Influence of acid-base equilibrium in emulsifier-free styrene polymerization with carboxyl-containing initiator on colloidal characteristics of the disperse system (original) (raw)

The role of acid-base equilibrium in emulsifier-free styrene polymerization with a carboxyl-containing initiator, namely, 4,4'-azobis(4-cyanovaieric acid) (CVA), was investigated at the pH of the starting emulsion from 8.3 to 11.5. It was found that the polymerization kinetics, the particle diameter, and the degree of polydispersity of the latexes synthesized at different CVA concentrations and styrene/water ratios depend substantially on both the initial pH of the reaction mixture and the pattern of the changes in pH during the synthesis. Both minima and maxima are observed in the kinetic dependences of pH in different periods of synthesis. The deviations of pH from the starting values were as large as two pH units. The influence of the buffer salt (NaJB'O,) concentration on the polymerization process and the parameters of the latexes synthesized was also studied. It was shown that the establishment of the acid-base equilibrium in the system depends also on the formation of the surface-active oligomers and their distribution between the emulsion phases. The results obtained indicate that the surface charge formed upon ionization of the end carboxyl groups of polymer chains is the main factor of stabilization of growing polymer particles in the system studied.