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