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Synthesis and NMR studies of the polymer membranes based on poly(4-vinylbenzylboronic acid) and phosphoric acid

2008    Sezgin, Aslihan; Akbey, Uemit; Hansen, Michael Ryan; Graf, Robert; Bozkurt, Ayhan; Baykal, Abduelhadi

Proton conduction in novel anhydrous membranes based on host polymer, poly(4-vinylbenzylboronic acid), (P4VBBA) and phosphoric acid, (H3PO4) as proton solvent was studied. The materials were prepared by the insertion of the proton solvent into P4VBBA at different stoichiometric ratios to get P4VBBA center dot chi H3PO4 composite electrolytes. Homopolymer and the composite materials were characterized by FT-IR, B-11 MAS NMR and P-31 MAS NMR. B-11 MAS NMR results suggested that acid doping favors or leads to a four-coordinated boron arrangement. P-31 MAS NMR results illustrated the immobilization of phosphoric acid to the polymer through condensation with boron functional groups (B-O-P and/or B-O-P-O-B). Thermogravimetric analysis (TGA) showed that the condensation of composite materials starts approximately at 140 degrees C. An exponential weight loss above this temperature was attributed to intermolecular condensation of acidic units forming cross-linked polymer. The insertion of phosphoric acid into the matrix softened the materials shifting T-g to lower temperatures. The temperature dependence of the proton conductivity was modeled with Arrhenius relation. P4VBBA center dot 2H(3)PO(4) has a maximum proton conductivity of 0.0013 S/cm at RT and 0.005 S/cm at 80 degrees C. (C) 2008 Elsevier Ltd. All rights reserved.