Fuel cell membranes via solvent-free polymerization

3. Results and discussion All base polymers were obtained after precipitation as white to beige powders in quantitative yields and with high molecular weights (hinh. > 0.5 dl/g). Membranes with a theoretical ionexchange capacity (IEC) ranging from 0 to 2.08 mmol/g (PES) or from 0 to 2.25 mmol/g (PPEK) should be obtained, assuming only a sulfonation of the pendant phenyl ring. The sulfonation of poly(ether ether ketone)s only took place at the para-position of the pendant phenyl ring (reaction time 24 h). Surprisingly, the sulfonation of the poly(ether sulfone)s led to a “double-sulfonation” of biphenyl unit. Reaction times up to 12 h gave products with almost the desired “single sulfonation”, whereas longer reaction times led to a second sulfonation of the biphenyl unit in meta-position to the pendant phenyl ring.