Particles having a radial variation

Abstract

To provide a good polymeric bead.SOLUTION: There is provided a polymeric bead having a radius R in which the polymer comprises 0.3 wt.% to 20 wt.% of polymerized units of one or more multifunctional vinyl monomers and 80 wt.% to 99.7 wt.% of polymerized units of one or more monofunctional vinyl monomers based on weight of the polymer, (a) wherein the polymerized units of the multifunctional vinyl monomers have a radial distribution factor MR of 0.9 to 1.1, and (b) wherein some of the vinyl groups in the polymerized units of multivinyl monomers are unreacted, and the unreacted vinyl groups have a radial distribution factor VR of 2.5 or higher.SELECTED DRAWING: None

Description

Technical Field

[0001] Polymer ion exchange resins in the form of beads are used in many applications, such as, for example, as chelating resins or as anion exchangers or as cation exchangers. In many of these applications, the resin is subjected to stresses that can cause substantial breakage of the beads. These stresses can be mechanical, for example, due to crushing or collisions between beads or between the beads and their containers; or they can be osmotic, such as when the beads are subjected to sudden and / or repeated changes in electrolyte concentration. The breakage of ion exchange beads in a column causes one or more of the following problems: a substantial loss of column efficiency; an increase in the pressure drop across the column; and contamination of the product stream. Any of these problems will result in significant costs for replacing the broken resin.

Background Art

[0002] Ion exchange resins are either of the gel type or the macroporous type. In some cases, gel type (microporous) resins have insufficient osmotic pressure characteristics. As a result, macroporous type resins are generally used when good osmotic pressure characteristics are essential. However, macroporous resins often have insufficient mechanical properties and often have a substantially lower ion exchange capacity than gel type resins. It would be desirable to provide a gel type ion exchange resin having one or more of the following: good osmotic pressure characteristics, good mechanical properties, and a high ion exchange capacity. It would be desirable to provide a gel type ion exchange resin having one or more of the following: good osmotic pressure characteristics, good mechanical properties, and a high ion exchange capacity.

[0003] One approach for manufacturing a gel-type resin is described in European Patent No. 0 101 943, which describes a method in which a polymer matrix containing radicals is contacted with a monomer feed to produce core / shell beads. This is a complex process in which a radical-containing polymer must be produced and then the monomer must be fed into a container having the radical-containing polymer. Further, this process described in European Patent No. 0 101 943 is most advantageous when the concentration of the polymerized units of the polyfunctional vinyl monomer in the shell is lower than the concentration of the polymerized units of the polyfunctional vinyl monomer in the core. It would be desirable to provide a high-strength gel-type resin in a process that does not require a separate monomer feed step. It would also be desirable to provide a high-strength gel-type resin in which the concentration of the polymerized units of the polyfunctional vinyl monomer is the same or substantially the same throughout the resin.

Summary of the Invention

Means for Solving the Problems

[0004] The following are statements of the present invention.

[0005] A first aspect of the present invention is (a) providing a suspension of monomer droplets in an aqueous medium at a pH of 7 or less, wherein the monomer droplets contain one or more monofunctional vinyl monomers, one or more polyfunctional vinyl monomers, and one or more initiators, and the aqueous medium contains one or more derivatives of nitrite in an amount of 0.005 wt% to 0.5 wt% based on the weight of the aqueous medium, (b) initiating polymerization of the monomer and wherein no pH-raising substance is added after the initiating step (b) until more than 60% by weight of all the monofunctional monomers have been converted to polymer. This is a method for producing polymer beads.

[0006] A second aspect of the present invention is polymer beads having a radius R, wherein the polymer comprises polymerization units of one or more polyfunctional vinyl monomers in an amount of 0.3% to 20% by weight based on the weight of the polymer, and polymerization units of one or more monofunctional vinyl monomers in an amount of 80% to 99.7% by weight based on the weight of the polymer. (a) Here, the polymerization units of the polyfunctional vinyl monomer have a radial distribution coefficient MR of 0.9 to 1.1, where MR = CMSHELL / CMCORE (where CMSHELL is the average concentration of the polymerization units of the polyfunctional vinyl monomer located at a distance from the center of the bead of 0.8*R to R, and where CMCORE is the average concentration of the polymerization units of the polyfunctional vinyl monomer located at a distance from the center of the bead of 0 to 0.5*R). And (b) Here, some of the vinyl groups in the polymerization units of the multivinyl monomer are unreacted, and the unreacted vinyl groups have a radial distribution coefficient VR of 2.5 or more, where VR is determined by Raman spectroscopy measurements performed on the beads, where VR = V1SHELL / V1CORE (where V1SHELL is the average of the ratio V1 for measurements taken at a distance from the center of the bead of 0.8*R to R, and where V1CORE is the average of the ratio V1 for measurements taken at a distance from the center of the bead of 0 to 0.5*R), where V1 = PCC / PAR (where PCC is the height of the Raman spectroscopic peak due to the stretching of the carbon-carbon double bond, and PAR is the height -1 of the Raman spectroscopic reference peak due to the stretching of the aromatic ring at 1000 cm ). These are polymer beads.

[0007] The following is a brief description of the drawings.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0009] The following is a detailed description of the present invention.

[0010] As used herein, the following terms have the designated definitions unless the context clearly indicates otherwise.

[0011] "Polymer", as used herein, is a relatively large molecule composed of reaction products of smaller chemical repeating units. Polymers can have structures that are linear, branched, star-shaped, loop-shaped, hyperbranched, cross-linked, or combinations thereof; polymers can have a single type of repeating unit ("homopolymer"), or they can have two or more types of repeating units ("copolymer"). Copolymers can have various types of repeating units arranged randomly, in an ordered manner, in blocks, in other arrangements, or any mixture or combination thereof.

[0012] Molecules that can react with each other to form the repeating units of a polymer are known herein as "monomers". The repeating units thus formed are known herein as the "polymerization units" of the monomer.

[0013] Vinyl monomers have the structure:

CHEMICAL FORMULA

[0014] In a styrene monomer, each of R 1 and R 2 is hydrogen, R 3 is hydrogen or alkyl, and -R 4 has the structure

Chemical formula

[0015] In an acrylic monomer, each of R 1 and R 2 is hydrogen; R 3 is either hydrogen or methyl; -R 4 has the following structure:

Chemical formula

[0016] The reaction between monomers to form one or more polymers is herein referred to as a polymerization process. When the amount of unreacted monomer in the vessel in which the polymerization process is carried out is 5% by mass or less based on the sum of the mass of the unreacted monomer and the mass of the polymer produced in the polymerization process, the polymerization process is herein said to be complete.

[0017] As used herein, an inhibitor is a molecule that interacts with a free radical to produce a portion that does not undergo free radical polymerization (referred to herein as the "dead end" portion). The inhibitor can interact with a free radical to directly form a dead end portion, or the inhibitor can first form one or more intermediates, and these intermediates can interact with radicals to form a dead end portion. When the inhibitor first forms an intermediate, the formation of the intermediate can occur by the reaction between the inhibitor and the free radical.

[0018] As used herein, an initiator is a molecule that is stable under ambient conditions but can generate one or more fragments having free radicals under specific conditions, and the fragments can interact with monomers to initiate a free radical polymerization process. Conditions that result in the generation of fragments having free radicals include, for example, high temperature, participation in an oxidation-reduction reaction, exposure to ultraviolet and / or ionizing radiation, or a combination thereof.

[0019] A porogen is a compound that is soluble in the monomer or mixture of monomers used in the implementation of the present invention. That is, at 25 °C, 100 grams or more of the porogen will dissolve in 100 grams of the monomer or mixture of monomers used in the implementation of the present invention. The polymer does not absorb a large amount of porogen. That is, at 25 °C, the polymer formed in the implementation of the present invention absorbs 5 grams or less of porogen per 100 grams of the polymer.

[0020] Macroporous polymer beads have a porous structure with an average pore diameter of 20 nm or more. The pore diameter is measured using the Brunauer-Emmett-Teller (BET) method using nitrogen gas. Macroporous polymer beads are usually produced by incorporating a porogen into monomer droplets. The porogen is soluble in the monomer, but the polymer does not dissolve the porogen, and as a result, when the polymer forms, the phase-separated domains of the porogen persist. After polymerization, the porogen is removed by evaporation or by washing with a solvent. The porous structure of the polymer beads is the empty space that remains when the porogen is removed from its phase-separated domains.

[0021] Gel-type polymer beads are produced without the use of a porogen. The pores in the gel-type polymer beads are the free volume between atoms in the entangled, cross-linked polymer chains of the polymer beads. The pores in the gel-type polymer beads are smaller than 20 nm. In some cases, the pores in the gel-type resin are too small to be detected using the BET method.

[0022] As used herein, ion exchange is the process by which ions in a solution bind to a solid resin (ion exchange resin) and those ions are exchanged for ions of the same type of charge that are released by the ion exchange resin. The functional groups located on the resin have a charge opposite to that of the ions being exchanged, and those functional groups are known in the present invention as ion exchange groups.

[0023] As used herein, a compound is said to be water-soluble if 5 grams or more of the compound forms a stable solution in 100 ml of water at 25°C. In the case of some water-soluble polymers, the water may need to be heated above 25°C to dissolve the polymer, but after cooling to 25°C, the solution is stable when maintained at 25°C.

[0024] As used herein, a base compound is a compound having the ability to accept a proton to form the conjugate acid of the compound, and the conjugate acid of the compound has a pKa of 9 or more. As used herein, an acid compound is a compound having the ability to release a proton, and this compound has a pKa of 5 or less. A buffer is either (i) a compound having the ability to accept a proton to form the conjugate acid of the compound, where the conjugate acid of the compound has a pKa of less than 9, or (ii) a compound having the ability to release a proton, where the compound has a pKa of more than 5.

[0025] As used herein, "ambient conditions" means a temperature of approximately 25°C and a pressure of 1 atmosphere.

[0026] A suspension is a composition having particles of one substance distributed throughout a liquid medium. The distributed particles can be liquid or solid; distributed liquid particles are called droplets. When the medium contains 90% by weight or more of water based on the weight of the medium, the medium is "aqueous". A suspension can be stable or unstable. That is, the distributed particles may or may not tend to settle to the bottom of the container or float to the top of the container, and mechanical agitation may or may not be required to keep the particles distributed in the medium.

[0027] Polymer beads are particles containing 90% by weight or more of an organic polymer, based on the weight of the particles. The polymer beads are spherical or substantially spherical. The polymer beads are characterized by their radius. If the beads are not spherical, the radius of the beads is considered herein to be the radius of a hypothetical "reference sphere" that has the same volume as the beads. Whether a particle is spherical or not is evaluated by the "sphericity", represented by the Greek letter Ψ. The sphericity is defined by the following formula, based on the three principal axes of the bead, a (longest), b (intermediate), and c (shortest): [Number]

[0028] As used herein, the polymerization process is a "single-stage" polymerization process in which monomers and optionally other compounds are placed in a vessel, then the polymerization reaction is initiated, and the polymerization proceeds to completion without any further addition of monomers after the start of polymerization. The single-stage polymerization process is not a seed process.

[0029] As used herein, a suspension polymerization process is a "seed" process if the process includes a state (S1) in which the monomer droplets contain 80% by weight or more of the monomer, based on the weight of the droplets; the monomer droplets have not undergone polymerization; and the monomer droplets contain the polymer in an amount of 1% by weight or more, based on the weight of the droplets. In the seed process, after state (S1), the polymerization of the monomer in the monomer droplets is initiated. In a typical seed process, a suspension of polymer particles is provided, then monomers are added to the suspension, the monomers are absorbed into the polymer particles, and then the polymerization of the monomers is initiated.

[0030] Ratios are described herein as follows. For example, when a ratio is said to be 3:1 or more, the ratio can be 3:1 or 5:1 or 100:1, but cannot be 2:1. The general statement of this concept is as follows: When a ratio is said to be X:1 or more herein, it means that the ratio is Y:1, where Y is equal to or greater than X. Similarly, for example, when a ratio is said to be 15:1 or less, the ratio can be 15:1 or 10:1 or 0.1:1, but cannot be 20:1. Generally speaking: When a ratio is said to be W:1 or less herein, it means that the ratio is Z:1, where Z is equal to or less than W.

[0031] Although the present invention is not bound by any particular theory, it is contemplated that the method of the present invention produces polymer beads having a relatively constant concentration of polymerized units of the polyfunctional vinyl monomer throughout the volume of the beads. The molecules of the polyfunctional vinyl monomer become polymerized units when one or more of the polymerizable functional groups participate in the polymerization reaction. The polymerized units of the polyfunctional vinyl monomer may retain one or more unreacted functional groups. In the present invention, the polymerized units of the polyfunctional vinyl monomer are evenly distributed throughout the beads, but it is contemplated that the unreacted functional groups attached to such polymerized units are more prevalent in the shell portion of the beads than in the core portion. Since more of the functional groups of the polyfunctional vinyl monomer react in the shell to create more crosslinking points, the density of crosslinking points in the polymer beads is considered to be higher in the core than in the shell. Thus, even though the distribution of the polymerized units of the polyfunctional vinyl monomer is approximately the same in the core and the shell, the lower density of crosslinking is believed to be in the shell.

[0032] The method of the present invention includes monomer droplets containing a vinyl monomer and an initiator. The monomer droplets optionally further contain a porogen.

[0033] It is useful to characterize the total amount of the monomer plus the amount of the porogen as a weight percentage based on the weight of the monomer droplets. Preferably, the total is 95% or more; more preferably 97% or more; more preferably 99% or more.

[0034] Preferably, the porogen is either absent or, if present, present in a relatively small amount. When the porogen is present in the monomer droplets, preferably, the amount of the porogen is limited to 10% by weight or less; more preferably 3% by weight or less; more preferably 1% by weight or less; more preferably 0.3% by weight or less, based on the weight of the monomer droplets. More preferably, the porogen is not present at all in the monomer droplets.

[0035] Preferably, the amount of the monomer in the monomer droplets is 95% by weight or more; more preferably 97% by weight or more; more preferably 99% by weight or more, based on the weight of the droplets.

[0036] Preferred vinyl monomers are styrenic monomers, acrylic monomers, and mixtures thereof. Preferably, all of the monomers used are selected from styrenic monomers, acrylic monomers, and mixtures thereof. More preferably, all of the monomers used are selected from styrenic monomers. The vinyl monomer contains one or more monofunctional vinyl monomers. Preferred monofunctional vinyl monomers are acrylic and styrenic monofunctional monomers; monofunctional styrenic monomers are more preferred; styrene is more preferred. The vinyl monomer also contains one or more polyfunctional vinyl monomers. Preferred polyfunctional vinyl monomers are polyfunctional styrenic monomers; divinylbenzene is more preferred. As used herein, the term "divinylbenzene" or "DVB" refers to a mixture containing approximately 63% by weight of pure chemical DVB and approximately 37% by weight of ethylvinylbenzene, with other chemical substances in a total amount of 1% or less. Preferably, the amount of vinyl chloride is 0 to 0.1% by weight, more preferably 0 to 0.01% by weight; more preferably 0% by weight, based on the total weight of all the monomers.

[0037] Preferably, the amount of the styrenic monomer is 50% by weight or more, more preferably 75% by weight or more, more preferably 88% by weight or more, more preferably 94% by weight or more, more preferably 97% by weight or more, more preferably 100% by weight, based on the weight of all the monomers.

[0038] Preferably, the amount of the monofunctional vinyl monomer is 80% by weight or more, more preferably 85% by weight or more, based on the weight of all the monomers. Preferably, the amount of the monofunctional vinyl monomer is 99.7% by weight or less, more preferably 99% by weight or less, more preferably 98% by weight or less, more preferably 96% by weight or less, more preferably 94% by weight or less, more preferably 92% by weight or less, based on the weight of all the monomers.

[0039] Preferably, the amount of the polyfunctional vinyl monomer is 0.3% by weight or more, preferably 1% by weight or more, more preferably 2% by weight or more, more preferably 4% by weight or more, more preferably 6% by weight or more, more preferably 8% by weight or more, based on the weight of all the monomers. Preferably, the amount of the polyfunctional vinyl monomer is 20% by weight or less, more preferably 15% by weight or less, based on the weight of all the monomers.

[0040] Preferably, the monomer droplets contain little or no polymer before the start of the polymerization. The amount of the polymer is preferably 1% by weight or less, more preferably 0.3% by weight or less, more preferably 0.1% by weight or less, more preferably zero, based on the weight of the monomer droplets.

[0041] The method of the present invention includes a suspension of monomer droplets in an aqueous medium. Preferably, the total amount of the monomers is 5% by weight or more, more preferably 10% by weight or more, more preferably 15% by weight or more, based on the total weight of the suspension. Preferably, the total amount of the monomers is 55% by weight or less, more preferably 35% by weight or less, more preferably 30 % by weight or less.

[0042] The aqueous medium contains one or more dissolved nitrates, derivatives of the nitrates, or combinations thereof. The nitrate has the formula M(NO2) v (wherein M is ammonium or an alkali metal cation or an alkaline earth metal cation, and v is 1 when M is ammonium or an alkali metal cation, and v is 2 when M is an alkaline earth metal cation). When the nitrate is dissolved in water, the nitrite ion may undergo a chemical reaction to form derivatives such as nitrous acid and / or compounds of the formula N x O y . The amount of these derivatives is characterized by the weight of the dissolved salt plus the amount of salt that must be dissolved to produce the amount of derivative present in the aqueous medium. The preferred amount of nitrate and its derivatives is 0.005% by weight or more, more preferably 0.008% by weight or more, more preferably 0.011% by weight or more, more preferably 0.014% by weight or more, based on the weight of the aqueous medium. The preferred amount of nitrate and its derivatives is 0.5% by weight or less, more preferably 0.4% by weight or less, more preferably 0.3% by weight or less, more preferably 0.2% by weight or less, based on the weight of the aqueous medium.

[0043] The preferred nitrate is sodium nitrite. Preferably, the derivative of the nitrate is a derivative of sodium nitrite.

[0044] The monomer droplets preferably contain one or more initiators. Preferred initiators have a solubility of 1 gram or less; more preferably 0.5 gram or less; more preferably 0.2 gram or less; more preferably 0.1 gram or less in 100 mL of water at 25°C. Peroxide and hydroperoxide initiators are preferred; peroxide initiators are more preferred; benzoyl peroxide and its derivatives are more preferred; benzoyl peroxide is more preferred. Preferably, the weight ratio of the initiator to the total monomer is 0.001:1 or more; more preferably 0.002:1 or more. Preferably, the weight ratio of the initiator to the total monomer is 0.02:1 or less; more preferably 0.01:1 or less; more preferably 0.007:1 or less.

[0045] The suspension preferably contains one or more water-soluble polymers. Preferred water-soluble polymers are water-soluble polyvinyl alcohol polymers, water-soluble derivatives of cellulose, and mixtures thereof. Among the water-soluble derivatives of cellulose, carboxymethyl cellulose is preferred. Among the polyvinyl alcohol polymers, those with a degree of hydrolysis of 80% to 90% are preferred. Preferably, the suspension contains one or more water-soluble polyvinyl alcohol polymers and one or more water-soluble derivatives of cellulose.

[0046] When one or more water-soluble polymers are used, preferably, the total amount of the water-soluble polymers is 0.02% by weight or more; more preferably 0.05% by weight or more; more preferably 0.1% by weight or more based on the weight of water. When one or more water-soluble polymers are used, preferably, the total amount of the water-soluble polymers is 1% by weight or less; more preferably 0.5% by weight or less based on the weight of water.

[0047] Gelatin may or may not be present in the suspension. When gelatin is present, its amount is 2% by weight or less, or 1% by weight or less, or 0.5% by weight or less, based on the weight of water. Preferred embodiments have little or no gelatin. Preferably, the amount of gelatin is sufficiently low such that the amount of gelatin is 0 to 0.01% by weight, more preferably 0 to 0.001% by weight, based on the weight of water. More preferably, the amount of gelatin is zero.

[0048] Before step (b) of initiating the polymerization of the monomer, the pH of the aqueous medium is 7 or less. Before step (b) of initiating the polymerization of the monomer, the pH of the aqueous medium is preferably 3 or more, more preferably 4 or more, more preferably 5 or more, more preferably 5.5 or more.

[0049] Although the present invention is not restricted by any specific theory or mechanism, the following is considered with respect to the action of the present invention. When a water-soluble nitrite is added to the suspension, it is considered that some or all of the water-soluble nitrite dissolves in the water in the aqueous medium, and the presence of hydrogen ions creates an equilibrium between the dissolved nitrite ions and nitrous acid at a pH of 7 or less. Nitrous acid is thought to undergo further chemical reactions to form nitric oxide or one or more other compounds of the formula NxOy (wherein x is 1 or 2, y is 1 to 5, and when x is 2, y is 1, 3, 4, or 5). Generally, it is expected that the lower the pH, the more the formation of compounds of the formula NxOy, including NO. The most likely NxOy compound to be formed is thought to be nitric oxide (NO), possibly in combination with one or more other NxOy compounds. The compounds of the formula NxOy formed when a water-soluble nitrite is added to the suspension are considered herein to be derivatives of the water-soluble nitrite. Since NO is a radical species, it is considered that NO will function as an inhibitor by reacting with monomer radicals or radicals on the growing polymer chains, thus stopping the polymerization reaction. It is also considered that other NxOy compounds may also function as inhibitors.

[0050] The presence of dissolved nitrite ions and acidic conditions in an aqueous medium are contemplated to create a system in which fresh inhibitor molecules are continuously being formed throughout the polymerization process, as long as the pH is kept below 7. Benefits similar to those obtained by the present invention are also contemplated to be obtainable by gradually adding an inhibitor (such as catechol, etc.) to the aqueous medium. Such a procedure would also have created a system in which fresh inhibitor molecules are continuously introduced. Whatever inhibitor is used, it should be partially or completely soluble in water to enable transport through the aqueous medium and should be partially or completely soluble in the monomer droplets to diffuse therein and react with radicals to stop the polymerization.

[0051] The pH of the suspension prior to the start of polymerization can optionally be established by the addition of one or more acids to the aqueous medium. When an acid is added, a preferred acid has a first pKa of 3 or greater; more preferably 4 or greater. When an acid is used, any type of acid can be used; organic acids are preferred. Preferably, no acid is added to the aqueous medium; i.e., it is preferred that the components listed above establish a suspension pH of 7 or less without the addition of an acid. Preferably, no buffer is present in the aqueous medium.

[0052] The nature of the step of initiating the polymerization depends in part on the nature of the initiator used. For example, when a thermal initiator is used, the initiation conditions include establishing a temperature above 25° C., high enough that a significant portion of the initiator molecules decompose to form free radicals. As another example, when a photoinitiator is used, the initiation conditions include exposing the initiator to radiation of a wavelength short enough and intensity high enough that a significant portion of the initiator molecules decompose to form free radicals. As another example, when the initiator is a redox initiator, the initiation conditions include the presence of both an oxidizing agent and a reducing agent at a concentration high enough that a significant number of free radicals are generated. Preferably, a thermal initiator is used. Preferably, the initiation conditions include a temperature of 65° C. or higher; more preferably 75° C. or higher. That is, preferably, the suspension is provided at a temperature below 40° C. and the initiator present does not generate a significant number of free radicals at that temperature. Next, preferably, step (b) includes raising the temperature to the initiation conditions.

[0053] After step (b), at any moment throughout the polymerization, the degree of free radical polymerization in the vessel containing the suspension can be characterized as follows. Degree of polymerization = 100 * PM / TM (where PM is the mass of the polymer formed by the free radical polymerization process and TM is the total mass of the monomer added to the vessel).

[0054] In some embodiments, a base or suitable buffer may be added to the suspension during the polymerization. A suitable buffer is one that will raise the pH of the suspension. One motivation for adding a base or suitable buffer is that it is thought that an increase in the pH of the suspension can react some of the nitrite derivative to reform nitrite. Some of the derivative, especially N x O yOne or more of the compounds are thought to inhibit polymerization, and the increase in pH is thought to remove some of the inhibitor from the suspension, which is thought to allow the polymerization to complete more rapidly. In the practice of the present invention, when a base or a suitable buffer is added, it is not added at any time from the first initiation of the polymerization until the degree of reaction progress is 60% or more; preferably 70% or more; preferably 80% or more. In some embodiments, no base or suitable buffer is added to the suspension during polymerization.

[0055] When a base is added, organic base compounds and inorganic base compounds are preferred. Inorganic base compounds are more preferred; alkali hydroxides and ammonium hydroxide are more preferred; alkali hydroxides are more preferred. Preferably, when a base compound is added to the suspension, the addition is carried out by first forming an aqueous solution of the base compound and then adding the solution to the suspension. Preferred aqueous solutions have a concentration of base compound of 1% by weight or more; more preferably 2% by weight or more; more preferably 5% by weight or more, based on the weight of the solution. Preferred aqueous solutions have a concentration of base compound of 50% by weight or less; more preferably 25% by weight or less; more preferably 15% by weight or less; more preferably 10% by weight or less, based on the weight of the solution.

[0056] When a suitable buffer is added, preferably, the buffer is a compound having the ability to accept a proton to form the conjugate acid of the compound, and the conjugate acid of the compound has a pKa of less than 9. Preferably, the conjugate acid of the compound has a pKa of 6 or more; more preferably 7 or more; more preferably 7.5 or more. Some suitable buffers include, for example, TES (2-[[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]amino]ethanesulfonic acid); HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid); DIPSO (3-(N,N-bis[2-hydroxyethyl]amino)-2-hydroxypropanesulfonic acid, N,N-bis(2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid); TAPSO (2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid, N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid); triethanolamine; N-ethylmorpholine; POPSO (2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid, N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid”; EPPS (4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid, 4-(2-hydroxyethyl)piperazine-1-propanesulfonic acid, N-(2-hydroxyethyl)piperazine-N’-(3-propanesulfonic acid), also known as HEPPS); HEPPSO (CAS number 865856-46-8); TRIS (2-amino-2-hydroxymethyl-propan-1,3-diol); tricine; glycylglycine; bicene; TAPS (N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid, [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid); morpholine; N-methyldiethanolamine; AMPO (2-amino-2-methyl-1,3-propanediol); diethanolamine.

[0057] The suspension may or may not contain boric acid. When boric acid is present, its amount is 2% by weight or less, or 1% by weight or less, or 0.5% by weight or less based on the weight of water. . Preferably, the suspension contains little or no boric acid. Preferably, the amount of boric acid in the suspension is 0 to 0.01% by weight, more preferably 0% by weight based on the weight of water.

[0058] Before the start of the polymerization process, droplets are present in the suspension, and the droplets contain vinyl monomer and initiator. Preferably, the droplets are distributed throughout the aqueous medium. Preferably, the composition of the aqueous medium contains water in an amount of 90% by weight or more, more preferably 95% by weight or more, even more preferably 97% by weight or more based on the weight of the continuous liquid medium. Compounds dissolved in water are considered to be part of the continuous liquid medium. Preferably, the volume average particle size of the droplets is 50 μm to 1,500 μm.

[0059] The suspension of monomer droplets is subjected to conditions that cause the initiator to initiate the polymerization of the monomer. Preferably, the initiator is a thermal initiator, and the start of the polymerization is above 40 °C, and begins when the suspension is heated to a temperature high enough to generate sufficiently many radicals in the initiator to initiate the polymerization sufficiently.

[0060] Preferably, the polymerization is a single-stage polymerization. That is, preferably, no monomer is added to the suspension after the start of the polymerization, or if any monomer is added, the amount of the added monomer is 1% by weight or less, more preferably 0.1% by weight or less based on the weight of all the monomers present in the suspension at the start of the polymerization. More preferably, no monomer is added to the suspension after the start of the polymerization.

[0061] Preferably, the process of the present invention is not a seed process.

[0062] The present invention also includes polymer beads. The polymer beads are preferably produced by the method of the present invention. Preferably, the polymer beads contain a polymer. The polymer beads are solid at 25°C and contain the polymer in an amount of 90% by weight or more, more preferably 95% by weight or more, based on the weight of the polymer particles.

[0063] Preferably, the polymer beads have a volume average particle size of 50 μm or more, more preferably 100 μm or more, more preferably 200 μm or more, more preferably 400 μm or more. Preferably, the polymer beads have a volume average particle size of 1,500 μm or less, more preferably 1,000 μm or less.

[0064] A preferred polymer in the polymer particles is a polymer formed by free radical polymerization of the preferred vinyl monomers described above. Preferably, the polymer contains polymerization units of styrene-based monomers in an amount of 5% by weight or more, more preferably 25% by weight or more, more preferably 50% by weight or more, more preferably 75% by weight or more, more preferably 85% by weight or more, more preferably 95% by weight or more, based on the weight of the polymer. The preferred types of monomers as polymerization units of the polymer are the same as those described above as being preferred for use in the polymerization process.

[0065] The preferred polymer has polymerization units of polyfunctional vinyl monomers in an amount of 0.3% by weight or more, more preferably 0.5% by weight or more, more preferably 1% by weight or more, more preferably 2% by weight or more, more preferably 3% by weight or more, more preferably 4% by weight or more, based on the weight of the polymer. The preferred polymer has polymerization units of polyfunctional vinyl monomers in an amount of 20% by weight or less, more preferably 15% by weight or less, based on the weight of the polymer.

[0066] The preferred polymer is 99.7% by weight or less, more preferably 99.5% by weight or less, more preferably 99% by weight or less, more preferably 98% by weight, based on the weight of the polymer. It has a polymerization unit of a monofunctional vinyl monomer in an amount of at most; more preferably at most 97% by weight; still more preferably at most 96% by weight. A preferred polymer has a polymerization unit of a monofunctional vinyl monomer in an amount of at least 80% by weight; more preferably at least 85% by weight, based on the weight of the polymer.

[0067] When two or more vinyl groups on a single molecule of a polyfunctional vinyl monomer participate in the polymerization reaction, it is contemplated that the molecule forms a crosslinking point between polymer chains. Considering the polymerization unit of the polyfunctional vinyl monomer in the polymer beads, in some but not all of such polymerization units, two or more vinyl groups will participate in the polymerization reaction and form crosslinking points. Sufficient crosslinking points are expected to create a polymer in the polymer beads that is a crosslinked polymer. At the same time, it is also contemplated that some polymerization units of the polyfunctional vinyl monomer will have one or more unreacted vinyl groups (i.e., vinyl groups that did not participate in the polymerization reaction and are still intact).

[0068] The polymer in the polymer beads has a relatively uniform distribution of the polymerization units of the polyfunctional vinyl monomer between the central region of the beads and the outer shell of the beads. This distribution can be evaluated as follows. The radius of the beads is defined as R. The shell is defined as the region of the beads located at a distance from the center of the beads of 0.8*R to R. The core is defined as the region of the beads located at a distance from the center of the beads of 0 to 0.5*R. The identification of shell 1, core 3, and intermediate region 2 is illustrated in FIG. 1.

[0069] The concentration of the polymerization unit of the polyfunctional vinyl monomer located in the shell is denoted as CMSHELL, and the concentration of the polymerization unit of the polyfunctional vinyl monomer located in the core is denoted as CMCORE. The radial distribution coefficient, denoted as MR, is defined as the quotient of CMSHELL divided by CMCORE: MR = CMSHELL / CMCORE

[0070] CMCORE and CMSHELL can be characterized in any convenient unit, for example millimoles per cubic centimeter. In practice, since the quotient MR is the important quantity, the units used for CMSHELL and CMCORE are not important as long as the same unit is used for both CMSHELL and CMCORE.

[0071] The quotient MR is 0.9 or more; preferably 0.95 or more. The quotient MR is 1.1 or less; more preferably 1.05 or less.

[0072] The polymerized units of the polyfunctional vinyl monomer are distributed relatively evenly throughout the polymer beads. However, in some polymerized units of the polyfunctional vinyl monomer, all of the vinyl groups participate in the polymerization reaction during bead formation, while in other polymerized units of the polyfunctional vinyl monomer, at least one vinyl group remains unreacted while at least one vinyl group participates in the polymerization reaction during bead formation. The spatial distribution of the unreacted vinyl groups is a feature of the present invention.

[0073] The distribution of the unreacted vinyl groups is characterized as follows. The core and shell of the beads are defined as described above. A representative bead is sliced open to reveal a cross-section including the center of the bead. Raman spectroscopy is performed on a micro-region of the bead. PCC is the height of the Raman peak at 1635 cm -1 due to the stretching of the carbon-carbon double bond. PAR is the height of the Raman reference peak at 1000 cm -1 due to the stretching of the aromatic ring. The quotient V1 = PCC / PAR characterizes the prevalence of double bonds in the polymer. The quantity V1SHELL is the average of V1 in the shell, and the quantity V1CORE is the average of V1 in the core. For unreacted carbon-carbon double bonds, the radial distribution coefficient is , VR = V1SHELL / V1CORE. When performing Raman spectroscopy, the beads are optionally swollen in a solvent; the solvent is optionally fully deuterated.

[0074] The accuracy of the above Raman spectroscopy can be optimized by removing any residual unreacted monofunctional monomers from the polymer beads, for example, removing residual styrene by washing with acetone and drying the beads to remove the acetone. This washing step is particularly useful when Raman spectroscopy is intended to be performed on beads that are not swollen in a solvent.

[0075] VR is 2.5 or more, preferably 2.7 or more; more preferably 2.9 or more. Preferably, VR is 10 or less; more preferably 5 or less.

[0076] The polymer beads preferably have an average sphericity of 0.8 or more; more preferably 0.85 or more; more preferably 0.9 or more; more preferably 0.95 or more.

[0077] Another method for evaluating the difference between the core region of the beads and the shell region of the beads is as follows. The core, shell, and quantity PAR are defined as above. The sample is swollen with fully deuterated toluene. The shell region is considered to have a lower crosslinking concentration than the core region, and therefore the shell region is expected to absorb more solvent in the swelling process. The quantity PCD is the height of the Raman peak at 2122 cm-1 due to the stretching and contraction of carbon-deuterium bonds in toluene. The quotient V2 = PCD / PCH represents the even distribution of deuterated toluene compared to the polymer.

[0078] The quotient V2 can be converted to the following mass per volume quotient (MPVQ). A reference solution of linear polystyrene with a known concentration in deuterated toluene is prepared. For this standard solution, both the mass per volume of deuterated toluene (MPVTOLREF) and the mass per volume of polystyrene (MPVPSREF) are known, and the quotient is MPVQREF = MPVTOLREF / MPVPSREF. Also, the quotient for the standard solution is measured and denoted as V2REF. Next, for any particular experimental sample, the quotient V2 can be converted to MPVQ as follows: MPVQ = V2 * MPVQREF / V2REF

[0079] In the beads swollen with deuterated toluene, the average value of MPVQ in the shell is MPVQSHELL, and the average value of MPVQ in the core is MPVQCORE. Next, the radial distribution coefficient for the solvent is RDFS = MPVQSHELL / MPVQCORE. Preferably, RDFS is 2.5 or more. Preferably, RDFS is 10 or less.

[0080] Another way to show the non-uniformity of the beads is to use nuclear magnetic resonance (NMR) spectroscopy. The analysis of the NMR results is based on the following preliminary observations. When chloroform (CHCl3) is studied in a pure state, characteristic chemical shifts are observed in the NMR spectrum. When chloroform is studied in a blend with toluene, changes in the chemical shift of chloroform are observed in a state where larger changes are observed at higher ratios of toluene in the blend. When chloroform is absorbed into polymer particles made of polymerized units of styrene-based monomers, it is observed that the chemical shift of chloroform shifts in the same way as was observed for the blend of chloroform and toluene. A difference ("DIFF1") is observed between the chemical shift of chloroform absorbed into the polymer and the chemical shift of pure chloroform, and it is concluded that the higher the DIFF1, the higher the ratio of polymerized units of styrene-based monomers in the proximity region surrounding the chloroform molecules.

[0081] The inhomogeneity of a non-functionalized copolymer containing polymerization units of a styrene monomer can be studied using NMR as follows. Polymer beads are swollen with chloroform. In some samples, two different peaks are observed for chloroform, with each peak having its own chemical shift and thus its own value of DIFF1. Each peak is thought to represent a different region within the beads. The peak with a larger DIFF1 is thought to represent chloroform molecules surrounded by a relatively larger proportion of the polymerization units of the styrene monomer, indicating that relatively less chloroform is absorbed into that region of the particle, and in turn indicating that that region has a higher density of cross-linking points. Similarly, the peak with a smaller DIFF1 is thought to represent chloroform molecules located in a region with a relatively lower density of cross-linking points.

[0082] The inhomogeneity of polymer beads can also be observed by microscopy. For example, optical microscopy and polarized light microscopy each show inhomogeneities that vary with the distance from the center of the particle.

[0083] A preferred use of the polymers produced in the free radical polymerization of the present invention is in a conversion process for producing ion exchange resins. Ion exchange resins are classified into the following categories. Weakly basic anion exchange resins have pendant amino groups that are primary, secondary, or tertiary. Strongly basic anion exchange resins have pendant quaternary amino groups. Weakly acidic cation exchange resins have pendant carboxylic acid groups. Strongly acidic cation exchange resins have pendant sulfonic acid groups.

[0084] Typically, in the preparation of weakly basic anion exchange resins from polymer beads such as crosslinked polystyrene beads, the beads are preferably haloalkylated, preferably halomethylated, most preferably chloromethylated, and the ion-active exchange groups are then attached to the haloalkylated copolymer. Typically, the haloalkylation reaction consists of swelling a crosslinked addition copolymer with a haloalkylating agent, preferably bromomethyl methyl ether, chloromethyl methyl ether or a mixture of formaldehyde and hydrochloric acid, most preferably chloromethyl methyl ether, and then reacting the copolymer with the haloalkylating agent in the presence of a Friedel-Crafts catalyst such as zinc chloride, iron chloride, or aluminum chloride. Typically, weakly basic anion exchange resins are prepared by contacting a haloalkylated copolymer with ammonia, a primary amine or a secondary amine. Typically, strongly basic anion exchange resins are prepared by contacting a haloalkylated copolymer with a tertiary amine.

[0085] Typically, in the preparation of strongly acidic cation exchange resins from polymer beads such as crosslinked polystyrene beads, the beads are preferably sulfonated. Generally, the beads are swollen using a suitable swelling agent and the swollen beads are reacted with sulfuric acid or chlorosulfonic acid or sulfur trioxide or a mixture thereof.

[0086] The heterogeneity of the polymer beads preferably still exists after sulfonation. This can be observed by NMR as described above except that the beads are swollen with water. The water molecules absorbed into the functionalized beads of the present invention show two peaks, demonstrating that there are two different environments within the beads with different densities of crosslinking points, as in the case of non-functionalized polymer beads swollen with CHCl3.

[0087] Preferably, when the polymer beads are sulfonated, after the sulfonation process, the polymer beads have a relatively uniform distribution of sulfur between the central region of the beads and the outer shell of the beads. This distribution can be evaluated as follows. The concentration of sulfur located in the shell is denoted as CSSHELL, and the concentration of sulfur located in the core is denoted as CSCORE. RDFS The radial distribution coefficient for the sulfur denoted as is defined as the quotient of CSSHELL divided by CSCORE: RDFS = CSSHELL / CSCORE

[0088] CSCORE and CSSHELL can be characterized in any convenient unit, for example, millimoles of sulfur per gram of polymer. In practice, since the quotient RDFS is the important quantity, the units used for CSSHELL and CSCORE are not important as long as the same unit is used for both CSSHELL and CSCORE. Further, a measurement proportional to CSSHELL (for example, such as the spectroscopic peak height, etc.) (denoted as PHSSHELL) can be made. That is, PHSSHELL = k*CSSSHELL, and the value of k may not be known. It is contemplated that the same measurement method can also produce a result (denoted as PHSCORE) proportional to CSCORE; that is, PHSCORE = k*CSSHELL. As long as the proportionality constant k is the same for both measurements, even if k is unknown, RDFS = PHSSHELL / PHSCORE, so RDFS can be measured.

[0089] The quotient RDFS is preferably 0.8 or more; preferably 0.9 or more, more preferably 0.95 or more. The quotient RDFS is preferably 1.2 or less; more preferably 1.1 or less; more preferably 1.05 or less.

[0090] The polymer beads of the present invention are contemplated to be useful for a variety of purposes. The functionalized polymer beads will be useful for many of the purposes for which ion exchange resins are useful. Ion exchange resins having improved physical stability - high crush strength and low breakage in response to osmotic stress - will be appreciated by almost all ion exchange resin end users. Such resins will be useful for a variety of end use applications such as, for example, water treatment, chromatography, and catalysis. For example, in the nuclear power industry, there are standards regarding the crush strength of ion exchange resins used for water treatment that all suppliers must meet, and there is a competitive advantage to those who can supply resins having the highest possible crush strength.

[0091] For example, generally in water treatment, the degree of bead breakage in the use - regeneration cycle (where the beads change size due to different ionic forms / water content) will be reduced. The reduction in bead breakage will reduce the amount of fines mixed with the beads. This will improve the resin life as well as the efficiency and pressure drop for the end user.

[0092] In virtually any use for ion exchange resins, resistance to mechanical stress (high crush strength) will minimize bead breakage that can occur from a bed of beads in an industrial scale column or from mechanical stress applied by pumps, pneumatic transport systems, etc.

[0093] The functionalized polymer beads produced according to the present invention are preferably cation exchange resins.

[0094] For example, the degree of bead breakage in the use - regeneration cycle (where the beads change size due to different ionic forms / water content) will be reduced. The reduction in bead breakage will reduce the amount of fines mixed with the beads. This will improve the resin life, increase the efficiency of resin operation, and reduce the pressure drop required to move liquid through a column of the functionalized polymer beads.

[0095] The following are examples of the present invention.

Example

[0096] Raman spectroscopy was performed as follows. The Raman microscope detects signals from the hourglass volume. The bead diameter at the focus is approximately 1 micrometer, and the vertical resolution from the depth of field is approximately 5 - 10 micrometers. The laser focus was adjusted downward in the sample to a depth of approximately 20 micrometers. The beads were swollen in deuterated toluene, a good solvent that gives high swelling and good spectral resolution. Renishaw TM Using a Renishaw RS - 1000 instrument, spectra were measured using a HeNe laser (25 mW, 633 nm), a 600 g / mm diffraction grating, a 1064 - element TE - cooled CCD detector, and a 100×ULWD (ultra - long working distance) objective lens. Spectra at different positions were measured manually by moving the compression cell holding the beads to span the bead diameter.

[0097] The beads were fully swollen and equilibrated with the solvent during the measurement. First, the beads were equilibrated with a large excess of toluene - D8 (30 mg copolymer and 200 mg toluene - D8) in a vial at room temperature (approximately 23°C) for 2 - 3 days, then removed from the solvent and cut in half with a razor blade. The flat surface was placed face - down on the diamond window of a compression cell (Spectra - Tech TM ) and sealed with a Kalrez TM O - ring. The Kalrez TM O - ring swelled minimally in the toluene solvent. Two or three drops of toluene - D8 were added around the hemispherical beads so that the hemispherical beads were immersed in the solvent. Next, the top of the diamond compression cell was attached and tightened until it just touched the round surface of the beads. The compression cell was turned over for Raman analysis so that the laser focus could be adjusted onto the surface of the beads exposed by the cut. The 6 - mm working distance of the ULWD objective lens was just sufficient for this experiment due to the distance between the stainless - steel plate of the diamond compression cell and the copolymer sample.

[0098] A schematic diagram of the cell is shown in FIG. 2. The cell is a circular object having circular symmetry about axis 4. The upper half 5 of the stainless steel structure and the lower half 6 of the stainless steel structure fix the O-ring 7 together. The upper half 2 of the stainless steel structure and the lower half 3 of the stainless steel structure are held together by a mechanical device (not shown). The diamond window 8 is held at a predetermined position in the stainless steel structures 5 and 6. Deuterated (D8) toluene 9 partially fills the space surrounded by the O-ring 7, the stainless steel structures 5 and 6, and the diamond window 8. The sample 10 is a bead cut in half. The sample 10 is held at a predetermined position between the diamond windows 8. The focus of the laser beam 11 is aligned onto the sample 10.

[0099] Nuclear magnetic resonance (NMR) analysis was performed as described by P.J. O’Connor et al., “1H NMR Characterization of Swelling in Cross-Linked Polymer Systems”, Macromolecules Volume 29, Number 24, Pages 7872 - 7884, 1996; and Kenji Ogino and Risa.ya Sato, “NMR Analysis of Interaction Between Styrene-Divinylbenzene Gel Beads and Small Molecules”, Journal of Polymer Science, Vol. 33, 50 189 - 195, 1995.

[0100] The crushing strength was measured as follows. The functionalized polymer beads were contacted with air at 50 °C and 100% humidity for 4 days. Next, the beads were covered with deionized water and stored at room temperature (approximately 23 °C) for 1 hour or more. A single bead was placed on one plate of a compression tester at room temperature, and the bead was covered with 1 drop of water. The plate was brought into contact at 6.0 mm / min until the particle was crushed, and the peak force was recorded. This procedure was repeated for at least 30 beads, and the average peak force was Report as the "crushing strength". The test apparatus was a Chatillon TM force tester model TCD 200 having a medium-slow motor (2.5 - 63.5 mm / min). The force gauge was model DFGS10.

[0101] Osmotic stability (OS) was measured as follows. The functionalized polymer beads were equilibrated by contact with a 10 wt% solution of NaCl in water at room temperature (approximately 23 °C) for 30 minutes. The NaCl solution was decanted, and the wet resin was passed through a mesh screen to produce a sample of resin having a diameter of 500 μm - 710 μm. Next, 4 ml of the resin was placed into a vertical straight-walled glass column with an inner diameter of 10 mm and a length of at least 60 mm. When placed into the column, all the fluid was pumped at 1 ml / sec. A single cycle was as follows: the fluid was drained from the column by gravity for 56 seconds; the resin in the column was contacted with solution #1 for 60 seconds (4 seconds to fill the column, 32 seconds for solution #1 to pass through the column, 4 seconds to fill the column, and a hold time of 20 seconds for solution #1 to stand still in the column); the fluid was drained from the column in 16 seconds, and the column was backwashed with water for 10 seconds; static water was held in the column for 8 seconds; the fluid was drained from the column by gravity for 56 seconds; the resin in the column was contacted with solution #2 for 60 seconds (4 seconds to fill the column, 32 seconds for solution #2 to pass through the column, 4 seconds to fill the column, and a hold time of 20 seconds for solution #2 to stand still in the column); the fluid was drained from the column in 16 seconds, and the column was backwashed with water for 10 seconds; static water was held in the column for 8 seconds. The test was repeated for 50 cycles. Solution #1 was 15 wt% H2SO4 in water. Solution #2 was 15 wt% NaOH in water. The cycles of exposure to different solutions break some of the particles. After the cycles of exposure, the beads are placed on a sieve (the "500 sieve") that passes objects with a diameter less than 500 μn. The material that passed through the 500 sieve is placed on a sieve (the "150 sieve") that passes objects with a diameter less than 150 μm. The material retained on the 500 sieve is considered intact beads; this material is dried at 105 °C for 16 hours or more, then cooled to approximately 23 °C in a desiccator, and then weighed; this weight is W 無傷It is reported as follows. The material retained on the 150 mesh sieve is considered to be fragments of beads; this material is dried at 105 °C for 16 hours or more, then cooled to approximately 23 °C in a desiccator, and then weighed; this weight is designated as W 断片 It is reported as follows. The osmotic pressure stability is OS(%) = 100×W 断片 / (W 無傷 +W 断片 ) where lower OS values are more desirable.

[0102] The sulfur distribution in the sulfonated polymer beads was measured as follows using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). Scanning electron microscopy (SEM) images were collected with a Hitachi 3400 VP-SEM in variable pressure mode at 15 keV. EDX spectra were collected with a Thermo Noran System 6 EDS equipped with an SDD detector. The radial concentration of S was measured as follows. The cross-section of the IER was prepared by breaking it with a surgical scalpel; X-ray spectral maps were collected for cross-sections from at least four beads; the net count (background subtracted) signal for the characteristic X-rays from sulfur was extracted from the X-ray spectral maps in the form of a spectral line passing through the center of the beads; the net count was plotted as a function of the radial distance.

[0103] The raw materials used in the following examples were as follows Gelatin = animal-based gelatin, isoelectric point approximately 8.5, commercial grade supplied by SOBEL NV (Rousselot) PADMAC = solution of poly(diallyldimethylammonium chloride) in water (20 wt%), commercial grade supplied by NALCO CMMC = carboxymethyl cellulose manufactured by The Dow Chemical Company PVOH = SELVOL™ 523 polyvinyl alcohol manufactured by Sekisui Specialty Chemicals Tris = Tris(hydroxymethyl)aminomethane, 20 wt% solution in water, supplied by Fisher Scientific DVB = Divinylbenzene (purity 63 wt%) BPO = Benzoyl peroxide (purity 75 wt%), supplied by Arkema VPBA = 4-Vinylphenylboronic acid, supplied by Beijing Pure Chemical pbw = parts by weight Caustic = NaOH, 25 wt% in water

[0104] The polymer beads were made from approximately 90 wt% styrene and approximately 10 wt% DVB. Four different recipes were used to make the polymer beads. During the preparation of the suspension of monomer droplets, some of the individual components or partial mixtures were temporarily heated, if necessary, to achieve good mixing, but the suspension of monomer droplets was provided at approximately 25 °C. The monomer droplets were introduced into the aqueous medium by jetting as described in U.S. Patent No. 4,444,960 and U.S. Patent No. 4,623,706. In all recipes, the weight ratio of droplet components to aqueous phase components was 0.61:1.

[0105] The recipes are summarized as follows. "Comp." means comparison. "Base addition" is the (approximate) conversion of monomer to polymer at the time the base was added.

[0106]

Table 1

[0107] Comparative Examples 1A and 1B did not initiate polymerization at a pH of 7 or below. Comparative Examples 2A and 2B had two additions of base to raise the pH, one of these additions being made at monomer conversions of 43% and 40% (i.e., prior to 60%). The details of the method for making the polymer beads were as follows:

[0108] Comparative Examples 1A and 1B (Gelatin / PADMAC, high pH) The droplet composition was as follows (weight % based on the total weight of the droplet components):

[0109] [Table 2]

[0110] The aqueous medium composition was as follows (weight % based on the total weight of the aqueous medium):

[0111] [Table 3]

[0112] Aqueous suspension polymerization was carried out with respect to a suspension of monomer droplets as follows. The suspension was heated to 72 °C and the progress of the reaction was monitored. As soon as the conversion to polymer was in the range of 80 - 85%, the suspension was heated to 92 °C. The pH started at 10.2 and ended at 9.5. After 1 hour, the suspension was cooled to ambient temperature, the beads were dehydrated, washed with water, and dried at ambient temperature.

[0113] Sulfonation was carried out as follows. 100 pbw of polymer beads, a solution of 96 wt% sulfuric acid in 449 pbw of water, 5.2 parts by weight of deionized water, and 35 pbw of EDC were added one by one to the reactor at ambient temperature and heated to 130 °C over 135 minutes. The system was held at 130 °C for 210 minutes and then cooled to 100 °C. Immediately at 100 °C, the acid was removed and the hydration process was started to introduce water. Hydration was carried out stepwise with 50% acid cut, 25% acid cut, and then water. Since the hydration fluid was added at ambient temperature, the batch temperature drifts from 100 °C to ambient temperature during hydration. After hydration, the water-swollen polymer beads were washed again with ambient temperature water, then 98 °C water, and then ambient temperature water. Excess water was filtered off and the water-swelled polymer beads were isolated.

[0114] Duplicate test samples were produced and labeled 1A and 1B.

[0115] Comparative Example 2A (CMMC only; NaOH addition at 43% and 84%): The droplet composition was as follows: (% by weight based on the total weight of the droplet components):

[0116] [Table 4]

[0117] The aqueous medium composition was as follows (% by weight based on the total weight of the aqueous medium):

[0118] [Table 5]

[0119] Aqueous suspension polymerization was carried out as follows. The suspension was heated to 83 °C for 90 minutes and then cooled to 80 °C over 10 minutes while monitoring the progress of the reaction. Caustic was added when the reaction progress was in the range of 40 - 45% and when the reaction progress (conversion rate) was in the range of 80 - 85%. As soon as the conversion rate to the polymer reached the range of 80 - 85%, the reaction system was heated to 92 °C. After 1 hour, the system was cooled to ambient temperature, the beads were dehydrated, washed with water, and dried at ambient temperature. The polymer beads were sulfonated using the same procedure as in Comparative Example 1A.

[0120] Comparative Example 2B (CMMC / PVOH / VPBA; NaOH addition at 42% and 85% conversion). The monomer droplet composition was as follows: (% by weight based on the total weight of the droplet components):

[0121] [Table 6]

[0122] The aqueous medium composition was as follows (% by weight based on the total weight of the aqueous medium):

[0123] [Table 7]

[0124] Aqueous suspension polymerization was carried out as follows. The suspension was heated to 83 °C for 90 minutes and then cooled to 80 °C over 10 minutes while monitoring the progress of the reaction. Caustic was added when the reaction progress was in the range of 40 - 45% and when the reaction progress (conversion rate) was in the range of 80 - 85%. As soon as the reaction progress reached the range of 80 - 85%, the reaction system was heated to 97 °C. After 1 hour, the system was cooled to ambient temperature, the beads were dehydrated, washed with water, and dried at ambient temperature. The polymer beads were sulfonated using the same procedure as in Comparative Example 1A.

[0125] Examples 3A and 3B (PVOH / VPBA; Tris addition at 82% conversion). The monomer droplet composition was the same as in Comparative Example 2B. The aqueous medium composition was as follows (weight % based on the total weight of the aqueous composition):

[0126] [Table 8]

[0127] Aqueous suspension polymerization was carried out as follows. The suspension was heated to 83 °C for 90 minutes and then cooled to 80 °C over 10 minutes while monitoring the progress of the reaction. Tris was added when the reaction progress (conversion rate) reached the range of 80 - 85%. As soon as the reaction progress reached the range of 80 - 85%, the reaction system was heated to 97 °C. After 1 hour, the system was cooled to ambient temperature, the beads were dehydrated, washed with water, and dried at ambient temperature. The polymer beads were sulfonated using the same procedure as in Comparative Example 1A. Duplicate test samples were produced and designated as 3A and 3B.

[0128] Example 4A (PVOH / VPBA; no pH adjustment). The monomer droplet composition and the aqueous medium composition were the same as in Example 3A. Aqueous suspension polymerization was carried out as follows. The suspension was heated to 83 °C for 90 minutes, cooled to 80 °C over 10 minutes, and the progress of the reaction was monitored. As soon as the reaction progress reached the range of 80 - 85%, the reaction system was heated to 92 °C. After 1 hour, the system was cooled to ambient temperature, the beads were dehydrated, washed with water, and dried at ambient temperature. The polymer beads were sulfonated using the same procedure as in Comparative Example 1A.

[0129] Example 4B (PVOH / VPBA; without pH adjustment). The monomer droplet composition was as follows (weight % based on the total weight of the droplet components):

[0130] [Table 9]

[0131] The composition of the aqueous medium, the polymerization procedure, and the sulfonation procedure were the same as in Example 4A.

[0132] Results of Raman spectroscopy of polymer beads: C=C double bond stretching.

[0133] Samples were prepared and Raman spectra were obtained at various points along the diameter of the beads as described above. PCC was the height of the Raman peak at 1635 cm due to the stretching of the carbon - carbon double bond. PAR was the height of the Raman reference peak at 1000 cm due to the stretching of the aromatic ring. The quotient V1 = PCC / PAR characterizes the extent of double bonds in the polymer. Figure 3 shows a plot of V1 vs. position for Comparative Example 1B. Figure 4 shows a plot of V1 vs. position for Example 4B. -1 for the stretching of the carbon - carbon double bond. PAR was the height of the Raman reference peak at 1000 cm -1 for the stretching of the aromatic ring. The quotient V1 = PCC / PAR characterizes the extent of double bonds in the polymer. Figure 3 shows a plot of V1 vs. position for Comparative Example 1B. Figure 4 shows a plot of V1 vs. position for Example 4B.

[0134] Figure 4 shows that Example 4A has relatively high values of V1 at the bead ends compared to the bead center. This means that Example 4A has a relatively high proportion of unreacted double bonds near the outer periphery of the beads compared to the bead center.

[0135] When referring to FIGS. 3 and 4, the "distance from the center of the bead" is considered herein to be the absolute value regardless of the direction from the center of the bead. Thus, a point having a value on the horizontal axis of minus 0.9 is considered to have the same distance from the center of 0.9*R as a point at a value on the horizontal axis of plus 0.9.

[0136] The relative peak height near the outer periphery of the bead compared to the peak height near the center of the bead was evaluated as follows. The values of V1 were averaged for points at a radial distance from the center of the bead of 0.8*R to R, and this average was designated as V1SHELL. Similarly, the values of V1 were averaged for points at a radial distance from the center of the bead of 0 to 0.5*R, and this average was designated as V1CORE. Next, the quotient, which is the radial distribution coefficient for the unreacted vinyl groups, was calculated: VR = V1SHELL / V1CORE It is contemplated that a curve such as in FIG. 3 will have a relatively low value of VR, and on the other hand, a curve such as in FIG. 4 will have a relatively high value of VR.

[0137] Using the Raman results, a similar evaluation can be made using the ratio of CD stretching to CH stretching to provide the radial distribution coefficient for the swelling solvent, RDFS.

[0138] To evaluate the crushing strength and osmotic stability, the polymer beads were functionalized as described above (i.e., sulfonic acid groups were attached).

[0139] The results of the tests were as follows:

[0140]

Table 10

[0141] Example polymers 3A, 3B, 4A, and 4B were all manufactured by the method of the present invention, all had a VR greater than 3.5, and, on the one hand, the comparative polymer had a VR less than 2.1. The example polymers also all had an RDFS greater than 2.6, and, on the one hand, the comparative polymer had an RDFS less than 2.3. The example polymers showed excellent performance characteristics (i.e., crush strength and osmotic pressure stability) compared to the comparative polymer.

[0142] Results of SEM-EDS tests of sulfonated polymer beads. The beads tested were sulfonated resins made from the copolymers of Comparative Examples 2A and 2B and Example 4A. In all samples, the SEM-EDS test yielded images showing the presence of sulfur in the cross-section of the beads through the center. Visual inspection of these images showed that sulfur was evenly distributed throughout the cross-section of the particles. Also, the images can be digitally analyzed to produce a graph of sulfur content as a function of position along a diameter line of the cross-section. Such a graph shows that the sulfur content is constant along the diameter line. These results indicate that the distribution of sulfur is uniform throughout the beads. Thus, any improved properties of the beads of the present invention do not depend on any non-uniformity in the distribution of sulfonic acid groups in the beads.

[0143] The results of the NMR analysis of the non-functionalized polymer beads were as follows. The solvent was CHCl3. When a comparative homogeneous bead was tested, one peak corresponding to the solvent swollen into the bead was observed at approximately 6.7 ppm, and a second peak corresponding to the free solvent was observed at approximately 7.2 ppm. When the sample of the present invention was tested, the free solvent peak at 7.2 ppm was observed as in the comparative sample, but in the sample of the present invention, the peak corresponding to the solvent swollen into the bead was split into two peaks, one higher than 6.7 ppm and one lower than 6.7 ppm. The two peaks above and below 6.7 ppm are thought to demonstrate that the absorbed solvent is present in two different environments. One environment is thought to be a relatively highly cross-linked core, and the other environment is thought to be a relatively lightly cross-linked shell.

[0144] The results of the NMR analysis of the sulfonated polymer beads were as follows. The solvent was water. In the comparative sample, which was homogeneous, a free water peak was observed at approximately 4.7 ppm, and a peak at approximately 6.4 ppm due to water absorbed into the beads was observed. When the polymer beads of the present invention were tested, the same free water peak at 4.7 ppm was observed, but the single peak at 6.4 ppm was replaced by a pair of peaks, one lower than 6.4 ppm and one higher than 6.4 ppm. The two peaks above and below 6.4 ppm are thought to demonstrate that the absorbed solvent is in two different environments. One environment is thought to be a relatively highly cross-linked core, and the other environment is thought to be a relatively lightly cross-linked shell. (Aspect) (Aspect 1) Polymer beads having a radius R, wherein the polymer comprises polymerized units of one or more polyfunctional vinyl monomers in an amount of 0.3% to 20% by weight based on the weight of the polymer, and polymerized units of one or more monofunctional vinyl monomers in an amount of 80% to 99.7% by weight based on the weight of the polymer, (a) Here, the polymerized units of the polyfunctional vinyl monomer have a radial distribution coefficient MR of 0.9 to 1.1, where MR = CMSHELL / CMCORE (where CMSHELL is the average concentration of the polymerized units of the polyfunctional vinyl monomer located at a distance from the center of the beads of 0.8*R to R, and in the formula, CMCORE is the average concentration of the polymerized units of the polyfunctional vinyl monomer located at a distance from the center of the beads of 0 to 0.5*R), and (b) Here, some of the vinyl groups in the polymerized units of the multivinyl monomer are unreacted, and the unreacted vinyl groups have a radial distribution coefficient VR of 2.5 or more, where VR is determined by Raman spectroscopy measurement performed on the beads, where VR = V1SHELL / V1CORE (where V1SHELL is the average of the ratio V1 for measurements taken at a distance from the center of the beads of 0.8*R to R, and in the formula, V1CORE is the average of the ratio V1 for measurements taken at a distance from the center of the beads of 0 to 0.5*R), where V1 = PCC / PAR (where PCC is the height of the Raman spectroscopic peak due to the stretching of the carbon-carbon double bond, and PAR is -1 the height of the Raman spectroscopic reference peak due to the stretching of the aromatic ring at 1000 cm Polymer beads. (Aspect 2) The polymer beads according to Aspect 1, wherein the polymer beads contain a gel-type resin. (Aspect 3) The polymer beads according to Aspect 1, wherein the monofunctional vinyl monomer contains one or more styrene-based monomers. (Aspect 4) The polymer beads according to Aspect 1, wherein the polyfunctional vinyl monomer contains one or more styrene-based monomers.

Claims

1. Polymer beads having a radius R, wherein the polymer of the polymer beads comprises, based on the weight of the polymer, polymerization units of one or more polyfunctional vinyl monomers in an amount of 0.3% by weight to 20% by weight and, based on the weight of the polymer, polymerization units of one or more monofunctional vinyl monomers in an amount of 80% by weight to 99.7% by weight, wherein (a) the polymerization units of the polyfunctional vinyl monomer have a radial distribution coefficient MR of 0.9 to 1.1, where MR = CMSHELL / CMCORE (wherein CMSHELL is the average concentration of the polymerization units of the polyfunctional vinyl monomer located at a distance from the center of the beads of 0.8×R to R, and wherein CMCORE is the average concentration of the polymerization units of the polyfunctional vinyl monomer located at a distance from the center of the beads of 0 to 0.5×R), and wherein (b) some of the vinyl groups in the polymerization units of the polyfunctional vinyl monomer are unreacted, and the unreacted vinyl groups have a radial distribution coefficient VR of 2.5 or more, where VR is determined by Raman spectroscopy measurement performed on the beads, where VR = V1SHELL / V1CORE (wherein V1SHELL is the average of the ratio V1 for measurements performed at a distance from the center of the beads of 0.8×R to R, and wherein V1CORE is the average of the ratio V1 for measurements performed at a distance from the center of the beads of 0 to 0.5×R), Here, V1 = PCC / PAR (where PCC is the height of the Raman spectroscopic peak due to the stretching and contraction of the carbon-carbon double bond, and PAR is the height of the Raman spectroscopic reference peak due to the stretching of the aromatic ring at 1000 cm －１ ), and each of the polyfunctional vinyl monomer and the monofunctional vinyl monomer is an aromatic ring, the polyfunctional vinyl monomer is divinylbenzene, and the monofunctional vinyl monomer is styrene polymer beads.

2. The polymer beads according to claim 1, wherein the polymer beads contain a gel-type resin.

3. The polymer beads according to claim 1, having a volume average particle diameter of 50 μm or more.

Images