Polyurethanes based on hydroxyl terminated polybutadiene: modelling of network parameters and correlation with mechanical properties

Abstract

Hydroxyl terminated polybutadiene (HTPB) based urethane networks were synthesized by reacting HTPB with toluene diisocyanate (TDI) at various stoichiometric ratios ( R) ranging from 1.0 to 1.5. The resulting networks would contain allophanate linkages in addition to urethane groups. The networks were characterized for mechanical and swell characteristics. The parameter X which is the extent of urethane groups involved in the allophanate formation and other network parameters, such as crosslink density ( ν e) and effective chain length ( L X ), were calculated using the α-model developed by Marsh with suitable modifications. The value of X showed very good correlation with R-value, and linear correlations were obtained between mechanical properties and the calculated network parameters. Crosslink densities, calculated from stress–strain data were found to be nearly 1.2 times the corresponding values calculated from swell data. Dynamic mechanical studies showed that R value did not influence the glass transition temperature ( T g); however tan δ max was shown to be a linear function of the crosslink density. Activation energy for the variation of storage moduli with temperature decreased with R-value, while that for loss moduli remained nearly unaffected by the R value.