Poly(tetrafluorostyrenephosphonic acid) - polysulfone block copolymers and membranes

A series of ionic ABA triblock copolymers having a central polysulfone (PSU) central block and poly(2,3,5,6,-tetrafluorostyrene-4-phosphonic acid) (PTFSPA) outer blocks with different lengths were prepared and studied as electrolyte membranes. PSU with terminal benzyl chloride groups was used as a bifunctional macroinitiator for the formation of poly(2,3,4,5,6-pentafluorostyrene) (PPFS) blocks by atom transfer radical polymerization (ATRP). Selective and complete phosphonation of the PPFS blocks was achieved via a Michaelis-Arbuzov reaction using tris(trimethylsilyl)phosphite at 170 °C. Copolymer films were cast from solution and subsequently fully hydrolyzed to produce transparent flexible proton conducting PTFSPA-b-PSU-b-PTFSPA membranes with a thermal stability reaching above 270 °C under air, and increasing with the PTFSPA content. Studies of thin copolymer electrolyte membranes by tapping mode atomic force microscopy showed phase separated morphologies with continuous proton conducting PTFSPA nano scale domains. Block copolymer membranes reached a proton conductivity of 0.08 S cm-1 at 120 °C under fully hydrated conditions, and 0.8 mS cm-1 under 50% relative humidity at 80 °C