Production of spherical polymers

Details Production of spherical polymers Production of spherical polymers

1999-12-10

2001-09-25

Teskin, Fred (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S083000, C526S084000, C526S209000, C526S212000, C526S245000, C526S279000, C526S329200, C526S329700, C526S346000

Reexamination Certificate

active

06294623

ABSTRACT:

The present invention relates to the production of spherical polymers having a mean particle size of 0.5 to 50 um and narrow particle size distribution.
Spherical polymers having a mean particle size of 0.5 to 50 um are widely used, for example as spacers for film materials, as catalyst supports, as calibrating substances for light scattering measurements, or as starting materials for chromatography resins and ion exchangers. For many applications polymers are desired having as uniform a particle size as possible.
So-called dispersion polymerization is generally used to produce polymers having mean particle sizes of 0.5 to ca. 10 um. In this process a solvent is used that dissolves the monomer but not the polymer that is formed. During the polymerization the polymer formed precipitates out in the form of small spheres. Suitable solvents are primarily alcohols, mixtures of various alcohols, and mixtures of alcohol and water. A characteristic feature of this process is that the reaction becomes less reproducible with increasing particle size and the particle size distribution becomes significantly broader.
A. J. Paine et al. describe in their work, “Dispersion Polymerization of Styrene in Polar Solvents”, Macromolecules 1990, 23, 3104-3109, that when using butyl mercaptan as chain transfer agent, polydisperse particles are obtained. A similar effect is found in EP 584 407 in the dispersion polymerization of methyl methacrylate using lauryl mercaptan as molecular weight regulator. In both these literature references the influence of the molecular weight regulator on the particle size is slight.
It has now surprisingly been found that by adding sulfur-free radical interceptors in the dispersion polymerization, the mean particle size is displaced to considerably higher values. In this way monodisperse bead polymers can be obtained in a size range that is not possible using the methods of the prior art. Furthermore, in many cases a narrower particle size distribution is achieved.
The present invention provides a process for producing bead polymers having a mean particle size of 0.5 to 50 um and a narrow particle size distribution by dispersion polymerization of at least one monomer in a solvent, characterized in that the solvent contains 5 to 3000 ppm of sulfur-free radical interceptors. A narrow particle size distribution &phgr;90/&phgr;10 value is at most about 2 &mgr;m, preferably at most about 1.6 &mgr;m.
The process according to the invention is preferably carried out using an initiator, in the presence of a high molecular weight dispersant.
Suitable monomers for the process are monoethylenically unsaturated compounds such as styrene, alpha-methyl styrene, chlorostyrene, (meth)acrylic acid esters, for example (meth)acrylic acid esters containing perfluoroalkyl groups. Styrene and methyl methacrylate are preferred. In order to achieve crosslinking small amounts of silane monomers may also be used according to EP-A-417 539.
The solvent comprises mainly non-aqueous solvents such as dioxane, acetone, acetonitrile, dimethyl formamide and alcohols. Lower alcohols are preferred, in particular methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol and tert.-butanol. Mixtures of various solvents, in particular mixtures of different alcohols, are also very suitable. The alcohols may also contain up to 50 wt. % of water, preferably up to 25 wt. % of water. When using solvent mixtures, non-polar solvents may also be used, in particular hydrocarbons such as hexane and heptane, in amounts of up to 50 wt. %.
The ratio of monomer to solvent is 1:1 to 1:20, preferably 1:3 to 1:10.
Soluble natural and synthetic macromolecular compounds are suitable as high molecular weight dispersants in the solvent that is employed. Examples include cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, partially saponified polyvinyl acetate, polyvinyl pyrrolidone, copolymers of vinyl pyrrolidone and vinyl acetate, as well as copolymers of styrene and maleic anhydride. Polyvinyl pyrrolidone is preferred. The amount of high molecular weight dispersant is 0.1 to 20 wt. %, preferably 0.2 to 10 wt. %, referred to the solvent.
In addition to the dispersants, ionic and non-ionic surfactants may also be used. Suitable surfactants are for example sodium sulfosuccinate, methyltricaprylammonium chloride or ethoxylated nonyl phenol. The surfactants may be used in amounts of 0.1 to 2 wt. % referred to the solvent.
Suitable initiators for the process according to the invention include compounds that form free radicals on raising the temperature. Examples of such initiators are: peroxy compounds such as dibenzoyl peroxide, dilauryl peroxide, bis(p-chlorobenzoyl peroxide), dicyclohexylperoxy dicarbonate and tert.-amylperoxy-2-ethylhexane, as well as azo compounds such as 2,2′-azobis(isobutyronitrile) and 2,2′-azobis(2-methylisobutyronitrile). If the polar medium contains water, then sodium peroxy-disulfate is also suitable.
Aliphatic peroxy esters corresponding to formulae I, II or III are also highly suitable:
wherein
R
1
denotes an alkyl radical or a cycloalkyl radical with 2 to 20 C atoms,
R
2
denotes a branched alkyl radical with 4 to 12 C atoms, and
L denotes an alkylene radical or cycloalkylene radical with 2 to 20 C atoms.
Examples of aliphatic peroxy esters according to formula I are:
tert.-butylperoxy acetate
tert.-butylperoxy isobutyrate
tert.-butylperoxy pivalate
tert.-butylperoxy octoate
tert.-butylperoxy-2-ethylhexanonate
tert.-butylperoxy neodecanoate
tert.-amylperoxy pivalate
tert.-amylperoxy octoate
tert.-amylperoxy-2-ethylhexanonate
tert.-amylperoxy neodecanoate.
Examples of aliphatic peroxy esters according to formula II are:
2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexane
2,5-dipivaloyl-2,5-dimethylhexane
2,5-bis(2-neodecanoylperoxy)-2,5-dimethylhexane.
Examples of aliphatic peroxy esters according to formula III are:
di-tert.-butylperoy azelate
di-tert.-amylperoy azelate.
The initiators are generally used in amounts of 0.05 to 6.0 wt. %, preferably 0.2 to 4.0 wt. %, referred to the monomer or the monomer mixture.
Radical interceptors in the context of this invention include polymerisation inhibitors as well as molecular weight regulators.
Inorganic as well as organic compounds are suitable as polymerisation inhibitors. Examples of inorganic inhibitors include e.g. nitrogen compounds such as hydroxylmine, hydrazine, sodium nitrite and potassium nitrite. Examples of organic inhibitors include phenolic compounds such as hydroquinone, hydroquinone monomethyl ether, resorcinol, pyrocatechol, tert.-butylpyrocatechol, and condensation products of phenols and aldehydes. Further suitable organic inhibitors are nitrogen-containing compounds such as diethylhydroxylamine and isopropylhydroxylamine.
Suitable molecular weight regulators are the sulfur-free regulators disclosed in for example DE 3 010 373, for example the enol ether according to formula IV.
The concentration of the radical interceptor is preferably 10-1500 ppm referred to the solvent. Inhibitors are particularly preferably used in amounts of 10-500 ppm, and molecular weight regulators preferably in amounts of 100-1500 ppm, in each case referred to the solvent.
The polymerisation temperature is governed by the decomposition temperature of the radical former as well as by the boiling point of the solvent, and is typically in the range from 50° C. to 150° C., preferably 60° to 120° C. The polymerisation is advantageously carried out at the boiling point of the solvent and the reactants are advantageously stirred during the polymerisation. The polymerisation time is generally several hours, for example 2 to 30 hours.
The polymers obtained according to the invention can be isolated from the reaction mixture by filtration or, particular preferably, by sedimentation by means of a centrifuge or a decanter.
The polymers obtained by the process according to the invention may be used for example as spacers for film materials, as catalyst supports, or as starting materials for chro

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