Simultaneous Monitoring of Polymer and Particle Characteristics during Emulsion Polymerization

Emulsion polymerization reactions constitute complex, nonequilibrium systems in which there is strong interaction between polymers, monomers, and the colloidal structures that mediate the reactions. A novel and general method was sought to monitor emulsion polymerization reactions. Instrumentation and methods were hence developed here to achieve, for the first time, simultaneous monitoring of the evolving characteristics of both the organosoluble components (monomer conversion, polymer molar mass, and reduced viscosity) and the colloidal components (particle size of monomer droplets and nucleated polymer particles). No empirical models were required for these determinations. This represents a new capability for the broadening ACOMP platform (automatic continuous online monitoring of polymerization reactions). The method was applied to free radical emulsion homopolymerization of methyl methacrylate and butyl acrylate over a wide monomer concentration range, with and without surfactant stabilization. A successful approach to soap-free emulsion polymerization (up to 15% solids) was developed and led to stable and uniform emulsions with no phase separation or coagulum buildup. Trends in the polymer characteristics were cross-correlated with evolving colloid particle distributions, and the model of mass transfer from large monomer droplets (microns) to much smaller, nucleated particles which are the loci of polymerization (ca. 100 nm) was confirmed. This was seen in the disappearance of the large monomer droplets and appearance of polymer particles during monomer conversion. Results were cross-checked with offline multi-detector size exclusion chromatography, dynamic light scattering, and cryogenic transmission electron microscopy. This new ACOMP approach should be widely applicable to monitoring many types of emulsion polymerization reactions.