Dye-partition method of analysis of end groups in nonpolar polymers re-examined: sulfate end groups in persulfate-initiated polystyrene

Abstract

Sulfate, sulfonate, and isothiouronium salt end groups in polystyrene prepared by using the initiator systems K₂S₂O₈, Na₂SO₃/Cu⁺²/O₂, FeCl₃/thiourea, respectively, have been estimated by the dye partition (extrapolation) method. It was observed that while the persulfate-initiated polymers analyzed to contain very low amount of sulfate end groups (about 0.05–0.3 per polymer molecule), the other two initiator systems yield polymers with about 2 salt end groups [SO^-₃ and SC(=N⁺H₂)-NH₂, respectively] per polymer molecule. The low amount of sulfate end group in persulfate-initiated polystyrene is in conformity of the initiation mechanism recently proposed by Ledwith et al. for persulfate-initiated emulsion polymerization of styrene. This study supports our earlier finding that polymer polarity does not affect the results of end-group analysis by the dye-partition technique, contrary to some recent reports which claimed otherwise.