Synthesis and characterisation of poly(sodium 4-styrenesulfonate) combs

A series of poly(sodium 4-styrenesulfonate) (NaPSS) combs has been synthesized. Architecturally and molecularly well-defined polystyrene combs were initially produced with the branch molecular mass fixed at 30,000 g/mol, the average number of branches being the major variable. Conditions were established whereby linear polystyrene (PS) synthesized via anionic polymerization was chloromethylated using zinc (II) chloride, side-reactions such as Friedel-Crafts alkylation being suppressed. An excess of diphenylethylene-capped polystyryllithium (PSLi) was then reacted with the functionalized backbone to yield materials having long chain branches. The polystyrene combs were then reacted with sulfuric acid to yield water-soluble poly(styrenesulfonic acid) combs and subsequently neutralized with sodium hydroxide to give the corresponding sodium 4-styrene sulfonate species. The extent of sulfonation was determined via titration and nuclear magnetic resonance spectroscopy (NMR). Aqueous triple-detector size exclusion chromatography (SEC) was used to characterize the sulfonated combs. Although the SEC traces were monomodal and the Mn values agreed well with the expected values, an increase in the polydispersity index compared to the polystyrene combs may reflect the susceptibility of the sulfonation reaction to cross-linking.