Monitoring a Polyurethane Synthesis by Fiber-Coupled Attenuated Total Reflection Fourier Transform Infrared...

The step-growth polymerization of 1,4-butanediol with 4,4'-diphenylmethanediisocyanate (MDI) was monitored in situ by fiber-coupled attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy between 40 and 70 °C. In contrast to previous kinetic and two-dimensional correlation spectroscopy (2D-COS) studies of this system, the present work applies multivariate curve resolution alternating least squares (MCR-ALS) to temperature-dependent spectral data. The method enables decomposition of overlapping urethane-related bands and extraction of concentration profiles for chemically and physically distinct species, including dissolved and precipitated polymer phases. The MCR-ALS results are consistent with previously reported kinetic trends while providing additional quantitative insight into transient species and phase evolution. These findings demonstrate the added value of multivariate analysis for the concise interpretation of complex polymerization processes.