Abstract: The near-infrared(NIR) spectroscopy was used to monitor the residual monomer in the styrene/butyl acrylate emulsion copolymerization reaction. There were nine semi-batch styrene/n-butyl acrylate emulsion copolymerization reactions. The samples were gotten in line, and the NIR spectroscopy of the emulsion were measured at the same time. It was shown that the emulsion particles scattered the NIR and affected the result of analysis, through the pretreatment of Multiplicative Scatter Correction(MSC) to the spectra. The NIR data of emulsion was analyzed by the method of Principal Component Analysis(PCA). The calibration model was established with 72 samples of six reactors, and the model was validated with 36 samples of three reactors. The amount of emulsifier was variational in the nine reactors in order that the calibration model could adapt the amount of emulsifier. The result of the research is that the Standard Error of Prediction of the calibration models for St and BA were 0.08026 and 0.05305.

Key words: In-line measurement, Emulsion copolymerization, Multiplicative scatter correction, Near-infrared spectroscopy, Residual monomer, Principal component analysis