Characteristics of Fuel Cell Membranes Prepared by EB Radiation Grafting onto FEP with Styrene Derivatives, Styrene and 2-Methylstyrene

This study used simultaneous electron beam (EB) irradiation to graft styrene derivatives onto a thick poly(tetrafluoroethylene-co-hexafluoro propylene) (FEP) film, with various grafting times ranging from 0.5 to 10 h, grafting temperatures ranging from 30 to , and radiation doses ranging from 10 to 100 kGy. The degree of grafting increased with increasing the dose to a maximum after a grafting time of 5–10 h. The electron spin resonance spectra for the produced radicals showed that the radicals were trapped in the FEP film for a long time even at room temperature, allowing continuous grafting for several hours. The grafting degree in the 2-methylstyrene monomer was lower than in the styrene one, with their grafting degrees differing by a maximum of at a grafting temperature of and a dose of 50 kGy. However, the sulfonation degree of 2-methylstyrene was higher than that of styrene, in which an average of 1.5 sulfonic acid groups were attached to one 2-methylstyrene, regardless of the grafting degree, whereas for styrene it ranged from 1.3 to 0.9 depending on the grafting degree. The ion conductivity values were 2.4 S/cm for 2-methylstyrene at a grafting degree of and 2.5 S/cm for styrene at a grafting degree of .