USE OF ~(13)C NUCLEAR MAGNETIC RESONANCE TO STUDY THE CATALYST MECHANISM OF POLYURETHANE NETWORK FORMATION

摘要

The formulation of propellant liner includes several alcohols: the polybutadiene with three different hydroxyl functions, two chain-extender alcohols (di and trifunctional) and an adhesion doping agent (monofunctional). They react with the isophorone diisocyanate (IPDI) and form a polyurethane network. Usually, the infrared spectroscopy is used to follow the curing kinetics. However, the alcohols consumption rate is difficult to measure by this technique. With the ~(13)C nuclear magnetic resonance spectroscopy, we were able to separate and identify signals of each carbon atom bonded to hydroxyl groups, the two belonging to isocyanate groups and also the ones corresponding to the urethane formed. For this reason, a step methodology was developed. It was used to compare the effect on the curing mechanism of two different catalysts. In this case, the results obtained point out a difference in the reaction kinetics between the three alcohols as a function of the nature of the catalyst. The two networks formed are different which leads to mechanical properties (tensile elongation) but different adhesion capacities on propellant (peeling test).