Polystyrene Chain\nGeometry Probed by Ion Mobility\nMass Spectrometry and Molecular Dynamics Simulations

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