Method of making highly adsorptive polymers

Abstract: A method of forming a highly adsorptive polymer. which includes the steps of: a) homogeneously mixing a solution of a monomer consisting exclusively of one or more types of polyunsaturated monomer, a monomer solvent and an initiator, b) polymerizing the monomers to form a polymer. wherein the monomer solvent is a solvent for the monomers and a non-swelling non-solvent for the polymers, and c) removing the solvent from the polymer to form a dry powder.

Description: The invention relates to a method of making highly adsorptive polymers, specifically by polymerization of monomers by the precipitation polymerization technique. In the art of making polymeric particles capable of entrapping fluids and/or solids (actives), there exists a few different techniques that are usually used. One such technique entails polymerization in the presence of actives giving monolithic articles where the actives stay in the monolithic article (in situ polymerization) or are extracted, leaving macroporous crosslinked polymeric structures. In the latter case, the actives, since they are forming pores, are sometimes called porogens. After extraction, the rigid porous polymer can be refilled by other actives. The porogen is soluble in the monomers, but does not swell the resulting polymer. Dependent on the physical properties of the porogen, the formation of the macropores can be achieved by proper (increased) crosslinking. A very convenient method of preparation of both of these systems is suspension polymerization in a medium (solvent) which does not dissolve the monomers and actives. Usually for hydrophobic systems, the solvent is water and for hydrophilic systems, the solvent is cyclohexane, benzene, toluene, xylene, chlorobenzenes, chloroethanes, etc. Protective colloids such as polyvinylpyrolidone, polyvinylalcohol, magnesium hydroxide, calcium phosphate, etc. are used to prevent the coalescence of the beads during polymerization. Both of the above mentioned systems are "in situ polymerization" techniques, using the same principle in that the polymerization is carried out in the presence of the active or porogen. The only difference between these systems is that, in the case of the actives, the product is used as such, while in the case of the porogen, the porogen is usually extracted and replaced by another material. The procedure of extracting and replacing is very often tedious, adding cost to the manufacturing. In situ polymerization is carried out by dissolving the monomers in a functional material to form a uniform solution and, thereafter, inducing polymerization. The functional material must be a solvent for the monomers, but not a swelling agent for the polymer. The resulting product of in situ polymerization is a solid material formed of a polymeric lattice entrapping the functional material. The amount of functional material used is such that when polymerization is complete, the functional material is substantially wholly contained within the polymeric lattice and does not exist freely in the product. If the functional material is extracted from the polymeric lattice, the resulting polymer is in the form of hard, porous beads. The third method of making polymers capable of entrapping other materials is by precipitation polymerization. The resulting product from precipitation polymerization is generally a polymer in the form of a powder and the powder is a combined system of particles. The system of powder particles includes unit particles, agglomerates of fused unit particles and aggregates of clusters of fused agglomerates. The particles themselves are not generally highly porous. This invention describes an improved method for making such powders using precipitation polymerization. U.S. Patent No. 4,414,278, in particular, describes a method for providing crosslinked polymer beads derived from homopolymers and copolymers of triacrylate and tetracrylate monomers. The polymer beads thus formed do not agglomerate but remain as discrete particles having an average diameter in the range of 0.7 to 20 µm. As described, the type of polymerization technique used is an important factor in the determination of the resulting product. In addition, within each type of polymerization, there are procedural alternatives which, too, can have a significant impact on the resulting product. The differences in the polymerization techniques are enough that a procedure used in one type of polymerization technique will not necessarily have the same effect if used in another polymerization technique. Therefore, techniques and procedures are carefully selected based on the product properties desired. With respect to the prior art, however, there remains a need for an easy, consistent method of making submicron size, highly adsorptive, powder-type polymers which are of a soft nature suitable for cleaning scratchable surfaces, such as contact lenses. The method of the invention provides a solution for the above-mentioned need. Specifically, the invention is a method of forming a highly adsorptive polymer, comprising the steps of: a) homogeneously mixing a solution comprising from 0.1 parts by weight to less than 25 parts by weight of a monomer consisting exclusively of one type of polyunsaturated monomer, from greater than 75 parts by weight up to 99.9 parts by weight of a monomer solvent, wherein the total weight of the monomers and the monomer solvent is 100 parts and 0.05 to 5 weight percent initiator based on the weight of said monomer, and b) polymerizing the monomers to form a polymer, wherein the monomer solvent is a solvent for the monomers and a non-swelling non-solvent for the polymer, and c) removing said solvent from said polymer to form a dry powder which comprises unit particles ranging in size from 0.1 to 0.5 microns in diameter, agglomerates of fused unit particles ranging in size from 10 to 80 microns in average diameter and aggregates of clusters of fused agglomerates ranging in size from 200 to 800 microns in average diameter. The method has the advantage of being simpler than prior art methods since only one monomer type is polymerized, because this results in a reduction of measuring steps required and reduces the variability of the product by reducing chances for error in measuring the ingredients. The resulting polymer can adsorb large quantities of various substances, having different structures and properties. The highly crosslinked polymeric systems of this invention are prepared by polymerizing monomers having at least two unsaturated bonds (hereinafter referred to as "polyunsaturated" monomers) and containing no comonomers having monounsaturated moiety. Examples of this group of monomers can be polyacrylates ("poly" meaning two or more), methacrylates or itaconates of: ethylene glycol, propylene glycol; di-, tri-, tetra- or polyethylene glycol and propylene glycol; trimethylol propane, glycerine, erythritol, xylitol, penta erythritol, di penta erythritol, sorbitol, mannitol, glucose, sucrose, cellulose, hydroxyl cellulose, methyl cellulose, 1,2 or 1,3 propanediol; 1,3 or 1,4 butanediol, 1,6 hexanediol, 1,8 octanediol, cyclohexanediol or cyclohexanetriol. Similarly, bis acrylamido or methacrylamido compounds can be used. These compounds are, for example, methylene bis acryl or methacrylamide, 1,2 dihydroxy ethylene bis acryl or methacrylamide, hexamethylene bis acryl or methacrylamide. Another group of valuable monomers could be represented by di- or polyvinyl esters such as divinyl oxalate, malonate, succinate glutarate, adipate, sebacate, divinyl maleate, fumarate, citraconate and mesaconate. Still another group of monomers is represented by di or poly vinyl ethers of ethylene, propylene, butylene, glycols, glycerine, penta erythritol, sorbitol, divinyl ether, di or poly allyl compounds such as those based on glycols and glycerine, or combinations of vinyl allyl or vinyl acryloyl compounds such as vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, methallyl methacrylate or methallyl acrylate. In addition, aromatic, cycloaliphatic and heterocyclic compounds are suitable for this invention. These compounds include divinyl benzene, divinyl toluene, divinyl diphenyl, divinyl cyclohexane, trivinyl benzene, divinyl pyridine and divinyl piperidine. Furthermore, divinyl ethylene or divinyl propylene urea and similar compounds may be used, e.g., as described in U.S. Patent Nos. 3,759,880, 3,992,562 and 4,013,825. Acryloyl- or methacryloyl-endcapped siloxane and polysiloxanes such as those described in U.S. Patent Nos. 4,276,402 and 4,341,889, French Patent No. 2,465,236 and German Publication GER OLS No. 3,034,505, are suitable for this invention. Methacryloyl-endcapped urethanes, such as those described in U.S. Patent Nos. 4,224,427, 4,250,322 and 4,423,099, German Publications GER OLS 2,365,631 and 2,542,314, Japanese Patent Applications 85/233,110, 86/09,424 and 86/30,566 and British Patent 1,443,715. Urethane acrylates of polysiloxane alcohols as described in U.S. Patents 4,543,398 and 4,136,250 and bisphenol A bis methacrylate and ethoxylated bisphenol A bis methacrylate are also suitable monomers for this invention. It should be understood that one type of the above-mentioned monomers is used in this invention. The type of monomer used may be selected according to the adsorption properties desired. The chemical structure and adsorption property can be adjusted via changing the structure of the chain between the unsaturated bonds. For example, if the monomer has a saturated hydrocarbon structure like 1,4 butanediol bis methacrylate, the adsorptivity of the powder will be shifted more to the hydrophobic side, while tetraethylene glycol bis methacrylate, having -CH₂CH₂O- units in its connecting chain will impart a more hydrophilic character. The polymerization is simply done by dissolving the monomers in a solvent which does not swell or dissolve the resulting polymer. Based on the parts by weight of the monomer and the solvent totalling 100 parts by weight, the monomers are used from 0.1 to less than 25 parts by weight, preferably, from 2 to less than 25 parts by weight and, more preferably, from 5 to 20 parts by weight. Correspondingly, the solvent is present from greater than 75 parts by weight to 99.9 parts by weight, preferably, from greater than 75 parts by weight to 98 parts by weight and, most preferably, from 80 parts by weight to 95 parts by weight. No surfactant or dispersing aid is required. In the majority of cases, alcohols can be used as the monomer solvent. It is important that the solvent does not swell the polymer or the polymer will become hard upon drying. Swelling is considered to be evidenced by an increase in volume or by dilation. The amount of swelling that is considered excessive or detrimental depends on the polymer. Detrimental swelling causes the gluing of unit particles together, resulting finally in a clear gel. For example, when isopropyl alcohol is used as the monomer solvent when making a polymer from tetraethylene dimethacrylate, it was surprisingly found that the isopropyl alcohol must be anhydrous or the water/isopropyl alcohol cosolvent will swell the poly(tetraethylene glycol methacrylate), causing the polymer to be hard upon drying. For this invention, swelling is determined to be minimal (thus, acceptable) when submicron particles are obtained. On the other hand, if the particles after drying are glued together, forming a hard mass, there is considered limited swelling. Preferably, the solvent is relatively volatile, having a boiling point of less than 80°C at one atmosphere and is water-miscible. The method of this invention is further simplified from many prior art methods in that the removal of the solvent is done simply by filtration and evaporation, e.g. by heat and/or vacuum. In the specific case of making poly(tetraethylene glycol methacrylate) with isopropyl alcohol, it was found that the drying had to be done under anhydrous conditions or the polymer would become hard upon drying. By anhydrous conditions, it is generally meant that humidity during drying be less than 40 % relative humidity. Generally, no solvent extraction is required. The polymer can be washed with a suitable solvent, e.g. the same solvent used in polymerization, before it is dried. The polymerization is achieved by using one of a variety of free radical initiators which can be, among others, an azo compound, a peroxy dicarbonate, a peroxy ester or a sulfonyl acid peroxide. Preferably, the free radical initiator will have a 10-hour half life temperature of 75°C. or less, i.e. it is a low to medium temperature initiator. The initiator is employed in an amount from 0.05 to 5 weight percent of the total monomer charge. Preferably, the initiators of this invention are redox initiators, preferably, secondary or tertiary amines and, more preferably, a tertiary amine and peroxide combination. The ratio between the peroxide and the amine may vary from 0.1 to 5 moles. It is useful to first dissolve the peroxide in a part of the solvent and separately dissolve the amine in the other part of the solvent, then mix the peroxide part with the monomer solution at room temperature and, subsequently, add the amine part. The charging of the peroxide and amine part can be done at the beginning of the reaction or in portions throughout the reaction period. These amines are generally of the formula R₂NH or R₃N wherein R is an alkyl or substituted alkyl, cycloalkyl or aryl group. Preferably, the amine is a tertiary amine. Illustrative redox initiators of this invention are methylbutyl amine, bis(2-hydroxyethyl)butyl amine, butyldimethyl amine, dimethyl amine, dibenzylethyl amine, diethylmethyl amine, dimethylpentyl amine, diethyl amine, 2,2′ ,2″-trihydroxy dipropyl ethyl amine, di-n-propylene amine, 2,2′ ,2″-trimethyl tributyl amine, triethyl amine. dimethyl aminoacetal, pentylhexyl amine, triethanolamine. trihexyl amine trimethyl amine, trioctadecyl amine, tripropyl amine, trisopropyl amine, tetramethylene diamine and esters of para-amino benzoic acid, e.g., p-dimethyl amino-2-ethylhexyl-benzoate, dimethyl aminoethyl acetate, 2-(n-butoxy)ethyl 4-dimethylaminobenzoate, 2-(dimethylamino) ethyl benzoate, ethyl-4 dimethylaminobenzoate, methyldiethanolamine, dibutyl amine, N,N-dimethylbenzylamine, methylethyl amine, dipentyl amine and peroxide Fe²⁺. Other preferred initiators are selected from inorganic initiators such as sodium, potassium or ammonium persulfates, as the decomposition products of such bisulfates are less harmful than many decomposition products of organic initiators. The reaction is carried out in the presence of an inert atmosphere. This condition may be achieved by the use of nitrogen, argon and carbon dioxide. Usually, no stirring or very slow stirring (e.g. zero to 300 rotations per minute) is employed. The reaction is maintained for such time as is required to achieve the desired yield of polymer. This time may be as little as one half hour. However, to approach the theoretical yield, 24 to 48 hours at room temperature or 4 to 10 hours at elevated temperatures, are required. The monomer solvent is subsequently removed by filtration and evaporation, resulting in a dry powder, which can be post adsorbed with a variety of functional active ingredients. As mentioned, the polymer is in the form of a powder and not hard spheres or beads. The powder is a combined system of particles. The system of particles includes submicron unit particles ranging in size from 0.1 to 0.5 microns in diameter. The particles may range from elliptical to spherical in shape. A typical diameter of a particle is about 0.3 microns. The powder also consists of agglomerates of fused unit particles of sizes in the range of about ten to eighty microns in average diameter and aggregates of clusters of fused agglomerates of sizes in the range of about two hundred to about eight hundred microns in average diameter. When mild pressure is applied to the powder, the aggregates and agglomerates are easily crushed into the small particles. Thus, the powder can be described as being "soft", in that the aggregate and agglomerate structure easily changes upon pressure and they cannot be easily felt when rubbed on the skin, between teeth or on sensitive human mucous membranes. The powders disappear when rubbed upon a surface. This phenomenon is believed to be due to the fact that large aggregates of the material scatter light rendering the appearance of a white particulate; however, upon rubbing, these large aggregates decrease in size approaching the range of visible light and, hence, seem to disappear. The materials do not swell in common solvents and are capable of physically adsorbing active ingredients by filling of interstitial voids by capillary action. The powders are often capable of adsorbing from sixty to eighty percent of a liquid and yet remain free flowing. The unit particles themselves do not have any significant porosity usually less than 2%. The size and adsorptive properties of these polymeric particles can be influenced by the concentration of the monomers and stirring rate. As a matter of rule, lower concentrations of the monomers and slower stirring result in higher adsorptivity. The powder produced by this invention exhibits adsorbent and abrasive properties which make them useful both, as cleaning agents and as delivery systems. The powder has great cleaning ability when employed as an abrasive in cleaners without the scratching, grinding and gouging, which is objectionable during cleaning optical surfaces and other fine surfaces. The nature of the powder permits it to adsorb surfactants and other cleaners so as to permit controlled application to the desired surface. The powder is useful in contact lens cleaners, facial scrubs, heavy duty hand cleaners, automotive or household cleaners, vinyl or leather cleaners, tile and sanitary ware cleaners. It may also be used as lubricants or as an additive in lubricants. Moreover, these polymeric particles can be used as carriers for bioactive agents such as drugs, pheromones, pesticides, insect repellants, herbicides and fungicides and also for cosmetics and perfumes. The following examples are presented for purposes of illustration and should not be construed as limiting the invention which is delineated in the claims. The following test procedures were used to determine various properties of the polymers prepared in the examples. The following procedure was used for determining the total adsorption capacity (TAC) of the polymers. A glass column, having a height of 110 mm and a diameter of 5 mm, made from a disposable capillary pipet and being sealed by glass wool at the bottom, was filled with approximately 0.05 grams of dry powder polymeric particles as prepared in the example. The top of the column was then sealed with glass wool. The bottom part of the column (conically-shaped) was connected to a "U"-shaped glass tubing, containing the liquid tested and the column was immersed into a constant temperature bath. The liquid was allowed to enter the column slowly by gravity from the bottom to the top of the column and left in the column for 5 minutes. The column was then disconnected from the tube and the liquid was sucked out of the column using a vacuum. The total adsorption capacity was calculated from the weight difference of the powder with the liquid and the dry powder according to the equation: Blind experiment for adsorption on the glass wool and walls of the column was deducted. The determination was done at 25°C. for all liquids except glycerine, which was done at 90°C. The following procedure was used for determining the free flowing capacity (FF) of the polymers. Free Flowing Capacity is the maximum percent liquid added while still maintaining the powder in the free flowing state. The free flowing adsorption capacity was determined by addition of incremental amounts of liquid to known amounts of powder, using gentle mixing, until the powder was no longer free flowing. All determinations were completed at 25°C. except when glycerine was used, which determinations were carried out at 90°C. The capacity (FF) as shown in Table I was determined by the following calculation: The following procedure was used for determining the apparent density of the polymers. A graduated cylinder was filled with a known weight of the powder and the corresponding volume was determined after gently tapping the sides of the cylinder. The following procedure was used for determining the dispersibility of the polymers. A sample of the powder with an excess of the liquid are shaken and observed for miscibility. Examples 1-21 In a three-necked resin reaction flask, 20 grams of the monomer in Table I were dissolved, at room temperature in 80 grams of isopropyl alcohol (or other solvent, if indicated) containing 0.4 grams of dibenzoyl peroxide. The solution was purged with nitrogen for 10 minutes and a slow nitrogen stream was kept during the entire reaction time. Under stirring, 0.4 grams of p-dimethylamino benzoic acid, 2-ethylhexyl ester were added. After five minutes, the stirring was stopped. Usually a slightly exothermic polymerization occurred, the temperature rising to 50 to 60°C. and, then, the polymer began to precipitate. After cessation of the exotherm, the system was heated to 60°C. for 6 hours and the contents of the flask solidified. If the reaction did not start at room temperature the solution was heated to 30-40°C. to initiate polymerization. After cooling to room temperature, the powder was washed with isopropyl alcohol (or other solvent, as indicated) and dried at room temperature or in vacuo, yielding 19.2 grams or 96% of theoretical. Examples 22-23 Free Flowing capacity for various pheromones, pesticides and their mixtures was determined. Some of the results are given in Table II. Example 24 Similarly following Examples 22 and 23, pheromones were entrapped in concentrations of more than 65% in polymers made from tetraethylene glycol dimethacrylate and 1,6 hexane diol dimethacrylate. Said phermones consisted of GOSSYPLURE (isomers of 7,11-hexadecadienyl acetate); GRANDLURE (isomers of dimethyl-Δ-α-cyclohexane acetaldehyde and alcohol; methyl eugenol; oriental fruit moth pheromone (9-dedecenyl acetate and alcohol); Z8,E8 dodecenyl acetate and alcohol; Z,11 hexadecenal aldehyde and alcohol; Z/E-11 tetradecenyl acetate; DISPARLURE (cis-7,8-epoxymethyl octadecane); alpha pinene; MUSCALURE (Z9 TRICOSENE); and apple maggot pheromone (hexyl acetate, butyl-2-methyl butanoate, propyl hexanoate, hexyl propanoate, butylhexanoate, hexylbutanoate). Example 25 The following pesticides were entrapped in concentrations of more than 65% in polymers made from tetraethylene glycol dimethacrylate and 1.6 hexane diol dimethacrylate. The pesticides consisted of TEMASEPT (2,4 dibromo salicyl 4′bromoanilide); SPB 1382 (5 benzyl-3-furyl) methyl-2,2-dimethyl-3 (2 methyl propenyl cyclopropane carboxylate); dimethoate (0,0-dimethyl-S-(n-methyl carbamoyl methyl) phosphorodithionate); ETHOPROP (S,S-dipropyl-0-ethyl phosphodithionate); NNDD (N,N-dimethyl dodecyl amine); DEET (N,N-diethyl-m-toluamide); TINACTIN (N-methyl-N-(3-tolyl) thiono carbamate); SUMITHRIN (3-phenoxy-benzyl-d-cis-transchrysantemate); DIAZINON (0,0 diethyl-0-(2-isopropyl-4 methyl)thiophosphate); OMITE (2-(4-(1,1-dimethylethyl) phenoxy) cyclohexyl-2-propynylsulfite); PHORATE (0,0-diethyl-s-[(ethylthio)methyl]phosphorodithionate); MALATHION (0,0-dimethyl-s-(1,2-dicarbethoxyethyl) dithionate); DDVP (2,2-dichlorovinyldimethylphosphate); D-TRANS-ALLETHRIN (d-1-2-allyl-4-hydroxy-3-methyl-2-cyclopenten-1-one ester of d-trans-chrysanthemum monocarboxylic acid); METHOPRENE (isopropyl(2E-4E)-11-methoxy-3,7,11-trimethyl-2,4 dodecadienoate); PYRETHRINS: CHLORPYRIFOS (0,0-diethyl-0-(3,5,6 trichloro-2 pyridyl) phosphonthionate); OXIRANE (2,2-dimethyl-3-(3 methyl-5-(4-methylethylphenoxy)-3-pentenyl)oxirane): and IRGASAN DP 300 (2,4,4′trichloro-2′hydroxydiphenyloxide). These and other variations of the present invention may be made which fall within the scope of the appended claims even though such variations were not specifically discussed above.

Claims: A method of forming a highly adsorptive polymer, comprising the steps of: a) homogeneously mixing a solution comprising from 0.1 parts by weight to less than 25 parts by weight of a monomer consisting exclusively of one type of polyunsaturated monomer, from greater than 75 parts by weight to 99.9 parts by weight of a monomer solvent, wherein the total weight of said monomers and said monomer solvent is 100 parts and 0.05 to 5 weight percent initiator based on the weight of said monomer, b) polymerizing said monomers to form a polymer, wherein said monomer solvent is a solvent for said monomers and a non-swelling non-solvent for said polymer, and c) removing said solvent from said polymer to form a dry powder which comprises unit particles ranging in size from 0.1 to 0.5 microns in diameter, agglomerates of fused unit particles ranging in size from 10 to 80 microns in average diameter and aggregates of clusters of fused agglomerates ranging in size from 200 to 800 microns in average diameter. A method as claimed in claim 1 further comprising the step of adsorbing a bioactive agent on said dry powder. A polymer powder obtainable by the method of claim 1. A bioactive agent-containing polymer powder obtainable by the method of claim 2.

Inventors: CHROMECEK RICHARD CHARLES, SOJKA MILAN FRANZ, WEISS LON LOUIS, CHROMECEK, RICHARD CHARLES, SOJKA, MILAN FRANZ, WEISS, LON LOUIS
Applicants: BIOSYS INC, BIOSYS, INC.
Application year: 1990
Main classification: C08F2
IPC codes: C08F8, A61K47, G02C13, C11D3, C08F2, A01N25, B01J20, G02C7, C08J3, A61K8, A61Q19