Monodisperse micron-sized polystyrene particles crosslinked with a novel poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) tri-block diol diacrylate (t-BDDA) were produced via simple dispersion polymerization. It was established that the monomer-diffusible surface characteristics of primary particles played a decisive role in producing the monodisperse crosslinked polymer particles. We named this concept a diffusion-controlled polymerization method, DPM. Here in this study, particularly, t-BDDA is proposed as a very useful crosslinker capable of self-assembling and crosslinking in the process of particle formation and particle growth.