A novel of positively charged asymmetry membrane prepared from poly(2,6-dimethyl-1,4-phenylene oxide) by in situ amination: Part III. Effect of benzyl and aryl bromination degrees of polymer on membrane performance and morphologies

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was brominated to different degrees of either benzyl or aryl position with simultaneous benzyl bromination degree around 80%. Membranes were prepared from the brominated PPO (BPPO) by adding the dimethylformamide (DMF) solution of trimethylamine (TMA) into the casting solution with phase inversion method. Membranes were characterized in terms of pure water flux, rejection to the cathodic electrodeposition paint, water content, ion exchange capacity (IEC) and SEM images. The results show that the membrane properties are significantly affected by the bromination processes. Benzyl-substitution enhances the pure water flux but reduces the rejection. The increase in water content of the membrane arises from the polarity of the bromination polymer while not from the charge density as proved by determining the water content of the membranes without adding TMA-DMF solution and the IEC values of the membranes. As for the aryl-substitution, it enhances the pure water permeability but has a negative effect on the rejection. The water content of the membrane increases and then reduces with an increase in the aryl bromination degree. The result is explained from the viewpoint of the polarity of the bromination polymer as well as the hydrophobicity of the bromine group and the charged density by determining IEC values. Furthermore, the SEM images are consistent well with the other measurements.