Probing the Cure and Postcure Reactions in Polyurethanes by FTIR and GPC

Fourier transform infrared (FTIR) and gel permeation chromatography (GPC) wre respectively utilized in determining the changes in isocyanate (NCO) concentration and molecular weight (MW) and its distribution (MWD) in polyurethanes during their cure and postcure stages. Samples, originally cured at 45°C, were taken through accelerate aging tests at various temperatures. The FTIR and GPC analytical conditions were optimized, for both molecular weight and molecular weight distribution and NCO group determination. In FTIR spectroscopy Beer's law was obeyed over the ranges: 2.33-22.34 and 0.03-1.61 mmol lit-1. RSD, detection limit and molar absortivity were found to be 1.46%, 4´10-6 mol lit-1 and 1095 lit mol-1 cm-1 respectively. It was found the NCO concentration decreases with the progress of polymerization and at the same time MW of the sol increases, going through a maximum and then decreases to a constant level. The time to reach this level and termination of NCO concentration, i.e., the end of polymerization decreases with the increase in temperature. The results obtained from GPC and FTIR methods in following the different steps of polymerization as well as those from the linear plots of the end time of reaction vs. the 1/T, were in good agreement.