Polymer end groups in persulfate-initiated styrene emulsion polymerization

Abstract

MALDI-TOF-MS investigations of the polymer inside the particles at the end of a persulfate-initiated emulsifier-free emulsion polymerization of styrene reveal - beside sulfate groups - a variety of different end groups of the polymer molecules almost independent of the buffer concentration employed during the polymerization. The results support at least the existence of the following end group combinations: H-H, H-OH, K +- OO-OH, K +- OO-K +- OO, HO +- OH, K +- OSO 3 -H, K +- OSO 3 -OH, and K +- OSO 3 K +- OSO 3 . These results lead to conclusions concerning particle nucleation and radical entry. As non-micellar particle nucleation is governed by the solubility of waterborne oligomers, chains started with radicals formed by side reactions in the aqueous phase obviously play an important role in particle nucleation. Concerning radical entry, the results suggest that surface activity of the entering radicals is not a prerequisite.