The microindentation hardness technique has been employed to examine the II --> I polymorphic transformation of i-PBul taking place upon aging at room temperature. The hardness values of form I are shown to be remarkably higher than those of form II due to the denser packing of chains in the hexagonal crystal modification. The kinetics of the II --> I transformation has been followed by means of microindentation hardness measurements in real time. The influence of molar mass and crystallization temperature on the kinetics of the polymorphic transformation is examined. Results suggest that the rate of polymorphic transformation is independent of molecular weight. In addition, it is seen that increasing the crystallization temperature (up to 105 degreesC) notably reduces the time required for a full transformation of form II into form I. The influence of the fraction of amorphous material on the rate of polymorphic transformation is discussed.