Abstract
To clarify the growth mechanism of polymeric particles in the soap-free emulsion polymerization, the growth process of polymeric particles was observed with molecular scale using atomic force microscope (AFM). The soap-free emulsion polymerization was carried out using 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50) as a cationic initiator. The initiator, V-50, enables us to synthesize cationic polymers and polymeric particles and make them adsorb on the negatively charged mica surface with molecular scale smoothness. Hence, the growth process of polymeric particles is able to be observed in situ on mica surface directly by tapping-mode AFM. In the case of polystyrene particles, we succeeded in observing the nucleation process and concluded that PSL particles generated through micellization nucleation process. It was found in this study that the growth mechanism of PSL particles after the nucleation process was composed of the following processes; coagulation, swelling process by the absorption of the monomers, solidification by the polymerization and adhesion of the small particles in the case of rich initiator. As for the forth adhesion process, hard particles which are formed by high polymerization grow with adhesion of tiny particles, which generate through the nucleation in the bulk even in the particle growth period, to their surfaces. Hence, in the case of PSL particle, as the amount of initiator increases, the size of final particles becomes larger.
