X-ray scattering characterization of polystyrene chains tagged with a single quaternary ammonium group per chain.

Polymers containing a moderate amount of covalently bound ionic groups are widely used as membrane materials for electrochemical energy conversion devices such as fuel cells and electrolyzers. The performance of these ion-containing polymers largely depends on the microstructures, especially the structures of ion aggregates. To investigate the effects of the local chemical environment of ionic groups to the ionic aggregate and chain structures, we synthesized and characterized polystyrene chains containing a single quaternary ammonium group at the end of chains, in the middle of the chains, and right next to the secondary-butyl initiator motif using amino-functionalized diphenylethylene monomer. X-ray scattering characterization reveals three structural features of these model polystyrene chains. First, the domain spacing between ion aggregates changes with the location of the ionic groups in chains. Second, ionic groups stretch the polystyrene chains. Third, all polystyrene chains even without an ionic group display strong upturn curves in the small-angle domain, and the features of the upturn curves vary with the location of ionic groups in chains and processing pathways.