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

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.