The novel application of trifluoromethyl group on flame retardancyproperties modification of Schiff Base modified PET copolyester

The novel application of trifluoromethyl group on flame retardancyproperties modification of Schiff Base modified PET copolyester | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The novel application of trifluoromethyl group on flame retardancyproperties modification of Schiff Base modified PET copolyester Xinxing Zhang, luxiang ma This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8600950/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract A novel Schiff Base as a flame-retardant monomer (FSB, 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid) was designed and made to synthesize FSB n PETs (PET copolyester) with flame retardancy and droplet resistance properties by copolymerization, where the functional group of -CF 3 here used to modify the Schiff Base flame retardant monomer to further adjust the high cyclizing temperature of its modified PET copolyesters. Results revealed that -CF 3 enhanced the temperature of the cyclizing reaction of Schiff Base in Schiff Base modified PET copolyesters from the scope of 250–348 °C to that of 350–398 °C by the influence of its electronic effect on passivating the Schiff Base cyclizing reaction, which further broadened its processing temperature window with better machinability. FSB increased the glass transition temperature (Tg), and reduced the melting temperature (Tm) and the crystallizability of FSB n PETs. FSB n PETs still possessed flame retardancy and droplet resistance properties, FSB 10 PET (7.4 mol% of FSB) owned V-0 level of UL-94 and 31% value of LOI without dripping phenomenon. The bond of -C-F had not broken down and the fluorine element (F) has not dispersed into the air phase to make an obvious influence on the flame retardancy property of PET modified by Schiff Base, and the FSB n PETs still obey the mechanism of the condense flame retardancy. Additionally, in the new preparing process, the dicarboxylic acid of FSB could speed up the condensation polymerization from the BHET precursors, which could save 50% of the preparation time, showing an exciting economic advantage. The newly synthesized functional group of -CF 3 modified Schiff Base could be an ideal selection to modify the Schiff Base modified PET. Schiff Base Trifluoromethyl copolymerization Poly (ethylene terephthalate) Flame retardancy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction Polymers are very important chemical materials in the application of industry, one of the earliest developed polymer materials is Poly (ethylene terephthalate), PET, which possessed good spinnability, mechanical properties and thermal stability 1 – 4 . Like most polymers, PET is flammable and must be modified in the aspect of its flame retardancy before its application. Hight effective flame retardancy is always a hot point in the field of the PET polymer researches 5 . In all research directions, the intrinsic flame retardancy by copolymerization was studied tensely due to its distinguish advantages of durable flame retardancy, good miscibility and good molecular structure designability except that it brings deteriorated dripping properties 6 – 8 . In recent studies, for the solvation of the problems of flame retardancy and droplet resistance problems, high temperature cyclizing method was invented to develop to meet this new need, in which different types of flame retardant monomer cyclizing in high temperature in their modified PET by copolymerization to form cyclic compounds to promote the property of flame retardancy 6 , 9 , 10 . wu 11 firstly introduced Schiff Base (BA) flame retardant monomer to make BA n PETs copolyester to improve the properties of the flame retardancy and droplet resistance for PET polymer, which showed excellent property, the new synthetic flame retardancy PET copolyesters was also machinable as PET, except that its cyclizing temperature was very low which made it cannot be processed in high temperature resulting from the high reacting activity of flame retardant monomer of Schiff Base, this will restrict its application. The methods need to be found to solve this problem to make progress in this field. The Schiff Base (BA) cyclizing reaction of BA n PETs copolyesters was a cycloaddition reaction by the imine (-C꞊N-) of several Schiff Base unit 12 . To low down the electronic density of -C꞊N- of Schiff Base monomer could deactivate its cyclizing reaction to enhance the cyclizing temperature of its modified PET copolyester. Electron absorption group could have such an ideal effect on Schiff Base monomers. Halogen was a kind of electron absorption group 13 , which was a kind of flame retardant element at the same time 14 . It could be an ideal modification group for the BA Schiff base flame retardant monomer. In the elements of Halogen (F, Cl, Br, I), F has the best effect of electronic absorption effect. The group of -CF 3 , which has a high F content, strong electron absorption, high lipophilicity and stable C-F bond could be a preferred choice 15 . The introduction group of -CF 3 into organic compounds can significantly change the acidity, polarity, chemical stability and metabolic stability of the compounds 16 . Therefore, compounds containing -CF 3 are widely used in medicine, pesticides and functional molecular materials 17 . Based on its strong electron absorption property, it might reduce the electronic density of -C꞊N- in the flame retardant monomer of Schiff Base to passive its high cyclizing reaction, and then to improve the cyclizing temperature of Schiff Base modified PET copolyesters which will further enhance its processability. Furthermore, economic factors are always considered as key conditions in the process of the modification of polymers. Flame retardant monomer should have dicarboxylic acid or dihydroxy structure in the method of the synthesis of PET polymer by esterification. Former studies of making process of PET polymer showed that reaction monomer with dicarboxylic acid could speed up the PET polycondensation process for saving time 18 , 19 . Considering economic factors, a flame retardant monomer with the dicarboxylic acid for speeding up the polycondensation reaction of PET copolyester could also better the making process of PET flame retardancy copolyester to save time and energy in its application as an additional advantage. Hence, in this work, a new flame retardancy and monomer of Schiff Base modified by -CF 3 with dicarboxylic acid was synthesized to enhance the processability and save preparing time of Schiff Bases modified PET by copolymerization. 2. Experimental 2.1 Materials 1,4-dicarboxybenzene (TPA, AR), ethanol (AR), ethylene glycol (EG, AR), antimony trioxide (Sb 2 O 3 , 99.99%), Acetic acid (C 2 H 4 O 2 , 99.9%) and was supplied by Aladdin Co., Ltd. (Shanghai, China). 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid and 5-amino-isophthalic acid were obtained from Macklin Co., Ltd. (Shanghai, China). 2.2 Preparation of 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid (FSB) FSB was prepared through reactants with aldehyde group (-CHO) and the amino (-NH 2 ), and the group of -CF 3 was attached to the reactant with the group of -CHO. Scheme 1 showed the synthetic route below. Keeping at 85 °C in a three-port reaction bottle with the N 2 protection, 5-aminoisophthalic acid (A) was completely solved in ethanol solvent, in which 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid (B) (A:B=1mol:1.2 mol) was added, then the reaction was started and lasted for 6 h. After the reaction was finished the precipitation was filtrated and cleaned with ethanol, which was dried for 8h at 80 °C in the vacuum drying oven. Yield: 74%. 1 H NMR: 8.63 (Ar-H, 2H), 8.40 (Ar-H, 1H), 8.33(Ar-H, 1H), 8.11 (Ar-H, 2H), 9.02 (-CH=N-, 1H) and 13.42 (-COOH, 2H), displayed in Figure 1. 2.3 BHET (Bis(2-hydroxyethyl) terephthalate) preparation The synthesis of BHET was prepared by 1,4-dicarboxybenzene (PTA) and ethylene glycol (EG), which was displayed in Scheme 2. TPA: EG (1mol:1.3 mol) were mixed in a 5 L autoclave to react at 245 °C for 2 h. 1 H NMR: 11.64(-COOH), 8.22-8.30 (Ar-H), 4.80-4.94 (-CH 2 -CH 2 - ), 4.73(-OH), shown in Figure 2. 2.4 Synthesis of PET copolyesters (FSB n PET) FSB n PET (“n” represents the mole percentage related to TPA) was made by the method of esterification and the preparation process was displayed in Scheme 3. The preparation method of FSB 10 PET was described in detailly below. BHET (BHET:TPA=1mol:1mol), FSB (FSB:TPA=1mol:10 mol) and Sb 2 O 3 (Sb 2 O 3 :TPA=4.1×10 -4 mol:1mol) were added into a three-port reaction bottle, then the mixture was heat to arrive at 240 °C under the protection of N 2 and vacuum to react for 60 min to obtain FSB 10 PET. The other FSB n PETs were synthesized at the same condition. 1 H NMR: 10.12 (-N=CH-), 8.67-8.77 (Ar-H), 8.51 (Ar-H), 8.30 (Ar-H), 8.22 (Ar-H), 8.06 (Ar-H), 4.89 (-CH 2 -O-), 4.76 (-CH 2 -O-), shown in Figure 3. 2.5 Test methods The intrinsic viscosities of copolymers were characterized by an ubbelohde viscometer at 25°C, 1,1,2,2-tetrachloroethane /phenol solution (1:1, mass ratio) was used as the solvent. The 1 H NMR was characterized by Bruker AV II 300 MHz NMR, FSB Schiff Base and polymers were solved by DMSO-d 6 and CF3COOD respectively, and etramethylsilane (TMS) was used as the reference. The thermal properties were tested by DSC (the differential scanning calorimetry, TA, Q2000). Firstly, the temperature of PET, FSB 5 PET, FSB 10 PET, FSB 15 PET and were enhanced to 230 °C, 250 °C, 260 °C and 280 °C to keep 3 min, respectively, and then the temperature was reduced to 40 °C and enhanced to 280 °C under the temperature change rate of 10 °C min -1 and the N 2 protection gas speed of 50 mL min -1 . Thermal stabilities of copolyesters were tested by TGA (Thermogravimetric analysis, NETZSCH, 209 F1) under N 2 , samples experienced temperature changes from 40 °C to 700 °C (10 °C min -1 ). The cyclizing behavior of Schiff Base modified copolyesters was characterized by SETARAM LABSYS EVO TGA/STA-EGA with Ar protection gas speed of 15 mL min -1 , scanning temperature from 40 °C to 550 °C with the temperature change rate of 10 °C min -1 . Flame retardancy of samples was characterized by Limiting oxygen index (LOI) and Underwriter Laboratory 94 vertical burning (UL-94). JF-3 apparatus was selected for LOI and the sample dimension was 120×6.5×3.2 mm 3 . GZF-5 instrument was selected for UL-94, the sample dimension was 120 × 13 × 3.2 mm 3 , and both were based on ASTM D 2863-97 standard. 3. Results and discussion 3.1 Reactivity of FSB in the copolymerization of FSB n PETs The synthesis conditions of FSB n PET were selected according to the former Schiff Base without the group of -CF 3 modified PET (BA n PET) 11 . According to our analysis, FSB was reacted with the BHET precursor could promote the reaction rate of PET copolyesters, the reaction condition and process were stated in Experimental part shown in scheme 2 , when the reaction processed for 60 min, the synthetic PET copolyester climbed the mixing rod in the reaction three-necked and round-bottomed flask, then the reaction was stopped to test its intrinsic viscosity. For BA 10 PET, it took 120 min for the polycondensation and its intrinsic viscosity was 0.78 dLg − 111 , but for FSB 10 PET, its reaction time was reduced to 60 min and its intrinsic viscosity was 0.97 dLg − 1 , which showed obvious advantages in the making process for time-saving. According to the principle of polycondensation, the reasons for FSB accelerating the polymerizing reaction was that the proton acid originating from -COOH of FSB could accelerate the polycondensation of PET, that -COOH of FSB could react with the end groups (-OH) of polyesters to promote the generation of the macromolecule of FSB n PETs, that H 2 O as a product of the BHET and -COOH of FSB was easier to get out of the reaction system than ethylene glycol (EG) which was the product of the BHET precursor, and that -COOH of FSB can capture the free EG to push the polymerizing reaction equilibrium to move in the direction of the generation of FSB n PET copolyesters 18 , 20 , 21 . 3.2 Thermal properties of FSB n PETs The incorporation of FSB will change the composition of the molecule chains of PET copolyesters after it experienced the modification by copolymerization. The thermal properties of the synthetic copolyesters were tested by DSC, which were shown in Table 1 and Fig. 4 . The glass transition temperature (Tg) of FSB n PETs showed an increasing trend, they were PET (78 °C), FSB 5 PET (82 °C), FSB 10 PET (84 °C) and FSB 15 PET (88°C), respectively, caused by the enhancement of the steric inhibition and intermolecular forces of the molecule chain movement of FSB n PETs, and T m (the melting point) dropped gradually, they were 242 °C, 221 °C, 207 °C for PET, FSB 5 PET and FSB 10 PET, respectively, caused by the changes of the structural properties of molecular chains of PET copolyesters after the incorporation of the FSB 22 , The increased content of FSB reduced ∆Hm (enthalpy of fusion), ∆Hc (enthalpy of crystallization) and Tc (The crystal temperature) of FSB n PETs, when it reached 15%, T m , ∆Hm and ∆Hc did not shown in the DSC figures in FSB 15 PET, resulting from the changes of the molecular structural properties of PET copolyesters after the incorporation of FSB, which influenced the crystallizability of the synthetic copolyesters 22 . Table 1 Thermal properties and intrinsic viscosity [η] testing results of FSB n PETs and PET Samples FSB content (mol%) [η] (dLg − 1 ) Tg (°C) Tm (°C) ∆Hm (°C) Tc (°C) ∆Hc (°C) Theoretical Actual a PET 0 0 0.87 78 242 30.6 195 43.3 FSB 5 PET 4.8 3.2 0.83 82 221 26.1 172 25.8 FSB 10 PET 9.1 7.4 0.97 84 207 22.5 FSB 15 PET 13.0 11.3 0.92 88 - - - a Actual value was obtained from 1 HNMR results 3.3 Thermostability of FSB n PETs The thermostability of PET copolyesters is essential when they experiencing high temperature 23 . TG was utilized to test these changes on thermostability, shown in Table 2 and Fig. 5 . The results demonstrated that PET and FSB n PET experienced the same mass loss process. T 5% gradually dropped, which were 401°C, 398 °C, 393 °C, and 389 °C to PET, FSB 5 PET, FSB 10 PET and FSB 15 PET, respectively, caused by the changes of the chemical molecular structure of PET copolyesters by the modification of FSB. T max had few changes, which were 435 °C, 431 °C, 434 °C and 433 °C for PET, FSB 5 PET, FSB 10 PET and FSB 15 PET, respectively. Compared to 13.7% of PET at 700 °C, the carbon residue of FSB n PET were 18.4%, 20.7% and 24.0% for FSB 5 PET, FSB 10 PET and FSB 15 PET, respectively, displaying a increasing trend attribute to that the cyclizing reaction of FSB in FSB n PETs promoted the generation of the carbon residue when it experienced high temperature, the carbon residue of FSB n PETs increases with the improvement of FSB content, which were higher than the Shift base modified PET without -CF 3 in the former studied work 11 , resulting from that the group of -CF 3 group can low down the electronic clouds density of benzene ring conjugated structure by its electronic effect, which can effectively protect the C-C bond from decomposition, leading to the improvement of thermal stability of FSB and further enhance the carbon residue of PET copolyesters (FSB n PET) 24 , that the fluorine atom has the characteristics of low polarizability, small van der Waals radius and electronegativity, and the building energy of bond of the C-F was large, which made the flame retardant monomer FSB difficult to decompose to enhance the carbon residue of its modified PET copolyesters 25 . Table 2 TGA testing results of PET and FSB n PETs under nitrogen Samples T 5% T max CR (wt%) PET 401 435 13.7% FSB 5 PET 396 431 18.4% FSB 10 PET 393 434 20.7% FSB 15 PET 389 433 24.0% RC: Carbon Residue. T 5% : The degradation temperature that the weight loss 5% took place. T max : The degradation temperature that the highest mass loss rate took place. 3.1 The high-temperature cyclizing behavior of FSB n PETs According to the designed method, the introduction of the group of -CF 3 should have a positive impact on the high temperature cyclizing reaction of FSB n PETs to enhance its machinability. The cyclizing reaction of FSB n PETs owns a heat changing process which will happen when it experienced high-temperature, TG-DSC technique was used to detect these changes 6 – 8 , with the result curves displayed in Fig. 6 . Between the range of the temperature of 350–398 °C, The DSC curves demonstrated that an obvious new exothermic peak appeared, caused by the cyclizing reaction of FSB in FSB n PETs, this was obviously different from the testing results of pure PET. Compared to the studied results, its cyclizing temperature range was 250–348 °C for BA n PETs copolyester modified by Schiff Base which did not modify by the group of -CF 3 11 , which is lower than the that of FSB n PETs. FSB Schiff base was a kind of an aromatic one, in which all the elements except the element of fluorine were coplanar to form a conjugate system, which was shown as the yellow shadow route of the atomic stereoscopic structure of FSB displayed in Fig. 7 , where π electrons can move to the adjacent aligned orbitals at the conjugated atomic system, and the named detail conjugated forms were also identified shown in Fig. 8 . The cyclizing reaction of Schiff Base reacted at high temperature to generate a six-membered cyclic chemical compound in Schiff base modified PET 11 . The Schiff Base cyclizing behavior could be inferred to the pericyclic reaction in its modified PET, where a small electronic density of -C = N- in Schiff Base led to a reduced reactivity. The electronic effect of -CF 3 , which could be classified detailly into conjugate effect and induction effect, could reduce electron density of -C = N- of FSB, which led to a reduced reactivity and enhanced the cyclizing temperature of its modified FSB n PETs further 12 .aa The functional theory (DFT) calculation was processed by the ORCA calculation software, the detailed conditions of calculation were b3lyp and 6-311G. The bond order calculation of the structure of -C = N- was carried out and the detailed data was displayed in Fig. 9 , which was 1.732 in BA n PETs copolyesters, compared to 1.747 for FSB n PETs, it was reduced caused by the powerful electronic effect of the introduction of the group of -CF 3 to modify the originating Schiff base BA, indicating that higher bond energy of -C = N- in FSB n PETs needs a higher temperature to provide enough energy for its decomposition according to the molecular orbital theory 26 . These two reasons may majorly lead to the cyclizing temperature increase of the new synthetic FSB n PETs copolyesters to further improve their processability. 3.4 Flame Retardant Properties and Mechanism of FSB n PETs Schiff Base has been used as an effective flame retardancy and droplet resistance agent for the property modification of PET polymer 11 . UL-94 and LOI were used to test the droplet resistance and flame retardancy properties of FSB n PETs, and the obtained data were displayed in Table 3 . PET dripped seriously due to its line structure in molecular chain 6 , 27 . UL-94 testing results of FSB 5 PET with the FSB of 3.2 mol% was V-2 level, showing a limited modification of its dripping property, and that of FSB 10 PET with FSB of 7.4 mol% arrived at V-0 level without dripping. The results of LOI for PET, FSB 5 PET, FSB 10 PET and FSB 15 PET were 22.0%, 29.0%, 31% and 32%, respectively, indicating that the new synthesized FSB Schiff Base with -CF 3 still has a good droplet resistance and flame retardancy function for the property modification of PET. The flame retardancy mechanism related to Schiff Base modified PET (BA n PET) complied with the condense phase flame retardancy mechanism, which was caused by the formation of the dense carbon layer originating from the high temperature cyclizing reaction of BA Schiff Base, and the droplet resistance properties originating from that Schiff Base cyclized in high temperature to generate cyclic compound which could increase the molten viscosity of its modified copolyesters to further prevent the droplet of the molten state of copolyesters 11 . Here -CF 3 as a kind of molecular modification was introduced to the BA Schiff Base, and Fluorine (F) was one of the halogen flame retardants and it had the possibility of achieving the gas phase flame retardancy mechanism when it was decomposed from the modified polymer (FSB n PETs) into its gas phase. To test whether the element of fluorine decomposed to change the flame retardancy mechanism when the modified polymer experienced a high temperature process, TG-IR was utilized to characterize the gaseous decomposing products of FSB n PET and PET, and their corresponding FTIR spectra of PET and FSB 10 PET were displayed in Fig. 10 (a) and Fig. 10 (b). As the result showed, the FTIR spectra of gaseous decomposing products of FSB 10 PET displayed the same product peaks as PET did, the detailed information was shown here. 1039 cm − 1 and 1407 cm − 1 (= C = CH 2 ), 1760 cm − 1 and 2740 cm − 1 (RCHO), 1755 cm − 1 and 3580 cm − 1 (RCOOH), -CH 3 (1353 cm − 1 ), 1088 cm − 1 and 1148 cm − 1 (C-O-C), 21057cm − 1 and 2177cm − 1 (CO), 899cm − 1 and 1180 cm − 1 (-C-O) and 725 cm − 1 and 2356cm − 1 (CO 2 ) 28 – 32 ,. The results demonstrated that -CF 3 in FSB did not thermally be decomposed, resulting from that the bond of -C-F was one of the strongest chemical bonds and it owned a very high dissociation energy, which made it difficult to decompose. Therefore, the group of -CF 3 did not change the mechanism of flame retardancy in Schiff Base modified PET copolyesters, FSB still performed the mechanism of the condense phase flame retardancy in FSB n PETs copolyesters. Table 3 The flame retardancy properties of FSB n PETs and PET Sample LOI (%) UL94 Rating Dripping PET 22 NR Serious FSB 5 PET 29 V-2 Modified FSB 10 PET 31 V-0 NO FSB 15 PET 32 V-0 NO 4. Conclusions In this work, 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid (FSB), a flame retardancy monomer of Schiff Base modified by the group of -CF 3 , was synthesized to prepare FSB n PETs copolyesters to ameliorate the flame retardancy and droplet resistance properties of PET polymer. The research demonstrated that -CF 3 can low down the reaction activity of the cyclizing reaction of Schiff Base in FSB n PETs copolyesters to increase the cyclizing temperature, which was improved to the temperature range of 350–398 °C, compared to 250–348 °C for the BA Schiff Base without -CF 3 modified PET (BA n PET), indicating that FSB n PETs has a better machinability with a broadened processing temperature window. Additionally, FSB Schiff Base could produce an effect of accelerating the PET polycondensation reaction to reduce 50% time for the making process of FSB n PETs by the acid catalysis effect originating from its dicarboxylic acid structure. The LOI and UL-94 of FSB 10 PETs (7.4 mol % of FSB) could reach 31% and V-0 level without dripping phenomenon, respectively, and the group of -CF 3 did not break down to affect the flame retardant mechanism of PET modified by Schiff Base. These results demonstrated that the newly synthesized monomer has a good modification effect on the flame retardancy and droplet resistance properties of PET polymer. As the experiments and data exhibited, the electronic effect of the functional group could produce a positive effect to modify the properties of polymers, especially for the ones which have chemical reaction of molecular chain because of the changes of environment, and the dicarboxylic acid of flame retardancy monomer to speed up the polycondensation of PET polymer could be an additional advantage when polymers were modified by copolymerization. Declarations Author Contributions: Xinxing zhang, Conceptualization Formal analysis, writing-original draft, writing-review and editing. Surpervisor; Luxiang Ma, Methodology and supervisor. All authors have read and agreed to the published version of this manuscript. 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Supplementary Files Scheme1.jpg Scheme 1 Preparation route of 5-((3,5 bis(trifluoromethyl)benzylidene)amino)isophthalic acid (FSB) Scheme2.jpg Scheme 2 Preparation route of BHET Scheme3.jpg Scheme 3 Preparation route of FSB n PETs Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 21 Jan, 2026 Reviewers invited by journal 21 Jan, 2026 Editor invited by journal 19 Jan, 2026 Editor assigned by journal 15 Jan, 2026 First submitted to journal 14 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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07:11:22","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":65552,"visible":true,"origin":"","legend":"\u003cp\u003eThe reduced intermediate reaction route related to the high temperature cyclizing reaction of FSB\u003csub\u003en\u003c/sub\u003ePETs\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8600950/v1/b7087503cf4cbea91e8b86b0.jpg"},{"id":100930382,"identity":"5d46be8a-92e3-4512-874b-e33ad7e14df2","added_by":"auto","created_at":"2026-01-23 00:40:38","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":45458,"visible":true,"origin":"","legend":"\u003cp\u003eThe DFT calculation of the structure of -C=N in BA\u003csub\u003en\u003c/sub\u003ePET (1) \u003csup\u003e[11]\u003c/sup\u003e and FSB\u003csub\u003en\u003c/sub\u003ePETs (2).\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8600950/v1/2536de897f04c0f91083429d.jpg"},{"id":100952278,"identity":"a76adb17-d9dd-42d8-89fb-68b02821f95f","added_by":"auto","created_at":"2026-01-23 07:12:27","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":103542,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR of the products of gas phase decomposition for PET (a) and FSB\u003csub\u003e10\u003c/sub\u003ePET (b)\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8600950/v1/4345fe85f2af4fc0fb531efb.jpg"},{"id":100953457,"identity":"661e5f62-2ab1-4887-8ddb-0b08dd9ae998","added_by":"auto","created_at":"2026-01-23 07:21:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1328757,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8600950/v1/834ad530-887c-4cb2-b28c-48dbf2ff35b3.pdf"},{"id":100930395,"identity":"df30e7da-a5c5-4278-8b24-a44b52e9cb96","added_by":"auto","created_at":"2026-01-23 00:40:38","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":38779,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1\u003c/strong\u003e Preparation route of 5-((3,5 bis(trifluoromethyl)benzylidene)amino)isophthalic acid (FSB)\u003c/p\u003e","description":"","filename":"Scheme1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8600950/v1/347c0ce3bd69be3ea08cdb66.jpg"},{"id":100952167,"identity":"5f8bd152-a767-420b-91d4-db5101c22c8d","added_by":"auto","created_at":"2026-01-23 07:12:06","extension":"jpg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":22000,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 2\u003c/strong\u003e Preparation route of BHET\u003c/p\u003e","description":"","filename":"Scheme2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8600950/v1/340ca8c2ab180aac4f54df23.jpg"},{"id":100930387,"identity":"6f132c05-197c-419a-a753-5cd85a82c2e8","added_by":"auto","created_at":"2026-01-23 00:40:38","extension":"jpg","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":33022,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 3\u003c/strong\u003e Preparation route of FSB\u003csub\u003en\u003c/sub\u003ePETs\u003c/p\u003e","description":"","filename":"Scheme3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8600950/v1/0393d4b742496dd1159f9cf6.jpg"}],"financialInterests":"","formattedTitle":"The novel application of trifluoromethyl group on flame retardancyproperties modification of Schiff Base modified PET copolyester","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003ePolymers are very important chemical materials in the application of industry, one of the earliest developed polymer materials is Poly (ethylene terephthalate), PET, which possessed good spinnability, mechanical properties and thermal stability\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Like most polymers, PET is flammable and must be modified in the aspect of its flame retardancy before its application. Hight effective flame retardancy is always a hot point in the field of the PET polymer researches\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. In all research directions, the intrinsic flame retardancy by copolymerization was studied tensely due to its distinguish advantages of durable flame retardancy, good miscibility and good molecular structure designability except that it brings deteriorated dripping properties\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. In recent studies, for the solvation of the problems of flame retardancy and droplet resistance problems, high temperature cyclizing method was invented to develop to meet this new need, in which different types of flame retardant monomer cyclizing in high temperature in their modified PET by copolymerization to form cyclic compounds to promote the property of flame retardancy \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. wu\u003csup\u003e11\u003c/sup\u003e firstly introduced Schiff Base (BA) flame retardant monomer to make BA\u003csub\u003en\u003c/sub\u003ePETs copolyester to improve the properties of the flame retardancy and droplet resistance for PET polymer, which showed excellent property, the new synthetic flame retardancy PET copolyesters was also machinable as PET, except that its cyclizing temperature was very low which made it cannot be processed in high temperature resulting from the high reacting activity of flame retardant monomer of Schiff Base, this will restrict its application. The methods need to be found to solve this problem to make progress in this field.\u003c/p\u003e \u003cp\u003eThe Schiff Base (BA) cyclizing reaction of BA\u003csub\u003en\u003c/sub\u003ePETs copolyesters was a cycloaddition reaction by the imine (-C꞊N-) of several Schiff Base unit\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. To low down the electronic density of -C꞊N- of Schiff Base monomer could deactivate its cyclizing reaction to enhance the cyclizing temperature of its modified PET copolyester. Electron absorption group could have such an ideal effect on Schiff Base monomers. Halogen was a kind of electron absorption group\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, which was a kind of flame retardant element at the same time\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. It could be an ideal modification group for the BA Schiff base flame retardant monomer. In the elements of Halogen (F, Cl, Br, I), F has the best effect of electronic absorption effect. The group of -CF\u003csub\u003e3\u003c/sub\u003e, which has a high F content, strong electron absorption, high lipophilicity and stable C-F bond could be a preferred choice\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. The introduction group of -CF\u003csub\u003e3\u003c/sub\u003e into organic compounds can significantly change the acidity, polarity, chemical stability and metabolic stability of the compounds\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Therefore, compounds containing -CF\u003csub\u003e3\u003c/sub\u003e are widely used in medicine, pesticides and functional molecular materials\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Based on its strong electron absorption property, it might reduce the electronic density of -C꞊N- in the flame retardant monomer of Schiff Base to passive its high cyclizing reaction, and then to improve the cyclizing temperature of Schiff Base modified PET copolyesters which will further enhance its processability.\u003c/p\u003e \u003cp\u003eFurthermore, economic factors are always considered as key conditions in the process of the modification of polymers. Flame retardant monomer should have dicarboxylic acid or dihydroxy structure in the method of the synthesis of PET polymer by esterification. Former studies of making process of PET polymer showed that reaction monomer with dicarboxylic acid could speed up the PET polycondensation process for saving time \u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Considering economic factors, a flame retardant monomer with the dicarboxylic acid for speeding up the polycondensation reaction of PET copolyester could also better the making process of PET flame retardancy copolyester to save time and energy in its application as an additional advantage.\u003c/p\u003e \u003cp\u003eHence, in this work, a new flame retardancy and monomer of Schiff Base modified by -CF\u003csub\u003e3\u003c/sub\u003e with dicarboxylic acid was synthesized to enhance the processability and save preparing time of Schiff Bases modified PET by copolymerization.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cp\u003e\u003cstrong\u003e2.1 Materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e1,4-dicarboxybenzene (TPA, AR), ethanol (AR), ethylene glycol (EG, AR), antimony trioxide (Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, 99.99%), Acetic acid (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 99.9%) and was supplied by Aladdin Co., Ltd. (Shanghai, China). 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid and 5-amino-isophthalic acid were obtained from Macklin Co., Ltd. (Shanghai, China). \u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Preparation of 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid (FSB)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFSB was prepared through reactants with aldehyde group (-CHO) and the amino (-NH\u003csub\u003e2\u003c/sub\u003e), and the group of -CF\u003csub\u003e3 \u003c/sub\u003ewas attached to the reactant with the group of -CHO. Scheme 1 showed the synthetic route below. Keeping at 85 \u0026deg;C in a three-port reaction bottle with the N\u003csub\u003e2\u003c/sub\u003e protection, 5-aminoisophthalic acid (A) was completely solved in ethanol solvent, in which 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid (B) (A:B=1mol:1.2 mol) was added, then the reaction was started and lasted for 6 h. After the reaction was finished the precipitation was filtrated and cleaned with ethanol, which was dried for 8h at 80 \u0026deg;C in the vacuum drying oven. \u003c/p\u003e\n\u003cp\u003eYield: 74%. \u003csup\u003e1\u003c/sup\u003eH NMR: 8.63 (Ar-H, 2H), 8.40 (Ar-H, 1H), 8.33(Ar-H, 1H), 8.11 (Ar-H, 2H), 9.02 (-CH=N-, 1H) and 13.42 (-COOH, 2H), displayed in Figure 1.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 BHET (Bis(2-hydroxyethyl) terephthalate) preparation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe synthesis of BHET was prepared by 1,4-dicarboxybenzene (PTA) and ethylene glycol (EG), which was displayed in Scheme 2. TPA: EG (1mol:1.3 mol) were mixed in a 5 L autoclave to react at 245 \u0026deg;C for 2 h. \u003c/p\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR: 11.64(-COOH), 8.22-8.30 (Ar-H), 4.80-4.94 (-CH\u003csub\u003e2\u003c/sub\u003e-CH\u003csub\u003e2\u003c/sub\u003e- ), 4.73(-OH), shown in Figure 2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.4 Synthesis of PET copolyesters\u003c/strong\u003e \u003cstrong\u003e(FSB\u003csub\u003en\u003c/sub\u003ePET)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFSB\u003csub\u003en\u003c/sub\u003ePET (\u0026ldquo;n\u0026rdquo; represents the mole percentage related to TPA) was made by the method of esterification and the preparation process was displayed in Scheme 3. The preparation method of FSB\u003csub\u003e10\u003c/sub\u003ePET was described in detailly below. BHET (BHET:TPA=1mol:1mol), FSB (FSB:TPA=1mol:10 mol) and Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3 \u003c/sub\u003e(Sb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e:TPA=4.1\u0026times;10\u003csup\u003e-4\u003c/sup\u003e mol:1mol) were added into a three-port reaction bottle, then the mixture was heat to arrive at 240 \u0026deg;C under the protection of N\u003csub\u003e2\u003c/sub\u003e and vacuum to react for 60 min to obtain FSB\u003csub\u003e10\u003c/sub\u003ePET. The other FSB\u003csub\u003en\u003c/sub\u003ePETs were synthesized at the same condition.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eH NMR: 10.12 (-N=CH-), 8.67-8.77 (Ar-H), 8.51 (Ar-H), 8.30 (Ar-H), 8.22 (Ar-H), 8.06 (Ar-H), 4.89 (-CH\u003csub\u003e2\u003c/sub\u003e-O-), 4.76 (-CH\u003csub\u003e2\u003c/sub\u003e-O-), shown in Figure 3.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e 2.5 Test methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe intrinsic viscosities of copolymers were characterized by an ubbelohde viscometer at 25\u0026deg;C, 1,1,2,2-tetrachloroethane /phenol solution (1:1, mass ratio) was used as the solvent. \u003c/p\u003e\n\u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH NMR was characterized by Bruker AV II 300 MHz NMR, FSB Schiff Base and polymers were solved by DMSO-d\u003csub\u003e6\u003c/sub\u003e and CF3COOD respectively, and etramethylsilane (TMS) was used as the reference. \u003c/p\u003e\n\u003cp\u003eThe thermal properties were tested by DSC (the differential scanning calorimetry, TA, Q2000). Firstly, the temperature of PET, FSB\u003csub\u003e5\u003c/sub\u003ePET, FSB\u003csub\u003e10\u003c/sub\u003ePET, FSB\u003csub\u003e15\u003c/sub\u003ePET and were enhanced to 230 \u0026deg;C, 250 \u0026deg;C, 260 \u0026deg;C and 280 \u0026deg;C to keep 3 min, respectively, and then the temperature was reduced to 40 \u0026deg;C and enhanced to 280 \u0026deg;C under the temperature change rate of 10 \u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e and the N\u003csub\u003e2\u003c/sub\u003e protection gas speed of 50 mL min\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThermal stabilities of copolyesters were tested by TGA (Thermogravimetric analysis, NETZSCH, 209 F1) under N\u003csub\u003e2\u003c/sub\u003e, samples experienced temperature changes from 40 \u0026deg;C to 700 \u0026deg;C (10 \u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e).\u003c/p\u003e\n\u003cp\u003eThe cyclizing behavior of Schiff Base modified copolyesters was characterized by SETARAM LABSYS EVO TGA/STA-EGA with Ar protection gas speed of 15 mL min\u003csup\u003e-1\u003c/sup\u003e, scanning temperature from 40 \u0026deg;C to 550 \u0026deg;C with the temperature change rate of 10 \u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e. \u003c/p\u003e\n\u003cp\u003eFlame retardancy of samples was characterized by Limiting oxygen index (LOI) and Underwriter Laboratory 94 vertical burning (UL-94). JF-3 apparatus was selected for LOI and the sample dimension was 120\u0026times;6.5\u0026times;3.2 mm\u003csup\u003e3\u003c/sup\u003e. GZF-5 instrument was selected for UL-94, the sample dimension was 120 \u0026times; 13 \u0026times; 3.2 mm\u003csup\u003e3\u003c/sup\u003e, and both were based on ASTM D 2863-97 standard.\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Reactivity of FSB in the copolymerization of FSB\u003csub\u003en\u003c/sub\u003ePETs\u003c/h2\u003e \u003cp\u003eThe synthesis conditions of FSB\u003csub\u003en\u003c/sub\u003ePET were selected according to the former Schiff Base without the group of -CF\u003csub\u003e3\u003c/sub\u003e modified PET (BA\u003csub\u003en\u003c/sub\u003ePET)\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. According to our analysis, FSB was reacted with the BHET precursor could promote the reaction rate of PET copolyesters, the reaction condition and process were stated in Experimental part shown in scheme \u003cspan refid=\"Sch2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, when the reaction processed for 60 min, the synthetic PET copolyester climbed the mixing rod in the reaction three-necked and round-bottomed flask, then the reaction was stopped to test its intrinsic viscosity. For BA\u003csub\u003e10\u003c/sub\u003ePET, it took 120 min for the polycondensation and its intrinsic viscosity was 0.78 dLg\u003csup\u003e\u0026minus;\u0026thinsp;111\u003c/sup\u003e, but for FSB\u003csub\u003e10\u003c/sub\u003ePET, its reaction time was reduced to 60 min and its intrinsic viscosity was 0.97 dLg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which showed obvious advantages in the making process for time-saving. According to the principle of polycondensation, the reasons for FSB accelerating the polymerizing reaction was that the proton acid originating from -COOH of FSB could accelerate the polycondensation of PET, that -COOH of FSB could react with the end groups (-OH) of polyesters to promote the generation of the macromolecule of FSB\u003csub\u003en\u003c/sub\u003ePETs, that H\u003csub\u003e2\u003c/sub\u003eO as a product of the BHET and -COOH of FSB was easier to get out of the reaction system than ethylene glycol (EG) which was the product of the BHET precursor, and that -COOH of FSB can capture the free EG to push the polymerizing reaction equilibrium to move in the direction of the generation of FSB\u003csub\u003en\u003c/sub\u003ePET copolyesters\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Thermal properties of FSB\u003csub\u003en\u003c/sub\u003ePETs\u003c/h2\u003e \u003cp\u003eThe incorporation of FSB will change the composition of the molecule chains of PET copolyesters after it experienced the modification by copolymerization. The thermal properties of the synthetic copolyesters were tested by DSC, which were shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The glass transition temperature (Tg) of FSB\u003csub\u003en\u003c/sub\u003ePETs showed an increasing trend, they were PET (78 \u0026deg;C), FSB\u003csub\u003e5\u003c/sub\u003ePET (82 \u0026deg;C), FSB\u003csub\u003e10\u003c/sub\u003ePET (84 \u0026deg;C) and FSB\u003csub\u003e15\u003c/sub\u003ePET (88\u0026deg;C), respectively, caused by the enhancement of the steric inhibition and intermolecular forces of the molecule chain movement of FSB\u003csub\u003en\u003c/sub\u003ePETs, and T\u003csub\u003em\u003c/sub\u003e (the melting point) dropped gradually, they were 242 \u0026deg;C, 221 \u0026deg;C, 207 \u0026deg;C for PET, FSB\u003csub\u003e5\u003c/sub\u003ePET and FSB\u003csub\u003e10\u003c/sub\u003ePET, respectively, caused by the changes of the structural properties of molecular chains of PET copolyesters after the incorporation of the FSB\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, The increased content of FSB reduced ∆Hm (enthalpy of fusion), ∆Hc (enthalpy of crystallization) and Tc (The crystal temperature) of FSB\u003csub\u003en\u003c/sub\u003ePETs, when it reached 15%, T\u003csub\u003em\u003c/sub\u003e, ∆Hm and ∆Hc did not shown in the DSC figures in FSB\u003csub\u003e15\u003c/sub\u003ePET, resulting from the changes of the molecular structural properties of PET copolyesters after the incorporation of FSB, which influenced the crystallizability of the synthetic copolyesters\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThermal properties and intrinsic viscosity [η] testing results of FSB\u003csub\u003en\u003c/sub\u003ePETs and PET\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eFSB content (mol%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e[η]\u003c/p\u003e \u003cp\u003e(dLg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTg (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTm (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e∆Hm (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTc (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e∆Hc (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTheoretical\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eActual\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e242\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e30.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e43.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e5\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e221\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e26.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e172\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e25.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e10\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e207\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e22.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e15\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"10\"\u003e\u003csup\u003ea\u003c/sup\u003e Actual value was obtained from \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003eHNMR results\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Thermostability of FSB\u003csub\u003en\u003c/sub\u003ePETs\u003c/h2\u003e \u003cp\u003eThe thermostability of PET copolyesters is essential when they experiencing high temperature\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. TG was utilized to test these changes on thermostability, shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The results demonstrated that PET and FSB\u003csub\u003en\u003c/sub\u003ePET experienced the same mass loss process. T\u003csub\u003e5%\u003c/sub\u003e gradually dropped, which were 401\u0026deg;C, 398 \u0026deg;C, 393 \u0026deg;C, and 389 \u0026deg;C to PET, FSB\u003csub\u003e5\u003c/sub\u003ePET, FSB\u003csub\u003e10\u003c/sub\u003ePET and FSB\u003csub\u003e15\u003c/sub\u003ePET, respectively, caused by the changes of the chemical molecular structure of PET copolyesters by the modification of FSB. T\u003csub\u003emax\u003c/sub\u003e had few changes, which were 435 \u0026deg;C, 431 \u0026deg;C, 434 \u0026deg;C and 433 \u0026deg;C for PET, FSB\u003csub\u003e5\u003c/sub\u003ePET, FSB\u003csub\u003e10\u003c/sub\u003ePET and FSB\u003csub\u003e15\u003c/sub\u003ePET, respectively. Compared to 13.7% of PET at 700 \u0026deg;C, the carbon residue of FSB\u003csub\u003en\u003c/sub\u003ePET were 18.4%, 20.7% and 24.0% for FSB\u003csub\u003e5\u003c/sub\u003ePET, FSB\u003csub\u003e10\u003c/sub\u003ePET and FSB\u003csub\u003e15\u003c/sub\u003ePET, respectively, displaying a increasing trend attribute to that the cyclizing reaction of FSB in FSB\u003csub\u003en\u003c/sub\u003ePETs promoted the generation of the carbon residue when it experienced high temperature, the carbon residue of FSB\u003csub\u003en\u003c/sub\u003ePETs increases with the improvement of FSB content, which were higher than the Shift base modified PET without -CF\u003csub\u003e3\u003c/sub\u003e in the former studied work\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, resulting from that the group of -CF\u003csub\u003e3\u003c/sub\u003e group can low down the electronic clouds density of benzene ring conjugated structure by its electronic effect, which can effectively protect the C-C bond from decomposition, leading to the improvement of thermal stability of FSB and further enhance the carbon residue of PET copolyesters (FSB\u003csub\u003en\u003c/sub\u003ePET)\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, that the fluorine atom has the characteristics of low polarizability, small van der Waals radius and electronegativity, and the building energy of bond of the C-F was large, which made the flame retardant monomer FSB difficult to decompose to enhance the carbon residue of its modified PET copolyesters\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTGA testing results of PET and FSB\u003csub\u003en\u003c/sub\u003ePETs under nitrogen\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eSamples T\u003csub\u003e5%\u003c/sub\u003e T\u003csub\u003emax\u003c/sub\u003e CR (wt%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e401\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e435\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e13.7%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e5\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e396\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e431\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e18.4%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e10\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e393\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e434\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20.7%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e15\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e389\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e433\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e24.0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eRC: Carbon Residue.\u003c/p\u003e \u003cp\u003eT\u003csub\u003e5%\u003c/sub\u003e: The degradation temperature that the weight loss 5% took place.\u003c/p\u003e \u003cp\u003eT\u003csub\u003emax\u003c/sub\u003e: The degradation temperature that the highest mass loss rate took place.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.1 The high-temperature cyclizing behavior of FSB\u003csub\u003en\u003c/sub\u003ePETs\u003c/h2\u003e \u003cp\u003eAccording to the designed method, the introduction of the group of -CF\u003csub\u003e3\u003c/sub\u003e should have a positive impact on the high temperature cyclizing reaction of FSB\u003csub\u003en\u003c/sub\u003ePETs to enhance its machinability. The cyclizing reaction of FSB\u003csub\u003en\u003c/sub\u003ePETs owns a heat changing process which will happen when it experienced high-temperature, TG-DSC technique was used to detect these changes\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, with the result curves displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Between the range of the temperature of 350\u0026ndash;398 \u0026deg;C, The DSC curves demonstrated that an obvious new exothermic peak appeared, caused by the cyclizing reaction of FSB in FSB\u003csub\u003en\u003c/sub\u003ePETs, this was obviously different from the testing results of pure PET. Compared to the studied results, its cyclizing temperature range was 250\u0026ndash;348 \u0026deg;C for BA\u003csub\u003en\u003c/sub\u003ePETs copolyester modified by Schiff Base which did not modify by the group of -CF\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e11\u003c/sup\u003e, which is lower than the that of FSB\u003csub\u003en\u003c/sub\u003ePETs.\u003c/p\u003e \u003cp\u003eFSB Schiff base was a kind of an aromatic one, in which all the elements except the element of fluorine were coplanar to form a conjugate system, which was shown as the yellow shadow route of the atomic stereoscopic structure of FSB displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, where π electrons can move to the adjacent aligned orbitals at the conjugated atomic system, and the named detail conjugated forms were also identified shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The cyclizing reaction of Schiff Base reacted at high temperature to generate a six-membered cyclic chemical compound in Schiff base modified PET\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. The Schiff Base cyclizing behavior could be inferred to the pericyclic reaction in its modified PET, where a small electronic density of -C\u0026thinsp;=\u0026thinsp;N- in Schiff Base led to a reduced reactivity. The electronic effect of -CF\u003csub\u003e3\u003c/sub\u003e, which could be classified detailly into conjugate effect and induction effect, could reduce electron density of -C\u0026thinsp;=\u0026thinsp;N- of FSB, which led to a reduced reactivity and enhanced the cyclizing temperature of its modified FSB\u003csub\u003en\u003c/sub\u003ePETs further \u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e.aa\u003c/p\u003e \u003cp\u003eThe functional theory (DFT) calculation was processed by the ORCA calculation software, the detailed conditions of calculation were b3lyp and 6-311G. The bond order calculation of the structure of -C\u0026thinsp;=\u0026thinsp;N- was carried out and the detailed data was displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, which was 1.732 in BA\u003csub\u003en\u003c/sub\u003ePETs copolyesters, compared to 1.747 for FSB\u003csub\u003en\u003c/sub\u003ePETs, it was reduced caused by the powerful electronic effect of the introduction of the group of -CF\u003csub\u003e3\u003c/sub\u003e to modify the originating Schiff base BA, indicating that higher bond energy of -C\u0026thinsp;=\u0026thinsp;N- in FSB\u003csub\u003en\u003c/sub\u003ePETs needs a higher temperature to provide enough energy for its decomposition according to the molecular orbital theory\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. These two reasons may majorly lead to the cyclizing temperature increase of the new synthetic FSB\u003csub\u003en\u003c/sub\u003ePETs copolyesters to further improve their processability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Flame Retardant Properties and Mechanism of FSB\u003csub\u003en\u003c/sub\u003ePETs\u003c/h2\u003e \u003cp\u003eSchiff Base has been used as an effective flame retardancy and droplet resistance agent for the property modification of PET polymer \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. UL-94 and LOI were used to test the droplet resistance and flame retardancy properties of FSB\u003csub\u003en\u003c/sub\u003ePETs, and the obtained data were displayed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. PET dripped seriously due to its line structure in molecular chain\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. UL-94 testing results of FSB\u003csub\u003e5\u003c/sub\u003ePET with the FSB of 3.2 mol% was V-2 level, showing a limited modification of its dripping property, and that of FSB\u003csub\u003e10\u003c/sub\u003ePET with FSB of 7.4 mol% arrived at V-0 level without dripping. The results of LOI for PET, FSB\u003csub\u003e5\u003c/sub\u003ePET, FSB\u003csub\u003e10\u003c/sub\u003ePET and FSB\u003csub\u003e15\u003c/sub\u003ePET were 22.0%, 29.0%, 31% and 32%, respectively, indicating that the new synthesized FSB Schiff Base with -CF\u003csub\u003e3\u003c/sub\u003e still has a good droplet resistance and flame retardancy function for the property modification of PET.\u003c/p\u003e \u003cp\u003eThe flame retardancy mechanism related to Schiff Base modified PET (BA\u003csub\u003en\u003c/sub\u003ePET) complied with the condense phase flame retardancy mechanism, which was caused by the formation of the dense carbon layer originating from the high temperature cyclizing reaction of BA Schiff Base, and the droplet resistance properties originating from that Schiff Base cyclized in high temperature to generate cyclic compound which could increase the molten viscosity of its modified copolyesters to further prevent the droplet of the molten state of copolyesters\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Here -CF\u003csub\u003e3\u003c/sub\u003e as a kind of molecular modification was introduced to the BA Schiff Base, and Fluorine (F) was one of the halogen flame retardants and it had the possibility of achieving the gas phase flame retardancy mechanism when it was decomposed from the modified polymer (FSB\u003csub\u003en\u003c/sub\u003ePETs) into its gas phase. To test whether the element of fluorine decomposed to change the flame retardancy mechanism when the modified polymer experienced a high temperature process, TG-IR was utilized to characterize the gaseous decomposing products of FSB\u003csub\u003en\u003c/sub\u003ePET and PET, and their corresponding FTIR spectra of PET and FSB\u003csub\u003e10\u003c/sub\u003ePET were displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e (a) and Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e (b). As the result showed, the FTIR spectra of gaseous decomposing products of FSB\u003csub\u003e10\u003c/sub\u003ePET displayed the same product peaks as PET did, the detailed information was shown here. 1039 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1407 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (=\u0026thinsp;C\u0026thinsp;=\u0026thinsp;CH\u003csub\u003e2\u003c/sub\u003e), 1760 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2740 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (RCHO), 1755 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (RCOOH), -CH\u003csub\u003e3\u003c/sub\u003e (1353 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), 1088 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1148 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C-O-C), 21057cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2177cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e(CO), 899cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1180 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (-C-O) and 725 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2356cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (CO\u003csub\u003e2\u003c/sub\u003e)\u003csup\u003e\u003cspan additionalcitationids=\"CR29 CR30 CR31\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e,. The results demonstrated that -CF\u003csub\u003e3\u003c/sub\u003e in FSB did not thermally be decomposed, resulting from that the bond of -C-F was one of the strongest chemical bonds and it owned a very high dissociation energy, which made it difficult to decompose. Therefore, the group of -CF\u003csub\u003e3\u003c/sub\u003e did not change the mechanism of flame retardancy in Schiff Base modified PET copolyesters, FSB still performed the mechanism of the condense phase flame retardancy in FSB\u003csub\u003en\u003c/sub\u003ePETs copolyesters.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe flame retardancy properties of FSB\u003csub\u003en\u003c/sub\u003ePETs and PET\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLOI (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eUL94\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRating\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDripping\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSerious\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e5\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eV-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eModified\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e10\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eV-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFSB\u003c/b\u003e\u003csub\u003e\u003cb\u003e15\u003c/b\u003e\u003c/sub\u003e\u003cb\u003ePET\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eV-0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this work, 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid (FSB), a flame retardancy monomer of Schiff Base modified by the group of -CF\u003csub\u003e3\u003c/sub\u003e, was synthesized to prepare FSB\u003csub\u003en\u003c/sub\u003ePETs copolyesters to ameliorate the flame retardancy and droplet resistance properties of PET polymer. The research demonstrated that -CF\u003csub\u003e3\u003c/sub\u003e can low down the reaction activity of the cyclizing reaction of Schiff Base in FSB\u003csub\u003en\u003c/sub\u003ePETs copolyesters to increase the cyclizing temperature, which was improved to the temperature range of 350\u0026ndash;398 \u0026deg;C, compared to 250\u0026ndash;348 \u0026deg;C for the BA Schiff Base without -CF\u003csub\u003e3\u003c/sub\u003e modified PET (BA\u003csub\u003en\u003c/sub\u003ePET), indicating that FSB\u003csub\u003en\u003c/sub\u003ePETs has a better machinability with a broadened processing temperature window. Additionally, FSB Schiff Base could produce an effect of accelerating the PET polycondensation reaction to reduce 50% time for the making process of FSB\u003csub\u003en\u003c/sub\u003ePETs by the acid catalysis effect originating from its dicarboxylic acid structure. The LOI and UL-94 of FSB\u003csub\u003e10\u003c/sub\u003ePETs (7.4 mol % of FSB) could reach 31% and V-0 level without dripping phenomenon, respectively, and the group of -CF\u003csub\u003e3\u003c/sub\u003e did not break down to affect the flame retardant mechanism of PET modified by Schiff Base. These results demonstrated that the newly synthesized monomer has a good modification effect on the flame retardancy and droplet resistance properties of PET polymer. As the experiments and data exhibited, the electronic effect of the functional group could produce a positive effect to modify the properties of polymers, especially for the ones which have chemical reaction of molecular chain because of the changes of environment, and the dicarboxylic acid of flame retardancy monomer to speed up the polycondensation of PET polymer could be an additional advantage when polymers were modified by copolymerization.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e Xinxing zhang, Conceptualization Formal analysis, writing-original draft, writing-review and editing. Surpervisor; Luxiang Ma, Methodology and supervisor. All authors have read and agreed to the published version of this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e: This research was funded by General Project of Hainan Provincial Colleges and Universities\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e: The authors would like to thank Shiyanjia Lab (www.shiyanjia.com) for the DSC analysis.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e: The authors declare no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDing L et al (2019) Modification of poly(ethylene terephthalate) by copolymerization of plant-derived α-truxillic acid with excellent ultraviolet shielding and mechanical properties. 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Compos Part B: Eng 42:1057\u0026ndash;1065\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eSchemes 1 to 3 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Schiff Base, Trifluoromethyl, copolymerization, Poly (ethylene terephthalate), Flame retardancy","lastPublishedDoi":"10.21203/rs.3.rs-8600950/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8600950/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA novel Schiff Base as a flame-retardant monomer (FSB, 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid) was designed and made to synthesize FSB\u003csub\u003en\u003c/sub\u003ePETs (PET copolyester) with flame retardancy and droplet resistance properties by copolymerization, where the functional group of -CF\u003csub\u003e3\u003c/sub\u003e here used to modify the Schiff Base flame retardant monomer to further adjust the high cyclizing temperature of its modified PET copolyesters. Results revealed that -CF\u003csub\u003e3\u003c/sub\u003e enhanced the temperature of the cyclizing reaction of Schiff Base in Schiff Base modified PET copolyesters from the scope of 250\u0026ndash;348 \u0026deg;C to that of 350\u0026ndash;398 \u0026deg;C by the influence of its electronic effect on passivating the Schiff Base cyclizing reaction, which further broadened its processing temperature window with better machinability. FSB increased the glass transition temperature (Tg), and reduced the melting temperature (Tm) and the crystallizability of FSB\u003csub\u003en\u003c/sub\u003ePETs. FSB\u003csub\u003en\u003c/sub\u003ePETs still possessed flame retardancy and droplet resistance properties, FSB\u003csub\u003e10\u003c/sub\u003ePET (7.4 mol% of FSB) owned V-0 level of UL-94 and 31% value of LOI without dripping phenomenon. The bond of -C-F had not broken down and the fluorine element (F) has not dispersed into the air phase to make an obvious influence on the flame retardancy property of PET modified by Schiff Base, and the FSB\u003csub\u003en\u003c/sub\u003ePETs still obey the mechanism of the condense flame retardancy. Additionally, in the new preparing process, the dicarboxylic acid of FSB could speed up the condensation polymerization from the BHET precursors, which could save 50% of the preparation time, showing an exciting economic advantage. The newly synthesized functional group of -CF\u003csub\u003e3\u003c/sub\u003e modified Schiff Base could be an ideal selection to modify the Schiff Base modified PET.\u003c/p\u003e","manuscriptTitle":"The novel application of trifluoromethyl group on flame retardancyproperties modification of Schiff Base modified PET copolyester","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-23 00:40:33","doi":"10.21203/rs.3.rs-8600950/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-01-21T10:44:40+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-21T06:31:59+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2026-01-19T14:27:26+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-15T10:23:47+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2026-01-14T22:07:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"90698e0c-18ea-4ef0-a683-4791095b030a","owner":[],"postedDate":"January 23rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-27T06:21:24+00:00","versionOfRecord":[],"versionCreatedAt":"2026-01-23 00:40:33","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8600950","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8600950","identity":"rs-8600950","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}