The influence of cooling rate on the structure and resulting mechanical performance is explored for a set of isotactic polypropylenes with varying molecular weight, insertion of counits, and addition of a nucleating agent. A continuous variation of crystal type (amesomorphic phase competition) and structural features is obtained with cooling rate. These variations are discussed in relation to the strain rate- and temperature-dependent yield stress and time-to-failure kinetics. The deformation kinetics, characterized by constant activation volumes and energies in the ReeEyring theory, prove to be the same for various structures. Differences in thermal history are solely captured by two rate constants that are function of the structure. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012