Overall enhanced properties of high performance semi-crystalline poly(ether ketone)-based multiblock copolymers via thermal treatment for proton exchange membranes

A series of multiblock copolymers based on semi-crystalline hydrophobic poly(ether ketone) segments and partially fluorinated hydrophilic poly(arylene ether sulfone) segments were prepared for applications as proton exchange membranes. Through acidification, poly(ether ketimine) precursors were transformed into semi-crystalline acid form poly(ether ketone) segments. Nanophase separated morphologies were observed via small angle X-ray scattering with ion cluster dimensions ranging from 15.1 nm to 17.5 nm. Due to semi-crystalline domains within the polymer, these membranes exhibited outstanding chemical and mechanical stabilities as well as enhanced conductivities under fully hydrated and reduced humidity conditions. Moreover, film processing studies indicated that enhanced nanophase separation and desired membrane properties could be achieved via thermal annealing. All annealed PEK-6FBPSH membranes exhibited increased ion cluster dimensions ranging from 19.3 nm to 27.9 nm with significantly improved proton conductivities. Annealed membrane 4-b-14 were superior to Nafion 212 at low humidity and a wide temperature range.