Morphological Studies of Lightly Sulfonated Polystyrene Using ²³Na NMR:  Effects of Polydispersity in Molecular Weight

Abstract

Ion content and molecular weight have been shown to affect the 23Na NMR spectra of monodisperse sodium-neutralized sulfonated polystyrene ionomers (MNaSPS). A new NMR peak at −2.7 ppm appears at ionization levels above 1.2% and molecular weights of a least 35 000; this peak is not present in polydisperse NaSPS. The fraction of NMR intensity due to this peak is relatively constant above M n ∼ 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 also have far fewer isolated ions than the corresponding polydisperse ionomers. It is possible that the greater chain uniformity of the monodisperse ionomers eliminates plasticization of the aggregates by the low molecular weight components and steric hindrances from the high molecular weight components and permits more complete aggregation of the ionic 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 or more monodisperse materials in solution followed by annealing resulted in an NMR spectrum similar to that of a polydisperse material; however, the behavior of the blend without annealing did not replicate that of polydisperse NaSPS.

Radial loop and extreme vessel tortuosity in the transradial approach: Advantage of hydrophilic‐coated guidewires and catheters

“…For the ionomer that was treated with TEOS using MeCl 2 , the peak is shifted to −7.9 ppm which indicates, based on prior similar studies,28–31 that the Na + ions, on the average, are less associated with each other than they would be in the unfilled control. Perhaps this peak shift might be accounted for by silicate structures that, in the course of their growth, have intruded between some of the associations of PET–SO Na + ion pairs so as to weaken interpair interactions.…”

“…These field gradients can be especially due to the strong electric fields posed by other Na + ions or to polymer‐affixed anions, such as—SO groups, in the vicinity. It has been established that as peaks shift to less negative values, the interactions with Na + ions become weaker 24–32. This concept can be put to use in determining whether Na + ions are isolated or exist in aggregates, although the absolute size of these aggregates cannot be derived from this method.…”

Review and critical analysis of the morphology of random ionomers across many length scales

“…23 Na NMR experiments can be used to determine quantitatively the amount of isolated ions in sodium-neutralized ionomers; these experiments are critically important since they represent the only quantitative example where the fraction of isolated ions was determined for nontransition-metal neutralized materials. In a series of papers [29,[50][51][52], Cooper and coworkers used NMR to study NaSPS in great detail. The authors found that in fully neutralized samples at $2 mol% sulfonation level, the sodium atoms were both isolated and aggregated; while at $4 mol% sulfonation level, all sodium atoms were aggregated.…”

Influence of ionic aggregation on the surface energies of crystallites in poly(butylene terephthalate) ionomers

“…The sodium nuclei existing in lone ion pairs yield a sharp peak centered around 7 ppm, while the sodium nuclei in the ionic aggregates (i.e. doublets, triplets,., multiplets) yield a broad peak centered in the range from K 8 to K12 ppm [22,[26][27][28][29]. Fig.…”

“…O'Connell et al [26][27][28][29] have shown that sodium ions in dry, lightly sulfonated polystyrene ionomers may exist in two distinctly different environments: (1) isolated sodium nuclei in lone sodium-sulfonate ion pairs and (2) sodium nuclei in close proximity to other sodium nuclei (i.e. in ionic aggregates).…”