Low critical solution temperature purification of oxazoline polymer solutions

Abstract

A method for purifying a polymer solution is provided. In particular, the method ensures the separation of impurities from an oxazoline polymer solution by raising the temperature of the polymer solution above its lower critical solution temperature (LCST), where separation of a water-rich phase from a polymer-rich phase occurs. The phases are then separated, with the polymer-rich phase containing a lower amount of impurities than before separation.

Description

Technical Field

[0001] In general, this disclosure relates to a method for purifying (refining) polymer solutions. Specifically, the method ensures the separation of impurities from the oxazoline polymer solution by raising the temperature of the polymer solution above its lower critical solution temperature (LCST), wherein water / polymer phase separation occurs, and the impurities are removed from the polymer phase. Background Technology

[0002] Polymer purification may be required to obtain regulatory approval and ensure safe use in food contact situations, such as when used in certain grades of paper. A low-cost method is needed to remove impurities such as residual monomers, initiators, manufacturing auxiliaries, and substances that may be formed from these impurities, such as hydrolyzed monomers. This occurs in many polymers, such as oxazolines, used in various industries requiring regulatory approval. One such oxazoline polymer is poly-2-ethyl-2-oxazoline (PEOx), which can be used in applications such as adhesives, pharmaceuticals, or industrial applications. However, the polymer solution may contain impurities such as residual monomers and oligomers, initiators, manufacturing auxiliaries, and non-polymer materials. Removal of these impurities is necessary.

[0003] One application of oxazoline, such as PEOx, is as a paper additive to improve the properties of paper made from Hewlett Packard (HP) Indigo ( TM The additive is applied to paper and then dried to improve the adhesion of the printed image. Since oxazoline can be easily extracted from paper, impurity levels must be low to obtain regulatory approval—that is, levels that are safe for paper applications involving food contact or, for example, levels approved by the EU BfR or the US FDA. Therefore, it is desirable for us to develop an aqueous solution or dried product based on the oxazoline polymer with impurity levels below those of concern to the industry.

[0004] For example, PEOx is most commonly formed via cationic ring-opening polymerization of ethyl oxazoline. This polymerization method allows the resulting PEOx to have a narrow molecular weight distribution. It can also be obtained as a polydisperse material with a wide range of molecular weights. An example of such a material can be found from Polymer Chemistry Innovations under the trade name... PEOx exhibits a low critical solution temperature (LCST) in both narrow and wide molecular weight compositions. The LCST varies with molecular weight, with compositions having a lower average molecular weight exhibiting a lower LCST.

[0005] The chemical and LCST behavior of oxazolines such as PEOx can be described in R. Hoogenboom (2009), "Poly(2-oxazoline)s: A polymer class with numerous potential applications". Angew.Chem.Int.Ed. , 48(43), pp. 7978-7994, and "Molecular Modeling of Poly(2-ethyl-2-oxazoline)", Ayanna Bernard, Georgia Institute of Technology, 2008.

[0006] Gravity separation is a technique used in the chemical industry to separate liquids of different densities, such as removing oil from water. However, for polymer solutions, by definition, there is no gravitational difference through which impurities such as those mentioned can be removed. For polymer solutions, the purification of low molecular weight compounds and sometimes oligomers is carried out by boiling to remove impurities or by utilizing some form of membrane filtration, where separation is based on molecular size rather than insolubility.

[0007] Processes requiring high temperatures (stripping) may be inefficient or impractical. For example, impurities in PEOx, such as excess oligomers, cannot be removed by heating. For instance, the monomer has a boiling point of approximately 128°C.

[0008] Membrane filtration requires specific equipment and therefore has limitations in production. Alternative purification methods are still needed, particularly for removing nonpolymeric materials, nonvolatile components, or oligomers from polymers.

[0009] As an alternative to steam stripping, another known purification technique uses the high-pressure LCST phenomenon to separate polymer solutions. This technique involves using a mixed solvent such as hexane and pentane to achieve phase separation of poly(ethylene-co-propylene). Other techniques for separating and purifying water-soluble polyphosphazenes have been attempted. However, these methods produce a "viscous substance" of the polymer from which the liquid phase is decanted.

[0010] Since conventional methods for removing such impurities may require changes to the polymerization process or separation methods such as membrane filtration, there is a continuous need for effective and easier purification methods. Summary of the Invention

[0011] A method is provided for purifying an aqueous polymer solution containing one or more non-polymer materials. Specifically, an aqueous oxazoline polymer solution containing one or more non-polymer materials is provided, wherein the weight-average molecular weight of the oxazoline polymer is greater than 5000. The temperature of the polymer aqueous solution is raised from a first temperature to a second temperature above the LCST. The LCST is observed as the polymer aqueous solution separates into an aqueous phase and a polymer phase. Unlike other materials, when the oxazoline polymer solution is raised above the LCST, the polymer phase remains a mixture of polymer and water and can remain a flowable mixture at the appropriate temperature. At this point, the aqueous phase separates from the polymer phase, with some impurities remaining in the aqueous phase. After separating the aqueous and polymer phases, the polymer phase is cooled until it returns to a soluble polymer solution. This process of heating the polymer phase above its LCST, separating the subsequent aqueous and polymer phases, and cooling can be repeated multiple times as needed. Each time, additional impurities remain in the aqueous phase.

[0012] A method for purifying poly-2-ethyloxazoline (PEOx) is also provided. The method includes providing an aqueous solution containing one or more impurities and PEOx. The temperature of the aqueous solution is raised from a first temperature to a second temperature above the LCST, wherein the aqueous solution is separated into a lighter, more aqueous phase and a turbid, more concentrated polymer-rich phase. The polymer-rich phase is then separated from the less concentrated aqueous phase. The lighter aqueous phase contains a larger proportion of the impurities. After phase separation, the polymer-rich phase can be used as is, dried, or diluted. The separation process can be repeated multiple times as needed. Detailed Implementation

[0013] The specific embodiments described below are merely exemplary in nature and are not intended to limit this disclosure or its application and use. Furthermore, there is no intention to limit oneself to any theory presented in the foregoing background or the following specific embodiments.

[0014] Current methods utilize the low critical solution temperature (LCST) of polymer solutions to obtain a simpler and less costly approach for purifying, separating, and reducing chemical impurities from polymers.

[0015] Some polymers exhibit a so-called low critical solution temperature (LCST) in aqueous solutions. This is indeed the case for oxazoline polymers in water, such as poly-2-ethyloxazoline (PEOx). LCST means that the polymer becomes less soluble as the temperature of the aqueous solution increases. After reaching the LCST, the polymer aqueous solution separates into a turbid, denser polymer phase and a lighter aqueous phase containing almost no polymer.

[0016] Few polymer solutions exhibit LCST behavior. Even fewer polymers still exhibit LCST when in aqueous solutions where LCST temperatures can be readily and easily achieved. Oxazolines such as PEOx are one such polymer; they are soluble in water at room temperature but become insoluble upon heating. The LCST of PEOx is approximately 60 °C, but varies with molecular weight.

[0017] It has been found that aqueous solutions of oxazoline polymers exhibiting LCST behavior can be purified by raising the temperature of the polymer aqueous solution to its LCST point, in which two phases are formed—a denser phase rich in oxazoline polymers and a lighter phase containing most impurities and very little or no oxazoline polymers, and these two phases can be separated. Uniquely, the polymer-rich phase still contains a significant amount of water and remains a fluid with a certain viscosity at a specific temperature, allowing this phase to be pumped through pipes or tubes.

[0018] In some aspects of this method, a polymer solution comprising water and an oxazoline polymer is provided, wherein the oxazoline polymer has a weight-average molecular weight greater than about 5,000 g / mol and wherein the polymer solution contains one or more impurities. The temperature of the polymer solution is raised from a first temperature to a second temperature above the LCST, wherein the polymer solution is separated into an aqueous phase or an aqueous phase and a more concentrated polymer-rich phase. The separation of these two phases occurs rapidly by simple gravity or by using centrifugation techniques known in the industry. Advantageously, the lighter aqueous phase, which contains most of the water, also contains most of the impurities proportionally. Once the two phases have been separated, the polymer phase can be dried, diluted, or used as is.

[0019] A denser polymer-rich phase can be cooled below its LCST, whereby the polymer redissolves in a soluble solution. The process of heating, separating, and cooling the soluble polymer solution can be repeated to further reduce impurity levels. The polymer phase can be cooled artificially or naturally by adding water to it.

[0020] In some aspects of this method, the oxazoline polymer solution is heated to a temperature above the LCST, wherein the polymer-rich phase retains a significant water content and remains fluid. Proper temperature selection is crucial. In one aspect of the invention, the polymer-rich phase comprises water and PEOx.

[0021] In one aspect of this method, the oxazoline polymer solution is PEOx and has LCST, and it is heated to a temperature in the range of about 65°C to 85°C, specifically about 70°C to about 85°C, and possibly about 75°C to about 83°C. It has been found that if the temperature of the polymer solution is too high, the ease of pumping the polymer-rich phase or separating the polymer-rich phase from the aqueous phase decreases. The optimal temperature range exists between the ease of pumping the polymer-rich phase and the flowability and separation degree of the polymer-rich phase, i.e., the polymer concentration in the polymer-rich phase.

[0022] In another aspect of this method, the viscosity of the polymer-rich phase is between 10 and 2000 cps or between 30 and 1000 cps.

[0023] In some aspects of this method, the weight-average molecular weight of the polymer is greater than about 50,000 g / mol and optionally greater than about 200,000 g / mol.

[0024] In one aspect of this method, the process of separating the polymer-rich phase from the aqueous or water-containing phase can be carried out in a single-stage reactor.

[0025] In other aspects of this method, the polymer-rich phase can be pumped into a separate container for immediate use or further purification.

[0026] In other aspects of this method, a polymer-rich phase can be separated from an aqueous or water-containing phase via a continuous flow process, wherein the polymer-rich phase is separated by equipment used for phase separation, such as for oil-water separation. Those familiar with gravity separation of oil and water phases will know what equipment is suitable for this separation process.

[0027] In other aspects of this method, the polymer solution is provided as a continuous feed.

[0028] In some aspects of this method, the polymer solution also contains a water-soluble aluminum salt.

[0029] In other aspects of this method, the total amount of impurities in the polymer solution is reduced by more than 50% by weight, more than 65% by weight, and more than 84% by weight, compared to the initial weight % of the polymer in the polymer solution.

[0030] In some aspects of this method, impurities include residual monomers and oligomers, initiators, production aids, and nonpolymer materials.

[0031] In other aspects of this method, the oxazoline polymer is PEOx and the impurities are residual oligomers. Oligomers are a major concern for regulatory agencies regarding polymers in food contact. As mentioned above, separating residual oligomers from PEOx by removing them through evaporation or boiling presents problems. Furthermore, oligomers are very similar to polymers. Therefore, unexpectedly, this method is effective in reducing oligomer levels in polymers.

[0032] In other aspects of this method, the level of oligomers in the polymer solution (in weight %) is reduced by more than 50% by weight, more than 65% by weight, more than 72% by weight, and more than 80% by weight, compared to the initial weight % of PEOx in the polymer solution.

[0033] In some aspects of this method, a temperature is selected where the polymer-rich phase remains free-flowing but the desired purification is achieved. When using PEOx, such separation temperatures are between 65 and 85 °C, or between 70 and 85 °C, or between 75 and 83 °C. Higher temperatures result in greater separation, but also higher viscosity of the polymer-rich phase. Therefore, an optimal temperature range exists. The solids content of the starting solution is chosen to be higher than the LCST so that the method can achieve a higher concentration of PEOx in the polymer-rich phase compared to the starting solution used in this method. Lower initial solids content results in greater purification. For example, a starting polymer solution with a solids content of 5% can be increased to a solids content of 20% by using a process temperature of approximately 80 °C.

[0034] In some aspects of this method, after the separation of the aqueous phase and the polymer-rich phase, the impurities in the polymer-rich phase are reduced by up to about 50% of the initial amount of impurities in the polymer solution, and can be about 65%, and can be about 72%, and can be about 84%, by weight percentage of the polymer.

[0035] It was also found that the upper aqueous or lighter phase contained a percentage of impurities equal to the relative volume percentage of these two phases. Therefore, the polymer-rich fraction will necessarily contain impurities below the initial level and, proportionally, a lower amount of impurities per polymer level. Impurities may include residual monomers and oligomers, initiators, production aids, and non-polymer materials.

[0036] An unexpected result of this method is how temperature affects phase separation and the ease of phase separation in oxazoline aqueous solutions. It was found that raising the temperature above the LCST increased the degree of separation between the polymeric or more concentrated polymer-rich phase and the lighter or more aqueous phase. That is, the amount of aqueous phase increased and the polymer concentration in the polymeric phase increased. The PEOx used in the following studies did not fall to form a pure or even highly concentrated polymeric phase, but rather formed a polymeric phase with a given concentration that separated from an aqueous phase containing almost no polymer. The polymer concentration in the polymer-rich phase varied with the separation temperature, as did the viscosity of the separated phase.

[0037] Example

[0038] Test methods

[0039] Solid content is determined using a moisture balance such as those sold by Mettler Toledo or Ohaus. Other standard methods may also be used, such as heating in an oven at 100°C until weight loss ceases. Ideally, for polymer samples, the sample size for testing should be kept small, such as 0.1 g, to avoid water trapping.

[0040] molecular weight of polymer

[0041] The molecular weight of the starting polymer was provided by the supplier. It was further analyzed by size exclusion chromatography.

[0042] The residual levels of monomers 2-ethyl-2-oxazoline (EOx) and N-(2-hydroxyethyl)acrylamide (NHEP) in the starting polymer and different layers generated by this method were determined by gas chromatography (GC) combined with mass spectrometry. Quantitative analysis was performed using a set of known amounts of sample in acetone as the solvent. 0.1 g of sample was added to a volumetric flask, followed by the addition of acetone to the 10 mL mark. The injection volume was 1 μL. The inlet temperature was 235 °C. The temperature of the GC oven was initially set at 50 °C and increased to 220 °C at a rate of 30 °C / min. The mass spectrometer transfer line and ion source were set at 280 °C. Values ​​were determined by peak area.

[0043] residual levels of oligomers

[0044] The oligomer level was determined by size exclusion chromatography. The mobile phase was tetrahydrofuran, the flow rate was 0.8 mL / min, the column temperature was 40 °C, and the column was calibrated with polyethylene glycol standards. The sample concentration was 1 mg / mL, and the injection volume was 50 μL. The oligomer level was defined as the amount of PEOx with a molecular weight less than 1000 g / mol, excluding other low molecular weight compounds.

[0045] Example 1

[0046] Prepare 100 parts of a 20% PEOx solution with a weight-average molecular weight of 500,000 in water. Heat the solution to 45°C. Add 100 parts of water at 80°C to the solution with stirring to form a 10% solution. Raise the temperature of the mixture to 67.3°C with stirring, which is above the LCST. Stop stirring and form two phases. Take samples of the two layers. The bottom layer is a polymer-rich phase, and the top layer is mainly water containing impurities. Both layers have very good flowability and low viscosity. Take out the polymer-rich phase and repeat the process, except that the separation temperature (LCST) is 80°C. At 80°C, the viscosity of the bottom layer is significantly higher than that when separated at 67.3°C. The bottom layer is still fluid and can be pumped. Repeat the process a third time, this time with a separation temperature of 90°C. The polymer in the bottom layer forms a viscous paste and both layers are opaque. In all cases, the bottom phase is polymer-rich while the top phase is almost entirely water. Table 1 below compares the characteristics of the two layers.

[0047] Table 1

[0048]

[0049] *NHEP = N-(2-hydroxyethyl)acrylamide

[0050] All concentrations are expressed in μg / g.

[0051] If the layers are perfectly separated, the degree of purification, i.e., the percentage reduction of monomer and NHEP based on different temperatures, will be as shown in Table 2 below.

[0052] Table 2 - Reduction % of monomers and NHEP

[0053] temperature Monomer reduction % NHEP reduction % 67.3 ＞62 51 80 74 57 Post-90s 78 67

[0054] Reduce based on weight%.

[0055] In this embodiment, it was further observed that the volumes of the aqueous phase and the polymer-rich phase changed with temperature. This was reflected in the polymer solids content of both phases, and further observation showed that the upper aqueous phase contained virtually no or very little polymer. The degree of purification was found to be proportional to the volumes of both phases.

[0056] This study revealed that the viscosity of the polymer-rich phase varies with separation temperature. In this respect, gravity separation methods are largely dependent on the viscosities of both phases. Therefore, the optimal temperature for separation depends on the polymer. It should be noted that the initial polymer sample was almost entirely composed of polymers with very few impurities, and thus the solid obtained in the lower phase was almost entirely polymer.

[0057] Example 2 - Changing Concentration Levels

[0058] Prepare a 20% aqueous solution of PEOx with a weight-average molecular weight of 500,000. Add 100 parts of boiling water to a container. Then, add 144.2 g of the 20% polymer solution to the container with continuous stirring. Heat and stir simultaneously to raise the temperature of the mixture to 80°C. After addition to the container, the polymer concentration is 11.8%. Stop stirring and allow two phases or layers to form: an aqueous layer and a polymer-rich layer. After 3 minutes, remove the top aqueous layer from the container, leaving the polymer-rich layer or phase. The separation time may vary depending on the batch size used in the process. Repeat the process, but adjust the amount to a polymer concentration of 7.9%. Repeat the process a third time with a polymer concentration of 5.0%. In each case, phase or layer separation occurs when stirring stops.

[0059] The volume of the extracted top aqueous layer was found to depend on the solids content of the starting solution. Surprisingly, the solids concentration of the polymer-rich phase remained approximately the same regardless of the initial overall polymer solids content. It was also found that the solids content of the polymer-rich phase depended on temperature rather than the initial solids content. The results in Table 3 indicate that higher purification can be achieved in a single pass by using a solution with a lower solids content as the starting material.

[0060] Table 3

[0061]

[0062] *The slight increase above 100% is due to water loss caused by evaporation during the process. The trend of the results is not altered in the slight way by such a slight loss. The solids content value is the solids content produced by all the upper and lower phases after the separation of the two phases.

[0063] During the methods of this and other embodiments, regions were observed where the two phases were difficult to distinguish. For this experiment, this region was small, and this small portion of the sample, which was not clearly separated, was considered part of the upper or aqueous portion opposite to the lower polymer-rich portion.

[0064] Example 3 - Adding alum

[0065] An aqueous polymer solution was prepared using 4.51% PEOx with a weight average molecular weight of 500,000 and 1.43% aluminum sulfate. The polymer solution was heated to 80°C in a container with continuous stirring. Once the temperature reached 80°C, stirring was stopped, and two phases or layers were formed: an aqueous rich layer and a polymer rich layer. The layers were separated. The top aqueous layer was 79.08% by weight, and the bottom polymer rich layer was 20.92%. This study showed that the separation of the 5% PEOx sample was quite good, with the weight percentages of the layers being 76.09% and 23.91%, respectively. As shown in Examples 1 and 2, the level of purification was approximately equal to the weight ratio of the layers. The addition of alum increased the percentage of impurities in the upper aqueous layer, thus improving the efficiency of separating residual monomers from the polymer. The addition of alum was demonstrated to reduce the LCST of the PEOx solution.

[0066] Example 4 - Multiple Separations

[0067] A 200 g sample of 10% polymer aqueous solution was prepared using PEOx with a weight average molecular weight of 500,000. The sample was heated to 80.8 °C in a container with continuous stirring, at which point stirring was stopped and two phases or layers formed: an aqueous layer and a polymer-rich layer. 97.8 g of the top aqueous layer was removed. The monomer and NHEP levels of the top aqueous layer and the bottom polymer-rich layer were analyzed. 97.9 g of the aqueous phase was removed and replaced with an equal volume of water. The sample became clear upon the addition of water and cooling of the polymer-rich phase. The temperature of the sample was increased to 86 °C, where two phases or layers formed again once stirring was stopped. The layers were separated and the monomer and NHEP levels of each layer were analyzed. Table 4 provides the results for solids content and residual levels.

[0068] Table 4

[0069]

[0070] *NHEP = N-(2-hydroxyethyl)acrylamide

[0071] All concentrations are expressed in μg / g, also known as ppm, and are based on weight.

[0072] These results indicate that the level of residual monomers decreased by 72% due to the first separation at 80.8°C. After the second separation, the level of residual monomers decreased by more than 80.7% based on the original polymer solution. At this point, the limit of analytical detection was reached. After the second separation, the level of NHEP was 84% ​​lower than in the starting polymer. This example demonstrates that the purification process can be repeated and is surprisingly effective in reducing the level of impurities still remaining in the product.

[0073] Example 5 - Oligomers

[0074] A 5% solution of PEOx with a weight average molecular weight of 500,000 was prepared as described above. The solution was heated to 80°C with continuous stirring. Stirring was stopped, and the solution was separated into a top or upper aqueous phase or layer and a lower polymer-rich phase or layer. A 25% volume sample was collected from the lower or polymer-rich layer. The amount of residual oligomers remaining in the sample from the initial solution before separation and the lower polymer-rich phase after separation was analyzed. Residual oligomers were defined as polymer molecules with a molecular weight of less than 1000 g / mol. The study showed that, based on the total solids percentage, the oligomer level in the initial solution was 514 ppm (parts per million). Based on the total solids percentage, the oligomer level in the lower collected portion or polymer-rich portion was 147 ppm. The results indicate that the oligomer level was reduced by approximately 71%. Surprisingly, the method was found to reduce the oligomer level. We conclude that when the temperature is raised to 80°C, oligomers are largely not separated from the polymer, and therefore, surprisingly, the method of the present invention can be used to reduce the oligomer level in the final purified polymer.

[0075] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that numerous variations exist. It should also be understood that the at least one exemplary embodiment is merely illustrative and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiments, and it should be understood that various changes can be made to the function and arrangement of the elements described in the exemplary embodiments without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.

[0076] Any references cited in this application, including books, patents, published applications, journal articles and other publications, are incorporated herein by reference in their entirety.

Claims

1. A method for purifying a polymer solution, comprising the following steps: a) Provide a polymer solution containing water and an oxazoline polymer with a weight-average molecular weight greater than 5000 g / mol, as well as one or more impurities; b) Raising the temperature of the polymer solution from a first temperature to a second temperature above the lower critical dissolution temperature, wherein the polymer solution is separated into a dominant aqueous phase and a polymer-rich phase; c) Separate the aqueous phase from the polymer phase; d) Cooling the polymer phase to a third temperature, thereby forming a purified soluble polymer solution containing a quantity of one or more of the impurities, the quantity being less than the quantity of the one or more impurities present in the polymer solution; and e) Optionally repeat steps b), c) and d).

2. The method of claim 1, wherein the polymer solution comprises poly-2-ethyloxazoline.

3. The method according to claim 1, wherein the impurity is a residual monomer, oligomer, or production aid.

4. The method according to claim 1, wherein the second temperature in step b) is 65°C to 85°C.

5. The method of claim 1, wherein step d) comprises cooling the polymer phase by adding water.

6. The method according to claim 1, wherein the viscosity of the polymer phase is 10 to 2000 cps and the weight-average molecular weight of the polymer is greater than 50,000 g / mol.

7. The method according to claim 1, wherein the weight-average molecular weight of the polymer is greater than 200,000 g / mol.

8. The method according to any one of claims 1-7, further comprising the step of drying the polymer phase after step d).

9. The method according to any one of claims 1-7, wherein the polymer solution is provided as a continuous feed.

10. The method according to any one of claims 1-7, wherein the polymer solution further comprises a water-soluble aluminum salt.

11. The method according to any one of claims 1-7, wherein the total amount of impurities in the final polymer layer is reduced by more than 50% based on the weight of the polymer.

12. The method of claim 11, wherein the total amount of impurities in the final polymer layer is reduced by more than 65% by weight, based on the weight of the polymer.

13. The method of claim 12, wherein the total amount of impurities in the final polymer layer is reduced by more than 75% by weight, based on the weight of the polymer.

14. The method of claim 3, wherein the impurities comprise oligomers, and wherein the level of oligomers in the final polymer layer is reduced by more than 50% by weight based on the weight of the polymer.

15. The method of claim 14, wherein the level of oligomers in the final polymer layer is reduced by more than 65% by weight, based on the weight of the polymer.

16. The method of claim 15, wherein the level of oligomers in the final polymer layer is reduced by more than 75% by weight, based on the weight of the polymer.

17. A method for purifying poly-2-ethyloxazoline, comprising the following steps: a) Provide an aqueous solution containing one or more impurities and poly-2-ethyloxazoline; b) Raising the temperature of the aqueous solution from a first temperature to a second temperature, the second temperature being a low critical solution temperature, wherein the aqueous solution is separated into an aqueous phase and a polymer-rich phase; c) Separating the polymer-rich phase from the aqueous phase; wherein the polymer-rich phase is more concentrated and contains a dominant poly-2-ethyloxazoline polymer and the aqueous phase contains a portion of the one or more impurities; d) Cool the polymer phase to a third temperature to allow the polymer phase to return to the aqueous solution; and e) Optionally repeat steps b), c) and d).

18. The method of claim 17, wherein the impurity is a residual monomer, oligomer, or production aid.

19. The method of claim 18, wherein the impurity is a residual oligomer.

20. The method of claim 17, wherein the impurities rich in the polymer phase are reduced to 50% of the initial aqueous solution.

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