Measurement of partial conversions during the solution copolymerization ofstyrene and butyl acrylate using on-line Raman spectroscopy

The copolymerization of styrene and n-butyl acrylate in dioxane was monitor ed by on-tine Raman spectroscopy. The calculation of the individual monomer concentrations on the basis of the individual vinyl peaks is not straightf orward for this system, as these bands are overlapping in the Raman spectru m. To tackle this problem, univariate and multivariate approaches were foll owed to obtain monomer concentrations and the results were validated by ref erence gas chromatography data. In the univariate analysis, linear relation s between various monomer peaks were used to calculate monomer concentratio ns from the Raman data. In principal component analysis, the main variation in the spectra could be ascribed to conversion of monomer. Furthermore, pr incipal component analysis pointed out that the second-largest effect in th e spectra could be attributed to experiment-to-experiment variation, probab ly attributable to instrumental factors. In the multivariate partial least squares regression approach, single factor models were used to calculate mo nomer concentrations. Both the univariate and the partial least squares reg ression approaches proved successful in calculating the individual monomer concentrations, showing very good agreement with off-line gas chromatograph y data. (C) 2000 John Wiley & Sons, Inc.