Method of making highly adsorptive copolymers

Abstract: A precipitation polymerization process for the production of a macroporous crosslinked copolymer in which there is added to a reactor equipped with a stirrer, at least one monounsaturated monomer and at least one polyunsaturated monomer, dissolving an inorganic polymerization reaction initiator in a homogeneous minimum-boiling binary azeotrope including a solvent and water and conducting the polymerization in the azeotrope.

Description: CH-A 458 743 describes a process for the polymerization of olefinically unsaturated monomers which are not miscible with water in the presence of hydrogenperoxide as catalyst. For preparing unique phase from the monomers and the catalyst an azeotrope of a hydrocarbon and an alcohol or a ketone can be used. This invention relates to an improvement in the process for the production of a macroporous, crosslinked, copolymer powder in a reactor equipped with a stirrer, by precipitation polymerization in a solvent containing at least one monounsaturated monomer and at least one polyunsaturated monomer soluble therein and in which the improvement involves conducting the polymerization in the reactor by dissolving an inorganic polymerization reaction initiator in a homogeneous minimum boiling binary azeotrope including water and a solvent selected from the group consisting of isopropyl alcohol, ethyl alcohol, 1-propanol, 1-butanol and methanol and conducting the polymerization in the azeotrope at a stirring rate of up to 300 rpm. The solvent can be removed from the porous copolymer at the conclusion of the polymerization, in which case, the copolymer is mixed with a functional material in order to disperse and uniformly distribute the functional material throughout the porous copolymer and to entrap the functional material there within. The functional material can be water,silicone oils, glycerine, mineral oil, organic esters, glycols and glutamates. One monomer of the copolymer is a monounsaturated monomer such as lauryl methacrylate and the other monomer of the copolymer is a polyunsaturated monomer such as ethylene glycol dimethacrylate. The copolymer can also be formed using only polyunsaturated monomers. The copolymer is in the form of a powder and the powder in a combined system of particles. The system of powder particles includes unit particles of less than one micron in average diameter, agglomerates of fused unit particles of sizes in the range of twenty to eighty microns in average diameter and aggregates of clusters of fused agglomerates of sizes in the range of two hundred to twelve hundred microns in average diameter. A precipitation polymerization process is used for producing the macroporous crosslinked copolymer. In the process, there is copolymerized at least one monounsaturated monomer and at least one polyunsaturated monomer in the presence of an organic liquid which is a solvent for and dissolves the monomers but not the copolymer. The copolymerization of the monomers is initiated by means of a free radical generating catalytic compound, precipitating a copolymer in the solvent in the form of a powder. A dry powder is formed by removing the solvent from the precipitated copolymeric powder. The solvent is selected from the group consisting of isopropyl alcohol, ethyl alcohol, 1-propanol, 1-butanol and methanol and preferably isopropyl alcohol. The monounsaturated monomer and the polyunsaturated monomer can be present in mol ratios of, for example, 20:80, 30:70, 40:60 or 50:50. The process includes the step of stirring the monomers, solvent and the free radical generating catalytic compound, during copolymerization. Preferably, the dry powder is formed by filtering excess solvent from the precipitated powder and the filtered powder is vacuum dried. The powder may then be "post adsorbed" with various functional materials. The powders of the present invention are highly adsorptive and may be used as carriers or adsorbents for materials such as water, aqueous systems emollients, moisturizers, fragrances, dyes, pigments, flavors, drugs such as ibuprofen, phosphoric acid, insect repellents, vitamins, sunscreens, detergents, cosmetics, pesticides, pheromones, herbicides, steroids, sweeteners, pharmaceuticals and antimicrobial agents. Finely divided solids such as analgesic materials can be adsorbed by dissolving the finely divided analgesic in a solvent, mixing the analgesic and solvent with the powder and removing the solvent. Other post adsorbable materials include alkanes, alcohols, acid eaters, silicones, glycols, organic acids, waxes and alcohol ethers. These and other objects, features and advantages, of the present invention will become apparent when considered in light of the following detailed description, including the accompanying drawings. Figure 1 in the drawings is a photomicrograph of the various components of the complex structure of the powder produced in Comparative Example I and including unit particles, agglomeratures and aggregates. Figures 2 and 3 are photomicrographs of the agglomerates and aggregates of Figure 1, respectively, shown on a larger scale. Figure 4 is a photomicrograph of a copolymeric powder material. The powder is shown in magnification as it appears when the agitation rate employed in the process for producing the powder is zero rpm. Figures 5-8 are additional photomicrographs of copolymeric powder materials. The powder is shown in magnification as it appears when the agitation rate employed in the process for producing the powder varies from seventy-five rpm up to eight hundred rpm. In the above figures in the drawing, the magnification is indicated in each instance. For example, the magnification in Figures 4-7 is 1000X and 2000X in Figure 8. Figures 4-8 also include an insert identifying a length approximating ten microns for comparative purposes. It should be pointed out, that in viewing the various figures, one will note that as the rate of stirring is increased from zero rpm up to eight hundred rpm, that the size of the unit particles increase. This is in direct opposition to what has been traditionally observed in suspension polymerization systems, wherein increases in stirring rates decrease particle size. Because of the increased size of the unit particles shown in Figure 8 and the resulting decrease in surface area, the adsorptive capacity of these large particles is less than the adsorptive capacity oft he smaller sized particles shown in Figures 4-7. According to the present invention a rate of stirring is maintained below three hundred rpm. The material of the present invention, can be broadly and generally described as a crosslinked copolymer capable of entrapping solids, liquids and gases. The copolymer is in particulate form and constitutes free flowing discrete solid particles even when loaded with an active material. When loaded, it may contain a predetermined quantity of the active material. One copolymer of the invention has the structural formula: where the ratio of x to y is 80:20, R' is -CH₂CH₂- and R'' is -(CH₂)₁₁CH₃. The copolymer is a highly crosslinked copolymer, as evidenced by the foregoing structural formula and is more particularly a highly crosslinked polymethacrylate copolymer. This material is manufactured by the Dow Corning Corporation, Midland, Michigan, U.S.A., and sold under the trademark POLYTRAP®. It is a low density, highly porous, free-flowing white particulate and the particles are capable of adsorbing high levels of lipophilic liquids and some hydrophilic liquids, while at the same time maintaining a free-flowing particulate character. In the powder form, the structure of the particulate is complex and consists of unit particles less than one micron in average diameter. The unit particles are fused into agglomerates of twenty to eighty microns in average diameter. These agglomerates are loosely clustered into macro-particles termed aggregates of about 200 to about 1200 microns in average diameter. Adsorption of actives to form post adsorbent powder, can be accomplished using a stainless steel mixing bowl and a spoon, wherein the active ingredient is added to the empty dry powder and the spoon is used to gently fold the active into the powder. Low viscosity fluids may be adsorbed by addition of the fluids to a sealable vessel containing the powder and tumbling the materials until a consistency is achieved. More elaborate blending equipment such as ribbon or twin cone blenders can also be employed. The following example illustrates the method for making a post adsorbent powder, of the type illustrated in Figures 1-3 and 4-8. Comparative Example I A hydrophobic porous copolymer was produced by the precipitation polymerization technique by mixing in a five hundred milliliter polymerization reactor equipped with a paddle type stirrer, 13.63 grams of ethylene glycol dimethacrylate monomer or eighty mole percent and 4.37 grams of lauryl methacrylate monomer or twenty mole percent. Isopropyl alcohol was added to the reactor as the solvent in the amount of 282 grams. The monomers were soluble in the solvent, but not the precipitated copolymer. The process can be conducted with only polyunsaturated monomers if desired. The mixture including monomers, solvent and 0.36 grams of catalytic initiator benzoyl peroxide, was purged with nitrogen. The system was heated by a water bath to about 60°C. until copolymerization was initiated, at which time, the temperature was increased to about 70-75°C. for six hours, in order to complete the copolymerization. During this time the copolymer precipitated from the solution. The copolymerization produced unit particles of a diameter less than about one micron. Some of the unit particles adhered together providing agglomerates of the order of magnitude of about twenty to eighty microns in diameter. Some of the agglomerates adhered further and were fused and welded one to another, forming aggregates of loosely held assemblies of agglomerates of the order to magnitude of about two to eight hundred microns in diameter. The mixture was filtered to remove excess solvent and a wet powder cake was tray dried in a vacuum oven. A dry hydrophobic copolymeric powder consisting of unit particles, agglomerates and aggregates was isolated. The adsorptive capacity of the hydrophobic particulates produced in Example I, as a function of the stirring rate, was determined. The stirring rate during the reaction in Example I significantly influenced the adsorption properties of the particulate materials. The adsorptivity of the particulate materials decreases with an increase in stirring rate and the density of the particulate increases. These results are set forth in Tables I-III. In the foregoing tables, it can be seen that adsorption and density, as a function of stirring rate, was determined for several fluids including a silicone oil, water, mineral oil, glycerine and an organic ester. From zero rpm up to about 250 rpm, the adsorptivity of the porous copolymeric powder particulates of Example I remained essentially consistent. However, at about three hundred rpm, there was a substantial decrease in adsorptivity, which decrease becomes more apparent as the stirring rate was increased up to about one thousand rpm. A similar pattern is evidenced by the data which are reflective of the density. This phenomenon is more apparent in the photomicrographic figures of the drawing. Thus, it can be seen from Figure 4, that the particle size of the unit particles increases as the stirring rate is increased, as evidenced by Figure 8. A progression in this phenomenon can be observed in Figures 5-7. Examples of polyunsaturated monomers suitable for use in accordance with the present invention are ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, trimethylol propane ethoxylated triacrylate, ditrimetholol propane dimethacrylate, propylene, dipropylene and higher propylene glycols, 1,3-butylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, pentaerythritol dimethacrylate, dipentaerythritol dimethacrylate, bisphenol A dimethacrylate divinyl and trivinyl benzene, divinyl and trivinyl toluene triallyl maleate, triallyl phosphate, diallyl maleate, diallyl itaconate and allyl methacrylate. The monounsaturated monomers include allyl methacrylates and acrylates having straight or branched chain alkyl groups with 1 to 30 carbon atoms, preferably 5 to 18 carbon atoms. Preferred monomers include lauryl methacrylate, 2-ethylhexyl methacrylate, isodecylmethacrylate, stearyl methacrylate, hydroxy ethyl methacrylate, hydroxy propyl methacrylate, diacetone acrylamide, phenoxy ethyl methacrylate, tetrahydrofurfuryl methacrylate and methoxy ethyl methacrylate. As noted previously, the copolymer can be formed by copolymerizing one monounsaturated monomer with one polyunsaturated monomer or with only polyunsaturated monomers. An azeotrope is a solution of two or more liquids which form a constant boiling solution at a particular composition. Azeotropic mixtures distill at constant temperature without change in composition and cannot be separated by normal distillation procedures. A solution of two components which form an azeotrope may be separated by distillation into one pure component and the azeotrope but not into two pure components. Mixtures which have boiling temperatures much lower than the boiling temperature of either component exhibit negative deviation when such mixtures have a particular composition range. For example, water which has a boiling point of 100°C. and isopropyl alcohol which has a boiling point of 82.4°C., form an azeotrope with 12.1 percent water that boils at 80.4°C. The azeotropes of water and C₂-C₅ alcohols all have minimum boiling points and are classified as homogeneous minimum boiling binary azeotropes. Such characteristics of azeotropes is utilized in accordance with the present invention and it has been bound that submicron sized polymers can be prepared by precipitation polymerization in such water containing systems. The catalyst is dissolved in an azeotrope and the polymerization is conducted in the azeotropic system. The azeotrope can be recovered following polymerization. Polymerization under such conditions permits the use of inorganic initiators in place of organic initiators which often decompose and contaminate the product with toxic substances. Organic solvents miscible with water are preferred such as the lower alcohols of methanol, ethanol, 1-propanol, 2-propanol and 1-butanol; and other solvents such as ketones, amines, amides and acids, can also be employed. The water content will vary with the particular solvent and in the case of ethanol, the water content required is 4.4 percent. Isopropyl alcohol requires 12.1 percent water, n-propyl alcohol requires 28.3 percent water and tert-butyl alcohol requires 11.8 percent water. Among the inorganic initiators preferred in accordance with the herein described invention are perborates, persulfates and peroxide sulfates. Exemplary of such inorganic initiators are ammonium persulfate, potassium persulfate, sodium persulfate and ammonium peroxysulfate. While it is not new to employ inorganic persalts as initiators as evidenced by U.S. Patent No. 3,418,262, issued December 24, 1968, the combination of inorganic initiators in an azeotrope is not believed to be taught in the prior art. Not only do such inorganic initiators decompose to harmless by-products in contrast to organic initiators, but the inorganic initiators can be employed in much lower concentrations than the organic initiator. The following examples are set forth to illustrate this unique concept of the present invention. Example I The equipment of Comparative Example I was employed and 0.9 grams of ammonium persulfate was dissolved in 397 grams of water. The solution was mixed with 2473 grams of anhydrous isopropyl alcohol to form an azeotrope containing 12.3 percent water. Into this solution was dissolved 43.74 grams of lauryl methacrylate and 136.26 grams of ethylene glycol dimethacrylate. The stirring speed of the reactor paddle was adjusted to 75 rpm and a positive nitrogen pressure applied. The temperature was raised to 60-65°C. and the precipitation of the polymer was initiated. The heating was continued for six hours at 75°C. in order to complete the polymerization. After cooling to room temperature, the polymer was filtered and air dried yielding 169.25 grams of product or a yield of ninety-four percent. Example II Example I was repeated with amounts of ammonium persulfate of 2.0, 1.0, 0.25 and 0.1 percent, resulting in yields of 93.0, 93.0, 92.0 and 85.0 percent, respectively. Example III Example I and II were repeated with sodium and potassium persulfate and similar results were obtained as noted above for Examples I and II.

Claims: Process for the production of a macroporous crosslinked copolymer powder in a reactor equipped with a stirrer by precipitation polymerization in a solvent containing at least one polyunsaturated monomer soluble therein and at least one monounsaturated monomer, characterized by conducting the polymerization by dissolving an inorganic persalt polymerization reaction initiator in a homogeneous minimum-boiling binary azeotrope including water and a solvent selected from the group consisting of isopropyl alcohol, ethyl alcohol, 1-propanol, 1-butanol and methanol, and conducting the polymerization in the azeotrope at a stirring rate of up to 300 rpm. The process of claim 1 wherein the polyunsaturated monomer is selected from the group consisting of divinylbenzene, tetraethylene glycol dimethacrylate and ethylene glycol dimethacrylate. The process of claim 1 wherein the initiator is selected from the group consisting of ammonium persulfate, potassium persulfate and sodium persulfate. The process of claim 1 in which the copolymer powder is a combined system of particles, the system of powder particles including unit particles of less than one micron in average diameter, agglomerates of fused unit particles of sizes in the range of twenty to eighty microns in average diameter and aggregates of clusters of fused agglomerates of sizes in the range of two hundred to twelve hundred microns in average diameter. The process of claim 4 wherein the copolymer is formed of a highly cross linked polymethacrylate copolymer. The process of claim 1 wherein the azeotrope is removed from the copolymer at the conclusion of the polymerization. The process of claim 6 wherein the copolymer is mixed with a functional material in order to disperse and uniformly distribute the functional material throughout the copolymer and to entrap the functional material therewithin. The process of claim 7 wherein the functional material is selected from the group consisting of water, glycols, glutamates, silicone oils, glycerine, mineral oil and organic esters. The process of claim 1 including adding to the reactor at least one monounsaturated monomer in addition to the polyunsaturated monomer and conducting the polymerization in the reactor by stirring the azeotrope, the monounsaturated monomer and the polyunsaturated monomer, at stirring rates in the reactor of from zero revolutions per minute to three hundred revolutions per minute; the polyunsaturated monomer being selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate, and tetraethylene glycol dimethacrylate; the monounsaturated monomer being selected from the group consisting of diacetone acrylamide, styrene, vinyl pyrrolidone, isobornyl methacrylate, phenoxyethyl methacrylate, isodecyl methacrylate, stearyl methacrylate, hydroxypropyl methacrylate, cyclohexyl methacrylate, dimethylaminoethyl methacrylate, t-butyl aminoethyl methacrylate, 2-acrylamido propane sulfonic acid, butyl methacrylate, 2-ethylhexyl methacrylate, methyl methacrylate, lauryl methacrylate and 2-hydroxyethyl methacrylate.

Inventors: CARMODY WALTER JAMES, CHROMECEK RICHARD CHARLES, KLEIN WILLIAM LEWIS, SOJKA MILAN FRANZ, CARMODY, WALTER JAMES, CHROMECEK, RICHARD CHARLES, KLEIN, WILLIAM LEWIS, SOJKA, MILAN FRANZ
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1990
Main classification: C08F2
IPC codes: C08J9, C08F6, C08F220, C08F2