Radiation-induced dispersion polymerization of 1-methacryloxybenzotriazole (MABt) in ethyl propionate starts as homogeneous mixture and the resulting polymer precipitates as spherical particles. Formation, size, and shape of polymer particles are strongly dependent on the initial monomer concentration. Three regions can be distinguished: formation of deformed particles at concentrations of ≦15 w/v-% MABt
formation of spherical particles at concentrations from 18 to 35 w/v-% MABt
no precipitation of polymer at concentrations of ≧ 40 w/v-% MABt. The spherical particles at 20 w/v-% MABt had a diameter of 0.54 ± 0.31 μm for 3 kGy irradiation and 2.93±0.68 μm for 30 kGy. The number distribution of the microspheres shows that the spherical particles with small sizes formed at low irradiation dose (low conversion) disappears with increasing irradiation dose because of multi-coating by newly produced polymer. © 1989 Steinkopff.