Polypropylene is a frequently used, semi-crystalline plastic, which is often processed under high pressure. For the kinetics of solidication under such conditions only inaccurate data are available so far, because direct measuring methods are missing. In this thesis, investigations on the growth rates of spherulites were performed on a pressure dilatometer with dierent crystallization temperatures, pressures and pressure intervals. For this purpose, an existing pressure dilatometer, which was built by Dr. Peter Hiert- zenberger while he did his diploma theses, was equipped with a lifting platform in order to achieve reproducible high pressures. Furthermore the pressure dilatometer was equipped with two additional temperature pro- bes to measure the average temperature over the entire sample. Polypropylene HB600TF from Borealis was chosen as the model material. It is a ho- mopolymer with a low melt rate, which is particularly suitable for extrusion and for thermoforming. Since it is only slightly nucleated, it seemed that it was particularly well suited to measure the pressure dependence of the growth rate. From the measured dilatometer curves and the morphologies obtained by the thin sections of the samples, in addition to the growth rates, the development of the number of nuclei was obtained. The half-value period of the crystallization, as well as the velocity constants were determined by Avrami-Fit from the dilatometer curves. These data were then combined to master curves according to Zoller. In addition, some samples which where crystallized under pressure, as well as a blank were analyzed using dierential scanning calorimetry (DSC). Since a double peak was formed in the DSC curves of the samples crystallized under high pressures, it was assumed that there could be a change in crystal modication. Because of this assumption, Raman spectra of these samples were recorded. Based on these spectra, the presence of gamma-phases of polypropylene was veried.