Solvent evaporation self-motivated continual synthesis of versatile porous polymer microspheres via foaming-transfer

• A method to prepare porous polymer microspheres via foaming-transfer was developed. • Foaming-transfer enabled a continuous production of porous polymer microspheres. • Introducing EtOH and acetone enabled versatility on porous polymer microspheres. A solvent evaporation self-motivated synthetic methodology based on foaming-transfer has been developed to fabricate porous polymer microspheres. The novel method is a technical improvement for the traditional solvent evaporation method, in which solvent evaporation enables foam formation and foaming-transfer. Foaming-transfer helps deliver oil droplets from the aqueous phase to the receiving vessel, while phase separation takes place in oil droplets between polymer and porogen to produce porous polymer microspheres. Because of foaming-transfer, the novel method enables a continuous production of polymer microspheres via continuous feeding. Additionally, high efficiency has been observed since solvent evaporation in foams is much quicker than that in the aqueous phase. The methodology was further developed to prepare versatile porous polymer microspheres by introducing extra organic solvents, including ethanol (EtOH), acetone and ethyl acetate. Solvents like EtOH and acetone that have relatively poor compatibilities with oil phase were able to control structure, surface morphology and particle size of polymer microspheres when varying the concentration of solvents; while introducing solvents like ethyl acetate having good miscibility with oil phase hardly changed these properties. It was mainly because the difference on the compatibilities led to different distributions of solvent molecules in the system, which altered the evaporation process of solvent and the surface tension of the system, leading to the variation on structure, particle size and surface roughness. This work is meaningful since it developed an efficient, continuous and versatile method for the production of porous polymer microspheres.