Direct observation of an isolated cyclic sodium poly(styrenesulfonate) molecule by atomic force microscopy

A cyclic sodium poly (styrenesulfonate) (c-PSS) from cyclic polystyrene by sulfonation reaction was prepared and the closed loop structure of the isolated cyclic polyelectrolyte was observed by scanning probe microscopy (SPM). Linear polystyrene, 1-PS was prepared by a living anionic polymerization using naphthalene potassium as an initiator and weight-averaged molecular weight of 1-PS was determined by multi-angle laser light scattering (MALLS). Degrees of sulfonation of c-PSS and 1-PSS, determined by inductively coupled plasma (ICP) mass spectroscopy, were 74% and 72% respectively. The PSS molecules were observed by atomic force microscopy (CFM) with intermittent contact mode and a cantilever tip, microfabricated from silicon, was used for the observation. The result shows that the ring-shaped structure of a synthetic cyclic polymer is evidently confirmed based on the direct observation of the individual chains by AFM.