Amorphous atactic polypropylene (PP) with an average molecular weight of 50,000-100,000 is produced by polymerizing propylene with a ternary Ti(Oiso-Pr)(4) - AlEt2Cl/MgBu2 catalyst at 30-50 degrees C. Main advantages of this catalyst compared with other catalysts capable of nearly exclusively producing atactic PP (such as some heterogeneous Ziegler-Natta, metallocene and postmetallocene catalysts) are high activity, low cost and the ease of use: the catalyst is prepared in situ from three commercially available compounds readily soluble in aliphatic and aromatic hydrocarbons. (C) 2015 Wiley Periodicals, Inc.