Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1997-08-26
1998-06-09
Teskin, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526173, 526346, 526909, C08F 214, C08F11208
Patent
active
057635510
DESCRIPTION:
BRIEF SUMMARY
Styrene polymers are used in particular for consumer products. They can be used alone or in the form of polymer blends with other thermoplastic polymers for the production of materials having many advantageous properties. Polystyrene is chemically inert to a large number of chemical compounds and has excellent proccessability. In general, the physical properties and the external form of styrene polymers depend on the method of their preparation.
The present invention relates to a process for the preparation of particulate polystyrene (for example in the form of a latex or powder) by anionic polymerization of styrene which is dispersed in a hydrocarbon nonsolvent, a special styrene/butadiene block copolymer being used as the dispersant.
There is considerable interest in particulate polymers. In some cases, attempts are made to obtain polymers having a particularly narrow molecular weight distribution and a particle size of more than 200 .mu.m. As described in U.S. Pat. No. 4,247,434, polymer microparticles in latex form are used in many applications, for example as a reference standard for the calibration of various instruments in medical research. Polystyrene in particle form is once again of particular interest here.
U.S. Pat. No. 3,645,959 describes the preparation of high molecular weight vinyl polymers, for example polystyrene, in nonaqueous dispersion. Up to one percent of a diolefin, for example norbornadiene, is added as a dispersant for this purpose.
U.S. Pat. No. 3,259,595 describes a polystyrene preparation starting from a suspension polymerization, which polystyrene preparation can be processed to a polymer film having an approximately cellular structure.
U.S. Pat. No. 4,029,869 describes a method for the preparation of polystyrene by free radical suspension polymerization (initiated by peroxide). Very broad molecular weight distributions are obtained.
The anionic emulsion polymerization permits the preparation of polstyrene dispersions having a narrow molecular weight distribution. This method is described, for example, in European Patent 290,195 and U.S. Pat. Nos. 4,942,209 and 4,871,814; styrene/diene two-block copolymers are used as dispersants.
Polystyrene particles which were prepared by means of anionic emulsion polymerization with the aid of such a two-block copolymer had a particle size of less than 15 .mu.m and proved to be non-filterable since such particles are not retained even by very fine filter cloths and blocked the finest filters used by way of experiment. Where it was possible to obtain such fine polystyrene particles from the dispersion on the pilot scale, the powders obtained could be very readily swirled up, so that production on the industrial scale would have given rise to the danger of dust explosions.
We have found that, in the anionic emulsion polymerization of styrene, polystyrene particles which have a diameter of more than 100 .mu.m, preferably from 200 to 1000 .mu.m, and which have proven capable of being filtered are formed as a result of the use of a styrene/butadiene/styrene (three-)block polymer as the dispersant. Such polystyrene dispersions avoid the danger of a dust explosion since the filter cake obtained can, if necessary, be processed directly to give an extrudate.
The present invention relates directly to a process for the preparation of polystyrene by anionic polymerization of styrene in nonaqueous dispersion, which is carried out in an aliphatic hydrocarbon as the dispersing medium and with a styrene/diene/styrene three-block copolymer as the dispersant.
The styrene/diene/styrene three-block copolymer to be used according to the invention is used, for example, in an amount of from 0.1 to 10% by weight, based on styrene, and the diene block may be hydrogenated or unhydrogenated. Suitable copolymers are commercially available and can be used directly for carrying out the invention.
Instead of copolymers having polybutadiene blocks, it is also possible to use those which contain polymerized polyisoprene, and these in turn may be hydrogenated or unhydrogen
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Brand Siegbert
Heinrich Fritz
Tuttelberg Lembit
Wunsch Josef
BASF - Aktiengesellschaft
Teskin Fred
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