structural unit containing a hydrophobic radical to the structural unit containing a hydrophilic radical. The weight average molecular weight of the statistical copolymer is usually in the range of Mw = 1000 to 1,000,000 g / mol, preferably in the range of 1500 to 100,000 g / mol, and particularly preferably in the range of 2000 to 40,000 g / mol.

In particular, copolymers according to formula (I) have been found:

[In the meal,

X and Y correspond to the radicals of conventional nonionic or ionic monomers,

R ¹ means hydrogen or a hydrophobic side group, preferably selected from branched or unbranched alkyl radicals having 4 or more carbon atoms, wherein at least one, preferably all H atoms can be replaced with fluorine atoms,

R ² means a hydrophilic side group, preferably has a phosphonate, sulfonate, polyol or polyether radical,

-XR ¹ and -YR ² may each have several different meanings that meet the requirements according to the invention in a particular way in the molecule.

Particularly preferred according to the invention are polymers in which -YR ² is a betaine structure.

X and Y, independently of one another, mean -O, -C (= 0) -0-, -C (= 0) -NH-,-(CH ₂ ) _n- , phenyl, naphthyl or pyridyl Particular preference is given here to polymers of the general formula (I). In addition, one or more structural units may comprise at least one quaternary nitrogen atom, wherein R ² is preferably-(CH ₂ ) _m- (N ⁺ (CH ₃ ) ₂ )-(CH ₂ ) _n -SO ₃ ^- side group or- (CH ₂ ) _m- (N ⁺ (CH ₃ ) ₂ )-(CH ₂ ) _n -PO ₃ ^2- side group, m being in the range of 1 to 30, preferably in the range of 1 to 6, particularly preferably Means an integer of 2, n is in the range from 1 to 30, preferably from 1 to 8, particularly preferably from 3).

Statistical copolymers to be used particularly preferably may be prepared according to the following scheme:

The desired amounts of lauryl methacrylate (LMA) and dimethyl aminoethyl methacrylate (DMAEMA) are copolymerized by free radicals in toluene via the method known here, preferably via the addition of AIBN. Thereafter, the betaine structure is obtained by a known method by reaction of amine with 1,3-propane sultone.

Alternative copolymers that will preferably be used may contain, but are not limited to, styrene, vinylpyrrolidone, vinylpyridine, halogen styrene or metoxystyrene. In another, likewise preferred embodiment of the present invention, the at least one structural unit is characterized in that it is an oligomer or a polymer, preferably a macromonomer, wherein polyethers, polyolefins and polyacrylates are particularly preferred as macromonomers. Polymers are used.

Precursors that can be used as the inorganic nanoparticles are water-soluble metal compounds, preferably silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron, yttrium and / or zirconium compounds, where such precursors are represented by corresponding metal-oxides. For the preparation of the particles it is preferably reacted with an acid or caustic alkali. Mixed oxides can be obtained simply by appropriate mixing of the corresponding precursors. Selection of suitable precursors is not difficult for those skilled in the art; Suitable compounds are all suitable for the precipitation of the corresponding target compounds from aqueous solutions. An overview of suitable precursors for the production of oxides is described, for example, in K. Osseo-Asare "Microemulsion-mediated Synthesis of nanosize Oxide Materials" in: Kumar P. Mittal KL, the content of which is expressly within the disclosure of the present application. , (editors), Handbook of microemulsion science and technology, New York: Marcel Dekker, Inc., pp. 559-573.

Hydrophilic melts can also be used as precursors of nanoparticles in the sense of the present invention. Chemical reactions for the production of nanoparticles are not necessary in this case.

In particular, alkali or alkaline earth metal silicates, preferably sodium silicates, as precursors can also be reacted with an acid or caustic alkaline solution to give silicon dioxide.

In a likewise preferred embodiment of the invention, at least one soluble compound of the noble metal, preferably silver nitrate, is reacted with a reducing agent, preferably citric acid to provide a metal.

For the preparation of nanoparticulate metal sulfides, which are likewise preferred according to the invention, soluble metal compounds, preferably soluble Pb, Cd or Zn compounds, are reacted with hydrogen sulfide to provide metal sulfides.

In another embodiment of the present invention, soluble metal compounds, such as, for example, calcium chloride, are preferably reacted with carbon dioxide to provide nanoparticulate metal carbonates.

Preferred nanoparticles are those consisting essentially 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 of 3 to 200 nm, in particular 20 to 80 nm and very particularly preferably 30 to 50 nm, as measured by dynamic light scattering or transmission electron microscopy. In certain, likewise preferred embodiments of the invention, the distribution of particle sizes is narrow, ie the variation range is less than 100% of the mean, particularly preferably 50% or less of the mean.

In the use of such nanoparticles for UV protection in polymers, it is particularly preferred that the nanoparticles have an absorption maximum point in the range of 300 to 500 nm, preferably in the range of 400 nm or less, particularly preferred nanoparticles here Absorbs radiation, especially in the UV-A region.

The emulsion process can be performed here in several ways:

As mentioned above, the particles are usually prepared by reaction of the precursor or cooling of the melt in step b). The precursor may here be reacted with an acid, caustic alkaline solution, reducing agent or oxide, depending on the method variant selected.

For the preparation of particles in the desired particle-size range, it is particularly advantageous when 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 of a given system is tailored in a manner known to those skilled in the art here, and the oil phase is individually tailored to the reaction system by those skilled in the art. For the production of ZnO particles, for example, it has been found that toluene and cyclohexane are successful in the oil phase.

In some cases, in addition to the statistical copolymers, it may be helpful to use additional coemulsifiers, preferably nonionic surfactants. Preferred oiling agents are relatively long-chain alkanols or alkylphenols (eg, adducts of 0 to 50 mol alkylene oxides), with varying degrees of ethoxylation or propoxylation, optionally ethoxylated or propoxylated. to be.

Dispersing aids, preferably polyvinylpyrrolidone, copolymers of vinylpyrrolidone and acetate or vinyl propionate, partially saponified copolymers of acrylates and acrylonitrile, polyvinyl alcohols having different residual acetate contents Using water-soluble, high molecular weight, organic compounds, or mixtures of these materials, which also contain polar groups such as cellulose ethers, gelatin, block copolymers, modified starches, low molecular weight, carboxy- and / or sulfonyl-containing polymers May be advantageous.

Particularly preferred protective colloids are polyvinyl alcohols having a residual acetate content of less than 40 mol%, in particular 5 to 39 mol%, and / or vinylpyrroli having a vinyl ester content of less than 35% by weight, in particular 5 to 30% by weight. Don-vinyl propionate copolymer.

The desired combination of properties of the nanoparticles required can be adjusted in the desired manner by control of reaction conditions such as temperature, pressure and reaction duration. Corresponding adjustment of these parameters is not difficult at all to the skilled person. For example, the operation can be carried out for various purposes at atmospheric pressure and at room temperature.

In a preferred method variant, a second emulsion in which the reactants for the precursor are in emulsified form is mixed in step b) with the precursor emulsion from step a). This two-emulsion method allows the preparation of particles with particularly narrow particle-size distributions. It may be particularly advantageous here that the two emulsions are mixed with each other by the action of ultrasound.

In another, likewise preferred method variant, the precursor emulsion is mixed with a precipitate which dissolves in the continuous phase of the emulsion in step b). Precipitation is then carried out by diffusion of the precipitate into the precursor-containing micelles. For example, titanium dioxide particles can be obtained by diffusion of pyridine to titanyl chloride-containing micelles, or silver particles can be obtained by diffusion of long chain aldehydes to silver nitrate-containing micelles.

 Nanoparticles according to the invention are used in particular in polymers. Polymers in which the nanoparticles according to the invention can be incorporated are, in particular, polycarbonate (PC), polyethylene terephthalate (PETP), polyimide (PI), polystyrene (PS), polymethyl methacrylate (PMMA). Or a copolymer containing at least part of one of the polymers.

Incorporation here can be carried out by conventional methods for the preparation of polymer compositions. For example, the polymeric material can be mixed with the nanoparticles according to the invention, preferably in an extruder or mixer. Depending on the polymer used, it is also possible to use mixers.

A particular advantage of the particles according to the invention is that only a low energy input is required compared to the prior art for the homogeneous distribution of the particles in the polymer.

The polymer herein may also be a dispersion of a polymer, for example paint. Incorporation here can be carried out by conventional mixing operations.

The polymer composition according to the invention containing nanoparticles is additionally particularly suitable for the coating of surfaces as well. This makes it possible to protect the material under the surface or the coating, for example from UV radiation.

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

Example 1 Synthesis of Macrosurfactants

The first step involves the synthesis of statistical copolymers of dodecyl methacrylate (lauryl methacrylate; LMA) and dimethylaminoethyl methacrylate (DMAEMA). Control of molecular weight can be achieved by the addition of mercaptoethanol. The copolymer obtained in this way is modified by 1,3-propane sultone to feed the saturation group.

For this reason, 7 g of LMA and DMAEMA were first introduced into 12 g of toluene in an amount corresponding to the following Table 1 after the start of the reaction by addition of 0.033 g of AIBN in 1 ml of toluene, and then at 70 ° C. Free-radical polymerization under argon. Chain enhancement can be controlled here by the addition of 2-mercaptoethanol (see Table 1). Crude polymers are described in [V. Butan, C. E. Bennett, M. Vamvkaki, A. B. Lowe, N. C. Billingham, S. P. Armes, J. Mater. Chem., 1997, 7 (9), 1693-1695, washed, lyophilized and then reacted with 1,3-propane sultone.

The characterization of the resulting polymer is shown in Table 1.

Characterization of the amount of monomers used and the resulting polymer obtained DMAEMA [g] DMAEMA [mol%] in the polymer 1-mercaptoethanol [g] M _n [g / mol] M _w [g / mol] Betaine group [mol%] E1 1.08 19 0.033 18000 31000 16 E2 1.08 19 0.011 28000 51000 19 E3 1.08 21 0.066 13000 21000 21 E4 1.09 20 - 59000 158000 14.6 E5 0.48 10.7 - 52000 162000 7.5

Example 2: Precipitation of ZnO Particles

ZnO particles are precipitated by the following method:

1. Preparation of an inverse emulsion of an aqueous solution of 0.4 g of Zn (AcO) ₂ * 2H ₂ O (emulsion 1) and 0.15 g of NaOH (emulsion 2) in 1.35 g of water by ultrasonic in each case. Emulsion 1 and Emulsion 2 each contain 150 mg of statistical copolymers E1 to E5 from Table 1.

2. After sonication of the mixture of emulsion 1 and emulsion 2, drying.

3. Purification of sodium acetate by water washing of the resulting solid.

4. Re-dispersion of the powder functionalized on the surface by emulsifier, by drying and stirring in toluene.

FT-IR spectroscopy and X-ray diffraction indicate the formation of ZnO. In addition, the reflection of sodium acetate does not appear in the X-ray plot.

Thus, Example 2 results in a product consisting of the synthesized macrosurfactant and zinc oxide particles.

Copolymer Diameter [nm] (light scattering) Variation [nm] Ratio of ZnO (% by weight) E1 37 30 30.3 E2 66 53 30.5 E3 50 41 32

Comparative Example 2a: Emulsifier ABIL EM 90 ^®  Use of

Example 1 instead of the statistical copolymer of from, a commercially available emulsifier ABIL EM 90 ^® (Cetyl dimethicone copolyol, Goldschmidt) carried the same way as described in Example 2 using the do not result in a stable emulsion. The obtained particles have a diameter of 500 to 4000 nm.

Example 3: Precipitation of Silicon Dioxide

Precipitation of SiO ₂ particles is carried out by the following method:

1. In each case, preparation of an inverse emulsion of aqueous solutions of Na ₂ SiO ₃ (emulsion 1) and H ₂ SO ₄ (emulsion 2) by ultrasound (concentrations corresponding to Table 2).

2. After sonication of the mixture of emulsion 1 and emulsion 2, drying.

3. Purification of the obtained product by water washing.

4. Drying and redispersion of the powder obtained.

FR-IR spectroscopy and X-ray diffraction indicate the formation of SiO ₂ and the non-existence / absence of sodium silicate.

Thus, this step provides a product consisting of the synthesized macrosurfactant and silicon dioxide particles.

Composition of the emulsion and characterization of the product Experiment Emulsion E1 Emulsion E2 Particle Size of Nanoparticles [nm] Standard Deviation [nm] 3a 0.15 g of polymeric surfactant (E4); 11.7 g of toluene; 1.25 g of water; Na ₂ SiO ₃ 1.25 g 0.15 g of polymeric surfactant (E4); 11.7 g of toluene; 2.2 g of water; 0.3 g H ₂ SO ₄ 59 19 3b 0.15 g of polymeric surfactant (E4); 11.7 g of toluene; 1.25 g of water; Na ₂ SiO ₃ 1.00 g 0.15 g of polymeric surfactant (E4); 11.7 g of toluene; 1.76 g of water; 0.24 g H ₂ SO ₄ 40 15 3c 0.15 g of polymeric surfactant (E4); 11.7 g of toluene; 0.75 g of water; Na ₂ SiO ₃ 0.75 g 0.15 g of polymeric surfactant (E4); 11.7 g of toluene; 1.32 g of water; H ₂ SO ₄ 0.18 g 50 20 3d 0.15 g of polymeric surfactant (E5); 11.7 g of toluene; 0.75 g of water; Na ₂ SiO ₃ 0.75 g 0.15 g of polymeric surfactant (E5); 11.7 g of toluene; 1.32 g of water; H ₂ SO ₄ 0.18 g 43 15 3e 0.15 g of polymeric surfactant (E5); 11.7 g toluene 1.25 g water; Na ₂ SiO ₃ 1.25 g 0.15 g of polymeric surfactant (E5); 11.7 g of toluene; 2.2 g of water; 0.3 g H ₂ SO ₄ 53 12 3f 0.15 g of polymeric surfactant (E5); 11.7 g of toluene; 1.0 g of water; Na ₂ SiO ₃ 1.0 g 0.15 g of polymeric surfactant (E5); 11.7 g of toluene; 1.76 g of water; 0.24 g H ₂ SO ₄ 93 30

Example 4: Polymer Composition

Dispersions in the PMMM lacquer of particles from Example 2-E1 are prepared by mixing, applied to a glass substrate and dried. The ZnO content after drying is 10% by weight. The film exhibits a substantially unacceptable haze. Measurements using a UV-VIS spectrometer confirmed this effect. The sample shows the following absorption values depending on the layer thickness (the percentage of incident light lost in transmission is shown).

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

1.2 μm 35% 4%

1.6 μm 40% 5%

2.2 μm 45% 7%

compare:

(ZnO (extra pure, Merck) in the same PMMA lacquer)

2 μm 64% 46%

Claims (20)

Use as a emulsifier of statistical copolymers containing at least one structural unit containing a hydrophobic radical and at least one structural unit containing a hydrophilic radical. 2. Use according to claim 1, characterized in that the copolymer is used as an emulsifier in the synthesis of nanoparticles from an emulsion. The weight ratio of the structural unit containing a hydrophobic radical to the hydrophilic radical in the statistical copolymer is in the range of 1: 2 to 500: 1, preferably 1: 1 to 100: 1, and particularly preferably in the range from 7: 3 to 10: 1. The method according to claim 1, wherein the weight average molecular weight of the statistical copolymer is in the range M _w = 1000 to 1,000,000 g / mol, preferably in the range 1500 to 100,000 g / mol, and particularly preferably 2000 To 40,000 g / mol. Use according to any of the preceding claims, characterized in that the copolymer is according to formula (I): [Formula I]

[In the meal, X and Y correspond to the radicals of conventional nonionic or ionic monomers, R ¹ means hydrogen or a hydrophobic side group, preferably selected from branched or unbranched alkyl radicals having 4 or more carbon atoms, wherein at least one, preferably all H atoms can be replaced with fluorine atoms, R ² means a hydrophilic side group, preferably has a phosphonate, sulfonate, polyol or polyether radical, -XR ¹ and -YR ² may each have several different meanings in the molecule]. 6. A compound according to claim 5, wherein X and Y independently of one another are -O, -C (= 0) -0-, -C (= 0) -NH-,-(CH ₂ ) _n- , phenylene or pyridyl. Use characterized in that it means. 7. Use according to any one of the preceding claims, wherein at least one structural unit contains at least one quaternary nitrogen atom, wherein R ² is preferably-(CH ₂ ) _m- ( N ⁺ (CH ₃ ) ₂ )-(CH ₂ ) _n -SO ₃ ^- side group or-(CH ₂ ) _m- (N ⁺ (CH ₃ ) ₂ )-(CH ₂ ) _n -PO ₃ ^2- side group M means an integer in the range 1 to 30, preferably in the range 1 to 6, particularly preferably 2, n is in the range 1 to 30, preferably in the range 1 to 8, particularly preferably 3 Use for integers. 8. A process according to any one of the preceding claims, wherein at least one structural unit is an oligomer or a polymer, preferably a macromonomer, wherein polyethers, polyolefins and polyacrylates are particularly preferred as macromonomers. Usage. A process for preparing polymer-modified nanoparticles, wherein in step a) an inverse emulsion containing at least one of the melt or the water soluble precursor of the nanoparticles contains at least one monomer containing hydrophobic radicals and a hydrophilic radical Prepared by a statistical copolymer of at least one monomer, wherein the particles are prepared in step b). 10. The process according to claim 9, wherein the particles are produced by reaction of the precursor in step b) or by cooling of the melt. The method of claim 10 wherein the precursor is reacted with an acid, caustic alkaline, reducing or oxidizing agent. 12. The process of claim 11, wherein sodium silicate as precursor reacts with the acid or caustic alkaline solution to provide silicon dioxide. 12. Process according to claim 11, characterized in that the noble metal, preferably silver nitrate, is reacted with a reducing agent, preferably citric acid to provide the metal. 12. The process according to claim 11, wherein the soluble metal compound, preferably the soluble Pb, Cd or Zn compound, reacts with hydrogen sulfide to provide metal sulfides. Process according to claim 11, characterized in that the soluble metal compound, preferably calcium chloride, is reacted with carbon dioxide to give the metal carbonate. Method according to any of the preceding claims, characterized in that the droplet size in the emulsion is in the range of 5 to 500 nm, preferably 10 to 200 nm. The method according to claim 1, wherein the second emulsion, in reacted form for the precursor, in emulsified form, is mixed in step b) with the precursor emulsion from step a). 18. The method of claim 17, wherein the two emulsions are mixed with each other by the action of ultrasound. 19. The method according to any one of the preceding claims, wherein at least one precursor is selected from water soluble metal compounds, preferably silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron, yttrium or zirconium compounds. The precursor is preferably reacted with an acid or caustic alkaline liquid (lye). 20. The process according to claim 1, wherein a coemulsifier, preferably a nonionic surfactant, is used.