Description:TITLE OF THE INVENTION

“SYNTHESIS OF A NEW CLASS OF TETRAAMINE MONOMER TO OBTAIN POLYBENZIMIDAZOLE-BASED MEMBRANE FOR PEM/AEM”

FIELD OF THE INVENTION
[0001] The present invention relates to the field of polymer chemistry and advanced materials. Specifically, the invention relates to a method for synthesizing a class of Piperidine-based tetramine monomer, called as PIP-TAB, with high purity and easy accessibility. More specifically, the invention relates to a simple, cost effective and industrially scalable process for synthesizing structurally modified piperidine-based polybenzimidazole polymer membranes by polymerisation of PIP-TAB monomer and different dicarboxylic acids monomers, which can be used in Proton Exchange Membrane Fuel Cells (PEMFCs) and Anion Exchange Membrane Fuel Cells (AEMFCs).
BACKGROUND OF THE INVENTION
[0002] Polybenzimidazole (PBI) was first synthesized by Vogel et al. in 1961 (J. Polym. Sci. 1961, 50, 511) and has since been recognized for its amorphous, high molecular weight, thermal stability, and resistance to oxidative and hydrolytic annihilation. These exceptional properties have made PBIs a preferred material in various advanced applications such as fuel cells, and water electrolyzers (Adv. Polym. Sci. 1982, 47, 1−42; Adv. Polym. Sci. 2008, 216, 63−124). The formed PBIs can be transformed into membranes with extremely favourable physical characteristics. The most often used tetraamine for producing PBI is 3,3',4,4'-tetraaminobiphenyl (TAB), this PBI is termed as poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole which is prepared by polycondensation of Tetramine-Based Monomers (TAB) with several dicarboxylic acids (DCAs) (Polym. 2009, 5, 145−169; Dawkins, B. G.; Baker, J. D. U.S. Patent US20080207869, 2008; Choe, E. W.; Conciatori, A. B. European Patent EP115945, 1984.). TAB remains the primary tetraamine monomer for synthesizing commercial PBI, raising questions regarding its exclusivity and lack of viable alternatives.
[0003] Attempts to replace TAB have been reported in literature; however, these efforts have been largely unsuccessful, as the resulting PBIs did not demonstrate significant advantages over conventional TAB-derived PBIs (Macromol. Chem. Phys. 1997, 198, 619425; Chem. Lett. 2010, 21, 976−978).

[0004] Furthermore, the procedure for TAB synthesis is quite complex, making it difficult to obtain. Also, the conventional TAB is carcinogenic, quite expensive and challenging to obtain in high purity (100% pure), posing major limitations for industrial applications. Further, the solubility of PBI-based polymers obtained from conventional TABs depends on the Dicarboxylic Acids (DCAs) structure. For that a lot of efforts have been made to modify DCAs, rather than redesigning the TAB structure itself. Later, in 2003, Yang and co-workers developed pyridine-bridged tetraamine (PyTAB), an alternative to TAB, which forms a PyPBI polymer that resolves solubility issues and introduced membrane homogeneity. However, PyTAB remains economically impractical, requiring multi-step synthesis with high production costs.

[0005] Despite their drawbacks, both conventional PBIs and PyPBIs have gained wider recognition due to the realization that phosphoric acid (PA)-loaded membranes are the most suitable choice for meeting the stringent requirements of fuel cells, while anion exchange membranes require enhanced alkaline media for stability. PyPBI has demonstrated higher PA retention than conventional PBIs, owing to its additional nitrogen content, yet cost and scalability concerns remain unresolved.

DRAWBACKS OF THE KNOWN PRIOR ART
[0006] Conventional polybenzimidazole (PBI), including PBI and PyPBI, are recognized for their remarkable thermal stability and resistance to oxidative/alkaline environments, making them suitable for demanding applications such as fuel cells and water electrolyzers. Despite these advantages, the existing procedures for making TAB and PyTAB are complex and tedious that hinders their industrial scalability and efficiency. Further, the synthesis of TAB and PyTAB, which are commonly used tetraamine monomers for PBI production, involves complex and multi-step procedures, making it difficult to obtain 100% pure TAB. This laborious process not only reduces overall yield but also increases manufacturing costs, making TAB-based PBIs economically unviable for large-scale applications.

[0007] While PyPBI has demonstrated improved solubility in high-boiling solvents but conventional TAB-based PBIs still struggle with solubility issues, limiting their compatibility with various dicarboxylic acids (DCAs) (Macromol. 2007, 40, 7487− 7492; Macromol. 2006, 39, 9409−9418). Despite extensive research focused on modifying DCA structures, very few efforts have explored changing the TAB backbone itself, which remains a bottleneck in optimizing polymer processability.

[0008] Additionally, the multistep synthesis required for TAB and PyTAB makes it challenging to achieve high yields, further limiting its commercial feasibility. Furthermore, after each synthetic step, the obtained products require frequent purification, typically through solvent washing, to eliminate residual reactants. However, even after thorough washing with solvents, impurities remains that can interfere with polymerization, leading to suboptimal performance and material losses, reducing the final yield. Other drawback includes obtaining commercial TABs are not economically viable.

[0009] Therefore, there is an increasing demand for the development of a synthesis method for a type of PBI (Pip-PBI) that minimizes the number of synthetic steps, is cost-effective, is economically viable and exhibits high tolerance to alkaline media.
OBJECTIVE OF THE INVENTION
[0010] An objective of the present invention is to develop a simple, cost-effective and scalable method for synthesizing a Piperidine-based tetramine monomer (Pip-TAB).

[0011] Another objective of the present invention is to provide a Piperidine-based tetramine monomer (Pip-TAB) that exhibits high compatibility with various dicarboxylic acid (DCA) configurations, enabling the formation of diverse high-performance polymers.

[0012] Another objective of the present invention is to develop a Piperidine-based tetramine monomer (Pip-TAB) with enhanced nitrogen content, enabling increased phosphoric acid (PA) loading for improved proton conductivity in proton exchange membrane fuel cells (PEMFCs), while also facilitating the creation of multi-cation sites for efficient anion transport in anion exchange membrane fuel cells (AEMFCs).

[0013] Another objective of the present invention is to develop a method for synthesizing Piperidine-based tetramine monomer (Pip-TAB) with enhanced yield, economically viability and reduced number of steps.

[0014] Another objective of the present invention is to develop a process for synthesizing Pip-TAB based polymers named as Pip-OPBI having Formula III, BP-Pip-PBI having Formula IV and TP-Pip-PBI having Formula V, from tetramine product PIP-TAB.

[0015] The foregoing and other objects, features, and advantages of the present invention will become readily apparent upon further review of the following overview and description of the preferred embodiment as illustrated in the accompanying drawings.
SUMMARY OF THE INVENTION
[0016] This section provides a general summary of the disclosure and is not meant to be a comprehensive disclosure of the full scope of all its features.

[0017] In an aspect, the present invention provides a process for synthesizing a piperidine-based tetraamine monomer (Pip-TAB) having Formula II, comprising the following steps:
a) treating 5-fluoro-2-nitroaniline with 1,3-di(piperidin-4-yl) propane in the presence of a strong base and an organic solvent to obtain 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I.

b) reducing the obtained 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I with a reducing agent in the presence of an organic solvent under an ambient condition to obtain 4,4'-(propane-1,3-diylbis(piperidine-4,1-diyl)) bis(benzene-1,2-diamine) (Pip-TAB) having Formula II.

[0018] In an embodiment, treating the 1, 3-di(piperidin-4-yl) propane with the 5-fluoro-2-nitroaniline in the presence of strong base and the organic solvent is performed at a temperature ranges from 100°C to 150°C.

[0019] In an embodiment, reducing the 5-5’-(propane-1, 3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I with the reducing agent in the presence of the organic solvent is performed at a temperature ranges from 250C to 800C.

[0020] In an embodiment, the organic solvent is selected from a group comprising: N-Methyl-2-Pyrrolidone (NMP), Dimethylformamide (DMF), Dimethyl Sulfoxide (DMSO) or a combination thereof.

[0021] In an embodiment, the strong base is selected from a group comprising: N, N-Diisopropylethylamine (DIPEA), 4-Dimethylaminopyridine (DMAP), Triethyl amine (NEt3) or Tributyl amine (NBu3).

[0022] In a preferred embodiment, the organic solvent comprises N-Methyl-2-Pyrrolidone (NMP), or Dimethylformamide (DMF), and the strong base comprises triethyl amine (NEt3).

[0023] In an embodiment, the reducing agent is selected from iron (Fe), zinc (Zn), or tin (Sn), in the presence of an acid such as hydrochloric acid (HCl); or, using a noble metal selected from palladium (Pd), platinum (Pt), or nickel (Ni) in the presence of hydrogen gas.

[0024] In another aspect, the present invention provides a process for synthesizing Pip-TAB based polymers named as Pip-OPBI having Formula III, BP-Pip-PBI having Formula IV and TP-Pip-PBI having Formula V, the process comprises the following steps:
1. Polymerising the Pip-TAB through polycondensation reaction with dicarboxylic acid, named 4,4'-oxybisbenzoic acid (OBA), using polyphosphoric acid (PPMA) as a catalyst under inert conditions to obtain a Pip-OPBI polymer having Formula III.

[0025] In an embodiment, the polymerization is performed at a temperature ranges from 50°C to 150°C for 48 h.
2. Polymerising the Pip-TAB through polycondensation reaction with dicarboxylic acid, named 1,1'-biphenyl-4,4'-dicarboxylic acid (BP-COOH), using PPMA as a solvent cum catalyst under inert conditions to obtain a BP-PIP-PBI polymer having Formula IV.

[0026] In an embodiment, the polymerization is performed at a temperature ranges from 50°C to 140°C for 48 h.
3. Polymerising the Pip-TAB through polycondensation reaction with dicarboxylic acid, named terephthalic acid (TP-COOH), using polyphosphoric acid (PPMA) as a solvent cum catalyst under inert conditions to obtain a TP-PIP-PBI having polymer Formula V.

[0027] In an embodiment, the polymerization is performed at a temperature ranges from 50°C to 140°C for 48 h.

[0028] In an embodiment, a molar ratio of Pip-TAB: DCA is 1:1.

[0029] Other features, benefits, and advantages of the present invention will be apparent upon a review of the present disclosure, including the specification, abstract, and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings or figures, of which:

[0031] Figure 1 illustrates a 1H-NMR spectrum of 5-5’-(propane-1, 3-diylbis(piperidine-4,1-diyl) bis (2-nitroaniline) having Formula I, in accordance with an embodiment of the invention.

[0032] Figure 2 illustrates a 13C-NMR spectrum of 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I, in accordance with an embodiment of the invention.

[0033] Figure 3 illustrates a HRMS of 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I, in accordance with an embodiment of the invention.

[0034] Figure 4 illustrates a crystal structure of 5-5’-(propane-1, 3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I, in accordance with an embodiment of the invention.

[0035] Figure 5 illustrates a 1H-NMR spectra of 4’4-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(benzene-1,2-diamine) having Formula II, in accordance with an embodiment of the invention.

[0036] Figure 6 illustrates a 13C-NMR spectra of 4’4-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(benzene-1,2-diamine) having Formula II, in accordance with an embodiment of the invention.

[0037] Figure 7 illustrates a HRMS of 4’4-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(benzene-1,2-diamine) having Formula II, in accordance with an embodiment of the invention.

[0038] Figure 8 illustrates a thermogravimetric analysis (TGA) curve of PIP-NO2 (Formula I) and PIP-NH2 (Formula II), in accordance with an embodiment of the invention.

[0039] Figure 9 illustrates a Differential Scanning Calorimetry (DSC) curve of PIP-NO2 (Formula I) and PIP-NH2 (Formula II), in accordance with an embodiment of the invention.

[0040] Figure 10 illustrates 1H-NMR spectra of PIP-OPBI having Formula III, BP-PIP-PBI having Formula IV, TP-PIP-PBI having Formula V, in accordance with an embodiment of the invention.

[0041] Figure 11 illustrates a Fourier Transform Infrared Spectroscopy (FTIR) of PIP-TAB, PIP-OPBI, BP-PIP-PBI and TP-PIP-PBI, in accordance with an embodiment of the invention.

[0042] Figure 12 illustrates the TGA curve of PIP-OPBI having Formula III, BP-PIP-PBI having Formula IV, TP-PIP-PBI having Formula V, in accordance with an embodiment of the invention.

[0043] Figure 13 illustrates a stress-strain profile of PIP-OPBI having Formula III, BP-PIP-PBI having Formula IV, TP-PIP-PBI having Formula V, in accordance with an embodiment of the invention.

[0044] Figure 14 illustrates a pictorial representation of membrane fabrication, in accordance with an embodiment of the invention.

[0045] Figure 15 illustrates pictorial representation of synthesized pipedine based polymer membranes-PIP-OPBI, BP-PIP-PBI and TP-PIP-PBI, in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0046] The following description discloses the preferred embodiments of the present invention. However, it will be clear from this description of the invention that the invention is not limited to these illustrated embodiments but may include a variety of modifications and embodiments thereto. Therefore, the present description should be seen as illustrative and not limiting.

[0047] Below is a description of various embodiments of the invention. Before describing selected embodiments of the present disclosure in detail, it is to be understood that the present invention is not limited to any embodiment described herein. The disclosure and description herein are illustrative and explanatory of one or more presently preferred embodiments and variations thereof, and it will be appreciated by those skilled in the art that various changes in the structures, materials or characteristics which may be made without departing from the spirit of the invention. Those of ordinary skill in the art can readily use the present application as a basis for designing or modifying derivatives to achieve the same objectives and/or the same advantages as the embodiments herein. It is also to be understood by those of ordinary skill in the art that these equivalent examples do not depart from the spirit and scope of the present application. Although the methods disclosed herein have been described with reference to the specific operations that are carried out in a specific order, it should be understood that these operations can be combined, subdivided, or reordered to form an equivalent method without departing from the teachings of the present application.

[0048] At the outset, for ease of reference, certain terms used in this application and their meanings as used in this context are set forth. To the extent a term used herein is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Further, the present techniques are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments, and terms or techniques that serve the same or a similar purpose are considered to be within the scope of the present claims.

[0049] The articles “a” and “an” as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of “a” and “an” does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used. The adjective “any” means one, some, or all indiscriminately of whatever quantity.

[0050] It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

[0051] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0052] As used herein, the term "or" includes "and/or" and the term "and/or" includes any and all combinations of one or more of the associated listed items. Expressions such as "at least one of," when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

[0053] The present invention relates to a simplified, cost-effective, industrially scalable and economically feasible process for the synthesis of a class of TAB, named as piperidine-based tetraamine monomer (PIP-TAB) and its polymerization with different dicarboxylic acids (DCAs) to form various polymers to make high performance membrane such as Proton Exchange Membrane/ Anion Exchange Membrane (PEM/AEM) in fuel cell applications. Unlike conventional polybenzimidazoles (PBIs), the monomer design of PIP-TAB of the present invention incorporates multiple nitrogen atoms, which significantly enhances phosphoric acid (PA) and potassium hydroxide (KOH) loading within the monomer, which brings more PA/KOH leading to superior proton and anion conductivity, and making PEM/AEMs in a much cheaper way than the conventional PBIs.

[0054] The synthesis process is simplified, featuring reduced number of steps, while maintaining cost-effectiveness, and scalability, which makes Pip-TAB a good alternative to existing TAB-based PBIs. This approach ensures higher efficiency, greater membrane stability, and reduced production costs, making it highly suitable for fuel cell applications.

[0055] In an aspect of the present invention, a process for synthesizing a piperidine-based tetraamine monomer (PIP-TAB) is disclosed. The process comprises the following two steps: a) Formation of Formula I; and b) Reduction of Formula I to obtain PIP-TAB of Formula II.

[0056] In step (a), the process begins with the formation of Formula I, wherein 5-fluoro-2-nitroaniline undergoes a nucleophilic aromatic substitution reaction with 1,3-di(piperidin-4-yl) propane. This reaction takes place in the presence of a strong base and an organic solvent at a temperature ranges from 100°C to 150 °C for 24-30h to produce 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) of Formula I.

Formula I

[0057] In an embodiment, the structure of Formula I contains one NO2 and one NH2 group at both the terminal.

[0058] In an embodiment, the strong base is selected from the group comprising: N, N-Diisopropylethylamine (DIPEA), 4-Dimethylaminopyridine (DMAP), Triethyl amine (NEt3) or Tri-n-butylamine (NBu3). In a preferred embodiment, the strong base includes triethyl amine (NEt3).

[0059] In an embodiment, the organic solvents include a polar aprotic solvent, selected from the group comprising: dimethyl sulphoxide (DMSO), dimethyl formamide (DMF) or N-methyl-2-pyrrolidone (NMP) or a combination thereof. In a preferred embodiment, the organic solvent comprises NMP or DMF.

[0060] In another embodiment, a molar ratio of 5-fluoro-2-nitroaniline, 1,3-di(piperidin-4-yl) propane, and triethylamine is maintained within a range of 1:0.5:1.96.

[0061] In step (b), the process involves reduction of piperidine based nitro product- 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) of Formula I obtained in step (a), in an organic solvent, in the presence of a reducing agent at temperature ranges from 250C to 800C to obtain corresponding piperidine based tetra amine compound (PIP-TAB) 4,4'-(propane-1,3-diylbis(piperidine-4,1-diyl))bis(benzene-1,2-diamine) of formula II.

Formula II
[0062] In an embodiment, the organic solvent to carry out the reduction reaction comprises high boiling point polar aprotic solvents, selected from the group comprising: dimethyl sulphoxide (DMSO), dimethyl formamide (DMF), N-methyl-2-pyrrolidone (NMP) or a combination thereof.

[0063] In an embodiment, the reducing agent is selected from a group comprising: a metal (iron-Fe, zinc-Zn, or tin-Sn) in the presence of an acid such as hydrochloric acid (HCl); or a noble metal selected from palladium (Pd), platinum (Pt), or nickel (Ni) in the presence of hydrogen gas.

[0064] In an embodiment, the reducing agent comprises a combination of metal and hydrogen gas.

[0065] In an embodiment, a molar ratio of PIP-TAB and Pd/C is maintained within a range of 1:0.03 to 1:0.045.

[0066] In an embodiment, the reduction reaction of Formula I to obtain Formula II is performed at a temperature ranges from 300C to 80 0C for 24h to 70h, preferably at a temperature ranges from 300C to 500C over a reaction period of 30 h to 48 h.

[0067] In another aspect, the present invention provides a process for synthesizing Pip-TAB based polymers such as Pip-OPBI has Formula III, BP-Pip-PBI having Formula IV and TP-Pip-PBI having Formula V from tetramine product PIP-TAB.

[0068] The process comprises polymerization of 4,4'-(propane-1,3-diylbis(piperidine-4,1-diyl)) bis(benzene-1,2-diamine) (PIP-TAB) monomer having Formula II with various di-carboxylic acids (DCAs), including OBA, BP-COOH, and TP-COOH, resulting in the formation of structurally modified piperidine based polybenzimidazole polymer membranes.

[0069] In an embodiment, the tetramine product-PIP-TAB monomer of Formula II, obtained in the first aspect of the invention, undergoes polymerization reaction with 4,4’-oxybis benzoic acid (OBA), a di-carboxylic acid, in the presence of a solvent under a nitrogen atmosphere at a temperature ranges from 50°C to 150°C to obtain Pip-OPBI polymer having Formula III.


Formula III

[0070] In an embodiment, the solvent used for the polymerization reaction comprises a mixture of dehydrating agent and a strong acid, wherein the strong acid is selected from polyphosphoric acid or methane sulfonic acid, functioning as solvent cum catalyst.

[0071] In an embodiment, the di carboxylic acid comprises commercially available 4, 4’-oxybis benzoic acid (OBA).

[0072] In an embodiment, the reaction is carried out over a period of 24h-48h, wherein the temperature is gradually increased from ambient conditions to a high temperature range of about 120°C to 150°C.

[0073] In an embodiment, a molar ratio of Pip-TAB to OBA is 1:1, while the ratio of Pip-TAB to PPMA is taken as 1mol:4mL in the polymerization reaction.

[0074] In another embodiment, a biphenyl containing dicarboxylic acid such as 1,1'-biphenyl-4,4'-dicarboxylic acid (BP-COOH) undergoes polymerization reaction with the 4,4'-(propane-1,3-diylbis(piperidine-4,1-diyl)) bis(benzene-1,2-diamine) (PIP-TAB) monomer having Formula II (obtained in the first aspect of the invention) in the presence of a solvent under a nitrogen atmosphere. This reaction is performed at a temperature ranges from 50°C to 140°C to obtain BP-PIP-PBI polymer having Formula IV.

[0075] In an embodiment, the solvent used for the polymerization reaction comprises a mixture of dehydrating agent and strong acid, wherein the strong acid is selected from polyphosphoric acid (PPA) or methane sulfonic acid (MSA) or a super acid such as triflic acid, functioning as solvent cum catalyst.

[0076] In an embodiment, the di carboxylic acid comprises commercially available 1,1'-biphenyl]-4,4'-dicarboxylic acid (BP-COOH).

[0077] In an embodiment, the reaction is carried out over a period of 24h-48h, wherein the temperature is gradually increased from ambient conditions to high temperature ranges of about 130°C to 140°C.

[0078] In an embodiment, a molar ratio of Pip-TAB to BP-COOH is 1:1, while the ratio of Pip-TAB to acid solvent is taken as 1mol:3mL.

[0079] In another embodiment, a phenyl ring containing di-carboxylic acid such as terephthalic acid (TP-COOH) undergoes polymerization reaction with the 4,4'-(propane-1,3-diylbis(piperidine-4,1-diyl)) bis(benzene-1,2-diamine) (PIP-TAB) monomer having Formula II (obtained in the first aspect of the invention) in the presence of acidic solvent under a nitrogen atmosphere. The reaction is carried out at a temperature ranges from 500C to 1400C to obtain TP-PIP-PBI polymer having Formula V.

[0080] In an embodiment, the acidic solvent used for the polymerization reaction comprises a mixture of dehydrating agent and an acid, wherein the acid is selected from polyphosphoric acid (PPA) or methane sulfonic acid (MSA) or a super acid such as triflic acid, functioning as solvent cum catalyst.

[0081] In an embodiment, the di carboxylic acid comprises commercially available terephthalic acid (TP-COOH).

[0082] In an embodiment, the reaction is carried out over a period of 24h-48h, wherein the temperature is gradually increased from ambient conditions to high temperature ranges of about 130°C to 140°C.

[0083] In an embodiment, a molar ratio of Pip-TAB to TP-COOH is 1:1, while the ratio of Pip-TAB to acidic solvent is taken as 1mol:3mL.

[0084] In an embodiment, polymerization includes a polycondensation reaction.

[0085] In an embodiment, the synthetic process of the present invention provides good to exceptional yields of Pip-TAB, which consists of two step procedures and the formation of polymers from Pip-TAB with different DCAs which includes OBA, BP-COOH, and TP-COOH. Furthermore, it is easier to scale up the synthesis process of Pip-TAB to an industrial scale due to its lower operating costs.

[0086] EXAMPLES

[0087] The following examples are provided to illustrate and further elucidate aspects of the present invention. These examples serve to exemplify the invention; however, they should not be construed as limiting its scope in any manner.

[0088] EXAMPLE 1: Synthesis of 5-5’-(propane-1, 3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I

[0089] 5-fluoro-2-nitroaniline (12.8 mmol), 1,3-di(piperidin-4-yl) propane (6.4 mmol) were dissolved in dry NMP (228.5, 22 mL) at room temperature (30 °C) in a sealed 50 mL tube. After its complete dissolution, triethyl amine (25 mmol, 3 mL) was added to the reaction mixture. Finally, the reaction contents were left for stirring for 24 h at the temperature of 100 - 150°C to complete the reaction. After 24 h, the reaction mixture was cooled to room temperature and was transferred in water for precipitation. Bright yellow colour precipitate was washed thoroughly with water several times and then it was dried in vacuum oven at 70°C. The obtained solid (5-5’-(propane-1, 3-diylbis (piperidine-4,1-diyl) bis(2-nitroaniline)) was used for the next step reaction without any further purification. Yield: 96.8%, 1H-NMR (400 MHz, DMSO-d6) δ 7.75 (d, 1H), 7.25 (s, 2H), 6.41 (d, 1H), 6.21(d, 1H), 3.95 (t, 2H), 2.95 (t, 2H) 1.68 (d, 2H), 1.52 (m, 2H), 1.36 (m, 1H), 1.18 (q, 2H), 1.06 (q, 2H), 13C-NMR (101 MHz, DMSO-d6) δ 155 , 149 , 127 , 122 , 105 , 95 , 45 , 38.3 , 37.2 , 39.42 , 31 , 22. HRMS-ESI (+) calc. Molecular mass for: 482.26: Observed value (m/z): 483.27.
Table 1:
Sample code PIP-NO2
Empirical formula C25 H34 N6 O4
Formula weight 482.26
Crystal system Triclinic
Space group P-1
a (Å) 13.5838(5)
b(Å) 15.0691(6)
c(Å) 20.6920(6)
α (°) 93.409(3)
β (°) 98.243(3)
γ (°) 116.669(4)
Volume/(Å3) 3709.0(2)
Z 6
Dcalcd [mg m-3] 1.296
Temperature (K) 293(2)
Reflections collected 48602
Independent reflections 13029 [R(int) = 0.0530]
Data / restraints / parameters 13029 / 11 / 994
F(000) 1548
Final R indices [I>2σ (I)] R1 = 0.0705, wR2 = 0.1717
R indices (all data) R1 = 0.2246, wR2 = 0.2294
GoF 0.888

Table: 1 Crystallographic data and structure refinement for 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) (PIP-NO2) having Formula I.
[0090] EXAMPLE 2: Synthesis of Pip-TAB having Formula II

[0091] 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) (1g, 2.07 mmol) was dissolved in NMP (62.3 mmol, 6 mL) in nitrogen atmosphere. Under this nitrogen atmosphere Pd/C (10 wt. %) (100mg, 0.0939 mmol) was added. After the Pd-C mixed with NMP completely, hydrogen bladder was inserted to it. Then the reaction mixture was stirred for 48h at the temperature ranges from 30 – 80°C. After completion of the reaction, the reaction mixture was filtered to remove Pd/C, and the filtrate was precipitated with diethyl ether and then washed with diethyl ether thoroughly and then was dried in open atmosphere to remove the excess of ether. After getting dry, the obtained mud colour powder was further dried using vacuum pump to become complete dry. This dried monomer (Pip-TAB) was used for next step reaction without any further purification. Yield: 67.2%, 1H-NMR (400 MHz, DMSO-d6) δ 6.39 ( 2H, d), 6.28 (2H, d), 6.02 (2H, d), 4.26 (s, 4H), 3.95 (s, 4H), 3.33 (t, 4H), 2.42 (t, 4H), 1.59 (q, 4H), 1.26 (m, 12 H) 13 C NMR (101 MHz, DMSO-d 6 ) δ [ppm]: 145.27, 136.26, 128.12, 116.17, 106.15, 106.08, 52.1, 37.2, 36.14, 32.26, 23.9. HRMS-ESI (+) calc. Molecular mass for: 422.32: Observed value (m/z): 423.32.

[0092] EXAMPLE 3: Synthesis of PIP-OPBI having Formula III

[0093] Pip-TAB (2.11g, 5 mmol), OBA (1.288g, 5 mmol) were taken in a 50 mL three-necked round bottom flask fitted with an overhead stirrer, connected with continuous nitrogen flow. 15 mL PPMA was added to the reaction mixture under inert conditions at room temperature (30 °C). The reaction mixture was stirred at room temperature. After 30 min, the temperature was increased to 50°C and the reaction mixture was stirred up to 1 h. After 1 h, the reaction mixture turned brown, further the reaction temperature was increased to 130 - 150°C. After 24 h, a dark brown viscous solution was formed which indicates the formation of PIP-OPBI completely. Later on, the viscous solution was poured into deionised water for precipitation and then it was stirred with saturated NaHCO3 solution to remove any traces of acid and was continuously washed with water several times to remove the residues of NaHCO3. The dark brown coloured PIP-OPBI solid obtained and was dried in vacuum oven at 100°C for 24 h. Yield: 87%, 1H-NMR (400 MHz, DMSO-d6) 8.4 (d, 2H), 8.12 (d, 1H), 7.98 (S, 1H), 7.72 (d, 1H), 7.43 (d, 2H),3.62(t,4H) 2.02 (m, 2H), 1.74 (3, 1H), 1.65 (m, 2H), 1.36 (m, 2H), 1.31 (m, 2H).

[0094] EXAMPLE 4: Synthesis of BP-PIP-PBI having Formula IV

[0095] A three-necked round-bottom flask containing 2.11g (4.99mmol) of Pip-TAB and 1.21 g (4.99 mmol) of BP-COOH was connected to a continuous flow of N2 and was mounted on an overhead stirrer. At room temperature (30 °C) and with the presence of N2, PPMA (1 mmol: 2ml) was added to the reaction mixture. For about half an hour, the reaction was agitated at room temperature to mix all the contents. After that, the temperature was raised to 50°C, and the reaction mixture was stirred for an hour. Additionally, the temperature was raised to 130 – 140 °C and maintained for 24 hours in order to finish the polymerization reaction. A dark brown, viscous solution was obtained after 24 hours, and it was added to the saturated NaHCO3 solution to eliminate the acid from the mixture. Following a thorough washing with DI water, the black chunks of the resulting polymer (BP-PIP-PBI) obtained, and were dried for 24 hours at 100°C in a vacuum oven. Yield: 85 %, 1H-NMR (400 MHz, DMSO-d6), δ 8.4 (d, 4H), 8.22 (d, 4H), 8.14 (d, 2H), 8.05 (S, 2H), 7.785 (d, 2H), 3.6 (m, 8H), 2.01 (m, 4H), 1.8 (m, 2H), 1.65 (m,4 H) ,1.3 (m, 2H), 1.2 (m,4H).

[0096] EXAMPLE 5: Synthesis of TP-PIP-PBI having Formula V

[0097] Pip-TAB (2g, 4.73mmol) and TP-COOH (0.725g, 4.73 mmol) were added to a three-necked round-bottom flask. This setup was placed on an overhead stirrer and connected to a constant flow of N2. Required amount of PPMA (1m mol: 1.5 ml), were added to the reaction mixture at room temperature (30°C) while N2 was present. The reaction mixture was stirred at room temperature for approximately 30 minutes in order to combine all of the components. The reaction mixture was then agitated for an hour while the temperature was increased to 50°C. In order to complete the polymerization reaction, the temperature was further increased to 130 – 140 °C and kept there for 24 hours. After a day, a dark brown, viscous solution was formed, which was then added to DI water and then it was stirred in saturated NaHCO3 solution to remove the acid from the mixture. The resulting polymer's dark brown chunks were thoroughly cleaned with DI water and then dried in a vacuum oven set at 100 °C for 24 hours to obtain pure TP-PIP-PBI. Yield: 85 %, 1H-NMR (400 MHz, DMSO-d6), δ 8.5 (d, 4H), 8.15 (d, 2H), 7.98 (S, 2H), 7.82 (d, 2H), 3.6 (t, 8H), 2.0 (m. 4H), 1.67 (m, 2H),1.6 (m,4H), 1.4 (m, 2H), 1.3 (m, 4H).
Table 2:
Sample code IV
(dl/g) Mv
(KDa) MSA FA
PIP-OPBI 1.059 51.59 ++ ++
BP-PIP- PBI 3.07 203.6 ++ ++
TP-PIP- PBI 1.26 65.92 ++ ++

Table: 2: represents inherent viscosity, viscosity average molecular weight and solubility results of the obtained piperidine based polymers. Where: ++ denotes complete solubility at room temperature up to a concentration of 2 wt. %.

[0098] Results and Explanation:
[0099] Figure 1 illustrates the 1H-NMR spectrum of 5-5’-(propane-1, 3-diylbis(piperidine-4,1-diyl) bis (2-nitroaniline) corresponding to Formula I, wherein the aromatic and amine peaks (signals) were observed in the range of 6.12–7.78 ppm, while the aliphatic peak (signals), corresponding to the piperidine ring and propyl chain, appeared in the range of 1.02–3.85 ppm, thereby confirming the presence of Formula I. Furthermore, the assignments of all peaks, correlating to the molecular structure, are depicted in Figure 1.

[0100] Figure 2 illustrates the 13C-NMR spectrum of 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) corresponding to Formula I, wherein all the aromatic carbon peaks (signals) were observed in the range of 90- 160 ppm, while the aliphatic peaks (signals) appeared within the range of 20- 50 ppm, thereby confirming the presence of Formula I. Furthermore, the assignments of all peaks, correlating to the molecular structure, are depicted in Figure 2.

[0101] Figure 3 illustrates the high-resolution mass spectrum (HRMS) of 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) corresponding to Formula I, wherein a sharp intense peak for C25H34N6O4 was observed at [M+1]: 483.27, while the calculated molecular ion peak was 482.26, thereby confirming the presence of Formula I.

[0102] Figure 4 illustrates the crystal structure of 5-5’-(propane-1, 3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) corresponding to Formula I, the identity of which was confirmed through single crystal X-ray diffraction (SC-XRD) analysis, as presented in Table 1.

[0103] Figure 5 illustrates the 1H-NMR spectra of 4’4-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(benzene-1,2-diamine) corresponding to Formula II, wherein all the aromatic peaks (signal) were observed within the range of 5.9-6.5 ppm, while four amine peaks (signal) appeared within the range of 3.9- 4.4 ppm. Additionally, all the aliphatic peaks (signals), corresponding to the piperidine ring and propyl chain, observed within the range of 1.1- 3.4 ppm, thereby confirming the presence of Formula II. Furthermore, the assignments of all peaks, correlating to the molecular structure, are depicted in Figure 5.

[0104] Figure 6 illustrates the 13C-NMR spectra of 4’4-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(benzene-1,2-diamine) corresponding to Formula II, wherein all the aromatic peaks (signals) were observed within the range of 100 - 150 ppm, while the aliphatic carbon peaks (signals) appeared within the range of 25- 55 ppm, thereby confirming the presence of Formula II. Furthermore, the assignments of all peaks, correlating to the molecular structure, are depicted in Figure 6.

[0105] Figure 7 illustrates the HRMS of 4’4-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(benzene-1,2-diamine) corresponding to Formula II, wherein a sharp intense peak for C25H38N6 was observed at [M+1]: 423.32 while the calculated molecular ion peak was 422.32, thereby confirming the presence of Formula II.

[0106] Figure 8 illustrates the thermogravimetric analysis (TGA) curve of PIP-NO2 (Formula I) and PIP-NH2 (Formula II). In the TGA curve, PIP-NO2 exhibits an initial sharp degradation at 255.6°C, corresponds to the degradation of the functional moiety. This is followed by a second degradation at 403.6 °C, corresponds to the degradation of backbone. Conversely, PIP-NH2 (Formula II) undergoes an initial slow degradation up to 388.9 °C, corresponding to the degradation of functional groups. Subsequently, at 403.6 °C, it exhibits a sharp degradation due to backbone degradation.

[0107] Figure 9 illustrates the Differential Scanning Calorimetry (DSC) curve of PIP-NO2 (Formula I) and PIP-NH2 (Formula II). In the DSC curve, PIP-NO2 exhibits a crystallization peak at 118.2 °C and a melting point peak at 205.34 °C, whereas PIP- NH2 displays a melting point peak at 98.3 °C.

[0108] Figure 10 illustrates the 1H-NMR spectra of PIP-OPBI having Formula III, BP-PIP-PBI having Formula IV, TP-PIP-PBI having Formula V. The chemical structures of all polymers were confirmed through 1H NMR analysis, as shown in Figure 10. Since all the polymers were insoluble in DMSO, the NMR spectra were recorded in a DMSO-d₆ and TFA mixture solution (20 vol%). Consequently, the imidazole peaks (signals) were absent due to the protonation of the benzimidazole ring in acidic medium. A distinct methylene peak at 3.6 ppm in all polymers corresponds to the methylene group adjacent to the piperidine nitrogen atom, clearly indicating the successful synthesis of piperidine-based polymers. The remaining aromatic proton signals appeared within the range of 7.1–8.6 ppm region, exhibiting chemical shift variations based on the distinct molecular environments of each polymer. Furthermore, the assignments of all peaks, correlating to the molecular structures, are depicted in Figure 10.

[0109] Figure 11 illustrates the Fourier Transform Infrared Spectroscopy (FTIR) of PIP-TAB, PIP-OPBI, BP-PIP-PBI and TP-PIP-PBI. The IR spectra of PIP-TAB monomers and piperidine-based PIP-PBI polymers were compared in Figure 11, with significant characteristic peaks of both monomers and polymers marked by dotted line and enclosed within rectangular box. The characteristic amine stretching mode at 3369 cm⁻¹, attributed to the PIP-TAB monomer, exhibits significant flattening after polymerization. Additionally, the emergence of new peaks at 1596 cm⁻¹ and 1470 cm⁻¹, corresponding to C=N and C=C stretching frequencies, respectively, provides strong spectral evidence confirming the successful formation of the benzimidazole ring within the polymer structure.

[0110] Figure 12 illustrates the thermographic analysis (TGA) curve of PIP-OPBI having Formula III, BP-PIP-PBI having Formula IV, TP-PIP-PBI having Formula V. The thermal stability of all membranes was evaluated using TGA over a temperature range of 30 to 700 °C under nitrogen (N2) atmosphere. From the thermogram, the initial weight loss occurs at nearly 150 °C, due to the removal of loosely bound water and formic acid associated with the polymer backbone. The second weight loss observed beyond 400 °C, which is due to the degradation of polymer backbone.

[0111] Figure 13 illustrates the stress-strain profile of PIP-OPBI having Formula III, BP-PIP-PBI having Formula IV, TP-PIP-PBI having Formula V. The mechanical stability (Stress-Strain plot) of all the membranes was evaluated using universal testing machine. The parameters such as tensile strength and elongation break, which predicts the mechanical robustness of the membrane, were also calculated from the stress-strain plot of the membranes. Among the analyzed membranes, BP-PIP-PBI exhibits the highest tensile strength (152.79 MPa) and elongation break (23.25 %), likely due to its higher inherent viscosity (IV) (detailed in Table 2) and also having less molecular spacing in between the polymer chain. This enhanced molecular rigidity leads to stronger intermolecular interactions that make the polymer more rigid, resulting in improved tensile strength and elongation at break. Conversely, PIP-OPBI, demonstrates the lowest tensile strength (79.13 MPa) but the highest elongation break (37.75%), which attributed to the presence of a flexible ether linkage in the polymer backbone. Meanwhile, TP-PIP-PBI shows the lowest elongation break (10.67%) due to lower IV among all the membranes.

[0112] Figure 14 illustrates the pictorial representation of membrane fabrication, depicting the polymerization process and subsequent purification, followed by the polymer dissolution in suitable solvent, and membrane casing.

[0113] Figure 15 illustrates the pictorial representation of synthesized pipedine based polymer membranes-PIP-OPBI, BP-PIP-PBI and TP-PIP-PBI-which exhibit high mechanical strength and flexibility.

[0114] Various embodiments of the present invention offer potential advantages that may be realized through its implementation. These advantages include enhanced efficiency, cost-effectiveness, and scalability, ensuring broader applicability across relevant industrial domains. Additionally, the invention provides simplified synthetic methodologies, increased yield, and improved material properties, thereby optimizing performance and utility. The disclosed embodiments further facilitate ease of purification and process adaptability, contributing to overall feasibility and commercial viability.

[0115] The present invention introduces an inexpensive and simple two-step synthetic process for Pip-TAB, which possesses extra nitrogen. The polymers derived from it prove beneficial for increased PA loading in PEMFCs and also facilitate the formation of a greater number of cationic sites (multication sites) for AEMFCs. The methodology described is conveniently scalable to an industrial level, ensuring broader application potential. This approach achieves a high yield of Pip-TAB, using readily available and cost-effective starting materials, solvents, bases, and catalysts. Additionally, the disclosed method facilitates high-yield purification processes, ensuring maximum recovery and minimal loss of valuable and final polymer products.

[0116] In comparison to conventional TABs, such as TAB (commercially available) and Py-TAB (obtained through a five-step synthetic procedure), the presently developed Pip-TAB significantly reduces costs. Additionally, the invention eliminates the need for complicated reaction pathways by relying on straightforward aromatic nucleophilic substitution and reduction reactions. Furthermore, the present invention specifies easy and efficient purification methods for each component, ensuring the high yield.

[0117] Although the present invention has been illustrated and described herein with reference to preferred embodiments, it will be readily apparent to those of ordinary skill in the art that other embodiments may perform similar functions and/or achieve similar results. All such equivalent embodiments are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.

[0118] The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might fall there within.
, Claims:We Claim:

1. A process for synthesizing a piperidine-based tetraamine monomer (PIP-TAB) of Formula II comprising the steps of:
(a) treating 1,3-di(piperidin-4-yl) propane with 5-fluoro-2-nitroaniline in the presence of a strong base and an organic solvent to obtain 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I; and

Formula I

(b) reducing the obtained 5-5’-(propane-1,3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I with a reducing agent in the presence of an organic solvent to obtain 4,4'-(propane-1,3-diylbis(piperidine-4,1-diyl))bis(benzene-1,2-diamine) (PIP-TAB) having formula II.

Formula II
2. The process as claimed in claim 1, wherein treating the 1, 3-di(piperidin-4-yl) propane with the 5-fluoro-2-nitroaniline in the presence of strong base and the organic solvent is performed at a temperature ranges from 100°C to 150°C.
3. The process as claimed in claim 1, wherein reducing the 5-5’-(propane-1, 3-diylbis(piperidine-4,1-diyl) bis(2-nitroaniline) having Formula I with the reducing agent in the presence of the organic solvent is performed at a temperature ranges from 250C to 800C.
4. The process as claimed in claim 1, wherein the organic solvent is selected from a group comprising: N-Methyl-2-Pyrrolidone (NMP), Dimethylformamide (DMF), Dimethyl Sulfoxide (DMSO) or a combination thereof, and the strong base is selected from a group comprising: N, N-Diisopropylethylamine (DIPEA), 4-Dimethylaminopyridine (DMAP), Triethyl amine (NEt3) or Tributyl amine (NBu3).

5. The process as claimed in claim 4, wherein the organic solvent comprises N-Methyl-2-Pyrrolidone (NMP), or Dimethylformamide (DMF), and the strong base comprises triethyl amine (NEt3).

6. The process as claimed in claim 1, wherein the reducing agent is selected from a metal including iron (Fe), zinc (Zn), or tin (Sn), in the presence of an acid such as hydrochloric acid (HCl), or, a noble metal selected from palladium (Pd), platinum (Pt), or nickel (Ni) in the presence of hydrogen gas.

7. The process as claimed in claim 1, wherein the obtained PIP-TAB is polymerized through polycondensation reaction with a dicarboxylic acid (4,4'-oxybisbenzoic acid (OBA)) using polyphosphoric acid (PPMA) as a catalyst under inert conditions to obtain a Pip-OPBI polymer having Formula III.

Formula III

8. The process as claimed in claim 7, wherein polymerization is performed at a temperature ranges from 50°C to 150°C for 24 h.

9. The process as claimed in claim 1, wherein the obtained PIP-TAB is polymerized through polycondensation reaction with a dicarboxylic acid (1,1'-biphenyl-4,4'-dicarboxylic acid (BP-COOH)) using PPMA as a solvent cum catalyst under inert conditions to obtain a BP-PIP-PBI polymer having Formula IV.

Formula IV

10. The process as claimed in claim 9, wherein the polymerization is performed at a temperature ranges from 50°C to 140°C for 48 h.

11. The process as claimed in claim 1, wherein the obtained PIP-TAB is polymerized through polycondensation reaction with a dicarboxylic acid (terephthalic acid (TP-COOH)) using polyphosphoric acid (PPMA) as a solvent cum catalyst under inert conditions to obtain a TP-PIP-PBI having polymer Formula V.

Formula V

12. The process as claimed in claim 11, wherein the polymerization is performed at a temperature ranges from 50°C to 140°C for 48 h.

13. The process as claimed in claims 7-12, wherein a molar ratio of Pip-TAB: DCA (Dicarboxylic Acid) is 1:1.