Polystyrene Chain Geometry Probed by Ion Mobility Mass Spectrometry and Molecular Dynamics Simulations

Abstract

Polystyrene (PS) is a thermoplastic polymer commonly used in various applications due to its bulk properties. Designing functional polystyrenes with well-defined structures for targeted applications is of significant interest due to the rigid and apolar nature of the polymer chain. Progress is hindered to date by the limitations of current analytical methods in defining the atomistic-level folding of the polymer chain. The integration of ion mobility spectrometry and molecular dynamics simulations is beneficial in addressing these challenges. However, data on gas-phase polystyrene ions are rarely reported in the literature. We herein investigate the gas phase structure of polystyrene ions with different end groups to establish how the nature and the rigidity of the monomer unit affect the charge stabilization. We find that, in contrast to polar polymers in which the charges are located deep in the ionic globules, the charges in the PS ions are rather located at the periphery of the polymer backbone, leading to singly and doubly charged PS ions adopting dense elliptic-shaped structures. Molecular dynamics (MD) simulations indicate that the folding of the PS rigid chain is controlled by phenyl ring interactions with the charge ultimately remaining excluded from the core of the globular ions, whereas the folding of polyether ions is initiated by the folding of the flexible polyether chain around the sodium ion that remains deeply enclosed in the core of the ions.