Highly phosphonated polypentafluorostyrene

摘要

The synthesis and conductivity of highly phosphonated polypentafluorostyrene are demonstrated. Efficient postphosphonation (90%) was achieved via the classical nucleophilic aromatic substitution (S _N~(Ar)) Michaelis-Arbuzov reaction of polypentafluorostyrene (PFS) with tris(trimethylsilyl) phosphite. The contrivance is in the cumulative electron-withdrawing effect of the fluorine functions. This simultaneously facilitates the S_N~(Ar) reaction and enhances acidity of the resulting phosphonic acid. The most important consequence is a substantial increase of the H~+ conductivity being the highest one measured on phosphonated polymer: σ = 0.1 S cm~(-1) at 108 °C, p = 10 5 Pa water vapor pressure. This value is 4 times higher than the one for poly(vinylphosphonic acid) (σ = 0.025 S cm~(-1)) and higher than Nafion 117 (σ = 0.075 S cm~(-1)) under the same conditions. Additionally, this polymer showed outstanding resistance to oxidative and thermal treatment (Tdecomp = 340 °C at 70% O2 atmosphere). All this makes the phosphonated PFS a very promising candidate as polymer electrolyte for fuel cell applications.