MORPHOLOGICAL-STUDIES OF LIGHTLY SULFONATED POLYSTYRENE USING NA-23 NMR - EFFECTS OF POLYDISPERSITY IN MOLECULAR-WEIGHT

Ion content and molecular weight have been shown to affect the Na-23 N MR spectra of monodisperse sodium-neutralized sulfonated polystyrene i onomers (MNaSPS). A new NMR peak at -2.7 ppm appears at ionization lev els above 1.2% and molecular weights of a least 35 000; this peak is n ot present in polydisperse NaSPS. The fraction of NMR intensity due to this peak is relatively constant above M(n) similar to 100 000. It is proposed that this peak is due to a distorted version of an isolated site. Along with the new -2.7 ppm peak, the monodisperse materials als o have far fewer isolated ions than the corresponding polydisperse ion omers. It is possible that the greater chain uniformity of the monodis perse ionomers eliminates plasticization of the aggregates by the low molecular weight components and steric hindrances from the high molecu lar weight components and permits more complete aggregation of the ion ic groups. The new NMR peak can be removed by casting from a cosolvent of THF/water, but not by casting from THF/methanol. Blending of two o r more monodisperse materials in solution followed by annealing result ed in an NMR spectrum similar to that of a polydisperse material; howe ver, the behavior of the blend without annealing did not replicate tha t of polydisperse NaSPS.