High capacity superabsorbent materials and methods for making the same

Abstract

Described herein are superabsorbent materials (SAMs) and methods of making SAMs. The SAMs are copolymerized after monomer complex formation to incorporate selected inorganic salts into the polymerized SAMs. The SAMs are copolymerized with selected stable inorganic salts and / or selected redox-active inorganic salts. The SAMs are copolymerized in a single-step polymerization process or a staged polymerization process. The copolymer-based SAMs have significantly improved absorption properties. The compositions and methods described herein can be used in a variety of absorbent products.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to novel superabsorbent materials (SAMs). The SAMs are copolymerized after monomer complex formation to incorporate selected inorganic salts into the polymerized SAMs. The SAMs are copolymerized with selected stable inorganic salts and / or selected redox-active inorganic salts. The SAMs are copolymerized in a single-step polymerization process or a staged polymerization process. The copolymer-based SAMs have significantly improved absorbent properties. Compositions and methods according to the present disclosure are useful in a variety of absorbent products. BACKGROUND

[0002] Superabsorbent polymers (SAPs) are three-dimensional networks that can absorb and retain water (or other aqueous media) and physiological fluids such as urine and blood in excess of their own dry weight by several hundred times, typically depending on the ionic concentration of the aqueous solution. SAPs have applications in multiple fields, including medicine, personal care products, biomaterials, biosorbents, and agriculture. The first commercial SAPs were produced by alkaline hydrolysis of starch-g-polyacrylonitrile in 1970. While these polymers can absorb up to 500 g / g of water, they are mechanically weak in their swollen state. SAPs were developed industrially in Japan and the United States in the early 1980s for sanitary applications. SAPs have been found to have the potential to replace fluff, making their use in sanitary products such as baby diapers and feminine sanitary napkins cost-effective.

[0003] Desirable features of SAPs include high absorbent capacity, high and tunable rate of swelling, absorbency under high load, good swelling gel strength, high gel fraction after crosslinking, excellent durability and stability upon swelling and during storage, non-toxicity, and low cost. While current hydrogel systems provide good performance in several of these different aspects, various formulations suffer from several drawbacks, including low absorbency under pressure, gel blocking (whereby the initial layer of SAPs forms a relatively impermeable barrier to subsequent water diffusion and deeper absorption into the material), and high sensitivity to electrolyte solutions. Various strategies have been employed to address these challenges, including formation of composite and nanocomposite hydrogels, interpenetrating polymer network (IPN) hydrogels, and various surface treatments; however, improvements are still needed to enable the use of minimal materials in as wide a range of applications as possible.

[0004] The nature of the monomers and crosslinker, their concentrations and molar ratios are known to be the most important factors affecting the SAP absorbent capacity. Acrylic acid, acrylamide and methacrylic acid are the most widely used monomers for the commercial production of SAP. However, the presence of some residual acrylamide in the gel poses a challenge for the practical use of such hydrogels for human health and personal care products. Conversely, the water absorption and swelling properties of ionic SAPs (e.g. based on acrylic or methacrylic acid) are significantly reduced in salt-containing liquids, including physiological fluids such as urine and blood. The reason for this salt sensitivity is that counterions such as sodium ions (Na + ) present in physiological fluids can effectively shield the polymer backbone charge, resulting in condensation of the counterions with the charged groups of the polymer and thus reducing the counterion entropy and direct chain-chain repulsion forces available to drive the swelling response.

[0005] Conventional SAMs are mainly made of two classes of SAPs: synthetic polymers and natural polymers. In general, synthetic superabsorbent polymers are charged polyelectrolytes such as salts of polyacrylic acid (PAA), polyvinyl sulfonic acid, polyvinyl phosphonic acid, and partially hydrolyzed maleic anhydride copolymers. Natural polymers include both neutral and charged polymers such as carboxymethyl cellulose, sodium alginate, chitosan salts, and modified starches. All of these known SAMs have substantial limitations. For example, the most widely used commercial PAA-based SAMs have limited absorbency under load (AUL) and are also very salt sensitive.

[0006] The salt sensitivity of SAMs results in reduced gel swelling capacity. To compensate for the capacity reduction due to salt sensitivity, personal care garments require more SAM material to ensure sufficient absorbent capacity to prevent leakage. Therefore, there is an urgent need in the personal care industry to improve or overcome the salt sensitivity of conventional SAM materials.

[0007] However, SAM salt sensitivity is a challenging problem that needs to be addressed. While there have been numerous attempts in the art, all proposed solutions remain impractical and cost prohibitive. It is well known in the art that a significant portion of the SAM is in the form of its neutralized salt, and the conventional wisdom is that all of these neutralized salt units are considered to be in their fully ionized form, e.g. metal ions (e.g. Na + ) are all free to move during swelling. It is also known in the art that salt is detrimental to capacity, and that higher valence inorganic salts inhibit SAM capacity more than monovalent salts such as sodium chloride. Therefore, past work on reducing the salt sensitivity of SAM materials has primarily focused on simply using more SAM material to compensate for capacity loss, removing / reducing salt from physiological fluids such as urine, or attempting to design new structures that are less salt sensitive.

[0008] The copolymerization of SAM monomers with selected inorganic salts having metal ions in oxidation state of at least 2 in PCT / US2020 / 053003 can provide a significant improvement in CRC performance without deleterious effects on other performance attributes such as AUL. However, these copolymerizations are achieved with non-staged one-pot synthesis procedures. One-pot synthesis procedures are simple to manufacture, but they have the obvious disadvantage of not being able to flexibly control / design the SAM polymer chain structure to mitigate salt sensitivity. For example, uniform crosslinking density throughout the gel network will limit elastic swelling, such that the potential capacity increase due to chain charge-charge repulsion will be reduced.

[0009] Furthermore, SAMs can be copolymerized with selected redox-active inorganic salts in a staged polymerization process. Such a process is described in detail in the unpublished PCT application entitled “STAGED POLYMERIZATION OF COPOLYMERIZED SUPERABSORBENT POLYMERS,” which is filed concurrently with the present application and incorporated herein by reference. The copolymer-based SAMs have significantly improved absorption properties due to the increased presence of permeating free ions. The copolymer-based SAMs also have interpenetrating networks due to the staged copolymerization procedure, which can mitigate the elastic forces that limit chain swelling. The copolymer-based SAMs also have structural design flexibility, where each stage of polymerization can have its own composition, crosslinking density, etc., which can further enhance the absorption capacity of the SAM while providing unique SAM properties that traditional uniform PAA-based SAM structures can not be able to provide.

[0010] However, despite the demonstrated potential of selected inorganic salts to increase SAM capacity, particularly for CRC, the synthesis procedures to produce these materials have not been optimized and improved. For example, in the staged polymerization process, the addition of selected inorganic salts to the polymerization mixture lacks precise control, and the resulting Stage 1 polymer exhibits a broad distribution with a polydispersity index (PDI) as high as 2.3. This problem has multiple sources. First, there is no control over how the selected salt coordinates with the monomers in the polymerization mixture. Second, there is no knowledge of the coordination number of each metal center in the polymerization mixture, e.g., mononuclear, dinuclear, or even higher coordination numbers. Third, for staged polymerizations involving redox-active Fe(II) salts for the initial polymerization, the initial initiation of polymerization can be very fast, so there is still a need for better control methods to provide a more uniform distribution of ionization-enhancing metal centers in the polymer network.

[0011] Accordingly, there is a need to improve the polymerization procedure for the copolymerization of SAM monomers with a selected inorganic salt. In particular, there is a need for better options for adding a selected inorganic salt to the polymerization mixture to know exactly where the metal center will be located and to know the exact structure of the monomer complex between the coordinating inorganic salt and the selected inorganic salt.

[0012] Described herein are SAMs and methods of making SAMs. The SAMs are copolymerized after monomer complex formation to incorporate a selected inorganic salt into the polymerized SAM. The monomer complex with the coordinating selected salt enhances ionization and also allows precise control of the location of the selected salt on the monomer. As a result, the resulting SAM polymer network structure can be better controlled and designed.

[0013] Compositions and methods according to the present disclosure can be used in a variety of absorbent products.

[0014] Summary

[0015] It is an object of the present disclosure to address the salt sensitivity of AA-based SAMs by inducing copolymerization after the formation of the monomer complex in order to precisely incorporate a selected inorganic salt into the polymerized SAM. SUMMARY

[0016] In one aspect, provided herein is a method of making a superabsorbent polymer comprising a polymer backbone comprising (i) a strongly or super strongly ionizable backbone monomer comprising an anion of a strong organic acid and a super ionizable counterion, (ii) a neutralized backbone monomer, and (iii) optionally an unneutralized backbone monomer, and optionally a crosslinker. The method comprises (i) forming a complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2; (ii) forming a mixture comprising a solvent, the monomer, the complex between the monomer and the salt comprising a metal ion in an oxidation state of at least 2, and optionally a crosslinker; (iii) initiating a reaction; and (iv) allowing the mixture to react. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a process depicting a non-staged SAM polymerization process including a stabilizing salt such as FeCl3, according to one exemplary embodiment of the present disclosure. The monomer complex with the coordinating selected salt can be added prior to polymerization.

[0018] Figure 2 is a process depicting FeCl2-induced staged SAM polymerization, according to one exemplary embodiment of the present disclosure. The monomer complex with the coordinating selected salt can be added at any stage of polymerization.

[0019] Figure 3AThis is a two-dimensional view depicting the polymer microstructure resulting from FeCl2-induced staged SAM polymerization, according to an exemplary embodiment of the present disclosure.

[0020] Figure 3B This is a three-dimensional view depicting the polymer microstructure produced by FeCl2-induced staged SAM polymerization, according to an exemplary embodiment of the present disclosure.

[0021] Figure 4A This illustration depicts FTIR data of a polymer produced by a single-step polymerization process, according to an exemplary embodiment of this disclosure. Boxes indicate regions of interest and further measurements.

[0022] Figure 4B This illustration depicts FTIR data of a polymer produced by a single-step metal complex monomer polymerization method, according to an exemplary embodiment of this disclosure. Boxes indicate regions of interest and further measurements.

[0023] Figure 5A According to an exemplary embodiment of this disclosure, a polymer produced by a single-step polymerization method is depicted at 1701 cm⁻¹. -1 FTIR data at the infrared peak.

[0024] Figure 5B According to an exemplary embodiment of this disclosure, a polymer produced by a single-step metal complex monomer polymerization method at 1701 cm⁻¹ is depicted. -1 FTIR data at the infrared peak.

[0025] Figure 6A According to an exemplary embodiment of this disclosure, a polymer produced by a single-step polymerization method is depicted at 1639 cm⁻¹. -1 FTIR data at the infrared peak.

[0026] Figure 6B According to an exemplary embodiment of this disclosure, a polymer produced by a single-step metal complex monomer polymerization method at 1639 cm⁻¹ is depicted. -1 FTIR data at the infrared peak. Detailed Implementation

[0027] According to this disclosure, the superabsorbent polymer is copolymerized after forming a monomer complex to introduce a selected inorganic salt into the polymerized SAM. The monomer complex with the selected salt coordinated enhances ionization and allows for precise control over the position of the selected salt on the monomer. Therefore, the resulting SAM polymer network structure can be better controlled and designed.

[0028] Formation of monomer complex with selected complexing salt.

[0029] Forming a monomer complex with a coordination selected salt prior to polymerization provides at least three unique advantages. First, there is precise control over how the metal salt coordinates with the desired monomer prior to polymerization. For example, it is preferred to coordinate the selected metal salt to a monomer that has already been neutralized, such as sodium acrylate (e.g., AANa), so that ionization enhancement can be maximized. Second, there is precise control over how the metal salt coordinates with the desired monomer prior to initiation of polymerization. For example, in a staged polymerization, the coordinated monomer complex can be the initiation point for polymerization, so it can influence the polymer network structure through steric constraints of the metal ion. Third, the flexibility to control crosslinking density at different stages can further optimize the benefits of ionization and structural design.

[0030] After the monomer complex with a coordination selected salt is formed, the SAM can be copolymerized with the desired monomer or monomer mixture in a single step polymerization process or a staged polymerization process. The SAM based copolymer has significantly improved absorbent properties.

[0031] Generally, the complex between the monomer and the selected inorganic salt can be formed according to any suitable method known in the art. In many embodiments, the polymerization process according to the present disclosure includes forming a complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2. In some embodiments, the method steps of forming a complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2 include: (i) forming a mixture comprising a monomer and a salt comprising a metal ion in an oxidation state of at least 2; (ii) isolating a solid precipitate produced in the mixture by complexation; (iii) optionally washing the solid precipitate; and (iv) optionally drying the solid precipitate.

[0032] In some embodiments, the monomer complex can be formed from an unneutralized monomer. In some embodiments, the monomer complex can be formed from a neutralized monomer or a partially neutralized monomer. Preferably, the monomer complex is formed from a neutralized monomer. In some embodiments, the monomer complex is formed only from a neutralized monomer.

[0033] In some embodiments, the complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2 is provided to the mixture in an amount sufficient to provide a loading ratio of about 0.005 to 1.00 weight percent relative to the weight of the superabsorbent polymer. In some embodiments, the complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2 is provided to the mixture in an amount sufficient to provide a loading ratio of about 0.05 to 0.30 weight percent relative to the weight of the superabsorbent polymer.

[0034] Generally, the formation of the metal complex monomer occurs as the first step of the polymerization process. The subsequent polymerization process can be any suitable polymerization process known in the art. In some embodiments, the polymerization process is a single step polymerization or a staged polymerization. Preferred polymerization conditions for single step and staged polymerization are described herein.

[0035] To demonstrate that monomer complexes with selected metal salts are superior to direct addition of the metal salt to the polymerization mixture, examples are disclosed herein of using such monomer complexes in single step polymerization. These exemplified polymerization conditions are representative and not limiting. The benefits observed for single step polymerization can be readily extended to other polymerization methods and processes. For example, the monomer complexes can be used in the processes described in detail in the co-pending PCT application entitled “STAGED POLYMERIZATION OF COPOLYMERIZED SUPERABSORBENT POLYMERS,” filed concurrently with the present application and incorporated herein by reference.

[0036] SAM co-polymerized with selected inorganic salt via single step polymerization.

[0037] The following description relates to single step, non-staged copolymerization methods of preparing SAMs copolymerized with selected inorganic salts. These methods and resulting polymers are known in the art, for example in PCT / US2020 / 053003, incorporated herein by reference.

[0038] Single step polymerization is achieved through a non-staged one-pot synthesis procedure. One example of a non-staged SAM polymerization process involving a stable salt, such as FeCl3, is shown in Figure 1 In this process, a pre-polymerization mixture is prepared at 0°C or room temperature and a stable monomer metal complex or mixture of monomer complexes is added to the pre-polymerization mixture. These stable monomer metal complexes do not initiate polymerization. Instead, single step polymerization occurs through single step thermal radical polymerization, where the temperature is raised to 60-70°C and held at that temperature to complete polymerization. This results in a nearly uniform polymer structure with uniform crosslinking density.

[0039] The superabsorbent polymers according to the present disclosure comprise a polymer backbone comprising (i) neutralized backbone monomers, (ii) neutralized backbone monomers complexed with a coordination complex comprising a metal ion having an oxidation state of at least 2, (iii) optional unneutralized backbone monomers, and (iv) optional unneutralized backbone monomers, and optionally a crosslinking agent.

[0040] The superabsorbent polymer is copolymerized from a selected inorganic salt, a neutralized monomer, an unneutralized monomer, and optionally a crosslinking agent. This copolymerized superabsorbent polymer reduces salt sensitivity to significantly improve CRC performance without deleterious effects on other performance attributes such as AUL. It is understood herein that if the gel strength of the SAM according to the present disclosure can be enhanced by using well-known techniques such as surface crosslinking of the SAM particles, then higher AUL can also be achieved.

[0041] The polymer backbone is random and lacks a structured ordering of neutralized backbone monomers, neutralized backbone monomers complexed with coordination complexes comprising metal ions in an oxidation state of at least 2, unneutralized backbone monomers, and unneutralized backbone monomers. The monomers of the polymer backbone can be arranged in a variety of ways. Individual monomers can be covalently bonded to the same or different monomers.

[0042] The superabsorbent polymer does not comprise a block copolymer of neutralized backbone monomers, neutralized backbone monomers complexed with coordination complexes comprising metal ions in an oxidation state of at least 2, unneutralized backbone monomers, and unneutralized backbone monomers. The superabsorbent polymer also does not comprise an alternating copolymer of neutralized backbone monomers, neutralized backbone monomers complexed with coordination complexes comprising metal ions in an oxidation state of at least 2, unneutralized backbone monomers, and unneutralized backbone monomers. Finally, the superabsorbent polymer does not comprise a graft copolymer of neutralized backbone monomers, neutralized backbone monomers complexed with coordination complexes comprising metal ions in an oxidation state of at least 2, unneutralized backbone monomers, and unneutralized backbone monomers.

[0043] The selected inorganic salt in the monomer complex suitable for single-step polymerization is typically a salt comprising metal ions in an oxidation state of at least 2, at least 3, or at least 4. The use of these selected metal salts is based on a key finding in the analysis of the interaction of inorganic salts with SAM polymer chain ion pairs. There is a major difference when metal salts, especially metal ions in the salt with an oxidation state greater than two, interact with the polymer chains of SAM from an external solution, and when the same salt is introduced into the polymer chain by forming a metal complex with the monomer prior to polymerization. In the former case, the salt approaches the ion pair of the polymer chain as an “external” ion, and they primarily act as chain charge screeners (mono counterions such as Na + ) and high oxidation ions such as Ca 2+ and Al 3+ ) and chelating crosslinkers (high oxidation ions such as Ca 2+ , Al 3+The shielding and sequestering of high oxidation state metal ions is more profound because they will accumulate on the outer layer of the SAM particles, thus the elastic portion of the SAM swelling will be significantly limited and reduced. However, for the latter case, the same high oxidation state metal ions, when they first form complexes with monomers such as AA or AANa and then polymerize, can actually contribute to more free ions for the polymer chains, thus increasing SAM absorbency. This observation is consistent with the osmotic pressure theory, i.e., osmotic pressure is directly proportional to the total particle count in a gel system.

[0044] These complexed salts are referred to as "internal" or "intrinsic" metal salts and metal ions.

[0045] However, even though SAM absorbency can be increased, too many internal salts can still be detrimental to SAM absorbency because they can also act as cross-linkers through chelation. Therefore, the beneficial effect and effective increase in SAM capacity can only be realized if the chelation between polymer chains during polymerization is minimized. To this end, the loading level of the metal salts used to form the complexes must be controlled so that ionization can be maximized while cross-linking can be minimized. In addition, only selected salts of metals with oxidation states greater than two can be suitable for the present disclosure. This is because high oxidation state salts are more favorable than salts with low oxidation state metal ions to form more free ions. More specifically, metal ions with oxidation state two (i.e., M 2+ ) are more favorable than metal ions with oxidation state one (i.e., M + ), and metal ions with oxidation state three or greater (i.e., M ≥3+ ) are more favorable than metal ions with oxidation state two (i.e., M 2+ ).

[0046] Since there are very few metal ions that are stable when the oxidation state is greater than three, the preferred salts are those with metal ions with oxidation state three. Some salts with M 3+ may still not be suitable for the present disclosure if they are prone to form chelation structures in aqueous solutions or polymerization mixtures.

[0047] Many inorganic salts have metal ions with oxidation state greater than two (i.e., metal halides, metal sulfates, and metal nitrates) that can be used to demonstrate the beneficial effects of the present disclosure. However, most of these salts are not readily available and have safety concerns in personal care applications. Therefore, the metal ions demonstrated herein are common in nature and are associated with biological-related processes. Thus, they are safe or considered safe in at least some personal care applications. In any event, it is not intended to limit the present disclosure, and any inorganic salt with metal ions with oxidation state at least two can be used in the present disclosure.

[0048] Selected inorganic salts according to the present disclosure include metal ions that can form coordination complexes with monomers in the prepolymerization mixture; these structures will become part of the polymer chain or network of SAMs after copolymerization. The structure of the coordination complex depends on the coordination number of the metal ion. The coordination number of a metal depends largely on how many donor atoms can be accommodated around the metal, which in turn is governed by the size. With respect to transition metals, the post-transition metals are smaller than the pre-transition metals. As one moves across the 3d transition series, the nuclear charge and atomic number increase, but the shielding due to filled electron shells remains the same. This pulls the outer electrons closer, and thus the atoms and ions get progressively smaller. For zinc, the last and smallest of the 3d metals, four is the most common coordination number. Thus, post-transition metals generally form smaller complexes than pre-transition metals.

[0049] In some embodiments, monomer complexes that have polymerized into one polymer chain can be able to form additional linkages with another monomer through chelation or charge-charge interactions. In some embodiments, two polymers linked through one monomer complex can have an initial geometric angle of 90 degrees, while in some other embodiments, the angle can be 180 degrees. Due to these geometric constraints of the coordinating metal center ion, SAM materials with this structure will result in more favorable gel properties, such as improved gel rigidity and mechanical properties.

[0050] The coordination mode between the monomer and the selected salt in the monomer complex can have two main modes, for example one is the coordination between the olefinic double bond of the monomer and the metal center, and the other is the coordination between the carboxylate side of the monomer and the metal center. Coordination between the carboxylate and the metal center is more complex compared to the olefinic double bond coordination, as it can present different modes. It is conceivable that this different coordination mode can exist in the polymerization mixture, and some of this initial simple complex can form more complex structures through chelation during the polymerization process, or even at later stages such as during the drying process. However, by fixing the metal ion onto the desired monomer (e.g. monomer neutralized with sodium ion) prior to polymerization to form the monomer complex, the formation of chelation points between different polymer chains can be largely limited, so that the true ionization of sodium ion can be achieved. As described in PCT / US2020 / 053003, the formation through the network of different chains is not desirable here for the purpose of ionization enhancement, and should be minimized.

[0051] Because different coordination modes and different selected metal salts can make one or more modes superior to others, it is understood herein that one skilled in the art can fine tune the polymerization and processing conditions for a given selected salt so that maximum capacity enhancement can be achieved. It is also contemplated that in some cases, CRC enhancement can be deeper than AUL enhancement, as with the polymerization conditions of the present disclosure. In other cases, AUL enhancement can be deeper than CRC increase. In yet other cases, both CRC and AUL increases can be achieved.

[0052] Transition metals are particularly advantageous in the present disclosure for forming monomeric complexes because they have many oxidation states and coordination complexes. In some embodiments, the coordination monomeric complex comprises a metal ion selected from the group consisting of transition metals. Preferably, the coordination complex comprises a metal ion selected from the group consisting of the first and second rows of transition metals. The most preferred transition metal ions are selected from the group consisting of the first row of transition metals and combinations thereof.

[0053] In some embodiments, the coordination complex comprises a metal ion selected from the group consisting of: Ca 2+ , Co 2+ , Zn 2+ , Mn 2+ , Al 3+ , Fe 3+ , Co 3+ , Mn 3+ , Ru 3+以 and combinations thereof. In some embodiments, the coordination complex comprises a complex selected from the group consisting of: ML x 2+ , ML x 3+ and combinations thereof, wherein L is an organic ligand, M is a metal ion selected from the group consisting of: Ca 2+ , Co 2+ , Zn 2+ , Mn 2+ , Al 3+ , Fe 3+ , Co 3+ , Mn 3+ , Ru 3+以 and combinations thereof.

[0054] In some embodiments, the coordination complex comprising a metal ion having an oxidation state of at least 2 is coordinated with more than one neutralized or unneutralized backbone monomer. Coordination with more than one neutralized or unneutralized backbone monomer can occur along the same or different polymer chains.

[0055] A particularly preferred metal salt is FeCl3. FeCl3is particularly effective and inexpensive. FeCl3exists in water in a variety of hydrated coordination complexes. The hydrated forms can form monodentate complexes, bidentate complexes, and even higher polydentate complexes from monomers, and they can remain and become source units for more free ions in the polymerized SAM. At most, the hydrated forms can form cluster complexes after polymerization with the SAM monomers, which are known in the literature. The selected inorganic salt can improve the salt sensitivity of the SAM through a number of mechanisms, primarily by increasing free ions as intrinsic internal salts directly incorporated into the polymer chains and chain network of the SAM.

[0056] While not specifically targeted, SAMs with metal ions can have other advantageous properties compared to SAMs without coordinating metal ions. For example, charged metal centers are known for trapping or killing bacteria, a property that is highly desirable for personal garments such as diapers and pants and feminine pads. In another aspect, metal ions are also known to adsorb various odor molecules such as ammonia, amines, and sulfur compounds. These odor compounds are well known to be present in physiological fluids such as urine, blood, sweat, and the like. In another aspect of the present application, the metal ions in the polymer chains and chain network can act as a starting point for degradation in order to more quickly decompose in nature or in an engineered process, such as by light radiation (e.g., commonly known as OXO-biodegradation processes). Thus, SAMs with coordinating metal ions can be superior to other SAMs at least because they have better biodegradability.

[0057] Generally, the neutralized backbone monomer is present in an amount ranging from about 50 to about 99 mole percent of the superabsorbent polymer, the neutralized backbone monomer complexed with a coordination complex comprising a metal ion in an oxidation state of at least 2 is present in an amount ranging from about 0.001 to about 0.3 mole percent of the superabsorbent polymer, the unneutralized backbone monomer is present in an amount ranging from about 0 to about 40 mole percent of the superabsorbent polymer, and the unneutralized backbone monomer complexed with a coordination complex comprising a metal ion in an oxidation state of at least 2 is present in an amount ranging from about 0.001 to about 0.3 mole percent of the superabsorbent polymer. More of the neutralized backbone monomer complexed with a coordination complex comprising a metal ion in an oxidation state of at least 2 can have a detrimental effect on the superabsorbent polymer. In some embodiments, the preferred total amount of neutralized and unneutralized monomers with coordinating selected salts is in the range of about 0.01 mole percent to about 0.3 mole percent of the final polymer.

[0058] In some other embodiments, the preferred total amount of neutralized and unneutralized monomers having a coordinating selected salt is in the range of about 0.01 mole % to about 0.15 mole % of the final polymer. In some other embodiments, the preferred total amount of neutralized and unneutralized monomers having a coordinating selected salt is in the range of about 0.01 mole % to about 0.1 mole % of the final polymer. In some other embodiments, the preferred total amount of neutralized and unneutralized monomers having a coordinating selected salt is in the range of about 0.01 mole % to about 0.05 mole % of the final polymer.

[0059] In some embodiments, the neutralized backbone monomers are present in an amount greater than about 50 mole %, 55 mole %, 60 mole %, 65 mole %, 70 mole %, 75 mole %, 80 mole %, 85 mole %, 90 mole %, 95 mole %, 96 mole %, 97 mole %, or 98 mole % of the superabsorbent polymer.

[0060] In some embodiments, the unneutralized backbone monomers are present in an amount greater than about 0 mole %, 5 mole %, 10 mole %, 15 mole %, 20 mole %, 25 mole %, 30 mole %, 35 mole %, 36 mole %, 37 mole %, 38 mole %, or 39 mole % of the superabsorbent polymer.

[0061] In some embodiments, the sum of the weight % of neutralized backbone monomers complexed with a coordinating complex comprising a metal ion in an oxidation state of at least 2 and the weight % of unneutralized backbone monomers complexed with a coordinating complex comprising a metal ion in an oxidation state of at least 2 is less than about 0.2 %, less than about 0.075 %, less than about 0.050 %, and less than about 0.025 % and less than 0.01 % of the total weight % of the polymer backbone.

[0062] The superabsorbent polymer can take a variety of forms depending on the final application. In some embodiments, the superabsorbent polymer is in a form selected from the group consisting of a particle, a gel, a fiber, a bead, a liquid, a solid, a paste, or a combination thereof. In some particular embodiments, the superabsorbent polymer is a gel or a particle, and preferably is in the form of a particle.

[0063] In some embodiments, the superabsorbent polymer is in a form having a diameter in a range of about 100 pm to about 1000 pm, about 100 pm to about 900 pm, about 100 pm to about 800 pm, about 100 pm to about 700 pm, about 100 pm to about 600 pm, about 100 pm to about 500 pm, about 100 pm to about 400 pm, about 100 pm to about 300 pm, or about 100 pm to about 200 pm. In some embodiments, the superabsorbent polymer is in a form having a diameter in a range of about 200 pm to about 900 pm, about 300 pm to about 800 pm, about 300 pm to 600 pm, about 400 pm to about 700 pm, or about 500 pm to about 600 pm.

[0064] In some particular embodiments, the superabsorbent polymer is in a form having a diameter in a range of about 300 pm to about 600 pm.

[0065] In various embodiments, the superabsorbent polymer exhibits substantially improved absorbency and salt sensitivity properties without being crosslinked. However, a crosslinking agent can be used to further enhance the properties of the superabsorbent polymer. The superabsorbent polymer can comprise one, two, or more crosslinking agents.

[0066] In some embodiments, the superabsorbent polymer comprises a crosslinking agent selected from the group consisting of methylene(bis)acrylamide (MBAA), poly(ethylene glycol diacrylate) (PEGDA), ethylene glycol diacrylate (EGDA), ethylene glycol dimethacrylate (EGDMA), poly(ethylene glycol dimethacrylate) (PEGDMA), and combinations thereof.

[0067] In some embodiments, the superabsorbent polymer is lightly crosslinked. In some embodiments, the superabsorbent polymer has a crosslinking agent density in a range of about 0.1 mole% to about 2.0 mole%. In some embodiments, the superabsorbent polymer has a crosslinking agent density in a range of about 0.2 mole% to about 2.0 mole%. In some embodiments, the superabsorbent polymer has a crosslinking agent density in a range of about 0.5 mole% to about 2.0 mole%. In some embodiments, the superabsorbent polymer has a crosslinking agent density in a range of about 1.0 mole% to about 2.0 mole%. In some embodiments, the superabsorbent polymer has a crosslinking agent density in a range of about 1.5 mole% to about 2.0 mole%.

[0068] The neutralized backbone monomer and the unneutralized backbone monomer are each individually selected according to the end use of the superabsorbent polymer. Monomers known in the art for superabsorbent polymers are suitable as the neutralized backbone monomer and the unneutralized backbone monomer. The neutralized backbone monomer and the unneutralized backbone monomer can be neutralized and unneutralized forms of the same monomer or neutralized and unneutralized forms of different monomers.

[0069] In some embodiments, the neutralized backbone monomer and the unneutralized backbone monomer are each individually selected from the group consisting of acrylic acid, methacrylic acid, vinyl sulfonic acid, vinyl phosphonic acid, partially hydrolyzed maleic anhydride, and combinations thereof.

[0070] Disclosed herein is a method of making a superabsorbent polymer comprising a polymer backbone comprising (i) a strong or superstrong ionizable backbone monomer comprising an anion of a strong organic acid and a superionizable counterion, (ii) a neutralized backbone monomer, and (iii) optionally an unneutralized backbone monomer, and optionally a crosslinking agent. The method comprises (i) forming a complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2; (ii) forming a mixture comprising a solvent, the monomer, the complex between the salt comprising a metal ion in an oxidation state of at least 2, and optionally a crosslinking agent; (iii) initiating a reaction; and (iv) allowing the mixture to react.

[0071] The method step of initiating a reaction can employ standard materials and procedures known in the art, including adding an initiator, a promoter, or a combination thereof to the mixture. In some particular embodiments, the initiator is an oxidizing agent.

[0072] The initiator can be an organic compound. In some embodiments, the initiator is selected from the group consisting of an azo compound, an organic peroxide compound, an organic persulfate compound, and combinations thereof.

[0073] The initiator can be an inorganic compound. In some embodiments, the initiator is selected from the group consisting of an inorganic peroxide compound. In some particular embodiments, the initiator is selected from the group consisting of potassium persulfate, ammonium persulfate, and combinations thereof.

[0074] Some reactions can proceed at a suitable rate in the absence of a promoter. When a promoter is used, the promoter is an organic compound. In some embodiments, the promoter is selected from the group consisting of an organic compound, an organic base, tetramethyl ethylene diamine (TEMED), sodium pyrosulfite (SPS), no promoter, and combinations thereof.

[0075] An inert atmosphere improves the reaction by limiting air oxidation. The inert atmosphere can be static or dynamic. When the inert atmosphere is dynamic, inert gas is constantly flowing through the reactants. The inert atmosphere includes chemically inert gases. In some embodiments, the inert atmosphere is selected from the group consisting of N2, CO2, a noble gas, helium, neon, argon, krypton, xenon, and combinations thereof. In some particular embodiments, the method step of reacting the mixture includes reacting the mixture in an inert atmosphere of N2.

[0076] In various embodiments, the method step of reacting the mixture includes heating the mixture. The mixture can be heated to any temperature that promotes the reaction. In some embodiments, the method step of reacting the mixture includes heating the mixture to a temperature in the range of about 20 °C to about 100 °C. In some particular embodiments, the method step of reacting the mixture includes heating the mixture to a temperature in the range of about 40 °C to about 70 °C.

[0077] In some embodiments, the method further includes drying the reaction product. The reaction product can be dried in an oven or with other known means of drying. The drying temperature and time can vary depending on the relative moisture content and nature of the reaction product. In some embodiments, the method further includes drying the reaction product at a temperature in the range of about 50 °C to about 100 °C. In some particular embodiments, the method further includes drying the reaction product at a temperature in the range of about 70 °C to about 90 °C.

[0078] In some embodiments, the method further includes grinding the reaction product. The reaction product is ground to a desired particle size. Suitable methods are known in the art. In some embodiments, the method further includes grinding the reaction product with a grinding device selected from the group consisting of a mechanical stirrer, a coffee grinder, a crusher, a pulverizer, a mill, a grinder, and combinations thereof.

[0079] In another aspect of the application, the particles as described herein can be further treated according to well-known procedures, such as surface crosslinking of the particles. Appropriately selected surface crosslinking agents can enhance the mechanical strength of the particles and help control the rate of ingestion, improve gel permeability, and fluid distribution between particles and within a given particle.

[0080] With respect to the properties of the final superabsorbent polymer, the ability of the polymer to absorb fluid under static load can be measured as absorbency under load (AUL). A typical AUL test format can be used. The ability of the pre-swollen polymer to retain water under force can be measured as centrifuge retention capacity (CRC). A typical CRC test format can be used.

[0081] The consumer product or superabsorbent material can comprise a superabsorbent polymer according to the present disclosure. The superabsorbent polymer can also be used in the consumer product or superabsorbent material.

[0082] Suitable consumer products include, but are not limited to, personal hygiene products, wipes, napkins, bibs, disposable bed pads, wound dressings, food packaging, baby and adult diaper products, child training pants, feminine pads and napkins, arm bands, agricultural and pet products containing superabsorbent components, disposable absorbent products, and combinations thereof.

[0083] SAM co-polymerized with selected inorganic salt via staged polymerization.

[0084] The following description relates to staged copolymerization processes to make SAMs copolymerized with selected inorganic salts. These processes and the resulting polymers are described in detail in a co-pending PCT application entitled "STAGED POLYMERIZATION OF COPOLYMERIZED SUPERABSORBENT POLYMERS," which is filed concurrently with this application and incorporated herein by reference.

[0085] In contrast to the above non-staged one-pot synthesis procedure and the resulting polymers, SAMs can be copolymerized with selected redox-active inorganic salts in a staged polymerization process. Figure 2 A staged polymerization process is described in the Example. This exemplary staged polymerization process has two stages. Typically, in this two-step process, a prepolymerization mixture containing a redox-active monomeric metal complex is prepared at a lower temperature (e.g., 0 °C and / or from an ice bath) or at room temperature. A crosslinker can or can not be added to the prepolymerization mixture. Then a first stage redox-induced polymerization is initiated. This produces a water-soluble oligomer. In the absence of a crosslinker added to the prepolymerization mixture, there will be no crosslinking or reduced crosslinking. A crosslinker can or can not be added to the water-soluble oligomer. Next, a second stage thermal free radical polymerization is initiated by raising the temperature to 60-70 °C and holding at that temperature to complete the polymerization. This produces a polymer containing a core-shell microstructure, where the first stage oligomer comprises 1-30% of the final polymer dry weight, and the second stage polymer comprises 60-99% of the final polymer dry weight. After the second stage polymerization, the polymer is insoluble in water.

[0086] The staged polymerization process provides a first function of incorporating a small amount of a selected inorganic salt (SIS) into a PAA-based superabsorbent material (SAM) for enhancing the absorbent capacity. In addition, the staged polymerization process according to the present disclosure provides a second function of controlling the polymerization process such that the gel properties of the SAM polymer can be further improved beyond the first capacity-enhancing function of the SIS. In this second function, the SIS will be part of the polymerization initiation step and must be redox-active. In other words, when the SIS reacts with a suitable free radical polymerization initiator (e.g., KPS) to start the polymerization process, they must be able to go from a lower oxidation state (e.g., M n+) to a higher oxidation state (e.g., M n+1 ) by initiating the polymerization process. Oxidized metal ion forms (e.g., M n+1 ) 将 By complexation incorporation into the polymer chain to provide a source of ionization enhancement. Non-redox active salts can still be added to enhance ionization, but they will not initiate polymerization.

[0087] Control of polymerization means that the second function of the redox active SIS will allow the polymerization process to proceed in pre-designed stages (such as Stage 1, Stage 2, Stage 3, etc.). Stage 1 is the polymerization initiation step, and its polymerization parameters can be the same or different compared to the other stages. Polymerization parameters here include, but are not limited to, temperature, time, oxygen level, crosslinker, initiator, monomer(s), concentration (e.g., loading level) of each monomer, initiator, crosslinker, and any specially designed reaction-related sequence (e.g., monomer or initiator or crosslinker addition sequence, etc.). For example, Stage 1 can or can not require a crosslinker, such that the polymer network formed in this step can be primarily long-chain polymers without crosslinking based on chemical bonds. In another example, Stage 1 and Stage 2 can both have a crosslinker, but two different temperatures and different polymerization times will be required to complete their respective polymerization processes.

[0088] The polymer networks formed from the different stages according to the present invention are not independent. Rather, the polymer networks formed in the different stages are interconnected through chemical crosslinking, physical chain-chain entanglement, or chain charge-charge interactions, etc. In some cases, such interconnections can result in a hierarchical network structure, while in other cases, the overall structure can be more like an interpenetrating network, as certain portions of the networks from different stages are effectively entangled together through chemical crosslinking, charge-charge interactions, and physical entanglements.

[0089] In a general embodiment using acrylic-based monomers as an example, a complex between the monomer and a selected inorganic salt (SIS), such as a salt containing a redox active metal ion in an oxidation state of at least 2, can be added to a mixture for polymerization. The complex can be added at any stage of the staged polymerization process.

[0090] A general structure for the SAM material of the present disclosure can be described as a staged overall network, where each stage has its own subnetwork:

[0091] [Network] 第1阶段 [Network] 第2阶段 …[Network] 第x阶段 [Network] 第x1阶段 …

[0092] Generally, the number of stages can be any suitable number known in the art. The number of stages can be one, two, three, four, five, or more than five. Preferably, the total number of stages should be controlled to be below five, and most preferably below three.

[0093] The networks of the different stages can be in any desired proportion, and can be controlled by varying the aggregation parameters as described above. In some embodiments, one stage will dominate. In some embodiments, the stages are evenly divided. In some embodiments, the transition from one stage to the next is considered a separate stage, as the transition can be time dependent or temperature dependent, etc. For example, it takes time for the polymerization mixture to transition from one temperature to another, as raising the temperature can take time (e.g. a continuous or pre-prepared temperature bath).

[0094] Due to the complexity of precisely defining the exact network structure of each polymerization stage, the present disclosure employs a simplified approach by using the total loading level of each monomer and the SIS-complexed form of each monomer to define the composition of the final polymer. For example, if the staged polymerization involves two monomers and one redox SIS salt, the composition of the final polymer can be described as [(monomer 1) x (monmer 1-SIS) y (monmer 2) z (monmer 2-SIS) w ], where x, y, z, w are the molar or weight ratios of each component. In terms of weight ratios, the combined Y and W ratios are generally limited to less than 1% of (x+y+z+w). In one specific example, for two monomers of acrylic acid and sodium salt of acrylic acid, the composition of the staged copolymer can be described as [(AA) x (AA-SIS) y (AANa) z (AANa-SIS) w ], where x, y, z, w are the molar or weight ratios of each monomer and its SIS-complexed form.

[0095] In many embodiments, the superabsorbent polymer according to the present disclosure comprises a polymer backbone comprising (i) neutralized backbone monomers, (ii) neutralized backbone monomers complexed with a coordination complex comprising a metal ion having an oxidation state of at least 2, (iii) optional unneutralized backbone monomers, and (iv) optional unneutralized backbone monomers, and optionally a crosslinking agent, wherein the superabsorbent polymer comprises a non-uniform microstructure.

[0096] In some embodiments, the superabsorbent polymer comprises a plurality of polymer portions, wherein each polymer portion is produced at a different polymerization stage. In some embodiments, the superabsorbent polymer comprises a first polymer portion and a second polymer portion, wherein the first polymer portion and the second polymer portion are produced at different polymerization stages.

[0097] In some embodiments, the superabsorbent polymer comprises a first polymer portion present in an amount ranging from about 1 to about 30 wt% of the superabsorbent polymer and a second polymer portion present in an amount ranging from about 60 to about 99 wt% of the superabsorbent polymer.

[0098] Generally, the superabsorbent polymer can comprise any suitable non-uniform microstructure known in the art. The non-uniform microstructure results in a non-uniform polymer structure. In some embodiments, the superabsorbent polymer comprises a non-uniform microstructure selected from the group consisting of a layered polymer structure having domains from different stages, a core-shell polymer structure comprising a core from one stage and a shell from another stage, an interpenetrating network comprising one stage as one network and another stage as another network, and combinations thereof.

[0099] Figure 3A a two-dimensional view in Figure 3B a three-dimensional view in

[0100] Generally, the superabsorbent polymer can have any suitable crosslinking density known in the art. In some embodiments, the superabsorbent polymer has a non-uniform crosslinking density. In some embodiments, the superabsorbent polymer comprises a first polymer portion having a first crosslinking density and a second polymer portion having a second crosslinking density, wherein the first crosslinking density and the second crosslinking density are different. In some embodiments, the superabsorbent polymer comprises a first polymer portion containing no crosslinks or containing minimal crosslinks and a second polymer portion comprising a high degree of crosslinks.

[0101] Also disclosed herein is a method of making a superabsorbent polymer, the method comprising: (i) a complexation stage comprising forming a complex between a first monomer and a salt comprising a redox-active metal ion in an oxidation state of at least 2; (ii) an initial polymerization stage comprising (iia) forming a mixture comprising a solvent, a second monomer, the first monomer, and the complex between the salt comprising a redox-active metal ion in an oxidation state of at least 2, an optional crosslinking agent, and an initiator, and (iib) reacting the mixture at a first temperature; and (iii) a final polymerization stage comprising (iiia) optionally adding a crosslinking agent to the mixture; (iiib) optionally adding the complex between the first monomer and the salt comprising a redox-active metal ion in an oxidation state of at least 2 to the mixture; (iiic) heating the mixture from the first temperature to a second temperature; and (iiid) reacting the mixture at the second temperature.

[0102] The salt comprising a redox-active metal ion is part of the metal monomer complex and is included in the polymerization initiation step. When reacted with a suitable free radical polymerization initiator (e.g., KPS) to start the polymerization process, the redox-active metal must be able to oxidize from a lower oxidation state (e.g., M n+ ) to a higher oxidation state (e.g., M n+1 ). By initiating the polymerization process, the oxidized metal ion form (e.g., M n+1 ) 将 is incorporated into the polymer chain through complexation to provide a source of ionization enhancement. Non-redox active salts can still be added to enhance ionization, but they will not initiate polymerization.

[0103] In some embodiments, the salt comprising a redox-active metal ion comprises a metal ion selected from the group consisting of Co 2+ , Mn 2+ , Al 2+ , Fe 2+ , Co 2+ , Mn 3+ , Ru 2+ , and combinations thereof. Generally, the salt can comprise any suitable salt anion known in the art. In some embodiments, the salt comprises an anion selected from the group consisting of Cl - , SO4 2- , NO3 - , BF4 - , and combinations thereof.

[0104] A particularly preferred redox-active metal salt is FeCl2. FeCl2is particularly effective and inexpensive. During polymerization, Fe 2+ is oxidized to Fe 3+ .

[0105] In some embodiments, the redox-active metal ion is oxidized to an oxidized metal ion selected from the group consisting of Co 3+ , Al 3+ , Fe 3+ , Co 3+ , Mn 3+ , and combinations thereof.

[0106] In some embodiments, the mixture further comprises a stabilizing salt comprising a metal ion having an oxidation state of at least 2.

[0107] In some embodiments, the method further comprises at least one intermediate polymerization stage between the initial polymerization stage and the final polymerization stage. The at least one intermediate polymerization stage can comprise any suitable conditions to initiate polymerization. In some embodiments, the at least one intermediate polymerization stage comprises adding a crosslinking agent to the mixture. In some embodiments, the at least one intermediate polymerization stage comprises a time-dependent transition or a temperature-dependent transition. As used herein, a time-dependent transition refers to a time period to induce a different polymerization stage, such as a time delay. As used herein, a temperature-dependent transition refers to a temperature to induce a different polymerization stage.

[0108] In some embodiments, the at least one intermediate polymerization stage comprises adding a complex between a first monomer and a salt comprising a redox-active metal ion having an oxidation state of at least 2 to the mixture.

[0109] Generally, the method can comprise any suitable number of polymerization stages known in the art. In some embodiments, the method comprises one, two, three, four, five, or more than five polymerization stages. In some embodiments, the method comprises a plurality of polymerization stages in the range of 2 to 5.

[0110] Generally, the first temperature can be any temperature that facilitates the reaction. In some embodiments, the first temperature is in the range of about -20 °C to about 40 °C. In some preferred embodiments, the first temperature is 0 °C. In some preferred embodiments, the first temperature is in the range of about 20 °C to about 25 °C.

[0111] Generally, the second temperature can be any temperature that facilitates the reaction. In some embodiments, the second temperature is in the range of about 20 °C to about 100 °C. In some embodiments, the second temperature is in the range of about 40 °C to about 70 °C. In some preferred embodiments, the second temperature is in the range of about 60 °C to about 70 °C.

[0112] The method step of initiating the reaction can implement standard materials and procedures known in the art, including adding an initiator, a promoter, or a combination thereof to the mixture. In some particular embodiments, the initiator is an oxidizing agent.

[0113] The initiator can be an organic compound. In some embodiments, the initiator is selected from the group consisting of azo compounds, organic peroxide compounds, organic persulfate compounds, and combinations thereof.

[0114] The initiator can be an inorganic compound. In some embodiments, the initiator is selected from the group consisting of inorganic peroxide compounds. In some particular embodiments, the initiator is selected from the group consisting of potassium persulfate, ammonium persulfate, and combinations thereof.

[0115] Some reactions can proceed at a suitable rate in the absence of a promoter. When a promoter is used, the promoter is an organic compound. In some embodiments, the promoter is selected from the group consisting of organic compounds, organic bases, tetramethyl ethylene diamine (TEMED), sodium pyrosulfite (SPS), no promoter, and combinations thereof.

[0116] An inert atmosphere improves the reaction by limiting air oxidation. The inert atmosphere can be static or dynamic. When the inert atmosphere is dynamic, the inert gas is constantly flowing through the reactants. The inert atmosphere includes chemically inert gases. In some embodiments, the inert atmosphere is selected from the group consisting of N2, CO2, noble gases, helium, neon, argon, krypton, xenon, and combinations thereof. In some particular embodiments, the method step of reacting the mixture includes reacting the mixture in an inert atmosphere of N2.

[0117] In some embodiments, the method further includes drying the reaction product. The reaction product can be dried in an oven or with other known means of drying. The drying temperature and time can vary depending on the relative moisture content and nature of the reaction product. In some embodiments, the method further includes drying the reaction product at a temperature ranging from about 50 °C to about 100 °C. In some particular embodiments, the method further includes drying the reaction product at a temperature ranging from about 70 °C to about 90 °C.

[0118] In some embodiments, the method further includes grinding the reaction product. The reaction product is ground to reduce the reaction product to a desired particle size. Suitable methods are known in the art. In some embodiments, the method further includes grinding the reaction product with a grinding device selected from the group consisting of a mechanical stirrer, a coffee grinder, a crusher, a pulverizer, a mill, a grinder, and combinations thereof.

[0119] In another aspect of the disclosure, the particles as described in the disclosure can be further treated according to well-known procedures, such as surface crosslinking of the particles. A properly selected surface crosslinking agent can enhance the mechanical strength of the particles and help control the rate of intake, improve gel permeability, and fluid distribution between particles and between the interior of a given particle.

[0120] With respect to the properties of the final superabsorbent polymer, the ability of the polymer to absorb fluid under static load can be measured as absorbency under load (AUL). A typical AUL test format can be used. The ability of the pre-swollen polymer to retain water under force can be measured as centrifuge retention capacity (CRC). A typical CRC test format can be used.

[0121] The consumer product or superabsorbent material can comprise the superabsorbent polymer according to the disclosure. The superabsorbent polymer can also be used in the consumer product or superabsorbent material.

[0122] Suitable consumer products include, but are not limited to, personal hygiene products, wipes, napkins, bibs, disposable bed pads, wound dressings, food packaging, baby and adult diaper products, child training pants, feminine pads and napkins, arm bands, agricultural and pet products containing superabsorbent ingredients, disposable absorbent products, and combinations thereof.

[0123] Examples

[0124] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present application to its fullest extent. The following examples are, therefore, to be construed as merely illustrative, and not limitative of the disclosure in any way whatsoever.

[0125] Measurement techniques.

[0126] The polymers according to the disclosure and examples were measured to determine their absorbency under load (AUL) and centrifuge retention capacity (CRC) properties.

[0127] Technique 1. AUL measurement of SAM particles.

[0128] AUL measures the ability of a polymer to absorb fluid under static load and can be considered a measure of gel swelling in conjunction with gel strength. Using a typical AUL test format, which consists of a simple cylindrical device with a large hole fritted filter plate on one end of a sintered plastic cylinder. For the sample being tested, 160 mg (W1) of dry SAP sample is weighed and placed evenly on the surface of a polyester gauze, which is placed on top of the sintered plastic. A desired load (e.g., a weight that can generate a 0.3-0.9 PSI pressure) is then placed on top of the dry SAP particles, where the load is designed so that it can move freely in the plastic cylinder. The device is placed in a petri dish of 0.9% saline solution on top of a screen (to ensure water can access the bottom of the sintered plastic) for 1-72 hours or any desired measurement time. The swollen sample is weighed (W2), and the AUL is calculated using Equation 1:

[0129]

[0130] Technique 2. CRC measurement of SAM particles.

[0131] In contrast to the AUL test, where dry powder of SAP is hydrated under load, the CRC test measures the ability of a pre-swollen SAP to retain water under force. To conduct the test, about 100 to 200 mg (W1) of dry SAP sample is weighed into a pre-weighed tea bag. The tea bag is immersed in a 0.9 wt% saline solution for 1-2 hours or any desired length of test time to swell the SAP. Subsequently, the tea bag is placed inside a cylindrical centrifuge tube with a porous interior to allow for drainage and centrifuged at 1600 rpm for 3 minutes. As a control, an empty tea bag is also placed in the saline and centrifuged at the same speed. After centrifugation, the tea bag is weighed again (W2), and the difference between the dry sample and the swollen sample is calculated. The CRC amount is calculated by Equation 2:

[0132]

[0133] SAM co-polymerized with selected stable inorganic salt.

[0134] The following examples are used to illustrate the single-step, non-staged copolymerization process for making SAMs copolymerized with selected inorganic salts. These processes and resulting polymers are known in the art, for example, in PCT / US2020 / 053003, which is incorporated herein by reference.

[0135] Selected inorganic salts (e.g., various inorganic salts, including metal ions with an oxidation state of at least 2) are copolymerized with sodium acrylate salt (e.g., the primary component of the base monomer currently used for commercial SAMs). Samples synthesized without these salts under the same polymerization conditions are used as controls.

[0136] Comparative Example 1. Preparation of PAA-based SAM particles without using a coordination complex comprising a metal ion having an oxidation state of at least 2.

[0137] Add 15 grams of acrylic acid (AA) monomer to a glass reaction flask (e.g., 120 mL wide mouth jar, beaker, or round bottom flask) with a magnetic stir bar. The glass reaction flask should be equipped with a sealed lid or glass or rubber stopper. Add about 45 mL of deionized (DI) water to the glass reaction flask with the AA monomer and then cool to about 0 °C with an ice water bath. After cooling, add 5.84 g of NaOH pellets with a purity greater than 97% to the cold solution. Then stir the mixture with a magnetic stirrer until the NaOH pellets are completely dissolved. Dissolution under stirring typically takes about 10-20 minutes. Alternatively, the neutralization can be performed by adding a pre-prepared aqueous NaOH solution dropwise to the AA / water mixture, with the same final total water volume.

[0138] Strictly degas the mixture with high purity nitrogen or argon to remove residual air in the reaction mixture and to displace the air in the glass reaction flask. A degassing time of at least 5-10 minutes is recommended. About 5 minutes after entering the degassing step, add the initiator (about 45 mg of 99.99% potassium persulfate (KPS)) and the crosslinker (about 68 mg of greater than 99% MBAA (N,N-methylenebis(acrylamide))) both of which are pre-dissolved in 4 mL of deionized water at room temperature to the cooled, neutralized AA solution dissolved in deionized water. Then continue the degassing process.

[0139] Then seal the glass reaction flask and transfer it to a pre-heated water bath equipped with a magnetic stirrer to start the one-step thermal free radical polymerization process. The polymerization temperature is controlled in the range of about 60 °C to about 70 °C, more specifically about 65 °C. Place the flask directly into a pre-heated bath, or into a temperature bath that starts at room temperature and gradually increases to about 65 °C or any desired final polymerization temperature.

[0140] Monitor the gel time (e.g., by determining when the magnetic stir bar stops stirring). Gelation of the control sample (e.g., the solution becomes viscous and then the stir bar stops stirring) is observed only when the temperature reaches above 50 °C - 65 °C for at least 5-20 minutes. After gelation, the gel is left in the heated bath for an additional 4 hours to ensure completion of the polymerization.

[0141] After polymerization, the gel is removed from the glass reaction flask. A small knife or scissors is used to cut the large gel pieces into small pieces for drying. A blender can be used to break the large gel pieces into small pieces. After cutting, the resulting gel pieces are dried in an oven at 85 °C for at least 24-48 hours. Drying can also be accomplished by accelerated drying procedures, using an air dryer, using the desired oven temperature, using a stream of hot air, and combinations thereof. The drying process can also be conducted by a dynamic belt system in combination with heating, vacuum, and through air drying techniques.

[0142] The dried gel pieces are then placed into a coffee blender or any suitable tool to break into the desired particle size. A U.S. standard sieve is used to collect the particles having the desired size range (e.g., 300-600 microns).

[0143] Comparative Example 2. Preparation of PAA-based SAM particles using a coordination complex comprising a metal ion having an oxidation state of at least 2.

[0144] The reaction procedure of Comparative Example 1 is followed, except that after the degassing step, the desired amount of one or more monomer complexes is added to the mixture along with the selected metal salt, and degassing is continued for an additional 5-10 minutes.

[0145] SAM co-polymerized with metal complexing monomer.

[0146] The following examples are used to demonstrate the feasibility of using metal complex monomers for polymerization to prepare SAMs co-polymerized with selected inorganic salts.

[0147] Example 1. Polymerization using metal complex monomers.

[0148] FeCl3-(AANa) is prepared by first adding an aqueous solution of FeCl3salt to an aqueous solution of acrylic acid (AA) that is completely neutralized with sodium hydroxide, and then isolating the solid precipitate by pouring the reaction mixture into cold methanol or diethyl ether. x Monomer complex. The collected solid is further washed with diethyl ether and then dried under vacuum at 60 °C overnight. The dried monomer complex powder is readily soluble in water and is used directly for the next step of co-polymerization.

[0149] Co-polymerization is achieved by adding the desired amount of FeCl3-(AANa) x Monomer complex to a pre-prepared solution of AANa and AA (70% : 30%) along with the desired amount of KPS initiator and crosslinker MBAA. Polymerization is completed under thermal free radical polymerization conditions (e.g., 65 °C for 4 hours), and then dried at 85 °C for 24-48 hours. The dried gel solid is processed into the desired particle size (e.g., 300-600 microns) for absorbency testing (e.g., CRC).

[0150] It was discovered that the use of metal complex monomers allowed for the determination of the location of the selected salt on the monomer. For example, if the Fe(III) salt was first reacted with the sodium acrylate (AANa) monomer, the complex formed and isolated would be the AANa-Fe (III) monomer complex. Likewise, if the Fe(III) salt was reacted with the acrylic acid (AA) monomer, the complex formed and isolated would be the acrylic acid AA-Fe(III) monomer complex. It was discovered that FeCl3-(AANa) x At about 0.05 % to 0.30 % weight loading levels of the monomer complex, a CRC increase of about 20-35% was found compared to control samples that did not contain such complexes. These results indicate that the use of metal complex monomers allows for more precise design and control of the SAM microstructure at the monomer level.

[0151] Table 1 compares the capacity data of polymers produced from metal complex monomers to the capacity data of polymers produced by conventional one-step polymerization. The “-” values indicate that no measurements were made. The polymers produced from metal complex monomers are superior to the polymers produced by conventional one-step polymerization.

[0152]

[0153] Example 2. Characterization of polymers polymerized with metal complex monomers.

[0154] Direct measurement of solid SAM samples by FTIR is not feasible due to the very broad absorption around the carboxylate region as well as interference from moisture (OH-bending overlaps with COO- stretching).

[0155] However, Fourier Transform Infrared Spectroscopy (FTIR) was used to characterize the polymers of Example 1 by first swelling the samples in D2O and then recording the spectra. D2O can effectively eliminate the moisture interference associated with regular moisture.

[0156] FTIR data for polymers produced by one-step polymerization are shown in Figure 4A , Figure 5A and Figure 6A and FTIR data for polymers produced by one-step metal complex monomer polymerization methods are shown in Figure 4B , Figure 5B and Figure 6B . As can be seen, by comparing the peaks directly related to COO- metal ion complexation, it is easy to observe and quantify the differences between samples from the salt and monomer complex methods. The use of monomer complexes effectively fixes the selected metal ion to the desired monomer (e.g. AANa) so that a higher ratio of the infrared peak of interest can be expected.

[0157] This written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any compositions or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements in common with the base language of the claims other than insubstantial differences or if they do not differ from the base language of the claims in meaning.

[0158] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," "characterized by" or any other variation thereof, are intended to cover a non-exclusive inclusion, subject to any limitation explicitly indicated. For example, a composition, mixture, process or method that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process or method.

[0159] The transitional phrase "consisting of" excludes any element, step, or ingredient not specified. If used in the claims, this phrase does not invoke the proviso, as the claim is then construed to cover only those components of the specific integer identified by the claim's recitation. The transitional phrase "consisting of" is used to define a composition or method that is limited to the recited elements, without including any additional unspecified elements.

[0160] The transitional phrase "consisting essentially of" is used to define a composition or method that includes the specified materials, steps, features, components or elements, plus any non- specified materials, steps, features, components or elements that do not materially affect the basic and novel characteristics of the claimed invention. The term "consisting essentially of" occupies a middle ground between "comprising" and "consisting of."

[0161] When the invention or a portion thereof is defined by open-ended terms such as "comprising," it should be readily understood (unless otherwise indicated) that the description is to be interpreted also to describe the invention using the terms "consisting essentially of" or "consisting of."

[0162] Furthermore, "or" is intended to mean inclusive or unless explicitly indicated otherwise. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0163] Also, the indefinite articles "a" and "an" preceding an element or component of the application are intended to be non-limiting regarding the number of elements or components. The indefinite articles "a" or "an" thus, should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number clearly indicates a singularity.

[0164] As used herein, the term "about" means plus or minus 10% of the value.

Claims

1. A method of making a superabsorbent polymer, the superabsorbent polymer comprising: a polymer backbone, the polymer backbone comprising: neutralized backbone monomers; neutralized backbone monomers complexed with a coordination complex comprising a metal ion in an oxidation state of at least 2; Optionally unneutralized backbone monomers; and optionally unneutralized backbone monomers complexed with a coordination complex comprising a metal ion in an oxidation state of at least 2; and optionally a crosslinking agent, the method comprising: forming a complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2; forming a mixture, the mixture comprising a solvent; the complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2; and optionally a crosslinking agent; initiating a reaction; and reacting the mixture; wherein the method step of reacting the mixture is an initial polymerization stage comprising reacting the mixture at a first temperature, and wherein the method further comprises a final polymerization stage comprising optionally adding a crosslinking agent to the mixture; optionally adding the complex between a first monomer and a salt comprising a redox active metal ion in an oxidation state of at least 2 to the mixture; heating the mixture from the first temperature to a second temperature; and reacting the mixture at the second temperature.

2. The method of claim 1, wherein the method step of forming a complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2 comprises forming a mixture comprising the monomer and the salt comprising a metal ion in an oxidation state of at least 2; isolating a solid precipitate produced in the mixture by complexation; optionally washing the solid precipitate; and optionally drying the solid precipitate.

3. The method of claim 1, wherein the complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2 comprises neutralized monomers.

4. The method of claim 1, wherein the monomer is an unneutralized monomer.

5. The method of claim 1, wherein the monomer is a neutralized monomer.

6. The method of claim 1, wherein the complex between a monomer and a salt comprising a metal ion in an oxidation state of at least 2 is provided to the mixture in an amount sufficient to provide a loading ratio of 0.005 to 1.00 weight percent relative to the weight of the superabsorbent polymer.

7. The method of claim 1, wherein the mixture further comprises a stabilizing salt, the stabilizing salt comprising a metal ion in an oxidation state of at least 2.

8. The method of claim 1, further comprising at least one intermediate polymerization stage between the initial polymerization stage and the final polymerization stage.

9. The method of claim 1, wherein the method comprises a plurality of polymerization stages in the range of 2 to 5.

10. The method of claim 1, wherein the method further comprises drying the reaction product.

11. The method of claim 1, wherein the method further comprises milling the reaction product.

12. A superabsorbent polymer produced according to the method of claim 1.

13. A method of using the superabsorbent polymer of claim 12, the method comprising using the superabsorbent polymer in a consumer product.

14. The method of claim 13, wherein the superabsorbent polymer is in the form of particles having a diameter in the range of 100 pm to 1000 pm.

15. The method of claim 13, wherein the consumer product is selected from the group consisting of personal hygiene products, wipes, bibs, disposable bed pads, wound dressings, food packaging, arm bands, agricultural and pet products containing superabsorbent ingredients, disposable absorbent products, and combinations thereof.

16. The method of claim 15, wherein the personal hygiene product is a napkin, baby and adult diaper products, child training pants, and combinations thereof.

17. The method of claim 15, wherein the disposable absorbent product is a feminine pad.

18. The method of claim 16, wherein the napkin is a feminine napkin.

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