Segmental dynamics of polyurea: Effect of stoichiometry

We study the effect of variations in the soft/hard segment ratio, achieved through stoichiometry changes, in elastomeric polyurea. These variations have a marked effect on the mechanical properties; however, the materials exhibit very similar glass transitions and local segmental relaxation dynamics. The latter differ only at elevated pressure, an increase in hard segment content associated with greater sensitivity to pressure and volume changes. In this respect the polyurea mimics the behavior found recently for an elastomer reinforced with hard filler particles. The resistance to ballistic penetration of the polyurea was unaffected by the stoichiometry variations, consistent with the idea that the impact performance of elastomers is governed by the segmental dynamics rather than properties measured in conventional mechanical tests.