In situ monitoring of styrene polymerization using Raman spectroscopy. Multi‐scale approach of homogeneous and heterogeneous polymerization processes

Abstract

International audienceFree radical polymerization of styrene was monitored in situ by combining Raman spectroscopy to other experimental techniques (gravimetry and rheology). Three different processes were investigated: bulk, emulsion and miniemulsion polymerization. A complete analysis of the evolution of Raman spectrum during the course of reaction showed that a lot of information about molecular dynamics could be extracted and related to chemical phenomena. In addition, we report for the first time the coupling of Raman spectroscopy to a rheometer in order to monitor styrene bulk polymerization both at the scale of chemical bonds and at the scale of macroscopic phenomena (viscosity variation)

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

“…Increasing surfactant concentration led to faster monomer consumption as was expected on the basis of classical theory of emulsion polymerization . In addition, in previous work, we showed that similar linear correlation existed in both emulsion and miniemulsion polymerization conditions . Even if the wavenumbers were slightly higher in miniemulsion conditions as compared with emulsion conditions, the slope of the linear variation with monomer conversion was almost the same for both processes.…”

“…Indeed, a Raman shift of 2 cm −1 of the wavenumber ( ω 0 ) as well as an increase of the bandwidth (linked with σ 1/2 ) was detected over the course of the reaction. Same changes have already been noticed independently of the studied polymerization process, bulk, emulsion, or miniemulsion . These observations suggested that this analysis of Raman data could be applied to other processes.…”

“…These values were very close to those reported in the present work. In the case of miniemulsion polymerization of styrene at 60°C, significantly different values were found, ω 0S ≈ 999.2 cm −1 and ω 0PS ≈ 1,001.5 cm −1 . Thus, we could conclude that the reference values ( ω 0S and ω 0PS ) were mainly dependent on the reaction conditions and process (bulk, miniemulsion, or emulsion).…”

“…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 .…”

“…For styrene polymerization, the most largely used reference band has been the one at 1,000 cm −1 , which was assigned to the trigonal ring breathing mode . Indeed, the latter kept the highest integrated intensity throughout the reaction because the aromatic ring was not consumed by the reaction.…”