Properties related to linear and branched network structure of hydroxyl terminated polybutadiene

The correlation between properties and the network structure of hydroxyl terminated polybutadiene (HTPB) based polyurethanes (PUs) was studied through linear and branched structure polymer matrixes formed by toluene diisocyanate (TDI) and an aliphatic polyisocyanate curing agent (N100). The curing reactions were monitored using differential scanning calorimetry (DSC) and viscosity build-up. The swelling capacity of PUs decreased with the increase of crosslink density with a stable solubility parameter according to the equilibrium swelling test. Tensile properties of PUs cured by TDI and N100 in different stoichiometric ratios of NCO/OH groups were tested. Both breaking elongation and tensile strength were remarkably improved by N100. The thermal decomposition processes of HTPB/TDI and HTPB/N100 indicated that a branched structure has higher depolymerization temperature, and hence, improved thermal stability. In addition, PU with a branched network prevented the migration of the plasticizer during isothermal accelerated aging due to the higher crosslink density.