Synthesis and characterization of fire-safety PET by Schiff base with nitro group

A new Schiff base flame retardant monomer with nitro group ( NO 2 ), 5-((4-nitrobenzylidene) amino) isophthalic acid (NBA) was firstly synthesized to prepare fire-safety PET copolyester (NBA n PET). The group of NO 2 passivated the cross-linking reactivity of Schiff Base by affecting the formation of the intermediate states of the cross-linking reaction and further to improve the cross-linking temperature of NBA n PET to the temperature range (347–372 °C) from that of (250–348 °C), which showed better machinability in a broad processing temperature zone. In additional findings, the new synthesized NBA Schiff Base helped to shorten the time of polycondensation of PET with the advantage to save 58% of the reaction time by its acid structure. And the group of NO 2 enhanced the thermal stability of NBA n PETs, which improved its residue char in high temperature to enhance its flame retardancy. NBA 10 PET with NBA (7.9 mol%) processed LOI of 32% and V-0 of UL-94 without drip. The analysis of mechanism showed that the group of NO 2 in NBA did not decompose into the gas phase and NBA performed the mechanism of condensed phase during combustion of Schiff Base modified PET. The newly prepared NBA n PET with these better properties could possess wider application prospects.