A method for preparing a vinylamine-containing polymer solution and a vinylamine-containing polymer solution prepared through said method

Abstract

A method for preparing a vinylamine-containing polymer solution and a vinylamine-containing polymer solution prepared by said method are provided herein. In one embodiment, a method for preparing a vinylamine-containing polymer solution comprises polymerizing an N-vinylcarboxamide monomer and hydrolyzing the resulting intermediate polymer formulation. The method involves determining the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation, changing one or more process parameters of the polymerization step accordingly, and repeating the polymerization step with the changed process parameter(s). A method for evaluating the amount of unreacted monomer includes directly measuring the amount of unreacted monomer in the intermediate, observing the color of the product, measuring the wavelength of the product, or measuring the dynamic viscosity of the product.

Description

Technology Field

[0001] The present disclosure generally relates to the manufacture of polymers, and more specifically to the polymerization of N-vinylcarboxamide monomers. Background Technology

[0002] Vinylamine-containing polymers are synthetic polymers that contain vinylamine units in their chemical structure. Vinylamine-containing polymers are inherently cationic. They are also highly water-soluble, making them suitable for use in aqueous solutions. Vinylamine-containing polymers are generally stable under a wide range of pH conditions, temperatures, and oxygen exposure. They can form films and coatings when applied to surfaces. Due to these properties, vinylamine-containing polymers are useful in various applications, including papermaking, water treatment, and adhesives and coatings.

[0003] One example of a vinylamine-containing polymer is polyvinylamine (PVAm). PVAm is a polymer with a high content of primary amine functional groups. Consequently, PVAm can form hydrogen and / or covalent bonds with functional surfaces or molecules, readily generating derivatives. PVAm adsorbs onto most surfaces in water to create cationic interfaces, which can form complexes with oppositely charged polymers or molecules, such as negatively charged surfactants. PVAm is highly hydrophilic. Because PVAm derivatives promote adhesion between wet and dry surfaces, PVAm is used as a papermaking additive.

[0004] A general synthesis method for vinylamine-containing polymers is known in the relevant industry. In one method, first, an N-vinylcarboxamide monomer is combined with a polymerization initiator to produce an intermediate polymer formulation containing a poly(N-vinylcarboxamide) prepolymer.

[0005] After the polymerization step is completed, an acid or base is added to the resulting intermediate polymer formulation to hydrolyze the poly(N-vinylcarboxamide) prepolymer and produce a vinylamine-containing polymer solution containing a vinylamine-containing polymer. The hydrolysis step converts the carboxamide functional groups of the poly(N-vinylcarboxamide) prepolymer into vinylamine functional groups. Depending on various factors, the resulting vinylamine-containing polymer solution may contain an unacceptably large amount of impurities, which can lead to unacceptably high dynamic viscosity or gel formation. Gelation produces a low-quality product, and such low-quality vinylamine-containing polymer solutions may be difficult to handle and use.

[0006] One example of an N-vinylcarboxamide monomer is a vinylformamide (VFA) monomer. If the VFA monomer is used in the polymerization step described above, the intermediate polymer formulation will contain a polyvinylformamide (poly-VFA) prepolymer. Subsequently, after the hydrolysis step is completed, the resulting vinylamine-containing polymer solution will contain a PVAm polymer. The PVAm polymer solution suffers from the same problems described above that other vinylamine-containing polymer solutions face.

[0007] To avoid some of the aforementioned problems, known methods for preparing vinylamine-containing polymer solutions are carried out under vacuum conditions or under an inert atmosphere. However, although vacuum conditions and an inert atmosphere are known to reduce the impurity content in vinylamine-containing polymer solutions, it is still difficult to assess whether the resulting vinylamine-containing polymer solution has an unacceptably high impurity content that can lead to poor performance (i.e., unacceptably high dynamic viscosity and / or gelation).

[0008] Accordingly, it is desirable to provide a method for preparing a vinylamine-containing polymer solution that enables quality evaluation of the vinylamine-containing polymer solution. More specifically, it is desirable to provide a method that enables the identification of unacceptably high impurity content leading to poor dynamic viscosity and / or gelation. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the following detailed description and the appended claims, together with the accompanying drawings and the background art.

[0009] This overview is provided to briefly introduce selected concepts among those further described in the detailed description below. This overview is not intended to identify the core or essential features of the claimed subject matter, nor is it intended to be used as a means to determine the category of the claimed subject matter.

[0010] A method for preparing a vinylamine-containing polymer solution and a vinylamine-containing polymer solution prepared by said method are provided herein. In one embodiment, a method for preparing a vinylamine-containing polymer solution comprises polymerizing an N-vinylcarboxamide monomer and hydrolyzing the resulting intermediate polymer formulation. The method involves determining the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation, changing one or more process parameters of the polymerization step accordingly, and repeating the polymerization step with the changed process parameter(s).

[0011] The method comprises the polymerization of a reaction mixture comprising a polymerization initiator and one or more N-vinylcarboxamide monomers of Formula I:

[0012] Here, R 1 and R 2is independently an H or C1 to C6 alkyl group. Optionally, one or more vinyl monomers having a chemical formula different from that of chemical formula I may also be added to the reaction mixture. The polymerization step produces an intermediate polymer formulation containing a poly(N-vinylcarboxamide) prepolymer. The carboxamide groups of the poly(N-vinylcarboxamide) prepolymer are hydrolyzed during the hydrolysis step to produce a vinylamine-containing polymer solution containing a vinylamine-containing polymer.

[0013] According to the method conceived herein, it is determined that the intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer. After this determination is made, one or more process parameters of the polymerization step are changed, and the polymerization step is repeated with the changed process parameters to form the modified intermediate polymer formulation. Specific details for implementing the invention

[0014] The following detailed description is for illustrative purposes only and is not intended to limit the content of this disclosure or its applications and uses. Furthermore, it is not intended to constrain the background art or any theories presented in the following detailed description.

[0015] The method as provided herein enables the preparation of a vinylamine-containing polymer solution containing a minimum amount of unreacted N-vinylcarboxamide monomer, resulting in an acceptablely low dynamic viscosity and resistance to gelation and mixing problems. More specifically, the degree of polymerization of the N-vinylcarboxamide monomer is an important factor in the preparation of a vinylamine-containing polymer solution through conventional unit operations (e.g., reaction of the N-vinylcarboxamide monomer with a polymerization initiator in a reaction mixture to form an intermediate polymer formulation containing a poly(N-vinylcarboxamide) prepolymer, followed by intentional hydrolysis of the carboxyl groups of the poly(N-vinylcarboxamide) prepolymer to form a vinylamine-containing polymer solution).

[0016] After the polymerization step, some residual N-vinylcarboxamide monomer may remain in the intermediate polymer formulation. Additionally, some N-vinylcarboxamide may unintentionally hydrolyze before or during the polymerization step to form byproducts, such as acetaldehyde and its reaction products. These byproducts are polymerization inhibitors that can further inhibit the polymerization of the remaining N-vinylcarboxamide monomer. Any residual N-vinylcarboxamide, acetaldehyde, or other byproducts present after the polymerization step may cause problems during downstream method steps, such as the hydrolysis step. It has been found that the amount of unreacted N-vinylcarboxamide present after the polymerization step but before the hydrolysis step correlates with the color, dynamic viscosity, crosslinking, and gelation of the vinylamine-containing polymer solution after the hydrolysis step. Therefore, to improve the quality of the vinylamine-containing polymer solution, it is desirable to minimize the amount of unreacted N-vinylcarboxamide present in the intermediate polymer formulation.

[0017] According to the method provided herein, various approaches may be used to determine whether an intermediate polymer formulation containing a poly(N-vinylcarboxamide) prepolymer—that is, an intermediate polymerization product of vinylcarboxamide after the reaction of one or more N-vinylcarboxamide monomers and a polymerization initiator in a reaction mixture, but before further processing, such as a hydrolysis step—contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer (including residual N-vinylcarboxamide monomers and their byproducts, such as aldehydes and ketones). One approach is to directly measure the amount of unreacted N-vinylcarboxamide in the intermediate polymer formulation. Additionally, it has been found that the color of a vinylamine-containing polymer solution correlates with the content of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation. Therefore, another approach to determine whether the intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer is to observe the color of the vinylamine-containing polymer solution and compare it to an acceptable color. Additionally, the wavelength of the vinylamine-containing polymer solution can be measured and compared to a predetermined limit wavelength value for an acceptable vinylamine-containing polymer solution. Another approach to determining whether the intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer is to measure the dynamic viscosity of the vinylamine-containing polymer solution and compare it to a predetermined limit dynamic viscosity value required for an acceptable vinylamine-containing polymer solution. If it is determined that the intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer, one or more process parameters may be modified, and the polymerization step may be repeated with a new batch of monomer to form a modified intermediate polymer formulation.Changes in process parameters and the repetition of the polymerization step into a new batch of monomer can be repeated until the desired content of unreacted N-vinylcarboxamide in the intermediate polymer formulation is achieved.

[0018] Unless specifically stated or evident from the context, the term “approximately” as used herein is understood to mean within the general tolerance range in the relevant art when measured using a standard measuring device, for example, within a range of two standard deviations of the mean for a specific measuring device. “Approximately” may be understood to mean within 10%, 5%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Alternatively, “approximately” may be understood to mean the stated exact value. Unless otherwise evident from the context, all numerical values ​​provided herein are modified by the term “approximately”.

[0019] A method as provided herein comprises a method for preparing a vinylamine-containing polymer solution comprising a vinylamine-containing polymer. The method involves a “polymerization step,” which is defined as an intended step of combining a polymerization initiator and one or more N-vinylcarboxamide monomers, and optionally one or more other vinyl monomers under reaction conditions to form an intermediate polymer formulation comprising a poly(N-vinylcarboxamide) prepolymer. Prior to the polymerization step, polymerization of residual monomers, impurities, or unintended reaction products of the monomers may also occur incidentally. Such incidental polymerization is not considered part of the “polymerization step.”

[0020] The method also involves a "hydrolysis step," which is defined as an intended step of intentionally hydrolyzing the functional groups of a poly(N-vinylcarboxamide) prepolymer to form a vinylamine-containing polymer solution containing a vinylamine-containing polymer. Prior to the hydrolysis step, hydrolysis of the existing monomers, polymers, and other compounds may also occur. Such incidental hydrolysis is not considered part of the "hydrolysis step."

[0021] The method as provided herein represents an improvement in the synthesis of vinylamine-containing polymers by implementing changes or repetitions of method steps based on the measurement or observation of an intermediate polymer formulation (after the polymerization step) or a vinylamine-containing polymer solution (after the hydrolysis step). Appropriate changes or repetitions of method steps produce vinylamine-containing polymer solutions having fewer impurities and more desirable characteristics.

[0022] A method as conceived herein involves first completing one or more method steps of a known method for preparing a vinylamine-containing polymer solution. In the first step, which is a polymerization step, one or more N-vinylcarboxamide monomers having Formula I are provided:

[0023]

[0024] Here, R 1 and R 2 The monomer(s) of formula I are independently H or C1 to C6 alkyl groups. A polymerization reaction is carried out by combining the monomer(s) of formula I with a polymerization initiator in a reaction mixture under appropriate reaction conditions.

[0025] Various vinylcarboxamide monomers having the chemical formula I may be used according to the present disclosure. For example, in some embodiments, R 1 and R 2 When both are H, the N-vinylcarboxamide monomer of formula I is N-vinylformamide. In another embodiment, R1 and R 2 In the case where both are methyl groups, the N-vinylcarboxamide monomer having the formula I is N-vinyl-N-methylacetamide. In another embodiment, R 1 and R 2 may be two different functional groups. Other examples of N-vinylcarboxamide monomers include, but are not limited to, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-ethylacetamide, N-vinylpropionamide, N-vinyl-N-methylpropionamide, and N-vinylbutyramide. One or more variations of the monomer having Formula I are reactants in the claimed method.

[0026] In some embodiments, one or more vinyl monomers having a formula different from Formula I may also be reactants. "Vinyl monomer(s)" refers to monomer(s) having a (H2C=C-) group in their structure. Vinyl monomers may alternatively be defined as ethylene-based unsaturated monomers. Examples of suitable vinyl monomers having a formula different from Formula I include, but are not limited to, N-vinylpyrrolidone, acrylamide, acrylic acid, vinyl acetate, methyl acrylate, or combinations thereof. Additional examples include, but are not limited to, methacrylamide, N-isopropylacrylamide, N-methylmethacrylamide, acrylonitrile, vinyl chloride, styrene, methacrylic acid, vinylphosphonic acid, vinylsulfonic acid, maleic acid, itaconic acid, diallyldimethylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC), methacrylamidopropyltrimethylammonium chloride, or combinations thereof. Any combination of the monomers mentioned above may be used.

[0027] The polymerization initiator may be a non-oxidizing radical initiator, such as an azo compound. Examples of azo initiators include 2,2'-azobis(2-methylpropionamidine)dihydrochloride (commercially available under the trade name V-50 from FUJIFILM Wako Chemicals USA, Corp.), 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutyramidine)dihydrochloride, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], azo-bis-isobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and 2,2'-azobis[2-(2-imidazoline-2-yl)propane]dihydrochloride. 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate, or 2,2'-azobis(2-methyl-butyronitrile), are included but not limited thereto. In other embodiments, the polymerization initiator may be hydrogen peroxide, an alkali metal or ammonium salt of peroxydisulfite, a peroxide, a hydroperoxide, or a redox catalyst. In some embodiments, the polymerization initiator may be used in an amount of about 0.01 to about 5 weight percent based on the total weight of the reaction mixture.

[0028] The reaction mixture may be an aqueous solution of at least about 30 weight percent of monomer based on the total weight of the reaction mixture. The concentration of monomer in the aqueous solution may be up to about 90 weight percent, or alternatively about 60 weight percent to about 85 weight percent based on the total weight of the reaction mixture.

[0029] The reaction mixture can be buffered to a pH of about 5 to about 8, or alternatively about 6 to about 7. To stabilize the pH during the polymerization step, the polymerization step can be carried out in the presence of a conventional buffer system.

[0030] The polymerization step may also be carried out under an inert gas, such as nitrogen, or under a vacuum. In another embodiment, the polymerization step may be carried out under evaporative cooling at a temperature of the reaction mixture of 20 mbar to atmospheric pressure and less than about 100°C, alternatively about 25°C to about 80°C.

[0031] In some embodiments, the polymerization step may be carried out in a mixing device in which the reactants can be thoroughly mixed. For example, the polymerization step may be carried out in a single-screw kneader or an extruder. During the polymerization step, the solid content of the reaction mixture may be about 30% by weight to about 90% by weight, or alternatively about 60% by weight to about 85% by weight, based on the total weight of the reaction mixture.

[0032] After the polymerization step, in some embodiments, the conversion of the monomer into a polymer may be at least 75 mol% based on the total moles of monomer present in the reaction mixture prior to polymerization. In other embodiments, the conversion of the monomer into a polymer may be less than 75 mol% based on the total moles of monomer present in the reaction mixture prior to polymerization. The conversion rate of the monomer may be improved through the method described herein.

[0033] After the polymerization step is completed, an intermediate polymer formulation is formed. The intermediate polymer formulation used herein is defined as a polymer formulation containing a poly(N-vinylcarboxamide) prepolymer. The intermediate polymer formulation may also contain other polymers, unreacted N-vinylcarboxamide monomers, residual polymerization initiators, or other byproducts or impurities. The poly(N-vinylcarboxamide) prepolymer is defined as a poly(N-vinylcarboxamide) polymer formed through the polymerization step but not yet subjected to intentional hydrolysis through the addition of an acid or base to form a vinylamine-containing polymer solution. The poly(N-vinylcarboxamide) prepolymer may be a homopolymer or a copolymer and may contain non-vinylcarboxamide units derived from one or more vinyl monomers of a chemical formula different from Chemical Formula I as described above. In one embodiment, the N-vinylcarboxamide monomer reacted in the polymerization step is N-vinylformamide, and the poly(N-vinylcarboxamide) prepolymer is a polyvinylformamide polymer. In some embodiments of the method, the poly(N-vinylcarboxamide) prepolymer has a molecular weight in the range of about 5,000 daltons to about 5,000,000 daltons.

[0034] As described above, an intermediate polymer formulation containing a poly(N-vinylcarboxamide) prepolymer is an intermediate product in a method for forming a vinylamine-containing polymer solution. The unreacted N-vinylcarboxamide monomer used herein is defined as an N-vinylcarboxamide monomer that was combined with a polymerization initiator in a reaction mixture but did not undergo the reaction to form a poly(N-vinylcarboxamide) prepolymer and remains in the intermediate polymer formulation as a monomer or reaction byproduct. Reaction byproducts included in this definition may include hydrolysis products of the N-vinylcarboxamide monomer, such as acetaldehyde or ketones.

[0035] The degree of polymerization of the monomer during the polymerization step is an important factor affecting the properties of the resulting vinylamine-containing polymer solution. Any residual N-vinylcarboxamide monomer or its byproducts present after the polymerization step can cause problems during downstream process steps, such as the hydrolysis step.

[0036] A method as provided herein also includes a hydrolysis step of hydrolyzing a poly(N-vinylcarboxamide) prepolymer contained in an intermediate polymer formulation to prepare a vinylamine-containing polymer solution containing a vinylamine-containing polymer.

[0037] In some embodiments, a scavenger to eliminate the effect of unreacted N-vinylcarboxamide monomers may be added to the reaction mixture before the hydrolysis step in an amount of about 0.01 wt% to about 10 wt%, or alternatively about 0.5 wt% to about 5 wt%, relative to the total weight of vinyl monomers in the reaction mixture.

[0038] In some embodiments, the hydrolysis step comprises hydrolyzing a poly(N-vinylcarboxamide) prepolymer in an intermediate polymer formulation by adding one or more acids or bases to prepare a vinylamine-containing polymer solution comprising a vinylamine-containing polymer. Examples of acids that may be used for the hydrolysis step include inorganic acids or organic acids. Examples of bases that may be used for the hydrolysis step include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, strontium hydroxide, and / or barium hydroxide.

[0039] In some embodiments, an acid or base may be added to the reaction mixture in an amount of about 0.05 to about 1.5 equivalents, or alternatively about 0.4 to about 1.2 equivalents, of base or acid per equivalent of the formyl group of the polymer during the hydrolysis step.

[0040] The hydrolysis step can be carried out at a temperature of the reaction mixture of about 20°C to about 100°C, or alternatively about 40°C to about 70°C.

[0041] The vinylamine-containing polymer used herein is defined as a polymer containing vinylamine functional groups formed through a polymerization step and a hydrolysis step. The vinylamine-containing polymer may be a homopolymer or a copolymer and may contain non-vinylamine units. The vinylamine-containing polymer solution is defined as a polymer formulation containing at least a vinylamine-containing polymer. It may also contain other polymers, unreacted N-vinylcarboxamide monomers, unreacted vinyl monomers having a chemical formula different from Formula I, residual polymerization initiators, or other by-products or impurities. In particular, residual N-vinylcarboxamide monomers or their hydrolysis products may still be present in the vinylamine-containing polymer solution.

[0042] After the hydrolysis step is completed, the resulting vinylamine-containing polymer may be the result of complete hydrolysis of the poly(N-vinylcarboxamide) prepolymer or partial hydrolysis of the poly(N-vinylcarboxamide) prepolymer. In one embodiment, if complete hydrolysis occurred, substantially all of the carboxyl moiety contained in the poly(N-vinylcarboxamide) prepolymer was hydrolyzed to form the vinylamine-containing polymer. This may produce a vinylamine homopolymer or vinylamine copolymer containing the hydrolysis products of the carboxyl moiety present in the prepolymer.

[0043] In other embodiments, complete hydrolysis may not have occurred. The degree of hydrolysis of the carboxyl moiety contained in the poly(N-vinylcarboxamide) prepolymer may be about 0.1 mol% to less than about 99 mol%, alternatively about 10 mol% to about 90 mol%, alternatively about 40 mol% to about 80 mol%, alternatively about 60 mol% to about 70 mol%, based on the total molar amount of the carboxyl moiety of the prepolymer.

[0044] In addition to the vinylamine-containing homopolymer or copolymer, the vinylamine-containing polymer solution may contain other polymers, unreacted N-vinylcarboxamide monomers, other unreacted vinyl monomers, residual polymerization initiators, or other by-products or impurities. By-products may include unintended hydrolysis products of the monomers or products of other side reactions.

[0045] Therefore, impurities in the intermediate polymer formulation can cause problems during the hydrolysis step, which can ultimately lead to a lower quality vinylamine-containing polymer solution. Specifically, it has been found that the presence of unreacted N-vinylcarboxamide monomers in the intermediate polymer formulation leads to a lower quality vinylamine-containing polymer solution after the hydrolysis step. Although not bound by any theory, this is thought to be the result of unreacted N-vinylcarboxamide monomers being unintentionally converted into their hydrolysis byproducts during the hydrolysis step. The presence of these byproducts, as well as residual non-polymerized and non-hydrolyzed N-vinylcarboxamide monomers, can cause crosslinking of the vinylamine-containing polymer or other undesirable side reactions.

[0046] To improve the quality of a vinylamine-containing polymer solution, it is desirable to minimize the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation. Accordingly, the method provided herein provides a feedback loop capable of quantitatively or qualitatively measuring the amount of unreacted N-vinylcarboxamide monomer present in the intermediate polymer formulation so as to determine whether the polymerization step should be modified and repeated with a new batch of monomer to reduce the amount of unreacted N-vinylcarboxamide monomer before the hydrolysis step is performed. In an embodiment of the method, specific characteristics of the vinylamine-containing polymer can be observed or measured to determine whether process parameters need to be modified to reduce the amount of unreacted N-vinylcarboxamide monomer present in the intermediate polymer formulation and thereby improve the quality of the vinylamine-containing polymer solution.

[0047] As used in this disclosure, the term "unacceptably high" means that the measured value is greater than the limit value. The term "acceptable" means that the measured value is not "unacceptably high" or that the measured value is less than or equal to the limit value. In relation to measuring the amount of unreacted N-vinylcarboxamide monomer in an intermediate polymer formulation, the predetermined N-vinylcarboxamide limit value was defined as the weight percentage of N-vinylcarboxamide monomer present in the intermediate polymer formulation when the resulting vinylamine-containing polymer solution is acceptable, or less than or equal to that amount.

[0048] The method is carried out by determining whether an intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer and using that information to change one or more process parameters. In particular, the method of the present invention relates to situations where an unacceptably large amount of unreacted N-vinylcarboxamide monomer is present, because the preparation of a vinylamine-containing polymer solution containing an acceptablely small amount of unreacted N-vinylcarboxamide does not require a change in process parameters. In one embodiment, determining whether an intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer involves directly measuring the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation after the polymerization step but before the hydrolysis step. The amount of unreacted N-vinylcarboxamide monomer can be measured, for example, by high-performance liquid chromatography. After measuring the amount of N-vinylcarboxamide monomer in the intermediate polymer formulation, the amount is compared with a predetermined N-vinylcarboxamide limit value. If the amount of unreacted N-vinylcarboxamide monomer is greater than the predetermined N-vinylcarboxamide limit value, it is determined that the intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer.

[0049] In one embodiment, the predetermined N-vinylcarboxamide limit value is 0.03 wt%, alternatively 0.05 wt%, and alternatively 0.06 wt%. In another embodiment, the predetermined N-vinylcarboxamide limit value may be 0.10 wt%, 0.13 wt%, 0.15 wt%, 0.20 wt%, or 0.25 wt%. In an embodiment, the limit value is 0.13% to 0.9%.

[0050] Other methods may also be used to determine whether an intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer. It has been found that characteristics of vinylamine-containing polymer solutions, such as visually observed color, measured wavelength, and dynamic viscosity, correlate with the amount of unreacted N-vinylcarboxamide monomer present in the intermediate polymer formulation from which the vinylamine-containing polymer solution was formed. Therefore, by observing and / or measuring these characteristics, it is possible to determine whether the amount of unreacted N-vinylcarboxamide monomer is unacceptably large, and accordingly, process parameters can be modified to produce a higher quality vinylamine-containing polymer solution.

[0051] Additional limit values ​​are used in some embodiments of the method. With respect to the visual color of the vinylamine-containing polymer solution, an acceptable color correlated with a limit value of an unacceptably large amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation will be presented herein. With respect to the wavelength of the vinylamine-containing polymer solution, a predetermined wavelength limit value is defined as the wavelength of the vinylamine-containing polymer solution correlated with an intermediate polymer formulation containing an acceptable amount of unreacted N-vinylcarboxamide monomer, or less than that. With respect to the dynamic viscosity of the vinylamine-containing polymer solution, a predetermined dynamic viscosity limit value is defined as the dynamic viscosity of the vinylamine-containing polymer solution correlated with an intermediate polymer formulation containing an acceptable amount of unreacted N-vinylcarboxamide monomer, or less than that.

[0052] In one embodiment, after the polymerization and hydrolysis steps are completed, the color of the resulting vinylamine-containing polymer solution is visually observed. For example, if the color is visually determined to be dark yellow, amber, or orange, or is objectively measured to have a wavelength visually correlated with dark yellow, amber, or orange, this leads to the determination that an unacceptably large amount of unreacted N-vinylcarboxamide monomer was present in the intermediate polymer formulation in which the vinylamine-containing polymer solution was formed. If the color is objectively determined to have a wavelength lower than dark yellow (e.g., pale yellow or clear), this leads to the determination that an acceptable amount of unreacted N-vinylcarboxamide monomer was present in the intermediate polymer formulation in which the vinylamine-containing polymer solution was formed.

[0053] In another embodiment, after the polymerization and hydrolysis steps are completed, the wavelength of the resulting vinylamine-containing polymer solution can be measured using a spectrophotometer. Subsequently, the wavelength of the vinylamine-containing polymer solution can be compared to a predetermined wavelength limit value. If the wavelength is greater than the predetermined wavelength limit value, it is determined that an unacceptably large amount of unreacted N-vinylcarboxamide monomer was present in the intermediate polymer formulation in which the vinylamine-containing polymer solution was formed. If the wavelength is less than or equal to the predetermined wavelength limit value, it is determined that an acceptable amount of unreacted N-vinylcarboxamide monomer was present in the intermediate polymer formulation in which the vinylamine-containing polymer solution was formed.

[0054] In one embodiment, the predetermined wavelength limit value is about 600 nm, alternatively about 575 nm, or alternatively about 575 nm to about 600 nm.

[0055] In another embodiment, after the polymerization and hydrolysis steps are completed, the dynamic viscosity of the resulting vinylamine-containing polymer solution may be measured. The dynamic viscosity may be measured, for example, at 25°C using a Brookfield viscometer at 6 rpm with LV spindle number 62 at a total solid content of 18%. Subsequently, the dynamic viscosity of the vinylamine-containing polymer solution may be compared to a predetermined dynamic viscosity limit value. If the dynamic viscosity is greater than the predetermined dynamic viscosity limit value, it is determined that an unacceptably large amount of unreacted N-vinylcarbamide monomer was present in the intermediate polymer formulation in which the vinylamine-containing polymer solution was formed. If the dynamic viscosity is less than or equal to the predetermined dynamic viscosity limit value, it is determined that an acceptable amount of unreacted N-vinylcarbamide monomer was present in the intermediate polymer formulation in which the vinylamine-containing polymer solution was formed.

[0056] In one embodiment, the predetermined dynamic viscosity limit value is about 700 cPs. In another embodiment, the predetermined dynamic viscosity limit value may be about 1000 cPs, alternatively about 1700 cPs, alternatively about 2000 cPs, or alternatively about 700 cPs to about 2000 cPs.

[0057] After the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation is determined to be greater than a predetermined N-vinylcarboxamide limit value (and thus unacceptably large), one or more process parameters are changed, and the polymerization step is repeated with a new batch of monomer. The process parameters to be changed may include, for example, reaction time, temperature, pressure, pH, initiator concentration, monomer concentration, and / or the purity of the process water.

[0058] After the polymerization step is repeated with the modified process parameter(s), the amount of unreacted N-vinylcarboxamide monomer in the newly produced intermediate polymer formulation can be measured again. If the amount of unreacted N-vinylcarboxamide monomer is still unacceptably large, the process parameters can be further modified, and the polymerization step can be repeated with a new batch of monomer to produce a new batch of the intermediate polymer formulation. This cycle can be continued until the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation is determined to be acceptable (below a predetermined N-vinylcarboxamide limit value). Subsequently, the intermediate polymer formulation is applied to a hydrolysis step to form a vinylamine-containing polymer solution. The resulting vinylamine-containing polymer solution can have improved properties compared to a solution prepared by simply completing the polymerization and hydrolysis steps without measuring the amount of unreacted monomer, because the method devised herein enables the identification of substandard intermediate polymer formulations and allows appropriate correction steps to be performed to obtain a higher quality vinylamine-containing polymer solution.

[0059] Subsequently, the characteristics of a new batch of vinylamine-containing polymer solution formed after changing one or more process parameters of the polymerization step may be observed or measured. For example, color may be visually observed, or wavelength or dynamic viscosity may be measured. If the observed or measured characteristics are still higher than the relevant threshold values, this indicates that the amount of unreacted N-vinylcarbamide in the intermediate polymer formulation is still unacceptably high. If this determination is made, the process parameters for the polymerization step may be further changed, and the polymerization and hydrolysis steps may be repeated with a new batch of monomer to produce a new batch of the intermediate polymer formulation. This cycle may continue until the observation or measurement of the characteristics of the intermediate polymer formulation and / or vinylamine-containing polymer yields a value below the relevant threshold values ​​according to the methodology described above. When an acceptable amount of unreacted N-vinylcarbamide in the intermediate polymer formulation is achieved, the vinylamine-containing polymer solution may be produced for commercial use.

[0060] The vinylamine-containing polymer solution consequently formed through the method described above may have improved properties compared to a solution prepared by simply completing the polymerization and hydrolysis steps without measuring the characteristics of the intermediate polymer formulation and / or the resulting vinylamine-containing polymer solution, and without repeating the modified method step to a new batch of monomer if necessary. Thus, the method as conceived herein produces a higher quality vinylamine-containing polymer solution, enables the preparation of a more acceptable solution, and consequently results in less waste.

[0061] The method provided herein enables the production of high-quality vinylamine-containing polymer solutions, thereby reducing the occurrence of gelation. This leads to an efficient vinylamine-containing polymer solution production process, consistent results, reduced waste, and reliable products. This ultimately results in fewer problems in papermaking processes and other applications where vinylamine-containing polymer solutions are used.

[0062] The vinylamine-containing polymer solution provided herein, prepared by the method disclosed herein, may be used in the manufacture of paper, cardboard, or thin paper, for example, as a reinforcing aid, a dehydration aid, a coagulant, an agglutinating agent, a retention agent, or a sizing promoter.

[0063] The following examples are intended to illustrate a method for preparing a vinylamine-containing polymer solution as described herein and should not be construed as limiting.

[0064] Examples

[0065] Example 1

[0066] 445 grams of deionized water, 1.2 grams of 75 wt% aqueous phosphoric acid, and 1.8 grams of 25 wt% aqueous sodium hydroxide were added to a 1-liter resin kettle equipped with an overhead stirrer, thermocouple, condenser, nitrogen inlet-outlet, and pressure gauge. The pH of the resulting solution was adjusted to 6.5 + / - 0.3. The kettle was heated to 80°C while stirring with the overhead stirrer. The pressure was gradually reduced to approximately 320 torr.

[0067] N-vinylformamide (VFA, 90.4 g) and 3.0 wt% aqueous V-50 (18.47 g) initiator (available from Waco Chemicals USA, Inc., Richmond, USA) were added simultaneously. The polymerization temperature was controlled at 78 ± 2°C. After the addition of V-50 was completed, the kettle vacuum was lowered to approximately 350 torr. After a total of 260 minutes, the vacuum was released, and the reactor was flushed with nitrogen (3 cycles of vacuum and nitrogen refill). After completion, the reactor was cooled to room temperature.

[0068] After carrying out the polymerization reaction, the resulting polyvinylformamide polymer formulation was divided into 8 parts and mixed with N-vinylformamide monomers of known concentrations. The additional amount of unreacted N-vinylformamide monomers was in the range of about 0.0 wt% to about 0.5 wt% based on the total weight of the intermediate polymer formulation, as shown in Table 1 below.

[0069] After the addition of an additional amount of unreacted N-vinylformamide monomer, each intermediate polymer formulation was subjected to an alkaline hydrolysis reaction by adding 51 grams of a 50% caustic solution. After 3 hours at 80°C, the reaction mixture was cooled to 40°C, and then 30 wt% aqueous hydrochloric acid was added over 5 minutes to adjust the pH to 9. Each of the eight resulting vinylamine-containing polymer solutions contained a polyvinylamine polymer.

[0070] The characteristics of each vinylamine-containing polymer solution were measured and observed as described below. The results are presented in Table 1.

[0071] Table 1: Characteristics of vinylamine-containing polymers based on intermediate polymer formulations containing various weight percentages of unreacted N-vinylformamide monomers

[0072]

[0073] The dynamic viscosity of the vinylamine-containing polymer solution was measured at 25°C using a Brookfield viscometer at 6 rpm with LV spindle number 62, at a total solid content of 18%. The vinylamine-containing polymer solution was also visually monitored for the occurrence of gelation. The color of each vinylamine-containing polymer solution was objectively determined by visual observation.

[0074] The results of this example demonstrate a correlation between the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation and the characteristics of the vinylamine-containing polymer solution (e.g., viscosity and color). Generally, as the amount of unreacted N-vinylformamide monomer in the intermediate polymer formulation increases, the viscosity of the vinylamine-containing polymer solution increases, and the color of the vinylamine-containing polymer solution becomes darker (higher wavelength).

[0075] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be recognized that numerous variations exist. Furthermore, it should be recognized that the exemplary embodiments or the exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide a convenient guide for those skilled in the art to implement the exemplary embodiments of the present disclosure. It should be understood that various changes may be made in the function and arrangement of the elements described in the exemplary embodiments without departing from the scope of the present disclosure as set forth in the appended claims.

Claims

Claim 1 A method for synthesizing a vinylamine-containing polymer solution comprising the following steps: (a) reacting a polymerization initiator, one or more N-vinylcarboxamide monomers, and optionally one or more additional vinyl monomers having a chemical formula different from that of the N-vinylcarboxamide monomers in a reaction mixture to produce an intermediate polymer formulation comprising a poly(N-vinylcarboxamide) prepolymer, wherein the N-vinylcarboxamide monomer has the chemical formula I: Here, R 1 and R 2 (a) H or C1 to C6 alkyl groups independently of each other; (b) hydrolyzing the carboxyl groups of a poly(N-vinylcarboxamide) prepolymer to produce a vinylamine-containing polymer solution containing a vinylamine-containing polymer; (c) determining whether the intermediate polymer formulation has an unacceptably large amount of unreacted N-vinylcarboxamide monomer; (d) after step (c), changing one or more process parameters of step (a); and after step (d), repeating step (a) to form a modified intermediate polymer formulation. Claim 2 A method according to claim 1, further comprising the following steps: (e) determining whether the amount of unreacted N-vinylcarboxamide monomer in the modified intermediate polymer formulation after repeating step (a) is less than or equal to a predetermined N-vinylcarboxamide limit value. Claim 3 A method according to claim 1, wherein determining whether an intermediate polymer formulation has an unacceptably large amount of unreacted N-vinylcarboxamide monomer comprises the following steps: measuring the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation; comparing the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation with a predetermined N-vinylcarboxamide limit value; and determining whether the amount of unreacted N-vinylcarboxamide monomer in the intermediate polymer formulation is greater than the predetermined N-vinylcarboxamide limit value. Claim 4 A method according to claim 3, wherein determining whether the amount of unreacted N-vinylcarboxamide monomer is greater than a predetermined unreacted N-vinylcarboxamide limit value includes determining whether the amount of unreacted N-vinylcarboxamide monomer is greater than about 0.03 weight% based on the total weight of the intermediate polymer formulation. Claim 5 A method according to claim 3, wherein determining whether the amount of unreacted N-vinylcarboxamide monomer is greater than a predetermined unreacted N-vinylcarboxamide limit value includes determining whether the amount of N-vinylcarboxamide monomer is greater than about 0.06 weight% based on the total weight of the intermediate polymer formulation. Claim 6 A method according to paragraph 3, wherein determining whether an intermediate polymer formulation has an unacceptably large amount of unreacted vinylformamide monomer further comprises the following steps: determining whether the color of the vinylamine-containing polymer solution is visually dark yellow or has a higher wavelength in the electromagnetic spectrum; and determining whether the dynamic viscosity of the vinylamine-containing polymer solution is greater than about 700 cPs. Claim 7 A method according to claim 1, wherein determining whether an intermediate polymer formulation has an unacceptably large amount of unreacted N-vinylcarboxamide monomer comprises the following steps: a step of visually observing the color of a vinylamine-containing polymer solution after performing step (b); and a step of determining whether the color of the vinylamine-containing polymer solution is dark yellow or has a higher wavelength in the electromagnetic spectrum. Claim 8 A method according to claim 1, wherein determining whether an intermediate polymer formulation has an unacceptably large amount of unreacted N-vinylcarboxamide monomer comprises the following steps: measuring the wavelength of a vinylamine-containing polymer solution; and determining whether the wavelength of the vinylamine-containing polymer solution is at least 600 nm using a spectrophotometer. Claim 9 A method according to claim 8, wherein the wavelength of the vinylamine-containing polymer solution is determined to be at least 575 nm. Claim 10 A method according to claim 1, wherein determining whether the intermediate polymer formulation has an unacceptably large amount of unreacted N-vinylcarboxamide monomer comprises determining whether the dynamic viscosity of the vinylamine-containing polymer solution exceeds a predetermined dynamic viscosity limit value. Claim 11 A method according to claim 10, wherein determining whether the dynamic viscosity of a vinylamine-containing polymer solution exceeds a predetermined dynamic viscosity limit value comprises the following steps: measuring the dynamic viscosity of the vinylamine-containing polymer solution at 25°C using a Brookfield viscometer at 6 rpm with LV spindle number 62 at a total solid content of 18%; and determining whether the dynamic viscosity of the vinylamine-containing polymer solution is greater than a predetermined dynamic viscosity limit value. Claim 12 In paragraph 11, a method in which a predetermined dynamic viscosity limit value of 700 cPs. Claim 13 In paragraph 11, a method in which a predetermined dynamic viscosity limit value is 1100 cPs. Claim 14 A method according to any one of claims 1 to 13, wherein one or more process parameters of step (a) are selected from the group consisting of reaction time, temperature, pressure, pH, initiator concentration, monomer concentration, or purity of process water. Claim 15 A method according to any one of claims 1 to 13, wherein hydrolyzing the carboxyl groups of a poly(N-vinylcarboxamide) prepolymer to produce a vinylamine-containing polymer solution comprises adding an acid or a base to a reaction mixture. Claim 16 A method in which, in any one of claims 1 to 13, the polymerization initiator is an azo initiator. Claim 17 A vinylamine-containing polymer solution formed by the following steps: (a) reacting one or more N-vinylcarboxamide monomers and a polymerization initiator in a reaction mixture to produce an intermediate polymer formulation comprising a poly(N-vinylcarboxamide) prepolymer, wherein the N-vinylcarboxamide monomer has the chemical formula I; (b) optionally adding one or more vinyl monomers having a chemical formula different from the chemical formula I during step (a); (c) hydrolyzing the carboxyamide groups of the poly(N-vinylcarboxamide) prepolymer to produce a vinylamine-containing polymer solution comprising a vinylamine-containing polymer; (d) determining whether the intermediate polymer formulation contains an unacceptably large amount of unreacted N-vinylcarboxamide monomer; (e) changing one or more process parameters of step (a); (f) repeating step (a) to form a modified intermediate polymer formulation; (g) unreacted in the modified intermediate polymer formulation A step of determining the amount of N-vinylcarboxamide monomer; (h) a step of repeating steps (a) and (g) until the amount of unreacted N-vinylcarboxamide monomer in the modified intermediate polymer formulation is less than or equal to a predetermined N-vinylcarboxamide limit value.

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