AVERAGE MOLECULAR-WEIGHT DETERMINATION OF A POLYESTER BY NIR SPECTROSCOPY

The average molecular weight has been determined on a polyester additive product manufactured by a major chemical company. This determination is done during the polyester preparation (in-process) by fiber optics near infrared spectroscopy (NIR) using the UOP Guided Wave software. The disappearance of one of the starting materials with hydroxylic functionality (1415 nm) is monitored. Average molecular weights are determined from a calibration curve (average molecular weight versus absorbance) which itself is derived from polyester samples that have been analyzed by GPC (Gel Permeation Chromatography). The calibration curve is best described by a third-order mathematical model determined using the shareware program Kurv + for Windows(C). The NIR and GPC methods generally agree to within 50-400 units.