Sample-sample and wavenumber-wavenumber two-dimensional correlation analyses of attenuated total reflection infrared spectra of polycondensation reaction of bis(hydroxyethylterephthalate)

Polycondensation reaction of bis(hydroxyethylterephthalate) was monitored i n situ by attenuated total reflection (ATR)/infrared (IR) spectroscopy. The obtained spectra are analyzed by means of generalized two-dimensional (2D) sample-sample and wavenumber-wavenumber correlation spectroscopies. The sa mple-sample correlation analysis reveals the correlations among the concent ration features of the components, and the wavenumber-wavenumber correlatio n analysis elucidates the relations among the spectral features. Before the experimental data are analyzed by the 2D correlation spectroscopies, a syn thetic two-component spectral model composed of the first and the last expe rimental spectra, is examined. The results of an analysis of the real data are related to those obtained from the synthetic data. It is found that the sample-sample correlation analysis of the IR data of polycondensation expl ains the concentration variance in the system and classifies two groups of the samples. The wavenumber-wavenumber correlations are derived upon the re sults of the sample-sample correlations and explained in terms of the spect ral variations of three components. The convolute patterns in both types of correlations are attributed to the weak presence of ethylene glycol.