A novel dilatometer has been used to measure the evolution of specific volume at different cooling rates and at elevated pressures under quiescent conditions and under shear for a series of commercial iPP homopolymers and polypropylene-ethylene random copolymers. Significant influences of cooling rates, pressures, and shear flow on the transition temperature T tr related to molecular weight and polydispersity and of course the temperature at which shearing was applied could be found for the iPP homopolymers. In the copolymers, the composition defined by the ethylene content determined the position of the transition temperature T tr .