On the ambiguity of self-modeling curve resolution: orthogonal projection approach analysis of the on-line Fourier transform-Raman spectra of styrene/1,3-butadiene block-copolymerization Original Research Article

The self-modeling curve resolution (SMCR) technique called orthogonal projection approach (OPA) was used to resolve a complex set of Fourier transform (FT)-Raman spectra acquired on-line during styrene/1,3-butadiene block-copolymerization. The routine application of OPA did not yield physically acceptable results and manual corrections of the erroneous parts of the styrene concentration profiles had to be employed to improve the resolved spectra and concentrations of the two monomers and polybutadiene. The failure of automatic resolution by OPA is due to the ambiguity of SMCR. This problem is convincingly illustrated in the present case wherein is shown that physically reasonable manual correction significantly improve the results. The present study demonstrates that the combination of an automatic method for curve resolution and a suitable, efficient spectroscopic set-up enables real-time monitoring of this industrially important polymer reaction better than any conventionally employed technique.