SYNOPSISThe concentrations and probable nature of charged oligomers formed by aqueous-phase termination in the persulfate-initiated emulsion polymerization of styrene were measured by isotachophoresis. Isotachophoresis has some advantages over other techniques (e.g., GPC, UV spectroscopy) in that it separates species according to their molecular weight, geometry, and charge. The charged water-soluble oligomeric species were detected in experiments in which particles were nucleated in a surfactant-free environment. Identification of the moieties present was made by comparison with model compounds. Evidence was found for bimolecular combination as a major mechanism of termination in the aqueous phase, although the possibility of disproportionation could not be ruled out. The species formed in the aqueous phase under saturated monomer conditions were found to be subject to further reaction towards the end of polymerization. The surface adsorption characteristics of the compounds formed were compared with those of known surfactants and showed good agreement with the assumptions in the model of Maxwell et al.

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SUMMARYStyrene and ethylmethacrylate were copolymerized in bulk at 62~and several monomer feed ratios. At moderately high conversion, anomalous copolymerization behaviour occurred. Although the onset of the departures from expected copolymerization behaviour seems to be related to the onset of the gel-effect, this relation did not hold when mimicking higher conversion by adding an amount of homopolymer.Obviously the propagation reactions are not only affected by changes in diffusion characteristics but also by changes in other medium characteristics e.g. interactions between monomeric and copolymeric species. INTRODUCTIONIn many cases the course of a copolymerization process can be described by models considering both monomer reactivity and ultimate unit dependent chain-end reactivity. Among these models, the well-known classical Alfrey-Mayo (AM) model is outstanding. From many studies on copolymers, however, the r-values appear to be dependent on the nature of the solvent (I-5) pressure (3) and temperature (6) but assumingly independent of conversion provided the degree of conversion is moderate and the system is diluted.However, from recent reviews it becomes clear that in some cases even the integrated Alfrey-Mayo model is inadequate to describe the copolymerization behaviour up to high conversions. For example, Johnson (7) and Dionisio (8) reported anomalous behaviour in the copolymerization of the system styrene methyl methacrylate, Kelen (9) in the copolymerization of vinylidene cyanide-maleic anhydride and Zil'Berman (10) in the copolymerization of methacrylamide-methacrylic acid. Recently, we have studied the system styrene-ethyl methacrylate in bulk. We found experimental curves of monomer feed ratio versus conversion that deviate significantly from the relationships to be expected on the grounds of the integrated AM model. Both monomer feed ratio (q) and conversion were calculated from data obtained by quantitatively monitoring monomer concentrations by means of GLC during the entire course of the reaction. This method, introduced by German and Heikens (11,12), is particularly useful in studies on high