Process for preparing a dispersion and for preparing polymer par

Details Process for preparing a dispersion and for preparing polymer par Process for preparing a dispersion and for preparing polymer par

1994-04-22

1997-10-14

Henderson, Christopher

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

523406, 524502, 524507, 524512, 525139, 423445R, C08L 6106, C08K 300

Patent

active

056773730

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a method for preparation of a dispersion of droplets which may subsequently be used for preparation of polymer particles, e.g. by step-growth polymerization, using seed particles that are highly swellable in ionizing liquids as polymerization loci, and to the products so obtained.


BACKGROUND OF THE INVENTION

Polymer particles, in particular step-polymerized particles based on polymers such as phenolic polymers, have previously been prepared by using a water in oil emulsification technique, wherein the reactants are dissolved in water and the resulting aqueous solution is then dispersed in a water-insoluble organic liquid. Thereafter polymerization is started, e.g. by heating and/or by introduction of catalysts. After polymerization the particles are isolated and if desired redispersed in water.
The methods based on water-in-oil emulsions have several drawbacks. It may be difficult to perform both the polymerization and the isolation of final particles without getting aggregation and coalescence. Another problem is to prevent the polymerization from starting too early, i.e. it should not start before the water-in-oil emulsion has been prepared. When catalytic polymerization is used, it may be necessary to introduce the catalyst through the continuous outer organic phase into the water droplets. Such methods are not suitable when it is desired to have simple and reproduceable control of particle size, and are in particular not at all suited to the preparation of monodisperse systems, that is systems where all particles are of the same size.


SUMMARY OF THE INVENTION

The present invention seeks to avoid these drawbacks by first preparing a dispersion of droplets and then, if polymer particles are desired, effecting polymerization of monomers in said droplets.
Thus according to one aspect of the invention there is provided a method for preparing a dispersion wherein dispersed slightly crosslinked polyvinyl seed particles are swollen with an ionizing liquid, said seed particles containing covalently linked ionizable groups causing a swelling of the seed particles by the ionizing liquid to form a dispersion of droplets, wherein the resulting droplets after the swelling have a volume which is at least 5, particularly 10 times that of the seed particles.
According to another aspect of the invention there is provided a process for preparing polymer particles wherein dispersed slightly crosslinked polyvinyl seed particles containing covalently linked ionizable groups are swollen with an ionizing liquid which is or contains polymerizable monomers or is charged with such monomers to form a dispersion of droplets, and polymerization of the monomers is effected in the droplets during or after swelling to form polymer particles.
The ionizable groups are groups which are capable of forming ions (i.e. ionize) or they may be present in ionic form. Well known examples of such groups are acid and base groups and salts thereof, which will be further described below. The ionizing liquid, also called swelling liquid, is capable of ionizing the above ionizable groups and thereby swell the seed particles to which the ionizable groups are covalently linked.
In these methods the original seed particle typically constitutes only a small fraction, e.g. <20 and preferably <10 per cent by weight, of the final polymer particle.
Suitable seed particles consist of slightly crosslinked polyvinyl polymers carrying chemical groups that bring about a high degree of swelling in ionizing liquids.
Seed particles Containing acid or base groups may in addition to being highly swellable, act as catalytic centres in acid and base catalyzed polymerizations.
The method of the invention is especially suitable for the preparation of monodisperse particles.


DESCRIPTION OF THE PREFERRED EMBODIMENTS

Seed particles for use in the method may be prepared by, for example, radical polymerization of vinyl monomers using known methods such as emulsion polymerization, suspension polymerization or minisuspension polymerization

REFERENCES:
patent: 4361676 (1982-11-01), Simpson
patent: 4539348 (1985-09-01), Gajria
patent: 4686260 (1987-08-01), Lindemann
patent: 4708981 (1987-11-01), Zupancic
patent: 4711913 (1987-12-01), Tateosian

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