Probing the cure and postcure reactions in polyurethanes by FTIR and GPC

Fourier transform infrared (FTIR) and gel permeation chro-matography (GPC) were respectively utilized in determining the changes inisocyanate (NCO) concentration and molecular weight (MW) and its dis-tribution (MWD) in polyurethanes during their cure and postcure stages. Samples, originally cured at 45ـC, were taken through accelerated agingtests at various temperatures. The FTIR and GPC analytical conditionswere optimized, for both molecular weight and molecular weight distri-bution and NCO group determination. In FTIR spectroscopy Beers lawwas 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%, 4خ10-6 mollit-1 and 1095 lit mol-1 cm-1 respectively. It was found the NCO concen-tration decreases with the progress of polymerization and at the same timeMW of the sol increases, going through a maximum and then decreases toa constant level. The time to reach this level and termination of NCO con-centration, i. e., the end of polymerization decreases with the increase intemperature. The results obtained from GPC and FTIR methods in follow-ing the different steps of polymerization as well as those from the linearplots of the end time of reaction vs. the 1/T, were in good agreement.