Plastic and nonmetallic article shaping or treating: processes – Encapsulating normally liquid material – Liquid encapsulation utilizing an emulsion or dispersion to...
Patent
1997-02-24
1999-11-02
Mullis, Jeffrey C.
Plastic and nonmetallic article shaping or treating: processes
Encapsulating normally liquid material
Liquid encapsulation utilizing an emulsion or dispersion to...
252 6254, 252 6255, C08F 244
Patent
active
059764260
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to new latices of magnetizable microspheres formed by a hydrophobic polymer matrix and magnetizable fillers.
It also relates to a process for the preparation of the said latices and to the application of these latices in biology, especially in diagnostic methods, in affinity chromatography, as carrier for nucleic acid probes, and in chemistry.
Magnetic latices are aqueous dispersions of microspheres including a polymer matrix and magnetizable fillers which impart magnetic, especially superparamagnetic, properties to these microspheres.
It will be briefly recalled that, besides paramagnetic and ferromagnetic fillers, there is a third category of fillers called superparamagnetic fillers, which are characterized by the fact that they do not remain magnetic in the absence of a magnetic field and that these fillers have a magnetic magnetization that is nearly as high as that of ferromagnetic fillers.
In most cases these are iron oxides such as magnetite, hematite or ferrite when they have a particle size smaller than a certain critical limit.
Under the influence of a magnetic field the magnetizable microspheres are drawn toward the magnet and as a result can be rapidly separated from the aqueous phase.
This separation is reversible since, in the absence of magnetic field, the microspheres lose their magnetization and redisperse spontaneously. The size of the microspheres is generally between a few tens of nanometers and several microns.
The high specific surface due to their small size can be advantageously exploited in applications of immunological type using the antigen antibody reaction. The magnetic latex acts as a support that will allow the quantitative determination of the species present in the medium after separation.
The separation and washing stages are in this case greatly simplified by virtue of the use of these magnetizable microspheres.
To this day the processes utilized, especially those resulting in the magnetic latices marketed under the trade name Estapor.RTM., rely on microsuspension polymerization mechanisms.
U.S. Pat. No. 4,339,337 makes it possible to prepare magnetizable microspheres of diameter ranging from 0.05 to 3 millimeters by suspension polymerization of a vinylaromatic monomer in the presence of one organosoluble initiator, of a dispersing agent and of a magnetizable filler dispersed within a solution of a water-insoluble polymer in the said monomer. The microspheres obtained enclose magnetizable fillers distributed in the polymer matrix.
In U.S. Pat. No. 4,358,388 it has also been proposed to prepare latices of magnetizable hydrophobic polymers by homogenization of an aqueous solution of emulsifier and of a dispersion of a magnetizable filler in an organic phase made up of an organosoluble initiator, of all or part of the hydrophobic monomer and/or of a water-insoluble organic compound, followed by polymerization. The latices obtained are made up of polymer microspheres from approximately 0.03 to 5 micrometers in diameter, enclosing magnetizable fillers distributed in the polymer matrix.
In suspension polymerization the monomer is dispersed in the form of droplets (size between 100 and 10,000 micrometers and 0.05 to 5 micrometers in the microsuspension) in the aqueous phase. The initiator is soluble in the organic phase and the suspension is maintained by mechanical stirring and addition of stabilizer (organic or inorganic colloid in the case of the conventional suspension, emulsifier in microsuspension). Each monomer droplet is considered to be a minireactor in which the polymerization kinetics are those of the bulk polymerization. They make it possible to obtain microspheres with a relatively broad particle size distribution in conventional suspension and a very polydisperse latex in the case of the microsuspension.
The latices obtained by the processes described in the prior art consequently produce very broad particle size distributions (typically from a few tens of microns to several microns). However, the effectiveness of the utilization of th
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Richard Joel
Vaslin Sophie
Mullis Jeffrey C.
Societe Prolabo
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