Ultra-high fire-safety unsaturated polyesters enabled by self-assembled micro/nano rod from Schiff base, diphenylphosphinyl group and nickel (II) metal

As one of the most flammable common commercially resins, high flammability and heat/smoke release characteristics of unsaturated polyesters (UP) lead to severe casualties and irreparable property loss. To solve these problem, a flame-retardant approach via the multiple synergic effects of promoting char-ability, physically shielding heat/mass transfer, and quenching small molecular fragments in burning is proposed. Herein, a novel micro/nano rod flame retardant SDPPNi, composed of diphenylphosphinyl groups, Schiff base and Nickel (II), are synthesized by self-assembly based on the coordination reactions. The UP with 25 wt% SDPPNi (UP/SDPPNi25), shows quite excellent fire-safety performance, and its limiting oxygen index (LOI) is as high as 38.0%, showing extremely high flame retardant efficiency. Meanwhile, its peak heat release rate (PHRR), total heat release (THR), fire growth rate (FIGRA), and maximum smoke density (Dsmax) values are significantly reduced by 69%, 40%, 72%, and 42%, respectively. During burning, the SDPPNi promotes UP to form compact char layers composed of pyridine derivatives, phosphoric-oxygenic compounds, and nickel-oxides, inhibiting the heat and mass transfer. Meanwhile, the SDPPNi also releases phosphorous-containing volatiles that can capture some small molecular fragments and break off the chain reaction of combustion. Therefore, a state-of-art strategy is proposed to endow UP resins with ultra-high fire-safety performance.