Abstract

Emulsion Polymerization in Ultrasonic Microreactors

Simon Kuhn, Professor, Department of Chemical Engineering, KU Leuven

Polymeric dispersions have broad applications in adhesives, coatings, catalyst support, encapsulation, and drug delivery. One approach is the generation of miniemulsions (50nm<d<1000nm) and subsequent polymerization to synthesize polymer nanoparticles that can achieve the desired size and morphology for targeting a specific application. Ultrasonic microreactors have proven to be effective in the generation of miniemulsions, although with a high polydispersity (PDI > 0.3). To address this issue, an ultrasonic microreactor was developed, which enables the generation of a monodisperse miniemulsion (PDI < 0.3) to synthesize polymer nanoparticles. This ultrasonic microreactor consists of serpentine channels with a square cross-section of 1.2 mm in borosilicate glass with a piezoelectric plate transducer attached to one side. The miniemulsion created by the cavitation activity in the ultrasonic microreactor is then fed into a temperature controlled (75°C) coiled loop reactor for the continuous polymerization of monomer droplets. Specifically, we study the cross-linking polymerization of butyl methacrylate, for which the continuous phase is water with a surfactant (Lutensol AT50), and the dispersed phase consists of the monomer butyl methacrylate, the cross-linking agent ethyl glycol dimethacrylate, the costabilizer hexadecane and the thermal initiator AIBN. Preliminary results highlight the performance of the developed system. For a dispersed to continuous volumetric flow rate ratio of 1:4, residence time of 4 min at a US frequency and power of 47kHz and 15W, particles with a mean hydrodynamic diameter of 94 nm and PDI of 0.15 were obtained. The influence of the operating parameters (load power, frequency, surfactant concentration, flow rate ratio and residence time) on the size of the miniemulsion droplets and to control the final particle size will be discussed in detail.