A method for improving the yield of ethylene-maleic anhydride alternating copolymer

Abstract

A method for improving the yield of ethylene-maleic anhydride alternating copolymers involves mixing maleic anhydride, a free radical initiator, and a polymerization catalyst in an organic solvent, then introducing ethylene gas to perform free radical polymerization. The polymerization catalyst is obtained by supporting a heteropoly acid with SiO2 and then activating it. This invention solves the problem of low molecular weight polymers prepared by solvent methods. While reducing reaction pressure and the use of reaction solvents, it increases the molecular weight of the polymer and the yield of the product, reduces the polymer molecular weight distribution, and minimizes side reactions. The prepared ethylene-maleic anhydride alternating copolymer has a number-average molecular weight between 60 and 90 kJ, a molecular weight distribution as low as 1.2, and excellent performance stability. This ethylene-maleic anhydride can be used as a highly efficient binder and dispersant in building insulation and sound insulation materials.

Description

Technical Field

[0001] This invention relates to the field of solvent-based copolymer preparation technology, specifically to a method for improving the yield of ethylene-maleic anhydride alternating copolymers based on solvent methods, and particularly to improving the yield of high molecular weight ethylene-maleic anhydride alternating copolymers. Background Technology

[0002] Ethylene-maleic anhydride alternating copolymer is a copolymer of ethylene and maleic anhydride in a 1:1 ratio. The structural units of this copolymer contain both hydrophobic ethylene structures and hydrophilic maleamide and maleate salt structures formed through amidation or hydrolysis, thus exhibiting amphiphilic properties. Therefore, this polymer can be used as an additive in the production of fertilizer dispersants, specialty papers, battery separators, or special inks. Simultaneously, this polymer can also be used as a forging lubricant and quenching fluid, avoiding the severe pollution caused by the large amounts of fumes generated during hot forging with oil-based lubricants. This helps improve production safety and product quality, and prevents fire hazards and splashing sparks.

[0003] Furthermore, polymers can be used in different fields depending on their molecular weight. High molecular weight polymers, in particular, can undergo esterification reactions with the hydroxyl groups in materials such as glass fibers and ceramics, and are thus used in novel formaldehyde-free adhesives. Lower molecular weight polymers, on the other hand, are often used as dispersants.

[0004] Currently, high-pressure methods are commonly used to produce high molecular weight ethylene-maleic anhydride alternating copolymers. However, the high-pressure method requires ethylene pressures exceeding 20 MPa, resulting in high costs. Therefore, some researchers have developed solvent-based methods for synthesizing ethylene-maleic anhydride alternating copolymers, reducing reaction pressure and shortening reaction time by adding Lewis acid catalysts. However, the molecular weight of copolymers prepared by solvent methods is relatively low. For example, patent 202310395202.X, by adding B(C6F5)3 to the system, yielded a polymer with Mn=36800 in 2 hours under reaction conditions of 0.6 MPa and 60°C. As the pressure increased to 2 MPa, the molecular weight Mn of the prepared polymer increased to 66000. However, 2 L of toluene is required as a solvent in the reaction, resulting in a product concentration of only 6.55%, which increases the difficulty of subsequent solvent recovery. Furthermore, the product molecular weight distribution is only 1.53, compromising the uniformity and stability of the polymer's properties. For example, although CN119060229A prepared ethylene-maleic anhydride with a molecular weight exceeding 8W, the molecular weight distribution was large, requiring a large amount of solvent and a long reaction time. This demonstrates that ethylene-maleic anhydride prepared by solvent methods typically has either a small or large molecular weight, a wide molecular weight distribution, and requires a large amount of solvent. Summary of the Invention

[0005] To address the aforementioned problems in the solvent-based preparation of ethylene-maleic anhydride, this invention aims to provide a method for controlling the molecular weight and yield of alternating ethylene-maleic anhydride copolymers using a solvent method. Specifically, by adjusting the catalyst and reaction solvent, the problem of uncontrollable polymer molecular weight (too low or too high) in solvent-based preparations is solved. This method reduces reaction pressure and solvent usage while controlling the polymer molecular weight between 60-90k, simultaneously improving product yield and reducing polymer molecular weight distribution.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for improving the yield of ethylene-maleic anhydride alternating copolymers is characterized by: mixing maleic anhydride, a free radical initiator, and a polymerization catalyst in an organic solvent, and then introducing ethylene gas to carry out free radical polymerization. The polymerization catalyst is obtained by supporting heteropoly acids with SiO2 as a support and then activating it.

[0008] Furthermore, the supported catalyst is prepared by dissolving a heteropoly acid in deionized water, stirring at 50-60°C to form an aqueous solution, adding the aqueous solution dropwise into a dry support SiO2 for impregnation, allowing it to stand for 10-15 hours after the addition is complete, and then drying it to obtain the supported catalyst.

[0009] Furthermore, the activation involves heating the supported catalyst in a nitrogen atmosphere to 200°C-250°C at a rate of 3-5°C / min and holding it therefore for 2-3 hours to obtain the polymerization catalyst.

[0010] Furthermore, the heteropolyacid is any one of phosphotungstic acid, phosphotomolybdic acid, silicotungstic acid, or silicotomolybdic acid.

[0011] Furthermore, the mass-to-volume ratio of SiO2, heteropolyacid, and deionized water is 100g: 15~25g: 100mL.

[0012] Furthermore, the organic solvent is composed of solvent A and solvent B in a volume ratio of 7:3 to 9:1, wherein solvent A is one of toluene, xylene, and cyclohexane, and solvent B is one of ethyl acetate, acetone, and methyl ethyl ketone.

[0013] Furthermore, the free radical initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and dicumyl peroxide, preferably azobisisobutyronitrile.

[0014] Furthermore, the free radical initiator added to the composite solvent is 20-30 mmol / L, the maleic anhydride is 3 mol / L, and the amount of polymerization catalyst is 20-30 g / L.

[0015] Furthermore, the catalytic reaction is carried out at an ethylene pressure of 0.3~0.8MPa, a reaction temperature of 50~60℃, and a reaction time of 2~5h.

[0016] Most specifically, a method for increasing the yield of ethylene-maleic anhydride alternating copolymers is characterized by comprising the following steps:

[0017] (1) Dissolve the heteropoly acid in deionized water and stir at 50~60℃ to form an aqueous solution. Add the aqueous solution dropwise to dry SiO2 for impregnation. After the addition is complete, let it stand for 10~15 h, then dry it at 100℃, and then heat it to 200℃~250℃ at 3~5℃ / min and keep it for 2~3 h in a nitrogen atmosphere to obtain a polymerization catalyst. The heteropoly acid is any one of phosphotungstic acid, phosphomolybdic acid, silicotungstic acid or silicotomolybdic acid. The mass-volume ratio of SiO2, heteropoly acid and deionized water is 100g: 15~25g: 100mL.

[0018] (2) Add a composite solvent, free radical initiator azobisisobutyronitrile, maleic anhydride and polymerization catalyst to a high-pressure reactor, replace with nitrogen three times, introduce ethylene at a pressure of 0.3~0.8MPa, react at an oil bath temperature of 50~60℃ for 2~5h, then discharge the remaining ethylene to obtain a milky white suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 7:3~9:1, wherein solvent A is any one of toluene, xylene and cyclohexane, and solvent B is any one of ethyl acetate, acetone and methyl ethyl ketone. The ratio of maleic anhydride, free radical initiator, polymerization catalyst and composite solvent is 1.5mol:10~15mmol:10~15g:500mL. The free radical initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide and dicumyl peroxide.

[0019] (3) The suspension was filtered through a 200-mesh filter to obtain the supported catalyst and the suspension. The suspension was then filtered and washed twice with ethanol to remove unreacted maleic anhydride. The washed solid was then vacuum dried to obtain ethylene-maleic anhydride polymer. The recovered supported catalyst was washed with DMF and could be reused.

[0020] The present invention has the following technical effects:

[0021] This invention utilizes a specific supported catalyst activated in combination with a composite solvent to effectively improve the solubility of maleic anhydride and ethylene in the solvent, thereby enhancing reactivity. This solves the problem of limited molecular weight tunability in polymers prepared by solvent methods. While reducing reaction pressure and solvent usage, the molecular weight of the polymer is adjusted, increasing product yield and reducing the polymer molecular weight distribution, while also minimizing side reactions. The prepared ethylene-maleic anhydride alternating copolymer has a number-average molecular weight between 60 and 90 kJ and a molecular weight distribution as low as 1.2, exhibiting excellent performance stability. This ethylene-maleic anhydride can be used as a highly efficient binder and dispersant in building insulation and soundproofing materials. Furthermore, the catalyst can be recovered and recycled. Detailed Implementation

[0022] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0023] Example 1

[0024] A method for improving the yield of ethylene-maleic anhydride alternating copolymers includes the following steps:

[0025] (1) Dissolve phosphomolybdic acid in deionized water and stir at 55°C to form an aqueous solution. Add the aqueous solution dropwise into dry SiO2 for impregnation. After the addition is complete, let stand for 12 h, then dry at 100°C, and then heat to 230°C at 4°C / min and keep warm for 3 h in a nitrogen atmosphere to obtain a polymerization catalyst. The mass-volume ratio of SiO2, phosphomolybdic acid and deionized water is 100 g: 20 g: 100 mL.

[0026] (2) Add 500 mL of composite solvent, 12 mmol of free radical initiator azobisisobutyronitrile, 1.5 mol of maleic anhydride and 15.0 g of polymerization catalyst to a high-pressure reactor, replace with nitrogen three times, introduce ethylene at a pressure of 0.6 MPa, react at an oil bath temperature of 60 °C for 2 h, and then discharge the remaining ethylene to obtain a milky white suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, wherein solvent A is toluene and solvent B is methyl ethyl ketone.

[0027] (3) The suspension was filtered through a 200-mesh filter to obtain the polymerization catalyst and the suspension. After collecting the polymerization catalyst, the suspension was filtered and washed twice with ethanol to remove unreacted maleic anhydride. The washed solid was then vacuum dried to obtain ethylene-maleic anhydride polymer.

[0028] Polymer weight-average molecular weight (M) was measured by gel permeation chromatography (GPC). w ) and number-average molecular weight (M n The M of the ethylene-maleic anhydride polymer prepared in this example w It is 78800, M n The yield was 65700, and the ethylene-maleic anhydride polymer was 158.3 g. The collected polymerization catalyst was 12.8 g.

[0029] Following the preparation process of Example 1, by adjusting the ratio of solvent A and solvent B in the composite solvent, the ethylene-maleic anhydride alternating copolymers prepared are shown in Table 1.

[0030] Table 1:

[0031]

[0032] It can be seen that as the proportion of solvent B in the composite solvent increases, the yield and molecular weight of the prepared ethylene-maleic anhydride alternating copolymer show a trend of first increasing and then decreasing, while the effect on the molecular weight distribution is first decreasing and then increasing, but the overall change in the molecular weight distribution is not significant. The highest polymer yield is achieved when the volume ratio of solvent A to solvent B is 8:2. This is because excessive ester and ketone solvents increase the polarity of the composite solvent, leading to a significant decrease in the solubility of ethylene gas, despite the increased solubility of maleic anhydride, which is detrimental to the reaction. Through the synergistic effect of the composite solvent and catalyst, the polymer yield can be effectively increased to over 300 g / L solvent even under relatively low ethylene pressure.

[0033] The ethylene-maleic anhydride alternating copolymers prepared by adjusting the ethylene pressure according to the preparation process of Example 1 are shown in Table 2.

[0034] Table 2:

[0035]

[0036] As shown in the table above, the molecular weight of the polymer generated in the reaction gradually increases with increasing ethylene pressure, but the pressure change has little effect on the molecular weight distribution. Furthermore, we tried further increasing the ethylene pressure; with increasing pressure, the molecular weight of the prepared ethylene-maleic anhydride gradually increased, but the molecular weight distribution remained essentially unchanged. Based on Example 1, when the ethylene pressure was increased to 2 MPa, the molecular weight of the prepared ethylene-maleic anhydride... n The molecular weight reached 146,000, with a molecular weight distribution of 1.24 and a polymer yield of 170.5 g. It can be expected that if the ethylene pressure is further increased, the molecular weight of the prepared ethylene-maleic anhydride copolymer will further increase, and the copolymer yield will also further improve.

[0037] Comparative Example 1

[0038] Under the conditions of a composite solvent with a volume ratio of solvent A to solvent B of 8:2, following the process steps of Example 1, Lewis acid B (C6F5)3 was used to replace the polymerization catalyst of the present invention (the amount added was 20 mmol; under this process, the polymer M synthesized with this amount of addition was...). n (Maximum), the remaining steps are the same as in Example 1. The prepared ethylene-maleic anhydride alternating polymer has a M... n The molecular weight was 38900, the molecular weight distribution was 1.39, and the polymer yield was 44.6 g. By adjusting the ethylene pressure to 0.8 MPa, M... n The value increased to 46,100, the molecular weight distribution was 1.36, and the polymer yield was 51.7g.

[0039] Therefore, even when using a composite solvent, if the catalyst is unsuitable and cannot produce a synergistic effect with the composite solvent, the polymer molecular weight will be too low and the yield will be poor. Even if the ethylene pressure is increased, the effect on improving the polymer molecular weight and yield is not significant.

[0040] Comparative Example 2

[0041] Compared to Example 1, the composite solvent was changed from methyl ethyl ketone to cyclohexanone, while the remaining steps were the same as in Example 1. The prepared ethylene-maleic anhydride alternating polymer had an M... n The molecular weight is 41,600, the molecular weight distribution is 1.33, and the polymer yield is 95.9g.

[0042] Example 2

[0043] A method for improving the yield of ethylene-maleic anhydride alternating copolymers includes the following steps:

[0044] (1) Dissolve phosphotungstic acid in deionized water and stir at 60°C to form an aqueous solution. Add the aqueous solution dropwise to dry SiO2 for impregnation. After the addition is complete, let stand for 10 h, then dry at 100°C, and then heat to 250°C at 5°C / min and keep warm for 2 h in a nitrogen atmosphere to obtain a polymerization catalyst. The mass-volume ratio of SiO2, phosphotungstic acid and deionized water is 100 g: 15 g: 100 mL.

[0045] (2) Add 500 mL of composite solvent, 12 mmol of free radical initiator, 1.5 mol of maleic anhydride and 10.0 g of polymerization catalyst to a high-pressure reactor, replace with nitrogen three times, introduce ethylene at a pressure of 0.3 MPa, react at an oil bath temperature of 60 °C for 2 h, and then discharge the remaining ethylene to obtain a milky white suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, wherein solvent A is toluene and solvent B is ethyl acetate.

[0046] (3) The suspension was filtered through a 200-mesh filter to obtain the polymerization catalyst and the suspension. After collecting the polymerization catalyst, the suspension was filtered and washed twice with ethanol to remove unreacted maleic anhydride. The washed solid was then vacuum dried to obtain ethylene-maleic anhydride polymer.

[0047] Polymer weight-average molecular weight (M) was measured by gel permeation chromatography (GPC). w ) and number-average molecular weight (M n The M of the ethylene-maleic anhydride polymer prepared in this example w For 70300, M n The yield was 58300, and the ethylene-maleic anhydride polymer yield was 138.1 g. 9.5 g of polymerization catalyst was collected.

[0048] Example 3

[0049] A method for improving the yield of ethylene-maleic anhydride alternating copolymers includes the following steps:

[0050] (1) Dissolve phosphotungstic acid in deionized water and stir at 60°C to form an aqueous solution. Add the aqueous solution dropwise to dry SiO2 for impregnation. After the addition is complete, let stand for 10 h, then dry at 100°C, and then heat to 250°C at 5°C / min and keep warm for 2 h in a nitrogen atmosphere to obtain a polymerization catalyst. The mass-volume ratio of SiO2, phosphotungstic acid and deionized water is 100 g: 15 g: 100 mL.

[0051] (2) Add 500 mL of composite solvent, 12 mmol of free radical initiator dicumyl peroxide, 1.5 mol of maleic anhydride and 10.0 g of polymerization catalyst to a high-pressure reactor, replace with nitrogen three times, introduce ethylene at a pressure of 0.3 MPa, react at an oil bath temperature of 50 °C for 5 h, and then discharge the remaining ethylene to obtain a milky white suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 9:1, wherein solvent A is toluene and solvent B is acetone.

[0052] (3) The suspension was filtered through a 200-mesh filter to obtain the polymerization catalyst and the suspension. After collecting the polymerization catalyst, the suspension was filtered and washed twice with ethanol to remove unreacted maleic anhydride. The washed solid was then vacuum dried to obtain ethylene-maleic anhydride polymer.

[0053] Polymer weight-average molecular weight (M) was measured by gel permeation chromatography (GPC). w ) and number-average molecular weight (M n The M of the ethylene-maleic anhydride polymer prepared in this example w For 90800, M nThe yield was 76,900, and the ethylene-maleic anhydride polymer production was 135.3 g. The collected polymerization catalyst was 9.7 g.

[0054] Example 4

[0055] A method for improving the yield of ethylene-maleic anhydride alternating copolymers includes the following steps:

[0056] (1) Dissolve phosphomolybdic acid in deionized water and stir at 50°C to form an aqueous solution. Add the aqueous solution dropwise to dry SiO2 for impregnation. After the addition is complete, let stand for 15 h, then dry at 100°C, and then heat to 200°C at 3°C / min and keep at 2.5 h in a nitrogen atmosphere to obtain a polymerization catalyst. The mass-volume ratio of SiO2, phosphomolybdic acid and deionized water is 100 g: 25 g: 100 mL.

[0057] (2) Add 500 mL of composite solvent, 15 mmol of free radical initiator benzoyl peroxide, 1.5 mol of maleic anhydride and 15 g of polymerization catalyst to a high-pressure reactor. Replace with nitrogen three times, introduce ethylene at a pressure of 0.8 MPa, react at an oil bath temperature of 60 °C for 2 h, and then discharge the remaining ethylene to obtain a milky white suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, wherein solvent A is xylene and solvent B is acetone.

[0058] (3) The suspension was filtered through a 200-mesh filter to obtain the polymerization catalyst and the suspension. After collecting the polymerization catalyst, the suspension was filtered and washed twice with ethanol to remove unreacted maleic anhydride. The washed solid was then vacuum dried to obtain ethylene-maleic anhydride polymer.

[0059] Polymer weight-average molecular weight (M) was measured by gel permeation chromatography (GPC). w ) and number-average molecular weight (M n The M of the ethylene-maleic anhydride polymer prepared in this example w It is 82800, M n The yield was 67,300, and the ethylene-maleic anhydride polymer was 164.9 g. The collected polymerization catalyst was 13.3 g.

[0060] Example 5

[0061] A method for improving the yield of ethylene-maleic anhydride alternating copolymers includes the following steps:

[0062] (1) Dissolve molybdenum silicoamic acid in deionized water and stir at 55°C to form an aqueous solution. Add the aqueous solution dropwise into dry SiO2 for impregnation. After the addition is complete, let stand for 12 h, then dry at 100°C, and then heat to 220°C at 4°C / min and keep warm for 2 h in a nitrogen atmosphere to obtain a polymerization catalyst. The mass-volume ratio of SiO2, molybdenum silicoamic acid and deionized water is 100g:20g:100mL.

[0063] (2) Add 500 mL of composite solvent, 10 mmol of azobisisobutyronitrile, 1.5 mol of maleic anhydride, and 15 g of polymerization catalyst to a high-pressure reactor. Replace the reactor with nitrogen three times, introduce ethylene at a pressure of 0.8 MPa, and react for 4 h at an oil bath temperature of 60 °C. Then discharge the remaining ethylene to obtain a milky white suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, wherein solvent A is cyclohexane and solvent B is ethyl acetate.

[0064] (3) The suspension was filtered through a 200-mesh filter to obtain the polymerization catalyst and the suspension. After collecting the polymerization catalyst, the suspension was filtered and washed twice with ethanol to remove unreacted maleic anhydride. The washed solid was then vacuum dried to obtain ethylene-maleic anhydride polymer.

[0065] Polymer weight-average molecular weight (M) was measured by gel permeation chromatography (GPC). w ) and number-average molecular weight (M n The M of the ethylene-maleic anhydride polymer prepared in this example w For 92200, M n The yield was 75800, and the ethylene-maleic anhydride polymer was 177.7 g. The collected polymerization catalyst was 13.1 g.

Claims

1. A method of increasing the yield of ethylene-maleic anhydride alternating copolymer, characterized by: The product is prepared by mixing maleic anhydride, a free radical initiator, and a polymerization catalyst in a composite solvent, and then introducing ethylene gas for free radical polymerization. The polymerization catalyst is obtained by supporting a heteropoly acid with SiO2 and then activating it. The activation involves heating the supported catalyst to 200℃~250℃ in a nitrogen atmosphere at a rate of 3~5℃ / min and holding it therefore for 2~3 hours. The heteropoly acid is phosphotungstic acid or phosphomolybdic acid. The composite solvent consists of solvent A and solvent B in a volume ratio of 7:3~9:1, wherein solvent A is one of toluene, xylene, and cyclohexane, and solvent B is one of ethyl acetate, acetone, and methyl ethyl ketone.

2. The method for improving the yield of ethylene-maleic anhydride alternating copolymers as described in claim 1, characterized in that: The supported catalyst is prepared by dissolving a heteropolyacid in deionized water, stirring at 50-60°C to form an aqueous solution, adding the aqueous solution dropwise into a dry support SiO2 for impregnation, allowing it to stand for 10-15 hours after the addition is complete, and then drying it.

3. A method for increasing the yield of ethylene-maleic anhydride alternating copolymers as described in claim 1 or 2, characterized in that: The free radical initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and dicumyl peroxide.

4. The method for improving the yield of ethylene-maleic anhydride alternating copolymers as described in claim 3, characterized in that: The amount of free radical initiator added to 1L of composite solvent is 20~30mmol, maleic anhydride is 3mol, and polymerization catalyst is 20~30g.

5. The method for improving the yield of ethylene-maleic anhydride alternating copolymers as described in claim 1, characterized in that: The free radical polymerization of ethylene is carried out at a pressure of 0.3~0.8MPa, a reaction temperature of 50~60℃, and a reaction time of 2~5h.

6. A method for improving the yield of ethylene-maleic anhydride alternating copolymers, characterized in that, Includes the following steps: (1) Dissolve the heteropoly acid in deionized water and stir at 50~60℃ to form an aqueous solution. Add the aqueous solution dropwise to dry SiO2 for impregnation. After the addition is complete, let it stand for 10~15 h, then dry it at 100℃, and then heat it to 200℃~250℃ at 3~5℃ / min and keep it for 2~3 h in a nitrogen atmosphere to obtain a polymerization catalyst. The heteropoly acid is phosphotungstic acid or phosphomolybdic acid. The mass-volume ratio of SiO2, heteropoly acid and deionized water is 100g:15~25g:100mL. (2) Add a composite solvent, free radical initiator azobisisobutyronitrile, maleic anhydride and polymerization catalyst to a high-pressure reactor, replace with nitrogen three times, introduce ethylene at a pressure of 0.3~0.8MPa, react at an oil bath temperature of 50~60℃ for 2~5h, then discharge the remaining ethylene to obtain a milky white suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 7:3~9:1, wherein solvent A is any one of toluene, xylene and cyclohexane, and solvent B is any one of ethyl acetate, acetone and methyl ethyl ketone. The ratio of maleic anhydride, free radical initiator, polymerization catalyst and composite solvent is 1.5mol:10~15mmol:10~15g:500mL; (3) The suspension was filtered through a 200-mesh filter to obtain the polymerization catalyst and the suspension. The suspension was then filtered and washed twice with ethanol to remove unreacted maleic anhydride. The washed solid was then vacuum dried to obtain ethylene-maleic anhydride polymer. The recovered polymerization catalyst could be reused after being washed with DMF.

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