DE10240956A1 - Core-shell microgels, for use as catalyst supports, comprise a microparticle core and at least one polymeric shell comprising at least two different thermosensitive polymers having different switch temperatures - Google Patents

Abstract

Core-shell microgels, comprising a microparticle (diameter of less than 1 microm) as core and at least one polymeric shell, comprising at least two different thermosensitive polymers having different switch temperatures. A core-shell microgel (I) comprises a microparticle (diameter of less than 1 microm) as core and at least one polymeric shell whereby the shell and optionally the core are prepared by emulsion, dispersion or suspension polymerization of monomers with the addition of cross-linking monomers whereby one of the shells comprises a thermosensitive microgel that is formed from a first monomer such that the first shell has a first switch temperature whereby at least one further shell or optionally the core comprises a second thermosensitive microgel formed from a monomer that is different to the first monomer such that the second shell or optionally the core has a second switch temperature different to the first switch temperature.

Description

The invention relates to thermal switchable core-shell microgels, made up of at least two different thermosensitive polymers with different switching temperatures, the core itself consists of a thermosensitive polymer, and Core-shell microgels with a non-thermosensitive core, at least of two shells made of different thermosensitive polymers with different Switching temperature is surrounded.

The prior art is thermosensitive microgels well known (e.g. Pelton and Chibante, Colloids and Surfaces, 20, 246-256 (1986), Pelton, Adv. Colloid Interface Sci., 85, 1-33 (2000)). These are long-chain macromolecules that e.g. by emulsion, Dispersion or suspension polymerization from a particular Moon formed by and by adding of crosslinkers during the Synthesis to cross-linked, spherical Particles are "shaped". Among the most used with this goal Monomers counts the N-isopropylacrylamide (NIPAM) so that cross-linked poly-N-isopropylacrylamide (PNIPAM) one of the most common is thermosensitive microgels.

The outstanding property of these microgels is their ability to change their size when the temperature changes. In doing so, water molecules throw reversibly into the structure of the microgels or outsource them, thus changing the physical properties. For example, the radius of a PNIPAM microgel can decrease by 2-2.5 times when the temperature rises, which means a reduction in volume by a factor of 10-16. Swollen PNIPAM microgels are largely transparent as a function of concentration, whereas PNIPAM dispersion is visibly cloudy when the particles shrink. With PNIPAM in particular, the water is stored during heating above a relatively sharply defined temperature limit of T _S = 32 ° C, which is referred to in the literature as the "lower critical solution temperature" (LCST) and here briefly as the switching temperature.

In addition to NIPAM, there are many known other monomers with which thermosensitive microgels with something like that Display behavior, for example N-diethylacrylamide, N-vinylisobotyramide, N-acryloylpyrolidine, N-acroyloylpiperidine, N-vinylpyrolidone, N-vinylpiperidone, N-vinylcaprolactam (PVCap), N-ethyl methacrylamide (NEMAM) or about N-isopropyl methacrylamide (NIPMAM), as well as a number of other substituted acrylamides.

The state of the art continues to know Process to shift the switching temperature of thermosensitive microgels. This can be done primarily by adding anionic / cationic or hydrophobic Copolymers can be achieved in the polymerization of the microgel. The swelling power again can be control primarily through the degree of crosslinking of the microgels, i.e. by the type and amount of crosslinker added during the polymerization. The main crosslinker is N, N'-methylenebisacrylamide is used, but also divinylbenzene (Senff and Richtering, Colloid Polym. Sci., 278, 830 pp. (2000)) or ethylene glycol dimethacrylamide (EGDMA) (Hazot et al., Macromol. Symp., 150, 291-296 (2000)). With radical Polymerizations are potassium peroxodisulfate, AIBN, hydrogen peroxide / UV, 4,4'-azobiscyanopentanoicacid or more specific, adapted to the monomer, Compounds used as radical initiators. By copolymerization with ionogenic monomers such as acrylic acid or acrylic acid amide (Pelton and Chibante, Colloids and Surfaces, 20, 247-256 (1986)), methacrylic acid (Zhou, J. Phys. Chem. B, 102, 1364-1371 (1998)) butyl methacrylamide, amino-functionalized Acrylamides (Duracher et al., Colloid Polym Sci., 276, 219-231 (1998), Zha et al., Colloid Polym Sci., 280, 1-6 (2002)) or other monomers like styrene can also be used in addition to switching temperature and swelling capacity Targeted functionalization of the microgels.

The application areas for thermosensitive microgels include cosmetics ( JP07285828A ), Dressing material ( JP05084288A ), breathable clothing ( JP06220775A ) or thermally changeable membrane filters ( JP01058303 A ).

Another application of thermosensitive polymers is their use as carriers of catalytically active compounds. Carrier-bound catalysts, in particular carrier-bound (immobile) enzymes, are used, for example, in medical analysis in the production of pharmaceutical and crop protection products, in the production of foodstuffs and in the production of optically active substances. The recovery and reuse of the usually very expensive catalyst is interesting not least for economic reasons. Already in the EP 277473 B1 describes the immobilization of enzymes, coenzymes, antibodies, antigens, amino acids and metals or metal complexes by binding in particular to NIPAM or NIPMAM. The thermosensitive behavior of the polymers allows the reversible precipitation of the polymer conjugates and their later reuse with only an insignificantly reduced activity. The fixed catalysts are often stabilized against the free form. The above-mentioned manipulation techniques for the swelling behavior of the microgels are used extensively to adapt the carrier polymers to the optimal reaction conditions. When preparing platinum particles on a polystyrene core surrounded by a PNIPAM shell, it was also found that the catalytic activity of the platinum particles is influenced by the swelling behavior of the shell (Chen et al., Chem. Commun., 831-832 (1998)). The Reacti on rates decrease measurably when the switching temperature of the NIPAM shell is exceeded.

The last-mentioned example system falls under the generic term of core-shell microgels, in which an approximately spherical core is surrounded by possibly several shells, which can consist of different polymers or copolymers. Such core-shell particles with a thermosensitive outer shell are used, among other things, in paint colors, as medical carriers for the transport of active substances or in biological research and for rheology manipulation, for example in the exploitation of petroleum reservoirs ( GB 262 2 117A ).

To date, only core-shell particles are included at the most a thermosensitive polymer that commonly used the shell forms. Core-shell microgels in which both core and shell are thermosensitive have so far only been described by basic researchers (Jones and Lyon, Macromolecules 33, 8301 (2000); Gan and Lyon, J. Am. Chem. Soc., 123, 7511 (2001)). These are particles from a cross-linked poly-N-isopropylacrylamide (PNIPAM) core and a shell of cross-linked PNIPAM copolymerized with acrylic acid or Butyl methacrylate. The peculiarity of such double thermosensitive molecules lies in the occurrence of a two-stage swelling behavior as a function the temperature due to two discrete switching temperatures of the used Components.

The disadvantage of such in principle only core-shell particles consisting of a monomer is that

• a) both switching temperatures by choice of the monomer are defined within narrow limits and are not arbitrary be chosen far apart can;
• b) the additional shell consisting of the copolymer contains ionic groups, which their reversible swelling ability across from weaken the pure monomer;
• c) the presence of salts (ions) in the solution Swelling behavior of the core-shell microgel through interaction with said ionic groups of the copolymer influenced.

It is the task of the present Invention, core-shell microgels with multi-stage switching behavior manufacture. This task is solved by a core-shell microgel, consisting of a microparticle (diameter <1 μm) as core and at least one shell consisting of a polymer, wherein the shell or the shells and possibly the core by emulsion, Dispersion or suspension polymerization from monomers with addition are formed by crosslinking monomers, one of the shells being made of a thermosensitive microgel consisting of a first monomer is formed so that this first shell has a first switching temperature having at least one further shell or possibly the core consists of a second thermosensitive microgel and another than the first monomer is formed, so this second shell or possibly the core has a second switching temperature, which is differs from said first switching temperature.

The invention is explained as follows:
The main disadvantage of the core-shell microgels known in the prior art with two-stage switching behavior lies in the use of ionic groups in the production of the copolymerized shell. Among other things, this causes additional storage of water in the microgel, which initially leads to greater swelling than with the pure monomer. However, this additional water is not released again or only to a small extent when heated, so that such a shell shrinks only relatively weakly when its switching temperature is exceeded.

If you make the shell from one second monomer, the polymer switching temperature differs from that of the nucleus (→ "heterogeneous microgel"), see above a two-stage switching behavior can be caused, the can be finely adjusted using some parameters, which are not in the prior art or only available within narrow limits. In particular let was also clearly pronounced Set up steps with approximately the same step height. The presence of ions in the solution also disrupts this switching behavior Not.

Another advantage is more heterogeneous Core-shell particles lies in the possibility of the two switching temperatures by specifying the specific choice of thermosensitive monomers. Basically you can Core-shell microgels are created, their switching temperatures also several 10 ° C from each other away, e.g. by making the core out of PNIPAM and the shell out Polyvinylpiperidone exists.

Networking the shell of a heterogeneous Microgel is particularly sensitive to the area between the switching temperatures. While the average particle size in the further out Temperature ranges for "structurally identical" microgels behaves very similarly with differently networked outer shell specific ramps of different incline or even set up a plateau. The fine adjustment of the hydrodynamic Radius as a function of temperature is particularly interesting for (medical) particle filters based on microgel arrays, e.g. a PNIPAM core / PNIPMAM shell system just that covers physiologically relevant temperature range (environment with human body temperature). It is also for medical purposes i. a. rather advantageous if the switching behavior by ions e.g. is not affected in the bloodstream.

In addition to the choice of monomers and the degree of crosslinking, the ratio of shell thickness is also important Core radius for the effective switching behavior of the heterogeneous microgel play an important role. It was found, for example, that with a given PNIPAM core, as the thickness of the PNIPMAM shell increases, a steady transition to the switching behavior of the pure PNIPMAM takes place, ie the thermosensitivity of the core can no longer be effectively recognized when the shells are too powerful. The best results are achieved if you make sure that the mass ratio between the core and the shell is approximately 1: 1, so that the switching behavior, in particular the formation of a plateau, can be fine-tuned between the switching temperatures by crosslinking the shell.

On the applications of the heterogeneous core-shell Count microgels the disperse turbidity and activity control of catalysts.

The switching behavior is more sensitive to heat Microgels express themselves immediately in its light transmissivity. If you choose the working point of the Microgel functionality in the vicinity of the first switching temperature, so that also represents still swollen outer shell sure the tarnished Cannot flocculate particles. At the same time, the flocculation can still be forced by a further increase in temperature be what may be a recovery the microgels allowed. The recovery is particularly important for expensive microgels, such as for those that contain catalytic compounds. It is the temperature-dependent swelling capacity of the carrier polymers suitable the activity to control the catalysts. Self-regulated catalysts through temperature change are interesting e.g. For exothermic reactions, which in their rate of flow or their Substance turnover should be throttled. To prevent flocculation during the activity control avoiding is adding Another thermosensitive gel bowl useful, the switching temperature is far enough from the operating point of the catalyst control and still the recovery through failures allows.

Further advantageous configurations consist in the synthesis of core-shell microgels with more than a thermosensitive shell, but the core is not necessarily itself must be switchable. Rather, the core can be considered as temperature stable carrier polymer (e.g. polystyrene, general latex) for largely any functional molecular groups that function essentially on the core surface are grafted on. A first surrounding, thermosensitive polymer shell takes during a cooling phase additional solvent from the microparticle solution on and enables its access to the functional groups, for example for a chemical Reaction. A second, i. a. the outermost thermosensitive shell prevents the microgel from flocculating until recovery is desired. At the subsequent Heat becomes liquid released into the solution with reaction products. Of particular Advantage in the "pumping effect" Such a thermosensitive bowl is the possibility of this bowl itself to be equipped with further functional groups, such as catalysts. In theory, complex, multi-stage switchable can also be done in this way Microgels think that too, loaded with a number of different functional molecules the implementation complicated Allow multi-phase reactions inside a microparticle.

The invention is described in more detail based on a core-shell microgel consisting of a PNIPAM core and a PNIPMAM shell, in which shell thickness and crosslinking vary (see example syntheses). The following pictures show associated Measurement results.

1 shows as a typical result the thermosensitive response of a PNIPAM microgel to temperature changes. The hydrodynamic radii were determined by dynamic light scattering measurements (DLS).

2 shows the result of a DLS measurement for poly-N-isopropyl methacrylamide (PNIPMAM). The switching temperature is not as sharply defined as with PNIPAM and is between 42 and 44 ° C. The swelling capacity in the example shown is also significantly lower than with PNIPAM, ie the radius ratio between swollen and non-swollen PNIPMAM microparticles is far below z. The PNIPMAM shown is a highly cross-linked microgel (9.0 mol%).

3 illustrates the increase in swelling capacity with decreasing degree of crosslinking of the microgel using the example of pure PNIPMAM. The switching temperature is also sharper.

4 shows the thermosensitive DLS response of a core-shell microgel consisting of a PNIPAM core and a PNIPMAM shell (with crosslinking 1.5 mol%, CS012). The switching temperatures of the individual components are transferred to the core-shell microgel.

5 outputs the result of a turbidity measurement of the microgel 4 again.

6 shows the switching behavior of different core-shell microgels with PNIPAM core and PNIPMAM shell, whereby the shell thickness is varied. With increasing shell thickness, the influence of the core disappears and the switching behavior approaches that of the pure shell monomer.

7 represents the hydrodynamic radius R _{h of} three PNIPAM / PNIPMAM particles (see example Syntheses II) compared to the PNIPAM core alone. The effect of different shell cross-links exists with otherwise similar particles, in particular CS011 and CS012, especially in the course of the function R _h ( T) in the temperature range between the switching temperatures of the core and the shell.

example syntheses

The core for all syntheses was the one above and in 1 described microgel M71 used. This is a PNIPAM microgel cross-linked with 1.4 mol% BIS. This microgel is referred to below as the core.

I. Core-shell microgels CS005 / CS006 / CS008 with variable shell thickness

In a 250 ml three-necked flask with mechanical stirrer, Reflux condenser and Gas inlet tube was dispersed 0.9 / 0.45 / 0.225 g in 50 ml of water Core submitted. By introducing nitrogen at 70 ° C. for 30 min Expelled oxygen from the reading.

In another flask were at 70 ° C 50 ml deion. Water made oxygen-free by introducing nitrogen, 1.19 g NIPMAM, 143.0 mg BIS and 10.3 / 10.0 / 10.0 mg SDS dissolved and others Nitrogen introduced for 15 min. This mixture was added to the core solution Nitrogen was introduced for a further 15 min and the polymerization was carried out Add 23.0 mg KPS, which in a few ml deion. Water has been dissolved started.

The reaction mixture was stirred at 70 ° C for 6 h, allowed to cool and then filtered through glass wool.

II. Core-shell microgels CS009 / CS011 / CS012 with variable networking

In a 250 ml three-necked flask with mechanical stirrer, Reflux condenser and Gas inlet tube were 0.54 / 0.45 / 0.45 g in 30/25/25 ml of water submitted dispersed core. By introducing nitrogen for 30 min at 70 ° C became the oxygen from the solution distributed.

In a second flask 70 ° C 30/25/25 ml deionized water by introducing nitrogen into nitrogen exempt, 0.57 / 0.47 / 0.47 g NIPMAM, 68.7 / 17.8 / 8.7 mg BIS and 4.8 / 4.1 / 4.1 mg SDS solved and nitrogen was introduced for a further 15 min. This mixture was to the core solution given, a further 15 min nitrogen and the polymerization by adding 11.1 / 9.2 / 9.2 mg KPS, which is deionized in a few ml Water dissolved was started. The reaction mixture was stirred at 70 ° C for 6 h, allowed to cool and then filtered through glass wool.

Abbreviations:

PNIPAM: poly-N-isopropylacrylamide, NIPMAM: N-isopropyl methacrylamide, BIS: N, N'-methylenebisacrylamide, SDS: sodium dodecyl sulfate, KPS: potassium peroxodisulfate

Claims (8)

Core-shell microgel, consisting of a microparticle (diameter <1 μm) as the core and at least one shell consisting of a polymer, the shell or the shells and optionally the core being polymerized from monomers by emulsion, dispersion or suspension Addition of crosslinking monomers are formed, one of the shells consisting of a thermosensitive microgel, which is formed from a first monomer, so that this first shell has a first switching temperature, characterized in that at least one further shell or possibly the core from a second consists of thermosensitive microgel which is formed from a monomer other than the first, so that this second shell or possibly the core has a second switching temperature which differs from said first switching temperature. Core-shell microgel according to claim 1, characterized in that the outer shell the core-shell microgel consists of a thermosensitive microgel. Core-shell microgel according to claim 2, characterized that the outer shell the highest Has switching temperature. Core-shell microgel according to claim 2, characterized gekennzeichnat, that the degree of cross-linking of the outer shell in the polymerization by adding crosslinking monomers in the range 1.5-15 mol% chosen becomes. Core-shell microgel according to one of the preceding Expectations, characterized in that the core or other than the outer shell a carrier polymer with functional groups attached to it. Core-shell microgel according to claim 5, characterized in that the functional groups of enzymes, coenzymes, antibodies, antigens, Amino acids, Metals or metal complexes exist. Core-shell microgel according to one of the preceding Expectations, characterized in that as monomers N-isopropylacrylamide (NIPAM) and N-isopropyl methacrylamide (NIPMAM) can be used. Core-shell microgel according to one of the preceding claims, characterized in that the core-shell particle consists of a thermosensitive core and a thermosensitive shell, the core and shell essentially being that Have a mass ratio of 1: 1.