AbstractThis article outlines a kinetic study of two different Ziegler–Natta type catalysts in multistep bulk‐/gas‐phase polymerization of propene in a reaction calorimeter. In the first stage, bulk‐phase polymerization of propene, the matrix material is produced and kinetic information about the polymerization is extracted from power compensation calorimetry data. Focus is set on the influence of hydrogen on polymerization kinetics and comparing the performance of the two catalysts. In the 2nd stage, gas‐phase copolymerization of propene and ethylene, an elastomeric copolymer is produced as impact modifier and kinetic information is obtained from semibatch operation in constant conditions. The influence of monomer/comonomer ratio on copolymerization behavior of the two catalysts is investigated and compared.