SynopsisThe polyaminocarboxylic acids, ethylenediaminetetraacetic acid (EDTA), cyclohexanedirtminetetraacetic acid (CDTA), and diethylenetriaminepentaacetic acid (DTPA) have been used to chelate the chromous and chromic ions when the system chromous ion-hydrogen peroxide is being used as an initiator for the emulsion polymerization of styrene. With CDTA and DTPA the zero-order rates of polymerization increase continuously with increasing pH but with EDTA the zero-order rate is constant over the range pH 5-7 and increases rapidly above pH 7. These results are to be anticipated from the variation of the redox potential of the chromous ion-chromic ion-chehting agent system with pH, since with CDTA and DTPA the redox potential decreases continuously with pH while with EDTA the redox potential varies only slightly over the range pH 5-7.The system, chromous ion-polyaminocarboxylic acids-hydrogen peroxide, has been studied as an initiator for the emulsion polymerization of styrene. The relative zero-order rates of polymerization, over the pH range 2-7, have been compared with the reducing power of the chromous chelates as indicated by the variation of redox potential of the chromous ion-chromic ion-polyaminocarboxylic acid system with pH. The polyaminocarboxylic acids which have been studied are, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) , and cyclohexanediaminetetraacetic acid (CDTA).
EXPERIMENTAL A. Preparation and Purification of MaterialsStyrene, the polyaminocarboxylic acids, nitrogen, the emulsifying agent which was prepared by sulfating the condensation product of capryl alcohol with 21 molecules of ethylene oxide, and hydrogen peroxide were purified as described by Bond and Jones.'S2In preparation of chromous sulfate, the apparatus (Fig. 1) was freed from oxygen by passing purified nitrogen through for 30 min. and a slow stream was maintained throughout the preparation. A 72 g. portion of analytical 2179
