Poly(vinyl alcohol)-based polymer electrolyte membranes containing polyrotaxane

Polymer electrolyte membranes featuring ionic channels have been prepared by sulfonation of crosslinked poly(vinyl alcohol)/polyrotaxane membranes. The ionic channels were prepared using rod-like polyrotaxanes, created as an inclusion complex between poly(ethylene glycol) (PEG) and α-cyclodextran. The size of the polyrotaxane was controlled by the molecular weight of PEG. Proton conductivity as well as methanol permeability increased as the amount of sulfonated polyrotaxane inside the membrane increased. Sulfonation of the membrane increased with increasing amount of polyrotaxane, as confirmed by determination of its ionic exchange capacity. While the proton conductivity showed no significant dependence on the size of the polyrotaxanes, resistance to methanol transport depended on their size, implying a barrier role for these polyrotaxanes within the membrane. Well-dispersed polyrotaxane inside the membrane, as a mimic of ionic channels, played a role in transporting proton as well as in blocking methanol crossover, indicating that this concept to prepare membranes may prove useful in direct methanol fuel cell applications.