SynopsisExtruded, injection-molded, unoriented crystallized specimens and capillary rheometer efflux strands of commercially stabilized polypropylene without nucleating agents were examined by optical microscopy and x-ray diffraction to determine the conditions for ,%form crystallization as a function of the distance from the surface and of the shear rate at commercial processing conditions. Results demonstrate that a t all "cooling conditions" AT = T,,, -Tb (defined as the melt temperature T , minus the bath temperature Tb) effects of strain flow initiate nucleation of &form crystals. The shear rate is demonstrated to be important for &form crystallization. A critical average threshold value for the shear rate of approximately 3 X lo2 sec-l has to be exceeded. The 0 modification is mostly connected with type-I11 spherulites and partly to row structures, and it is observed at processing conditions in oriented structures only.