Enhancement of thermal stability of polystyrene and poly(methyl methacrylate) by cyclotriphosphazene derivatives

Abstract

The thermal stability and degradation behavior of polystyrene (PSt) and poly(methyl methacrylate) (PMMA) blended with organic cyclotriphosphazenes (N 3P 3(OR) 6) were investigated by thermogravimetric analysis and gel permeation chromatography. The thermal degradation behaviors of polymers are strongly dependent on the organic groups attached to the phosphazene ring (R: S-4,-C 6H 3(-OCH 2O-); S-5,-C 6H 4CH 2OPO(OPh) 2; S-6,-C 6H 4OPO(OPh) 2; S-7,-C 6H 4OCH 2OCH 3). The onset temperature of decomposition ( T 0) of PSt increased from 303 °C to 351 °C in air by the addition of 5 wt.% S-4, whereas S-6 has no ability to increase T 0 value of PSt. The GPC traces of PSt/ S-4 film heated at 180 °C for 30 min in air showed no significant decrease of molecular weight of PSt. A similar enhancement of thermal stability was observed for the PMMA/ S-4 system. From the reaction of radical initiators with S-4, it appears that –OCH 2O– group in S-4 acts as an effective trapping site of peroxy radical. As expected, the physical loss of S-4 with molecular weight increased by using cyclotriphosphazene core from PSt film was significantly suppressed, i.e., the diffusion coefficient of S-4 was three orders of magnitude smaller than that of 3,4-methylenedioxyphenol ( MOP). The enhancement of thermal stability of PSt and PMMA blended with cyclotriphosphazene derivatives were described.