AbstractThe relation between stereoregularity of active centers on a MgCl2/TiCl4catalyst and functions of inside donor (ID) and outside donor (OD) was investigated in the case of ethyl benzoate (EB)/methyl p‐toluate (MPT) as an ID/OD pair. The results indicate that stereregularity depends merely on the amount of MPT supported on the catalyst.On the other hand, regioregularity of active centers was investigated with a MgCl2/TiCl4/dioctyl phthalate(DOP)‐Et3Al/diphenyldimethoxysilane(DPDMS) catalyst system. Regio‐irregular inserted units were detected only in end groups of PP. It indicates that regio‐irregular insertion leads to dormant centers with respect to propene insertion, though such centers are active for hydrogen t