A flow process for the production of poly(methyl methacrylate) (PMMA) particles is proposed by soap‐free emulsion polymerization using a water‐in‐oil (W/O) slug flow in a microreactor. Thin oil films generated around the dispersed aqueous phase of the W/O slug prevent the prepared particles from adhesion to the microchannel wall, enabling the continuous production of PMMA particles without clogging. The effects of the linear flow rate of the slug flow and the addition of ethanol in the dispersed aqueous phase on the polymerization are evaluated. It is found that increasing the linear flow rate of the slug flow or the addition of ethanol in the dispersed aqueous phase results in PMMA particles with high molecular weight (≈1500 kg mol−1) in 20 min reaction time. It is believed that this process would be a promising way to prepare polymer particles with high molecular weight in a short reaction time.

Flow synthesis of poly(methyl methacrylate) particles were performed by heterogeneous polymerization of methyl methacrylate using a water-in-oil (W/O) slug flow with or without a non-ionic surfactant in the continuous organic phase. It was found that undesired phenomena in this polymerization system; clogging of the channel and broadening particle size distribution can be occurred when growing polymer particles adsorb to the W/O interface during polymerization, and that the addition of non-ionic surfactant to the continuous organic phase prevents the particles from adsorption to the W/O interface and gives monodisperse polymer particles. In addition, it was shown that as increasing the initiator concentration, the particle diameter becomes larger, resulting in monodisperse micron-sized polymer particles with 100% monomer conversion at 120 min reaction time. These results indicated that heterogeneous polymerization process using W/O slug flow can be a promising way to continuously prepare monodisperse polymer particles with micron-sizes in a short reaction time.

We develop a sequential flow process for the production of monodisperse poly (methyl methacrylate) (PMMA)/polystyrene (PS) composite particles through a soap-free emulsion polymerization of methyl methacrylate (MMA) using the first water-in-oil (W/O) slug flow and a subsequent seeded emulsion polymerization of styrene (St) using the second W/O slug flow. In this process, monodisperse PMMA seed particles are first formed in the dispersed aqueous phase of the first W/O slug flow. Subsequently, removal of the oil phase from the slug flow is achieved through a porous hydrophobic tubing, resulting in a single flow of the aqueous phase containing the seed particles. The aqueous phase is then mixed with an oil phase containing St monomer to form the second W/O slug flow. Finally, monodisperse PMMA/PS composite particles are obtained by a seeded emulsion polymerization of St using the second W/O slug flow. We compared the reaction performance between the slug flow and the batch processes in terms of particle diameter, monomer conversion, particle size distribution, and the number of particles in the system. We found that internal circulation flow within the slugs can enhance mass transfer efficiency between them during polymerization, which results in monodisperse PMMA/PS composite particles with a large particle diameter and a high monomer conversion in a short reaction time, compared to those prepared using the batch process. We believe that this sequential microflow process can be a versatile strategy to continuously produce monodisperse composite particles or core-shell particles in a short reaction time.