You might want to check out "NMR and FT-IR studies of sulfonated styrene-based homopolymers and copolymers" by Jin Chuan Yang, et al., Polymer, Volume 43, Issue 19, 1 September 2002, Pages 5125-5132. The homopolymers studied included sodium poly(styrene sulfonate). I do not have access to the full article, and do not know if it shows an actual NMR spectrum of NaPSS. Good luck in your research. AF.