Kinetic and chemorheological modelling of the polymerization of 2,4- Toluenediisocyanate and ferrocene-functionalized hydroxyl-terminated polybutadiene

Abstract

The reaction of 2,4-toluenediisocyanate (2,4-TDI) and a metallocenic-prepolymer derived from hydroxyl-terminated polybutadiene (HTPB) was studied in bulk and under isothermal conditions (50–80 °C) by rheological methods. Two regions distinguished and limited by the gel point, identified as the crossover of loss tangent (tan δ) at different frequencies, were analysed from different rheological properties during the curing process of this novel metallo-polyurethane (PU). The initial part of this polymerization, dominated by the viscous behaviour (from η0 ≈ 5 Pa s to η = 250 Pa s), was modelled through the Arrhenius isothermal model, in which the presence of two rheokinetic stages, due to different isocyanate groups in the 2 and 4 positions for this asymmetric monomer, was found until the gelation is reached. The contributions of the main reactions for the region analysed, before the gel point of this polyaddition, are discussed. The gel transition was identified, and the viscoelastic behaviour of the gelation process was studied in depth. In addition, from the evolution of the storage modulus (G′) recorded, the overall polymerization reaction was described by a Kamal-Sourour kinetic expression for the reaction rate. The different kinetic parameters obtained for the autocatalytic model used yielded predictions that agree very well with the experimental data, finding a significant autocatalytic effect. An isoconversional method allowed the determination of the dependence of the activation energy on the conversion degree during the network formation of this advanced functional ferrocene-PU, which is of great interest in rocket technology research for the development of the aerospace industry.