Synthesis of Anion Electrolyte Membrane through Radiation-induced Graft Polymerization of Poly(4vinylbenzyl chloride) onto Isotactic Polypropylene Film

Radiation grafting, a widely used process for preparing different functional materials, allows the facile amalgamation of desirable properties from two or more polymers without altering the inherent properties of the base substrate. In this study, an anion electrolyte membrane (AEM) was successfully prepared through radiation grafting of poly(vinylbenzyl chloride) (PVBC) from isotactic polypropylene (iPP) film using gamma-ray irradiation. It was shown that the amount of grafted PVBC increased with increasing absorbed dose, which yielded iPP-g-PVBC with 127% degree of grafting at 50 kGy. The iPP-g-PVBC was reacted with aqueous trimethylamine hydrochloride solution to introduce quaternary ammonium ions, thereby producing the AEM membrane in chloride form (iPP-g-PVBC-TMA-Cl), which was further reacted with potassium hydroxide (KOH) to convert it into hydroxide form (iPP-g-PVBC-TMA-OH). The pristine, grafted and functionalized iPP films were characterized using attenuated total reflectance – Fourier transform infrared spectrometer, thermogravimetric analyzer and scanning electron microscopy – energy dispersive X-ray spectrometer. The effect of degree of grafting on the ionic conductivity, ion exchange capacity and water uptake were evaluated in both AEM’s chloride and hydroxide forms. Results showed that a higher degree of grafting films achieved higher ionic conductivity, ion exchange capacity and water uptake for both chloride and hydroxide forms. The synthesized AEM with a degree of grafting of 70% (IEC = 1.87 meq/g) obtained a conductivity of 129.34 mS/cm, which is higher than the AEMs reported in previous works.