Rheological cure characterization of an advanced functional polyurethane

Abstract As part of our continuing study of the curing kinetic and chemorheological analysis of a functional polyurethane (PU) segmented block copolymer formation, in the current paper, we focus on the use the rheological measurements to monitor the entire curing process. The curing reaction was between a metallo-polyol derived of hydroxyl-terminated polybutadiene (HTPB), i.e. , (ferrocenylbutyl) dimethylsilane grafted HTPB, and isophorone diisocyanate (IPDI). The evolution of viscoelastic properties, such as storage modulus ( G ′), loss modulus ( G ″) and complex viscosity ( η * ) was recorded in isothermal conditions, at four different temperatures in the range of 50–80 °C. The gel times ( t gel s) were determined by the loss tangent (tan  δ ) crossover at different frequencies, and the activation energy obtained from them was 69.8 kJ/mol. The rheological properties in the region of the gel point have shown that they follow the percolation theory, demonstrating a power law dependence for the shear modulus with a critical exponent n  = 0.67 ± 0.01, for the higher curing temperatures, 70 and 80 °C, and a slightly lower one at lower temperatures, 50 and 60 °C. In addition, three different empirical models, among them the Arrhenius and Kiuna rheokinetic models, were used to predict the change in viscosity of this system with the time in the pre-gel region. These results illustrate the rheological curing behavior of this PU resin, its final application being found in the development of advanced energetic composite materials.