In Situ Monitoring of Emulsion Polymerization by Raman Spectroscopy: A Robust and Versatile Chemometric Analysis Method

摘要

Emulsion polymerization remains a challenging system for in situ Raman spectroscopic analysis despite extensive research on the necessary instrumentation and chemometric data analysis methods. In this study, we demonstrate a new and facile data analysis method, making in situ Raman spectroscopy a more versatile research tool for monitoring the concentrations of monomers in reactions spanning a wide range of compositions. The method improvement stems from the use of the homopolymer as an internal standard for the corresponding monomer. Classical least-squares or indirect hard modeling is used for the spectral analysis to determine the spectral responses of major monomers and polymers within the system. Once the relative response factor ratios for a number of monomer-homopolymer pairs are determined in the calibration, they can be used to calculate the concentration ratio for such pairs based on reaction spectra. This approach offers two important advantages in determining the conversion of monomer to polymer. First, because the polymer internal standard will always be present for the corresponding monomer, it is straightforward to compensate for variable signal intensity due to changes in light scattering or instrumental fluctuations. Second, it is possible to calibrate based on a small set of monomer and homopolymer standards. The appropriate pairs can then be selected to establish a calibration method for any polymer product involving a combination of monomers from this set without the need for recalibration. To demonstrate this technique, we provide examples of in situ Raman monitoring for both batch and semibatch emulsion polymerizations.