by water-borne latex, increasing the importance of conventional emulsion and miniemulsion polymerization.In comparison with conventional emulsion polymerization processes, miniemulsion polymerization presents clear advantages because polymerization takes place inside the monomer droplets, which allows using monomers and other highly hydrophobic components in the formulation. Therefore, these components do not need to diffuse in the aqueous medium as in emulsion polymerization. [1][2][3][4] The miniemulsion polymerization process starts with the preparation of the monomer miniemulsion and, after that, the addition of an initiator starts the polymerization. A standard miniemulsion formulation uses water as continuous phase, monomer as disperse phase, surfactant to stabilize the particles droplets, costabilizer to avoid diffusional degradation (Oswald Ripening), and buffer to stabilize the pH of the medium. [5] Constant particle size, use of costabilizers, use of surfactant below the critical micellar concentration, and inexistence of mass transport through the aqueous phase are Miniemulsion polymerization has been extensively studied in the last decade due to its advantages when compared with conventional emulsion polymerization. In this work, monomer conversion and particle size are monitored during miniemulsion polymerization of styrene using in-line near-infrared (NIR) spectroscopy and at-line Raman spectroscopy. Gravimetric analysis and dynamic light scattering have been used as off-line reference measurements. Good agreement has been found between off-line data and the values predicted by NIR and Raman spectroscopy for conversion. The values of average particle size are well predicted from the NIR spectra with the respective calibration model, but the predictions from Raman spectra present some slight discrepancies for particle size. The results show a decrease of the average particle size during the initial period of the polymerization, indicating the occurrence of nucleation mechanisms other than the classical droplet nucleation. These results indicate that insightful information can be obtained by monitoring miniemulsion polymerizations with the use of spectroscopic techniques.

This work studied the at-line Raman spectroscopy monitoring for the inverse miniemulsion polymerization of acrylamide. The conversion was determined from the Raman spectra without previous calibration using the peaks corresponding to CH 2  and CC functional groups of acrylamide. Gravimetric data was used to validate the results of conversion obtained with the Raman spectra. Dynamic light scattering was used to measure the particle size. The results show that high energy in the homogenization step increases the surface area of the droplets and generates a lack of surfactant, which results in larger diameters. It is possible to make at-line monitoring of monomer conversion directly from the Raman spectra without using calibration models. The data obtained show an incomplete conversion that is also confirmed by gravimetric analysis.

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