298 This work is licensed under a Creative Commons Attribution 4.0 International License IHJPAS.37 (1) 2024 Ibn Al-Haitham Journal for Pure and Applied Sciences Journal homepage: jih.uobaghdad.edu.iq PISSN: 1609-4042, EISSN: 2521-3407 1Mustafa Salah Hasan* 2Ahlam Marouf AL-Azzawi 1,2Department of Chemistry, College of Scince, University of Baghdad, Baghdad, Iraq. *Corresponding Author: Mustafasalahhassan776@gmail.com Abstract Polyimides are widely used in high-temperature plastics, adhesives, dielectrics, photoresists, nonlinear optical materials, separation membrane materials, and Langmuir-Blodgett (LB) films. They are commonly regarded as the most heat-resistant polymers. This work involved the synthesis of a new bismaleimide homopolymer and copolymer by performing many steps. The synthesis of compound (1) (bis [4-(amino phenyl) Schiff base] tolidine) via condensation of o- tolidine with two moles of 4-aminoacetophenone. Secondly, compound (1) was combined with maleic anhydride to form compound (2) (4, 4ˉ-bis[4-(N-maleamic acid) phenyl Schiff base] toluidine). Thirdly, a dehydration reaction was carried out affording compound (3) (4,4ˉ-bis [4- (N-maleimidyl) phenyl Schiff base] toluidine). Compound (3) represents the new vinylic monomer, which was successfully introduced in addition to homopolymerization and copolymerization with selected vinylic monomers, affording homopolymer (4) and copolymers (5, 6), respectively. The new homopolymer and copolymers showed good fusibility and solubility in many organic solvents, leading to easy processing and expected to serve a broad spectrum of applications. Keywords: Bismaleimide, Homopolymer, Copolymerization, Maleamic acid, Polyimides, Schiff base. Received 2 February 2023, Received 7 March 2023, Accepted 14 March 2023, Published 20 January 2024 Synthesis of New Bismaleimide Homopolymer and Copolymers Derived from 4, 4ˉ-Bis[4-(N-maleimidyl) Phenyl Schiff Base] Tolidine doi.org/10.30526/37.1.3264 https://creativecommons.org/licenses/by/4.0/ https://jih.uobaghdad.edu.iq/index.php/j/index#1609-4042 https://jih.uobaghdad.edu.iq/index.php/j/index#2521-3407 mailto:Mustafasalahhassan776@gmail.com https://orcid.org/0000-0003-3708-8635 mailto:mustafasalahhassan776@gmail.com https://orcid.org/0000-0000-0000-0000 mailto:A.MAL-Azzawi@sc.uobaghdad.edu.iq IHJPAS. 37(1) 2024 299 1. Introduction Polyimides are an essential class of polymers due to their excellent properties, such as high chemical and thermal resistance [1, 2] and mechanical and electrical properties [3]. Because of all these properties, polyimides are used in essential applications like electric insulators, protective coatings, enamel membranes, and composites [4]. On the other hand, aromatic polyimides are often known as insoluble, infusible, and intractable materials due to their rigid backbone and high chain crystallinity [5]. These disadvantages lead to complex processing, and this, in turn, limits their applications [6]. Different attempts have been used to solve these problems, including copolymerization or, producing flexible segments or introductions into polyimide backbone, leading to dpolyimiderbackbonety and interchain forces making polyester-chain better solubility and fusibility [4]. In the present work, a new bismaleimide monomer containing two Schiff base components was synthesized by multistep synthesis, including preparation of bisschiff base [7], corresponding bismaleamic acid, and corresponding bismaleimide. The new monomer was introduced in addition to homopolymerization; Copolymerization yields the desired homopolymer and copolymer [8]. The presence of both Schiff base bulk components, in addition to copolymerization, play a vital role in the physical properties of the newly prepared polymers; thus, they showed good solubility and fusibility, leading to easy processing and the ability for introduction in various applications [9-12]. 2. Materials and Methods All synthetic compounds used in this study were purchased from GCC, Merck, and BDH. The compounds' and polymers' FT-IR spectral data were collected using a Shimadzu FTIR-8400 Fourier Infrared. Some prepared compounds' 1H-NMR and 13C-NMR spectra were recorded on a Bruker BioSpin GmbH apparatus with tetramethylsilane as the internal standard and DMSO-d6 as the solvent. The melting points were measured using a Gallenkamp apparatus, while the softening points of the prepared polymers were determined using a Riecher thermover thermal microscope. 2.1 Synthesis of bis[(4-amino phenyl) Schiff base] tolidine (1) The o-Tolidine (0.01 mol, 2.1 g) was dissolved in absolute ethanol (15 mL) and added dropwise to a solution of 4-amino acetophenone (0.02 mol, 2.7 g) dissolved in (20 mL) ethanol with three drops of glacial acetic acid, then the mixture was refluxed for 6 hours [13,14]. After the completion of reflux time, it was washed with cold ethanol [15] and recrystallized from acetone [16]. 2.2 Synthesis of 4, 4ˉ-bis[4-(N-maleamic acid)phenyl Schiff base] tolidine (2) A solution of (0.005 mol, 2.23 g) of compound (1) dissolved in (15 mL) acetone, the mixture was added drop by drop to (0.01 mol, 0. 98 g) of maleic anhydride that dissolved in (7 mL) of dried acetone with stirring and cooling [17]. After all the additions had been made [14], the mixture was stirred for two hours at room temperature. The formed residue was then washed with ether and re- crystallized from ethanol. 2.3 Synthesis of 4, 4ˉ-bis[4-(N-maleimidyl)phenyl Schiff base] tolidine (3) Dehydration of compound (2) has led to compound synthesis (3). Compound (2) was fused to remove water. Until complete melting [17], followed by heating to about 10 degrees above (amic acid melting point) for one hour. The formed solid recrystallization from ethanol. IHJPAS. 37 (1) 2024 300 2.4 Synthesis of homopolymer /poly (4, 4ˉ-bis[4-(N-maleimidyl)phenyl Schiff base] tolidine) (4) In a suitable polymerization bottle (1 g) of compound (3) was dissolved in (10 mL) of THF, then (0.001 g) of initiator AIBN (Azo bis isobutyro nitrile) was added, and the bottle contents were flushed with nitrogen gas for a few minutes before stoppered [13]. The mixture was heated at (75 0C) for 3 hours before pouring into (15 mL) of methanol. The formed polymer was washed with ether. The polymer was purified by dissolving it in THF and then precipitating it with methanol. 2.5 Synthesis of copolymers (5-7) In a suitable polymerization bottle, (1 g) of compound (3) was dissolved in (10 mL) of THF, and 2 mL of vinylic compounds such as (acrylonitrile, methyl acrylate, and methyl methacrylate) were added. Then (0.001 g) of initiator AIBN (Azo bis isobutyric nitrile) was added, and the bottle contents were flushed with nitrogen gas for a few minutes before being stopped [4]. The prepared copolymers were purified by dissolving them in THF and precipitating them from methanol. 3. Results and Discussion Since polymeric chains in polyimides have high rigidity and crystallinity, polyimides are infusible and insoluble in organic solvents, leading to crucial processability and considerably limiting their applications [18,19]. Thus, this work aims to synthesize new maleimide polymers with enhanced fusibility and solubility through two strategies. The first strategy involved incorporating bulk Schiff base components in polymeric chains, while the second was copolymerization [20,13, 21, 22]. Synthesis of the target polymers was accomplished by multistep synthesis, as shown in Scheme 1. Physical properties of compounds (1-3) and (4-7) are listed in Tables 1 and 2, respectively. Chemical structures of the prepared compounds and polymers are confirmed by FT-IR spectral data and 1HNMR and 13CNMR spectra for some of them. Clear absorption bands could be seen in compound (1) FT-IR spectrum at (3336-3469) cm-1 due to asym. and sym. v NH2 while absorption bands at (1625) cm-1 and (1569) cm-1 are due to v C=N imine and v C=C aromatic respectively [15]. The FT-IR spectrum for compound (2) exhibited absorption bands at (3228-3334) cm-1 due to v O-H carboxyl and v NH amide [23]. Besides, the spectrum showed characteristic absorption bands at (1712) cm-1 and (1676) cm-1, which are due to v C=O carboxyl and v C=O amide, respectively [24]. On the other hand, the FT-IR spectrum of compound (3) showed important absorption bands at (1774) cm-1 and (1714) cm-1, which are due to asymmetry. And sym. v C=O imide and another band at (1392) cm-1 due to v C-N imide [25]. All details of FT-IR spectral data of compounds (1-3) are detailed in Table 4. The 1HNMR spectra of compounds (1-3) exhibited signals in the range (2.1-2.44) ppm belonging to the protons of two methyl groups bonded to phenyl rings, signals at (2.38-2.61) ppm belonging to protons of two methyl groups connected to imine and signals at (6.03-8.11) ppm belong to aromatic protons [15]. The 1HNMR spectrum of compound (1) displayed a signal at (4.75) ppm belonging to NH2 groups protons, while the 1HNMR spectrum of compound (2) showed signals at (7.95-7.97) ppm and (9.97-10.66) ppm belonging to NH and OH carboxyl protons. The 1HNMR spectrum of compounds (2, 3) showed signals at (6.03-6.37) ppm belonging to vinylic protons [26]. The 13CNMR spectra of compounds (2,3) showed signals at (18.04-18.53) ppm belong to carbons of CH3 groups bonded to phenyl rings, signals at (26.31-26.93) ppm belong to carbons of CH3 groups bonded to imine and signals at (111.2-154.08) ppm belong to vinylic and romatic carbons IHJPAS. 37 (1) 2024 301 [27]. The 13CNMR spectrum of compound (2) showed signals at (164.16, 167.09-167.20) ppm and at (167.39-167.49) ppm represent C=N, C=O amide and C=O carboxyl carbons respectively while 13C NMR spectrum of compound (3) exhibited signals at (152.13-154.08) ppm and at (174.20- 176.44) ppm represent C=N and C=O imide carbons. Details of 1HNMR and 13CNMR spectral data of compounds (1-3) are listed in Tables 6 and 7, respectively. As indicated before, the purpose of this paper is to synthesize new maleimide polymers with enhanced fusibility and solubility, so we depend on performing this target first on the incorporation of bulk Schiff base moieties in the polymers through the synthesis of bis maleimide monomer already have two Schiff base moieties in its structure. Bulk Schiff base moiety in the polymer effectively reduces the packing efficiency of polymeric chains, improving fusibility and solubility [28]. On the other hand, the second strategy in this work is copolymerization since it is the most successful method to create compounds with desired properties by joining two structures with different chemical and physical properties in the same polymer chains [13]. Thus, it was noticeable that these two strategies, the producing new polymers, show good solubility in many organic solvents besides good fusibility. Softening points of polymers (4-7) are shown in Table 2, while their solubility in different organic solvents is shown in Table 3. The FT-IR spectra of polymers (4-7) exhibited absorption bands at (1765-1782) cm-1 and (1714-1728) cm-1 due to asym. And sym. v C=O imide and other bands at (1668-1679) cm-1, (1569-1598) cm-1 and (1379- 1388) cm-1 which are due to v C=N, v C=C aromatic and v C-N imide respectively [15]. The FT-IR spectrum of polymer (5) showed a characteristic absorption band at (2243) cm-1 due to v CN nitrile [29], while FT-IR spectra of polymers (6) and (7) displayed clear absorption bands at (1144, 1193) cm-1 and (1244-1269) cm-1 due to sym., asym—the v C-O ester. The 1HNMR spectrum of polymer (6) exhibited signals at (1.43-1.87) ppm belonging to aliphatic protons, and –CH-CH- in imide ring signals belonging to protons of two methyl groups bonded to phenyl rings appeared at (2.21-2.27) ppm while signals belong to protons of two methyl groups linked to imine appeared at (2.62-2.89) ppm [30] while signals belong to aromatic protons appeared at (6.78-8.11) ppm. The 13CNMR spectrum of polymer (6) exhibited signals at (18.0- 19.2) ppm belonging to carbons of 2CH3 bonded to the phenyl ring, while signals at (26.10-27.4) ppm belonged to carbons of two CH3 bonded to imine. Signals that belong to aliphatic carbons and aliphatic carbons in the imide ring appeared at (30.75-34.07) ppm, and a signal at (52.01) ppm belongs to OCH3 carbons. Other signals appeared at (125.29-152.03) ppm, (162.78) ppm, and (174.77-174.83) ppm, which belong to aromatic carbons, C=N carbons, and C=O imide, C=O ester carbons, respectively [15]. So, this work provides new important polyimides with desired properties (good fusibility and solubility), and this results in easy processing and is expected to serve a broad spectrum of applications [31]. IHJPAS. 37 (1) 2024 302 Scheme 1. Synthesis of new bismaleimide homopolymer and copolymers Table 1. Physical properties of compounds (1-3) Comp. No. Compound Structure Color Yield, % Melting point,0C Recrystallization solvent 1 Light brown 90 124-126 Acetone 2 yellow 95 170-172 Ethanol 3 Dark pink 85 240-243 Methanol IHJPAS. 37 (1) 2024 303 Table 2 . Physical properties of polymers (4-7) Table 3. Solubility of polymers (4-7) in different solvents (Ins. = insoluble, S. =soluble, Sh. = soluble hot). Table 4 . The FT-IR spectral data (v, cm-1) of compounds (1-3) Compound number v NH2 v C-H Aromatic v C-H Aliphatic v C=N v C=C v C=O Acid,A mide 1 3469 3409 3375,3336 3014 2983 2933 286 1625 1569 2 v O-H v N-H 3058 2923 2856 1631 1593 1535 1712 1676 3334 3263 3238 3 v C-H Aromatic v C-H Aliphatic v C=O Acid, Amide 1637 1595 1564 v C-N Imide 3050 2925 2856 1774 1714 1392 Polymer number Polymer structure color Conversio n ratio (%) Softening pointn (°C) Purification solvent 4 Light yellow 88 ˃ 360 Dissolving in THF then precipitation by methanol 5 brown 85 120-130 6 Dark Brown 90 Gumy 7 yellow 80 85-98 Com. NO. Aceton CHCl3 THF DMF DMSO EtOH Dioxane Et2O 4 Ins. Ins. Sh S. S. Ins. Ins. Ins. 5 Ins. Sh. S. S. S. Ins. Sh. Ins. 6 Ins. Sh. S. S. S. Ins. Sh. Ins. 7 Sh. Sh. S. S. S. Ins. Sh. Ins. IHJPAS. 37 (1) 2024 304 Table 5. The FT-IR spectral data (v, cm-1) of polymers (4-7) Polymer number v C-H Aromatic v C-H Aliphatic v C=O Imide v C=N v C=C v C-N Imide Others 4 3057 2974 2927 2856 1782 1714 1683 1598 1379 - 5 3037 2921 2852 1780 1716 1668 1596 1571 1386 v CN 2243 6 3056 2952 2866 1765 1716 1675 1596 1577 1384 v C=O ester 1716 v C-O ester 1269 7 3089 2993 2952 2842 1728 1679 1596 1569 1388 v C=O ester 1728 v C-O ester 1244 1193 1144 Table 6. The 1H NMR spectral data of compounds (1, 2, 3, 6) Compound number 1H NMR spectral data (ppm) 1 2.15 (6H, 2CH3), 2.43(6H,2CH3-C=N-), 4.75 (4H, 2NH2), 6.03-7.69 (14H, Ar-H) 2 2.16-2.27, (6H, 2CH3), 2.38(6H, 2CH3-C=N-), 6.21-6.37 (4H, CH2=CH2), 6.49-7.78 (14H, Ar- H), 7.95-7.97 (2H, 2NH), 9.97-10.66 (2H, 2OH). 3 2.10-2.44, (6H, 2CH3), 2.54-2.61 (6H, 2CH3-C=N-), 6.03-6.15 (4H, CH2=CH2), 6.56- 8.11 (14H, Ar-H). 6 1.43-1.87 (10H, Aliphatic), 2.21-2.27 (6H, 2CH3), 2.62-2.89 (6H, 2CH3-C=N-), 3.57 (6H, 2OCH3), 6.78-8.11 (14H, Ar-H). Table 7. The 13C NMR spectral data of compounds (2, 3, 6) Compound number 13C NMR spectral data (ppm) 2 18.04-18.44, (2C, 2CH3), 26.32-26.93(2C, 2CH3-C=N-), 112.92-154.08 (28C,vinylic, Ar-C), 164.16 (2C,2C=N),167.09-167.20 (2C, 2CONH), 167.39-167.49 (2C,-COOH) 3 18.07-18.53, (2C, 2CH3), 26.31-26.90(2C, 2CH3-C=N-), 111.2-136.77 (28C,vinylic, Ar-C), 152.13-154.08 (2C,2C=N),174.20-176.44 (2C, 2CONH). 6 18.0-19.2, (2C, 2CH3), 26.10-27.4 (2C, 2CH3-C=N-),30.75-34.07 (C aliph.-CH3CON-),52.01 (2C,2OCH3) 125.29-152.03 (24C, Ar-C), 162.78 (2C,2C=N),174.77-174.83 (2C, 2CON-) and (C=O) ester. 4. Conclusion The work supplies new maleimides containing the important bulk group (Schiff bases) component. It was then that homopolymerization and copolymerization with vinylic groups were introduced. The presence of these groups in the newly developed polymers exhibits high degree of fusibility and good solubility in many organic solvents and these properties give these polymers the possibility of easy processing and being introduced in aerospace, military, optic-electronics, composites, liquid crystal alignments, electrochromic materials, electroluminescent devices, polymer electrolyte fuel cells, polymer memory, etc. are just a few of the applications that utilize polymers. \ IHJPAS. 37 (1) 2024 305 Acknowledgment The authors thank the Department of Chemistry/ College of Science/ University of Baghdad staff for their assistance in performing this research. Conflict of Interest The authors declare that they do not have any competing interests. Funding There is no financial support. Ethical Clearance This work has been approved by the Scientific Committee at the University of Baghdad/ College of Science. References 1. 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