Phase structure and mechanical properties of modified poly(phenylene oxide) with high fluidity

Polyphenylene oxide (PPO) possesses excellent mechanical properties and heat resistance but extremely high viscosity. Virgin PPO has to be blended with polystyrene (PS) to reduce the viscosity. However, PS is miscible with PPO; it reduces not only the viscosity but also the heat distortion temperature and, consequently, narrows the applications. This paper is an attempt to develop crystalline additives that will dissolve in PPO at processing temperature but precipitate and recrystallize after molding. Thereby, the additives are able to reduce the viscosity of PPO melts but will not reduce the heat distortion temperature of PPO materials. In the present work, a PPO was compounded with bisphenol-A and bisphenol-S as well as PS separately on Haake Rheometer and the mixing torque was recorded. The dynamic properties of the modified PPO were analyzed with DMA and the mechanical properties were tested at ambient and elevated temperatures. The phase structures were examined with DSC and TEM. The effect of the additives on the fluidity, mechanical properties, and heat distortion temperature of the PPO compounds was investigated. All three additives dissolved in the PPO during mixing and reduced the mixing torque. But bisphenol-S precipitated after molding and is present as 40nm crystalline phases in the molded materials; it did not affect the glass transition nor did it deteriorate the performance at elevated temperature. While bisphenol-A did not recrystallize after molding; it reduced the T _g and heat distortion temperature as does PS. General principles about such plasticizers with phase transition for PPO were proposed.