FR2485546A2 - 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

PROCESS FOR THE PREPARATION OF MAGNETIC PEARLS
OF VINYLAROMATIC POLYMERS
The present invention relates to an improvement to the process for preparing magnetic beads of vinyl aromatic polymers, which is the subject of French patent application No. 79.21342 filed on August 24, 1979.

 The process described in this patent application consists in carrying out a polymerization in aqueous suspension 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 dispersed in a solution of vinyl aromatic homo- or copolymer in the monomer (s).

 The Applicant has found that the process can be carried out with a solution, in the vinyl aromatic compound alone or in admixture with a copolymerizable monomer, of a homo- or co-polymer other than a vinyl aromatic polymer; which increases the possibilities of variation of the viscosity of the organic phase, as well as of the properties of the products obtained, such as glass transition temperature and hot viscosity of the polymer, adsorption capacity of the surface of the magnetic beads.

 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 in the monomer (s) of at least one water-insoluble polymer and represented by a vinyl homo- or co-polymer or a polycondensate of polyol and acid or unsaturated polycarboxylic anhydride, then the dispersion obtained is suspended in water and the monomer (s) are polymerized.

 The solution of homo- or co-polymer insoluble in water in the monomer (s), constituting the organic phase, is obtained by dissolution, in all or part of the monomer (s) to be polymerized, of at least one soluble polymer in the monomer (s) to be polymerized and insoluble in water.

 Depending on the nature of the polymer and its concentration in the organic phase, which is less than 60% by weight and preferably less than 45% 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 to the stirred organic phase obtained by dissolving polymer (s) in the monomer (s). The dispersion is then suspended by adding one or more times water containing one or more # iants suspending agents or vice versa by adding the dispersion to the aqueous phase The amount of water used is such that the ratio weight 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 1300C.

The vinyl aromatic compounds used in the process of the invention are represented by styrene, alpha-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene. They are used alone or in mixtures with one another, or else in mixtures containing at least 20 x by weight of said compound and one or more monomers copolymerizable with the compound, to give a copolymer soluble in the monomers. As copolymerizable monomers can be mentioned: vinyl compounds, such as: acrylates and alkyl methacrylates having 1 to 10 carbon atoms, acrylic and methacrylic nitriles; alkyl esters having 1 to 8 carbon atoms of ethylenic acids having 4 or 5 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, diviflylbenzene, vinyl methacrylate, diacrylate or dimethacrylate of mono or polyethylene glycol, esters of acrylic and methacrylic acids and of polyols, such as as pentaerythritol or trimethylolpropane triacrylates or trimethacrylates, in proportions of between 0 and 10% by weight of the monomer (s). It is also possible to add a chain limiting agent such as for example the digester of alphamethylstyrene, the alkylmercaptans with straight or branched chain, halogenated hydrocarbons, in proportions of between 0 and 5% by weight relative to (x ) monomer (s).

 The polymers soluble in the monomer (s) to be polymerized and insoluble in water, are represented by: homopolymers of vinyl monomers, such as alkyl acrylates and methacrylates (1-10 C), acrylic and methacrylic nitriles -and the copolymers of these vinyl monomers with each other or with alkyl esters (1-8C) of ethylenic acids (4-5C); polycondensates of polyols with one or more unsaturated polycarboxylic acids or anhydrides and optionally one or more saturated polycarbuxylic acids or anhydrides.

your 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 10 μm. 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, manganese, aluminum, titanium - oxides iron: Fe304 or g Vie203 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 a colloidal suspension of the particles in an organic medium compatible with the organic phase. The organic medium is chosen from halogenated or non-halogenated hydrocarbons, 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 the peroxides of benzoyl, of dicumyl, of ditiobutyl, of diacetyl, of lauroyl, of methyl ethyl ketone, of caprylyl, of 2,4-dichloro benzoyl, of parachlorobenzoyl, the perpivalate, diethylpera acetate, perbenzoate terti ditertiobutyl diperphthalate, 1, l-ditertiobutyle-peroxy-3 '3, 5-trimethylcyclohexane, azobis-isobutyronitrile, azobiscyclohexane carbonitrile.

 It is possible to use one or more initiators introduced into the reaction medium as a mixture or successively; the choice of initiator (s) being a function of the polymerization temperature.

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

As organic colloids, there may be mentioned: polyvinyl alcohol, polyvinylpyrrolidone, styreneanhydride copolymers, sulfonated polystyrenes, polyglycolic ethers, gelatin, alkyl- and hydroxyalkyl-cellu ~ loses; and as mineral colloids: calcium and magnesium carbonates, barium sulphate, zinc and aluminum oxides, magnesium and barium phosphates, and more particularly trical cic. 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 of 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 acid solution. mineral, 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 of average size 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 non-limiting example, in which the viscosity of the polymer solution in the monomer is measured using a Brookfield viscosi meter, speed 50 rpm, needles and temperatures adapted to each solution.

Example 1
560 g of a homogeneous solution at 7% by weight in the distilled styrene of propylene glycol fumarophthalate with a molecular weight of approximately 1,500 are introduced into a 4-liter reactor fitted with an agitator. The Brookfield viscosity of the solution at 20 C, needle # 1, is 10 mPa.S.

 16.8 g of needles of # Fe203 0.2 to 1 Am in length are added to the solution. The stirred dispersion is kept at room temperature for 1 hour, with the addition after 3.80 minutes of 3.85 g of benzoyl peroxide.

2815 g of an aqueous solution containing 9.6 g of disodium phosphate and 0.32 g of polyvinyl alcohol are then added, then the dispersion is heated to 900C and maintained at this temperature for 10 hours.

After cooling, the product formed is filtered, washed with water and finally dried at 60 C.

 543 g of brown pearls are obtained, which contain 2.3% by weight of Fie 203 They can be attracted by a magnet.

Example 2
Into a 4 liter reactor, fitted with an agitator, are introduced
- 240 g of a solution at 5% by weight in distilled styrene of polymethyl methacrylate of viscosity 500 mPa.S (determined by flow in a capillary tube of the solution at 30% by weight of the polymer in toluene at 250C) . The Brookfield viscosity of the solution at 200C, needle n01, is 13 mPa.S.

 - 320 g of the same polymethyl methacrylate solution, in which are dispersed 16.8 g of needles of + e203 of 0.2 to ltum in length.

To the stirred mixture is then added 4.97 g of benzoyl peroxide, then 2862 g of an aqueous solution containing 9.6 g of disodium phosphate and 2.52 g of polyvinyl alcohol. your dispersion is then heated to 900C, then kept at this temperature for 10 hours.

After cooling, the product formed is filtered, washed with water and dried at 60 C.

533 g of brown pearls are obtained. Their particle size distribution is as follows
<0.20 mm 14.9% by weight
between 0.20 and 0.40 mm 78.5% by weight
between 0.40 and 0.50 mm 4.7% by weight
. between 0.50 and 1 mm 1.4% by weight
. > 1 mm 0.6% by weight.

The size fraction 0.20-0.40 mm contains 1.4% by weight of
Fe203. Pearls can be attracted to a magnet.

Claims (12)

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 filler magnetic and is characterized in that the magnetic charge is dispersed in a solution, in the monomer (s), of at least one polymer insoluble in water and represented by a vinyl homo- or co-polymer or a polycondensate of polyol and unsaturated polycarboxylic acid or anhydride, 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 solution of homo- or co-polymer in the monomer (s) is obtained by dissolution, in all or part of the monomer (s) to be polymerized, of at least one polymer soluble in the monomer (s) to be polymerized and insoluble in water. 3) Method according to claim 1, characterized in that the polymer concentration of the organic phase is less than 60% by weight.  4) Process according to claim 1, characterized in that the vinyl aromatic compounds, used alone or as a mixture between them, are represented by styrene, alpha-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene. 5) Method according to claim 1, characterized in that the copolymerizable monomers are vinyl compounds or alkyl esters of ethylenic acids.  6) Method according to claim 1, characterized in that a crosslinking monomer is used in proportions of between 0 and 10 Z by weight relative to the (x) monomer (s).  7) Method according to claim 1, characterized in that a chain limiter is implemented in proportions between O and 5 Z by weight relative to the monomer (s).  8) 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.  9) Method according to claim 1, characterized in that the size of the magnetic charge particles is between 0.005 and 10 / in. 10) 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. 11) 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.  12) Vinyl aromatic polymers obtained by the process of claim 1, in the form of magnetic beads of average size between 0.05 and 3 mm.