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Reaction calorimetry and Raman spectroscopy were simultaneously implemented to monitor high solids content (∼50 wt %) semibatch emulsion polymerization reactions for two comonomer systems:  vinyl acetate/butyl acrylate, VAc/BA, and butyl acrylate/methyl methacrylate, BA/MMA. Overall and instantaneous conversions and free concentration of monomer were measured by means of each technique. It was found that both techniques provided comparable results for the overall conversion, no matter whether the reactions were carried out under starved (BA/MMA) or nonstarved conditions (VAc/BA). However, instantaneous conversion and free monomer concentrations were better estimated by Raman spectroscopy when the polymerization was carried out under starved conditions. Under nonstarved conditions (higher free monomer concentration and lower instantaneous conversions), Raman spectroscopy also provided slightly better estimates.

This work describes the estimation of polymer particle size from NIR spectra collected in situ and online in an automated reactor. A good linearity between spectra and average polymer particle diameter is found. The multivariate linear model is also tested with an independent data set not used in the model fitting. Despite varying monomer and polymer concentrations and temperature changes along the process, the average particle sizes are well predicted and can be monitored by NIR spectroscopy during emulsion polymerization reactions.Evolution of average particle diameter with polymer content for three different BA/Sty semi‐continuous emulsion polymerization reactions. Open symbols correspond to spectra used in the model fitting and solid symbols to the test data set. The different symbol types correspond to the three different reactions.magnified imageEvolution of average particle diameter with polymer content for three different BA/Sty semi‐continuous emulsion polymerization reactions. Open symbols correspond to spectra used in the model fitting and solid symbols to the test data set. The different symbol types correspond to the three different reactions.

In this work, Raman and Near InfraRed (NIR) spectroscopies are evaluated for the monitoring of different semicontinuous emulsion homo‐ and co‐polymerization reactions. Important process variables, namely monomer concentrations and average particle sizes, were monitored by both techniques under realistic conditions that would be found in an industrial environment (e.g. low signal/noise ratio, probe placed in the reaction medium). Results suggest that Raman and NIR are suitable for on‐line monitoring of emulsion polymerization reactions and that the success of their application is mainly related to representative calibration models used for the estimation of the properties of interest.