The kinetics of stress aging are markedly increased by H2O additions to nylon. This increase in rate is taken as evidence that the aging process takes place in amorphous regions of the polymer. The breakup of the stress‐aged structure is also greatly accelerated by H2O. The activation enthalpy ΔH* and shear activation volume V* for breakup are constant up to ∼0.7 wt% H2O, and then decrease to about one‐half their dry values at ∼2.0 wt% H2O. These changes in the activation parameters are consistent with the activated step in breakup being the synchronous shear of stress‐induced microcrystals, the size of microcrystals which nucleate during stress aging being limited by the average spacing between H2O molecules in the amorphous regions.

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