The concentrations and probable nature of charged oligomers formed by aq.-phase termination in the persulfate-initiated emulsion polymn. of styrene were measured by isotachophoresis. Isotachophoresis has some advantages over other techniques in that it separates species according to their mol. wt., geometry, and charge. The charged water-sol. oligomeric species were detected in expts. in which particles were nucleated in a surfactant-free environment. Identification of the moieties present was made by comparison with model compds. Evidence was found for bimol. combination as a major mechanism of termination in the aq. phase, although the possibility of disproportionation could not be ruled out. The species formed in the aq. phase under satd. monomer conditions were subject to further reaction towards the end of polymn. The relatively large concns. of nonradical aq.-sol. oligomeric compds. demonstrate conclusively that initiator efficiencies are not 100%, as is often assumed in such systems.
|Journal||Journal of Polymer Science, Part A: Polymer Chemistry|
|Publication status||Published - 1993|