A sensitive fluorescence method for monitoring the kinetics of microemulsion polymerization

Abstract

We present a fluorescence method that allows one to monitor the kinetics of microemulsion polymerization of very low monomer contents (water-to-monomer ratio can readily be superior to 1000). The microemulsion polymerization of methyl methacrylate (MMA) was investigated using N-(2-anthracene)methacrylamide (AnMA) as the probe whose fluorescence emission intensity was proportional to the conversion of MMA into the polymer. The real-time-measurement results show that in the regime of very low monomer contents, the surfactant exerted a profound effect on the kinetic process. In a microemulsion containing 0.1 wt% of MMA with respect to water, with the anionic surfactant of sodium dodecyl sulfate (SDS), the fast polymerization was preceded by an induction period whose length increased with reducing the concentration of the water-soluble initiator of potassium persulfate (KPS). By contrast, with the non-ionic surfactant of polyoxyethylene (20) oleyl ether (Brij98), the induction period was short and the decrease in the KPS concentration mainly resulted in a decrease of the reaction rate. The unprecedented sensitivity of this fluorescence method made it possible to access kinetic data of microemulsion polymerization with very low monomer contents for the first time, providing new insight into the effects of surfactant and initiator on this heterophase polymerization process.