In-line monitoring and control of conversion and weight-average molecular weight of polyurethanes in solution step-growth polymerization based on near infrared spectroscopy and torquemetry

It is well known that the weight-average molecular weight ((M) over bar (w)) is strictly dependent on conversion in step-growth polymerizations performed in batch and that the (M) over bar (w) is very sensitive to impurities and molar imbalance. This makes the work of controlling (M) over bar (w) a non trivial job. In this paper a new methodology is introduced for in-line monitoring and control of conversion and (M) over bar (w) of polyurethanes produced in solution step-growth polymerizations, based on near-infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight-average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of (M) over bar (w). The proposed monitoring and control procedures can also be applied to other step growth polymerizations.