Abstract: A caged phosphorothioate flame retardant, tricalcium silicatemethyl-1-thiophospha-2,6,7-trioxabicyclo ［2.2.2］ octyl-4-methyl ester (MSTSPE), was synthesized by a reaction between methyl trimethoxysilane (MTMS) and 1-thiophospha-4-hydroxymethyl-2,6,7-trioxabicyclo ［2.2.2］ octane (SPEPA), and its structure and properties were characterized by means of Fouriertransform infrared spectroscopy, 1HNMR and thermogravimetric analysis. The effects of solvent, reaction temperature, reaction time and mass ratio of raw materials on product yield were investigated. The results indicated that the optimum synthetic method for MSTSPE was a solventfree synthesis, the molar ratio of MTMS and SPEPA was determined as 1∶3.1, and the synthetic temperature was set to 100 ℃ for 2 h and then 140 ℃ for 5 h. In such a synthetic condition, the production yield reached 92.4 %. The melting point of the resultant MSTSPE was (191±2) ℃, and its decomposition temperature was (340±5) ℃. The MSTSPE product synthesized in this work exhibited a high flameretardant effect and charring efficiency on poly(butylece terephthalate) (PBT). In addition, a combination of MSTSPE with melamine pyrophosphate could generate a synergistic flameretardant effect on PBT.

Key words: methyltrimethoxysilane, caged shape, phosphorothioate, synthesis, flame retardancy