Hydrophobic networks for advanced proton conducting membrane: Synthesis, transport properties and chemical stability

The design of interpenetrated networks (IPN) membranes for fuel cell applications requires both an electrolyte and a neutral network. The composition and architecture of the latter are of major importance for the final IPN membrane properties. In this work, networks based on a fluorinated diepoxy oligomer (DFODDE) and a non-fluorinated triepoxy monomer (TMPTGE) were synthesized. The network composition was varied from 100% DFODDE to 100% TMPTGE, resulting in an increase of the crosslinking density and concomitantly a decrease of the fluorine content. The curing process was optimized to achieve a total epoxy conversion and the chemical structure of the networks was characterized by Raman and Infrared spectroscopies. The physical, thermal and chemical membrane properties were studied and discussed as a function of the crosslinking density and of the fluorine content. Increasing the crosslinking density led to a decrease of the membrane permeability to oxygen. Water sorption properties depended on both parameters, with a prevailing role of the fluorine content on the water uptake and a major influence of the crosslinking density on the diffusion parameter. The thermal stability increased also with the fluorine content. All materials exhibited a good stability in water at 80°C but a significant weight loss after immersion in a concentrated H2O2 solution. Altogether, these results indicate that networks containing 20% of TMPTGE exhibit an interesting set of properties (low oxygen permeability, high Tg, good chemical and thermal stability) to behave as a neutral partner in an IPN membrane. Moreover, the low water uptake and diffusion rate measured in these networks make them attractive for water barrier membranes. •We investigate a series of fluorinated networks for membrane fuel cell applications.•The crosslinking density is controlled by the network composition.•Water sorption properties are related to both fluorine content and crosslinking density.•Gas permeability is governed by the crosslinking degree.•The hydrolytic and oxidative stabilities of the membranes are investigated.