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

Abstract

Emulsion polymerization remains a challenging system for in situ Raman spectroscopic analysis, despite extensive research in 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 monomerhomopolymer 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 re-calibration. To demonstrate this technique, examples of in situ Raman monitoring for both batch and semi-batch emulsion polymerizations are provided.

Monitoring Microgel Synthesis by Copolymerization of N‐isopropylacrylamide and N‐vinylcaprolactam via In‐Line Raman Spectroscopy and Indirect Hard Modeling

“…IHM has also been applied to monitor copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The authors used the homopolymer spectral response as internal standard for the corresponding monomer, which compensated changes in Raman signal intensity due to light scattering of polymer particles . Recently, first‐derivative indirect hard modeling (FD‐IHM) was introduced to analyze spectra with strong background signals …”

“…The authors used the homopolymer spectral response as internal standard for the corresponding monomer, which compensated changes in Raman signal intensity due to light scattering of polymer particles. [25] Recently, first-derivative indirect hard modeling (FD-IHM) was introduced to analyze spectra with strong background signals. [26] While component fractions have been monitored in-line during microgel homopolymerization based on VCL, component fractions during copolymerization based on VCL and N-isopropylacrylamide (NIPAM) have previously been studied only by sampling and subsequent off-line analysis.…”

In situ conversion monitoring of styrene emulsion polymerization by deconvolution of a single reference band near 1,000 cm−1

“…Raman spectroscopy was effective for monitoring monomer consumption for any kind of polymerization process . Its compatibility with aqueous medium made it a suitable technique for emulsion polymerization processes (homopolymerization or copolymerization of various monomers) . Monitoring monomer conversion by Raman spectroscopy generally relied on the variation of a ratio of intensities or integrated intensities of a specific monomer band to a reference band, which was assumed unaffected by the reaction .…”

A Quantitative Analysis of an Oil Component in an Emulsion by Multiphoton Ionization Mass Spectrometry

“…Chen et al reported in situ monitoring of emulsion polymerization by Raman spectroscopy using a homopolymer as an internal standard, although the absolute Raman intensity depends on many factors, such as the solution turbidity and the particle size distribution of the dispersed phase. 13 Using mass spectrometry (MS), which offers unique analytical power, Smith et al reported the mass spectra of proteins in droplets, as measured by electrospray ionizationquadrupole mass spectrometry (ESI-QMS). 14 The constituents and their concentrations influence the stability of emulsions, such as creaming, aggregation, and coalescence.…”