All the solvents used in this synthesis were deoxidized by water removal before use. The water used in the laboratory is deionized water produced by the pure water equipment system. The reagent used in the experiment was anhydrous ethanol, which was purchased from Nanjing Chemical Reagent Co., LTD. P-benzoyl chloride, anhydrous calcium chloride CaCl₂ was purchased from Sinopharm Group Chemical Reagent Co., LTD. P-benzoyl chloride, 1-methyl-2-pyrrolidinone (NMP), purchased from Anhui Zesheng Technology Co., LTD.; 4,4'-diaminobenzanilide from Tixiai (Shanghai) Chemical Industry Development Co., LTD.

The synthesis diagram is shown in Figure 1, and the specific steps are as follows:

Purging dinitrogen gas into a 250 mL three-port flask and drying the flask. Under the condition of heating, anhydrous calcium chloride (6.1 g, 55 mmol) and 1-methyl-2-pyrrolidinone (NMP) 100 mL were added in sequence. The complexation of solvent molecules with metal cations improved the solvation of the system and increased the solubility of 4,4'-diaminobenzanilide. Addition of 4,4'-diaminobenzanilide (1.14 g, 5 mmol) under dinitrogen atmosphere, stirring

fully at 60˚C for about 30 min, to be completely dissolved, appearing in a pink solution. Cool down with an ice water bath, the temperature was controlled between 0˚C - 5˚C, addition of terephthaloyl chloride (1.01 g, 5 mmol) and stirring fully, appearing in a purple solution, reaction at low-temperature for 8 hours, continue to react at room temperature for 8 hours. After the reaction, the brown solution was poured into about 10 times deionized water to precipitate gray precipitation, stirred for about 1 hour, pumped and filtered under reduced pressure, washed with anhydrous ethanol (3 × 50 mL), and dried for 5 hours in vacuum at 120˚C to obtain gray precipitated polymeric p-benzoyl-4,4'-diaminobenzoylaniline 2.02 g (93.9%).

The solid ¹³C NMR was measured using a Bruker ALX 400 MHz nuclear magnetic resonance (NMR) spectrometer. The chemical shift (δ, ppm) was referenced to the standard substance SiMe₄. The infrared spectrum was obtained by using the KBr pellet method for sample preparation and measured on a Perkin-Elmer 16 PC FT-IR Fourier transform infrared spectrometer. The Raman spectrum was obtained by using a Renishaw inVia confocal Raman spectrometer. The UV-visible spectrum was measured by using a Shimadzu UV-2600 double-beam UV-visible spectrophotometer. The fluorescence spectrum was measured on a PerkinElmer LS-55 fluorescence spectrometer. The thermogravimetric curve data of the sample were obtained by using a Shimadzu DTG-60H instrument. The scan electron microscopy was performed by using a JEM-6480 scanning electron microscope with a tungsten filament.

According to the solid ¹³C NMR spectrum as shown in Figure 2, the signal observed at the chemical shift 123 - 136 ppm is attributed to the characteristic peak of the carbon atom on the benzene ring, and the signal at 166 ppm is attributed to the characteristic peak of the middle carbon atom of the amide group, which mirrors the chemical shift of the characteristic peak of the polyamide unit in the literature [11] .

In the FT-IR spectrum of polymeric p-benzoyl-4,4'-diaminobenzoylaniline, the stretching vibration absorption peak of amide N-H bond is at 3342 cm⁻¹, the absorption peak of the C=O stretching vibration of the amide bond at 1658 cm⁻¹, which is the absorption band of amide I. It is bent by the N-H bending vibration in the amide group at 1515 cm⁻¹, which is the amide II absorption band. It is the bending vibration peak of the C-N bond at 720 cm⁻¹. By comparing the product with the raw material, it was found that the characteristic double peaks of

primary amine disappeared, and by comparing it with terephthaloyl chloride, it was found that the stretching vibration peak of terephthaloyl chloride C-Cl disappeared at about 856 cm⁻¹. The above analysis indicates that 4,4'-diaminobenzanilide reacted with terephthaloyl chloride to form polyamide, as shown in Figure 3 below.

As shown in Figure 4, comparing the Raman spectrum of terephthaloyl chloride and 4,4'-diaminobenzanilide, the characteristic absorption band of amide I band (stretching vibration of C=O bond) near 1604 cm⁻¹ can be obviously observed on the spectra of polymeric p-benzoyl-4,4'-diaminobenzoylaniline. The band near 1100 - 1276 cm⁻¹ belongs to the absorption peak of the para-substituted benzene ring, while the bands near 2977 and 3342 cm⁻¹ are the stretching vibration absorption peak of the amide N-H bond and the C-H stretching vibration peak on the benzene ring, respectively. The reaction of 4,4'-diaminobenzanilidee with terephthaloyl chloride to form polymeric p-benzoyl-4,4'-diaminobenzoylaniline can be demonstrated by combining FT-IR and Raman spectroscopies.

The spectral absorption peaks in the near ultraviolet and visible regions can reflect the characteristics of conjugated π electrons. The degree of electron delocalization varies in different polymers resulting in differences in their ultraviolet absorption wavelengths. Generally, as the degree of conjugation increases, the absorption peak moves towards longer wavelengths [12] . As shown in Figure 5, the absorption of oligomers in the ultraviolet region is related to the degree of conjugation. The peak near 310 nm is the absorption peak of the benzene ring.

The production of fluorescence is completed through two stages: molecular excitation and deactivation. In the molecular excitation stage, the molecule absorbs external energy and enters an excited state, producing excited-state molecules. In the deactivation stage, excited-state molecules return to the ground state via non-radiative or fluorescent transitions, releasing fluorescence. A conjugated structure is a favorable structure for increasing fluorescence intensity. The probability of fluorescence generation is increased by enhancing the energy and vibrational intensity of intramolecular π-π jumps. Therefore, blue fluorescence of polymers with conjugated structures can be produced through π-π transitions. When solid-state polymers were excited at 360 nm, the resulting emission spectrum shown in Figure 6, which showed a strong blue fluorescence near 420 nm, it was indicated that this polymer has potential applications as a blue electroluminescent polymer material in fields such as light-emitting diodes and fluorescent probes.

The sample was heated from room temperature to 800˚C under a nitrogen atmosphere with a gas flow rate of 25 mL/min and a heating rate of 10˚C/min. The thermal behavior of the polymer was studied by thermal gravimetric analysis (TGA), as shown in Figure 7, which is the TGA curve of polymeric p-benzoyl-4,4'-diaminobenzoylaniline. During TGA testing, the polymer was measured at a heating rate of 10˚C/min under a nitrogen atmosphere of 25 mL/min. It can be seen from the figure that the polymer is stable before 300˚C, and significant weight loss begins after 300˚C, so it is concluded that it has good thermal stability. There are two main reasons for good thermal stability. First, the amide bond on the molecular chain is para-combined with the benzene ring. Due to the conjugation effect, the molecular chain structure is more regular and stable, the

molecular rigidity is strong, and the heat resistance is increased. Second, a large number of benzene rings are introduced into the main chain, and the increase of molecular weight makes its decomposition temperature higher, thus improving its thermal stability.

The surface morphology of polymeric p-benzoyl-4,4'-diaminobenzoylaniline was observed by scanning electron microscopy as shown in Figure 8. Figure 8(a),

measured at 500×, is an image of the overall distribution, where a large number of irregular flakes can be seen. Figure 8(b) and Figure 8(c) are the images measured at 900×, and you can see that the lamellae have agglomerations and are more tightly structured. Figure 8(d) is an image measured at 2000×, which shows the details of the material, i.e., the particles of the product have an average particle size of approximately 12 μm and exhibit a lamellar structure. The reason for this aggregation behavior of the products may be due to the fact that one of the end groups of p-benzoyl-4,4'-diaminobenzoyl-aniline is an amino group, and the amino groups are very prone to form hydrogen bonds with each other.