Multivariate curve resolution analysis on the multi-component water sorption process into a poly(2-methoxyethyl acrylate) film

In our previous study, sorption process of water into a biocompatible polymer film, poly(2-methoxyethyl acrylate) (PMEA) was monitored by time-resolved in situ attenuated total reflection infrared (ATR-IR) spectroscopy [S. Morita, et al., Langmuir 23, 3750 (2007)]. In the present study, noisy and heavily overlapped O-H stretching vibrational bands of diffusing water have been analyzed from the series spectra where the spectral shapes change irregularly with time. In spite of these complications, a powerful spectral analysis technique, multivariate curve resolution (MCR) by means of alternating least squares (ALS), yielded smooth and meaningful pure component spectra and detailed kinetic sorption profiles of each component, excluding noise. Ordinary smoothing techniques and Gaussian curve fitting would not achieve these significant results. The quantification of the kinetic parameters such as amplitudes (a) and relaxation time constants (τ) is significant for the systematic development of biocompatible materials and also for revealing the mechanisms of biocompatibility of a material. Moreover, the ratios of coefficients of each component at saturation corresponded well to the values obtained by Tanaka et al. measured by gravimetric analysis. This study is the first to report the detailed concentration profile of each water component whose sorption kinetics is discussed comprehensively.