Synthesis And Characterization Of Cyclic Sodium Polystyrene Sulfonate

Cyclic polymers have attracted great attention due to their unique properties.Recently,with the development of synthetic methodologies,various cyclic polyelectrolytes have been synthesized and exhibited quite different properties compared with the linear analogues.However,as one of the most important parts of polyelectrolytes,the synthetic approach of cyclic polystyrene sulfonate(PSS)has encountered great challenge.Herein,we introduce a versatile synthetic strategy toward the synthesis of cyclic PSSs through rational design of the initiator structure and synthetic pathway.(1)An ATRP initiator with oxygen-free structure was successfully synthesized through Sonogashira coupling reaction.Then the initiator was used to the synthesis of cyclic PS precursors with triazole ring as the only linkage through the combination of ATRP and copper-catalyzed alkyne azide cycloaddition process.Further GPC,1H NMR and IR characterization demonstrated the successful synthesis of the high-purity cyclic PS.Additionally,the stability of triazole ring under different sulfonating conditions was investigated using designed diblock PS with triazole ring as the linkage,and therefore "acetyl sulfate" was used as the sulfonating agent since the well tolerance of the triazole linkage.On the other hand,ester linkage was also tested under such condition and proved considerable degradation.Further kinetic study revealed that 12 h was the proper period for sulfonation process when acetyl sulfate was used as the sulfonating agent.(2)Cyclic PSSs were successfully synthesized from the sulfonation of neutral c-PS precursors adopting the proper sulfonating condition and then subjected to analytical ultracentrifugation(AUC)analysis.The number of repeating units(N)dependence of sedimentation coefficient(s)of linear and cyclic PSS was determined,namely,for linear PSS,sl =(0.34±0.06)N0.41±0.03,and for cyclic PSS,sc =(0.43±0.03)N0.38±0.01,where N was in the range of 63?140.The scaling index indicated that the sedimentation coefficient of cyclic PSS was always larger than that of the linear counterpart due to the smaller hydrodynamic radius.On the other hand,cyclic PSS adopted a random-coil conformation similar to the linear counterpart in 100 mM NaCl aqueous solution,since the electrostatic interaction was well shielded.