Revisiting the Preparation of Disc-Like Polymer Particles Based on Seeded Dispersion Polymerization: Multihollow Particles Achieved over a Wide Range of Conditions.

The preparation of disc-like polystyrene (PS) particles via seeded dispersion polymerization of 2-ethylhexyl methacrylate (EHMA) was previously demonstrated using a shaker with the PS particles as seeds in methanol/water medium in the presence of decane and subsequent removal of PEHMA and decane, but only under restrictive conditions. Moreover, no structural visualization of the disc-like particles by transmission electron microscope (TEM) was conducted. In this work, we revisit this synthesis using a conventional magnetic stirring apparatus, significantly broadening the range of feasible conditions (i.e., methanol/water mass ratios of 10/0-5/5, stirring rates of 80-360 rpm, and polymerization times of 2-24 h). Systematic studies reveal that disc-like morphology can be achieved even with smaller PS seed particles (>730 nm) or alternative hydrocarbons (e.g., hexadecane). Crucially, we recognize for the first time that these disc-like particles exhibit a multihollow structure with compartmentalized voids (50-300 nm), formed via phase separation between PS and decane during polymerization and subsequent decane removal. A mechanism for this unique structure is proposed based on experimental evidence. This work is expected to provide useful insights into the preparation of polymer particles with both disc-like shape and multihollow structure.