Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) films. II. Properties of sulfonated membranes

Abstract

Proton exchange membranes were prepared by radiation‐induced grafting of styrene onto commercial poly(tetrafluoroethylene‐co‐hexafluoropropylene) films using a simultaneous irradiation technique followed by a sulfonation reaction. The resulting membranes were characterized by measuring their physicochemical properties such as water uptake, ion exchange capacity, hydration number, and proton conductivity as a function of the degree of grafting. The thermal properties (melting and glass transition temperatures) and thermal stability of the membrane were also investigated using differential scanning calorimetry and thermal gravimetric analysis, respectively. Membranes having degrees of grafting of 16% and above showed proton conductivity of the magnitude of 10−2 Ω−1 cm−1 at room temperature, as well as thermal stability at up to 290°C under an oxygen atmosphere. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2443–2453, 2000

Estudo do comportamento de compostos de PVC com adição de amido

“…O processo oposto a reticulação é a cisão ou quebra da cadeia principal, na qual, sob ação da energia de radiação, ocorre a quebra de ligações C-C, levando à redução do peso molecular médio e a degradação do polímero [9,17] . Na modificação polimérica por irradiação em solução, o solvente possui a função de promover o inchamento da matriz polimérica, e assim aumentar a mobilidade das cadeias nas camadas internas do polímero, favorecendo a sua interação com os sítios ativos, levando a graus de reticulação mais elevados [23,24] . Mecanismos de formação das ligações cruzadas têm sido propostos para a PSU, através de ligações-H nos grupamentos isopropilidenos e ligações-Y, ou ligações terminais, por meio dos grupamentos aromáticos.…”

Radiation-grafted membranes based on polyethylene for direct methanol fuel cells

“…Nasef et al [29] and Gubler et al [30] outlined in detail the problems encountered during proton conduction measurements for the grafted PEMs, in which grafting was conducted on polymer film substrates. It was described that at low DG, the polystyrene grafts are located near the surface of the film while the membrane interior remains ungrafted and subsequently exerts a high local resistance to proton conduction due to inhomogeneous distribution of ion exchange sites over the area of the membrane.…”

Radiation-induced grafting of styrene onto ultra-high molecular weight polyethylene powder for polymer electrolyte fuel cell application

“…In many previous studies, a wide variation in the DS was observed when film (rather than powder in the present study) was used as substrate for the grafting reaction and subsequently sulfonated [37,38]. The origin of this variation is due to the local differences in graft level due to inhomogeneities over the area of the membrane.…”

“…It is also described in the literature [16,37,38] that as the DG approaches ∼20%, more grafts are distributed near the membrane interior, resulting in a diminution of the local resistance. Consequently, the proton conductivity increases and an additional increase in the DG does not bring about considerable increases in the conductivity because of the achievement of a possibly more homogenous distribution of the sulfonated polystyrene grafts within the membrane.…”

“…Nasef et al [37] and Gubler et al [38] outlined in detail the problems encountered during proton conduction measurements for the grafted PEMs, in which grafting was conducted on polymer film substrates. It was described that at low DG, the polystyrene grafts are located near the surface of the film while the membrane interior remains ungrafted and subsequently exerts a high local resistance to proton conduction due to inhomogeneous distribution of ion exchange sites over the area of the membrane.…”