Structures and transport properties of hydrated water-soluble dendrimer-grafted polymer membranes for application to polymer electrolyte membrane fuel cells

The concept of a dendrimer-grafted polymer using precisely-defined water-soluble dendritic architecture in a copolymer with a linear polymer backbone for PEMFC was presented. The second-generation sulfonic poly aryl ether dendrimers were grafted onto three different types of linear backbone polymers, e.g., PECH, PS, and PTFE for the preparation of three different types of dendrimer-grafted polymer such as PECH-D2, PS-D2, and PTFE-D2. In all cases, the equilibrium systems exhibited nanophase-segregation in which water phase was formed and associated with the hydrophilic dendrimers. The water coordination number for water molecules in the water phase increased with increasing water content for all cases. At the same water content, the water coordination number increased in order of PECH-D2 < PS-D2 < PTFE-D2, indicating that the similarity of the water structure to the bulk water was also in order of PECH-D2 > PS-D2 > PTFE-D2. It was suggested that the structure of the water phase and the structure factor analysis can be understood consistently in terms of the hydrophilicity (or hydrophobicity) of backbone polymer. The PTFE-D2 dendrimer-grafted polymer membrane may have comparable performance to Nafion and Dendrion membranes in a PEM fuel cell. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).