Study on preparation of irregular shaped particle in seeded emulsion polymerization accompanied with regulated electrostatic coagulation by counter-ion species

The seeded emulsion polymerization, basically designed similar to the previous reports except raising the reaction temperature at the end, was conducted for preparing irregular shaped polymer particles incorporating hydrophilic polymer inside the particles as well as on the surface. A 30 wt.% solid and anionic seed latex, poly(methylmethacrylate- co-methyl acrylate), was produced by a conventional emulsion polymerization with anionic initiator and emulsifier. Then, the seeded emulsion polymerization accompanied with the controlled electrostatic coagulation process was carried out with an addition of cationic dimethylaminoethylmethacrylate (DM) and 2,2′-azobis(2-methylamidinopropane) · 2HCl. The coagulation of polymer particles progressed rapidly in the initial 2 h with decreasing the zeta potential of the particles. The polymer yield increased almost linearly until 50% of the monomer was consumed despite the significant decrease in the number of polymer particles. The mechanism of polymerization was speculated on a basis of the nucleation of hydrophilic short chains in the aqueous phase and the slow termination in a polymer particle with the desorption of radicals. The reaction temperature was raised from 333 to 353 K prior to the end of polymerization (1–5 h). The fraction of the irregular-shaped particles in the final latex increased as the duration of raising the temperature was set longer, while the irregularity developed from dumbbell to more progressive shapes.