New Fluorinated Polymers Bearing Pendant Phosphonic Acid Groups. Proton Conducting Membranes for Fuel Cell

Abstract

The synthesis and characterizations of original fluorinated copolymers bearing phosphonic acid side functions for novel membranes potentially involved in fuel cell applications are presented. These copolymers were obtained by chemical modifications of various poly(CTFE-alt-IEVE) and poly[(CTFE-alt-IEVE)-co-(CTFE-EVE)] terpolymers (where CTFE, IEVE, and EVE stand for chlorotrifluoroethylene, 2-iodoethyl vinyl ether, and ethyl vinyl ether) via the Arbuzov reaction. Then, the hydrolysis of the phosphonate moieties into phosphonic acid groups was carried out quantitatively in mild conditions, in the presence of bromotrimethylsilane. The ionic exchange capacities (IECs) determined by potentiometric titration were ranging from 2.9 to 6.8 mequiv/g. The thermal and electrochemical properties of the resulting membranes (processed by casting) were investigated. Whatever the phosphonic acid content, the main degradation started from 250°C, showing a high thermo-oxidative stability of these copolymers. At 25°C and 100% relative humidity (RH), the level of conductivity was found in the range 0.02-20 mS/cm and highly dependent on the IEC. Finally, moderate to good conductivity values (about 0.25 mS/cm) at higher temperature (120°C) and lower RH (25%) were observed, which demonstrated a limited dependence toward both temperature and RH.

Membrane materials and technology for low temperature fuel cells

“…Phosphonic acid-based systems may offer the possibility of adequate proton conductivity over a broad temperature range, although the propensity to condensation by phosphonic acids at high temperature is greater than that of sulfonic acids, and the involvement of water in proton transfer at T < 100 °C is not avoided. Notwithstanding these considerations, and although earlier work on model compounds or polymers having a low concentration of grafted phosphonic groups led to materials of rather low conductivity, 108 the recent literature 109,110 provides some encouraging results. Polvinylphosphonic acid (PVPA) is attracting particular interest as a graft component as in blend and interpenetrating network membranes.…”

Grafting of phosphonate groups onto PVA by acetalyzation. Evaluation of the anti-corrosive properties for the acetalyzed PVA coatings

“…Then, when butyral groups are totally replaced by phosphonate ones, i.e. PVAP4, thermal degradation clearly occurs in two steps: the first one at about 120°C corresponds to phosphonate ester groups cleavage, leading to the corresponding phosphonic acid groups [51]. Then degradation of vinyl alcohol units occurs until about 300°C, temperature at which a plateau was reached due to condensation of phosphonic acid to thermally stable anhydride bonds: at 600°C less than 60% of weight loss was observed.…”

Facile method towards functionalization of partially fluorinated polyarylethers via sequential post-polymerization modification

“…This encourages us to develop a new strategy to incorporate a variety of functionalities into fluoropolymers to broaden their applications. Although PPM has been widely used to prepare non-fluorinated functional polymers [29][30][31][32][33][34], very few functional fluoropolymers were prepared via PPM [7,[35][36][37][38][39]. Recently a new class of fluoropolymers, partially fluorinated arylene vinylene ether (FAVE) polymers, was developed [5,10].…”