Rheokinetic analysis on the formation of metallo-polyurethanes based on hydroxyl-terminated polybutadiene

• Rheokinetics of a functional polyurethane was studied through viscosity build-up.
• The curing process presents two chemorheological stages due to the NCO groups.
• A new interpretation of the reactions which take place in each stage is discussed.
• This metallo-PU finds its application in the area of the advanced energetic materials.

Rheokinetics for the formation of an advanced functional polyurethane (PU) from Butacene, which is (ferrocenylbutyl)dimethylsilane grafted hydroxyl-terminated polybutadiene (HTPB), and from isophorone diisocyanate (IPDI), has been studied through viscosity build-up during cure reaction in bulk and in isothermal conditions at different temperatures (50–80 °C). The viscosity increases with curing time in an exponential way, and hence the kinetic model of Arrhenius was applied before gelation. The rheokinetic graphs obtained by plotting ln (viscosity) versus time, showed the presence of two well-defined stages. This fact is due to the nature of this functional metallo-polyol and to the use of a diisocyanate with two non-equivalent reactive groups. The rate constants in both stages, kη1 and kη2, were determined from these plots and the contributions of the different chemical reactions to each stage is discussed. In addition, activation energies were determined for the curing reaction under study. The catalytic effect of the ferrocenyl group covalently linked to the polybutadiene chain has been evaluated. This catalytic activity for the macrodiol Butacene was compared with those obtained when a conventional organometallic compound, such as dibutyltin dilaurate (DBTL) or ferrocene, is used as catalyst instead of this novel prepolymer.

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