Liquid hydroxyl-terminated cis-polybutadiene (cis-HTPB) having various molecular weights were cured with trimethylol propane (TMP) and isophorone diisocyanate (IPDI) by the one-shot method and the physical properties of these elastomers obtained were measured. The effect of pseudo-crosslinks was not observable and the calculated value of the number average molecular weight of the network chain (McBAR) between each TMP crosslink unit was found to be pertinent in determining the tensile strength, modulus, tear strength, and hardness. The mechanical properties increased with increase in the 1/McBAR value and showed a linear relationship with the high 1/McBAR values (McBAR below about 3000). On the other hand, chain entanglement becomes more important in affecting the mechanical properties when McBAR was higher than 3000, and physical properties were less dependent on 1/McBAR values in the lower range.
