Effect of molecular weights of confined single-chain poly(allylamine) toward proton conduction in inorganic frameworks based on Preyssler-type polyoxometalate

摘要

In this work, poly(allylamine) (PAA) of different average molecular weights (MW = 1600 (I), 3000 (II), and 5000 (III)) are confined in an inorganic framework composed of K+ and Preyssler-type polyoxometalate [Na (H2O)P5W30O110](14-), and the effects toward proton conduction are investigated. All compounds possess one-dimensional channels with a minimum aperture of ca. 6 angstrom, where water molecules and PAA reside. Proton conductivities at 348 K, RH 75% are 2.1-3.5 x 10(-3) S cm(-1) and in the same range, while activation energies of the proton conductions are I (0.46 eV) > II (0.33 eV) similar or equal to III (0.29 eV) and quite large for I. Relaxation times estimated from C-13-CPMASNMR show that the mobility of the PAA backbone is I < II similar or equal to III, suggesting that PAA with a low molecular weight is anchored in the inorganic framework. On the other hand, the mobility of the PAA sidechain is I > II similar or equal to III. Considering the large activation energy of I and that protonated amine group resides on the sidechain of PAA, sidechain mobility of PAA is crucial to the proton conduction in I, while those in II and III occur via rearrangement of hydrogen-bonding networks composed of water molecules and PAA.