FR2463778A1 - Magnetic vinyl! aromatic polymer pearls - made by suspension polymerisation of aq. dispersion of magnetic filler particles in soln. of a water insol. (co)polymer - Google Patents

Abstract

Magnetic vinylaromatic polymer pearls are made by dispersing a magnetic filler in a soln. of at least one water-insol. (co)polymer (I) in the monomeric vinylaromatic cpd. (II) and opt. a copolymerisable monomer (III), then dispersing the resulting dispersion in water and polymerising the monomer(s). The soln. of the(co)polymer in the monomers is made e.g. by partial polymerisation of the (II) or (II) and (III) in the presence of an initiator. (II) is e.g. styrene, alpha methyl styrene, ethylstyrene, tert. butyl styrene or vinyl toluene. (III) is e.g. vinyl cpds. or alkyl esters of alkenic acids, esp. alkyl (meth)acrylates, (meth)acrylonitrile, etc. A crosslinking monomer such as divinyl benzene, vinyl methacrylate, polyethyleneglycoldiacrylate, etc., may also be present. The magnetic filler is e.g. of metals, metal alloys, pure iron oxides, CrO2, etc., with a particle size of 0.005-10 micrometres. Process gives polymer pearls with an even distribution of magnetic particles and uses less energy than previous processes comprising compounding of the polymer with the filler. The prods. are usefulin reprography, paints, inks, electrophotography, ion exchangers, carriers for biological molecules and esp. for immunoenxymatic determn.

Description

 The invention relates to a process for the preparation of magnetic beads of vinyl aromatic polymers by suspension polymerization.

 Magnetic polymers, in the form of gels or particles, are products whose use is generalized in many fields, such as reprography, paints, inks, electrophotography, ion exchangers, carriers of biological molecules, in particular for immunoenzymat assays ics.

 These magnet1.q # es polymers are generally obtained by mixing the magnetic charge with the polymer prepared by conventional techniques of mass polymerization, solution, emulsion or suspension. However, mixing constitutes an additional stage in the preparation of magnetic polymers, such as atomization, coagulation, extrusion, solvent distillation, which requires appropriate equipment and a non-negligible consumption of energy. N often presents difficulties in dispersion and leads To polymers, in the form of more or less regular particles, which have defects in the distribution of the magnetic charge and whose properties can be modified.

 To avoid these mixtures, it has been proposed to add the magnetic charge to the polymerization medium of water-soluble monomers, but hydrophilic polymers of limited applications are then formed.

 As for the water-insoluble monomers, it is known that the dispersion of the magnetic charge in the monomer, before suspension in the water of the latter and polymerization, does not give satisfactory results, because during the polyraerization, there is migration of the charge in the aqueous phase.

 The process which is the subject of the invention avoids these disadvantages and allows beads of polymers containing a magnetic charge to be obtained in a simple manner, which retain all their physical and magnetic properties and do not change during processing.

 The process for obtaining magnetic beads of vinyl aromatic polymers consists in carrying out a suspension polymerization of a vinyl aromatic compound alone or in admixture with a copolymerizable monomer in the presence of an initiator, a suspending agent and a magnetic charge. and is characterized in that the magnetic charge is dispersed in a solution of homo- or co-polymer in the monomer (s), then the dispersion obtained is suspended in water and the monomer (s) are polymerized.

 The solution of homo- or co-polymer in the monomer (s) constituting the organic phase is obtained either by partial mass polymerization of the monomer (s) in the presence of an initiator, or by dissolution of a polymer of vinyl aromatic compound, identical or different from that to be polymerized, in all or part of the monomer (s) to be polymerized. This second possibility of obtaining the organic phase being more reproducible than the first constitutes a preferred form of the invention.

 Depending on the polymer concentration of the organic phase, which is less than 6% by weight, it is possible to vary the viscosity of said organic phase.

This makes it possible to adjust the particle size of the polymer beads to be obtained, in a manner known per se, and according to the size and the amount of the magnetic charge, to obtain a regular dispersion of said charge in the beads.

 To obtain a homogeneous dispersion of the magnetic charge in the organic phase, the charge is added either to the monomer before partial mass polymerization, or to the agitated organic phase, obtained after partial polymerization or by dissolution of polymer in the or the monomers. The dispersion is then suspended by adding one or more times water containing one or more suspending agents or vice versa by adding the dispersion to the aqueous phase. The amount of water used is such that the weight ratio of organic phase containing the filler / aqueous phase is between 0.1 and 0.5.

 The monomer (s) are then polymerized according to all known techniques of suspension polymerization of vinyl aromatic compounds at temperatures between 30 and 1500C and preferably between 50 and 1300 C.

 The vinyl aromatic compounds used in the process of the invention are represented by styrene, alpha-methylstyrene, ethylstyrene, vinyltoluene. They are used alone or as mixtures with one another, or alternatively as mixtures containing at least 20% by weight of said compound and one or more monomers copolymerizable with the compound, to give a copolysbre soluble in the monomers. As copolymerizable monomers can be mentioned: vinyl compounds, such as: alkyl acrylates and methacrylates having 1 to 10 carbon atoms, acrylic and methacrylic nitriles; esters of ethylenic acids having 4 or 5 carbon atoms and of alkyl having 1 to 8 carbon atoms, such as: heptyl fumarate, octyl fumarate, methyl itaconate, ethyl itaconate.

 Depending on the reaction conditions, it is possible to add a crosslinking monomer, such as, for example, divinylbenzene, vinyl methacrylate, mono- or polyethylene glycol diacrylate or dimethacrylate, in proportions of between 0 and 10% by weight of the or monomers. It is also possible to add a chalne limiting agent such as for example the dimer of alphamethylstyrene, the alkylmercaptans with a straight or branched chain, the halogenated hydrocarbons, in proportions of between 0 and 5% by weight relative to (x ) mono mother (s) ..

The magnetic charge is in the form of particles which are sufficiently fine to be able to be included in the polymer beads, that is to say that their size is generally between 0.005 and tO> wm. It is more particularly represented by
- metals, such as: iron, iron-silicon, nickel,
cobalt, or the alloys of each of these metals with molybdenum, chromium, copper, vanadium, rranga nèse, aluminum, titanium
- iron oxides: Fe304 or t-Fe203 pure or in
combination or mixture with other oxides - such as cobalt, manganese, zinc, barium, rare earth oxides
- chromium dioxide.

 The magnetic particles, alone or as a mixture, are dispersed in all or part of the organic phase, either as such, or in the form of colloidal suspension of the particles in an organic medium compatible with the organic phase The organic medium is chosen from halogenated hydrocarbons or not, organic esters, polyphenyl ethers.

 The amount of magnetic filler to be used is between 0.2 and 50% by weight of the organic phase and preferably between 0.5 and 20%.

The initiators used in the process, in an amount of between 0.02 and 3% by weight relative to the monomer (s), are chosen from the conventional organosoluble initiators of the radical polymerization of vinyl aromatic compounds, such as peroxides and azonitriles represented in particular by benzoyl, dicumyl, ditertiobutyl, diacetyl, lauroyl, methyl ethyl ketone, caprylyl, 2,4-dichloro-benzoyl, parachlorobenzoyl, perpivalate, diethylperacetate, perbenzo ditertiobutyl diperphthalate, 1, 1-ditert iobutyle-peroxy-3, 3, 5-trimethylqyclohexane, azobisisobutyronitrile, azobiscyclohexane carbonitrile
One or more initiators can be used, introduced into the reaction medium as a mixture or successively; successive introductions being particularly suited to the case where a mass polymerization is carried out in the first step of the process. The choice of initiator (s) depends on the polymerization temperature.

 The suspending agents, which maintain the organic phase in suspension in the aqueous phase and influence the size of the beads to be obtained, are those generally used in the polymerization of vinyl aromatic compounds. They are represented by organic and mineral protective stiff necks, possibly associated with surfactants.

 As organic colloids, there may be mentioned: polyvinyl alcohol, polyvinylpyrrolidone, styrene-maleic anhydride copolymers, sulfonated polystyrenes, polyglycolic ethers, gelatin, alkyl- and hydroxyalkyl-celluloses; and as mineral colloids, calcium and magnesium carbonates, barium sulphate, zinc and aluminum oxides, magnesium and barium phosphates, and more particularly tricalcium. These organic or mineral colloids are used alone or as a mixture in proportions of between 0.05 and 5% by weight relative to the organic phase.

 At least one surfactant can be associated with the protective colloid (s), in an amount between 5 and 50 ppm by weight relative to the organic phase. They are chosen more particularly from the alkaline salts of fatty acids, of alkylsulfuric acids or of alkylarylsulfonic acids such as: sodium stearate, sodium oleate, sodium lauryl sulfate, sodium dodecylbenzenesulfonate.

 The protective colloid (s) and optionally the surfactant (s) are introduced, either together or separately, generally in the aqueous phase before polymerization. However, in certain cases, it may be advantageous to introduce them either during polymerization, by successive fractions or continuously, or one part before polymerization, the other part during polymerization, by successive fractions or continuously.

 Although this is not essential, it may be advantageous to add a pH regulator, such as disodium phosphate, to the polymerization suspension.

 After polymerization, the beads formed are separated, washed with water and / or with a water-miscible liquid which is non-solvent for the polymer, such as for example an alcohol, such as methanol ethanol and / or an aqueous solution of mineral acid. , and finally dried.

 The polymers of the vinyl aromatic compounds obtained according to the process of the invention are in the form of magnetic beads with an average size of between 0.05 and 3 mm and preferably between 0.1 and 2 mm.

 The pearls are easily attracted by a magnet, which makes it possible, in certain applications, to separate them from the ambient liquid medium. In addition, they can be modified by any chemical reaction to give, among other things, ion exchangers.

 The beads of magnetic polymers can be used in the industries of paints, inks, in reprography, in biology, in particular like supports of biological molecules.

 Examples of embodiment of the invention are given below by way of indication and without limitation.

In the examples
- The viscosity of the polymers used is determined by element in a capillary tube of the solution at 10 to 60 by weight of the polymer in toluene at 250C.

 - The viscosity of the polymer solution in the monomer is measured with a Brookfield viscometer, speed 50 rpm, needles and temperatures adapted to each solution.

Example 1
, In a 0.5 liter reactor, fitted with a stirrer, are introduced - 70 g of distilled styrene, - 0.07 g of α-methylstyrene dimer, - 0.07 g of tert-butyl perbenzoate, - 2 , 2 g of a dispersion at 16% by weight in a
? e304 mineral oil, of which the size of the party
cules is about 0.01 # im.

The stirred mixture is heated to 90 C. When this temperature is reached, 0.2 g of benzoyl peroxide is added, then the mixture is kept at 900C for 2 hours.

 163 g of deionized water at 900C are then introduced into the reactor, then, a minute later, 2.33 g of hydroxyapatite and 0.47 ml of an aqueous solution at 0.5% by weight of sodium dodecylbenzenesulfonate. The stirred mixture is kept at 900C for 20 hours.

 After cooling to room temperature, 0.2 ml of an aqueous hydrochloric acid solution at 38% by weight is added, then the beads formed are separated by sedimentation and filtration. After washing with methanol and drying at 30 ° C., 65 g of beads of red brown color and with an average diameter of 1 mm are obtained.

 Beads suspended in a batten are easily separated from the medium by attraction along the walls of the container by means of a magnet.

Example 2
Into a 4 liter reactor, fitted with an agitator, are introduced
- 560 g of distilled styrene and
- 21 g of a dispersion at 16% by weight in a
Fe304 mineral oil, the size of which
cules is about O, O1 m.

 The stirred mixture is heated to 750 C. After 30 min at this temperature, 4.75 g of benzoyl peroxide are added and the mixture # polymerized at 750C for 2 h 30 min.

 To the homogeneous and viscous mixture then obtained and maintained at 75075 C, is added a solution formed of 2615 g of deionized water, 9.6 g of disodium phosphate and 3.92 g of polyvinyl aloool. The dispersion obtained, stirred, is heated to 9 ° C., a temperature which is maintained for 10 hours.

 After cooling, the beads formed are filtered, washed with water and then with methanol, dried at room temperature and sieved.

552 g of magnetic polystyrene beads, brown in color, are obtained. These pearls have the following particle size distribution
- (0.25 mm 10% by weight
- between 0.25 and 0.50 mm 78% by weight
- between 0.50 and 1 mm 12% by weight
Example 3
Into a 0.5 liter reactor fitted with an agitator, are introduced
- 62.7 g of a 35% by weight solution in styrene distilled from a polystyrene, the viscosity of which is 41 mPa.S. The Brookfield viscosity of the solution at 200C, needle No. 7, is 23,600 mPa.S.

 - 4 g of a dispersion, in a 20% by weight solution of the same polystyrene as above in distilled styrene, of magnetic iron oxide (Fe203 + FeO) powder of 0.5 - 5 pu, at 24.6% by weight based on the solution. The Brookfield viscosity of the solution at 20.7 C, needle No. 3 is 830 mPa # S.

 - 0.86 g of benzoyl peroxide.

 To the stirred mixture obtained, 310 g of an aqueous solution containing 0.4 g of polyvinyl alcohol and 1.13 g of disodium phosphate are added. The dispersion obtained is heated to 900C with stirring. After 4 hours at this temperature, 50.8 g of a solution containing 0.03 g of polyvinyl alcohol are added. The reaction mixture is kept under stirring and at 900C for 6 hours.

 After cooling, the product formed is filtered, washed with water and methanol, then dried at room temperature.

 57.5 g of dark gray pearls are obtained. They have a diameter between 0.5 and 2 mm, contain 0.8% by weight of magnetic charge and are attracted by a magnet.

Example 4
Into a 4 liter reactor, fitted with an agitator, are introduced
- 560 g of a 30% solution in polystyrene styrene, the viscosity of which is 41 mPa.S. The viscosity
Brookfield of the 190 C solution, needle # 6, is 8,500 mPa.S.

 - 21 g of a dispersion at 16% by weight in a mineral oil of Fe304, whose particle size is about 0.01 # m.

 - 3.33 g of benzoyl peroxide.

 The stirred mixture is homogeneous after 30 minutes. 2472 g of an aqueous solution containing 3.1 g of polyvinyl alcohol and 9.6 g of disodium phosphate are then added thereto. The dispersion obtained is heated to 900 C. After 4 hours at this temperature, 406 g of an aqueous solution containing 0.3 g of polyvinyl alcohol are added, then the suspension is kept under stirring at 900C for 6 hours.

 After cooling, the product formed is filtered, washed with water and methanol, then dried at room temperature.

531.5 g of brown pearls are obtained. These pearls can be attracted by a magnet and have the following particle size distribution
- <0.25 inni 8.1% by weight
- between 0.25 and 0.50 mm 57.7% by weight
- between 0.50 and 1 mm 30.4% by weight
- between 1 and 2 mm 2.3% by weight -> 2 mm 1.5% by weight
Example 5
Into a 4 liter reactor, fitted with an agitator, are introduced
- 240 g of a 10% by weight solution in styrene distilled from a polystyrene with a viscosity of 41 mPa.S. The Brookfield viscosity of the 1905 solution, needle n01, is 76 mPa.S.

 - 320 g of the same polystyrene solution, in which are dispersed 16.8 g of needles of # Fe203 from 0.2 to 3 mm in length.

The mixture is stirred for 30 min. 3.73 g of peroxy
of benzoyl are then added, then 2858 g of a solu
A tion containing 9.6 g of disodium phosphate and 2.52 g of polyvinyl alcohol. The dispersion is then
heated to 90 ° C, then maintained at this temperature during
within 10 hours.

After cooling, the product formed is filtered,
washed with water, then dried at 600C.

530 g of brown pearls are obtained. Their distribution
particle size is as follows
- <0.20 mm 7.1% by weight
- between 0.20 and 0.40 mm 80.6% by weight
-> 0.40 mm 12.3% by weight
The size fraction 0.20-0.40 mm contains 1.5%
by weight of Fe203. Pearls can be attracted to
a magnet.

Example 6
Repeat example 5, replacing the 16.8 g
of Fe2O3 needles per 16.8 g of fine powdered iron
from 3 to 5 m.

494 g of light gray pearls are obtained. The distributed
granulometric tion is as follows
- <0.25 mm 11% by weight
- between 0.25 and 0.50 mm 88.5% by weight
-> 0.50 mm 0.5% by weight
0.25-0.50 mm size fraction contains 1.4%
by weight of magnetic charge. Pearls can be
attracted to a magnet.

Example 7
The procedure is as in Example 5 with the constituents
following
- 400 g of the same polystyrene solution as in
example 5
- 160 g of the same polystyrene solution, in
which were dispersed by stirring 11.2 g of needles g-Fe203 of O, 2 to 1 m oum in length,
- 3.73 g of benzoyl peroxide,
- 2,967 g of an aqueous solution containing 9.6 g of
disodium phosphate and 2.52 g of polyvinyl alcohol.

538 g of brown pearls are obtained. The distribution
particle size is as follows
- <0.20 mm 4.3% by weight
- between 0.20 and 0.40 mm 85.1% by weight
- between 0.40 and 1 mm 10.4% by weight
-> 1 mm 0.2% by weight
The part between 0.20 and 0.40mm contains
1.5% by weight of magnetic charge. Hanging pearls
may be attracted to a magnet.

Example 8
In a 4-liter reactor, fitted with an agitator,
560 g of distilled styrene are introduced, containing as
lution 10% by weight of polystyrene with a viscosity of 41 mPa.S.

The Brookfield viscosity at 19.50C, needle n0 --1, is
76 mPa.S.

56 g &alpha; -Fe2O3 needles 0.2 to 1 µm long
are added to the solution. The stirred dispersion is maintained at ambient temperature for 1 hour, with ad
addition after 30 min of 3.73 g of benzoyl peroxide.

2858 g of an aqueous solution containing 9.6 g of
disodium phosphate and 2.52 g of polyvinyl alcohol are
then added; then the dispersion is fairy lime at 900C
and kept at this temperature for 10 hours.

after cooling, the product formed is filtered,
washed with water and finally dried at 600 C.

547 g of brown-colored pearls are obtained. Their
particle size distribution is as follows
- <0.25 mm 17.7% in. weight
- between 0.215 and 0.50 mm 78.3% by weight
-> O, 50 mm 4% by weight
0.25-0.50 mm size fraction contains 2.7%
by weight of Fe2O3. Pearls can be attracted to
a magnet.

Example 9
Example 8 is repeated, with the following components:
- 560 g of a solution formed of 64% by weight of
distilled styrene, 16% by weight of methyl methacrylate,
20% by weight of polystyrene with a viscosity of 41 mPa.S. The opinion
Brookfield cosity of the solution at 20 C, needle No. 4, is
765 mPQ.S.

- 11.2 of &gamma; 0.2 to 1 m long Fe2O3
- 3.73 g of benzoyl peroxide
- 2859 g of an aqueous solution containing 9.6 g of disodium phosphate and 2.52 g of polyvinyl alcohol.

507 g of brown pearls are obtained. Their particle size distribution is as follows
- <0.20 mm 0.4% by weight
- between 0.20 and 0.40 mm 3% by weight
- between 0.40 and 1 mm 92% by weight -> 1 mm 4.6% by weight
The size fraction 0.40-1 mm contains 0.9% by weight of Fe203. Pearls can be attracted to a magnet.

Claims (13)

 1) Process for the preparation # of magnetic beads of vinyl aromatic polymers which consists in carrying out a suspension polymerization of a vinyl aromatic compound alone or in mixture with a copolymerizable monomer in the presence of an initiator, a suspending agent and a magnetic charge and is characterized in that the magnetic charge is dispersed in a homo- or copolymer solution in the monomer (s) then the dispersion obtained is suspended in water and the monomer (s) are polymerized.  2) Process according to claim 1, characterized in that the organic phase constituted by the homo or co-polymer solution in the monomer (s) is obtained by partial mass polymerization of the monomer (s) in the presence of an initiator.  3) Process according to claim 1, characterized in that the organic phase constituted by the homo or co-polymer solution in the monomer or monomers is obtained by dissolution of a polymer of vinyl aromatic compound, identical or different from that to be polymerized, in all or part of the monomer (s) to be polymerized.  4) Method according to claim 1, characterized in that the polymer concentration of the organic phase is less than 60% by weight.  5) Process according to claim 1, characterized in that the vinyl aromatic compounds, used alone or as a mixture between them, are represented by styrene, 1 'alpha-methylstyrene, 1' ethylstyrene, vinyltoluene.  6) Method according to claim 1, characterized in that the copolymerizable monomers are vinyl compounds or esters of ethylenic and alkyl acids.  7) Method according to claim 1, characterized in that a crosslinking monomer is used in proportions of between 0 and 10% by weight relative to the (x) monomer (s).  8) Method according to claim 1, characterized in  that a chain limiter is used in proportions of between 0 and 5% by weight relative to the (x) monomer (s).  9) Method according to claim 1, characterized in that the magnetic charge is represented by metals or their alloys, pure iron oxides, in combination or in mixture, chromium dioxide.  10) Method according to claim 1, characterized in that the size of the magnetic charge particles is between 0.005 and lO, jum.  11) Method according to claim 1, characterized in that the amount of magnetic charge is between 0.2 and 50% by weight of the organic phase.  12) Method according to claim 1, characterized in that the weight ratio organic phase containing the magnetic charge / aqueous phase is between 0.1 and 0.5.  13) Vinylaromatic polymers obtained by the method of claim 1, in the form of magnetic beads of average size between 0.05 and 3 mm.