Preparation of monodisperse melamine-formaldehyde microspheres via dispersed polycondensation

We have successfully synthesized relatively monodisperse and cross-linked melamine-formaldehyde (M-F) microspheres by dispersed polycondensation and subsequent pH adjustment with serum replacement cleaning. The average particle sizes (D̄_w: weight-average and D̄_n: number-average), the polydispersity index (D̄_w/D̄ _n), the number of particles N_p, and the gel content of the M-F microspheres were observed by varying the pH, the surfactant concentration, and the polymerization temperature. We observed that both the pH and the polymerization temperature were predominant factors in determining D̄_n and N_p, but the effect that the temperature and pH had on the gel content (> 94% for all samples) was negligible. The exponents of the slopes of plots of N_p, versus pH and surfactant concentration were -10 and 0.6, respectively. Particle nucleation and growth were achieved within short periods; the incessant coagulation occurred even in the presence of surfactants.