Preparation of monodisperse melamine-formaldehyde microspheres via dispersed polycondensation

Abstract

We have successfully synthesized relatively monodisperse and cross-linked melamine-formaldehyde (MF) microspheres by dispersed polycondensation and subsequent pH adjustment with serum replacement cleaning. The average particle sizes ($\overline {D_w }$: weight-average and$\overline {D_n }$: number-average), the polydispersity index ($\overline {D_w } /\overline {D_n }$), the number of particlesN _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$\overline {D_n }$ andN _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 ofN _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.