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<p>A novel Schiff Base as a flame-retardant monomer (FSB, 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid) with -CF<sub>3</sub> was designed and used to synthesize FSB<sub>n</sub>PETs (PET copolyester) by copolymerization, which shows good flame retardancy and anti-dripping. The introduction of the –CF₃ group increases the cyclization temperature of the FSB Schiff base unit by suppressing the cyclization reaction through its strong electron-withdrawing effect, which is 350–398&#xa0;°C, higher than 250–348&#xa0;°C from the PET copolyesters modified by Schiff Base without -CF<sub>3</sub>, indicating that FSB<sub>n</sub>PETs exhibits a broadened processing temperature window. And FSB also increased the glass transition temperature (Tg), reduced the melting temperature (Tm) and the crystallizability of FSB<sub>n</sub>PETs. FSB<sub>n</sub>PETs possessed good flame retardancy and anti-dripping properties, FSB<sub>10</sub>PET (7.4&#xa0;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 into the air phase to make an obvious influence on the flame retardancy property of FSB<sub>n</sub>PETs, whose flame retardancy mechanism is still type of the condense flame retardancy. Additionally, in the new preparation process for FSB<sub>n</sub>PETs, the dicarboxylic acid structure of FSB could speed up the condensation polymerization between the BHET precursors, which could save 50% of the preparation time, showing an exciting economic advantage. The -CF₃ modified Schiff base (FSB) is an effective modifier for PET copolyesters, offering improved processing performance and good flame-retardant properties.</p>

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Synthesis and characterization of trifluoromethyl-modified Schiff base flame-retardant PET copolyesters

  • 期刊论文

  • 发表日期：

    2026年7月30日

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  • Xinxing Zhang,
  • Luxiang Ma

摘要

A novel Schiff Base as a flame-retardant monomer (FSB, 5-((3,5-bis(trifluoromethyl) benzylidene) amino) isophthalic acid) with -CF3 was designed and used to synthesize FSBnPETs (PET copolyester) by copolymerization, which shows good flame retardancy and anti-dripping. The introduction of the –CF₃ group increases the cyclization temperature of the FSB Schiff base unit by suppressing the cyclization reaction through its strong electron-withdrawing effect, which is 350–398 °C, higher than 250–348 °C from the PET copolyesters modified by Schiff Base without -CF3, indicating that FSBnPETs exhibits a broadened processing temperature window. And FSB also increased the glass transition temperature (Tg), reduced the melting temperature (Tm) and the crystallizability of FSBnPETs. FSBnPETs possessed good flame retardancy and anti-dripping properties, FSB10PET (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 into the air phase to make an obvious influence on the flame retardancy property of FSBnPETs, whose flame retardancy mechanism is still type of the condense flame retardancy. Additionally, in the new preparation process for FSBnPETs, the dicarboxylic acid structure of FSB could speed up the condensation polymerization between the BHET precursors, which could save 50% of the preparation time, showing an exciting economic advantage. The -CF₃ modified Schiff base (FSB) is an effective modifier for PET copolyesters, offering improved processing performance and good flame-retardant properties.