CS200302B1 - Process for preparing spheric polymere microcomponents - Google Patents

Description

The invention relates to the preparation of polymeric microparticles by suspension free-radical polymerization of a suitable dispersion stabilizer, which makes it possible to obtain particles with a narrow distribution in the 2 to 30 µm size range. These particles can then be used as packed columns for chromatography, to form chromatographic spindles, as carriers of synthetic and natural catalysts, sorbents, reagents, in medicine, hydrometallurgy, water treatment, and the like. The increasing importance as well as the scope of use is to some extent limited by the difficulty of obtaining particles of the above dimension. Conventional slurry polymerizations make it possible to obtain particles with a size of 50 µm up to several mm without extra effort. It is evident from the file that the suspension polymerization product contains particles of various sizes. Then, of course, in view of the size distribution, a portion of the polymer in the form of very small particles with a size below, e.g., 50 µm, must necessarily be present. However, their amount is very low and the cost of small particles is disproportionately high due to the necessity of their separation from larger particles and a large number of substantially undesirable fractions.

The particle size reduction can be achieved in several ways. According to MS. No. 196,794, microparticles are obtained using the principle of polymer intolerance by dispersing the monomer or monomer mixture in a macromolecular liquid medium and, after heating, initiating the polymerization, to remove the formed polymer in the form of regular spheres.

This process is particularly useful in the production of microparticles from inorganic polymers

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(e.g., silica gel). In the field of organic polymers, a certain disadvantage is the difficulty of removing the dispersing medium from the finished product and, where necessary, the macroporous polymeric material, the complex choice of the dispersant-inert phase system, which should be immiscible with each other.

In contrast to the foregoing principle, which requires a complete change in the polymerization system, others are available which allow small particles to be obtained with a handle identical to that of larger particles. The reduction in size results in an increase in agitation efficiency, which can be achieved both by increasing the agitator speed and by changing the shape of the agitator for greater efficiency. However, both of these methods are also limited since the mixing efficiency cannot be increased without limitation.

Further, the particle size into the micron area can be reduced by selecting a suitable dispersant - suspension stabilizer, which prevents coalescence of the particles during polymerization. Block copolymers of the AB type consisting of a lipophilic and hydrophilic block of different lengths (polymerization stages) and of different chemical compositions are known as stabilizers for the production of microparticles according to DOS 2519949, e.g. methacrylate, polyvinyl chloride-polyvinyl acetate, polystyrene-polyvinylpyrrolidone. However, these dispersants are not commercially available and their synthesis requires the handling of relatively demanding ionic polymerization. According to US Pat. Nos. 1,864,976 and 1,732,795 and to German Patent No. 558,590, they are used as emulsifiers in suspension polymerization of soaps which, however, increase the solubility of the monomers in the aqueous phase as well as the proportion of emulsified polymer in the form of submicroscopic particles.

Disadvantages of said stabilizers are eliminated by the process according to the invention which consists in using a commercially available water-soluble polymer in increased concentration as a suspension stabilizer enabling the production of microparticles from 3 µm in size as macroporous spherical bodies with a very narrow size distribution. Accordingly, the present invention provides a process for the preparation of spherical polymeric microparticles by suspension radical polymerization, characterized in that a 0.5 to 5% by weight aqueous solution of polyvinyl alcohol having a molecular weight greater than 100,000 is used as the dispersion phase.

An essential advantage of this process is that a product can be obtained directly from the polymerization, from which up to 90% of the particles can be labeled as microparticles and used in the indicated applications. Furthermore, the system operates universally for various monomer mixtures and also makes it possible to obtain macroporous products and, finally, that these particles are formed under industrially feasible conditions, in particular at the mixing intensity feasible in conventional suspension polymerization reactors.

Example 1

A mixture of glycidyl methacrylate (14 ml), ethylene dimethyl methacrylate (6 ml), cyclohexanol (27 ml) and lauryl alcohol (3 ml) was dissolved in a 250 ml anchor stirrer reactor in which 0.2 g of 2,2'-azobls ( isobutyronitrile). This mixture was poured in a 0.5% by weight aqueous solution of polyvinyl alcohol (BDH England, molecular weight 125,000) and both phases were deoxygenated with a nitrogen stream for 10 minutes. The reactor was closed and stirring was started

200 302 (800 min "*) and heating. The polymerization was carried out for 8 hours at 70 ° C. Upon completion, the product was obtained as a microparticle having a distribution center of 22 µm, with $ 0% of all particles having a diameter in the range of 7 to 33 µm.

Example 2-6

Using the same procedure as in Example 1, with the difference that other concentrations of polyvinyl alcohol solution were used, particles having the dimensions given in the table were prepared.

polyvinyl alcohol concentration,% distribution center, yum 80% of the particles in the range, yum Example 2 1 18 6.5 - 31 Example 3 2 13 7.5 - 17.5 Example 4 3 6.9 4 - 10 Example 5 4 5.5 3,5 - 7,5 Example 6 5 3.2 2-5 Example 7 Like in Example 4, polymerization with the difference is that instead of glycidyl-

of methacrylate 2-hydroxyethylraethacrylate was used as monomer in the same volume. The product was obtained in the form of microparticles with a mean distribution of 5 µm and 80% of the particles had a diameter of 3 to 7 µm.

Example 8

Using the procedure of Example 3, except that 2-hydroxypropylene dimethacrylate was used instead of ethylene dimethacrylate, microparticles with a center of distribution of 14.2 µm were prepared and 80% of all particles had a diameter in the range of 8.1-16 µm.

Example 9

Using the procedure of Example 3, except that 5 ml of acrylonitrile and 8 ml of glycidyl acrylate were used instead of glycidyl methacrylate, microparticles were obtained having a mean distribution center of 2.5 µm and 80% of all particles had a diameter in the range 7.6-14.8 µm. .

Claims (1)

a process for the preparation of spherical polymeric microparticles and suspension by free-radical polymerization cured by using 0.5 to 5 wt. polyvinyl alcohol solution having a molecular weight greater than 100,000.