Dynamic mechanical characterization of the crosslinked and chainextended HTPB based polyurethanes

The viscoelastic response of two different polyurethane (PU) systems (crosslinked and chain-extended) based on hydroxyl terminated polybutadiene (HTPB) were analyzed and compared. The PU elastomers were fabricated by reacting HTPB with isophorone diisocyanate. A tri-functional alcohol (1,2,6 hexanetriol) and a bi-functional aliphatic diol (1,4 butanediol) were used as the crosslinking agent and the chain extender respectively. Hydrogen bonding between the hard segments is indentified by the IR spectroscopy. The segregation of these segments was manifested by dynamic mechanical analysis at characteristic frequency over a wide range of temperature. The intensity and temperature location of the relaxation peaks was identified and discussed. The phenomenon of viscous dissipation was evaluated by recording the viscoelastic parameters as a function of temperature across a series of frequencies. The results obtained indicate that the chain-extended polymer is phase segregated and more sensitive to temperature rise via viscous dissipation as compared to crosslinked polymer. Both the polymers showed similar glass transition temperature (T_g) and characteristic relaxation times. Master curves for the polymer systems investigated are produced and discussed.