On-line monitoring and composition control of the emulsion copolymerization of VeoVa 9 and butyl acrylate by Raman spectroscopy

The batch and semi-continuous emulsion copolymerization of n-butyl acrylate and vinyl neononanoate (VeoVA 9) were monitored by remote on-line Raman sp ectroscopy. Monomer concentrations were calculated in real-time by a classi cal least squares (CLS) approach using the vinyl regions of the Raman spect ra. During the batch copolymerization, conversion and copolymer composition calculated from on-line data showed good agreement with off-line gravimetr y and NMR results, indicating that the CLS procedure indeed enables the cal culation of individual monomer concentrations and on-line characterization of the copolymer formed. Real-time analysis of the data enabled control of the copolymer composition by suggesting how one of the comonomers should be added in a semi-continuous polymerization. NMR and gradient polymer elutio n chromatography corroborated the Raman results for the cc,polymer composit ion. Further, it was shown that only at high conversions (> 80%) monomer pa rtitioning influences the copolylmerization behavior, since both monomers h ave a low solubility in water. The results demonstrate that Raman spectrosc opy is very well suited Is on-line sensor in emulsion copolymerization proc esses.