Method for preparing dicarbamate based on waste electrolyte
The preparation of dicarboxylate by reacting waste electrolyte with diamine solves the toxicity and environmental pollution problems of traditional polyurethane synthesis, realizes the high-value utilization of waste electrolyte and the expansion of green synthesis process, and provides a stable intermediate for polyurethane synthesis.
Patent Information
- Application Number
- CN202511000917.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-21
- Publication Date
- 2025-10-31
AI Technical Summary
Traditional polyurethane synthesis methods suffer from high toxicity of raw materials and serious environmental pollution. Green synthesis processes are costly, have low performance, and are not scaled up. There is also insufficient high-value utilization of waste electrolytes, especially in the field of thermoplastic elastomers.
Dicarbamates were prepared by reacting waste electrolyte with diamines as intermediates for polyurethane synthesis, replacing traditional isocyanates. Stable dicarbamates were prepared by optimizing reaction conditions by adjusting the type of diamine and the ratio of catalysts.
This technology enables the high-value utilization of waste electrolytes, provides stable dicarboxylate for polyurethane synthesis, avoids the release of toxic gases, reduces production costs, and expands the application scope of green synthesis processes.
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Figure CN120865026A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fine chemical technology, and in particular relates to a method for preparing dicarboxylate based on waste electrolyte. Background Technology
[0002] Through long-term accumulation, the international polyurethane research field has established a comprehensive theoretical system and research methods. Current international research mainly focuses on two major synthesis routes: traditional synthesis processes and green synthesis processes, each forming unique technical paths and reaction mechanisms.
[0003] Traditional synthesis processes mainly employ techniques such as the "one-step method," "prepolymer method," and "semi-prepolymer method." Their core reaction mechanism involves the polycondensation reaction of the active functional groups (-N=C=O) of diisocyanates with polyester diols and polyether diols. Although this process has achieved mature industrial application, it still has significant drawbacks: isocyanate raw materials are extremely sensitive to moisture, releasing highly toxic gases upon contact with water. This not only increases safety production costs but also poses a potential threat to the ecological environment. Therefore, international research has shifted its focus to developing more environmentally friendly green synthesis methods.
[0004] Green synthesis processes (non-isocyanate methods) mainly include innovative routes such as the "carbamate method" and the "bicyclic carbonate method". By using diamine compounds to replace traditional isocyanate raw materials, safer and more environmentally friendly polyurethane synthesis is achieved.
[0005] Since the Industrial Revolution, pollutants emitted by gasoline-powered vehicles have exacerbated the greenhouse effect and climate change, posing serious challenges. Against this backdrop, zero-emission, pollution-free electric vehicles have become a global priority, and power battery technology is key to this transformation.
[0006] Organic solvents account for over 80% of lithium-ion batteries, mainly including dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), and propylene carbonate (PC). These carbonates are highly volatile, have low flash points, and are flammable, and are widely used as mainstream chemical raw materials. Therefore, recycling electrolytes has significant environmental, safety, and economic value.
[0007] With the rapid growth of the global new energy industry, especially the number of electric vehicles, the safe recycling of waste lithium batteries and the effective utilization of their high-value components have become increasingly prominent issues, posing a key constraint to the industry's sustainable development. Therefore, with the ever-increasing number of end-of-life lithium batteries, the recycling and high-value utilization of waste electrolytes is imperative.
[0008] In summary, the following core issues currently exist: traditional polyurethane synthesis routes suffer from technical problems such as high toxicity of raw materials, severe environmental pollution, difficulty in process control, and product limitations. Regarding the bicyclic carbonate synthesis mechanism in green synthesis processes, China is currently in the transition stage from pilot-scale production to industrialization. The synthesized polyurethane is mainly used in coatings and adhesives, rather than thermoplastic elastomers. Furthermore, the synthesis technology suffers from high production costs, low performance, lack of large-scale production systems, missing supporting industrial chains, and a shortage of necessary additives. The urethane synthesis mechanism studied in this invention is currently a blank in the domestic research and production fields. Summary of the Invention
[0009] The purpose of this invention is to provide a method for preparing diurethane based on waste electrolyte, so as to solve the problems of high toxicity, serious environmental pollution and high-value utilization of waste electrolyte in traditional polyurethane synthesis methods.
[0010] The objective of this invention is achieved as follows:
[0011] A method for preparing dicarbamates based on waste electrolyte, the specific steps of which are as follows:
[0012] Step 1: Weigh an appropriate amount of waste electrolyte, diamine, and catalyst, and add the above reactants to a dry Soxhlet extractor; add 4A molecular sieve to the extraction tube; purge with nitrogen for protection, and heat to 95-130℃, and continue the reaction for 6-8 hours; after the reaction is terminated, allow it to cool naturally, extract the product with hydrochloric acid until the solid is completely precipitated, wash with ethyl acetate, and then vacuum filter. Transfer the washed product to a vacuum drying oven to dry, and obtain crude dicarboxylate product.
[0013] Step 2: Add the obtained crude dicarboxylate product to an excess of alkaline solution to provide an alkaline environment for the purification of methyl dicarboxylate, and then add benzenesulfonyl chloride; stir thoroughly with a magnetic stirrer to allow the unreacted diamine to react with benzenesulfonyl chloride to form a salt, which is soluble in the alkaline solution. Dicarboxylate is insoluble in the alkaline solution, thus obtaining a turbid liquid; perform vacuum filtration on the turbid liquid, wash the filter residue with hydrochloric acid and ethyl acetate, and then perform vacuum filtration again. Transfer the washed product to a vacuum drying oven to dry, obtaining dicarboxylate.
[0014] Furthermore, the molar ratio of the waste electrolyte, diamine, and catalyst in step 1 is 4–16:1–1.5:0.01.
[0015] Further, the washing with ethyl acetate described in step 1 is followed by vacuum filtration, and the washing and filtration process is repeated three times.
[0016] After washing, the product was transferred to a vacuum drying oven and dried at 40°C for 12 hours.
[0017] Further, in step 2, the filter residue is washed with hydrochloric acid and ethyl acetate, and then vacuum filtered. The washing and filtration process is repeated three times. The washed product is then transferred to a vacuum drying oven and dried at 40°C for 12 hours.
[0018] Further, the diamine is at least one of 1,8-naphthyldiamine (1,8-NDA), p-phenylenediamine (1,4-PDA), and m-phenylenediamine (1,3-PDA).
[0019] Furthermore, the waste electrolyte is distilled under reduced pressure at 120℃~140℃ for 3h to obtain a low-boiling-point carbonate, and the carbonate is a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a mixture recovery rate of 85~92%.
[0020] Furthermore, the catalyst is an organic base, and the organic base is at least one of TBD, DBU and sodium methoxide, or the organic base is a mixture of TBD, DBU and sodium methoxide, with a molar ratio of TBD:DBU:sodium methoxide = 1~3:1~2:1~2.
[0021] Further, the dicarboxylate is at least one of 1,8-naphthalene dicarboxylate (1,8-MNDA), terephthalic dicarboxylate (1,4-MPDA), and m-phenylenediamine dicarboxylate (1,3-MPDA).
[0022] Compared with the prior art, the present invention has the following advantages:
[0023] The technical solution of this invention uses waste electrolyte to react with diamine to prepare dicarboxylate as an intermediate in the synthesis of polyurethane, which replaces the isocyanate used in the traditional process. The synthesized dicarboxylate is more stable than the isocyanate, is not sensitive to water, does not release toxic gases, and the performance of polyurethane can be adjusted by adjusting different diamines. Attached Figure Description
[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0025] Figure 1 The infrared spectrum of dicarbamate;
[0026] Figure 2Figure a shows the 1H NMR spectrum of dicarbamate; Figure b shows the 13C NMR spectrum of dicarbamate.
[0027] Figure 3 The graph shows the linear fit of the activation energy of dicarbamate. Detailed Implementation
[0028] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.
[0029] The main solution proposed in this invention is to use waste electrolyte as a raw material to react with diamine to prepare dicarboxylate. This method can be used as an upstream reaction in polyurethane synthesis to replace the isocyanate used in traditional processes. Moreover, the synthesized dicarboxylate is more stable than the isocyanate, is not sensitive to water, does not release toxic gases, and the performance of polyurethane can be adjusted by adjusting different diamines.
[0030] This invention provides a method for preparing dicarbamates based on waste electrolyte, the specific steps of which are as follows:
[0031] Step 1: Weigh an appropriate amount of waste electrolyte, diamine, and catalyst, and add the above reactants to a dry Soxhlet extractor; add 4A molecular sieve to the extraction tube; purge with nitrogen for protection, and heat to 95-130℃, and continue the reaction for 6-8 hours; after the reaction is terminated, allow it to cool naturally, extract the product with hydrochloric acid until the solid is completely precipitated, wash with ethyl acetate, and then vacuum filter. Transfer the washed product to a vacuum drying oven to dry, and obtain crude dicarboxylate product.
[0032] Step 2: Add the obtained crude dicarboxylate product to an excess of alkaline solution, and then add benzenesulfonyl chloride. Stir thoroughly with a magnetic stirrer to allow the unreacted diamine to react with benzenesulfonyl chloride to form a salt, which is soluble in the alkaline solution, while the dicarboxylate is insoluble in the alkaline solution, thus obtaining a turbid liquid. Vacuum filter the turbid liquid, wash the filter residue with hydrochloric acid and then with ethyl acetate, and then vacuum filter it. Transfer the washed product to a vacuum drying oven and vacuum dry it to obtain dicarboxylate.
[0033] Alternatively, an excess of alkali solution can ensure the purification effect of methyl dicarbamate.
[0034] Optionally, the molar ratio of the waste electrolyte, diamine, and catalyst in step 1 is 4–16:1–1.5:0.01.
[0035] Optionally, the product washed with ethyl acetate in step 1 is then vacuum filtered, and the washing and filtration process is repeated three times to ensure the purification effect. The washed product is then transferred to a vacuum drying oven and vacuum dried at 40°C for 12 hours.
[0036] Optionally, in step 2, the filter residue is first washed with hydrochloric acid and then with ethyl acetate, and then vacuum filtered. The washing and filtration process is repeated three times to ensure the purification effect. The washed product is then transferred to a vacuum drying oven and vacuum dried at 40°C for 12 hours.
[0037] Optionally, the diamine is at least one of 1,8-naphthyldiamine (1,8-NDA), p-phenylenediamine (1,4-PDA), and m-phenylenediamine (1,3-PDA).
[0038] Optionally, the waste electrolyte is distilled under reduced pressure at 120°C to 140°C for 3 hours to obtain a low-boiling-point carbonate, and the carbonate is a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a mixture recovery rate of 85% to 92%.
[0039] Optionally, the catalyst is an organic base, and the organic base is at least one of TBD, DBU and sodium methoxide, or the organic base is a mixture of TBD, DBU and sodium methoxide, with a molar ratio of TBD:DBU:sodium methoxide = 1~3:1~2:1~2.
[0040] Optionally, the dicarboxylate is at least one of 1,8-naphthalene dicarboxylate (1,8-MNDA), terephthalic dicarboxylate (1,4-MPDA), and m-phenylenediamine dicarboxylate (1,3-MPDA).
[0041] The specific embodiments of the present invention will be described in detail below:
[0042] Example 1
[0043] The waste electrolyte was distilled under reduced pressure at 120°C for 3 hours to obtain a low-boiling-point carbonate, which was a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a mixture recovery rate of 85%.
[0044] Example 2
[0045] The waste electrolyte was distilled under reduced pressure at 130°C for 3 hours to obtain a low-boiling-point carbonate, which was a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a mixture recovery rate of 89.6%.
[0046] Example 3
[0047] The waste electrolyte was distilled under reduced pressure at 140°C for 3 hours to obtain a low-boiling-point carbonate, which was a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a mixture recovery rate of 92%.
[0048] Example 4
[0049] The oven was adjusted to 110℃, and all glassware used in the experiment was dried for at least 24 hours. Waste electrolyte, 1,8-NDA, and catalyst were weighed according to a molar ratio of 4:1:0.001. TBD, DBU, and sodium formate in the catalyst were compounded in a 1:1:1 ratio. The reactants were added to a dried Soxhlet extractor. 4A molecular sieves were added to the extraction tube. Nitrogen gas was introduced for protection, and the temperature was raised to 95℃ and the reaction was continued for 8 hours. After the reaction was terminated, the mixture was allowed to cool naturally. The product was extracted with hydrochloric acid until the solid completely precipitated, washed with ethyl acetate, and then vacuum filtered. The washing and filtration were repeated. The washing and filtration process was repeated three times. The washed product was transferred to a vacuum drying oven and dried at 40°C for 12 hours to obtain crude 1,8-MNDA. The dried crude 1,8-MNDA was added to an excess of alkaline solution, and then benzenesulfonyl chloride was added. The mixture was stirred thoroughly with a magnetic stirrer to obtain a turbid liquid. The turbid liquid was vacuum filtered, and the filter residue was washed with hydrochloric acid and ethyl acetate, and then vacuum filtered again. The washing and filtration process was repeated three times. The washed product was transferred to a vacuum drying oven and dried at 40°C for 12 hours to obtain 1,8-naphthalenedicarbamate (1,8-MNDA).
[0050] Example 5
[0051] The oven was adjusted to 110℃, and all glassware used in the experiment was dried for at least 24 hours. Waste electrolyte, 1,4-PDA, and catalyst B were weighed according to a molar ratio of 8:1.25:0.01. TBD, DBU, and sodium formate in catalyst B were compounded in a ratio of 2:1.5:1.5. The above reactants were added to a dried Soxhlet extractor. 4A molecular sieves were added to the extraction tube. Nitrogen gas was introduced for protection, and the temperature was raised to 115℃ and the reaction was continued for 7 hours. After the reaction was terminated, the mixture was allowed to cool naturally. The product was extracted with hydrochloric acid until the solid completely precipitated, washed with ethyl acetate, and then vacuum filtered. The washing and filtration process was repeated three times. The washed product was transferred to a vacuum drying oven and dried at 40°C for 12 hours to obtain crude 1,4-MPDA. The dried crude 1,4-MPDA was added to an excess of alkaline solution, and then benzenesulfonyl chloride was added. The mixture was stirred thoroughly with a magnetic stirrer to obtain a turbid liquid. The turbid liquid was vacuum filtered, and the filter residue was washed with hydrochloric acid and ethyl acetate, and then vacuum filtered again. The washing and filtration process was repeated three times. The washed product was transferred to a vacuum drying oven and dried at 40°C for 12 hours to obtain terephthalic dicarboxylate (1,4-MPDA).
[0052] Example 6
[0053] The oven was adjusted to 110℃, and all glassware used in the experiment was dried for at least 24 hours. Waste electrolyte, 1,3-PDA, and catalyst B were weighed according to a molar ratio of 16:1.5:0.01. TBD, DBU, and sodium formate in catalyst B were compounded in a ratio of 3:2:2. The reactants were added to a dried Soxhlet extractor. 4A molecular sieves were added to the extraction tube. Nitrogen gas was introduced for protection, and the temperature was raised to 130℃ and the reaction was continued for 6 hours. After the reaction was terminated, the mixture was allowed to cool naturally. The product was extracted with hydrochloric acid until the solid completely precipitated, washed with ethyl acetate, and then vacuum filtered. The washing process was repeated. The washing and filtration process was repeated three times. The washed product was then transferred to a vacuum drying oven and dried at 40°C for 12 hours to obtain crude 1,3-MPDA. The dried crude 1,3-MPDA was added to an excess of alkaline solution, followed by the addition of benzenesulfonyl chloride. The solution was stirred thoroughly with a magnetic stirrer to obtain a turbid liquid. The turbid liquid was then vacuum filtered, and the filter residue was washed with hydrochloric acid and ethyl acetate before being vacuum filtered again. The washing and filtration process was repeated three times. The washed product was then transferred to a vacuum drying oven and dried at 40°C for 12 hours to obtain m-phenylenedicarbamate (1,3-MPDA).
[0054] Depend on Figure 1 It can be seen that in the above reaction products, 3200 cm⁻¹ is an imino group, 2850 cm⁻¹ is a methoxy group single peak, 1720 cm⁻¹ is an ester group C=O, and 1050 cm⁻¹ and 1250 cm⁻¹ are ester group CO. The above test results indicate that the product is the target product.
[0055] Depend on Figure 2 As can be seen, the molecular formulas on the left, from top to bottom, are 1,8-MNDA, 1,4-MPDA, and 1,3-MPDA. In Figure a, the characteristic hydrogen peak of methyl groups is present at 3.56 ppm, and the peak area is the largest. Due to their different symmetrical structures, the number of hydrogen characteristic peaks of the three dicarboxylate esters is consistent with the expected structure. In Figure b, the characteristic peak at 150 ppm changes little, but gradually moves to the lower frequency region with the change of cyclic groups and substituent sites within the structure.
[0056] The yield f of three different diamines reacting at different temperatures was fitted with time t to obtain the reaction rate constant k of the three diamines. The result was obtained by fitting 1 / T to k. Figure 3 .
[0057] Depend on Figure 3 It can be seen that the activation energies E of 1,8-NDA, 1,4-PDA, and 1,3-PDA are... a The activation energies were 55.8 kJ / mol, 54.2 kJ / mol, and 68.7 kJ / mol, respectively. 1,4-PDA and 1,3-PDA have the same molecular weight, but different activation energies. This indicates that structural differences may affect the reaction energy barrier. 1,3-PDA has the highest activation energy, indicating that its reaction is more sensitive to temperature. 1,4-PDA has the lowest activation energy, indicating that its reaction is the easiest to proceed.
[0058] The theoretical molar ratio for preparing dicarboxylate by reacting carbonates with low-boiling-point substances from waste electrolyte is 2:1. However, since the generated byproduct, a small-molecule alcohol, undergoes azeotropy with the low-boiling-point substance at the reaction temperature, the actual reaction process should increase the reaction ratio. Through several experiments, it was found that when the ratio of low-boiling-point substance to diamine reaches 4:1, the yield of dicarboxylate increases significantly. Considering the differences in the types of diamine, it was found that the yield of dicarboxylate reaches saturation when the ratio reaches 8–16:1.
[0059] Similarly, after several experiments, it was found that when the molar ratio of the three components in the compound catalyst is TBD:DBU:sodium methoxide = 1~3:1~2:1~2, the catalytic effect and subsequent washing can be satisfactory. If the proportion of TBD is too high, the production cost will increase; if the proportion of DBU is too high, the cost of subsequent hydrochloric acid washing will increase; if the proportion of sodium methoxide is too low, the alkaline environment in the reaction process will be insufficient, and the catalytic effect will be poor.
[0060] In summary, the three diamines selected in this invention can successfully react with waste electrolyte to obtain the corresponding dicarbamates, and their structures do not contain isocyanate functional groups. Therefore, it can be concluded that dicarbamates can be prepared by reacting diamines with waste electrolyte as substitutes for isocyanates in the synthesis of polyurethane. This method not only achieves the high-value utilization of waste electrolyte, but also takes into account the green synthesis of polyurethane and achieves the goal of finding substitutes for isocyanates.
[0061] This invention relates to a method for preparing dicarboxylate based on waste electrolyte. The invention utilizes low-boiling-point substances in waste electrolyte to react with diamines via a carbamate reaction mechanism to synthesize dicarboxylate, providing a new approach for the synthesis of downstream thermoplastic elastomer polyurethanes. It fills a gap in the domestic non-isocyanate production field and simultaneously solves the problems of toxicity, high production costs, and lack of additives in existing polyurethane processes, as well as the issues of waste electrolyte recycling and high-value utilization. It can be used in the industrial production of non-isocyanate polyurethanes.
[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing dicarboxylate based on waste electrolyte, characterized in that, The specific steps are as follows: Step 1: Weigh appropriate amounts of waste electrolyte, diamine, and catalyst, and add the above reactants to a dry Soxhlet extractor; add 4A molecular sieve to the extraction tube; Nitrogen gas was introduced for protection, and the temperature was raised to 95-130℃ and the reaction was continued for 6-8 hours. After the reaction was terminated, the temperature was naturally lowered, and the product was extracted with hydrochloric acid until the solid was completely precipitated. The product was washed with ethyl acetate and then vacuum filtered. The washed product was transferred to a vacuum drying oven and dried to obtain crude dicarboxylate product. Step 2: Add the obtained crude dicarboxylate product to an excess of alkaline solution to provide an alkaline environment for the purification of methyl dicarboxylate, and then add benzenesulfonyl chloride; use a magnetic stirrer to stir thoroughly so that the unreacted diamine reacts with benzenesulfonyl chloride to form a salt, which is soluble in the alkaline solution. Dicarboxylate is insoluble in the alkaline solution, thus obtaining a turbid solution. The turbid liquid was vacuum filtered, and the filter residue was washed with hydrochloric acid and ethyl acetate, and then vacuum filtered again. The washed product was transferred to a vacuum drying oven and dried to obtain dicarboxylate.
2. The method for preparing dicarboxylate based on waste electrolyte according to claim 1, characterized in that, The molar ratio of the waste electrolyte, diamine, and catalyst mentioned in step 1 is 4-16:1-1.5:0.
01.
3. The method for preparing dicarboxylate based on waste electrolyte according to claim 1, characterized in that, The product described in step 1 is washed with ethyl acetate and then vacuum filtered. The washing and filtration process is repeated three times. After washing, the product is transferred to a vacuum drying oven and dried at 40°C for 12 hours.
4. The method for preparing dicarboxylate based on waste electrolyte according to claim 1, characterized in that, In step 2, the filter residue is washed with hydrochloric acid and ethyl acetate, and then vacuum filtered. The washing and filtration process is repeated three times. The washed product is then transferred to a vacuum drying oven and dried at 40°C for 12 hours.
5. The method for preparing dicarboxylate based on waste electrolyte according to claim 1, characterized in that, The diamine is at least one of 1,8-naphthyldiamine (1,8-NDA), p-phenylenediamine (1,4-PDA), and m-phenylenediamine (1,3-PDA).
6. The method for preparing dicarboxylate based on waste electrolyte according to claim 1, characterized in that, The waste electrolyte is distilled under reduced pressure at 120℃ to 140℃ for 3 hours to obtain a low-boiling-point carbonate, and the carbonate is a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a mixture recovery rate of 85% to 92%.
7. The method for preparing dicarboxylate based on waste electrolyte according to claim 1, characterized in that, The catalyst is an organic base, and the organic base is at least one of TBD, DBU and sodium methoxide, or the organic base is a mixture of TBD, DBU and sodium methoxide, with a compound molar ratio of TBD:DBU:sodium methoxide = 1~3:1~2:1~2.
8. The method for preparing dicarboxylate based on waste electrolyte according to claim 1, characterized in that, The dicarboxylate is at least one of 1,8-naphthalene dicarboxylate (1,8-MNDA), p-phenylenediamine dicarboxylate (1,4-MPDA), and m-phenylenediamine dicarboxylate (1,3-MPDA).