Microfluidic Reactor for Studying Aqueous Phase Polymerization Events of Relevance to Emulsion Polymerization: Methyl Methacrylate
Juan F. Hincapié, Estíbaliz González de San Román, Carlos A. Castor, Hugo M. Vale, Zhong Zeng, Bernd Reck, Nicholas Ballard, José M. Asúa
Abstract
Emulsion polymerization is a complex multiphase process that, despite many decades of study, contains aspects that are still not fully understood. Unresolved questions remain over events occurring in the aqueous phase in particular, largely due to the inability to decouple chain growth and radical entry/nucleation phenomena. These phenomena are decoupled in this work by using a microfluidic reactor system designed to enable the study of the polymerization of methyl methacrylate in aqueous solution in the absence of particles. The molar mass distribution (MMD) determined by matrix-assisted-laser-desorption/ionization time-of-flight mass-spectroscopy (MALDI-ToF-MS) contained water-soluble chains of up to 45 monomer units that display a Poisson-like distribution. A mathematical model was developed to describe these experimental results, highlighting, in particular, the importance of chain length dependent propagation and termination reactions in aqueous phase polymerization. This work offers a unique insight into aqueous phase polymerization kinetics in the context of the relatively hydrophobic monomers used in emulsion polymerization.